2021/06/21 更新

写真a

イコマ タダアキ
生駒 忠昭
IKOMA Tadaaki
所属
教育研究院 自然科学系 数理物質科学系列 教授
理学部 理学科 教授
自然科学研究科 数理物質科学専攻 教授
職名
教授
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外部リンク

学位

  • 博士(理学) ( 1993年1月   東北大学 )

研究キーワード

  • Photochemistry

  • Magnetic Resonance

  • 量子輸送現象

  • Quantum Transpot

  • 磁気共鳴

  • 光化学

  • Organic Solid Materials

  • 有機固体材料

研究分野

  • ナノテク・材料 / 分析化学

  • ナノテク・材料 / 基礎物理化学

経歴(researchmap)

  • 長岡技術科学大学   大学院工学研究科 物質材料工学専攻   非常勤講師

    2020年4月 - 2021年3月

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    国名:日本国

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  • 京都大学   大学院工学研究科   非常勤講師

    2019年4月 - 2020年3月

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  • 大阪大学   工学部   非常勤講師

    2017年10月 - 2018年3月

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  • 埼玉大学   大学院理工学研究科   非常勤講師

    2017年9月 - 2018年3月

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  • 新潟大学   理学部 理学科   教授

    2017年4月 - 現在

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  • 大阪市立大学   大学院理学研究科   非常勤講師

    2013年11月

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  • 新潟大学   研究推進機構 共用設備基盤センター   部門長

    2013年4月 - 2017年1月

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  • 新潟大学   研究推進機構 機器分析センター   館長

    2013年4月 - 2017年1月

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  • 国立大学法人 名古屋大学   非常勤講師

    2012年10月 - 2013年3月

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  • 新潟大学   自然科学研究科 数理物質科学専攻   教授

    2012年4月 - 現在

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  • 新潟大学   理学部 化学科   教授

    2012年4月 - 2017年3月

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  • 新潟大学   理学部 化学科   准教授

    2007年6月 - 2012年3月

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  • 東北大学   多元物質科学研究所   助教

    2007年4月 - 2007年5月

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  • 独立行政法人 科学技術振興機構   研究員

    2006年10月 - 2010年3月

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  • 東北大学   多元物質科学研究所   助手

    2001年4月 - 2007年3月

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  • 東北大学   反応化学研究所   助手

    1991年4月 - 2001年3月

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  • 東北大学   非水溶液化学研究所   助手

    1989年7月 - 1991年3月

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経歴

  • 新潟大学   化学科   プログラム長

    2019年4月 - 現在

  • 新潟大学   理学部 理学科   教授

    2017年4月 - 現在

  • 新潟大学   自然科学研究科 数理物質科学専攻 化学   コース主任

    2017年4月 - 2018年3月

  • 新潟大学   研究推進機構 共用設備基盤センター   部門長

    2017年2月 - 2019年3月

  • 新潟大学   化学科   学科長

    2014年4月 - 2015年3月

  • 新潟大学   研究推進機構 機器分析センター   センター長

    2013年4月 - 2017年1月

  • 新潟大学   化学科   教授

    2012年4月 - 2017年3月

  • 新潟大学   自然科学研究科 数理物質科学専攻 化学   コース主任

    2012年4月 - 2013年3月

  • 新潟大学   化学科   准教授

    2007年6月 - 2012年3月

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学歴

  • 東北大学   大学院理学研究科博士後期課程   化学専攻

    1988年4月 - 1989年7月

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  • 東北大学   大学院理学研究科博士前期課程   化学専攻

    1986年4月 - 1988年3月

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    国名: 日本国

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  • 東北大学   理学部   化学科

    1982年4月 - 1986年3月

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    国名: 日本国

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所属学協会

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論文

  • Recombination of Free Carriers and Space Charges in Poly(3-hexylthiophene), as Revealed by Electrically and Capacitively Detected Magnetic Resonances 査読

    Yusuke Wakikawa, Tadaaki Ikoma

    The Journal of Physical Chemistry C124 ( 37 ) 19945 - 19952   2020年9月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/acs.jpcc.0c04904

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  • Sterically Regulated α-Oxygenation of α-Bromocarbonyl Compounds Promoted Using 2-Aryl-1,3-dimethylbenzimidazolines and Air 査読

    Eietsu Hasegawa, Naoki Yoshioka, Tsukasa Tanaka, Taisei Nakaminato, Kazuki Oomori, Tadaaki Ikoma, Hajime Iwamoto, Kan Wakamatsu

    ACS Omega5 ( 13 ) 7651 - 7665   2020年4月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/acsomega.0c00509

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  • Spin-dependent electron transfer dynamics in a platinum-complex–donor–acceptor triad studied by transient-absorption detected magnetic field effect 査読 国際誌

    Tomoaki Miura, Kio Miyaji, Takafumi Horikoshi, Shuichi Suzuki, Masatoshi Kozaki, Keiji Okada, Tadaaki Ikoma

    The Journal of Chemical Physics151 ( 23 ) 234306 - 234306   2019年12月

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    担当区分:最終著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AIP Publishing  

    For realization of efficient organic light-energy conversion systems, controlling the lifetime of photogenerated charge separated states in donor (D)–acceptor (A) molecules is of much importance; the spin dynamics is one of the important controlling factors. We previously reported that the covalently-linked 1,3-bis(2-pyridylimino)-isoindolate platinum (BPIPt)–dimethoxytriphenylamine (D)–naphthaldiimide (A) triad molecule (BPIPt–DA) exhibits a triplet-born long-lived charge separated state (BPIPt–D+A−), the lifetime of which is significantly increased from 4 ms to 10 ms by an applied magnetic field of 270 mT in room temperature tetrahydrofuran (THF). The purpose of the present study is to clarify detailed dynamics of spin-dependent generation and the decay of BPIPt–D+A−. For this purpose, we measured transient optical absorption (TA) and the TA-detected magnetic field effect (MFE) as functions of temperature and dispersion media. In THF at 183 K, MFE-detected transient spectra of the intermediate BPIPt−–D+A state are observed. We have successfully quantified the recombination loss at this state by a kinetic simulation of MFE without using any reference molecules. The lifetime of the final BPIPt–D+A− state in a cellulose acetate polymer matrix at room temperature is significantly prolonged to 20 ms at 0 mT and 96 ms at 250 mT compared to those in THF. From the comparison of temperature dependences of the two media, effects of molecular motions on the electronic coupling and the spin relaxation are discussed.

    DOI: 10.1063/1.5127940

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  • An impact of higher fullerene on charge recombination in organic solar cell studied by magnetoconductance 査読

    Ryota Shoji, Tomoaki Miura, Tadaaki Ikoma

    Organic Electronics75   105383 - 105383   2019年12月

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    担当区分:最終著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.orgel.2019.105383

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  • Effects of the Peripheral Substituents, Central Metal, and Solvent on the Photochemical and Photophysical Properties of 5,15‐Diazaporphyrins 査読

    Satoshi Omomo, Ryosuke Fukuda, Tomoaki Miura, Tatsuya Murakami, Tadaaki Ikoma, Yoshihiro Matano

    ChemPlusChem84 ( 6 ) 740 - 745   2019年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Wiley  

    DOI: 10.1002/cplu.201900087

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    その他リンク: https://onlinelibrary.wiley.com/doi/full-xml/10.1002/cplu.201900087

  • Using magneto-electroluminescence as a fingerprint to identify the spin polarization and spin–orbit coupling of magnetic nanoparticle doped polymer light emitting diodes 査読

    Weiyao Jia, Tadaaki Ikoma, Lixiang Chen, Hongqiang Zhu, Xiantong Tang, Fenlan Qu, Zuhong Xiong

    RSC Advances9 ( 28 ) 15845 - 15851   2019年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry (RSC)  

    <p>The existence of spin polarization was confirmed while spin–orbit coupling was ruled out in Fe<sub>3</sub>O<sub>4</sub>-based PLEDs by magneto-electroluminescence analysis.</p>

    DOI: 10.1039/c9ra01501a

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  • Gigantic Magnetic Field Effect on the Long-Lived Intermolecular Charge-Separated State Created at the Nonionic Bilayer Membrane 査読

    Tomoaki Miura, Kiminori Maeda, Yoshimi Oka, Tadaaki Ikoma

    The Journal of Physical Chemistry B122 ( 50 ) 12173 - 12183   2018年12月

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    担当区分:最終著者   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/acs.jpcb.8b08389

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  • Visible Light and Hydroxynaphthylbenzimidazoline Promoted Transition-Metal-Catalyst-Free Desulfonylation of N-Sulfonylamides and N-Sulfonylamines 査読

    Eietsu Hasegawa, Yuto Nagakura, Norihiro Izumiya, Keisuke Matsumoto, Tsukasa Tanaka, Tomoaki Miura, Tadaaki Ikoma, Hajime Iwamoto, Kan Wakamatsu

    The Journal of Organic Chemistry83 ( 18 ) 10813 - 10825   2018年9月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/acs.joc.8b01536

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  • Magnetoconductance Study on Nongeminate Recombination in Solar Cell Using Poly(3-hexylthiophene) and [6,6]-Phenyl-C61-butyric Acid Methyl Ester 査読

    Ryota Shoji, Takuya Omori, Yusuke Wakikawa, Tomoaki Miura, Tadaaki Ikoma

    ACS Omega3 ( 8 ) 9369 - 9377   2018年8月

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    担当区分:最終著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/acsomega.8b01746

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  • Recent Developments in Electron Spin Science and Technology in Japan 査読

    Toshikazu Nakamura, Tadaaki Ikoma, Ken-ichi Yamada

    Applied Magnetic Resonance49 ( 8 ) 755 - 756   2018年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Springer Science and Business Media LLC  

    DOI: 10.1007/s00723-018-1035-9

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    その他リンク: http://link.springer.com/content/pdf/10.1007/s00723-018-1035-9.pdf

  • Transient Photocurrent Elucidating Carrier Dynamics and Potential of Bulk Heterojunction Solar Cells Fabricated by Thermal Precursor Approach 査読

    Naoki Kudo, Ken Uchida, Tadaaki Ikoma, Kohtaro Takahashi, Daiki Kuzuhara, Mitsuharu Suzuki, Hiroko Yamada, Daichi Kumagai, Yuji Yamaguchi, Ken-Ichi Nakayama

    Solar RRL2 ( 5 ) 1700234 - 1700234   2018年5月

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    担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Wiley  

    DOI: 10.1002/solr.201700234

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  • Benzimidazolium Naphthoxide Betaine Is a Visible Light Promoted Organic Photoredox Catalyst 査読

    Eietsu Hasegawa, Norihiro Izumiya, Tomoaki Miura, Tadaaki Ikoma, Hajime Iwamoto, Shin-ya Takizawa, Shigeru Murata

    The Journal of Organic Chemistry83 ( 7 ) 3921 - 3927   2018年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/acs.joc.8b00282

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  • Temperature Dependence of Magnetophotoconductance in One-Dimensional Molecular Assembly of Hexabenzocoronene 査読

    Yusuke Wakikawa, Tadaaki Ikoma, Yohei Yamamoto, Takanori Fukushima, Kimio Akiyama

    ACS Omega2 ( 7 ) 3260 - 3266   2017年7月

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    担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/acsomega.7b00474

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  • Magnetic Control of the Charge-Separated State Lifetime Realized by Covalent Attachment of a Platinum Complex 査読

    Tomoaki Miura, Dai Fujiwara, Kimio Akiyama, Takafumi Horikoshi, Shuichi Suzuki, Masatoshi Kozaki, Keiji Okada, Tadaaki Ikoma

    The Journal of Physical Chemistry Letters8 ( 3 ) 661 - 665   2017年2月

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    担当区分:最終著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/acs.jpclett.6b02887

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  • Simultaneous Two-Photon Absorption to Gerade Excited Singlet States of Diphenylacetylene and Diphenylbutadiyne Using Optical-Probing Photoacoustic Spectroscopy 査読

    Tasuku Isozaki, Hikari Oba, Tadaaki Ikoma, Tadashi Suzuki

    The Journal of Physical Chemistry A120 ( 31 ) 6137 - 6145   2016年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/acs.jpca.6b02929

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  • Solvent Viscosity Effect on Triplet–Triplet Pair in Triplet Fusion 査読

    Kana Yokoyama, Yusuke Wakikawa, Tomoaki Miura, Jun-ichi Fujimori, Fuyuki Ito, Tadaaki Ikoma

    The Journal of Physical Chemistry B119 ( 52 ) 15901 - 15908   2015年12月

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    担当区分:最終著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/acs.jpcb.5b11208

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  • What Can Be Learned from Magnetic Field Effects on Singlet Fission: Role of Exchange Interaction in Excited Triplet Pairs 査読

    Masanobu Wakasa, Mana Kaise, Tomoaki Yago, Ryuzi Katoh, Yusuke Wakikawa, Tadaaki Ikoma

    The Journal of Physical Chemistry C119 ( 46 ) 25840 - 25844   2015年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/acs.jpcc.5b10176

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  • Aryl-substituted dimethylbenzimidazolines as effective reductants of photoinduced electron transfer reactions 査読

    Eietsu Hasegawa, Taku Ohta, Shiori Tsuji, Kazuma Mori, Ken Uchida, Tomoaki Miura, Tadaaki Ikoma, Eiji Tayama, Hajime Iwamoto, Shin-ya Takizawa, Shigeru Murata

    Tetrahedron71 ( 34 ) 5494 - 5505   2015年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.tet.2015.06.071

    Web of Science

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  • Mechanism of Intersystem Crossing of Thermally Activated Delayed Fluorescence Molecules 査読

    Toshinari Ogiwara, Yusuke Wakikawa, Tadaaki Ikoma

    The Journal of Physical Chemistry A119 ( 14 ) 3415 - 3418   2015年4月

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    担当区分:最終著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/acs.jpca.5b02253

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  • Long-Distance Sequential Charge Separation at Micellar Interface Mediated by Dynamic Charge Transporter: A Magnetic Field Effect Study 査読

    Tomoaki Miura, Kiminori Maeda, Hisao Murai, Tadaaki Ikoma

    The Journal of Physical Chemistry Letters6 ( 2 ) 267 - 271   2015年1月

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    担当区分:最終著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/jz502495u

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  • Carrier Dynamics in Pentacene|C60 Bilayer Solar Cell Investigated through the Magnetoconductance 査読

    Takuya Omori, Yusuke Wakikawa, Tomoaki Miura, Yuji Yamaguchi, Ken-ichi Nakayama, Tadaaki Ikoma

    The Journal of Physical Chemistry C118 ( 49 ) 28418 - 28424   2014年12月

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    担当区分:最終著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/jp508799j

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  • Thermal Annealing Effects on the Photocarrier Dynamics in PCBM Films 査読

    Christopher E. Ambe, Yusuke Wakikawa, Tadaaki Ikoma

    Bulletin of the Chemical Society of Japan86 ( 9 ) 1051 - 1058   2013年9月

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    担当区分:最終著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:The Chemical Society of Japan  

    DOI: 10.1246/bcsj.20130097

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  • Effect of Acceptor Lamination on Photocarrier Dynamics in Hole Transporting Hexabenzocoronene Nanotubular Self-Assembly 査読

    Yusuke Wakikawa, Tadaaki Ikoma, Yohei Yamamoto, Takanori Fukushima, Takuzo Aida, Kimio Akiyama

    The Journal of Physical Chemistry C117 ( 29 ) 15295 - 15305   2013年7月

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    担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/jp402640k

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  • “Dark” Excited States of Diphenylacetylene Studied by Nonresonant Two-Photon Excitation Optical-Probing Photoacoustic Spectroscopy 査読

    T. Suzuki, M. Nakamura, T. Isozaki, T. Ikoma

    International Journal of Thermophysics33 ( 10-11 ) 2046 - 2054   2012年11月

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    担当区分:最終著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Springer Science and Business Media LLC  

    DOI: 10.1007/s10765-012-1296-8

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    その他リンク: http://link.springer.com/article/10.1007/s10765-012-1296-8/fulltext.html

  • Molecular spintronics 査読

    Masashi Shiraishi, Tadaaki Ikoma

    Physica E: Low-dimensional Systems and Nanostructures43 ( 7 ) 1295 - 1317   2011年5月

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    担当区分:最終著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.physe.2011.02.010

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  • Structural and Electronic Properties of Extremely Long Perylene Bisimide Nanofibers Formed through a Stoichiometrically Mismatched, Hydrogen-Bonded Complexation 査読

    Shiki Yagai, Tomohiro Seki, Haruno Murayama, Yusuke Wakikawa, Tadaaki Ikoma, Yoshihiro Kikkawa, Takashi Karatsu, Akihide Kitamura, Yoshihito Honsho, Shu Seki

    Small6 ( 23 ) 2731 - 2740   2010年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Wiley  

    DOI: 10.1002/smll.201001344

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  • Giant magnetoresistance due to electron-hole pair mechanism in poly(N-vinylcarbazole) 査読

    Tadaaki Ikoma, Toshinari Ogiwara, Yutaka Takahashi, Kimio Akiyama, Shozo Tero-Kubota, Yuka Takahashi, Tomohiro Suzuki, Yusuke Wakikawa

    Synthetic Metals160 ( 3-4 ) 285 - 290   2010年2月

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    担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.synthmet.2009.10.003

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  • Magnetic field effect on the photocarriers in self-assembled hexabenzocoronene nanotubes 査読

    Yusuke Wakikawa, Tadaaki Ikoma, Yohei Yamamoto, Takanori Fukushima, Takuzo Aida

    Synthetic Metals160 ( 3-4 ) 275 - 279   2010年2月

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    担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.synthmet.2009.08.052

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  • Peculiarity in the Electronic Structure of Cu(II) Complex Ferromagnetically Coupled with Bisimino Nitroxides 査読

    Tadaaki Ikoma, Hiroki Oshio, Masashi Yamamoto, Yasunori Ohba, Masayuki Nihei

    The Journal of Physical Chemistry A112 ( 37 ) 8641 - 8648   2008年9月

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    担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/jp802810s

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  • Time-resolved EPR study on photoreduction of sodium anthraquinone-2-sulfate in liposomes 査読

    Shinya Moribe, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota

    Chemical Physics Letters457 ( 1-3 ) 66 - 68   2008年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.cplett.2008.03.089

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  • Synthesis and Intramolecular Pericyclization of 1-Azulenyl Thioketones 査読

    Shunji Ito, Tetsuo Okujima, Shigeru Kikuchi, Taku Shoji, Noboru Morita, Toyonobu Asao, Tadaaki Ikoma, Shozo Tero-Kubota, Jun Kawakami, Akio Tajiri

    The Journal of Organic Chemistry73 ( 6 ) 2256 - 2263   2008年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/jo702309b

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  • Spin-Correlated Radical Pairs in Synthetic Hairpin DNA 査読

    Satoru Nakajima, Kimio Akiyama, Kiyohiko Kawai, Tadao Takada, Tadaaki Ikoma, Tetsuro Majima, Shozo Tero-Kubota

    ChemPhysChem8 ( 4 ) 507 - 509   2007年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Wiley  

    DOI: 10.1002/cphc.200600621

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  • EPR study on paramagnetic species in nitrogen-doped ZnO powders prepared by a mechanochemical method 査読

    Shinya Moribe, Tadaaki Ikoma, Kimio Akiyama, Qiwu Zhang, Fumio Saito, Shozo Tero-Kubota

    Chemical Physics Letters436 ( 4-6 ) 373 - 377   2007年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.cplett.2007.01.067

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  • Characterization of the Phenoxyl Radical in Model Complexes for the CuBSite of CytochromecOxidase:  Steady-State and Transient Absorption Measurements, UV Resonance Raman Spectroscopy, EPR Spectroscopy, and DFT Calculations for M-BIAIP 査読

    Yasutomo Nagano, Jin-Gang Liu, Yoshinori Naruta, Tadaaki Ikoma, Shozo Tero-Kubota, Teizo Kitagawa

    Journal of the American Chemical Society128 ( 45 ) 14560 - 14570   2006年11月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/ja061507y

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  • Visible light induced paramagnetic sites in nitrogen-doped TiO2prepared by a mechanochemical method 査読 国際誌

    Y. Yamamoto, S. Moribe, T. Ikoma, K. Akiyama, Q. Zhang, F. Saito, S. Tero-Kubota

    Molecular Physics104 ( 10-11 ) 1733 - 1737   2006年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Informa UK Limited  

    The radical sites generated by the visible light irradiation of nitrogen-doped TiO2 particles prepared by a mechanochemical method have been studied using cw-EPR spectroscopy. The powders prepared by planetary milling of the anatase TiO2 with urea clearly show an absorption in the visible region, indicating doping of nitrogen. Visible light irradiation with wavelengths longer than 420nm induces a nitrogen-centred radical site. The radical site is assigned to the interstitial NO22- radical. In the presence of air, a reversible response of the growth and decay of paramagnetic sites was observed during and after photolysis. In contrast, in degassed samples, the decay of the NO22- signals is accompanied by the concomitant growth of the neutral NO radical site after irradiation, suggesting breaking of the N-O bond.

    DOI: 10.1080/00268970600551387

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  • Carrier Generation Process on Photoconductive Polymer Films as Studied by Magnetic Field Effects on the Charge-Transfer Fluorescence and Photocurrent 査読

    Fuyuki Ito, Tadaaki Ikoma, Kimio Akiyama, Akira Watanabe, Shozo Tero-Kubota

    The Journal of Physical Chemistry B110 ( 10 ) 5161 - 5162   2006年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/jp0565857

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  • Evidence of Photocarrier Generation via the Singlet and Triplet States in a Poly(N-vinylcarbazole) Film 査読

    Tadaaki Ikoma, Fuyuki Ito, Toshinari Ogiwara, Kimio Akiyama, Shozo Tero-Kubota

    Chemistry Letters34 ( 10 ) 1424 - 1425   2005年10月

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    担当区分:筆頭著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:The Chemical Society of Japan  

    A significant wavelength dependence of the excitation light was observed in the magnetic field effects (MFE) on the photocarrier generation of a benzene-1,2,4,5-tetracarbonitrile-doped poly(N-vinylcarbazole) film. The excitation of the carbazole induces positive MFEs, indicating an enhancement of the photoconductivity originating from the charge separation through the triplet exciton. In contrast, a singlet spin state governs the photocarrier generation in the case of the charge transfer band excitation, because negative MFEs are induced.

    DOI: 10.1246/cl.2005.1424

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  • Preliminary Investigation of the Supply of Chemical Species to an Aqueous Solution Using a Hydrogen−Oxygen Flame 査読

    Miho Uchida, Takahiro Sogabe, Tadaaki Ikoma, Akitsugu Okuwaki

    Environmental Science & Technology39 ( 15 ) 5851 - 5855   2005年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/es048299z

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  • Spin dynamics of carrier generation in a photoconductive C60-doped poly(N-vinylcarbazole) film 査読

    Toshinari Ogiwara, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota

    Chemical Physics Letters411 ( 4-6 ) 378 - 383   2005年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.cplett.2005.06.066

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  • Study of Anisotropic Interfacial Electron Transfer Across a Semiconductor/Solution Interface by Time-Resolved EPR Spectroscopy 査読

    Kimio Akiyama, Shinji Hashimoto, Sachiko Tojo, Tadaaki Ikoma, Shozo Tero-Kubota, Tetsuro Majima

    Angewandte Chemie International Edition44 ( 23 ) 3591 - 3594   2005年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Wiley  

    DOI: 10.1002/anie.200461681

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  • Carrier generation in photoconductive poly(N-vinylcarbazole) as revealed by multifrequency time-resolved ESR 査読 国際誌

    Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota

    Physical Review B71 ( 19 )   2005年5月

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    担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society (APS)  

    Using the multifrequency time-resolved electron-spin-resonance (TRESR) method, we have investigated the carrier-generation dynamics in a photoconductive film sample of poly(N-vinylcarbazole), The TRESR spectra, due to spin-polarized geminate electron-hole (e-h) pairs captured in deep-trap sites, were observed at several fields that were achieved using microwaves with different frequencies, The spectra detected at room temperature were interpreted in terms of the ST0 polarization in trapped e-h pairs and the ST+ polaritation induced in canonical e-h pairs. The spectral simulation clarified the distribution of e-h separation distance (r) and the r-dependent recombination of the trapped pairs. The initial spatial distribution of the trapped e-h pairs exponentially decreased with an increase in r. There is no large population of long-distant c-h pairs with r &gt; 1.5 nm. Based on the appearance of the ST+ polarization in the long-distant pairs that is generated in middle-distant pairs and the initial exponential distribution of the trapped pairs, it was concluded that stepwise hole hops rather than a long-range hole jump represent the proper dynamics of the geminate pair in the charge-separation process. The r-dependent recombination rate suggests a single-step tunneling recombination of the trapped pairs.

    DOI: 10.1103/physrevb.71.195206

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    その他リンク: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.71.195206/fulltext

  • Carrier Generation Process on Photoconductive Polymer Films as Studied by Magnetic Field Effects on the Charge-Transfer Fluorescence and Photocurrent 査読

    Fuyuki Ito, Tadaaki Ikoma, Kimio Akiyama, Akira Watanabe, Shozo Tero-Kubota

    The Journal of Physical Chemistry B109 ( 18 ) 8707 - 8717   2005年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/jp0453212

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  • Spin Dynamic Study on the Electric Field Dependence of Carrier Generation 査読

    Fuyuki Ito, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota

    The Journal of Physical Chemistry B109 ( 15 ) 7208 - 7213   2005年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/jp044475e

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  • Azulene-Substituted Aromatic Amines. Synthesis and Amphoteric Redox Behavior ofN,N-Di(6-azulenyl)-p-toluidine andN,N,N‘,N‘-Tetra(6-azulenyl)-p-phenylenediamine and Their Derivatives 査読

    Shunji Ito, Takahiro Kubo, Noboru Morita, Tadaaki Ikoma, Shozo Tero-Kubota, Jun Kawakami, Akio Tajiri

    The Journal of Organic Chemistry70 ( 6 ) 2285 - 2293   2005年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/jo048489s

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  • Synthesis, Stabilities, and Redox Behavior of Di(1-azulenyl)(6-azulenyl)methylium Hexafluorophosphates. Generation of a Donor−Acceptor-Substituted Neutral Radical by Azulenes 査読

    Shunji Ito, Takahiro Kubo, Noboru Morita, Tadaaki Ikoma, Shozo Tero-Kubota, Akio Tajiri

    The Journal of Organic Chemistry68 ( 25 ) 9753 - 9762   2003年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/jo035053o

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  • Symmetry Switching of the Fluorescent Excited State in α,ω-Diphenylpolyynes 査読

    Yasutomo Nagano, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota

    Journal of the American Chemical Society125 ( 46 ) 14103 - 14112   2003年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    y using MO calculations based on DFT, absorption, and fluorescence spectroscopy, we have comprehensively studied the low-lying excited singlet states of alpha,omega-diphenylpolyynes (DPY) having 1-6 triple bonds. The a(g) vibrational modes of the CdropC stretching and of the phenyl ring motion were observed in the fluorescence spectra of diphenylacetylene and 1,4-diphenylbutadiyne. On the other hand, in the fluorescence spectra of the long DPY with the triple-bond number (N) more than two, the phenyl ring motion with ag symmetry disappeared and the big modes of the phenyl ring twisting (similar to400 cm(-1)) and of the C-H bending (similar to900 cm(-1)) were detected. The observed fluorescent states of DPY with N less than or equal to 2 and N greater than or equal to 3 are assigned to the 1(1)B(1u) (pi(x)pi(x)(*)) and 1(1)A (pi(x)pi(y)(*) and/or pi(y)pi(x)(*)) states, respectively, based on the vibronic structures, the relatively short lifetimes, and the solvatochromic shifts of the fluorescence spectra. Not only the allowed transition of 1(1)B(1u) &lt;-- So but also the forbidden transition of 1(1)A(u) &lt;-- S-0 was detected in the fluorescence excitation spectra of the long DPY with N greater than or equal to 3. The low-lying excited state with A(u) symmetry is characteristic in polyyne, which does not exist in polyene. The oscillator strength (f) of the first absorption band in DPY decreases with an increase in N, which is the opposite behavior of the all-trans-alpha,omega-diphenylpolyenes. The N-dependence of the f value is understood by the configuration interaction between the 1(1)B(1u) and 2(1)B(1u) (pi(y)pi(y)(*)) states, which is consistent with the reduction of the nonlinear optical response of polyyne.

    DOI: 10.1021/ja035173d

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  • Angle-selective measurements of spin soliton in ladder polydiacetylene by pulsed 94 GHz EPR 査読

    T. Ikoma, S. Okada, S. Tero-Kubota, H. Nakanishi, T. Kato, P. Höfer, A. Kamlowski, K. Akiyama

    Applied Magnetic Resonance23 ( 3-4 ) 445 - 453   2003年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Springer Science and Business Media LLC  

    DOI: 10.1007/bf03166633

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    その他リンク: http://link.springer.com/article/10.1007/BF03166633/fulltext.html

  • EPR studies on defects in sol–gel derived alumina films 査読

    T. Ishizaka, S. Tero-Kubota, Y. Kurokawa, T. Ikoma

    Journal of Physics and Chemistry of Solids64 ( 5 ) 801 - 806   2003年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    We have studied the defect structures and mechanism for the luminescence of non-doped, Tb3+-doped and Tb3+-Zn2+ codoped alumina films treated at various temperatures from 300 to 800°C. The electron paramagnetic resonance (EPR) spectra observed before UV-irradiation are attributable to the non-bridging oxygen radicals Al-O-O at treatment temperatures of 300-500°C and Al-O at 800°C. The UV-light irradiation of the non-doped alumina films gives the EPR spectra with the 27Al hyperfine splitting. There exists a good correlation between the treatment temperature dependence on the light-induced EPR signal intensity of the trapped electron and the NMR peak intensity due to the five-coordinated aluminum ion. We concluded that the electron is captured at the oxygen vacancy connected with the five-coordinated aluminum. The broad EPR spectra due to the ground state of the Tb3+ ion were observed in the Tb3+-doped and Tb3+-Zn2+ codoped alumina films. The Tb3+ concentration dependence of the EPR signal intensity due to the non-bridging oxygens suggests that Tb3+ prefers to form Al-O-Tb bonds and prevent to form a cluster of rare earth ions itself. The light-induced EPR signal of the electron trapped at oxygen vacancy next the five-coordinated aluminum was also observed for the Tb3+-Zn2+ codoped alumina film, which produced a long-lasting luminescence. The photogenerated trapped electron remained for several minutes under the room temperature. These experimental facts indicate that the five-coordinated aluminum ions act as the trapping sites to produce the long-lasting luminescence. © 2002 Published by Elsevier Science Ltd.

    DOI: 10.1016/s0022-3697(02)00377-3

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  • Long-Range Jump versus Stepwise Hops:  Magnetic Field Effects on the Charge-Transfer Fluorescence from Photoconductive Polymer Films 査読

    Fuyuki Ito, Tadaaki Ikoma, Kimio Akiyama, Yasuhiro Kobori, Shozo Tero-Kubota

    Journal of the American Chemical Society125 ( 16 ) 4722 - 4723   2003年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/ja029443o

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  • Substrate Specificities of Deuterolysin fromAspergillus oryzaeand Electron Paramagnetic Resonance Measurement of Cobalt-substituted Deuterolysin 査読 国際誌

    Yuko DOI, Byung Rho LEE, Masamichi IKEGUCHI, Yasunori OHOBA, Tadaaki IKOMA, Shozo TERO-KUBOTA, Seigo YAMAUCHI, Koji TAKAHASHI, Eiji ICHISHIMA

    Bioscience, Biotechnology, and Biochemistry67 ( 2 ) 264 - 270   2003年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Informa UK Limited  

    The substrate specificities of deuterolysin, a 19-kDa zinc-protease (EC 3.4.24.39) from Aspergillus oryzae, were investigated at pH 9.0 with various fluorogenic acyl-peptide-4-methylcoumaryl-7-amides (peptide-MCAs). N-Butoxycarbonyl-Arg-Val-Arg-Arg-MCA was the best substrate for deuterolysin. We therefore measured its kinetic parameters. Deuterolysin had high activity toward the peptide bonds next to pairs of basic residues in calf thymus histone H4. The specificity of cobalt-substituted deuterolysin (Co-deuterolysin) for peptide-MCAs was similar to that of native deuterolysin. The CD spectrum of Co-deuterolysin was similar to that of the native deuterolysin. The metal coordination sphere of Co-deuterolysin was analyzed by Q-band (33.9570 GHz) electron paramagnetic resonance (EPR) spectroscopy. Using computer simulation of EPR, we found the g principal values to be g(xx) = 5.20, g(yy) = 4.75, and g(zz) = 2.24; the metal center was a divalent cobalt ion in a high spin state.

    DOI: 10.1271/bbb.67.264

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  • Spin soliton in aπ-conjugated ladder polydiacetylene 査読

    Tadaaki Ikoma, Shuji Okada, Hachiro Nakanishi, Kimio Akiyama, Shozo Tero-Kubota, Klaus Möbius, Stefan Weber

    Physical Review B66 ( 1 ) 014423-1 - 014423-9   2002年7月

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    担当区分:筆頭著者, 責任著者   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society (APS)  

    DOI: 10.1103/physrevb.66.014423

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    その他リンク: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.66.014423/fulltext

  • Electronic structure of the lowest excited triplet state of 5,12-naphthacenequinone 査読 国際誌

    Takuji Shimokage, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota

    Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy58 ( 6 ) 1201 - 1208   2002年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    Continuous-wave time-resolved EPR (cw-TREPR) and pulsed electron nuclear double resonance (ENDOR) studies have been carried out to clarify the electronic structure of the lowest excited triplet (T,) state of 5,12-naphthacenequinone (5,12-NpQ) as well as 1,4-anthraquinone (1,4-AQ) and 6,13-pentacenequinone (6,13-PeQ). The T, energy level and the D value of the zero-field splitting (ZFS) parameters only slightly decreased with the increasing pi-conjugated system. The T-1 states of these linear para-acenequinones were assigned to the pipi* character. In triplet 5,12-naphthacenequinone, more than 80% of the unpaired electron spins are localized on the naphthalene aromatic sub-system. (C) 2002 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/s1386-1425(01)00710-7

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  • Exploring Radicals in Carbonaceous Solids by Means of Pulsed EPR Spectroscopy 査読

    Tadaaki Ikoma, Osamu Ito, Shozo Tero-Kubota

    Energy & Fuels16 ( 1 ) 40 - 47   2002年1月

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    担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    Pulsed electron paramagnetic resonance (EPR) spectroscopy has been applied to elucidate the radical structures of Argonne premium coals and the reaction processes in coal tar pitches (CTP). Using two-dimensional nutation spectroscopy, the main EPR signals around g = 2.00 for the coals were confirmed to be attributed to free radicals rather than spin clusters with higher spin multiplicities. The broad H-1- and C-13-hyperfine spectra of the coals were detected separately by hyperfine sublevel correlation (HYSCORE) spectroscopy. It is concluded that the main coal radicals are pi radicals delocalized in pericondensed aromatic hydrocarbons with more than seven aromatic rings, which are larger than those of the most probable aromatic molecules in coals. HYSCORE spectroscopy, furthermore, helped us to understand the chemical change in the cation radicals in the charge-transfer complexes that accelerate the dehydrogenative polymerization of I-2-treated CTP.

    DOI: 10.1021/ef010148j

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  • Effects of Quartz Addition on the Mechanochemical Dechlorination of Chlorobiphenyl by Using CaO 査読

    Qiwu Zhang, Fumio Saito, Tadaaki Ikoma, Shozo Tero-Kubota, Kiyotaka Hatakeda

    Environmental Science & Technology35 ( 24 ) 4933 - 4935   2001年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    Grinding a mixture of 3-chlorobiphenyl (BP-Cl) and CaO with or without the addition of quartz was conducted in air by a planetary ball mill to investigate the mechanochemical dechlorination of BP-Cl. The dechlorinating reaction proceeds with an increase in grinding time, and over 99% of BP-Cl is decomposed at 360 min. Washing the ground sample with different solvents results in different products. Addition of quartz to the grinding mixture facilitates dechlorination efficiency, especially in the case of a high weight ratio of BP-Cl to CaO.

    DOI: 10.1021/es010638q

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  • Radicals in the Mechanochemical Dechlorination of Hazardous Organochlorine Compounds Using CaO Nanoparticles 査読 国際誌

    Tadaaki Ikoma, Qiwu Zhang, Fumio Saito, Kimio Akiyama, Shozo Tero-Kubota, Tatsuhisa Kato

    Bulletin of the Chemical Society of Japan74 ( 12 ) 2303 - 2309   2001年12月

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    担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:The Chemical Society of Japan  

    For the first time, we detected paramagnetic products generated during the grinding of 3-chlorobiphenyl (BP-Cl) with calcium oxide (CaO) nanoparticles by a ball mill method, which is one of the promising ways to detoxify hazardous chlorinated organic compounds. Those products were assigned to oxygen-centered aromatic radicals coming from BP-Cl and trapped electrons in oxygen vacancies on the surfaces of the CaO reactants using high-frequency and pulsed electron paramagnetic resonance spectroscopies. The observed good correlation between the dechlorination efficiency and the radical yield suggests that a radical mechanism plays an important role in the destruction of organochlorine compounds. The mechanochemical dechlorination could be interpreted by the following mechanism. First of all, the mechanical stressing induces the electron transfer from O2- sites on the surface of the CaO particle to the organic compounds. The produced organic anion radicals then undergo the effective self-dissociation of a chlorine-carbon bond.

    DOI: 10.1246/bcsj.74.2303

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  • Experimental and Theoretical Studies on Ferromagnetically Coupled Metal Complexes with Imino Nitroxides 査読 国際誌

    Hiroki Oshio, Masashi Yamamoto, Tasuku Ito, Hidekazu Kawauchi, Nobuaki Koga, Tadaaki Ikoma, Shozo Tero-Kubota

    Inorganic Chemistry40 ( 22 ) 5518 - 5525   2001年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    Copper(II), zinc(II), and nickel(II) complexes with tridentate imino nitroxyl diradicals, [CuCl(bisimpy)(MeOH)]-(PF6) (1), [ZnCl2(bisimpy)] (2), and [NiCl(bisimpy)(H2O)(2)]Cl . 2H(2)O (3) (bisimpy = 2,6-bis(1'-oxyl-4',4',5',5'-tetramethyl-4',5'-dihydro-1'H-imidazol-2'-yl)pyridine), were prepared, and their magnetic properties were studied. In 1, the Cu(II) ion has a square pyramidal coordination geometry, of which the equatorial coordination sites are occupied by three nitrogen atoms from the bisimpy and a chloride ion. The coordination geometry of the Zn(II) ion in 2 can be described as a trigonal bipyramid, with two chloride ions and a bisimpy. In 3, the Ni(II) ion has a distorted octahedral coordination geometry, of which four coordination sites are coordinated by the bisimpy and chloride ion, and two water molecules occupy the remaining cis positions. Magnetic susceptibility and EPR measurements revealed that in 1 and 3 the Cu(II) and Ni(II) ions with imino nitroxyl diraicals were ferromagnetically respectively, and the coupled, with the coupling constants J (H = -2J(ij)SigmaS(i)S(j)) of +165(1) and 109(2) cm(-1), intraligand ferromagnetic interactions in 1-3 were very weak. DFT molecular orbital calculations were performed on the diradical ligand, 1, and 2 to study the spin density distribution before and after coordination to the metal ions.

    DOI: 10.1021/ic0102384

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  • Direct Observation of a Distant Ion Pair Generated in a Photoconductive Poly(N-vinylcarbazole) Film with Dopant 査読

    Tadaaki Ikoma, Mototada Nakai, Kimio Akiyama, Shozo Tero-Kubota, Toru Ishii

    Angewandte Chemie International Edition40 ( 17 ) 3234 - 3236   2001年9月

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    担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Wiley  

    DOI: 10.1002/1521-3773(20010903)40:17<3234::aid-anie3234>3.0.co;2-b

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  • Electronic structures and dynamics of the excited triplet states of α,ω-diphenylpolyynes 査読

    Yasutomo Nagano, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota

    The Journal of Chemical Physics114 ( 4 ) 1775 - 1784   2001年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AIP Publishing  

    The lowest excited triplet (T-1) states of diphenylacetylene and several alpha,omega -diphenylpolyynes (DPY) having two, three, four and six triple bonds were studied using continuous wave time-resolved electron paramagnetic resonance (CW-TREPR), pulsed EPR, and phosphorescence spectroscopy. Linear and planar molecular structures in the T-1 states of DPY were suggested from the magnetophotoselection experiments and observation of a strong 0-0 band in the well-resolved phosphorescence spectra. The spin density distributions, which were obtained by electron spin echo envelope modulation measurements and semi-empirical molecular orbital calculations, and the phosphorescence polarization normal to the long axis of molecule for the 0-0 bands suggested that the T-1 states of DPY have a B-3(1u) (pi (x)pi (x)*) electronic configuration. DPY showed an abnormally large \D\ value of the zero-field splitting parameters that increased with increasing molecular size. Such an unusual behavior of the D values is interpreted in terms of the spin-orbit interaction between the T-1 and (3)A(u)(pi (x)pi (y)*) states mainly due to their energy proximity which is probably characteristic of the excited states for the polyynes. The estimated energy gap between the (3)pi (x)pi (y)* and (3)pi (x)pi (x)* states for DPY ranges from 2900 cm(-1) to 1400 cm(-1). There existed a good correlation between the acceleration of the nonradiative decay rate constant from the T1 state and appearance of a ring twisting vibronic band with b(1g) symmetry in the phosphorescence spectra for DPY. Therefore, we concluded that the vibronic interaction between the (3)pi (x)pi (y)* and (3)pi (x)pi (x)* states promoted by the b(1g) vibration leads to a broadening of the potential surface of the T-1 state which results in the fast radiationless decay Co the ground state, (C) 2001 American Institute of Physics.

    DOI: 10.1063/1.1331614

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  • ESEEM study on a stable paramagnetic center in polydiacetylene having a π-conjugated ladder structure 査読 国際誌

    T Ikoma, S Okada, H Nakanishi, K Akiyama, S Tero-Kubota

    Solid State Communications117 ( 5 ) 285 - 289   2001年1月

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    担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    Using two-, three- and five-pulse methods, we have measured the electron spin echo envelope modulation (ESEEM) of a stable paramagnetic center existing in a non-doped ladder polymer, in which two polydiacetylenes are conjugated in each repeating unit. A relatively deep modulation effect owing to weak hyperfine interaction with protons was observed. The number of interacting protons was estimated to be a few tens based on the analysis of the modulation amplitude. The interaction with many protons implies that the paramagnetic center in the ladder polydiacetylene also possesses a wavefunction delocalized on several units in the pi -conjugated system like the spin solitons in polyacetylene. (C) 2001 Elsevier Science Ltd. All rights reserved.

    DOI: 10.1016/s0038-1098(00)00471-3

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  • Electron paramagnetic resonance studies on microcrystalline silicon prepared by sputtering method 査読 国際誌

    Takashi Ehara, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota

    Journal of Applied Physics88 ( 3 ) 1698 - 1700   2000年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AIP Publishing  

    Dangling bond (DB) defects in unhydrogenated microcrystalline silicon (mu c-Si) prepared by rf sputtering have been studied. Raman spectra and x-ray diffraction indicate that the mu c-Si fraction has been formed at the Ar sputtering pressure higher than 26.6 Pa while only amorphous silicon (a-Si) has been produced at the lower pressure. The electron paramagnetic resonance (EPR) spectrum in the mu c-Si film is broad and unsymmetrical with the average g value of g=2.006 compared with that of a-Si (g=2.0055). The X- and Q-band EPR measurements suggest that the line shape is mainly governed by the inhomogeneous broadening due to the g anisotropy, indicating relatively large distribution of the structure of the DB defects. (C) 2000 American Institute of Physics. [S0021-8979(00)06712-8].

    DOI: 10.1063/1.373875

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  • Multi-band electron paramagnetic resonance study of the defects in microcrystalline silicon 査読

    Takashi Ehara, Tadaaki Ikoma, Shozo Tero-Kubota

    Journal of Non-Crystalline Solids266-269   540 - 543   2000年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    We report electron paramagnetic resonance (EPR) studies in dangling bond (DB) defects in the hydrogenated microcrystalline silicon (mu c-Si:H) film prepared by a plasma enhanced chemical vapor deposition (PECVD), unhydrogenated microcrystalline silicon (mu c-Si) film prepared by RF sputtering, and mu c-Si embedded in SiO2 film formed by co-sputtering followed by annealing. Multi-band EPR measurements showed that their line widths originate primarily from a distribution of the g-values. We have detected a signal at g = 2.006 in the microcrystalline fraction of the mu c-Si, mu c-Si:H and mu c-Si embedded SiO2 films. The signal has a greater width than the DB signal in amorphous silicon (a-Si), indicating a larger distribution of g-values of the defects in the microcrystalline material. The DB signal in the mu c-Si embedded in SiO2 was reproduced by the computer simulation taking into account the distribution of the g-values. (C) 2000 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/s0022-3093(00)00027-2

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  • Nitrogen-Doping Effects on Electrical Properties of Hydrogenated Microcrystalline Silicon as Studied by Electron Paramagnetic Resonance and Conductivity 査読 国際誌

    Takashi Ehara, Tetsuya Amino, Hiroyuki Shinomiya, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota

    Japanese Journal of Applied Physics39 ( Part 1, No. 1 ) 31 - 34   2000年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP Publishing  

    We have examined Raman scattering, X-ray diffraction, electron paramagnetic resonance (EPR) spectra and the conductivity of nitrogen-doped hydrogenated microcrystalline silicon. The EPR signals due to conduction electrons have been observed in the doped films, except for highly doped samples that have no microcrystalline fraction. The result indicates that the doped nitrogen atom acts as an electron donor in the microcrystalline silicon. The temperature dependence of the conductivity clarify that the activation energy depends on the doping level. The influence of the doping level on the conductivity can be interpreted in terms:of the balance of the effective electron donation and the decrease of carrier mobility due to a decrease of the microcrystalline phase volume ratio. At temperatures lower than approximately 180 K, the conductivity shows little variation. This is explained using a model of the hopping conduction, in terms of defect states for all samples.

    DOI: 10.1143/jjap.39.31

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  • A role of charge-transfer complex with iodine in the modification of coal tar pitch 査読 国際誌

    N Miyajima, T Akatsu, T Ikoma, O Ito, B Rand, Y Tanabe, E Yasuda

    Carbon38 ( 13 ) 1831 - 1838   2000年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    Iodine introduced into coal tar pitch (CTP) can drastically alter its reology and carbonization behavior. Here, the mechanism of interaction between iodine and CTP has been investigated by using various spectroscopic methods such as I-127-NMR, EPR and FT-IR. It is shown that some iodine molecules infiltrated into the CTP and form charge transfer complexes with the relative large aromatic components of the CTP. Hyperfine sublevel correlation spectroscopy (HYSCORE) revealed the molecular size of cation radicals, which contain more than ten benzene rings, and the location of iodine anion that is incorporated at ca. 0.3 nm from the aromatic cation radicals. The elemental H/C ratio decreased and the viscosity of CTP increased with the density of the charge-transfer complexes, which was also increased by the iodine treatment. These results strongly suggest that dehydrogenative polymerization of CTP occurs during the iodine treatment. The cation radicals in the charge-transfer complexes accelerate the dehydrogenative polymerization and result in a high carbon yield. (C) 2000 Elsevier Science Ltd. All rights reserved.

    DOI: 10.1016/s0008-6223(00)00022-1

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  • Cyanide-Bridged Iron−Copper Molecular Squares with Doublet and Quintet Spin Ground States 査読 国際誌

    Hiroki Oshio, Osamu Tamada, Hironori Onodera, Tasuku Ito, Tadaaki Ikoma, Shozo Tero-Kubota

    Inorganic Chemistry38 ( 25 ) 5686 - 5689   1999年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    Reactions of [Fe-II(CN)(2)(bpy)(2)] and [Fe-III(CN)(2)(bpy)(2)](PF6) with [Cu-II(bpy)(CH3OH)(2)](PF6)(2) in methanol yielded cyanide-bridged cyclic tetranuclear complexes of [(Fe2Cu2II)-Cu-II(mu-CN)(4)(bpy)(6)](PF6)(4). 2H(2)O . 4CHCl(3) (1) and [Fe-2(III)-Cu-2(II) (mu-CN)(4)(bpy)(6)](PF6)(6) . 4CH(3)CN . 2CNCl(3) (2), respectively. Zn the squares of 1 and 2, the Fe2+/3+ (low-spin) and Cu2+ ions are alternately bridged by the cyanide ions, the carbon atoms of which coordinate to the iron ions. Variable-temperature magnetic susceptibility studies of complexes revealed that the Cu2+ ions in 1 are magnetically isolated. In the square of 2, the adjacent Fe3+ and Cu2+ ions were ferromagnetically coupled through the cyanide bridges with a J(1) value of +6.3(1) cm(-1) and the weaker antiferromagnetic interactions between the orthogonal Fe3+... Fe3+ and Cu2+...Cu2+ pairs are operative (J(2) = -3.1(1) cm(-1)). The propagation of the ferromagnetic interaction in 2 can be understood by the orthogonal magnetic orbitals of the low-spin Fe3+ (d pi) and Cu2+ (d sigma) ions. Cyclic voltammograms of the squares have been recorded and discussed. Crystal data for 1: triclinic space group P (1) over bar, a = 14.491(4) Angstrom, b = 15.312(4) Angstrom, c = 12.959(3) Angstrom, alpha = 91.38(2)degrees , beta = 109.56(2)degrees, gamma = 65.41(2)degrees, Z = 1. Crystal data for 2: triclinic space group P (1) over bar, a = 14.472(9) Angstrom, b = 15.310(6) Angstrom, c = 12.523(5) Angstrom, alpha 102.58(3)degrees beta = 107.19(4)degrees, gamma = 75.08(4)degrees, Z = 1.

    DOI: 10.1021/ic990617l

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  • Proton tunneling of tropolone in durene single crystal as studied by time-resolved EPR detected excitation spectroscopy 査読 国際誌

    Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota, Yusaku Ikegami

    The Journal of Chemical Physics111 ( 15 ) 6875 - 6883   1999年10月

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    担当区分:筆頭著者, 責任著者   掲載種別:研究論文(学術雑誌)   出版者・発行元:AIP Publishing  

    We have measured the excitation spectra for tropolone-OH in durene single crystal and tropolone-OD in deuterated durene using a time-resolved electron paramagnetic resonance (TREPR) detection method that makes possible to separate the signals due to magnetically different sites. The tunneling doublet with 3 cm(-1) was observed in the sharp zero-phonon line. The small splitting indicates that the crystal field increases the barrier of double-minimum potential for the proton tunneling in the S-1 state. Moderately asymmetric potentials of the S-0 and S-1 states, where the energetic imbalance between two wells in the S-1 state potential is opposite the S-0 state potential, reasonably explained the observed unusual intensity ratio of the tunneling doublet (0(1)(+) &lt; 0(1)(-)). A well-resolved progression of a phonon band with a 15 cm(-1) separation was also obtained in durene crystal at very low temperature. From a Franck-Condon analysis of the relative intensity of the phonon band, it was clarified that the stable configuration of the excited state tropolone in durene differed from that of the ground state. (C) 1999 American Institute of Physics. [S0021-9606(99)00439-0].

    DOI: 10.1063/1.479980

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  • Electronic and molecular structures of α,ω-diphenylpolyynes in the lowest excited triplet states 査読 国際誌

    Yasutomo Nagano, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota

    Chemical Physics Letters303 ( 1-2 ) 201 - 208   1999年4月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    Unusually large \D\ values of zero-field splitting parameters were observed for 1,6-diphenylhexatriyne (\D\ = 0.396 cm(-1)) and 1,8-diphenyloctatetrayne (\D\ = 0.533 cm(-1)) by using time-resolved EPR (TREPR) spectroscopy. The lowest excited triplet (T-1) states of these diphenylpolyynes were assigned to B-3(1u)((3)pi(x)pi(x)(*)) in character from the degree of the polarization of phosphorescence. It has been concluded that the present diphenylpolyynes have a linear planar structure in the T-1 states, although the TREPR and phosphorescence spectra indicate interactions between the T-1((3)pi(x)pi(x)(*)) and T-n((3)pi(x)pi(y)(*)) states through spin-orbit and vibronic interactions. (C) 1999 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/s0009-2614(99)00189-x

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  • Twist conformational effects on the excited triplet states of aromatic ketones studied by multifrequency TREPR and pulsed EPR spectroscopy 査読

    TADAAKI IKOMA, KIMIO AKIYAMA, SHOZO TERO-KUBOTA

    Molecular Physics96 ( 5 ) 813 - 820   1999年3月

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    担当区分:筆頭著者, 責任著者   掲載種別:研究論文(学術雑誌)   出版者・発行元:Informa UK Limited  

    Employing X- and Q-band time-resolved EPR and pulsed EPR techniques, we have investigated effects of twist conformation on the electronic structures and magnetic properties of the lowest excited triplet states of alkyl phenyl ketones. The conformational variation due to steric hindrance of a bulky substituent on the alpha-position drastically leads to a decrease of the zero-field splitting constant of |D| and an increase of the energy gap between 3np* and 3pp* states. Hydrogen bonding with H2O destabilized significantly the 3np* state and switched the T1 state to the 3pp* state. t-Butyl phenyl ketone gave unusually broad EPR spectra in rigid glassy matrices. The multifrequency and pulsed EPR measurements clarified that the inhomogeneously broadening spectra were ascribable to the distribution of the dihedral angle about a twist conformation. Asymmetric distribution of the ZFS parameters was interpreted in terms of the perturbation of spin-orbit interactions to the spin sublevels.

    DOI: 10.1080/00268979909483018

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  • HYSCORE Study on Coal Radicals 査読 国際誌

    Tadaaki Ikoma, Osamu Ito, Shozo Tero-Kubota, Kimio Akiyama

    Energy & Fuels12 ( 6 ) 1363 - 1368   1998年11月

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    担当区分:責任著者   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    Hyperfine sublevel correlation spectroscopy (HYSCORE) spectra have been measured for the radicals in eight well-characterized Argonne Premium coals and their model compounds. The broad H-1 and C-13 hyperfine spectra of all coals were detected at room temperature. The hyperfine structure was analyzed by the comparison with model radicals and semiempirical molecular orbital calculations. The main coal radicals are considered as two-dimensionally condensed pi radicals with more than seven aromatic rings. The C-13/H-1 ratio of the hyperfine spectra increases with coal rank, suggesting a new index of coal rank.

    DOI: 10.1021/ef980130h

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  • Two-Dimensional EPR Spectroscopic Studies on the Radicals in Argonne Premium Coals 査読 国際誌

    Tadaaki Ikoma, Osamu Ito, Shozo Tero-Kubota, Kimio Akiyama

    Energy & Fuels12 ( 5 ) 996 - 1000   1998年9月

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    担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    Two-dimensional electron paramagnetic resonance (BD-EPR) spectra of Illinois No. 6 and Upper Freeport coals have been measured. From 2D-nutation spectroscopy, it is confirmed that the main EPR signal around g = 2 is attributed to free radicals, but not to radical pairs. Both coals showed nuclear modulation effects due to H-1 and naturally abundant C-13 nuclear spins. Spin-echo correlation spectroscopy (SECSY) experiments elucidate the distribution of modulation frequencies included in a broad EPR spectrum. The observed dip in the C-13 matrix spectrum obtained from SECSY is interpreted in terms of the decrease of vitrinite radicals, which are weakly interacting with C-13 nuclei, in the central region of the EPR spectrum. The analysis of the broad hyperfine spectra due to H-1 and C-13 nuclei in the hyperfine sublevel correlation spect-ra suggests the existence of several kinds of radicals in coal. Most of unpaired electrons are considered to be trapped in aromatic rings. The ratio of C-13/H-1 of hyperfine spectra increases with coal rank, suggesting a new index of coal rank.

    DOI: 10.1021/ef980053q

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  • Time-Resolved and Pulsed EPR Studies on the Lowest Excited Triplet State of 1,4-Diphenylbutadiyne 査読 国際誌

    Yasutomo Nagano, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota

    The Journal of Physical Chemistry A102 ( 29 ) 5769 - 5774   1998年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    The short-lived T-1 state of 1,4-diphenylbutadiyne (DPB) has been investigated in various glassy matrices at low temperatures using time-resolved EPR and pulsed EPR methods. Zero-field splitting parameters of D = -0.250 cm(-1) and E = +0.018 cm(-1) were determined. The negative D value was verified from the M-S dependence of the ENDOR frequencies. The hyperfine splitting constants of ring protons were obtained from the electron spin-echo envelope modulation with three-pulse stimulated echo. The spin density distribution on the phenyl groups was estimated from the analysis of the hyperfine splittings at each of the canonical orientations. The moderate spin densities on the phenyl rings indicated that the T-1 state was (3)pi(x)pi(x)* in electronic character. The origin of the large negative D value of DPB has been discussed in terms of the spin-orbit interaction between the close lying (3)pi(x)pi(x)* and (3)pi(x)pi(y)* states.

    DOI: 10.1021/jp9812740

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  • Photo-properties of rare earth ion (Er3+, Eu3+ and Sm3+)-doped alumina films prepared by the sol–gel method 査読 国際誌

    Youichi Kurokawa, Takayuki Ishizaka, Tadaaki Ikoma, Shozo Tero-Kubota

    Chemical Physics Letters287 ( 5-6 ) 737 - 741   1998年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    Rare earth ion (Er3+, Eu3+ and Sm3+)-doped alumina films have been prepared by the sol-gel method, using AlCl3-derived alumina sol. The effects of dopant concentration and treatment temperatures on the photo-properties of absorption and emission have been examined for the doped films. These sol-gel-derived alumina matrices gave a high-dopant concentration(similar to 15 mol% per alumina). (C) 1998 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/s0009-2614(98)00132-8

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  • Electronic structure of the deep boron acceptor in boron-doped6H-SiC 査読 国際誌

    A. v. Duijn-Arnold, T. Ikoma, O. G. Poluektov, P. G. Baranov, E. N. Mokhov, J. Schmidt

    Physical Review B57 ( 3 ) 1607 - 1619   1998年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society (APS)  

    A high-frequency (95 GHz) and conventional-frequency (9.3 GHz) pulsed electron paramagnetic resonance and electron-nuclear double resonance (ENDOR) study is reported on the deep boron acceptor in 6H-SiC. The results support a model in which the deep boron acceptor consists of a boron on a silicon position with an adjacent carbon vacancy. The carbon vacancy combines with a boron along the hexagonal c axis. It is concluded that 70-90% of the spin density resides in the silicon dangling bonds surrounding the vacancy and another 9% on the neighboring carbon atoms. The spin-density distribution is more localized than in the case of the shallow boron acceptor as deduced from the ENDOR experiments.

    DOI: 10.1103/physrevb.57.1607

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    その他リンク: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.57.1607/fulltext

  • Molecular and Electronic Structures of the Short-Lived Excited Triplet State of Tropone 査読 国際誌

    Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota, Yusaku Ikegami

    The Journal of Physical Chemistry A102 ( 2 ) 446 - 451   1998年1月

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    担当区分:筆頭著者, 責任著者   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    Time-resolved electron paramagnetic resonance experiments on the short-lived Ti state of nenphosphorescent tropone were carried out using mixed crystals. Well-resolved hyperfine splittings due to allowed and forbidden transitions were observed at principal axes of the zero-field tenser. The spin density distribution, C-H bond angles, and the sign of the D value were deduced from the hyperfine spectra. It has been concluded that the T-1 state of tropone mainly has a (3) pi pi* configuration and holds its molecular structure of C-2v symmetry. The experiments and molecular orbital calculations indicate that the large Franck-Condon factor between the T-1 and the So states arises from the change of the potential surfaces due to the antibonding character of the pi* orbital at the C-4-C-5 bond in the T-1 state.

    DOI: 10.1021/jp9721154

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  • Transparent alumina films derived from two sources of AlCl3 center dot 6H2O and aluminium iso-propoxide by sol-gel method 査読 国際誌

    Y. KUROKAWA, T. SUGA, S. NAKATA, T. IKOMA, S. TERO-KUBOTA

    Journal of Materials Science Letters17 ( 4 ) 275 - 278   1998年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Springer Science and Business Media LLC  

    DOI: 10.1023/a:1006517219037

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  • Electronic structure of the excited triplet state of nonphosphorescent tropolone studied by time-resolved EPR 査読 国際誌

    Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota, Yusaku Ikegami

    Journal of the Chemical Society, Faraday Transactions94 ( 9 ) 1197 - 1201   1998年

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    担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry (RSC)  

    Time-resolved EPR measurements and semi-empirical MO calculations have been carried out to clarify the electronic structure of the T-1 state of nonphosphorescent tropolone. The observed zero-field splitting parameters indicate that the T-1 state has a pure pi pi* character and the energy order among the spin sublevels was T-Y (in-plane) > T-X (in-plane) > 0 > T-Z (out-of-plane), which is the same as tropone for a parent molecule. However, the principal X-axis slightly turns out of the carbonyl bond direction so that the intersystem crossing from the S-1 state to the T-Y sublevel becomes more active. The spin densities obtained from hyperfine splittings of protons and MO calculation of AM1 method show an asymmetric distribution of unpaired pi-electrons over two oxygens as well as the seven-membered ring. This unbalanced distribution makes the deviation of the X-axis from the carbonyl bond clear. We found two sites that can exchange each other by intramolecular proton transfer in a durene single crystal.

    DOI: 10.1039/a708678d

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  • High-Frequency EPR Studies of Shallow and Deep Boron Acceptors in 6H-SiC 査読

    J. Schmidt, T. Matsumoto, O.G. Poluektov, Alexander Arnold, Tadaaki Ikoma, P.G. Baranov, E.N. Mokhov

    Materials Science Forum258-263   703 - 708   1997年12月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Trans Tech Publications, Ltd.  

    DOI: 10.4028/www.scientific.net/msf.258-263.703

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  • Substituent and Matrix Effects on the Excited Triplet States of 1,4-Naphthoquinones 査読

    Takuji Shimokage, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota, Minoru Yamaji, Haruo Shizuka

    The Journal of Physical Chemistry A101 ( 49 ) 9253 - 9256   1997年12月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    Phosphorescence and TREPR spectra have been measured for 2-methyl-1,4-naphthoquinone (MNQ), 2,3-dimethyl-1,4-naphthoquinone (DMNQ), and 2-methoxynaphthoquinone (MeONQ) in several matrices at low temperatures. The \D\ value of ZFS parameter decreases with increasing the electron-donating character of the substituent group. For MNQ, the T-1 state is clearly assigned to be (3)n pi* in character. The broad phosphorescence spectra and minor effects of the matrix polarity on the ZFS parameters lead to the conclusion that the character of the T-1 states are mainly 3 pi pi* in DMNQ and MeONQ. The T-1 states of the present naphthoquinone derivatives have more or less mixed character of the 3n pi* and 3 pi pi* states.

    DOI: 10.1021/jp971818i

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  • Ferromagnetic Interactions between Imino Nitroxides through Diamagnetic Metal Ions:  Crystal Structures, Magnetism, and Electronic Properties of [MI(imino nitroxide)2](PF6) (M = CuIand AgI) 査読

    Hiroki Oshio, Takashi Watanabe, Akihiro Ohto, Tasuku Ito, Tadaaki Ikoma, Shozo Tero-Kubota

    Inorganic Chemistry36 ( 14 ) 3014 - 3021   1997年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    An orthogonal arrangement of imino nitroxide ligands in Cu-I and Ag-I complexes results in propagation of an intramolecular ferromagnetic interaction between the coordinated imino nitroxides through these diamagnetic ions. Reaction of [Cu-I(CH3CN)(4)](PF6) and Ag-I(PF6) with imino nitroxides in ethanol solution gave [Cu-I(immepy)(2)-(PF6) (1) and [Ag-I(impy)(2)](PF6) (2), respectively (immepy 2-(2-(6-methylpyridyl))-4,4,5,5-tetramethyl-4,5-dihydro-1H imidazolyl-l-oxy and impy 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy). Complex 1 crystallizes in the orthorhombic space group Pba2, which has a unit cell with a 11.251(2) Angstrom, b = 14.745(3) Angstrom, c = 9.747(2) Angstrom, V = 1617.0(5) Angstrom(3), and Z = 2. Refinement with 991 reflections observed [\I-0\ &gt; 3 sigma(I-0)] gave R = 0.044 (R-w = 0.053). In 1, imino nitroxides coordinate to the Cu-I ions in a tetrahedral fashion, the dihedral angle between coordinating imino nitroxides being 88.7 degrees. Magnetic susceptibility measurement for 1 shows typical triplet-singlet behavior with strong ferromagnetic interactions (J = 55.1(6) cm(-1) with g = 2.0; H = -JS(1).S-2) The UV-visible absorption spectrum of 1 shows strong bands at 454 and 766 nm assignable to charge-transfer bands from the Cu ion to the ligand NLUMO and SOMO, respectively. The pi-back-donation to the SOMO induces the spin on the Cu ion and results in the strong ferromagnetic interaction. Complex 2 crystallizes in the orthorhombic space group P2(1)cn which has a unit cell with a = 10.535(6) Angstrom, b = 31.295(3) Angstrom, c 8.921(4) Angstrom, V = 2941(1) Angstrom(3), and Z = 4. Refinement with 1882 reflections [\I-0\ &gt; 3 sigma(I-0)] gave R = 0.058 (R-w = 0.074). Ln 2, the four coordination sites of the Ag-I ion were completed with two imino nitroxides and the dihedral angle between the imino nitroxides is 79.2 degrees. The EPR spectrum of a frozen ethanol solution of 2 shows a typical triplet signal with zero field splitting (\D\ = 0.043 cm(-1) and \E\ = 0.014 cm(-1)). Curie plots for the rim = 2 signal below 80 K gave a positive Weiss constant (theta = 4 K), suggesting an intramolecular ferromagnetic interaction in 2.

    DOI: 10.1021/ic960939e

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  • Magnetic Interactions in Cu(I) and Ag(I) Iminonitroxides 査読 国際誌

    Hiroki Oshio, Takashi Watanabe, Akihiro Ohto, Tasuku Ito, Tadaaki Ikoma, Shozo Tero-kubota

    Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals273 ( 1 ) 47 - 56   1995年11月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Informa UK Limited  

    Orthogonal arrangement of iminonitroxides in [CuI(immepy)2](PF6) (1) and [AgI(impy)2](PF6) (2) results in propagation on intramolecular ferromagnetic interaction between coordinating iminonitroxides through these diamagnetic ion. In 1, iminonitroxides coordinate to the CuI ion in a tetrahedral fashion, the dihedral angle between coordinating iminonitroxides being 88.7 degrees. Magnetic susceptibility and epr measurements for 1 show the typical ferromagneic behavior with large zero field splitting (2J = 91(1) cm-1 (H = -2JS1S2); D = 3.62 cm-1). In 2, the four coordination sites of AgI ion were completed with two iminonitroxides and the dihedral angle between the iminonitroxides is 79.2 degrees. Temperature dependence of teh epr spectra for frozen ethanol solution of 2 shows that the intramolecular mangetic interaction between radicals is ferromagnetic (q = 4 K).

    DOI: 10.1080/10587259508031841

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  • Effects of Geometry and Hydrogen Bonding on the Excited Triplet States of 4-Nitropyridine N-Oxide and Derivatives 査読 国際誌

    Takashi Ehara, Kimio Akiyama, Tadaaki Ikoma, Yusaku Ikegami, Shozo Tere-Kubota

    The Journal of Physical Chemistry99 ( 8 ) 2292 - 2295   1995年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    Time-resolved EPR and phosphorescence spectra have been observed for the lowest excited triplet states of 4-nitropyridine N-oxide and its alkyl derivatives. It has been shown that the ratio of the zero-field-splitting (zfs) parameters reflects the molecular geometry: the |E/D| value decreases with increasing the twisting angle of the nitro group from the molecular plane. Protic solvents induce significant changes in the zfs parameters and the population ratio of the triplet sublevels. The results are discussed in terms of formation of the hydrogen bonding complex at the N-oxide oxygen atom.

    DOI: 10.1021/j100008a009

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  • Spin Polarization Conservation during Intramolecular Triplet-Triplet Energy Transfer Studied by Time-Resolved EPR Spectroscopy 査読 国際誌

    Kimio Akiyama, Shozo Tero-Kubota, Tadaaki Ikoma, Yusaku Ikegami

    Journal of the American Chemical Society116 ( 12 ) 5324 - 5327   1994年6月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    Transient triplet EPR spectra of two types of spirans, spiro[9,10-dihydro-9-oxoanthracene-10,2'-benz[f]indan] and spiro[9,10-dihydro-9-oxoanthracene-10,2'-3H-phenalene],were measured in a glassy matrix at 77 K. Spin polarization conservation during the intramolecular triplet-triplet energy-transfer process was observed. The results clearly indicate that spin orientation is conserved in the molecular frame in the presence of an external magnetic field and that the high-field approximation cannot explain the spin polarization pattern observed in the X-band EPR spectra. The results contribute to the understanding of the relaxation processes of the excited states.

    DOI: 10.1021/ja00091a042

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  • Structural effects on the radiationless transition from the T1 states of tropone derivatives 査読 国際誌

    Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota, Yusaku Ikegami

    The Journal of Physical Chemistry97 ( 2 ) 303 - 305   1993年1月

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    担当区分:筆頭著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    The T1 states of nonphosphorescent 2,3-benzotropone and phosphorescent 4,5-benzotropone were studied by a time-resolved EPR method. For 2,3-benzotropone, the observed magnetic parameters and the decay rate (the average decay rate 1.1 x 10(5) s-1 at 4.2 K) are very similar to those of the parent tropone. On the other hand, 4,5-benzotropone has different magnetic properties and a much slower radiationless decay rate (&lt;30 s-1) than tropone. The mechanism of the fast radiationless transition between the T1 and S0 states of tropone has been discussed.

    DOI: 10.1021/j100104a008

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  • Time-resolved EPR study on the excited triplet state of nonphosphorescent tropone 査読 国際誌

    Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota, Yusaku Ikegami

    The Journal of Physical Chemistry95 ( 19 ) 7119 - 7121   1991年9月

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    担当区分:筆頭著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    The magnetic property and decay kinetics of the nonphosphorescent triplet (T1) state of tropone in glassy matrices have been studied by employing the time-resolved EPR (TREPR) method with excimer and dye laser excitations. The T1 state was assigned to be nearly pure 3pp* in character from the small zero-field splitting (zfs) parameters (|D| = 0.077 cm-1 and |E| = 0.011 cm-1 in a toluene glassy matrix) and their small dependency on the matrix polarity. The directions of the principal axes of the zfs tensor were determined by magnetophotoselection experiments with two colors of lasers. It was found that the T1(pp*) state of tropone has very short lifetime; the average rate constant from the zero-field spin sublevels is 2 x 105 s-1.

    DOI: 10.1021/j100172a003

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  • Time-resolved EPR studies on the photochemical hydrogen abstraction reactions and the excited triplet states of 4-substituted pyridines 査読 国際誌

    Shozo Tero-Kubota, Kimio Akiyama, Tadaaki Ikoma, Yusaku Ikegami

    The Journal of Physical Chemistry95 ( 2 ) 766 - 770   1991年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    Photochemical hydrogen abstraction reactions and the lowest excited triplet states taking part in the initial process have been investigated for several pyridine derivatives by using the time-resolved EPR method. The emissive CIDEP spectrum obtained from the laser photolysis of 4-acetylpyridine (1) in 2-propanol was assigned to the corresponding ketyl radical, proving initial hydrogen abstraction by the carbonyl group. In the cases of 4-cyano-(2) and 4-methoxycarbonyl-(3) pyridines, and 4-pyridinecarboxamide (4), enhanced absorptive CIDEP spectra due to the corresponding 1-hydropyridinyl radicals were observed, suggesting the preferential population to the lowest sublevel in the intersystem crossing. The triplet EPR and phosphorescence spectra observed at 77 K indicate that T1 of 1 is mainly the carbonyl np* state with a small contribution from the pp* state. The T1 states of 2, 3, and 4 are considered to be of mixed character between the pyridine 3B1 (np*) and 3A1(pp*) states, though the interaction is smaller than that of unsubstituted pyridine because of raising the pp* state by electron-withdrawing groups. It is proposed that the T1 states of 2-4 have smaller deviation from the planar conformation than the T1 state of unsubstituted pyridine.

    DOI: 10.1021/j100155a051

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  • CIDEP Studies on Radicals Produced from Photochemical Reactions of Some Aromatic Carbonyl Compounds 査読 国際誌

    Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota, Yusaku Ikegami

    Chemistry Letters19 ( 9 ) 1491 - 1494   1990年9月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:The Chemical Society of Japan  

    CIDEP spectra of radicals generated from photoinduced hydrogen abstraction and a-cleavage reactions of several alkyl phenyl ketones were studied. The participation of radical pair mechanism on the spectra was discussed from the magnitude of hyperfine interaction.

    DOI: 10.1246/cl.1990.1491

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  • Time-resolved ESR studies on the excited triplet states and photoenolization of 2-methylacetophenone and related molecules 査読 国際誌

    Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota, Yusaku Ikegami

    The Journal of Physical Chemistry93 ( 20 ) 7087 - 7091   1989年10月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    Nonphosphorescent excited triplet (3pp*) states of photoenols (3E) generated from the intramolecular hydrogen transfer of o-methylacetophenone (OMAP) and related compounds were measured, together with their phosphorescent excited triplet state (3K), by time-resolved ESR techniques at low temperatures. The triplet ESR spectrum with zero-field splitting parameters, |D| = 0.060 and IEI = 0.0025 cm-', clearly different from those of the parent molecules (3K), was assigned to 3E. The observed small ID| value suggests the biradical character of 3E. It was pointed out from the examination of substituent and matrix effects that the ease of photoenol generation clearly depends on the character of the T1 state of the parent molecules and also on the coplanarity of the carbonyl group with the aromatic ring. The presence of water induces a striking change in the character of the T1 state of OMAP; i.e., np* of T1 in nonpolar or absolute ethanol glassy matrices is altered by pp* in 0.5% H2O/ethanol. CIDEP spectra observed from the quenching reaction with methylviologen proved that 3E behaves as an excellent electron donor.

    DOI: 10.1021/j100357a015

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  • o‐およびp‐アミノアセトフェノンの励起三重項状態の時間分解ESR 査読

      ( 8 ) 1463 - 1465   1989年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1246/nikkashi.1989.1463

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  • Theory of nonradiative decay from the lowest singlet state of benzene: Excess energy dependence 査読 国際誌

    Makoto Takahashi, Tadaaki Ikoma, Yuichi Fujimura, Azumao Toyota, Takeshi Nakajima

    Collection of Czechoslovak Chemical Communications53 ( 9 ) 1902 - 1909   1988年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Institute of Organic Chemistry & Biochemistry  

    A time-independent Green function formalism is developed to study the excess energy dependence on the nonradiative decay in the <italic>S</italic><sub>1</sub> state of benzene. Effects of purely electronic relaxation (internal conversion, IC) and intramolecular vibrational redistribution, IVR, are taken into account at the same time. Model calculations show that the drastic increase in the nonradiative decay rate at around 3 000 cm<sup>-1</sup> excess energy is due to the same onset of both IC and IVR rates. Our theory can explain the difference in rate constant between IVR and IC observed by Moss and Parmenter.

    DOI: 10.1135/cccc19881902

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書籍等出版物

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  • Addition and correction of “Carrier Generation Process on Photoconductive Polymer Films as Studied by Magnetic Field Effects on the CT Fluorescence and Photocurrent” of J. Phys. Chem. B, 109, 8707 (2005)

    The Journal of Physical Chemistry B110 ( 10 ) 5161 - 5162   2006年3月

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  • スピン相関分光としての時間領域ESR

    生駒 忠昭

    分光研究55 ( 1 ) 21 - 30   2006年

  • ポリビニルカルバゾール薄膜の巨大磁気抵抗効果

    東北大学金属材料研究所強磁場超伝導材料研究センター平成17年度年次報告書,187-189   2006年

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  • Carrier generation in photoconductive poly(N-vinylearbazole) as revealed by multifrequency time-resolved ESR

    T Ikoma, K Akiyama, S Tero-Kubota

    PHYSICAL REVIEW B71 ( 19 ) 195206-1-195206-13   2005年5月

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    記述言語:英語   出版者・発行元:AMERICAN PHYSICAL SOC  

    Using the multifrequency time-resolved electron-spin-resonance (TRESR) method, we have investigated the carrier-generation dynamics in a photoconductive film sample of poly(N-vinylcarbazole), The TRESR spectra, due to spin-polarized geminate electron-hole (e-h) pairs captured in deep-trap sites, were observed at several fields that were achieved using microwaves with different frequencies, The spectra detected at room temperature were interpreted in terms of the ST0 polarization in trapped e-h pairs and the ST+ polaritation induced in canonical e-h pairs. The spectral simulation clarified the distribution of e-h separation distance (r) and the r-dependent recombination of the trapped pairs. The initial spatial distribution of the trapped e-h pairs exponentially decreased with an increase in r. There is no large population of long-distant c-h pairs with r &gt; 1.5 nm. Based on the appearance of the ST+ polarization in the long-distant pairs that is generated in middle-distant pairs and the initial exponential distribution of the trapped pairs, it was concluded that stepwise hole hops rather than a long-range hole jump represent the proper dynamics of the geminate pair in the charge-separation process. The r-dependent recombination rate suggests a single-step tunneling recombination of the trapped pairs.

    DOI: 10.1103/PhysRevB.71.195206

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  • Carrier generation process on photoconductive polymer films as studied by magnetic field effects on the charge-transfer fluorescence and photocurrent

    F Ito, T Ikoma, K Akiyama, A Watanabe, S Tero-Kubota

    JOURNAL OF PHYSICAL CHEMISTRY B109 ( 18 ) 8707 - 8717   2005年5月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    We have studied the magnetic field effects (MFEs) on the charge-transfer fluorescence and transient photocurrent of a 1,2,4,5-tetracyanobenzene-doped poly(N-vinylcarbazole) film, which reflect the recombination and escape yields of the carriers, respectively. The recombination yield dependence of the external magnetic field (B) clearly shows two types of the MFEs, growth with increasing B due to the hyperfine mechanism (HFM) and a negative dip due to the level-crossing mechanism (LCM). On the other hand, the escape yield indicates complementary MFEs with a sharp decrease in yield with increasing B and then a positive dip. Simultaneous observation of the HFM- and LCM-MFEs proves the stepwise hole-hopping mechanism rather the long-range hole-jumping one. The quantitative analysis of the recombination and escape MFEs is performed using the stochastic Liouville equations (SLE) for a one-dimensional lattice model in which the stepwise hole hops take place between the nearest neighbor carbazole units with spin conservation. The SLE analysis provides the recombination and hole transfer rate constants of 7.0 x 10(7) and 4.5 x 10(8) s(-1), respectively. The boundary site number for the ion pairs in the one-dimensional model is estimated by the best fit to the experimental results. The interionic distance of the boundary ion pair in the one-dimensional model including eight sites agrees with the thermalization distance in the Onsager model. Hence, it is concluded that the elementary processes in the Onsager model applied to molecular amorphous solids are the stepwise hole hops rather than a long-range hole jump.

    DOI: 10.1021/jp0453212

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  • Spin dynamic study on the electric field dependence of carrier generation

    Fuyuki Ito, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota

    Journal of Physical Chemistry B109 ( 15 ) 7208 - 7213   2005年4月

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    記述言語:英語  

    Using an acceptor-doped poly(N-vinylcarbazole) film, the magnetic field effect (MFE) on the generation efficiency of photoinduced charge was measured under various electric fields in order to clarify how the applied electric field affects the elementary processes in the photocarrier generation in photoconductive polymeric molecular solids. The external magnetic field influenced the electron spin dynamics among the geminate electron-hole pairs within a scale of a few nanometers and decreased the photocarrier generation efficiency. The observed MFE due to a hyperfine mechanism was almost independent of the electric field. By employing the stochastic Liouville equations based on a one-dimensional lattice model, we performed some model calculations for the dissociation, hopping, and recombination rate dependence of MFE on the generation efficiency. From a comparison between the observed and calculated MFE, it was concluded that the electric field affects the dissociation more than the hopping and the recombination. This coincides with the concepts in the Onsager model that is used to analyze the electric field dependence of carrier generation efficiency so far. The one-dimensional lattice model is a proper model for the carrier generation in polymeric molecular solids, which is qualitatively consistent with the Onsager model except for the long-range hole jump. © 2005 American Chemical Society.

    DOI: 10.1021/jp044475e

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  • Dependence of mechanochemically induced decomposition of mono-chlorobiphenyl on the occurrence of radicals

    TANAKA Yasumitsu, ZHANG Qiwu, SAITO Fumio, IKOMA Tadaaki, TERO-KUBOTA Shozo

    Chemosphere60 ( 7 ) 939 - 943   2005年

  • The magnetic and electric field effects on the photoconductive polymer films

    Photochemistry35   20 - 26   2005年

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  • 光導電性高分子薄膜におけるキャリア生成過程に対する磁場・電場効果

    生駒 忠昭

    光化学35   20 - 26   2005年

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  • Carrier generation in photoconductive poly (N -vinylcarbazole) as revealed by multifrequency time-resolved ESR

    Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota

    Physical Review B - Condensed Matter and Materials Physics71 ( 19 ) 195206-1-195206-13   2005年

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    記述言語:英語  

    Using the multifrequency time-resolved electron-spin-resonance (TRESR) method, we have investigated the carrier-generation dynamics in a photoconductive film sample of poly (N -vinylcarbazole). The TRESR spectra, due to spin-polarized geminate electron-hole (e-h) pairs captured in deep-trap sites, were observed at several fields that were achieved using microwaves with different frequencies. The spectra detected at room temperature were interpreted in terms of the S T0 polarization in trapped e-h pairs and the S T+ polarization induced in canonical e-h pairs. The spectral simulation clarified the distribution of e-h separation distance (r) and the r -dependent recombination of the trapped pairs. The initial spatial distribution of the trapped e-h pairs exponentially decreased with an increase in r. There is no large population of long-distant e-h pairs with r&gt
    1.5 nm. Based on the appearance of the S T+ polarization in the long-distant pairs that is generated in middle-distant pairs and the initial exponential distribution of the trapped pairs, it was concluded that stepwise hole hops rather than a long-range hole jump represent the proper dynamics of the geminate pair in the charge-separation process. The r -dependent recombination rate suggests a single-step tunneling recombination of the trapped pairs. © 2005 The American Physical Society.

    DOI: 10.1103/PhysRevB.71.195206

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  • The excited states of polyyne and the soliton of polydiacetylene

      ( 3 ) 67 - 73   2004年

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  • The excited states of polyyne, the soliton of polydiacetylene

      ( 3 ) 67 - 73   2004年

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  • ポリインの励起状態とポリジアセチレンのソリトン

    電子スピンサイエンス学会会報 ( 3 ) 67 - 73   2004年

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  • ポリインの励起状態とポリジアセチレンのソリトン

    電子スピンサイエンス学会会報 ( 3 ) 67 - 73   2004年

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  • Synthesis, Stabilities, and Redox Behavior of Di(1-azulenyl) (6-azulenyl) methylium Hexafluorophosphates. Generation of a Donor-Acceptor-Substituted Neutral Radical by Azulenes

    Shunji Ito, Takahiro Kubo, Noboru Morita, Tadaaki Ikoma, Shozo Tero-Kubota, Akio Tajiri

    Journal of Organic Chemistry68 ( 25 ) 9753 - 9762   2003年12月

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    記述言語:英語  

    Several di(1-azulenyl)(6-azulenyl)methanes and 1,3-bis[(1-azulenyl)(6-azulenyl)methyl]azulenes were prepared by the condensation reaction of azulenes with diethyl 6-formylazulene-1, 3-dicarboxylate under acidic conditions. The products were converted into di(1-azulenyl)(6-azulenyl)-methylium hexafluorophosphates and azulene-1,3-diylbis[(1-azulenyl)(6-azulenyl)methylium] bis- (hexafluorophosphate)s via hydride abstraction reaction with DDQ following the exchange of counterions. These mono- and dications exhibited high stability with large pKR + values (5.6- 10.1), despite the capto-dative substitution of azulenes. The electrochemical reduction of the monocations upon cyclic voltammetry (CV) exhibited a reversible two-step, one-electron reduction wave with a small difference between the first reduction potential (E1 red) and the second one (E2 red), which exhibited the generation of highly amphoteric neutral radicals in solution. The electrochemical reduction of dications showed voltammograms, which were characterized by subsequent two single-electron waves and a two-electron transfer upon CV attributable to the formation of a radical cation, a diradical (or twitter ionic structure), and a dianionic species, respectively. Formation of a persistent neutral radical from a monocation was revealed by ESR and UV-vis spectroscopies and theoretical calculations. The ESR spectra of the neutral radical gave two hyperfine coupling constants: a H = 0.083 (6H) and 0.166 mT (9H) (g = 2.0024), indicating that an unpaired electron delocalizes over all three of the azulene rings. The stable monoanion, which shows the localization of the charge on the 6-azulenyl substituent, was also successfully generated from the di(1-azulenyl)(6-azulenyl)-methane derivative.

    DOI: 10.1021/jo035053o

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  • Synthesis, Stabilities, and Redox Behavior of Di(1-azulenyl)(6-azulenyl)methylium Hexafluorophosphates. Generation of a Donor−Acceptor-Substituted Neutral Radical by Azulenes 査読

    Shunji Ito, Takahiro Kubo, Noboru Morita, Tadaaki Ikoma, Shozo Tero-Kubota, Akio Tajiri

    The Journal of Organic Chemistry68 ( 25 ) 9753 - 9762   2003年12月

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    記述言語:英語   出版者・発行元:American Chemical Society (ACS)  

    Several di(1-azulenyl)(6-azulenyl)methanes and 1,3-bis[(1-azulenyl)(6-azulenyl)methyl]azulenes were prepared by the condensation reaction of azulenes with diethyl 6-formylazulene-1,3-dicarboxylate under acidic conditions. The products were converted into di(l-azulenyl)(6-azulenyl)methylium hexafluorophosphates and azulene-1,3-diylbis[(l-azulenyl)(6-azulenyl)methylium] bis-(hexafluorophosphate)s via hydride abstraction reaction with DDQ following the exchange of counterions. These mono- and dications exhibited high stability with large pK(R)(+) values (5.6-10.1), despite the capto-dative substitution of azulenes. The electrochemical reduction of the monocations upon cyclic voltammetry (CV) exhibited a reversible two-step, one-electron reduction wave with a small difference between the first reduction potential (E red) and the second one (E-2(red)), which exhibited the generation of highly amphoteric neutral radicals in solution. The electrochemical reduction of dications showed voltammograms, which were characterized by subsequent two single-electron waves and a two-electron transfer upon CV attributable to the formation of a radical cation, a diradical (or twitter ionic structure), and a dianionic species, respectively. Formation of a persistent neutral radical from a monocation was revealed by ESR and UV-vis spectroscopies and theoretical calculations. The ESR spectra of the neutral radical gave two hyperfine coupling constants: a(H) = 0.083 (6H) and 0.166 mT (9H) (g = 2.0024), indicating that an unpaired electron delocalizes over all three of the azulene rings. The stable monoanion, which shows the localization of the charge on the 6-azulenyl substituent, was also successfully generated from the di(1-azulenyl)(6-azulenyl)methane derivative.

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  • Symmetry Switching of the Fluorescent Excited State in a, w-Diphenylpolyyenes

    NAGANO Y, IKOMA T, AKIYAMA K, TERO(KUBOTA) S

    Journal of the American Chemical Society125 ( 46 ) 14103 - 14112   2003年11月

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    記述言語:英語   掲載種別:書評論文,書評,文献紹介等  

    DOI: 10.1021/ja035173d

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  • Symmetry switching of the fluorescent excited state in alpha,omega-diphenylpolyynes

    Y Nagano, T Ikoma, K Akiyama, S Tero-Kubota

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY125 ( 46 ) 14103 - 14112   2003年11月

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    記述言語:英語   掲載種別:書評論文,書評,文献紹介等   出版者・発行元:AMER CHEMICAL SOC  

    By using MO calculations based on DFT, absorption, and fluorescence spectroscopy, we have comprehensively studied the low-lying excited singlet states of alpha,omega-diphenylpolyynes (DPY) having 1-6 triple bonds. The a(g) vibrational modes of the CdropC stretching and of the phenyl ring motion were observed in the fluorescence spectra of diphenylacetylene and 1,4-diphenylbutadiyne. On the other hand, in the fluorescence spectra of the long DPY with the triple-bond number (N) more than two, the phenyl ring motion with ag symmetry disappeared and the big modes of the phenyl ring twisting (similar to400 cm(-1)) and of the C-H bending (similar to900 cm(-1)) were detected. The observed fluorescent states of DPY with N less than or equal to 2 and N greater than or equal to 3 are assigned to the 1(1)B(1u) (pi(x)pi(x)(*)) and 1(1)A (pi(x)pi(y)(*) and/or pi(y)pi(x)(*)) states, respectively, based on the vibronic structures, the relatively short lifetimes, and the solvatochromic shifts of the fluorescence spectra. Not only the allowed transition of 1(1)B(1u) &lt;-- So but also the forbidden transition of 1(1)A(u) &lt;-- S-0 was detected in the fluorescence excitation spectra of the long DPY with N greater than or equal to 3. The low-lying excited state with A(u) symmetry is characteristic in polyyne, which does not exist in polyene. The oscillator strength (f) of the first absorption band in DPY decreases with an increase in N, which is the opposite behavior of the all-trans-alpha,omega-diphenylpolyenes. The N-dependence of the f value is understood by the configuration interaction between the 1(1)B(1u) and 2(1)B(1u) (pi(y)pi(y)(*)) states, which is consistent with the reduction of the nonlinear optical response of polyyne.

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  • EPR studies on defects in sol-gel derived alumina films

    T Ishizaka, S Tero-Kubota, Y Kurokawa, T Ikoma

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS64 ( 5 ) 801 - 806   2003年5月

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    記述言語:英語   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    We have studied the defect structures and mechanism for the luminescence of non-doped, Tb3+ -doped and Tb3+- Zn2+ codoped alumina films treated at various temperatures from 300 to 800 degreesC. The electron paramagnetic resonance (EPR) spectra observed before UV-irradiation are attributable to the non-bridging oxygen radicals; AI-O-O-. at treatment temperatures of 300-500degreesC and AI-O-. at 800degreesC. The UV-light irradiation of the non-doped alumina films gives the EPR spectra with the Al-27 hyperfine splitting. There exists a good correlation between the treatment temperature dependence on the light-induced EPR signal intensity of the trapped electron and the NMR peak intensity due to the five-coordinated aluminum ion. We concluded that the electron is captured at the oxygen vacancy connected with the five-coordinated aluminum. The broad EPR spectra due to the ground state of the Tb3+ ion were observed in the Tb3+-doped and Tb3+ - Zn2+ codoped alumina films. The Tb3+ concentration dependence of the EPR signal intensity due to the non-bridging oxygens suggests that Tb3+ prefers to form Al-O-Tb bonds and prevent to form a cluster of rare earth ions itself. The light-induced EPR signal of the electron trapped at oxygen vacancy next the five-coordinated aluminum was also observed for the Tb3+ - Zn2+ codoped alumina film, which produced a long-lasting luminescence. The photogenerated trapped electron remained for several minutes under the room temperature. These experimental facts indicate that the five-coordinated aluminum ions act as the trapping sites to produce the long-lasting luminescence. (C) 2002 Published by Elsevier Science Ltd.

    DOI: 10.1016/S0022-3697(02)00377-3

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  • EPR studies on defects in sol-gel derived alumina films

    T. Ishizaka, S. Tero-Kubota, Y. Kurokawa, T. Ikoma

    Journal of Physics and Chemistry of Solids64 ( 5 ) 801 - 806   2003年5月

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    記述言語:英語  

    We have studied the defect structures and mechanism for the luminescence of non-doped, Tb3+-doped and Tb3+-Zn2+ codoped alumina films treated at various temperatures from 300 to 800°C. The electron paramagnetic resonance (EPR) spectra observed before UV-irradiation are attributable to the non-bridging oxygen radicals
    Al-O-O at treatment temperatures of 300-500°C and Al-O at 800°C. The UV-light irradiation of the non-doped alumina films gives the EPR spectra with the 27Al hyperfine splitting. There exists a good correlation between the treatment temperature dependence on the light-induced EPR signal intensity of the trapped electron and the NMR peak intensity due to the five-coordinated aluminum ion. We concluded that the electron is captured at the oxygen vacancy connected with the five-coordinated aluminum. The broad EPR spectra due to the ground state of the Tb3+ ion were observed in the Tb3+-doped and Tb3+-Zn2+ codoped alumina films. The Tb3+ concentration dependence of the EPR signal intensity due to the non-bridging oxygens suggests that Tb3+ prefers to form Al-O-Tb bonds and prevent to form a cluster of rare earth ions itself. The light-induced EPR signal of the electron trapped at oxygen vacancy next the five-coordinated aluminum was also observed for the Tb3+-Zn2+ codoped alumina film, which produced a long-lasting luminescence. The photogenerated trapped electron remained for several minutes under the room temperature. These experimental facts indicate that the five-coordinated aluminum ions act as the trapping sites to produce the long-lasting luminescence. © 2002 Published by Elsevier Science Ltd.

    DOI: 10.1016/S0022-3697(02)00377-3

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  • Long-range jump versus stepwise hops: Magnetic field effects on the charge-transfer fluorescence from photoconductive polymer films

    F Ito, T Ikoma, K Akiyama, Y Kobori, S Tero-Kubota

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY125 ( 16 ) 4722 - 4723   2003年4月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    DOI: 10.1021/ja029443o

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  • Long-range jump versus stepwise hops: Magnetic field effects on the charge-transfer fluorescence from photoconductive polymer films

    F Ito, T Ikoma, K Akiyama, Y Kobori, S Tero-Kubota

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY125 ( 16 ) 4722 - 4723   2003年4月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

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  • Substrate specificities of deuterolysin from Aspergillus oryzae and electron paramagnetic resonance measurement of cobalt-substituted deuterolysin

    Y Doi, BR Lee, M Ikeguchi, Y Ohoba, T Ikoma, S Tero-Kubota, S Yamauchi, K Takahashi, E Ichishima

    BIOSCIENCE BIOTECHNOLOGY AND BIOCHEMISTRY67 ( 2 ) 264 - 270   2003年2月

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    記述言語:英語   出版者・発行元:TAYLOR & FRANCIS LTD  

    The substrate specificities of deuterolysin, a 19-kDa zinc-protease (EC 3.4.24.39) from Aspergillus oryzae, were investigated at pH 9.0 with various fluorogenic acyl-peptide-4-methylcoumaryl-7-amides (peptide-MCAs). N-Butoxycarbonyl-Arg-Val-Arg-Arg-MCA was the best substrate for deuterolysin. We therefore measured its kinetic parameters. Deuterolysin had high activity toward the peptide bonds next to pairs of basic residues in calf thymus histone H4. The specificity of cobalt-substituted deuterolysin (Co-deuterolysin) for peptide-MCAs was similar to that of native deuterolysin. The CD spectrum of Co-deuterolysin was similar to that of the native deuterolysin. The metal coordination sphere of Co-deuterolysin was analyzed by Q-band (33.9570 GHz) electron paramagnetic resonance (EPR) spectroscopy. Using computer simulation of EPR, we found the g principal values to be g(xx) = 5.20, g(yy) = 4.75, and g(zz) = 2.24; the metal center was a divalent cobalt ion in a high spin state.

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  • Substrate specificities of deuterolysin from Aspergillus oryzae and electron paramagnetic resonance measurement of cobalt-substituted deuterolysin

    Y Doi, BR Lee, M Ikeguchi, Y Ohoba, T Ikoma, S Tero-Kubota, S Yamauchi, K Takahashi, E Ichishima

    BIOSCIENCE BIOTECHNOLOGY AND BIOCHEMISTRY67 ( 2 ) 264 - 270   2003年2月

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    記述言語:英語   出版者・発行元:TAYLOR & FRANCIS LTD  

    The substrate specificities of deuterolysin, a 19-kDa zinc-protease (EC 3.4.24.39) from Aspergillus oryzae, were investigated at pH 9.0 with various fluorogenic acyl-peptide-4-methylcoumaryl-7-amides (peptide-MCAs). N-Butoxycarbonyl-Arg-Val-Arg-Arg-MCA was the best substrate for deuterolysin. We therefore measured its kinetic parameters. Deuterolysin had high activity toward the peptide bonds next to pairs of basic residues in calf thymus histone H4. The specificity of cobalt-substituted deuterolysin (Co-deuterolysin) for peptide-MCAs was similar to that of native deuterolysin. The CD spectrum of Co-deuterolysin was similar to that of the native deuterolysin. The metal coordination sphere of Co-deuterolysin was analyzed by Q-band (33.9570 GHz) electron paramagnetic resonance (EPR) spectroscopy. Using computer simulation of EPR, we found the g principal values to be g(xx) = 5.20, g(yy) = 4.75, and g(zz) = 2.24; the metal center was a divalent cobalt ion in a high spin state.

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  • Substrate specificities of deuterolysin from Aspergillus oryzae and electron paramagnetic resonance measurement of cobalt-substituted deuterolysin

    Y Doi, BR Lee, M Ikeguchi, Y Ohoba, T Ikoma, S Tero-Kubota, S Yamauchi, K Takahashi, E Ichishima

    BIOSCIENCE BIOTECHNOLOGY AND BIOCHEMISTRY67 ( 2 ) 264 - 270   2003年2月

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    記述言語:英語   出版者・発行元:TAYLOR & FRANCIS LTD  

    The substrate specificities of deuterolysin, a 19-kDa zinc-protease (EC 3.4.24.39) from Aspergillus oryzae, were investigated at pH 9.0 with various fluorogenic acyl-peptide-4-methylcoumaryl-7-amides (peptide-MCAs). N-Butoxycarbonyl-Arg-Val-Arg-Arg-MCA was the best substrate for deuterolysin. We therefore measured its kinetic parameters. Deuterolysin had high activity toward the peptide bonds next to pairs of basic residues in calf thymus histone H4. The specificity of cobalt-substituted deuterolysin (Co-deuterolysin) for peptide-MCAs was similar to that of native deuterolysin. The CD spectrum of Co-deuterolysin was similar to that of the native deuterolysin. The metal coordination sphere of Co-deuterolysin was analyzed by Q-band (33.9570 GHz) electron paramagnetic resonance (EPR) spectroscopy. Using computer simulation of EPR, we found the g principal values to be g(xx) = 5.20, g(yy) = 4.75, and g(zz) = 2.24; the metal center was a divalent cobalt ion in a high spin state.

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  • Substrate specificities of deuterolysin from aspergillus oryzae and electron paramagnetic resonance measurement of cobalt-substituted deuterolysin

    Yuko Doi, Byung Rho Lee, Masamichi Ikeguchi, Yasunori Ohoba, Tadaaki Ikoma, Shozo Tero-Kubota, Seigo Yamauchi, Koji Takahashi, Eiji Ichishima

    Bioscience, Biotechnology and Biochemistry67 ( 2 ) 264 - 270   2003年1月

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    記述言語:英語  

    The substrate specificities of deuterolysin, a 19-kDa zinc-protease (EC 3.4.24.39) from Aspergillus oryzae, were investigated at pH 9.0 with various fluorogenic acyl-peptide-4-methylcoumaryl-7-amides (peptide- MCAs). N-Butoxycarbonyl-Arg-Val-Arg-Arg-MCA was the best substrate for deuterolysin. We therefore measured its kinetic parameters. Deuterolysin had high activity toward the peptide bonds next to pairs of basic residues in calf thymus histone H4. The specificity of cobalt-substituted deuterolysin (Co-deuterolysin) for peptide-MCAs was similar to that of native deuterolysin. The CD spectrum of Co-deuterolysin was similar to that of the native deuterolysin. The metal coordination sphere of Co-deuterolysin was analyzed by Q-band (33.9570 GHz) electron paramagnetic resonance (EPR) spectroscopy. Using computer simulation of EPR, we found the g principal values to be gxx=5.20, gyy=4.75, and gzz=2.24
    the metal center was a divalent cobalt ion in a high spin state. © 2003 by Japan Society for Bioscience, Biotechnology, and Agrochemistry.

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  • Infra-Red Spectra, Electron Paramagnetic Resonance, and Proton Magnetic Thermal Analysis

    Osamu Ito, Tadaaki Ikoma, Richard Sakurovs

    Carbon Alloys: Novel Concepts to Develop Carbon Science and Technology,269-281   269 - 283   2003年

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    記述言語:英語   出版者・発行元:Elsevier Ltd.  

    This chapter describes the characterization of the carbon alloys using the infra-red spectroscopy (IR spectra), the electron paramagnetic resonance (EPR), and the proton magnetic resonance thermal analysis (PMRTA). The broad absorption bands of the IR spectra observed using the diffuse reflectance methods-provide information about the ring size of the aromatic molecules within a sample, and the extent to which these are ordered. The sharp C-H stretching peaks are quantitatively compared with the peaks using the solid-state nuclear magnetic resonance (NMR). Two magnetic resonance methods employed pulse techniques-where the relative hydrogen contents are evaluated as the ratios to carbon contents. PMRTA, which measures the temperature dependence of the signal intensities and the relaxation times of the proton magnetic resonance, provides information about the molecular motion in the heat-treated carbons and in coals. These spectroscopic techniques give information about the composition of the carbon precursors prepared at temperatures below 500-600°C. © 2003 Elsevier B.V. All rights reserved.

    DOI: 10.1016/B978-008044163-4/50017-6

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  • Transient radical pairs in the photoinduced electron transfer mediated by the double strand DNA

    XXIst International Conference on Photochemistry   2003年

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  • Infra-Red Spectra, Electron Paramagnetic Resonance, and Proton Magnetic Thermal Analysis

    Carbon Alloys: Novel Concepts to Develop Carbon Science and Technology Chap.17J. Phys. Chem. A 107 (15) 2635 − 2641 (2003).,269-281   2003年

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  • Angle-Selected Measurements of Spin Soliton in Ladder Polydiacetylene by Pulsed 94 GHz EPR

    Applied Magnetic Resonance23   445 - 453   2003年

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  • Angle-selective measurements of spin soliton in ladder polydiacetylene by pulsed 94 GHz EPR

    T Ikoma, S Okada, S Tero-Kubota, H Nakanishi, T Kato, P Hofer, A Kamlowski, K Akiyama

    APPLIED MAGNETIC RESONANCE23 ( 3-4 ) 445 - 453   2003年

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    記述言語:英語   出版者・発行元:SPRINGER WIEN  

    Angle-selection experiments of a spin soliton in randomly oriented ladder polydiacctylene were carried out by pulsed electron paramagnetic resonance (EPR) at W-band. EPR measurement using 94 GHz microwaves increased the difference in the resonance field due to g anisotropy of the spin soliton to allow the orientation dependence of transient nutation, electron nuclear double resonance (ENDOR) and spin relaxations to be investigated. The shape of the g anisotropy-resolved nutation spectrum was discussed on the basis of the EPR transition moments and the differences between spin relaxation times. Reliable assignments of hyperfine couplings to the beta protons (H-beta) of the alkyl side chains were achieved with the support of W-band ENDOR measurements. No significant orientational dependence in the T-1 and T-2 processes was found in terms of isotropy of the H-beta-hyperfine interaction.

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  • Angle-selective measurements of spin soliton in ladder polydiacetylene by pulsed 94 GHz EPR

    T Ikoma, S Okada, S Tero-Kubota, H Nakanishi, T Kato, P Hofer, A Kamlowski, K Akiyama

    APPLIED MAGNETIC RESONANCE23 ( 3-4 ) 445 - 453   2003年

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    記述言語:英語   出版者・発行元:SPRINGER WIEN  

    Angle-selection experiments of a spin soliton in randomly oriented ladder polydiacctylene were carried out by pulsed electron paramagnetic resonance (EPR) at W-band. EPR measurement using 94 GHz microwaves increased the difference in the resonance field due to g anisotropy of the spin soliton to allow the orientation dependence of transient nutation, electron nuclear double resonance (ENDOR) and spin relaxations to be investigated. The shape of the g anisotropy-resolved nutation spectrum was discussed on the basis of the EPR transition moments and the differences between spin relaxation times. Reliable assignments of hyperfine couplings to the beta protons (H-beta) of the alkyl side chains were achieved with the support of W-band ENDOR measurements. No significant orientational dependence in the T-1 and T-2 processes was found in terms of isotropy of the H-beta-hyperfine interaction.

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  • Transient radical pairs in the photoinduced electron transfer mediated by the double strand DNA

    XXIst International Conference on Photochemistry   2003年

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  • Angle-selective measurements of spin soliton in ladder polydiacetylene by pulsed 94 GHz EPR

    T Ikoma, S Okada, S Tero-Kubota, H Nakanishi, T Kato, P Hofer, A Kamlowski, K Akiyama

    APPLIED MAGNETIC RESONANCE23 ( 3-4 ) 445 - 453   2003年

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    記述言語:英語   出版者・発行元:SPRINGER WIEN  

    Angle-selection experiments of a spin soliton in randomly oriented ladder polydiacctylene were carried out by pulsed electron paramagnetic resonance (EPR) at W-band. EPR measurement using 94 GHz microwaves increased the difference in the resonance field due to g anisotropy of the spin soliton to allow the orientation dependence of transient nutation, electron nuclear double resonance (ENDOR) and spin relaxations to be investigated. The shape of the g anisotropy-resolved nutation spectrum was discussed on the basis of the EPR transition moments and the differences between spin relaxation times. Reliable assignments of hyperfine couplings to the beta protons (H-beta) of the alkyl side chains were achieved with the support of W-band ENDOR measurements. No significant orientational dependence in the T-1 and T-2 processes was found in terms of isotropy of the H-beta-hyperfine interaction.

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  • Spin soliton in a pi-conjugated ladder polydiacetylene

    T Ikoma, S Okada, H Nakanishi, K Akiyama, S Tero-Kubota, K Mobius, S Weber

    PHYSICAL REVIEW B66 ( 1 ) 014423-1-014423-9   2002年7月

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    記述言語:英語   出版者・発行元:AMERICAN PHYSICAL SOC  

    The electronic structure and the spin dynamics of a spin soliton observed in a "ladder"-structured polydiacetylene have been investigated using multifrequency pulsed and continuous-wave (cw) electron paramagnetic resonance (EPR), electron spin echo (ESE) spectroscopy, electron-nuclear double resonance (ENDOR), and electron-nuclear-nuclear triple resonance (TRIPLE). The undoped ladder polymer in which two polydiacetylene wires are linked by bridges consisting of two triple bonds exhibits a strong EPR signal. In contrast, no EPR signal is observed in the ladder-structured polydiacetylene, where the bridges consist of single bonds. The observed bridge effect on the probability of formation of paramagnetic centers is interpreted in terms of a quasidegenerate ground state due to the pi-conjugated ladder structure that creates a pi-bond kink corresponding to a spin soliton. High-frequency and high-field EPR reveals a small anisotropy of the g tensor (principal values g(1)=2.0037, g(2)=2.0028, and g(3)=2.0023) for the spin soliton. By nutation spectroscopy, the spin multiplicity was confirmed to be S=1/2. The hyperfine pattern attributed to the beta protons was detected by ENDOR and TRIPLE methods, providing evidence for both the positive and negative spin densities of the soliton wave function. These experimental results led to the conclusion that the unpaired electron of the spin soliton was substantially delocalized over the two polydiacetylenes through the pi-conjugation. At temperatures (T) below 50 K, the width of the EPR spectrum narrows by about 45% with increasing temperature and the width remains nearly constant for T&gt;50 K. The pronounced change in the line width for T&lt;50 K suggests the presence of a mobile spin soliton in the ladder-structured polydiacetylene. A temperature dependence of the electron spin system's phase memory time T-M for T&lt;50 K was also observed by ESE spectroscopy. The decay of the ESE exhibits a nonexponential behavior, with T-M increasing monotonically with rising temperature. These findings represent clear experimental evidence for motional narrowing phenomena. Based on a one-dimensional random-walk model for the unpaired electron spin along the ladder polymer, the soliton's diffusion rate constant was estimated from an analysis of the ESE dephasing process. An Arrhenius plot of the diffusion rate was asymptotic to approximate to8x10(7) s(-1) at very low temperature, which is two orders of magnitude slower than that of the soliton in trans-polyacetylene.

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  • Spin Soliton in a π-Conjugated Ladder Polydiacetylene

    Physical Review B66 ( 1 ) 1 - 9   2002年7月

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  • Electronic structure of the lowest excited triplet state of 5, 12-naphthacenequinone

    T Shimokage, T Ikoma, K Akiyama, S Tero-Kubota

    SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY58 ( 6 ) 1201 - 1208   2002年4月

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    記述言語:英語   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Continuous-wave time-resolved EPR (cw-TREPR) and pulsed electron nuclear double resonance (ENDOR) studies have been carried out to clarify the electronic structure of the lowest excited triplet (T,) state of 5,12-naphthacenequinone (5,12-NpQ) as well as 1,4-anthraquinone (1,4-AQ) and 6,13-pentacenequinone (6,13-PeQ). The T, energy level and the D value of the zero-field splitting (ZFS) parameters only slightly decreased with the increasing pi-conjugated system. The T-1 states of these linear para-acenequinones were assigned to the pipi* character. In triplet 5,12-naphthacenequinone, more than 80% of the unpaired electron spins are localized on the naphthalene aromatic sub-system. (C) 2002 Elsevier Science B.V. All rights reserved.

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  • Electronic structure of the lowest excited triplet state of 5, 12-naphthacenequinone

    T Shimokage, T Ikoma, K Akiyama, S Tero-Kubota

    SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY58 ( 6 ) 1201 - 1208   2002年4月

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    記述言語:英語   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Continuous-wave time-resolved EPR (cw-TREPR) and pulsed electron nuclear double resonance (ENDOR) studies have been carried out to clarify the electronic structure of the lowest excited triplet (T,) state of 5,12-naphthacenequinone (5,12-NpQ) as well as 1,4-anthraquinone (1,4-AQ) and 6,13-pentacenequinone (6,13-PeQ). The T, energy level and the D value of the zero-field splitting (ZFS) parameters only slightly decreased with the increasing pi-conjugated system. The T-1 states of these linear para-acenequinones were assigned to the pipi* character. In triplet 5,12-naphthacenequinone, more than 80% of the unpaired electron spins are localized on the naphthalene aromatic sub-system. (C) 2002 Elsevier Science B.V. All rights reserved.

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  • Exploring radicals in carbonaceous solids by means of pulsed EPR spectroscopy

    T Ikoma, O Ito, S Tero-Kubota

    ENERGY & FUELS16 ( 1 ) 40 - 47   2002年1月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    Pulsed electron paramagnetic resonance (EPR) spectroscopy has been applied to elucidate the radical structures of Argonne premium coals and the reaction processes in coal tar pitches (CTP). Using two-dimensional nutation spectroscopy, the main EPR signals around g = 2.00 for the coals were confirmed to be attributed to free radicals rather than spin clusters with higher spin multiplicities. The broad H-1- and C-13-hyperfine spectra of the coals were detected separately by hyperfine sublevel correlation (HYSCORE) spectroscopy. It is concluded that the main coal radicals are pi radicals delocalized in pericondensed aromatic hydrocarbons with more than seven aromatic rings, which are larger than those of the most probable aromatic molecules in coals. HYSCORE spectroscopy, furthermore, helped us to understand the chemical change in the cation radicals in the charge-transfer complexes that accelerate the dehydrogenative polymerization of I-2-treated CTP.

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  • Exploring radicals in carbonaceous solids by means of pulsed EPR spectroscopy

    T Ikoma, O Ito, S Tero-Kubota

    ENERGY & FUELS16 ( 1 ) 40 - 47   2002年1月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    Pulsed electron paramagnetic resonance (EPR) spectroscopy has been applied to elucidate the radical structures of Argonne premium coals and the reaction processes in coal tar pitches (CTP). Using two-dimensional nutation spectroscopy, the main EPR signals around g = 2.00 for the coals were confirmed to be attributed to free radicals rather than spin clusters with higher spin multiplicities. The broad H-1- and C-13-hyperfine spectra of the coals were detected separately by hyperfine sublevel correlation (HYSCORE) spectroscopy. It is concluded that the main coal radicals are pi radicals delocalized in pericondensed aromatic hydrocarbons with more than seven aromatic rings, which are larger than those of the most probable aromatic molecules in coals. HYSCORE spectroscopy, furthermore, helped us to understand the chemical change in the cation radicals in the charge-transfer complexes that accelerate the dehydrogenative polymerization of I-2-treated CTP.

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  • A Nanoscale Measure -Spectroscopy using Electron Spin Dipolar Interaction-

    Tadaaki Ikoma

    Chemistry and Chemical Industry55   576 - 576   2002年

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    担当区分:筆頭著者, 責任著者  

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  • ナノスケールの“ものさし” ─電子スピン間双極子相互作用分光─

    化学と工業55   576 - 576   2002年

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  • Radical Ion Pair in Carrier Generation Process of Photoconductive Organic Polymer Films

    RIKEN Review44   119 - 120   2002年

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  • Spin Soliton in a p-Conjugated Ladder Polydiacetylene

    Physical Review B66 ( 1 ) 014423-1-014423-9   2002年

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  • Spin Soliton in a π-conjugaed Ladder Polydiacetylene

    Physical Review B66 ( 14423 ) 1 - 9   2002年

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  • Spin Soliton in a π-conjugaed Ladder Polydiacetylene

    Physical Review B66 ( 14423 ) 1 - 9   2002年

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  • Spin Soliton in a π-Conjugated Ladder Polydiacetylene

    Physical Review B66 ( 14423 ) 1 - 9   2002年

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  • Exploring radicals in carbonaceous solids by means of plused EPR spectroscopy

    Energy & Fuels16 ( 1 ) 40 - 47   2002年

  • Exploring radicals in carbonaceous solids by means of plused EPR spectroscopy

    IKOMA T, ITO O, TERO‐KUBOTA S

    Energy & Fuels16 ( 1 ) 40 - 47   2002年

  • Radical Ion Pair in Carrier Generation Process of Photoconductive Organic Polymer Films

    RIKEN Review44   119 - 120   2002年

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  • ナノスケールの“ものさし” ─電子スピン間双極子相互作用分光─

    化学と工業55   576 - 576   2002年

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  • Effects of quartz addition on the mechanochemical dechlorination of chlorobiphenyl by using CaO

    Qiwu Zhang, Fumio Saito, Tadaaki Ikoma, Shozo Tero-Kubota, Kiyotaka Hatakeda

    Environmental Science and Technology35 ( 24 ) 4933 - 4935   2001年12月

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    記述言語:英語  

    Grinding a mixture of 3-chlorobiphenyl (BP-Cl) and CaO with or without the addition of quartz was conducted in air by a planetary ball mill to investigate the mechanochemical dechlorination of BP-Cl. The dechlorinating reaction proceeds with an increase in grinding time, and over 99% of BP-Cl is decomposed at 360 min. Washing the ground sample with different solvents results in different products. Addition of quartz to the grinding mixture facilitates dechlorination efficiency, especially in the case of a high weight ratio of BP-Cl to CaO.

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  • Radicals in the mechanochemical dechlorination of hazardous organochlorine compounds using CaO nanoparticles

    T Ikoma, QW Zhang, F Saito, K Akiyama, S Tero-Kubota, T Kato

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN74 ( 12 ) 2303 - 2309   2001年12月

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    記述言語:英語   出版者・発行元:CHEMICAL SOC JAPAN  

    For the first time, we detected paramagnetic products generated during the grinding of 3-chlorobiphenyl (BP-Cl) with calcium oxide (CaO) nanoparticles by a ball mill method, which is one of the promising ways to detoxify hazardous chlorinated organic compounds. Those products were assigned to oxygen-centered aromatic radicals coming from BP-Cl and trapped electrons in oxygen vacancies on the surfaces of the CaO reactants using high-frequency and pulsed electron paramagnetic resonance spectroscopies. The observed good correlation between the dechlorination efficiency and the radical yield suggests that a radical mechanism plays an important role in the destruction of organochlorine compounds. The mechanochemical dechlorination could be interpreted by the following mechanism. First of all, the mechanical stressing induces the electron transfer from O2- sites on the surface of the CaO particle to the organic compounds. The produced organic anion radicals then undergo the effective self-dissociation of a chlorine-carbon bond.

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  • Effects of quartz addition on the mechanochemical dechlorination of chlorobiphenyl by using CaO

    QW Zhang, F Saito, T Ikoma, S Tero-Kubota

    ENVIRONMENTAL SCIENCE & TECHNOLOGY35 ( 24 ) 4933 - 4935   2001年12月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    Grinding a mixture of 3-chlorobiphenyl (BP-Cl) and CaO with or without the addition of quartz was conducted in air by a planetary ball mill to investigate the mechanochemical dechlorination of BP-Cl. The dechlorinating reaction proceeds with an increase in grinding time, and over 99% of BP-Cl is decomposed at 360 min. Washing the ground sample with different solvents results in different products. Addition of quartz to the grinding mixture facilitates dechlorination efficiency, especially in the case of a high weight ratio of BP-Cl to CaO.

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  • Radicals in the mechanochemical dechlorination of hazardous organochlorine compounds using CaO nanoparticles

    Tadaaki Ikoma, Qiwu Zhang, Fumio Saito, Kimio Akiyama, Shozo Tero-Kubota, Tatsuhisa Kato

    Bulletin of the Chemical Society of Japan74 ( 12 ) 2303 - 2309   2001年12月

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    記述言語:英語  

    For the first time, we detected paramagnetic products generated during the grinding of 3-chlorobiphenyl (BP-Cl) with calcium oxide (CaO) nanoparticles by a ball mill method, which is one of the promising ways to detoxify hazardous chlorinated organic compounds. Those products were assigned to oxygen-centered aromatic radicals coming from BP-Cl and trapped electrons in oxygen vacancies on the surfaces of the CaO reactants using high-frequency and pulsed electron paramagnetic resonance spectroscopies. The observed good correlation between the dechlorination efficiency and the radical yield suggests that a radical mechanism plays an important role in the destruction of organochlorine compounds. The mechanochemical dechlorination could be interpreted by the following mechanism. First of all, the mechanical stressing induces the electron transfer from O 2- sites on the surface of the CaO particle to the organic compounds. The produced organic anion radicals then undergo the effective self-dissociation of a chlorine-carbon bond.

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  • Experimental and theoretical studies on ferromagnetically coupled metal complexes with imino nitroxides

    H Oshio, M Yamamoto, T Ito, H Kawauchi, N Koga, T Ikoma, S Tero-Kubota

    INORGANIC CHEMISTRY40 ( 22 ) 5518 - 5525   2001年10月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    Copper(II), zinc(II), and nickel(II) complexes with tridentate imino nitroxyl diradicals, [CuCl(bisimpy)(MeOH)]-(PF6) (1), [ZnCl2(bisimpy)] (2), and [NiCl(bisimpy)(H2O)(2)]Cl . 2H(2)O (3) (bisimpy = 2,6-bis(1'-oxyl-4',4',5',5'-tetramethyl-4',5'-dihydro-1'H-imidazol-2'-yl)pyridine), were prepared, and their magnetic properties were studied. In 1, the Cu(II) ion has a square pyramidal coordination geometry, of which the equatorial coordination sites are occupied by three nitrogen atoms from the bisimpy and a chloride ion. The coordination geometry of the Zn(II) ion in 2 can be described as a trigonal bipyramid, with two chloride ions and a bisimpy. In 3, the Ni(II) ion has a distorted octahedral coordination geometry, of which four coordination sites are coordinated by the bisimpy and chloride ion, and two water molecules occupy the remaining cis positions. Magnetic susceptibility and EPR measurements revealed that in 1 and 3 the Cu(II) and Ni(II) ions with imino nitroxyl diraicals were ferromagnetically respectively, and the coupled, with the coupling constants J (H = -2J(ij)SigmaS(i)S(j)) of +165(1) and 109(2) cm(-1), intraligand ferromagnetic interactions in 1-3 were very weak. DFT molecular orbital calculations were performed on the diradical ligand, 1, and 2 to study the spin density distribution before and after coordination to the metal ions.

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  • Experimental and theoretical studies on ferromagnetically coupled metal complexes with imino nitroxides

    H Oshio, M Yamamoto, T Ito, H Kawauchi, N Koga, T Ikoma, S Tero-Kubota

    INORGANIC CHEMISTRY40 ( 22 ) 5518 - 5525   2001年10月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    Copper(II), zinc(II), and nickel(II) complexes with tridentate imino nitroxyl diradicals, [CuCl(bisimpy)(MeOH)]-(PF6) (1), [ZnCl2(bisimpy)] (2), and [NiCl(bisimpy)(H2O)(2)]Cl . 2H(2)O (3) (bisimpy = 2,6-bis(1'-oxyl-4',4',5',5'-tetramethyl-4',5'-dihydro-1'H-imidazol-2'-yl)pyridine), were prepared, and their magnetic properties were studied. In 1, the Cu(II) ion has a square pyramidal coordination geometry, of which the equatorial coordination sites are occupied by three nitrogen atoms from the bisimpy and a chloride ion. The coordination geometry of the Zn(II) ion in 2 can be described as a trigonal bipyramid, with two chloride ions and a bisimpy. In 3, the Ni(II) ion has a distorted octahedral coordination geometry, of which four coordination sites are coordinated by the bisimpy and chloride ion, and two water molecules occupy the remaining cis positions. Magnetic susceptibility and EPR measurements revealed that in 1 and 3 the Cu(II) and Ni(II) ions with imino nitroxyl diraicals were ferromagnetically respectively, and the coupled, with the coupling constants J (H = -2J(ij)SigmaS(i)S(j)) of +165(1) and 109(2) cm(-1), intraligand ferromagnetic interactions in 1-3 were very weak. DFT molecular orbital calculations were performed on the diradical ligand, 1, and 2 to study the spin density distribution before and after coordination to the metal ions.

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  • Electronic structures and dynamics of the excited triplet states of alpha,omega-diphenylpolyynes

    Y Nagano, T Ikoma, K Akiyama, S Tero-Kubota

    JOURNAL OF CHEMICAL PHYSICS114 ( 4 ) 1775 - 1784   2001年1月

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    記述言語:英語   出版者・発行元:AMER INST PHYSICS  

    The lowest excited triplet (T-1) states of diphenylacetylene and several alpha,omega -diphenylpolyynes (DPY) having two, three, four and six triple bonds were studied using continuous wave time-resolved electron paramagnetic resonance (CW-TREPR), pulsed EPR, and phosphorescence spectroscopy. Linear and planar molecular structures in the T-1 states of DPY were suggested from the magnetophotoselection experiments and observation of a strong 0-0 band in the well-resolved phosphorescence spectra. The spin density distributions, which were obtained by electron spin echo envelope modulation measurements and semi-empirical molecular orbital calculations, and the phosphorescence polarization normal to the long axis of molecule for the 0-0 bands suggested that the T-1 states of DPY have a B-3(1u) (pi (x)pi (x)*) electronic configuration. DPY showed an abnormally large \D\ value of the zero-field splitting parameters that increased with increasing molecular size. Such an unusual behavior of the D values is interpreted in terms of the spin-orbit interaction between the T-1 and (3)A(u)(pi (x)pi (y)*) states mainly due to their energy proximity which is probably characteristic of the excited states for the polyynes. The estimated energy gap between the (3)pi (x)pi (y)* and (3)pi (x)pi (x)* states for DPY ranges from 2900 cm(-1) to 1400 cm(-1). There existed a good correlation between the acceleration of the nonradiative decay rate constant from the T1 state and appearance of a ring twisting vibronic band with b(1g) symmetry in the phosphorescence spectra for DPY. Therefore, we concluded that the vibronic interaction between the (3)pi (x)pi (y)* and (3)pi (x)pi (x)* states promoted by the b(1g) vibration leads to a broadening of the potential surface of the T-1 state which results in the fast radiationless decay Co the ground state, (C) 2001 American Institute of Physics.

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  • Electronic Structures and Dynamics of the Excited Triplet States of α, ω-Diphenylpolyynes

    NAGANO Y, IKOMA T, AKIYAMA K, TERO‐KUBOTA S

    The Journal of Chemical Physics114 ( 4 ) 1775 - 1784   2001年1月

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  • ESEEM study on a stable paramagnetic center in polydiacetylene having a pi-conjugated ladder structure

    T Ikoma, S Okada, H Nakanishi, K Akiyama, S Tero-Kubota

    SOLID STATE COMMUNICATIONS117 ( 5 ) 285 - 289   2001年

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    記述言語:英語   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Using two-, three- and five-pulse methods, we have measured the electron spin echo envelope modulation (ESEEM) of a stable paramagnetic center existing in a non-doped ladder polymer, in which two polydiacetylenes are conjugated in each repeating unit. A relatively deep modulation effect owing to weak hyperfine interaction with protons was observed. The number of interacting protons was estimated to be a few tens based on the analysis of the modulation amplitude. The interaction with many protons implies that the paramagnetic center in the ladder polydiacetylene also possesses a wavefunction delocalized on several units in the pi -conjugated system like the spin solitons in polyacetylene. (C) 2001 Elsevier Science Ltd. All rights reserved.

    DOI: 10.1016/S0038-1098(00)00471-3

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  • Direct observation of a distant ion pair generated in a photoconductive poly(N-vinylcarbazole) film with dopant

    T Ikoma, M Nakai, K Akiyama, S Tero-Kubota, T Ishii

    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION40 ( 17 ) 3234 - +   2001年

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    記述言語:英語   出版者・発行元:WILEY-V C H VERLAG GMBH  

    DOI: 10.1002/1521-3773(20010903)40:17<3234::AID-ANIE3234>3.0.CO;2-B

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  • Iron-hydrogen complexes in Si studied by EPR measurement

    T Takahashi, M Suezawa, T Ikoma, S Tero

    PROCEEDINGS OF THE 25TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF SEMICONDUCTORS, PTS I AND II87   1461 - 1462   2001年

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    記述言語:英語   出版者・発行元:SPRINGER-VERLAG BERLIN  

    We studied iron-hydrogen (Fe-H) complexes in Si by EPR measurements. Specimens prepared from an n-type FZ-Si crystal (phosphorus concentration: 1X10(16)cm(-3)) were doped with Fe and H by heating in Fe vapor and H-2 gas, respectively. EPR spectra were measured with use of an X-band and a Q-band spectrometer. New EPR absorption spectra were observed at around 2.067 of g-value. We identified them to be due to Fe-H pair from the EPR spectrum, the isotope effect of hydrogen and thermal stability. To explain a peculiar dependence of EPR spectrum on the measurement frequencies (X-band and Q-band), we propose that the H atom in Fe-H pair moves around the Fe atom by tunneling.

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  • Direct observation of a distant ion pair generated in a photoconductive poly(N-vinylcarbazole) film with dopant

    T Ikoma, M Nakai, K Akiyama, S Tero-Kubota, T Ishii

    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION40 ( 17 ) 3234 - +   2001年

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    記述言語:英語   出版者・発行元:WILEY-V C H VERLAG GMBH  

    DOI: 10.1002/1521-3773(20010903)40:17<3234::AID-ANIE3234>3.0.CO;2-B

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  • Iron-hydrogen complexes in Si studied by EPR measurement

    T Takahashi, M Suezawa, T Ikoma, S Tero

    PROCEEDINGS OF THE 25TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF SEMICONDUCTORS, PTS I AND II87   1461 - 1462   2001年

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    記述言語:英語   出版者・発行元:SPRINGER-VERLAG BERLIN  

    We studied iron-hydrogen (Fe-H) complexes in Si by EPR measurements. Specimens prepared from an n-type FZ-Si crystal (phosphorus concentration: 1X10(16)cm(-3)) were doped with Fe and H by heating in Fe vapor and H-2 gas, respectively. EPR spectra were measured with use of an X-band and a Q-band spectrometer. New EPR absorption spectra were observed at around 2.067 of g-value. We identified them to be due to Fe-H pair from the EPR spectrum, the isotope effect of hydrogen and thermal stability. To explain a peculiar dependence of EPR spectrum on the measurement frequencies (X-band and Q-band), we propose that the H atom in Fe-H pair moves around the Fe atom by tunneling.

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  • ESEEM Study on a Stable Paramagnetic Center in Polydiacetylene Having a π-Conjugated Ladder Structure

    IKOMA T, OKADA S, NAKANISHI H, AKIYAMA K, TERO‐KUBOTA S

    Solid State Communications117 ( 5 ) 285 - 289   2001年

  • Attempts to Explore Coal Radicals by Using Pulsed Electron Paramagnetic Resonance Spectroscopy

    International Symposium on Chemical, Higher-ordered Structures, Reactivity of Coal, Japan,103-107   2001年

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  • Attempts to Explore Coal Radicals by Using Pulsed Electron Paramagnetic Resonance Spectroscopy

    International Symposium on Chemical, Higher-ordered Structures, Reactivity of Coal, Japan,103-107   2001年

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  • 微結晶シリコン中の欠陥に関する多周波EPR研究

    Material Research Society Symposium Proceedings609 ( A24.7 )   2001年

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  • Electron paramagnetic resonance studies on microcrystalline silicon prepared by sputtering method

    T Ehara, T Ikoma, K Akiyama, S Tero-Kubota

    JOURNAL OF APPLIED PHYSICS88 ( 3 ) 1698 - 1700   2000年8月

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    記述言語:英語   出版者・発行元:AMER INST PHYSICS  

    Dangling bond (DB) defects in unhydrogenated microcrystalline silicon (mu c-Si) prepared by rf sputtering have been studied. Raman spectra and x-ray diffraction indicate that the mu c-Si fraction has been formed at the Ar sputtering pressure higher than 26.6 Pa while only amorphous silicon (a-Si) has been produced at the lower pressure. The electron paramagnetic resonance (EPR) spectrum in the mu c-Si film is broad and unsymmetrical with the average g value of g=2.006 compared with that of a-Si (g=2.0055). The X- and Q-band EPR measurements suggest that the line shape is mainly governed by the inhomogeneous broadening due to the g anisotropy, indicating relatively large distribution of the structure of the DB defects. (C) 2000 American Institute of Physics. [S0021-8979(00)06712-8].

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  • Electron paramagnetic resonance studies on microcrystalline silicon prepared by sputtering method

    T Ehara, T Ikoma, K Akiyama, S Tero-Kubota

    JOURNAL OF APPLIED PHYSICS88 ( 3 ) 1698 - 1700   2000年8月

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    記述言語:英語   出版者・発行元:AMER INST PHYSICS  

    Dangling bond (DB) defects in unhydrogenated microcrystalline silicon (mu c-Si) prepared by rf sputtering have been studied. Raman spectra and x-ray diffraction indicate that the mu c-Si fraction has been formed at the Ar sputtering pressure higher than 26.6 Pa while only amorphous silicon (a-Si) has been produced at the lower pressure. The electron paramagnetic resonance (EPR) spectrum in the mu c-Si film is broad and unsymmetrical with the average g value of g=2.006 compared with that of a-Si (g=2.0055). The X- and Q-band EPR measurements suggest that the line shape is mainly governed by the inhomogeneous broadening due to the g anisotropy, indicating relatively large distribution of the structure of the DB defects. (C) 2000 American Institute of Physics. [S0021-8979(00)06712-8].

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  • Multi-band electron paramagnetic resonance study of the defects in microcrystalline silicon

    T Ehara, T Ikoma, S Tero-Kubota

    JOURNAL OF NON-CRYSTALLINE SOLIDS266 ( Pt.A ) 540 - 543   2000年5月

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    記述言語:英語   出版者・発行元:ELSEVIER SCIENCE BV  

    We report electron paramagnetic resonance (EPR) studies in dangling bond (DB) defects in the hydrogenated microcrystalline silicon (mu c-Si:H) film prepared by a plasma enhanced chemical vapor deposition (PECVD), unhydrogenated microcrystalline silicon (mu c-Si) film prepared by RF sputtering, and mu c-Si embedded in SiO2 film formed by co-sputtering followed by annealing. Multi-band EPR measurements showed that their line widths originate primarily from a distribution of the g-values. We have detected a signal at g = 2.006 in the microcrystalline fraction of the mu c-Si, mu c-Si:H and mu c-Si embedded SiO2 films. The signal has a greater width than the DB signal in amorphous silicon (a-Si), indicating a larger distribution of g-values of the defects in the microcrystalline material. The DB signal in the mu c-Si embedded in SiO2 was reproduced by the computer simulation taking into account the distribution of the g-values. (C) 2000 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0022-3093(00)00027-2

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  • Multi-band electron paramagnetic resonance study of the defects in microcrystalline silicon

    T Ehara, T Ikoma, S Tero-Kubota

    JOURNAL OF NON-CRYSTALLINE SOLIDS266 ( Pt.A ) 540 - 543   2000年5月

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    記述言語:英語   出版者・発行元:ELSEVIER SCIENCE BV  

    We report electron paramagnetic resonance (EPR) studies in dangling bond (DB) defects in the hydrogenated microcrystalline silicon (mu c-Si:H) film prepared by a plasma enhanced chemical vapor deposition (PECVD), unhydrogenated microcrystalline silicon (mu c-Si) film prepared by RF sputtering, and mu c-Si embedded in SiO2 film formed by co-sputtering followed by annealing. Multi-band EPR measurements showed that their line widths originate primarily from a distribution of the g-values. We have detected a signal at g = 2.006 in the microcrystalline fraction of the mu c-Si, mu c-Si:H and mu c-Si embedded SiO2 films. The signal has a greater width than the DB signal in amorphous silicon (a-Si), indicating a larger distribution of g-values of the defects in the microcrystalline material. The DB signal in the mu c-Si embedded in SiO2 was reproduced by the computer simulation taking into account the distribution of the g-values. (C) 2000 Elsevier Science B.V. All rights reserved.

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  • Nitrogen-doping effects on electrical properties of hydrogenated microcrystalline silicon as studied by electron paramagnetic resonance and conductivity

    T Ehara, T Amino, H Shinomiya, T Ikoma, K Akiyama, S Tero-Kubota

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS39 ( 1 ) 31 - 34   2000年1月

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    記述言語:英語   出版者・発行元:JAPAN J APPLIED PHYSICS  

    We have examined Raman scattering, X-ray diffraction, electron paramagnetic resonance (EPR) spectra and the conductivity of nitrogen-doped hydrogenated microcrystalline silicon. The EPR signals due to conduction electrons have been observed in the doped films, except for highly doped samples that have no microcrystalline fraction. The result indicates that the doped nitrogen atom acts as an electron donor in the microcrystalline silicon. The temperature dependence of the conductivity clarify that the activation energy depends on the doping level. The influence of the doping level on the conductivity can be interpreted in terms:of the balance of the effective electron donation and the decrease of carrier mobility due to a decrease of the microcrystalline phase volume ratio. At temperatures lower than approximately 180 K, the conductivity shows little variation. This is explained using a model of the hopping conduction, in terms of defect states for all samples.

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  • Nitrogen-doping effects on electrical properties of hydrogenated microcrystalline silicon as studied by electron paramagnetic resonance and conductivity

    T Ehara, T Amino, H Shinomiya, T Ikoma, K Akiyama, S Tero-Kubota

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS39 ( 1 ) 31 - 34   2000年1月

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    記述言語:英語   出版者・発行元:JAPAN J APPLIED PHYSICS  

    We have examined Raman scattering, X-ray diffraction, electron paramagnetic resonance (EPR) spectra and the conductivity of nitrogen-doped hydrogenated microcrystalline silicon. The EPR signals due to conduction electrons have been observed in the doped films, except for highly doped samples that have no microcrystalline fraction. The result indicates that the doped nitrogen atom acts as an electron donor in the microcrystalline silicon. The temperature dependence of the conductivity clarify that the activation energy depends on the doping level. The influence of the doping level on the conductivity can be interpreted in terms:of the balance of the effective electron donation and the decrease of carrier mobility due to a decrease of the microcrystalline phase volume ratio. At temperatures lower than approximately 180 K, the conductivity shows little variation. This is explained using a model of the hopping conduction, in terms of defect states for all samples.

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  • 混在状態に迫るパルス電子スピン共鳴

    表面38 ( 1 ) 39 - 53   2000年

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  • カーボン用語辞典

    アグネ承風社   2000年

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  • A role of charge-transfer complex with iodine in the modification of coal tar pitch

    N Miyajima, T Akatsu, T Ikoma, O Ito, B Rand, Y Tanabe, E Yasuda

    CARBON38 ( 13 ) 1831 - 1838   2000年

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    記述言語:英語   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Iodine introduced into coal tar pitch (CTP) can drastically alter its reology and carbonization behavior. Here, the mechanism of interaction between iodine and CTP has been investigated by using various spectroscopic methods such as I-127-NMR, EPR and FT-IR. It is shown that some iodine molecules infiltrated into the CTP and form charge transfer complexes with the relative large aromatic components of the CTP. Hyperfine sublevel correlation spectroscopy (HYSCORE) revealed the molecular size of cation radicals, which contain more than ten benzene rings, and the location of iodine anion that is incorporated at ca. 0.3 nm from the aromatic cation radicals. The elemental H/C ratio decreased and the viscosity of CTP increased with the density of the charge-transfer complexes, which was also increased by the iodine treatment. These results strongly suggest that dehydrogenative polymerization of CTP occurs during the iodine treatment. The cation radicals in the charge-transfer complexes accelerate the dehydrogenative polymerization and result in a high carbon yield. (C) 2000 Elsevier Science Ltd. All rights reserved.

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  • A role of charge-transfer complex with iodine in the modification of coal tar pitch

    N Miyajima, T Akatsu, T Ikoma, O Ito, B Rand, Y Tanabe, E Yasuda

    CARBON38 ( 13 ) 1831 - 1838   2000年

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    記述言語:英語   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Iodine introduced into coal tar pitch (CTP) can drastically alter its reology and carbonization behavior. Here, the mechanism of interaction between iodine and CTP has been investigated by using various spectroscopic methods such as I-127-NMR, EPR and FT-IR. It is shown that some iodine molecules infiltrated into the CTP and form charge transfer complexes with the relative large aromatic components of the CTP. Hyperfine sublevel correlation spectroscopy (HYSCORE) revealed the molecular size of cation radicals, which contain more than ten benzene rings, and the location of iodine anion that is incorporated at ca. 0.3 nm from the aromatic cation radicals. The elemental H/C ratio decreased and the viscosity of CTP increased with the density of the charge-transfer complexes, which was also increased by the iodine treatment. These results strongly suggest that dehydrogenative polymerization of CTP occurs during the iodine treatment. The cation radicals in the charge-transfer complexes accelerate the dehydrogenative polymerization and result in a high carbon yield. (C) 2000 Elsevier Science Ltd. All rights reserved.

    DOI: 10.1016/S0008-6223(00)00022-1

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  • Cyanide-bridged iron-copper molecular squares with doublet and quintet spin ground states

    H Oshio, O Tamada, H Onodera, T Ito, T Ikoma, S Tero-Kubota

    INORGANIC CHEMISTRY38 ( 25 ) 5686 - 5689   1999年12月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    Reactions of [Fe-II(CN)(2)(bpy)(2)] and [Fe-III(CN)(2)(bpy)(2)](PF6) with [Cu-II(bpy)(CH3OH)(2)](PF6)(2) in methanol yielded cyanide-bridged cyclic tetranuclear complexes of [(Fe2Cu2II)-Cu-II(mu-CN)(4)(bpy)(6)](PF6)(4). 2H(2)O . 4CHCl(3) (1) and [Fe-2(III)-Cu-2(II) (mu-CN)(4)(bpy)(6)](PF6)(6) . 4CH(3)CN . 2CNCl(3) (2), respectively. Zn the squares of 1 and 2, the Fe2+/3+ (low-spin) and Cu2+ ions are alternately bridged by the cyanide ions, the carbon atoms of which coordinate to the iron ions. Variable-temperature magnetic susceptibility studies of complexes revealed that the Cu2+ ions in 1 are magnetically isolated. In the square of 2, the adjacent Fe3+ and Cu2+ ions were ferromagnetically coupled through the cyanide bridges with a J(1) value of +6.3(1) cm(-1) and the weaker antiferromagnetic interactions between the orthogonal Fe3+... Fe3+ and Cu2+...Cu2+ pairs are operative (J(2) = -3.1(1) cm(-1)). The propagation of the ferromagnetic interaction in 2 can be understood by the orthogonal magnetic orbitals of the low-spin Fe3+ (d pi) and Cu2+ (d sigma) ions. Cyclic voltammograms of the squares have been recorded and discussed. Crystal data for 1: triclinic space group P (1) over bar, a = 14.491(4) Angstrom, b = 15.312(4) Angstrom, c = 12.959(3) Angstrom, alpha = 91.38(2)degrees , beta = 109.56(2)degrees, gamma = 65.41(2)degrees, Z = 1. Crystal data for 2: triclinic space group P (1) over bar, a = 14.472(9) Angstrom, b = 15.310(6) Angstrom, c = 12.523(5) Angstrom, alpha 102.58(3)degrees beta = 107.19(4)degrees, gamma = 75.08(4)degrees, Z = 1.

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  • Cyanide-bridged iron-copper molecular squares with doublet and quintet spin ground states

    H Oshio, O Tamada, H Onodera, T Ito, T Ikoma, S Tero-Kubota

    INORGANIC CHEMISTRY38 ( 25 ) 5686 - 5689   1999年12月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    Reactions of [Fe-II(CN)(2)(bpy)(2)] and [Fe-III(CN)(2)(bpy)(2)](PF6) with [Cu-II(bpy)(CH3OH)(2)](PF6)(2) in methanol yielded cyanide-bridged cyclic tetranuclear complexes of [(Fe2Cu2II)-Cu-II(mu-CN)(4)(bpy)(6)](PF6)(4). 2H(2)O . 4CHCl(3) (1) and [Fe-2(III)-Cu-2(II) (mu-CN)(4)(bpy)(6)](PF6)(6) . 4CH(3)CN . 2CNCl(3) (2), respectively. Zn the squares of 1 and 2, the Fe2+/3+ (low-spin) and Cu2+ ions are alternately bridged by the cyanide ions, the carbon atoms of which coordinate to the iron ions. Variable-temperature magnetic susceptibility studies of complexes revealed that the Cu2+ ions in 1 are magnetically isolated. In the square of 2, the adjacent Fe3+ and Cu2+ ions were ferromagnetically coupled through the cyanide bridges with a J(1) value of +6.3(1) cm(-1) and the weaker antiferromagnetic interactions between the orthogonal Fe3+... Fe3+ and Cu2+...Cu2+ pairs are operative (J(2) = -3.1(1) cm(-1)). The propagation of the ferromagnetic interaction in 2 can be understood by the orthogonal magnetic orbitals of the low-spin Fe3+ (d pi) and Cu2+ (d sigma) ions. Cyclic voltammograms of the squares have been recorded and discussed. Crystal data for 1: triclinic space group P (1) over bar, a = 14.491(4) Angstrom, b = 15.312(4) Angstrom, c = 12.959(3) Angstrom, alpha = 91.38(2)degrees , beta = 109.56(2)degrees, gamma = 65.41(2)degrees, Z = 1. Crystal data for 2: triclinic space group P (1) over bar, a = 14.472(9) Angstrom, b = 15.310(6) Angstrom, c = 12.523(5) Angstrom, alpha 102.58(3)degrees beta = 107.19(4)degrees, gamma = 75.08(4)degrees, Z = 1.

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  • Proton tunneling of tropolone in durene single crystal as studied by time-resolved EPR detected excitation spectroscopy

    T Ikoma, K Akiyama, S Tero-Kubota, Y Ikegami

    JOURNAL OF CHEMICAL PHYSICS111 ( 15 ) 6875 - 6883   1999年10月

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    記述言語:英語   出版者・発行元:AMER INST PHYSICS  

    We have measured the excitation spectra for tropolone-OH in durene single crystal and tropolone-OD in deuterated durene using a time-resolved electron paramagnetic resonance (TREPR) detection method that makes possible to separate the signals due to magnetically different sites. The tunneling doublet with 3 cm(-1) was observed in the sharp zero-phonon line. The small splitting indicates that the crystal field increases the barrier of double-minimum potential for the proton tunneling in the S-1 state. Moderately asymmetric potentials of the S-0 and S-1 states, where the energetic imbalance between two wells in the S-1 state potential is opposite the S-0 state potential, reasonably explained the observed unusual intensity ratio of the tunneling doublet (0(1)(+) &lt; 0(1)(-)). A well-resolved progression of a phonon band with a 15 cm(-1) separation was also obtained in durene crystal at very low temperature. From a Franck-Condon analysis of the relative intensity of the phonon band, it was clarified that the stable configuration of the excited state tropolone in durene differed from that of the ground state. (C) 1999 American Institute of Physics. [S0021-9606(99)00439-0].

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  • Proton tunneling of tropolone in durene single crystal as studied by time-resolved EPR detected excitation spectroscopy

    T Ikoma, K Akiyama, S Tero-Kubota, Y Ikegami

    JOURNAL OF CHEMICAL PHYSICS111 ( 15 ) 6875 - 6883   1999年10月

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    記述言語:英語   出版者・発行元:AMER INST PHYSICS  

    We have measured the excitation spectra for tropolone-OH in durene single crystal and tropolone-OD in deuterated durene using a time-resolved electron paramagnetic resonance (TREPR) detection method that makes possible to separate the signals due to magnetically different sites. The tunneling doublet with 3 cm(-1) was observed in the sharp zero-phonon line. The small splitting indicates that the crystal field increases the barrier of double-minimum potential for the proton tunneling in the S-1 state. Moderately asymmetric potentials of the S-0 and S-1 states, where the energetic imbalance between two wells in the S-1 state potential is opposite the S-0 state potential, reasonably explained the observed unusual intensity ratio of the tunneling doublet (0(1)(+) &lt; 0(1)(-)). A well-resolved progression of a phonon band with a 15 cm(-1) separation was also obtained in durene crystal at very low temperature. From a Franck-Condon analysis of the relative intensity of the phonon band, it was clarified that the stable configuration of the excited state tropolone in durene differed from that of the ground state. (C) 1999 American Institute of Physics. [S0021-9606(99)00439-0].

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  • Electronic and molecular structures of α,ω-diphenylpolyynes in the lowest excited triplet states

    Yasutomo Nagano, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota

    Chemical Physics Letters303 ( 1-2 ) 201 - 208   1999年4月

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    記述言語:英語   出版者・発行元:Elsevier  

    Unusually large D values of zero-field splitting parameters were observed for 1,6-diphenylhexatriyne (D=0.396 cm-1) and 1,8-diphenyloctatetrayne (D=0.533 cm-1) by using time-resolved EPR (TREPR) spectroscopy. The lowest excited triplet (T1) states of these diphenylpolyynes were assigned to 3B1u(3πxπ * x) in character from the degree of the polarization of phosphorescence. It has been concluded that the present diphenylpolyynes have a linear planar structure in the T1 states, although the TREPR and phosphorescence spectra indicate interactions between the T1(3πxπ* x) and Tn(3πxπ* y) states through spin-orbit and vibronic interactions.

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  • Electronic and molecular structures of alpha,omega-diphenylpolyynes in the lowest excited triplet states

    Y Nagano, T Ikoma, K Akiyama, S Tero-Kubota

    CHEMICAL PHYSICS LETTERS303 ( 1-2 ) 201 - 208   1999年4月

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    記述言語:英語   出版者・発行元:ELSEVIER SCIENCE BV  

    Unusually large \D\ values of zero-field splitting parameters were observed for 1,6-diphenylhexatriyne (\D\ = 0.396 cm(-1)) and 1,8-diphenyloctatetrayne (\D\ = 0.533 cm(-1)) by using time-resolved EPR (TREPR) spectroscopy. The lowest excited triplet (T-1) states of these diphenylpolyynes were assigned to B-3(1u)((3)pi(x)pi(x)(*)) in character from the degree of the polarization of phosphorescence. It has been concluded that the present diphenylpolyynes have a linear planar structure in the T-1 states, although the TREPR and phosphorescence spectra indicate interactions between the T-1((3)pi(x)pi(x)(*)) and T-n((3)pi(x)pi(y)(*)) states through spin-orbit and vibronic interactions. (C) 1999 Elsevier Science B.V. All rights reserved.

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  • Twist conformational effects on the excited triplet states of aromatic ketones studied by multifrequency TREPR and pulsed EPR spectroscopy

    T Ikoma, K Akiyama, S Tero-Kubota

    MOLECULAR PHYSICS96 ( 5 ) 813 - 820   1999年3月

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    記述言語:英語   出版者・発行元:TAYLOR & FRANCIS LTD  

    Employing X- and Q-band time-resolved EPR and pulsed EPR techniques, we have investigated effects of twist conformation on the electronic structures and magnetic properties of the lowest excited triplet states of alkyl phenyl ketones. The conformational variation due to steric hindrance of a bulky substituent on the alpha-position drastically leads to a decrease of the zero-field splitting constant of \D\ and an increase of the energy gap between (3)n pi* and (3)pi pi* states. Hydrogen bonding with H2O destabilized significantly the (3)n pi* state and switched the T-1 state to the (3)pi pi* state. t-Butyl phenyl ketone gave unusually broad EPR spectra in rigid glassy matrices. The multifrequency and pulsed EPR measurements clarified that the inhomogeneously broadening spectra were ascribable to the distribution of the dihedral angle about a twist conformation. Asymmetric distribution of the ZFS parameters was interpreted in terms of the perturbation of spin-orbit interactions to the spin sublevels.

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  • Twist conformational effects on the excited triplet states of aromatic ketones studied by multifrequency TREPR and pulsed EPR spectroscopy

    T Ikoma, K Akiyama, S Tero-Kubota

    MOLECULAR PHYSICS96 ( 5 ) 813 - 820   1999年3月

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    記述言語:英語   出版者・発行元:TAYLOR & FRANCIS LTD  

    Employing X- and Q-band time-resolved EPR and pulsed EPR techniques, we have investigated effects of twist conformation on the electronic structures and magnetic properties of the lowest excited triplet states of alkyl phenyl ketones. The conformational variation due to steric hindrance of a bulky substituent on the alpha-position drastically leads to a decrease of the zero-field splitting constant of \D\ and an increase of the energy gap between (3)n pi* and (3)pi pi* states. Hydrogen bonding with H2O destabilized significantly the (3)n pi* state and switched the T-1 state to the (3)pi pi* state. t-Butyl phenyl ketone gave unusually broad EPR spectra in rigid glassy matrices. The multifrequency and pulsed EPR measurements clarified that the inhomogeneously broadening spectra were ascribable to the distribution of the dihedral angle about a twist conformation. Asymmetric distribution of the ZFS parameters was interpreted in terms of the perturbation of spin-orbit interactions to the spin sublevels.

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  • 新しいESR法を用いた石炭ラジカルの研究

    生駒 忠昭, 伊藤 攻, 手老 省三

    日本エネルギー学会誌78 ( 12 ) 980 - 987   1999年

  • 電子スピン共鳴法による石炭ラジカルの最近の研究例

    生駒 忠昭

    石炭利用技術情報20 ( 6 ) 4 - 6   1999年

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    担当区分:筆頭著者, 責任著者  

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  • Application of New ESR Spectroscopies to Coal Studies

    Tadaaki IKOMA, Osamu ITO, Shozo TERO(KUBOTA

    Journal of the Japan Institute of Energy78 ( 12 ) 980 - 987   1999年

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  • HYSCORE study on coal radicals

    T Ikoma, O Ito, S Tero-Kubota, K Akiyama

    ENERGY & FUELS12 ( 6 ) 1363 - 1368   1998年11月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    Hyperfine sublevel correlation spectroscopy (HYSCORE) spectra have been measured for the radicals in eight well-characterized Argonne Premium coals and their model compounds. The broad H-1 and C-13 hyperfine spectra of all coals were detected at room temperature. The hyperfine structure was analyzed by the comparison with model radicals and semiempirical molecular orbital calculations. The main coal radicals are considered as two-dimensionally condensed pi radicals with more than seven aromatic rings. The C-13/H-1 ratio of the hyperfine spectra increases with coal rank, suggesting a new index of coal rank.

    DOI: 10.1021/ef980130h

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  • Time-resolved and pulsed EPR studies on the lowest excited triplet state of 1,4-diphenylbutadiyne

    Y Nagano, T Ikoma, K Akiyama, S Tero-Kubota

    JOURNAL OF PHYSICAL CHEMISTRY A102 ( 29 ) 5769 - 5774   1998年7月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    The short-lived T-1 state of 1,4-diphenylbutadiyne (DPB) has been investigated in various glassy matrices at low temperatures using time-resolved EPR and pulsed EPR methods. Zero-field splitting parameters of D = -0.250 cm(-1) and E = +0.018 cm(-1) were determined. The negative D value was verified from the M-S dependence of the ENDOR frequencies. The hyperfine splitting constants of ring protons were obtained from the electron spin-echo envelope modulation with three-pulse stimulated echo. The spin density distribution on the phenyl groups was estimated from the analysis of the hyperfine splittings at each of the canonical orientations. The moderate spin densities on the phenyl rings indicated that the T-1 state was (3)pi(x)pi(x)* in electronic character. The origin of the large negative D value of DPB has been discussed in terms of the spin-orbit interaction between the close lying (3)pi(x)pi(x)* and (3)pi(x)pi(y)* states.

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  • Time-resolved and pulsed EPR studies on the lowest excited triplet state of 1,4-diphenylbutadiyne

    Y Nagano, T Ikoma, K Akiyama, S Tero-Kubota

    JOURNAL OF PHYSICAL CHEMISTRY A102 ( 29 ) 5769 - 5774   1998年7月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    The short-lived T-1 state of 1,4-diphenylbutadiyne (DPB) has been investigated in various glassy matrices at low temperatures using time-resolved EPR and pulsed EPR methods. Zero-field splitting parameters of D = -0.250 cm(-1) and E = +0.018 cm(-1) were determined. The negative D value was verified from the M-S dependence of the ENDOR frequencies. The hyperfine splitting constants of ring protons were obtained from the electron spin-echo envelope modulation with three-pulse stimulated echo. The spin density distribution on the phenyl groups was estimated from the analysis of the hyperfine splittings at each of the canonical orientations. The moderate spin densities on the phenyl rings indicated that the T-1 state was (3)pi(x)pi(x)* in electronic character. The origin of the large negative D value of DPB has been discussed in terms of the spin-orbit interaction between the close lying (3)pi(x)pi(x)* and (3)pi(x)pi(y)* states.

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  • Photo-properties of rare earth ion (Er3+, Eu3+ and Sm3+)-doped alumina films prepared by the sol-gel method

    Youichi Kurokawa, Takayuki Ishizaka, Tadaaki Ikoma, Shozo Tero-Kubota

    Chemical Physics Letters287 ( 5-6 ) 737 - 741   1998年5月

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    記述言語:英語   出版者・発行元:Elsevier  

    Rare earth ion (Er3+, Eu3+ and Sm3+)-doped alumina films have been prepared by the sol-gel method, using AlCl3-derived alumina sol. The effects of dopant concentration and treatment temperatures on the photo-properties of absorption and emission have been examined for the doped films. These sol-gel-derived alumina matrices gave a high-dopant concentration (~15 mol% per alumina).

    DOI: 10.1016/S0009-2614(98)00132-8

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  • Photo-properties of rare earth ion (Er3+, Eu3+ and Sm3+)-doped alumina films prepared by the sol-gel method

    Y Kurokawa, T Ishizaka, T Ikoma, S Tero-Kubota

    CHEMICAL PHYSICS LETTERS287 ( 5-6 ) 737 - 741   1998年5月

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    記述言語:英語   出版者・発行元:ELSEVIER SCIENCE BV  

    Rare earth ion (Er3+, Eu3+ and Sm3+)-doped alumina films have been prepared by the sol-gel method, using AlCl3-derived alumina sol. The effects of dopant concentration and treatment temperatures on the photo-properties of absorption and emission have been examined for the doped films. These sol-gel-derived alumina matrices gave a high-dopant concentration(similar to 15 mol% per alumina). (C) 1998 Elsevier Science B.V. All rights reserved.

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  • Electronic structure of the excited triplet state of nonphosphorescent tropolone studied by time-resolved EPR

    T Ikoma, K Akiyama, S Tero-Kubota, Y Ikegami

    JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS94 ( 9 ) 1197 - 1201   1998年5月

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    記述言語:英語   出版者・発行元:ROYAL SOC CHEMISTRY  

    Time-resolved EPR measurements and semi-empirical MO calculations have been carried out to clarify the electronic structure of the T-1 state of nonphosphorescent tropolone. The observed zero-field splitting parameters indicate that the T-1 state has a pure pi pi* character and the energy order among the spin sublevels was T-Y (in-plane) &gt; T-X (in-plane) &gt; 0 &gt; T-Z (out-of-plane), which is the same as tropone for a parent molecule. However, the principal X-axis slightly turns out of the carbonyl bond direction so that the intersystem crossing from the S-1 state to the T-Y sublevel becomes more active. The spin densities obtained from hyperfine splittings of protons and MO calculation of AM1 method show an asymmetric distribution of unpaired pi-electrons over two oxygens as well as the seven-membered ring. This unbalanced distribution makes the deviation of the X-axis from the carbonyl bond clear. We found two sites that can exchange each other by intramolecular proton transfer in a durene single crystal.

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  • Electronic structure of the excited triplet state of nonphosphorescent tropolone studied by time-resolved EPR

    T Ikoma, K Akiyama, S Tero-Kubota, Y Ikegami

    JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS94 ( 9 ) 1197 - 1201   1998年5月

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    記述言語:英語   出版者・発行元:ROYAL SOC CHEMISTRY  

    Time-resolved EPR measurements and semi-empirical MO calculations have been carried out to clarify the electronic structure of the T-1 state of nonphosphorescent tropolone. The observed zero-field splitting parameters indicate that the T-1 state has a pure pi pi* character and the energy order among the spin sublevels was T-Y (in-plane) &gt; T-X (in-plane) &gt; 0 &gt; T-Z (out-of-plane), which is the same as tropone for a parent molecule. However, the principal X-axis slightly turns out of the carbonyl bond direction so that the intersystem crossing from the S-1 state to the T-Y sublevel becomes more active. The spin densities obtained from hyperfine splittings of protons and MO calculation of AM1 method show an asymmetric distribution of unpaired pi-electrons over two oxygens as well as the seven-membered ring. This unbalanced distribution makes the deviation of the X-axis from the carbonyl bond clear. We found two sites that can exchange each other by intramolecular proton transfer in a durene single crystal.

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  • Transparent alumina films derived from two sources of AlCl3 center dot 6H(2)O and aluminium iso-propoxide by sol-gel method

    Y Kurokawa, T Suga, S Nakata, T Ikoma, S Tero-Kubota

    JOURNAL OF MATERIALS SCIENCE LETTERS17 ( 4 ) 275 - 278   1998年2月

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    記述言語:英語   出版者・発行元:KLUWER ACADEMIC PUBL  

    DOI: 10.1023/A:1006517219037

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  • Transparent alumina films derived from two sources of AlCl3 center dot 6H(2)O and aluminium iso-propoxide by sol-gel method

    Y Kurokawa, T Suga, S Nakata, T Ikoma, S Tero-Kubota

    JOURNAL OF MATERIALS SCIENCE LETTERS17 ( 4 ) 275 - 278   1998年2月

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    記述言語:英語   出版者・発行元:KLUWER ACADEMIC PUBL  

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  • Molecular and electronic structures of the short-lived excited triplet state of tropone

    T Ikoma, K Akiyama, S Tero-Kubota, Y Ikegami

    JOURNAL OF PHYSICAL CHEMISTRY A102 ( 2 ) 446 - 451   1998年1月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    Time-resolved electron paramagnetic resonance experiments on the short-lived Ti state of nenphosphorescent tropone were carried out using mixed crystals. Well-resolved hyperfine splittings due to allowed and forbidden transitions were observed at principal axes of the zero-field tenser. The spin density distribution, C-H bond angles, and the sign of the D value were deduced from the hyperfine spectra. It has been concluded that the T-1 state of tropone mainly has a (3) pi pi* configuration and holds its molecular structure of C-2v symmetry. The experiments and molecular orbital calculations indicate that the large Franck-Condon factor between the T-1 and the So states arises from the change of the potential surfaces due to the antibonding character of the pi* orbital at the C-4-C-5 bond in the T-1 state.

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  • Molecular and Electronic Strustures of the Short-Lived Excited Triplet State of Tropone

    The Journal of Physical Chemistry A102 ( 2 ) 446 - 451   1998年

  • HYSCORE Study on Coal Radicals

    Energy & Fuels12 ( 6 ) 1363 - 1368   1998年

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  • Two-Dimensional EPR Spectroscopic Studies on the Radicals in Argonne Premium Coals

    Energy & Fuels12 ( 5 ) 996 - 1000   1998年

  • Two-Dimensional EPR Spectroscopic Studies on the Radicals in Argonne Premium Coals

    IKOMA T, ITO O, TERO‐KUBOTA S, AKIYAMA K

    Energy & Fuels12 ( 5 ) 996 - 1000   1998年

  • Electronic Structure of the Deep Boron Acceptor in Boron-doped 6H-SiC

    V. DUJIN‐ARNOLD A, IKOMA T, POLUEKTOV O G, BARANOV P G, MOKHOY E N, SCHMIDT J

    Physical Review B57 ( 3 ) 1607 - 1619   1998年

  • Electronic Structure of the Deep Boron Acceptor in Boron-doped 6H-SiC

    Physical Review B57 ( 3 ) 1607 - 1619   1998年

  • Substituent and matrix effects on the excited triplet states of 1,4-naphthoquinones

    Takuji Shimokage, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota, Minoru Yamaji, Haruo Shizuka

    Journal of Physical Chemistry A101 ( 49 ) 9253 - 9256   1997年12月

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    記述言語:英語   出版者・発行元:American Chemical Society  

    Phosphorescence and TREPR spectra have been measured for 2-methyl-1,4-naphthoquinone (MNQ), 2,3-dimethyl-1,4-naphthoquinone (DMNQ), and 2-methoxynaphthoquinone (MeONQ) in several matrices at low temperatures. The |D| value of ZFS parameter decreases with increasing the electron-donating character of the substituent group. For MNQ, the T1 state is clearly assigned to be 3nπ* in character. The broad phosphorescence spectra and minor effects of the matrix polarity on the ZFS parameters lead to the conclusion that the character of the T1 states are mainly 3ππ* in DMNQ and MeONQ. The T1 states of the present naphthoquinone derivatives have more or less mixed character of the 3nπ* and 3ππ* states.

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  • Substituent and matrix effects on the excited triplet states of 1,4-naphthoquinones

    Takuji Shimokage, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota, Minoru Yamaji, Haruo Shizuka

    Journal of Physical Chemistry A101 ( 49 ) 9253 - 9256   1997年12月

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    記述言語:英語   出版者・発行元:American Chemical Society  

    Phosphorescence and TREPR spectra have been measured for 2-methyl-1,4-naphthoquinone (MNQ), 2,3-dimethyl-1,4-naphthoquinone (DMNQ), and 2-methoxynaphthoquinone (MeONQ) in several matrices at low temperatures. The |D| value of ZFS parameter decreases with increasing the electron-donating character of the substituent group. For MNQ, the T1 state is clearly assigned to be 3nπ* in character. The broad phosphorescence spectra and minor effects of the matrix polarity on the ZFS parameters lead to the conclusion that the character of the T1 states are mainly 3ππ* in DMNQ and MeONQ. The T1 states of the present naphthoquinone derivatives have more or less mixed character of the 3nπ* and 3ππ* states.

    DOI: 10.1021/jp971818i

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  • Ferromagnetic interactions between imino nitroxides through diamagnetic metal ions: Crystal structures, magnetism, and electronic properties of [M-I(imino nitroxide)(2)](PF6) (M=Cu-I and Ag-I)

    H Oshio, T Watanabe, A Ohto, T Ito, T Ikoma, S TeroKubota

    INORGANIC CHEMISTRY36 ( 14 ) 3014 - 3021   1997年7月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    An orthogonal arrangement of imino nitroxide ligands in Cu-I and Ag-I complexes results in propagation of an intramolecular ferromagnetic interaction between the coordinated imino nitroxides through these diamagnetic ions. Reaction of [Cu-I(CH3CN)(4)](PF6) and Ag-I(PF6) with imino nitroxides in ethanol solution gave [Cu-I(immepy)(2)-(PF6) (1) and [Ag-I(impy)(2)](PF6) (2), respectively (immepy 2-(2-(6-methylpyridyl))-4,4,5,5-tetramethyl-4,5-dihydro-1H imidazolyl-l-oxy and impy 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy). Complex 1 crystallizes in the orthorhombic space group Pba2, which has a unit cell with a 11.251(2) Angstrom, b = 14.745(3) Angstrom, c = 9.747(2) Angstrom, V = 1617.0(5) Angstrom(3), and Z = 2. Refinement with 991 reflections observed [\I-0\ &gt; 3 sigma(I-0)] gave R = 0.044 (R-w = 0.053). In 1, imino nitroxides coordinate to the Cu-I ions in a tetrahedral fashion, the dihedral angle between coordinating imino nitroxides being 88.7 degrees. Magnetic susceptibility measurement for 1 shows typical triplet-singlet behavior with strong ferromagnetic interactions (J = 55.1(6) cm(-1) with g = 2.0; H = -JS(1).S-2) The UV-visible absorption spectrum of 1 shows strong bands at 454 and 766 nm assignable to charge-transfer bands from the Cu ion to the ligand NLUMO and SOMO, respectively. The pi-back-donation to the SOMO induces the spin on the Cu ion and results in the strong ferromagnetic interaction. Complex 2 crystallizes in the orthorhombic space group P2(1)cn which has a unit cell with a = 10.535(6) Angstrom, b = 31.295(3) Angstrom, c 8.921(4) Angstrom, V = 2941(1) Angstrom(3), and Z = 4. Refinement with 1882 reflections [\I-0\ &gt; 3 sigma(I-0)] gave R = 0.058 (R-w = 0.074). Ln 2, the four coordination sites of the Ag-I ion were completed with two imino nitroxides and the dihedral angle between the imino nitroxides is 79.2 degrees. The EPR spectrum of a frozen ethanol solution of 2 shows a typical triplet signal with zero field splitting (\D\ = 0.043 cm(-1) and \E\ = 0.014 cm(-1)). Curie plots for the rim = 2 signal below 80 K gave a positive Weiss constant (theta = 4 K), suggesting an intramolecular ferromagnetic interaction in 2.

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  • Ferromagnetic interactions between imino nitroxides through diamagnetic metal ions: Crystal structures, magnetism, and electronic properties of [M-I(imino nitroxide)(2)](PF6) (M=Cu-I and Ag-I)

    H Oshio, T Watanabe, A Ohto, T Ito, T Ikoma, S TeroKubota

    INORGANIC CHEMISTRY36 ( 14 ) 3014 - 3021   1997年7月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    An orthogonal arrangement of imino nitroxide ligands in Cu-I and Ag-I complexes results in propagation of an intramolecular ferromagnetic interaction between the coordinated imino nitroxides through these diamagnetic ions. Reaction of [Cu-I(CH3CN)(4)](PF6) and Ag-I(PF6) with imino nitroxides in ethanol solution gave [Cu-I(immepy)(2)-(PF6) (1) and [Ag-I(impy)(2)](PF6) (2), respectively (immepy 2-(2-(6-methylpyridyl))-4,4,5,5-tetramethyl-4,5-dihydro-1H imidazolyl-l-oxy and impy 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy). Complex 1 crystallizes in the orthorhombic space group Pba2, which has a unit cell with a 11.251(2) Angstrom, b = 14.745(3) Angstrom, c = 9.747(2) Angstrom, V = 1617.0(5) Angstrom(3), and Z = 2. Refinement with 991 reflections observed [\I-0\ &gt; 3 sigma(I-0)] gave R = 0.044 (R-w = 0.053). In 1, imino nitroxides coordinate to the Cu-I ions in a tetrahedral fashion, the dihedral angle between coordinating imino nitroxides being 88.7 degrees. Magnetic susceptibility measurement for 1 shows typical triplet-singlet behavior with strong ferromagnetic interactions (J = 55.1(6) cm(-1) with g = 2.0; H = -JS(1).S-2) The UV-visible absorption spectrum of 1 shows strong bands at 454 and 766 nm assignable to charge-transfer bands from the Cu ion to the ligand NLUMO and SOMO, respectively. The pi-back-donation to the SOMO induces the spin on the Cu ion and results in the strong ferromagnetic interaction. Complex 2 crystallizes in the orthorhombic space group P2(1)cn which has a unit cell with a = 10.535(6) Angstrom, b = 31.295(3) Angstrom, c 8.921(4) Angstrom, V = 2941(1) Angstrom(3), and Z = 4. Refinement with 1882 reflections [\I-0\ &gt; 3 sigma(I-0)] gave R = 0.058 (R-w = 0.074). Ln 2, the four coordination sites of the Ag-I ion were completed with two imino nitroxides and the dihedral angle between the imino nitroxides is 79.2 degrees. The EPR spectrum of a frozen ethanol solution of 2 shows a typical triplet signal with zero field splitting (\D\ = 0.043 cm(-1) and \E\ = 0.014 cm(-1)). Curie plots for the rim = 2 signal below 80 K gave a positive Weiss constant (theta = 4 K), suggesting an intramolecular ferromagnetic interaction in 2.

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  • EFFECTS OF GEOMETRY AND HYDROGEN-BONDING ON THE EXCITED TRIPLET-STATES OF 4-NITROPYRIDINE N-OXIDE AND DERIVATIVES

    T EHARA, K AKIYAMA, T IKOMA, Y IKEGAMI, S TEROKUBOTA

    JOURNAL OF PHYSICAL CHEMISTRY99 ( 8 ) 2292 - 2295   1995年2月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    Time-resolved EPR and phosphorescence spectra have been observed for the lowest excited triplet states of 4-nitropyridine N-oxide and its alkyl derivatives. It has been shown that the ratio of the zero-field-splitting (zfs) parameters reflects the molecular geometry: the \E/D\ value decreases with increasing the twisting angle of the nitro group from the molecular plane. Protic solvents induce significant changes in the zfs parameters and the population ratio of the triplet sublevels. The results are discussed in terms of formation of the hydrogen bonding complex at the N-oxide oxygen atom.

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  • EFFECTS OF GEOMETRY AND HYDROGEN-BONDING ON THE EXCITED TRIPLET-STATES OF 4-NITROPYRIDINE N-OXIDE AND DERIVATIVES

    T EHARA, K AKIYAMA, T IKOMA, Y IKEGAMI, S TEROKUBOTA

    JOURNAL OF PHYSICAL CHEMISTRY99 ( 8 ) 2292 - 2295   1995年2月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    Time-resolved EPR and phosphorescence spectra have been observed for the lowest excited triplet states of 4-nitropyridine N-oxide and its alkyl derivatives. It has been shown that the ratio of the zero-field-splitting (zfs) parameters reflects the molecular geometry: the \E/D\ value decreases with increasing the twisting angle of the nitro group from the molecular plane. Protic solvents induce significant changes in the zfs parameters and the population ratio of the triplet sublevels. The results are discussed in terms of formation of the hydrogen bonding complex at the N-oxide oxygen atom.

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  • Magnetic interactions in Cu(I) and Ag(I) iminonitroxides

    H Oshio, T Watanabe, A Ohto, T Ito, T Ikoma, S TeroKubota

    MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY SECTION A-MOLECULAR CRYSTALS AND LIQUID CRYSTALS273   47 - 56   1995年

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    記述言語:英語   出版者・発行元:GORDON BREACH SCI PUBL LTD  

    Orthogonal arrangement of iminonitroxides in [Cu-I(immepy)(2)](PF6) (1) and [Ag-I(impy)(2)](PF6) (2) results in propagation on intramolecular ferromagnetic interaction between coordinating iminonitroxides through these diamagnetic ion. In 1, iminonitroxides coordinate to the Cu-I ion in a tetrahedral fashion, the dihedral angle between coordinating iminonitroxides being 88.7 degrees. Magnetic susceptibility and epr measurements for 1 show the typical ferromagneic behavior with large zero field splitting (2J = 91(1) cm(-1) (H = -2JS(1) . S-2); D = 3.62 cm(-1)). In 2, the four coordination sites of Ag-I ion were completed with two iminonitroxides and the dihedral angle between the iminonitroxides is 79.2 degrees. Temperature dependence of teh epr spectra for frozen ethanol solution of 2 shows that the intramolecular mangetic interaction between radicals is ferromagnetic (theta = 4 K).

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  • Magnetic interactions in Cu(I) and Ag(I) iminonitroxides

    H Oshio, T Watanabe, A Ohto, T Ito, T Ikoma, S TeroKubota

    MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY SECTION A-MOLECULAR CRYSTALS AND LIQUID CRYSTALS273   47 - 56   1995年

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    記述言語:英語   出版者・発行元:GORDON BREACH SCI PUBL LTD  

    Orthogonal arrangement of iminonitroxides in [Cu-I(immepy)(2)](PF6) (1) and [Ag-I(impy)(2)](PF6) (2) results in propagation on intramolecular ferromagnetic interaction between coordinating iminonitroxides through these diamagnetic ion. In 1, iminonitroxides coordinate to the Cu-I ion in a tetrahedral fashion, the dihedral angle between coordinating iminonitroxides being 88.7 degrees. Magnetic susceptibility and epr measurements for 1 show the typical ferromagneic behavior with large zero field splitting (2J = 91(1) cm(-1) (H = -2JS(1) . S-2); D = 3.62 cm(-1)). In 2, the four coordination sites of Ag-I ion were completed with two iminonitroxides and the dihedral angle between the iminonitroxides is 79.2 degrees. Temperature dependence of teh epr spectra for frozen ethanol solution of 2 shows that the intramolecular mangetic interaction between radicals is ferromagnetic (theta = 4 K).

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  • SPIN POLARIZATION CONSERVATION DURING INTRAMOLECULAR TRIPLET-TRIPLET ENERGY-TRANSFER STUDIED BY TIME-RESOLVED EPR SPECTROSCOPY

    K AKIYAMA, S TEROKUBOTA, T IKOMA, Y IKEGAMI

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY116 ( 12 ) 5324 - 5327   1994年6月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    Transient triplet EPR spectra of two types of spirans, spiro[9,10-dihydro-9-oxoanthracene-10,2'-benz[f]indan] and spiro[9,10-dihydro-9-oxoanthracene-10,2'-3H-phenalene],were measured in a glassy matrix at 77 K. Spin polarization conservation during the intramolecular triplet-triplet energy-transfer process was observed. The results clearly indicate that spin orientation is conserved in the molecular frame in the presence of an external magnetic field and that the high-field approximation cannot explain the spin polarization pattern observed in the X-band EPR spectra. The results contribute to the understanding of the relaxation processes of the excited states.

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  • Spin Polarization Conservation during Intramolecular Triplet-Triplet Energy Transfer Studied by Time-Resolved EPR Spectroscopy

    The Journal of the American Chemical Society116 ( 12 ) 5324 - 5327   1994年

  • STRUCTURAL EFFECTS ON THE RADIATIONLESS TRANSITION FROM THE T1 STATES OF TROPONE DERIVATIVES

    T IKOMA, K AKIYAMA, S TEROKUBOTA, Y IKEGAMI

    JOURNAL OF PHYSICAL CHEMISTRY97 ( 2 ) 303 - 305   1993年1月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    The T1 states of nonphosphorescent 2,3-benzotropone and phosphorescent 4,5-benzotropone were studied by a time-resolved EPR method. For 2,3-benzotropone, the observed magnetic parameters and the decay rate (the average decay rate 1.1 x 10(5) s-1 at 4.2 K) are very similar to those of the parent tropone. On the other hand, 4,5-benzotropone has different magnetic properties and a much slower radiationless decay rate (&lt;30 s-1) than tropone. The mechanism of the fast radiationless transition between the T1 and S0 states of tropone has been discussed.

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  • STRUCTURAL EFFECTS ON THE RADIATIONLESS TRANSITION FROM THE T1 STATES OF TROPONE DERIVATIVES

    T IKOMA, K AKIYAMA, S TEROKUBOTA, Y IKEGAMI

    JOURNAL OF PHYSICAL CHEMISTRY97 ( 2 ) 303 - 305   1993年1月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    The T1 states of nonphosphorescent 2,3-benzotropone and phosphorescent 4,5-benzotropone were studied by a time-resolved EPR method. For 2,3-benzotropone, the observed magnetic parameters and the decay rate (the average decay rate 1.1 x 10(5) s-1 at 4.2 K) are very similar to those of the parent tropone. On the other hand, 4,5-benzotropone has different magnetic properties and a much slower radiationless decay rate (&lt;30 s-1) than tropone. The mechanism of the fast radiationless transition between the T1 and S0 states of tropone has been discussed.

    DOI: 10.1021/j100104a008

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  • TIME-RESOLVED EPR STUDY ON THE EXCITED TRIPLET-STATE OF NONPHOSPHORESCENT TROPONE

    T IKOMA, K AKIYAMA, S TEROKUBOTA, Y IKEGAMI

    JOURNAL OF PHYSICAL CHEMISTRY95 ( 19 ) 7119 - 7121   1991年9月

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    記述言語:英語   掲載種別:速報,短報,研究ノート等(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The magnetic property and decay kinetics of the nonphosphorescent triplet (T1) state of tropone in glassy matrices have been studied by employing the time-resolved EPR (TREPR) method with excimer and dye laser excitations. The T1 state was assigned to be nearly pure 3-pi-pi* in character from the small zero-field splitting (zfs) parameters (\D\ = 0.077 cm-1 and \E\ = 0.011 cm-1 in a toluene glassy matrix) and their small dependency on the matrix polarity. The directions of the principal axes of the zfs tensor were determined by magnetophotoselection experiments with two colors of lasers. It was found that the T1(pi-pi*) state of tropone has very short lifetime; the average rate constant from the zero-field spin sublevels is 2 x 10(5) s-1.

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  • TIME-RESOLVED EPR STUDY ON THE EXCITED TRIPLET-STATE OF NONPHOSPHORESCENT TROPONE

    T IKOMA, K AKIYAMA, S TEROKUBOTA, Y IKEGAMI

    JOURNAL OF PHYSICAL CHEMISTRY95 ( 19 ) 7119 - 7121   1991年9月

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    記述言語:英語   掲載種別:速報,短報,研究ノート等(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The magnetic property and decay kinetics of the nonphosphorescent triplet (T1) state of tropone in glassy matrices have been studied by employing the time-resolved EPR (TREPR) method with excimer and dye laser excitations. The T1 state was assigned to be nearly pure 3-pi-pi* in character from the small zero-field splitting (zfs) parameters (\D\ = 0.077 cm-1 and \E\ = 0.011 cm-1 in a toluene glassy matrix) and their small dependency on the matrix polarity. The directions of the principal axes of the zfs tensor were determined by magnetophotoselection experiments with two colors of lasers. It was found that the T1(pi-pi*) state of tropone has very short lifetime; the average rate constant from the zero-field spin sublevels is 2 x 10(5) s-1.

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  • TIME-RESOLVED EPR STUDIES ON THE PHOTOCHEMICAL HYDROGEN ABSTRACTION REACTIONS AND THE EXCITED TRIPLET-STATES OF 4-SUBSTITUTED PYRIDINES

    S TEROKUBOTA, K AKIYAMA, T IKOMA, Y IKEGAMI

    JOURNAL OF PHYSICAL CHEMISTRY95 ( 2 ) 766 - 770   1991年1月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    Photochemical hydrogen abstraction reactions and the lowest excited triplet states taking part in the initial process have been investigated for several pyridine derivatives by using the time-resolved EPR method. The emissive CIDEP spectrum obtained from the laser photolysis of 4-acetylpyridine (1) in 2-propanol was assigned to the corresponding ketyl radical, proving initial hydrogen abstraction by the carbonyl group. In the cases of 4-cyano-(2) and 4-methoxycarbonyl-(3) pyridines, and 4-pyridinecarboxamide (4), enhanced absorptive CIDEP spectra due to the corresponding 1-hydropyridinyl radicals were observed, suggesting the preferential population to the lowest sublevel in the intersystem crossing. The triplet EPR and phosphorescence spectra observed at 77 K indicate that T1 of 1 is mainly the carbonyl n-pi* state with a small contribution from the pi-pi* state. The T1 states of 2, 3, and 4 are considered to be of mixed character between the pyridine B3(1) (n-pi*) and A3(1)(pi-pi*) states, though the interaction is smaller than that of unsubstituted pyridine because of raising the pi-pi* state by electron-withdrawing groups. It is proposed that the T1 states of 2-4 have smaller deviation from the planar conformation than the T1 state of unsubstituted pyridine.

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  • TIME-RESOLVED EPR STUDIES ON THE PHOTOCHEMICAL HYDROGEN ABSTRACTION REACTIONS AND THE EXCITED TRIPLET-STATES OF 4-SUBSTITUTED PYRIDINES

    S TEROKUBOTA, K AKIYAMA, T IKOMA, Y IKEGAMI

    JOURNAL OF PHYSICAL CHEMISTRY95 ( 2 ) 766 - 770   1991年1月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    Photochemical hydrogen abstraction reactions and the lowest excited triplet states taking part in the initial process have been investigated for several pyridine derivatives by using the time-resolved EPR method. The emissive CIDEP spectrum obtained from the laser photolysis of 4-acetylpyridine (1) in 2-propanol was assigned to the corresponding ketyl radical, proving initial hydrogen abstraction by the carbonyl group. In the cases of 4-cyano-(2) and 4-methoxycarbonyl-(3) pyridines, and 4-pyridinecarboxamide (4), enhanced absorptive CIDEP spectra due to the corresponding 1-hydropyridinyl radicals were observed, suggesting the preferential population to the lowest sublevel in the intersystem crossing. The triplet EPR and phosphorescence spectra observed at 77 K indicate that T1 of 1 is mainly the carbonyl n-pi* state with a small contribution from the pi-pi* state. The T1 states of 2, 3, and 4 are considered to be of mixed character between the pyridine B3(1) (n-pi*) and A3(1)(pi-pi*) states, though the interaction is smaller than that of unsubstituted pyridine because of raising the pi-pi* state by electron-withdrawing groups. It is proposed that the T1 states of 2-4 have smaller deviation from the planar conformation than the T1 state of unsubstituted pyridine.

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  • CIDEP STUDIES ON RADICALS PRODUCED FROM PHOTOCHEMICAL-REACTIONS OF SOME AROMATIC CARBONYL-COMPOUNDS

    T IKOMA, K AKIYAMA, S TEROKUBOTA, Y IKEGAMI

    CHEMISTRY LETTERS ( 9 ) 1491 - 1494   1990年9月

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    記述言語:英語   出版者・発行元:CHEMICAL SOC JAPAN  

    DOI: 10.1246/cl.1990.1491

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  • CIDEP STUDIES ON RADICALS PRODUCED FROM PHOTOCHEMICAL-REACTIONS OF SOME AROMATIC CARBONYL-COMPOUNDS

    T IKOMA, K AKIYAMA, S TEROKUBOTA, Y IKEGAMI

    CHEMISTRY LETTERS ( 9 ) 1491 - 1494   1990年9月

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    記述言語:英語   出版者・発行元:CHEMICAL SOC JAPAN  

    DOI: 10.1246/cl.1990.1491

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  • TIME-RESOLVED ESR STUDIES ON THE EXCITED TRIPLET-STATES AND PHOTOENOLIZATION OF 2-METHYLACETOPHENONE AND RELATED MOLECULES

    T IKOMA, K AKIYAMA, S TEROKUBOTA, Y IKEGAMI

    JOURNAL OF PHYSICAL CHEMISTRY93 ( 20 ) 7087 - 7091   1989年10月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    DOI: 10.1021/j100357a015

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  • TIME-RESOLVED ESR STUDIES ON THE EXCITED TRIPLET-STATES AND PHOTOENOLIZATION OF 2-METHYLACETOPHENONE AND RELATED MOLECULES

    T IKOMA, K AKIYAMA, S TEROKUBOTA, Y IKEGAMI

    JOURNAL OF PHYSICAL CHEMISTRY93 ( 20 ) 7087 - 7091   1989年10月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    DOI: 10.1021/j100357a015

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  • TIME-RESOLVED ESR STUDY ON THE EXCITED TRIPLET-STATES OF ORTHO-AMINOACETOPHENONES AND PARA-AMINOACETOPHENONES IN RIGID GLASS MATRIX

    K AKIYAMA, S TEROKUBOTA, T IKOMA, Y IKEGAMI

    NIPPON KAGAKU KAISHI8 ( 8 ) 1463 - 1465   1989年8月

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    記述言語:日本語   掲載種別:記事・総説・解説・論説等(学術雑誌)   出版者・発行元:CHEMICAL SOC JAPAN  

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  • o-およびp-アミノアセトフェノンの励起三重項状態の時間分解ESR

    秋山 公男, 手老 省三, 生駒 忠昭, 池上 雄作

    日本化学会誌1989 ( 8 ) 1463 - 1465   1989年

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  • THEORY OF NONRADIATIVE DECAY FROM THE LOWEST SINGLET-STATE OF BENZENE - EXCESS ENERGY-DEPENDENCE

    M TAKAHASHI, T IKOMA, Y FUJIMURA, A TOYOTA, T NAKAJIMA

    COLLECTION OF CZECHOSLOVAK CHEMICAL COMMUNICATIONS53 ( 9 ) 1902 - 1909   1988年9月

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    記述言語:英語   出版者・発行元:INST ORGANIC CHEM AND BIOCHEM  

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  • THEORY OF NONRADIATIVE DECAY FROM THE LOWEST SINGLET-STATE OF BENZENE - EXCESS ENERGY-DEPENDENCE

    M TAKAHASHI, T IKOMA, Y FUJIMURA, A TOYOTA, T NAKAJIMA

    COLLECTION OF CZECHOSLOVAK CHEMICAL COMMUNICATIONS53 ( 9 ) 1902 - 1909   1988年9月

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    記述言語:英語   出版者・発行元:INST ORGANIC CHEM AND BIOCHEM  

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▶ 全件表示

受賞

  • 電子スピンサイエンス学会奨励賞

    2003年  

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    受賞国:日本国

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    配分額:18330000円 ( 直接経費:14100000円 、 間接経費:4230000円 )

    元素戦略に基づいたグリーンイノベーションを希求する社会的要請を背景に、有機材料を用いた次世代の光電エネルギー変換デバイスに対する期待が著しく高まっている。しかしながら、有機電界発光ダイオードや有機太陽電池の変換効率は著しく低いため、本格的実用化には至っていない。有機電子デバイスの超高効率化を実現するためには、三重項励起子の有効利用(三重項ハーベスト)が鍵を握っている。本研究課題では、三重項ハーベストである三重項融合の遷移状態におけるスピン角運動量制御によって、反応効率を上げることに成功した。

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  • 光活性化に基づく新規スーパー有機ドナー試薬の開発と触媒化

    研究課題/領域番号:16K05689  2016年04月 - 2019年03月

    日本学術振興会  科学研究費助成事業 基盤研究(C)  基盤研究(C)

    長谷川 英悦, 生駒 忠昭, 三浦 智明, 岩本 啓, 滝沢 進也, 村田 滋, 若松 寛

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    配分額:4940000円 ( 直接経費:3800000円 、 間接経費:1140000円 )

    新規な高性能電子・水素ドナー光試薬の開発とその触媒化を目指して, 光捕集置換基(R)を有するベンズイミダゾリン(BIH-R)の光誘起電子移動反応について研究した。まず,ナフトール置換BIH(BIH-NapOH)の光励起により生じる強力電子ドナーのナフトキシド励起状態を活用してスルホンアミドの脱スルホニル化を達成した。BIH-NapOHの酸化体(BI+-NapO-)をベタイン分子として初めて光触媒として用い,BIH-Phとの電子移動を触媒再生に利用する手法(電子移動法)とヒドリド還元剤により強力電子・水素ドナーのBIH-NapO-を系内発生させる手法(ヒドリド法)の新規触媒法の開発に成功した。

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  • 非イオン性二分子膜の光磁気機能材料化へ向けた界面電子移動の研究

    研究課題/領域番号:15K05384  2015年10月 - 2019年03月

    日本学術振興会  科学研究費助成事業 基盤研究(C)  基盤研究(C)

    三浦 智明, 生駒 忠昭, 前田 公憲

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    配分額:4680000円 ( 直接経費:3600000円 、 間接経費:1080000円 )

    ニオソームは安価な界面活性剤分子を用いて水中で簡便に作製できる二分子膜カプセルであり、生体内のドラッグデリバリー材料として近年注目を集めている。本研究では光と磁場で薬剤放出を制御できるドラッグデリバリーや、磁場によって効率を制御できる人工光合成などの新しい材料を開発するための基礎研究として、色素とビタミン類を埋め込んだニオソームを新たに開発し、光照射による酸化還元、これにより生じた長寿命な「電荷分離状態」、さらにその磁場効果を詳細に調べた。ここから人工光合成において重要となる多段階の電子伝達や、ドラッグデリバリーにおいて重要となる光による膜形態変化を示す結果を得ることができた。

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  • 電子スピン角運動量保存則による有機太陽電池の磁気伝導効果

    研究課題/領域番号:26410088  2014年04月 - 2017年03月

    日本学術振興会  科学研究費助成事業 基盤研究(C)  基盤研究(C)

    生駒 忠昭, 脇川 祐介

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    配分額:5070000円 ( 直接経費:3900000円 、 間接経費:1170000円 )

    有機物質からなる薄膜における電気の流れやすさが外部磁場によって変化する現象を磁気伝導効果という。本研究は、磁気伝導効果を利用して有機太陽電池の中でおこる荷電キャリアが関係する反応を明らかにした。電子と正孔の再結合反応・励起子とキャリアの衝突に由来するトラップ反応・一重項励起子解裂の存在を明らかにした。本研究で開発した解析方法は、太陽電池素子を破壊せず動作条件下(室温・太陽光照射・低電圧)におけるキャリア反応を半定量的に評価できる新しいデバイス評価技術である。

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  • ポリジアセチレンにおける巨大スピンキャリアの創出

    研究課題/領域番号:17655055  2005年

    日本学術振興会  科学研究費助成事業 萌芽研究  萌芽研究

    生駒 忠昭

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    配分額:3000000円 ( 直接経費:3000000円 )

    高速かつ携帯できる通信機器の需要が高まる背景のもと分子レベルでの新しい機能の開発が望まれている。そこで、巨大π共役分子系を使った新しい光電子物性を創成するために、本研究はπ架橋網目構造ポリジアセチレンの光励起により巨大な磁気モーメントをもつ可動性中心(キャリア)を分子ワイヤー上に発生させることを目的に行う。巨大スピンキャリアは分子磁石などのミクロ記憶素子間の情報伝達メディアとしての応用が期待されている。
    光照射によって発生する巨大スピンキャリアを検出するためには過渡的現象を捉える必要があるので、現有する電子スピン共鳴(ESR)装置に改良を加え、多角励起時間分解ESR装置を組み上げた。ポリジアセチレンを固相重合反応で合成するために、いくつかのジアセチレンモノマーを合成した。また、新規に購入した真空蒸着器を用いて、石英ガラス基板上にモノマージアセチレンの配向膜の作成を試みた。基盤温度依存性や蒸着速度依存性を調べたが、完全配向膜を作成することが出来なかった。今後は、単結晶基盤を用いて分子エピタキシャル成長した配向膜作成に挑戦する予定である。良好な膜は作成できなかったので、溶液から再結晶させてジアセチレンモノマーの単結晶をつくり、熱重合によってポリジアセチレン結晶を準備した。フォークト配置およびファラデー配置下におけるポリジアセチレン結晶の選択的光励起ESR実験を行った。しかしながら、当初目指していたスピンキャリア由来の信号は観測されなかった。組み上げた装置は室温条件でしか実験できないところに問題があると考えられる。今後は、低温実験ができるような装置を組み上げ、キャリア検出を試みる予定である。

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  • 時間分解EPR法による高効率電界発光機構の解明

    研究課題/領域番号:15350074  2003年 - 2005年

    日本学術振興会  科学研究費助成事業 基盤研究(B)  基盤研究(B)

    秋山 公男, 生駒 忠昭

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    配分額:13600000円 ( 直接経費:13600000円 )

    1.低分子・共役高分子の逆項間交差緩和
    低分子の有機色素(Rhodamine系、シアニン系、ポルフィリン・フタロシアニン類)化合物について、レーザー二段階励起時間分解EPR(TREPR)測定により逆項間交差緩和の量子収率を決定した。ポルフィリン・フタロシアニン類については、中心金属の効果について詳細に検討を進めた。また、有機共役高分子の均一溶液中あるいはFilm試料を用いてTREPR測定を進めたが、励起三重項状態に帰属される信号は観測されなかった。しかしながら、電荷分離状態に由来する過渡的信号が観測され、電荷輸送過程に関与するラジカル対に帰属された。一連の高分子フィルム試料の結果から、TREPR法が不均一系中の過渡種の同定と電子構造を明らかにする有力な手法であることが明らかにされた。
    2.レーザー二段階励起発光スペクトル
    レーザー二段階励起発光スペクトルとTREPRの同時測定から、極低温における励起状態間の緩和過程を明らかにすることにより、電荷再結合に伴い生成する発光状態のスピン状態を含めた解析が可能なシステムとして整備した。広い温度範囲で観測を進め、有機共役高分子の発光スペクトルの二段階励起に伴う発光強度変化を時間分解EPR測定の結果と対応させて解析を進めた。
    3.低分子発光材料の励起三重項状態
    PtおよびIrを含む錯体の励起三重項状態の性質を、多周波時間分解EPR測定により明らかにするために、34GHz(Qバンド)帯での測定を進めた。しかしながら、いずれの錯体化合物においてもスピン軌道相互作用が大きく、直接観測に成功していない。そこで、電子状態が類似していると期待されるラジカル種を発生させて、この種の電子構造についての解析を進めた。Xバンド(9GHz)の観測結果と併せて整理し、高効率EL発光に対する三重項リン光機構についての検討を進めた。

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  • スピン分極で増感した光導電性有機ナノ構造体

    研究課題/領域番号:15310069  2003年 - 2005年

    日本学術振興会  科学研究費助成事業 基盤研究(B)  基盤研究(B)

    生駒 忠昭

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    配分額:11900000円 ( 直接経費:11900000円 )

    有機物質はナノ微細加工技術なくして分子レベルで起こっている量子効果をそのままマクロな物性に反映させることのできるポテンシャルを本質的に持っている。しかしながら、有機物の量子スピン選択的な電子移動反応を利用したナノ構造体の開発はほとんど行われていない。そこで、光導電性有機ナノ構造体を対象に光誘起電子スピン分極を利用した高い電気伝導性を実証することを目的とした研究を行った。得られた成果を以下にまとめた。
    1)三重項増感剤として働く分子(アゾベンゼンやルミクロムなど)をドープした薄膜で、キャリア収率が磁場中で異常に大きくなる系を初めて見出した。巨大な磁場効果は、光励起で生成される励起三重項状態のスピン分極および電子正孔対のスピン緩和が重要な役割を果たしていることを明らかにした。
    2)10Tまでの強磁場実験を行うことで、近接電子正孔対のスピン状態のレベル交差が原因の磁場効果を初めて観測した。これは、キャリア生成が擬一次元格子で段階的正孔移動をしていることを証明する決定的な結果となった。また、1T以上の領域ではレベル交差由来の磁場効果以外にも興味深い現象が検出され、光導電性研究における強磁場実験の有用性が示された。
    3)世界最高の光伝導度を示すことで注目されているC_<60>をドープしたPVCz薄膜の詳細なスピンダイナミクスを初めて明らかにした。電荷移動錯体の電子励起で生成する電子正孔対は、C_<60>の局在励起一重項状態へ再結合し、局在励起三重項状態への再結合はほとんどないことが分かった。ただし、再結合で生成した励起一重項状態は励起三重項状態を経由して基底状態へ緩和する。
    分子性導体における光磁気伝導効果の新しい側面が明らかにされ、磁性キャリア輸送研究にとって磁場効果実験が有用であることが示され導電性における光誘起電子スピン分極の重要性を示した。

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  • ファラデー効果による開殻分子の光学的電子スピン制御

    研究課題/領域番号:12740310  2000年 - 2001年

    日本学術振興会  科学研究費助成事業 奨励研究(A)  奨励研究(A)

    生駒 忠昭

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    配分額:2300000円 ( 直接経費:2300000円 )

    平成13年度は、前年度に組み上げた時間分解電子常磁性共鳴(EPR)検出型ファラデー実験装置を用いて幾つかの化合物を対象に実験を試みた。
    スピン二重項である安定な中性ラジカルとして、2,2,6,6-テトラメチルピペリジン-1ーオキシル(TEMPO)ラジカルおよび2,2,6,6-テトラメチル-4-ヒドロキシピペリジン-1ーオキシル(TANOL)ラジカルについて磁気光学効果実験を行った。酸素による影響を避けるために3mMの試料濃度に調整したエタノール溶液を真空ライン内で脱気処理した後、室温においてファラデー効果の測定を行った。ナノ秒YAGレーザーの第2高調波(532nm)を励起光源として用いた。ラジカルのスピン副準位間の占有数差(スピン分極)を検出するため、安定ラジカルからの応答信号である自由誘導減衰(FID)あるいは電子スピンエコー(ESE)をナノ秒パルスマイクロ波を用いて観測した。右回り偏光励起を行ったときの応答信号と左回り偏光励起時の信号の強度変化を調べたところ、どの中性ラジカルについても有意な偏向方向依存性は認められなかった。そこで、イオン性の有機ラジカルであるペリレンカチオンラジカルについて同様な実験を行った。しかしながら、この場合も明瞭な磁気光学効果が観測されなかった。有機分子のスピン軌道相互作用が小さいことが磁気光学効果を起こしにくい原因と考え、S=1/2である銅二価イオン(CuSO_4, CuCl_2)について測定を行った。しかし、これらの無機イオンの室温中におけるスピン横緩和が装置の不感時間よりも短いため、EPR信号自身を捕らえることができなかった。

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  • 三重結合共役分子の励起状態における電子構造と反応に関する研究

    研究課題/領域番号:11440210  1999年 - 2000年

    日本学術振興会  科学研究費助成事業 基盤研究(B)  基盤研究(B)

    手老 省三, 生駒 忠昭, 秋山 公男

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    配分額:8900000円 ( 直接経費:8900000円 )

    本研究は三重結合共役分子(ポリイン)の光反応性にとって重要な励起状態の電子構造と三重結合の数の関係を系統的に研究することを目的として行った。本研究により、近接した電子状態間のスピン-軌道相互作用や振電相互作用が明らかにされた。本研究によりポリインの励起状態に関する基礎科学に大きな貢献を果たすことができた。
    本研究で得られた結果を以下に示す。
    (1)α,ω-diphenylpolyynesの励起三重項状態は、直線かつ2つのphenyl基が平面であるD_<2h>対称をもつ。
    (2)励起三重項状態は、^3B_<1u>(π_xπ_x^*)の対称性をもつ。
    (3)電子スピン密度は、三重結合数の増加と共に三重結合鎖部分に多く分布する傾向をもち、1,12-diphenyldodecahexayneにおいては、phenyl基上における電子スピン密度は無視できるほど小さい。
    (4)α,ω-diphenylpolyynesのT_1(π_xπ_x^*)状態は、異常に大きな負の零磁場分裂定数(D値)を持ち、三重結合数の増加と共に|D|値が増大する.
    (5)異常に大きな負の零磁場分裂定数(D値)は、T_1(π_xπ_x^*)-^3A_u(π_xπ_y^*)間のスピン軌道相互作用に由来すると解釈できる。
    (6)これら2つ励起状態間エネルギー差がD値から求められ、三重結合数の増加と共に減少することが明らかとなった。
    (7)T_1(π_xπ_x^*)状態からの速い無輻射遷移が示され、T_1-S_0間のFranck-Condon因子の重要性を指摘した。
    (8)りん光スペクトルにおけるb_<1g>振動バンドの出現は、フエニル基のねじれ振動によるT_1(π_xπ_x^*)-^3Au(π_xπ_y^*)間の相互作用を示唆している。
    (9)T_1(π_xπ_x^*)-Tn(^3Au:π_xπ_y^*)間は、スピン軌道相互作用のみならずフエニル基のねじれ振動による相互作用が最低励起状態のポテンシャルに大きな影響を与えている。

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  • 光電導度およびマイクロ波同時検出ESR法を用いた高分子中における光電子移動の研究

    研究課題/領域番号:10740315  1998年 - 1999年

    日本学術振興会  科学研究費助成事業 奨励研究(A)  奨励研究(A)

    生駒 忠昭

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    配分額:2100000円 ( 直接経費:2100000円 )

    高い機能性をもつ光導電性高分子を設計する上で、光導電現象に関わる基礎的な諸過程を明らかにすることが重要と考えられる。(1)キャリア生成、(2)キャリア輸送、(3)キャリア再結合過程に分けられる素過程のメカニズムを複合的分光手段で解明しようと計画した。キャリアが電荷を持つだけでなく、スピン磁気モーメントを有することに注目し、磁気共鳴法と電気分光法を組合わせた観測手段を考案した。
    透明電極を蒸着した石英ガラス基盤上にポリビニルカルバゾールをスピンコート法で塗布した。試料の膜厚は10μm程度のものである。伝導度検出法では、サンドイッチタイプに挟まれた薄膜試料に電圧を印加し、電極まで拡散してきたキャリアを検出する。また、同時に試料に磁場を印加し、マイクロ波を用いることで電子スピン共鳴も観測することにした。薄膜試料に紫外線照射したときのキャリア生成過程でつくられる異常スピン分極がキャリアスピンに観測された。これは、生成反応における前駆状態の電子スピン多重度に関する情報を含んでおり、キャリアのスピン履歴を明らかにすることができた。また、正電荷キャリアと負電荷キャリアが相関しているイオン対状態の観測に初めて成功し、イオン対の寿命がマイクロ秒程度もあることが明らかとなった。さらに、外部磁場存在下にあっては、励起一重項状態から生成したキャリアの寿命に対し励起三重項状態から生成したキャリアの寿命が著しく長いことを見出した。このようなスピン多重度に依存したキャリア寿命の違いは、伝導性の向上を目指す上で重要な概念につながることを示唆している。

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  • パルス電子スピン共鳴法によるカーボンアロイのキャラクタリゼーション

    研究課題/領域番号:10137203  1998年

    日本学術振興会  科学研究費助成事業 特定領域研究(A)  特定領域研究(A)

    伊藤 攻, 生駒 忠昭, 藤塚 守

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    配分額:1700000円 ( 直接経費:1700000円 )

    本研究ではパルス電子スピン共鳴法(パルスEPR法)を用いて有機物の加熱による炭化度の解明を目的とした。2次元EPR法を炭素に適用した初めての例である。該当年度において以下のような結果を得た。
    成分の電子スピン緩和過程と水素分子の核スピン緩和過程を分離して測定できるパルス列を見いだし、芳香族炭化水素(コロネン)のカチオンラジカルの2次元EPR測定を実現した。
    水素ENDORシグナルが観測したことにより、プロトンNMRと同様な解析が可能となり、炭素由来のシグナルとC-NMRとの類似性から、H/C比を積分比を用いることにより決定できた。さらに石炭化度の異なる10種の石炭の2次元EPRスペクトルを測定し、モデル物質の比較より諸情報の帰属を行った。
    以上の結果は、パルスEPR法という新しい測定装置が石炭やメソフェース炭素の研究に有効であることを実証したものである。

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  • 高周波時間分解EPR法による短寿命常磁性種の研究

    研究課題/領域番号:07404040  1995年 - 1997年

    日本学術振興会  科学研究費助成事業 基盤研究(A)  基盤研究(A)

    手老 省三, 生駒 忠昭, 秋山 公男

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    配分額:30200000円 ( 直接経費:30200000円 )

    本科学研究費により、Q-バンド時間分解EPRシステムを完成し、現有のパルスレーザーと組み合わせて研究を行い、また、X-バンド時間分解EPR法の結果と合わせて次の成果を得た。
    1. 時間分解EPRスペクトルの周波数依存性
    (a) CIDEPスペクトルにおける主要なスピン分極である三重項機構とラジカル対機構の寄与の割合が観測周波数で異なり、また、三重項の熱分布からの寄与も増大することを明らかにした。
    (b) 励起三重項状態の時間分解スペクトルの周波数依存性から、スペクトルのブロードニングに寄与する原因がg-値の異方性によるか他の原因であるかを明確にした。
    2. 反応中間体ラジカルイオン対の交換相互作用の符号
    光化学反応で生成するラジカルイオン対の交換相互作用の符号が電子供与体および受容体の酸化還元電位の差に依存することを見出し、交換相互作用を支配する機構について新しい提案を行った。溶媒座標系を考慮し、ラジカルイオン対と基底状態のポテンシャル表面の交差位置によって交換相互作用の符号が決まることを明らかにした。
    3. 励起状態カルベンの電子構造
    基底三重項分子であるジフェニカルベンの励起状態の直接観測に成功し、零磁場分裂定数を決定し、電子構造、緩和過程について研究を行った。
    4. シリコン微結晶におけるダングリングボンドの構造
    QバンドおよびXバンドEPRスペクトルの比較から、シリコンダングリングボンドのスペクトル線形がg値の分布によって決まっていることを明らかにし、構造との関連を明らかにした。
    5. 大きな零磁場分裂相互作用定数を持つ励起三重項分子の電子状態
    三重結合共役系を有する分子は、非常に大きな零磁場分裂相互作用定数を示すことを見出し、その原因が接近した励起状態間相互作用によることを明らかにした。

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  • パルスレーザーを用いた光検出パルスEPRの時間領域測光

    研究課題/領域番号:07740449  1995年

    日本学術振興会  科学研究費助成事業 奨励研究(A)  奨励研究(A)

    生駒 忠昭

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    配分額:1000000円 ( 直接経費:1000000円 )

    パルスレーザーとパルスマイクロ波を用いて、EPRと結合した光信号を時間領域で検出できるシステムを設計し、既存の測定法との比較から本測定法の有用性を明らかにすることを目的として研究をおこなった。本研究では、発光および散乱光の磁場効果を時間領域で測定することになる。そこで、以下に示した順にしたがって研究を進めた。
    1、 単結晶系の実験を行うため、現有するパルスEPR装置に適合したゴニオメーターを制作した。
    2、 パルスレーザー励起された試料からの発光と散乱光のみを取り出せるように、マイクロ波共振器に光ファイバーを設置した。光電子増倍管により検出した光を分光し、デジタルオシロスコープにより観測できるように組み立てた。
    3、 ベンジルラジカルの蛍光を検出し、励起二重項(D_1)状態のEPR現象の観測を試みたが、期待された磁場効果は得られなかった。これは、ベンジルラジカルを効率よくD_1状態へ励起できなかったことに由来すると考えられる。今後はこのレーザー光用の窓の設計を吟味してゆく予定である。
    4、 研究開始当初予定していたキノキサリンの励起三重項(T_1)状態の測定は、測光システムの立ち上げに予想以上の時間が必要であったため、助成期間中に行うことができなかったが、今後継続して研究を進めてゆく予定である。

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  • 有機光反応系におけるスピン分極保持エネルギ-移動の研究

    研究課題/領域番号:02453002  1990年 - 1991年

    日本学術振興会  科学研究費助成事業 一般研究(B)  一般研究(B)

    池上 雄作, 生駒 忠昭, 秋山 公男

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    配分額:6200000円 ( 直接経費:6200000円 )

    1.ピリジニルラジカルモノマ-ーダイマ-平衡と光化学
    中性ピリジニルラジカルは、一般的にはラジカルとそのダイマ-との間に一つの平衡系をつくっていると考えてよい。時間分解ESR法によりダイマ-の光開裂時の初期過程を研究し、その光開裂が一重項ラジカル対を前駆体とする反応であることを明らかにした。その光反応系に三重項増感剤が存在すると三重項ー三重項(TーT)エネルギ-移動が起こり、この過程での電子スピン分極の保存について検討し、スピン分極保持TーTエネルギ-移動の新規現象を立証することになった。その結果、ピリジニルラジカル化学の研究を整然とした形にまとめることができ、本研究の重要な成果の一つである。
    2.分子内スピン分極保持TーTエネルギ-移動の新規現象
    三重項ー三重項エネルギ-移動過程におけるスピン分極の保存について、分子間過程について実験的に検証をしたので、新しい着想によりエネルギ-供与体・受容体間のスピン配向について研究した。その結果、分子内スピン分極保持TーTエネルギ-移動の新規現象を初めて実験的に立証し、その過程に関与する諸因子を明らかにした。
    3.芳香族カルボニル化合物の光反応で成生する中間体ラジカルのスピン分極に関する研究、4ー置換ピリジン誘導体の最低励起三重項状態から起こる水素引き抜き反応機構、無りん光性トロポンの励起三重項状態の電子構造の解明を目的として研究を行い、種々の有機化学反応系の初期過程について明らかにした。

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    資金種別:競争的資金

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    資金種別:競争的資金

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