Updated on 2025/10/09

写真a

 
IKOMA Tadaaki
 
Organization
Academic Assembly Institute of Science and Technology Fundamental Sciences Professor
Faculty of Science Department of Science Professor
Graduate School of Science and Technology Fundamental Sciences Professor
Title
Professor
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Degree

  • Ph. D. ( 1993.1   Tohoku University )

Research Interests

  • 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

Research Areas

  • Nanotechnology/Materials / Fundamental physical chemistry

Research History (researchmap)

  • Nagaoka University of Technology   Graduate School of Engineering Department of Materials Science and Technology

    2020.4 - 2021.3

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    Country:Japan

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  • Kyoto University   Graduate School of Engineering

    2019.4 - 2020.3

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  • Osaka University   School of Engineering

    2017.10 - 2018.3

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  • Saitama University   Graduate School of Science and Engineering

    2017.9 - 2018.3

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  • Niigata University   Faculty of Science Department of Science   Professor

    2017.4

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  • Osaka City University   Graduate School of Science

    2013.11

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  • Niigata University   Institute for Research Promotion Center for Coordination of Research Facilities

    2013.4 - 2017.1

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  • Niigata University   Institute for Research Promotion Center for Instrumental Analysis   Director

    2013.4 - 2017.1

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  • University Nagoya

    2012.10 - 2013.3

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  • Niigata University   Graduate School of Science and Technology Fundamental Sciences   Professor

    2012.4

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  • Niigata University   Faculty of Science Department of Chemistry   Professor

    2012.4 - 2017.3

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  • Niigata University   Faculty of Science Department of Chemistry   Associate Professor

    2007.6 - 2012.3

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  • Tohoku University   Institute of Multidisciplinary Research for Advanced Materials   Assistant Professor

    2007.4 - 2007.5

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  • Japan Science and Technology Agency   Researcher

    2006.10 - 2010.3

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  • Tohoku University   Institute of Multidisciplinary Research for Advanced Materials   Research Assistant

    2001.4 - 2007.3

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  • Tohoku University   Institute for Chemical Reaction Science   Research Assistant

    1991.4 - 2001.3

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  • Tohoku University   The Chemical Research Institute of Non-aqueous Solutions   Research Assistant

    1989.7 - 1991.3

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Research History

  • Niigata University   Graduate School of Science and Technology Fundamental Sciences Chemistry

    2022.4

  • Niigata University   Faculty of Science Department of Chemistry

    2019.4 - 2020.3

  • Niigata University   Faculty of Science Department of Science   Professor

    2017.4

  • Niigata University   Graduate School of Science and Technology Fundamental Sciences Chemistry

    2017.4 - 2018.3

  • Niigata University   Institute for Research Promotion Center for Coordination of Research Facilities

    2017.2 - 2019.3

  • Niigata University   Faculty of Science Department of Chemistry

    2014.4 - 2015.3

  • Niigata University   Center for Instrumental Analysis

    2013.4 - 2017.1

  • Niigata University   Faculty of Science Department of Chemistry   Professor

    2012.4 - 2017.3

  • Niigata University   Graduate School of Science and Technology Fundamental Sciences Chemistry

    2012.4 - 2013.3

  • Niigata University   Faculty of Science Department of Chemistry   Associate Professor

    2007.6 - 2012.3

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Education

  • Tohoku University   Graduate School of Science   Department of Chemistry

    1988.4 - 1989.7

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  • Tohoku University   Graduate School of Science   Chemistry

    1986.4 - 1988.3

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    Country: Japan

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  • Tohoku University   Faculty of Science   Department of Chemistry

    1982.4 - 1986.3

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    Country: Japan

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Professional Memberships

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Papers

  • Transient charge carrier dynamics in organic solar cell devices studied by simultaneous optical and electric detection Invited Reviewed

    Tomoaki Miura, Naoya Muramatsu, Tomoaki Takeuchi, Kazuhiko Seki, Tadaaki Ikoma

    The Journal of Chemical Physics   161 ( 24 )   241101   2024.12

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1063/5.0245921

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  • Magnetic Field Effect on Photocarriers in an Organic Film Studied by Simultaneous Optical and Electrical Detection Reviewed

    Tomoaki Miura, So Kobayashi, Tadaaki Ikoma

    The Journal of Physical Chemistry C   128 ( 45 )   12942 - 12947   2024.11

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.1021/acs.jpcc.4c05290

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  • Synthesis and optical properties of 3,5-bis(10-phenylanthracen-9-yl)benzene-appended porphyrins

    Akane Umemiya, Haruyuki Nakano, Nanami Iwaya, Tadaaki Ikoma, Yoshihiro Matano

    Journal of Porphyrins and Phthalocyanines   A - L   2023.6

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:World Scientific Pub Co Pte Ltd  

    <jats:p> Singlet–singlet and triplet-triplet energy-transfer processes between anthracenes and porphyrins have received considerable attention in materials chemistry. Herein, we report the first examples of 3,5-bis(10-phenylanthracen-9-yl)benzene-appended porphyrins (BPABPs) designed to study intramolecular energy transfer between two chromophores. The Curtius rearrangement of 3,5-bis(10-phenylanthracen-9-yl)benzoyl azide in the presence of the platinum(II) complex of 5,10,15-tris(3,5-di-tert-butylphenyl)-20-(3-hydroxyphenyl)porphyrin or its free base in toluene afforded the corresponding BPABP. Spectroscopy, cyclic voltammetry, and density functional theory calculations revealed that the anthracene and porphyrin [Formula: see text]-electron systems of the BPABPs are not conjugated and consequently do not affect each other’s absorption properties. In contrast, the BPABPs exhibited considerably different luminescence properties to those of phenyl 3,5-bis(10-phenylanthracen-9-yl)carbamate and 5,10,15-tris(3,5-di-tert-butylphenyl)-20-(3-methoxyphenyl)porphyrins; the anthracene units of the BPABPs show considerably quenched fluorescence compared to that of the reference anthracene, indicative of efficient intramolecular singlet–singlet energy transfer from the anthracene to the porphyrin unit. The phosphorescence quantum yield of the Pt complex of BPABP is comparable to that of the reference Pt-porphyrin, which suggests that intramolecular triplet-triplet energy transfer from the Pt-porphyrin to the anthracene unit is inefficient. The present findings improve our understanding of how structural factors and excited-state energy levels affect energy transfer and triplet-triplet annihilation upconversion processes of covalently linked bisanthracene-appended porphyrins. </jats:p>

    DOI: 10.1142/s1088424623500840

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  • Origin of the Delayed Fluorescence by Triplet–Triplet Annihilation in Solids with a Power Law Exponent of between −1/2 and −1

    Kazuhiko Seki, Tomoaki Miura, Tadaaki Ikoma

    The Journal of Physical Chemistry C   127 ( 20 )   9562 - 9572   2023.5

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    Publishing type:Research paper (scientific journal)   Publisher:American Chemical Society (ACS)  

    DOI: 10.1021/acs.jpcc.3c02128

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  • Triarylamine-Substituted Benzimidazoliums as Electron Donor–Acceptor Dyad-Type Photocatalysts for Reductive Organic Transformations

    Ryo Miyajima, Yuuki Ooe, Tomoaki Miura, Tadaaki Ikoma, Hajime Iwamoto, Shin-ya Takizawa, Eietsu Hasegawa

    Journal of the American Chemical Society   145 ( 18 )   10236 - 10248   2023.5

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    Publishing type:Research paper (scientific journal)   Publisher:American Chemical Society (ACS)  

    DOI: 10.1021/jacs.3c01264

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  • Radio-wave Effect on Singlet Fission in Polycrystalline Tetracene near Zero Magnetic Field

    Yusuke Wakikawa, Tadaaki Ikoma

    The Journal of Physical Chemistry Letters   3907 - 3911   2023.4

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    Publishing type:Research paper (scientific journal)   Publisher:American Chemical Society (ACS)  

    DOI: 10.1021/acs.jpclett.3c00341

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  • Transient photocurrent and optical absorption of disordered thin-film semiconductors: In-depth injection and nonlinear response

    Kazuhiko Seki, Naoya Muramatsu, Tomoaki Miura, Tadaaki Ikoma

    JOURNAL OF CHEMICAL PHYSICS   158 ( 11 )   2023.3

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1063/5.0143683

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  • Photon Upconversion with a Low Threshold Excitation Intensity in Plain Water Reviewed

    Yuki Nakadai, Shuta Tsuchiya, Masumi Uehara, Sena Umezawa, Reina Motoki, Hibiki Umezawa, Tadaaki Ikoma, Tatsuto Yui

    The Journal of Physical Chemistry B   126 ( 41 )   8245 - 8250   2022.10

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Chemical Society (ACS)  

    DOI: 10.1021/acs.jpcb.2c04109

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  • Triplet–Triplet Annihilation via the Triplet Channel in Crystalline 9,10-Diphenylanthracene Reviewed

    Tomoaki Yago, Manami Tashiro, Kiichi Hasegawa, Masao Gohdo, Syuta Tsuchiya, Tadaaki Ikoma, Masanobu Wakasa

    The Journal of Physical Chemistry Letters   13 ( 37 )   8768 - 8774   2022.9

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Chemical Society (ACS)  

    DOI: 10.1021/acs.jpclett.2c01839

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  • Temperature-induced structural transition in an organic-inorganic hybrid layered perovskite (MA)(2)PbI2-xBrx(SCN)(2) Reviewed

    Takuya Ohmi, Tomoaki Miura, Kei Shigematsu, Alexandra A. Koegel, Brian S. Newell, James R. Neilson, Tadaaki Ikoma, Masaki Azuma, Takafumi Yamamoto

    CRYSTENGCOMM   24 ( 30 )   5428 - 5434   2022.8

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1039/d2ce00733a

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  • Single-molecule Magnetoluminescence from a Spatially Confined Persistent Diradical Emitter

    Ryota Matsuoka, Shojiro Kimura, Tomoaki Miura, Tadaaki Ikoma, Tetsuro Kusamoto

    2022.7

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    Publisher:American Chemical Society (ACS)  

    Luminescent radicals are an emerging class of materials that exhibit unique photofunctions not found in closed-shell molecules due to their open-shell electronic structure. Particularly promising are photofunctions in which radical’s spin and luminescence are correlated; for example, when a magnetic field can affect luminescence (i.e., magnetoluminescence, ML). These photofunctions could be useful in the new science of spin photonics. However, previous observations of ML in radicals have been limited to systems in which radicals are randomly doped in host crystals or polymerized through metal complexation. This study shows that a covalently linked luminescent radical dimer (diradical) can exhibit the ML as a single-molecular property. This facilitates detailed elucidation of the requirements for and mechanisms of ML in radicals and can aid the rational design of ML-active radicals based on synthetic chemistry.

    DOI: 10.26434/chemrxiv-2022-1wscq

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  • Microscopic Structures, Dynamics, and Spin Configuration of the Charge Carriers in Organic Photovoltaic Solar Cells Studied by Advanced Time-Resolved Spectroscopic Methods Invited Reviewed

    Kaoru Ohta, Keisuke Tominaga, Tadaaki Ikoma, Yasuhiro Kobori, Hiroko Yamada

    Langmuir   38 ( 24 )   7365 - 7382   2022.6

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    Authorship:Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Chemical Society ({ACS})  

    DOI: 10.1021/acs.langmuir.2c00290

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  • 9-(Diphenylphosphoryl)-10-(phenylethynyl)anthracene Derivatives: Synthesis and Implications for the Substituent and Solvent Effects on the Light-Emitting Properties Reviewed

    Nina Murayama, Joel Hao Jorolan, Mao Minoura, Haruyuki Nakano, Tadaaki Ikoma, Yoshihiro Matano

    ChemPhotoChem   6 ( 9 )   e202200100   2022

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    Authorship:Corresponding author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1002/cptc.202200100

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  • Copper(II) Complexes of 10,20-Diaryl-5,15-diazaporphyrin: Alternative Synthesis, Excited State Dynamics, and Substituent Effect on the <sup>1</sup>O<inf>2</inf>-Generation Efficiency Reviewed

    Hikari Ochiai, Tomoaki Miura, Tadaaki Ikoma, Mao Minoura, Haruyuki Nakano, Yoshihiro Matano

    Bulletin of the Chemical Society of Japan   95 ( 3 )   427 - 432   2022

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1246/bcsj.20220002

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  • Radiowave Effects on an Electron–Hole Pair in a Poly(3-hexylthiophene) near Zero Magnetic Field Reviewed

    Yusuke Wakikawa, Tadaaki Ikoma

    The Journal of Physical Chemistry C   125 ( 48 )   26613 - 26618   2021.11

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Chemical Society (ACS)  

    DOI: 10.1021/acs.jpcc.1c07807

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  • Realtime Observation of Carrier Trapping and Recombination in a Bulk Heterojunction Film by Simultaneous Optical and Electrical Detection Reviewed

    Tomoaki Miura, Ryoya Akiyama, So Kobayashi, Tadaaki Ikoma

    The Journal of Physical Chemistry C   125 ( 41 )   22668 - 22673   2021.10

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    Authorship:Last author, Corresponding author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1021/acs.jpcc.1c06879

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  • Synthesis, Optical Properties, and Electrochemical Behavior of 5,10,15,20‐Tetraaryl‐5,15‐diazaporphyrin‐Amine Hybrids Reviewed

    Yuna Satoh, Yutaro Fujita, Naoya Muramatsu, Ko Furukawa, Tadaaki Ikoma, Mao Minoura, Haruyuki Nakano, Yoshihiro Matano

    ChemPlusChem   86 ( 10 )   1476 - 1486   2021.10

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1002/cplu.202100429

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    Other Link: https://onlinelibrary.wiley.com/doi/full-xml/10.1002/cplu.202100429

  • An Element‐Substituted Cyclobutadiene Exhibiting High‐Energy Blue Phosphorescence Reviewed

    Yoshiaki Shoji, Yasuhiro Ikabata, Ivan Ryzhii, Rabia Ayub, Ouissam El Bakouri, Taiga Sato, Qi Wang, Tomoaki Miura, Buddhika S. B. Karunathilaka, Youichi Tsuchiya, Chihaya Adachi, Henrik Ottosson, Hiromi Nakai, Tadaaki Ikoma, Takanori Fukushima

    Angewandte Chemie International Edition   60 ( 40 )   21817 - 21823   2021.9

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    Authorship:Corresponding author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1002/anie.202106490

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    Other Link: https://onlinelibrary.wiley.com/doi/full-xml/10.1002/anie.202106490

  • An Element‐Substituted Cyclobutadiene Exhibiting High‐Energy Blue Phosphorescence

    Yoshiaki Shoji, Yasuhiro Ikabata, Ivan Ryzhii, Rabia Ayub, Ouissam El Bakouri, Taiga Sato, Qi Wang, Tomoaki Miura, Buddhika S. B. Karunathilaka, Youichi Tsuchiya, Chihaya Adachi, Henrik Ottosson, Hiromi Nakai, Tadaaki Ikoma, Takanori Fukushima

    Angewandte Chemie   2021.7

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Wiley  

    DOI: 10.1002/ange.202108413

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  • Photogenerated Radical Pair between Flavin and a Tryptophan-Containing Transmembrane-Type Peptide in a Large Unilamellar Vesicle Reviewed

    Yoshimi Oka, Tomoaki Miura, Tadaaki Ikoma

    The Journal of Physical Chemistry B   125 ( 16 )   4057 - 4066   2021.4

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    DOI: 10.1021/acs.jpcb.1c01231

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

    Yusuke Wakikawa, Tadaaki Ikoma

    The Journal of Physical Chemistry C   124 ( 37 )   19945 - 19952   2020.9

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher: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 Reviewed International journal

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

    ACS Omega   5 ( 13 )   7651 - 7665   2020.4

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Chemical Society (ACS)  

    A debrominative oxygenation protocol has been developed for the conversion of α-bromo-α,α-dialkyl-substituted carbonyl compounds to their corresponding α-hydroxy analogues. For example, stirring a solution of α-bromoisobutyrophenone and 2-aryl-1,3-dimethylbenzimidazoline (BIH-Ar) at room temperature under an air atmosphere leads to the efficient formation of α-hydroperoxyisobutyrophenone, which can be converted to α-hydroxyisobutyrophenone using Me2S reduction. In contrast, reaction of α-bromoacetophenone under the same conditions produces the α-hydrogenated product acetophenone. α-Keto-alkyl and benzimidazolyl radicals (BI•-Ar), generated via dissociative electron transfer from BIH-Ar to α-bromoketone substrates, serve as key intermediates in the oxidation and reduction processes. The dramatic switch from hydrogenation to oxygenation is attributed to a steric effect of α-alkyl substituents, which causes hydrogen atom abstraction from sterically crowded BIH-Ar to α-keto-alkyl radicals to be slow and enable preferential reaction with molecular oxygen. Generation of the α-keto-alkyl radical and BI•-Ar intermediates in these process and their sterically governed hydrogen atom transfer reactions are supported by results arising from DFT calculations. Moreover, an electron spin resonance study showed that visible light irradiation of phenyl benzimidazoline (BIH-Ph) in the presence of molecular oxygen produces the benzimidazolyl radical (BI•-Ph). The addition of thiophenol into the reaction of α-bromoisobutyrophenone and BIH-Ph predominantly produced α-phenylthiolated isobutyrophenone even if a high concentration of molecular oxygen exists. Furthermore, the developed protocol was applied to other α-bromo-α,α-dialkylated carbonyl compounds.

    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 Reviewed International journal

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

    The Journal of Chemical Physics   151 ( 23 )   234306 - 234306   2019.12

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    Authorship:Last author, Corresponding author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1063/1.5127940

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

    Ryota Shoji, Tomoaki Miura, Tadaaki Ikoma

    Organic Electronics   75   105383 - 105383   2019.12

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    Authorship:Last author, Corresponding author   Language:English   Publishing type:Research paper (scientific journal)  

    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 Reviewed

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

    ChemPlusChem   84 ( 6 )   740 - 745   2019.6

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1002/cplu.201900087

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    Other Link: 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 Reviewed

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

    RSC Advances   9 ( 28 )   15845 - 15851   2019

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher: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 Reviewed

    Tomoaki Miura, Kiminori Maeda, Yoshimi Oka, Tadaaki Ikoma

    The Journal of Physical Chemistry B   122 ( 50 )   12173 - 12183   2018.12

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)  

    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 Reviewed International journal

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

    The Journal of Organic Chemistry   83 ( 18 )   10813 - 10825   2018.9

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    A visible light promoted process for desulfonylation of N-sulfonylamides and -amines has been developed, in which 1,3-dimethyl-2-hydroxynaphthylbenzimidazoline (HONap-BIH) serves as a light absorbing, electron and hydrogen atom donor, and a household white light-emitting diode serves as a light source. The process transforms various N-sulfonylamide and -amine substrates to desulfonylated products in moderate to excellent yields. The observation that the fluorescence of 1-methyl-2-naphthoxy anion is efficiently quenched by the substrates suggests that the mechanism for the photoinduced desulfonylation reaction begins with photoexcitation of the naphthoxide chromophore in HONap-BIH, which generates an excited species via intramolecular proton transfer between the HONap and BIH moieties. This process triggers single electron transfer to the substrate, which promotes loss of the sulfonyl group to form the free amide or amine. The results of studies employing radical probe substrates as well as DFT calculations suggest that selective nitrogen-sulfur bond cleavage of the substrate radical anion generates either a pair of an amide or amine anion and a sulfonyl radical or that of an amidyl or aminyl radical and sulfinate anion, depending on the nature of the N-substituent on the substrate. An intermolecular version of this protocol, in which 1-methyl-2-naphthol and 1,3-dimethyl-2-phenylbenzimidazoline are used concomitantly, was also examined.

    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 Reviewed

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

    ACS Omega   3 ( 8 )   9369 - 9377   2018.8

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    DOI: 10.1021/acsomega.8b01746

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

    Toshikazu Nakamura, Tadaaki Ikoma, Ken-ichi Yamada

    Applied Magnetic Resonance   49 ( 8 )   755 - 756   2018.8

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

    DOI: 10.1007/s00723-018-1035-9

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    Other Link: 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 Reviewed

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

    Solar RRL   2 ( 5 )   1700234 - 1700234   2018.5

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    Authorship:Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Wiley  

    DOI: 10.1002/solr.201700234

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  • Benzimidazolium Naphthoxide Betaine Is a Visible Light Promoted Organic Photoredox Catalyst Reviewed International journal

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

    The Journal of Organic Chemistry   83 ( 7 )   3921 - 3927   2018.4

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Chemical Society (ACS)  

    Benzimidazolium naphthoxide (-ONap-BI+) was first synthesized and utilized as an unprecedented betaine photoredox catalyst. Photoexcited state of -ONap-BI+ generated by visible light irradiation catalyzes the reductive deiodination as well as desulfonylation reactions in which 1,3-dimethyl-2-phenylbenzimidazoline (Ph-BIH) cooperates with as an electron and hydrogen atom donor. Significant solvent effects on the reaction progress were discovered, and specific solvation toward imidazolium and naphthoxide moieties of -ONap-BI+ was proposed.

    DOI: 10.1021/acs.joc.8b00282

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

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

    ACS Omega   2 ( 7 )   3260 - 3266   2017.7

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    Authorship:Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher: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 Reviewed

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

    The Journal of Physical Chemistry Letters   8 ( 3 )   661 - 665   2017.2

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    Authorship:Last author, Corresponding author   Language:English   Publishing type:Research paper (scientific journal)  

    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 Reviewed

    Tasuku Isozaki, Hikari Oba, Tadaaki Ikoma, Tadashi Suzuki

    The Journal of Physical Chemistry A   120 ( 31 )   6137 - 6145   2016.8

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    DOI: 10.1021/acs.jpca.6b02929

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

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

    The Journal of Physical Chemistry B   119 ( 52 )   15901 - 15908   2015.12

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    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 Reviewed

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

    The Journal of Physical Chemistry C   119 ( 46 )   25840 - 25844   2015.11

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    DOI: 10.1021/acs.jpcc.5b10176

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

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

    Tetrahedron   71 ( 34 )   5494 - 5505   2015.8

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    DOI: 10.1016/j.tet.2015.06.071

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

    Toshinari Ogiwara, Yusuke Wakikawa, Tadaaki Ikoma

    The Journal of Physical Chemistry A   119 ( 14 )   3415 - 3418   2015.4

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    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 Reviewed

    Tomoaki Miura, Kiminori Maeda, Hisao Murai, Tadaaki Ikoma

    The Journal of Physical Chemistry Letters   6 ( 2 )   267 - 271   2015.1

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    DOI: 10.1021/jz502495u

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

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

    The Journal of Physical Chemistry C   118 ( 49 )   28418 - 28424   2014.12

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    DOI: 10.1021/jp508799j

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

    Christopher E. Ambe, Yusuke Wakikawa, Tadaaki Ikoma

    Bulletin of the Chemical Society of Japan   86 ( 9 )   1051 - 1058   2013.9

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    The thermal annealing effects on the photocarrier dynamics in thin films of [6,6]-phenyl C<sub>61</sub> butyric acid methyl ester (PCBM) on quartz substrates are investigated. Both the photocarrier generation via charge-transfer state and the charge transport in PCBM films are studied by time-resolved photoconductance (PC) measurement. More than 90% of external photocarrier generation efficiency relative to the non-annealed film is reduced upon annealing of the PCBM film at high temperatures. Excitation light power dependence of PC indicates that the photocarrier in the non-annealed film is generated by a one-photon process, while photons of more than one are required in highly annealed films. The multiphotonic process for carrier generation and the substantial reduction of carrier density caused by the thermal treatment are associated with trap formation. The density of photoinjected carrier is also affected by applying external magnetic field. The observed positive magnetophotoconductance (MPC) in non-annealed film is understood in terms of the incoherent spin conversion in nongeminate electron–hole (e–h) pairs with a selective recombination from singlet e–h pairs. In highly annealed film, the broad magnetic field dependence of MPC with negative phase is suggested to originate from the detrapping of trapped carrier assisted by collision with the triplet exciton.

    DOI: 10.1246/bcsj.20130097

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

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

    The Journal of Physical Chemistry C   117 ( 29 )   15295 - 15305   2013.7

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    DOI: 10.1021/jp402640k

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

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

    International Journal of Thermophysics   33 ( 10-11 )   2046 - 2054   2012.11

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    DOI: 10.1007/s10765-012-1296-8

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  • Molecular spintronics Reviewed

    Masashi Shiraishi, Tadaaki Ikoma

    Physica E: Low-dimensional Systems and Nanostructures   43 ( 7 )   1295 - 1317   2011.5

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    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 Reviewed

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

    Small   6 ( 23 )   2731 - 2740   2010.12

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    DOI: 10.1002/smll.201001344

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

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

    Synthetic Metals   160 ( 3-4 )   285 - 290   2010.2

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    DOI: 10.1016/j.synthmet.2009.10.003

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

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

    Synthetic Metals   160 ( 3-4 )   275 - 279   2010.2

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    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 Reviewed

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

    The Journal of Physical Chemistry A   112 ( 37 )   8641 - 8648   2008.9

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    DOI: 10.1021/jp802810s

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  • ChemInform Abstract: Synthesis and Intramolecular Pericyclization of 1‐Azulenyl Thioketones.

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

    ChemInform   39 ( 30 )   2008.7

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    Abstract

    ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

    DOI: 10.1002/chin.200830061

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

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

    Chemical Physics Letters   457 ( 1-3 )   66 - 68   2008.5

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    DOI: 10.1016/j.cplett.2008.03.089

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  • Synthesis and Intramolecular Pericyclization of 1-Azulenyl Thioketones Reviewed International journal

    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 Chemistry   73 ( 6 )   2256 - 2263   2008.3

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    Several azulene-substituted thioketones, 1-thiobenzoylazulene (1a) and di(1-azulenyl) thioketone (2a) and their derivatives (1b and 2b-d) with alkyl substituents on each azulene ring, were prepared and their intramolecular pericyclization reaction was examined. The thioketones with a 3-alkyl substituent on each azulene ring exhibited the presumed pericyclization reaction under thermal and acid-catalyzed conditions, although the cases of the 1-azulenyl thioketones without the 3-alkyl substituents afforded a complex mixture under similar conditions. The intramolecular reaction following the intramolecular hydrogen transfer afforded the products 13b, 14b, and 14c. The products 13b and 14b were converted into the corresponding cations 18(+) and 19(+), which have structural similarity with that of the phenalenyl cation. These cations exhibited the expected two-step reduction waves upon CV, although the ESR analysis revealed that the neutral radical state did not have the presumed high stability.

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  • Spin-Correlated Radical Pairs in Synthetic Hairpin DNA Reviewed

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

    ChemPhysChem   8 ( 4 )   507 - 509   2007.3

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    DOI: 10.1002/cphc.200600621

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

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

    Chemical Physics Letters   436 ( 4-6 )   373 - 377   2007.3

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    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 Reviewed

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

    Journal of the American Chemical Society   128 ( 45 )   14560 - 14570   2006.11

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    DOI: 10.1021/ja061507y

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  • Visible light induced paramagnetic sites in nitrogen-doped TiO2prepared by a mechanochemical method Reviewed International journal

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

    Molecular Physics   104 ( 10-11 )   1733 - 1737   2006.5

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    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 Reviewed

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

    The Journal of Physical Chemistry B   110 ( 10 )   5161 - 5162   2006.3

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    DOI: 10.1021/jp0565857

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  • Electron spin dynamics on the photoconductivity in oriented polydiacetylene films

    Yutaka Takahashi, Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota, Shuji Okada

    Polymer Preprints, Japan   55 ( 2 )   4722 - 4723   2006

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  • Giant magnetoresistance of photoconductive polymer film

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

    Polymer Preprints, Japan   55 ( 2 )   4720 - 4721   2006

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

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

    Chemistry Letters   34 ( 10 )   1424 - 1425   2005.10

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    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 Reviewed

    Miho Uchida, Takahiro Sogabe, Tadaaki Ikoma, Akitsugu Okuwaki

    Environmental Science & Technology   39 ( 15 )   5851 - 5855   2005.8

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    DOI: 10.1021/es048299z

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

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

    Chemical Physics Letters   411 ( 4-6 )   378 - 383   2005.8

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    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 Reviewed

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

    Angewandte Chemie International Edition   44 ( 23 )   3591 - 3594   2005.6

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    DOI: 10.1002/anie.200461681

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

    Tadaaki Ikoma, Kimio Akiyama, Shozo Tero-Kubota

    Physical Review B   71 ( 19 )   2005.5

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    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 Reviewed

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

    The Journal of Physical Chemistry B   109 ( 18 )   8707 - 8717   2005.5

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    DOI: 10.1021/jp0453212

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

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

    The Journal of Physical Chemistry B   109 ( 15 )   7208 - 7213   2005.4

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    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 Reviewed

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

    The Journal of Organic Chemistry   70 ( 6 )   2285 - 2293   2005.3

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    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 Reviewed

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

    The Journal of Organic Chemistry   68 ( 25 )   9753 - 9762   2003.12

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    DOI: 10.1021/jo035053o

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

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

    Journal of the American Chemical Society   125 ( 46 )   14103 - 14112   2003.11

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    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 Reviewed

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

    Applied Magnetic Resonance   23 ( 3-4 )   445 - 453   2003.9

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    DOI: 10.1007/bf03166633

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

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

    Journal of Physics and Chemistry of Solids   64 ( 5 )   801 - 806   2003.5

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    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 Reviewed

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

    Journal of the American Chemical Society   125 ( 16 )   4722 - 4723   2003.4

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    DOI: 10.1021/ja029443o

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  • Substrate Specificities of Deuterolysin fromAspergillus oryzaeand Electron Paramagnetic Resonance Measurement of Cobalt-substituted Deuterolysin Reviewed International journal

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

    Bioscience, Biotechnology, and Biochemistry   67 ( 2 )   264 - 270   2003.1

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    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 Reviewed

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

    Physical Review B   66 ( 1 )   014423-1 - 014423-9   2002.7

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    DOI: 10.1103/physrevb.66.014423

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

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

    Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy   58 ( 6 )   1201 - 1208   2002.4

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    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 Reviewed

    Tadaaki Ikoma, Osamu Ito, Shozo Tero-Kubota

    Energy & Fuels   16 ( 1 )   40 - 47   2002.1

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    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 Reviewed

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

    Environmental Science & Technology   35 ( 24 )   4933 - 4935   2001.12

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    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 Reviewed International journal

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

    Bulletin of the Chemical Society of Japan   74 ( 12 )   2303 - 2309   2001.12

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    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 Reviewed International journal

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

    Inorganic Chemistry   40 ( 22 )   5518 - 5525   2001.10

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    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 Reviewed

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

    Angewandte Chemie International Edition   40 ( 17 )   3234 - 3236   2001.9

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    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 Reviewed

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

    The Journal of Chemical Physics   114 ( 4 )   1775 - 1784   2001.1

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    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 Reviewed International journal

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

    Solid State Communications   117 ( 5 )   285 - 289   2001.1

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    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 Reviewed International journal

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

    Journal of Applied Physics   88 ( 3 )   1698 - 1700   2000.8

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    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 Reviewed

    Takashi Ehara, Tadaaki Ikoma, Shozo Tero-Kubota

    Journal of Non-Crystalline Solids   266-269   540 - 543   2000.5

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    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 Reviewed International journal

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

    Japanese Journal of Applied Physics   39 ( Part 1, No. 1 )   31 - 34   2000.1

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    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 Reviewed International journal

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

    Carbon   38 ( 13 )   1831 - 1838   2000

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    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 Reviewed International journal

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

    Inorganic Chemistry   38 ( 25 )   5686 - 5689   1999.12

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    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 Reviewed International journal

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

    The Journal of Chemical Physics   111 ( 15 )   6875 - 6883   1999.10

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    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 Reviewed International journal

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

    Chemical Physics Letters   303 ( 1-2 )   201 - 208   1999.4

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    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 Reviewed

    TADAAKI IKOMA, KIMIO AKIYAMA, SHOZO TERO-KUBOTA

    Molecular Physics   96 ( 5 )   813 - 820   1999.3

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    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 Reviewed International journal

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

    Energy & Fuels   12 ( 6 )   1363 - 1368   1998.11

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    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 Reviewed International journal

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

    Energy & Fuels   12 ( 5 )   996 - 1000   1998.9

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    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 Reviewed International journal

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

    The Journal of Physical Chemistry A   102 ( 29 )   5769 - 5774   1998.7

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    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 Reviewed International journal

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

    Chemical Physics Letters   287 ( 5-6 )   737 - 741   1998.5

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    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 Reviewed International journal

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

    Physical Review B   57 ( 3 )   1607 - 1619   1998.1

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    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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  • Molecular and Electronic Structures of the Short-Lived Excited Triplet State of Tropone Reviewed International journal

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

    The Journal of Physical Chemistry A   102 ( 2 )   446 - 451   1998.1

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    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 Reviewed International journal

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

    Journal of Materials Science Letters   17 ( 4 )   275 - 278   1998

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    DOI: 10.1023/a:1006517219037

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

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

    Journal of the Chemical Society, Faraday Transactions   94 ( 9 )   1197 - 1201   1998

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    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 Reviewed

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

    Materials Science Forum   258-263   703 - 708   1997.12

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    Publishing type:Research paper (scientific journal)   Publisher: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 Reviewed

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

    The Journal of Physical Chemistry A   101 ( 49 )   9253 - 9256   1997.12

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    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) Reviewed

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

    Inorganic Chemistry   36 ( 14 )   3014 - 3021   1997.7

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    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 Reviewed International journal

    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 Crystals   273 ( 1 )   47 - 56   1995.11

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    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 Reviewed International journal

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

    The Journal of Physical Chemistry   99 ( 8 )   2292 - 2295   1995.2

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    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 Reviewed International journal

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

    Journal of the American Chemical Society   116 ( 12 )   5324 - 5327   1994.6

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    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 Reviewed International journal

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

    The Journal of Physical Chemistry   97 ( 2 )   303 - 305   1993.1

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    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 Reviewed International journal

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

    The Journal of Physical Chemistry   95 ( 19 )   7119 - 7121   1991.9

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    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 Reviewed International journal

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

    The Journal of Physical Chemistry   95 ( 2 )   766 - 770   1991.1

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    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 Reviewed International journal

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

    Chemistry Letters   19 ( 9 )   1491 - 1494   1990.9

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    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 Reviewed International journal

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

    The Journal of Physical Chemistry   93 ( 20 )   7087 - 7091   1989.10

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    DOI: 10.1021/j100357a015

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  • Time-resolved ESR study on the excited triplet states of o- and p-aminoacetophenones in rigid glass matrix. Reviewed

    Kimio AKIYAMA, SHOZO TERO-KUBOTA, Tadaaki IKOMA, Yusaku IKEGAMI

    NIPPON KAGAKU KAISHI   ( 8 )   1463 - 1465   1989

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    Publishing type:Research paper (scientific journal)   Publisher:The Chemical Society of Japan  

    Time-resolved ESR spectrum was observed for the triplet enol generated by intramolecular proton transfer in the excited singlet state of o-aminoacetophenone at 77 K. The phase of the polarization and the zero field splitting (ZFS) parameters suggested the formation of the corresponding enol in accordance with previous results. Polarized ESR spectrum due to the excited triplet state was also obtained under laser pulse irradiation to p-aminoacetophenone.

    DOI: 10.1246/nikkashi.1989.1463

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  • Theory of nonradiative decay from the lowest singlet state of benzene: Excess energy dependence Reviewed International journal

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

    Collection of Czechoslovak Chemical Communications   53 ( 9 )   1902 - 1909   1988

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    Publishing type:Research paper (scientific journal)   Publisher: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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Books

  • 進化する有機半導体―有機エレクトロニクス創成へ向けた光・電子機能デバイ

    生駒 忠昭, 手老 省三( Role: Contributor)

    エヌ・ティー・エス  2021.12  ( ISBN:4860431030

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    Total pages:4, 13, 505, 13, 6p, 図版4p   Language:Japanese

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  • 光化学フロンティア : 未来材料を生む有機光化学の基礎

    生駒, 忠昭( Role: Contributor)

    化学同人  2018.12  ( ISBN:9784759814194

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    Total pages:xiv, 436p   Language:Japanese

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  • 光化学の事典 = Encyclopedia of photochemistry

    生駒 忠昭( Role: Contributor)

    朝倉書店  2014.6  ( ISBN:9784254140965

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    Total pages:xvi, 418p   Language:Japanese

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  • Selectivity, control, and fine tuning in high-energy chemistry

    Tadaaki Ikoma( Role: Contributor)

    2011 

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  • 第5版 実験化学講座20-1 分析化学

    山内 清語, 生駒 忠昭( Role: Contributor)

    丸善  2007.1  ( ISBN:9784621073193

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    Total pages:xxii, 720p   Language:Japanese

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  • Carbon alloys : novel concepts to develop carbon science and technology

    Ito Osamu, Ikoma Tadaaki, Sakurovs R( Role: Contributor)

    Elsevier  2003  ( ISBN:0080441637

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    Total pages:xiv, 569 p.   Language:English

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MISC

  • Carrier generation process on photoconductive polymer films as studied by magnetic field effects on the charge-transfer fluorescence and photocurrent (vol 109, pg 8707, 2005)

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

    JOURNAL OF PHYSICAL CHEMISTRY B   110 ( 10 )   5161 - 5162   2006.3

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  • Time-domain ESR as Interspin Correlation Spectroscopy

    IKOMA Tadaaki

    Bunko Kenkyu   55 ( 1 )   21 - 30   2006

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    Language:Japanese   Publisher:The Spectroscopical Society of Japan  

    A growth of nanoscience requires spectroscopy which allows us to measure a nanometer scale with a high accuracy. Time-domain ESR spectroscopy has been recently developed to detect small exchange and dipolar interactions that are effective even between two spins with subnano or nano meter separations. This review focuses the advanced time-domain ESR spectroscopic studies on nanoscale structure and dynamics in amorphous or glassy samples.

    DOI: 10.5111/bunkou.55.21

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    Other Link: https://jlc.jst.go.jp/DN/JALC/00274656767?from=CiNii

  • 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

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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

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

    Yasumitsu Tanaka, Qiwu Zhang, Fumio Saito, Tadaaki Ikoma, Shozo Tero-kubota

    Chemosphere   60   939 - 943   2005

  • 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

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    Language:English   Publisher:Elsevier Ltd.  

    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

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  • Ion pair photogenerated in a doped poly(N-vinylcarbazole) solid

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

    Meeting abstracts of the Physical Society of Japan   57 ( 2 )   694 - 694   2002.8

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

    T Ikoma, O Ito, S Tero-Kubota

    ENERGY & FUELS   16 ( 1 )   40 - 47   2002.1

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

    Tadaaki Ikoma

    Chemistry and Chemical Industry   55   576 - 576   2002

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

    RIKEN Review   44   119 - 120   2002

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  • Spin Soliton in a p-Conjugated Ladder Polydiacetylene

    Physical Review B   66 ( 1 )   014423-1-014423-9   2002

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  • Spin Soliton in a π-conjugaed Ladder Polydiacetylene

    Physical Review B   66 ( 14423 )   1 - 9   2002

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

    IKOMA T, ITO O, TERO‐KUBOTA S

    Energy & Fuels   16 ( 1 )   40 - 47   2002

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

    RIKEN Review   44   119 - 120   2002

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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

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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 Technology   35 ( 24 )   4933 - 4935   2001.12

  • 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 JAPAN   74 ( 12 )   2303 - 2309   2001.12

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

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

    ENVIRONMENTAL SCIENCE & TECHNOLOGY   35 ( 24 )   4933 - 4935   2001.12

  • 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 Japan   74 ( 12 )   2303 - 2309   2001.12

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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 CHEMISTRY   40 ( 22 )   5518 - 5525   2001.10

  • 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 PHYSICS   114 ( 4 )   1775 - 1784   2001.1

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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 PHYSICS   114 ( 4 )   1775 - 1784   2001.1

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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 COMMUNICATIONS   117 ( 5 )   285 - 289   2001

  • 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 COMMUNICATIONS   117 ( 5 )   285 - 289   2001

  • 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

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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

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  • Multi-band Electron Paramagnetic Resonance Study of Microcrystalline or Cluster Silicon Embedded in SiO<SUB>2</SUB>

    Takashi Ehara, Tadaaki Ikoma, Shozo Tero-Kubota

    Material Research Society Symposium Proceedings   609 ( A24.7 )   2001

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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 II   87   1461 - 1462   2001

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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 EDITION   40 ( 17 )   3234 - +   2001

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

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

    JOURNAL OF APPLIED PHYSICS   88 ( 3 )   1698 - 1700   2000.8

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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 SOLIDS   266 ( Pt.A )   540 - 543   2000.5

  • 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 PAPERS   39 ( 1 )   31 - 34   2000.1

  • 混在状態に迫るパルス電子スピン共鳴

    生駒 忠昭, 手老 省三, 伊藤 攻

    表面   38 ( 1 )   39 - 53   2000

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  • カーボン用語辞典

    アグネ承風社   2000

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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

    CARBON   38 ( 13 )   1831 - 1838   2000

  • 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 CHEMISTRY   38 ( 25 )   5686 - 5689   1999.12

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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 PHYSICS   111 ( 15 )   6875 - 6883   1999.10

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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 Letters   303 ( 1-2 )   201 - 208   1999.4

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    DOI: 10.1016/S0009-2614(99)00189-X

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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 LETTERS   303 ( 1-2 )   201 - 208   1999.4

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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 PHYSICS   96 ( 5 )   813 - 820   1999.3

  • Application of New ESR Spectroscopies to Coal Studies

    IKOMA Tadaaki, ITO Osamu, TERO-KUBOTA Shozo

    Journal of the Japan Institute of Energy   78 ( 12 )   980 - 987   1999

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  • 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

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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 Energy   78 ( 12 )   980 - 987   1999

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  • HYSCORE study on coal radicals

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

    ENERGY & FUELS   12 ( 6 )   1363 - 1368   1998.11

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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 A   102 ( 29 )   5769 - 5774   1998.7

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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 Letters   287 ( 5-6 )   737 - 741   1998.5

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    Language:English   Publisher:Elsevier  

    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 LETTERS   287 ( 5-6 )   737 - 741   1998.5

  • 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 TRANSACTIONS   94 ( 9 )   1197 - 1201   1998.5

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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 LETTERS   17 ( 4 )   275 - 278   1998.2

  • 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 A   102 ( 2 )   446 - 451   1998.1

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

    The Journal of Physical Chemistry A   102 ( 2 )   446 - 451   1998

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

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

    Physical Review B   57 ( 3 )   1607 - 1619   1998

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

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

    Physical Review B   57 ( 3 )   1607 - 1619   1998

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

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

    Energy & Fuels   12 ( 5 )   996 - 1000   1998

  • HYSCORE Study on Coal Radicals

    Energy & Fuels   12 ( 6 )   1363 - 1368   1998

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

    Energy & Fuels   12 ( 5 )   996 - 1000   1998

  • 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 A   101 ( 49 )   9253 - 9256   1997.12

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    Language:English   Publisher:American Chemical Society  

    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 CHEMISTRY   36 ( 14 )   3014 - 3021   1997.7

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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 CHEMISTRY   99 ( 8 )   2292 - 2295   1995.2

  • 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 CRYSTALS   273   47 - 56   1995

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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 SOCIETY   116 ( 12 )   5324 - 5327   1994.6

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

    The Journal of the American Chemical Society   116 ( 12 )   5324 - 5327   1994

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

    T IKOMA, K AKIYAMA, S TEROKUBOTA, Y IKEGAMI

    JOURNAL OF PHYSICAL CHEMISTRY   97 ( 2 )   303 - 305   1993.1

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

    T IKOMA, K AKIYAMA, S TEROKUBOTA, Y IKEGAMI

    JOURNAL OF PHYSICAL CHEMISTRY   95 ( 19 )   7119 - 7121   1991.9

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    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

    S TEROKUBOTA, K AKIYAMA, T IKOMA, Y IKEGAMI

    JOURNAL OF PHYSICAL CHEMISTRY   95 ( 2 )   766 - 770   1991.1

  • 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   1990.9

  • 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 CHEMISTRY   93 ( 20 )   7087 - 7091   1989.10

  • 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 KAISHI   8 ( 8 )   1463 - 1465   1989.8

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  • Time-resolved ESR Study on the Excited Triplet States of o- and p-Aminoacetophenones in Rigid Glass Matrix

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

    NIPPON KAGAKU KAISHI   1989 ( 8 )   1463 - 1465   1989

  • 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 COMMUNICATIONS   53 ( 9 )   1902 - 1909   1988.9

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Awards

  • 学会賞

    2021.8   電子スピンサイエンス学会   分子性材料における磁気構造ならびに励起状態のスピン動力学

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  • 奨励賞

    2003.10   電子スピンサイエンス学会   ESR法による有機材料機能の分子論的研究

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    Country:Japan

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Research Projects

  • Breakdown of the Quantum Spin Statistical Limit in Triplet Fusion

    Grant number:23K17901

    2023.6 - 2026.3

    System name:Grants-in-Aid for Scientific Research

    Research category:Grant-in-Aid for Challenging Research (Exploratory)

    Awarding organization:Japan Society for the Promotion of Science

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    Grant amount:\6370000 ( Direct Cost: \4900000 、 Indirect Cost:\1470000 )

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  • Spin-sublevel dynamics of triplet exciton

    Grant number:23H03945

    2023.4 - 2025.3

    System name:Grants-in-Aid for Scientific Research

    Research category:Grant-in-Aid for Transformative Research Areas (A)

    Awarding organization:Japan Society for the Promotion of Science

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    Grant amount:\7540000 ( Direct Cost: \5800000 、 Indirect Cost:\1740000 )

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  • Magnetoimpedance Study on Carrier Dynamics in Orgaic Semiconductor

    Grant number:18H01951

    2018.4 - 2021.3

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

    Research category:Grant-in-Aid for Scientific Research (B)

    Awarding organization:Japan Society for the Promotion of Science

    Ikoma Tadaaki

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    Grant amount:\17940000 ( Direct Cost: \13800000 、 Indirect Cost:\4140000 )

    In recent years where green return is required, organic molecules having a function of photoelectric conversion are attracting attention as materials that are eco-friendly and include no toxic or rare elementals. Controlling carrier reactions at the molecular level is a central issue for improving the performance of electronic devices using organic materials. “In-situ observation” of exciton/carrier dynamics in a device under operation is important for the device development, but there is no powerful measurement methods for investigating the dynamics that occur in devices with complex internal structures. In this study, we have developed a new impedance (magnetoimpedance) spectroscopy based on the law of conservation of spin angle momentum in energy and electron transfer reactions.

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  • Triplet Harvesting by Control of the Transition State

    Grant number:16KT0049

    2016.7 - 2019.3

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

    Research category:Grant-in-Aid for Scientific Research (B)

    Awarding organization:Japan Society for the Promotion of Science

    Ikoma Tadaaki, YAGO Tomoaki

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    Grant amount:\18330000 ( Direct Cost: \14100000 、 Indirect Cost:\4230000 )

    Because of the social demands for green innovation based on the strategy to reduce consumption of precious many elements, expectations for the next generation of photoelectric energy conversion devices using organic materials are significantly increasing. However, since the conversion efficiency of the organic electroluminescent diode or the organic solar cell is extremely low, it has not been put into practical use in full scale. Effective utilization of triplet excitons (triplet harvesting) holds the key to achieving ultra-high efficiency of organic electronic devices. In this research, we succeeded in raising the triplet fusion efficiency by spin angular momentum control in the transition state.

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  • Development of New Super-organic-donor Reagents by Photo-activation and Their Application to Photo-catalysts

    Grant number:16K05689

    2016.4 - 2019.3

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Research category:Grant-in-Aid for Scientific Research (C)

    Awarding organization:Japan Society for the Promotion of Science

    HASEGAWA EIETSU, IKOMA Tadaaki, MIURA Tomoaki, IWAMOTO Hajime, TAKIZAWA Shin-ya, MURATA Shigeru, WAKAMATSU Kan

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    Grant amount:\4940000 ( Direct Cost: \3800000 、 Indirect Cost:\1140000 )

    In order to develop new and effective photo-stimulated electron and hydrogen donor reagents, we have investigated the electron transfer reactions of visible light absorbing moiety (R) substituted benzimidazoline (BIH) derivatives (BIH-R). Photo-desulfonylation of various sulfoneamides was achieved by using naphthol substituted BIH (BIH-NapOH). Then, it was proposed that an excited naphthoxide is generated and acts as a strong electron donor to promote this reduction reaction. An oxidized form derived from BIH-NapOH (BI+-NapO-) was discovered to act as an unprecedented betaine photocatalyst. We have succeeded in developing two photocatalytic protocols in which single electron transfer from BIH-Ph to the catalyst radical cation is utilized to regenerate the catalyst (Electron transfer protocol) and hydride transfer from an appropriate hydride reagent to the catalyst generates naphthoxide substituted BIH (BIH-NapO-) as strong electron and hydrogen donor (Hydride protocol).

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  • Studies on interfacial electron transfer in the nonionic vesilcels towards development of photo and magneto functional materials

    Grant number:15K05384

    2015.10 - 2019.3

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Research category:Grant-in-Aid for Scientific Research (C)

    Awarding organization:Japan Society for the Promotion of Science

    MIURA Tomoaki, Ikoma Tadaaki, Maeda Kiminori

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    Grant amount:\4680000 ( Direct Cost: \3600000 、 Indirect Cost:\1080000 )

    Niosomes are bilayer membrane capsules, which can be prepared very easily by dispersing low cost detergent molecules in water. They recently draws much attention as drug delivery materials for medical uses. In this project, basic researches have been carried out for development of novel materials such as photo- and magnetically controlable drug delivery and magnetically enhanecd artificial photosynthesis. Newly developed niosome capsules that involve a pigment and a vitamin molecule give the long-lived charge-separated state upon photo-irradiation, of which the lifetime is greatly enhanced by applied magnetic field. Multi-step electron transfer, which is important for artificial photosynthesis, is realized by utizling the niosome capsule. Preliminary results that indicate photo-control of the membrane structure, which is important for drug delivery, have also been presented.

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  • Magnetoconductance Effect of Organic Solar Cell due to the Conservation Rule of Electron Spin Angular Momentum

    Grant number:26410088

    2014.4 - 2017.3

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Research category:Grant-in-Aid for Scientific Research (C)

    Awarding organization:Japan Society for the Promotion of Science

    Tadaaki Ikoma, WAKIKAWA Yusuke

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    Grant amount:\5070000 ( Direct Cost: \3900000 、 Indirect Cost:\1170000 )

    To overcome main factors lowering the energy conversion efficiency of organic solar cells (OSCs), recently there is great interest in singlet fission and triplet fusion because of the potentially ultrahigh efficiency of the conversion from photon to charge. In those elementary dynamics, the electron spin plays an essential role due to the conservation of angular momentum. Here we show that the magnetoconductance (MC) effect originated from depressing the spin mixing in encounter pairs under the external magnetic field provides quantitative information about the singlet fission, the charge recombination and the trap-related dynamics with triplet exciton in a bilayer device of pentacene|fullerene. The results obtained by the simple non-destructive MC measurements indicate that energy turning and/or harvest of the triplet excitons are key issues for enhancing the performance of OSCs.

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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

    Grant number:17655055

    2005

    System name:科学研究費助成事業 萌芽研究

    Research category:萌芽研究

    Awarding organization:日本学術振興会

    生駒 忠昭

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    Grant amount:\3000000 ( Direct Cost: \3000000 )

    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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  • Origin of the highly efficient electroluminescence as studied by Time-resolved EPR

    Grant number:15350074

    2003 - 2005

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

    Research category:Grant-in-Aid for Scientific Research (B)

    Awarding organization:Japan Society for the Promotion of Science

    AKIYAMA Kimio, IKOMA Tadaaki

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    Grant amount:\13600000 ( Direct Cost: \13600000 )

    The research was carried out to elucidate the mechanisms of highly efficient electroluminescence in organic dyes and π-conjugated polymers systems. Using by time-resolved EPR technique polarized EPR spectra were observed both in the rigid matrices and film samples at low temperature. The paramagnetic species generated by the irradiation were assigned to their excited triplet states, followed by the reverse intersystem crossing (RISC) from their higher excited triplet state upon excitation by the second laser pulse. The RISC yields were determined for several organic dyes from the two-color two-laser TREPR experiments. The signals due to radical pairs were also obtained and analyzed in terms of the spin correlated radical pair mechanism. The results gave the information on the relaxation processes in excited states of organic dyes and π-conjugated polymers and the electronic structures of the transient radical pair species, playing important roles in the charge transport processes.
    The metal (Ir and Pt) complexes were also of the subject because of their high quantum yields of the phosphorescence induced by the large spin-orbit coupling (SOC) interactions. No TREPR signals were obtained in the system of Ir and Pt complexes even at cryogenic temperatures. The facts were interpreted by the large SOC leading to disturb the observation of triplet EPR spectra because of large dipole-dipole interactions and also the effective relaxation in their excited states. To obtain the information on the excited triplet states of these metal complexes the EPR measurements were carried out to observe the ion radical species, which were expected to have similar electronic properties with corresponding excited triplet states, generated by the electrochemical method at room temperature. Although the optimum experimental conditions such as solvents and/or applied voltages for electrolysis of the samples were examined, no significant signals were observed.

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  • Spin polarization enhanced molecular photoconductivity

    Grant number:15310069

    2003 - 2005

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

    Research category:Grant-in-Aid for Scientific Research (B)

    Awarding organization:Japan Society for the Promotion of Science

    IKOMA Tadaaki

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    Grant amount:\11900000 ( Direct Cost: \11900000 )

    Without any process using nanotechnology, molecule-based material has a potential for the exotic properties originated from the quantum effect happening in molecular level. However reports of this type of research have apparently not almost been published to date. Therefore, we have studied on magnetic field effect on photoconductivity of molecular film sample, in order to clarify the magnetoconductivity enhanced by photo induced spin polarization. The achievements of this research are summarized as following.
    1) We found film samples in which the carrier yield was enhanced dramatically by generation from the excited triplet state of dopants. It was shown that the spin polarization and relaxation of electron-hole pair played an important role for the observed giant magnetoconductive effect.
    2) In the experiment performed under strong magnetic field, the signals due to short distance electron hole pairs were detected for the first time. The observation confirms the stepwise hole hops in quasi-one dimensional lattice model.
    3) Using magnetic field effect experiments, the spin dynamics in carrier generation for C60-doped polyvinylcarbazole film, which shows the highest photoconductivity, was clarified for the first time. The electron-hole pair created by excitation of charge transfer complex recombines to the local excited singlet state of C60 rather than the excited triplet state. The excited singlet state C60 relaxs to the ground state via the excited triplet state of C60.
    The project succeeded to demonstrate the importance of spin polarization of carrier in conduction in molecular solid.

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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

    Grant number:12740310

    2000 - 2001

    System name:科学研究費助成事業 奨励研究(A)

    Research category:奨励研究(A)

    Awarding organization:日本学術振興会

    生駒 忠昭

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    Grant amount:\2300000 ( Direct Cost: \2300000 )

    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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  • Study on the Electronic Structure of the Excited States and its Reaction of Triple Bond Conjugated Molecules

    Grant number:11440210

    1999 - 2000

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

    Research category:Grant-in-Aid for Scientific Research (B)

    Awarding organization:Japan Society for the Promotion of Science

    TERO Shozo, IKOMA Tadaaki, AKIYAMA Kimio

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    Grant amount:\8900000 ( Direct Cost: \8900000 )

    The following are the main results obtained in the present study.
    (1) Diphenylpolyynes (DPY) have a linear planar structure belonging to the D_<2h> point group in the T_1 states, which were assigned to ^3B_<1u> (π_xπ_x^*) in character.
    (2) The T_1 (π_xπ_x^*) states of DPY have unusually large negative D values for the ZFS parameters that increase with increasing the molecular size.
    (3) The large negative D value was interpreted in terms of the spin-orbit interaction between the T_1(^3π_xπ_x^*) state and the upper-lying ^3Au (π_xπ_y^*) state.
    (4) The energy gap between these two states was determined from the observed D values and the calculation of the spin-orbit matrix, indicating that the value decreases with increasing the number of triple bonds.
    (5) The rapid radiationless transition was also found in the decay from the T_1 state to the S_0 state. The k_<nr> value increases with the decrease in the energy separation between the T_1 and S_0 states, indicating the importance of the Franck-Condon factor between them for the nonradiative deactivation.
    (6) The appearance of the satellites due to the b_<1g> vibronic bands in the phosphorescence spectra of DPY suggests that the potential surface in the T_1 states would be shallow along the b_<1g> coordinate by the vibronic coupling between the T_1 (π_xπ_x^*) and the ^3π_xπ_y states promoted by the ring twisting motion.
    (7) Therefore, it is concluded that the energy proximity between the T_1 (^3B_<1u>:π_xπ_y^*) and Tu(^3Au:π_xπ_y^*) states in DPY not only increases the negative D values of the ZFS parameters by the spin-orbit interaction but also accelerates the nonradiative decay from the T_1 state by the vibronic interaction.

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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

    Grant number:11124202

    1999

    System name:科学研究費助成事業

    Research category:特定領域研究(A)

    Awarding organization:日本学術振興会

    伊藤 攻, 藤塚 守, 生駒 忠明, 小野寺 真治

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    Grant amount:\1700000 ( Direct Cost: \1700000 )

    本研究では、有機物の加熱による炭化過程をパルス電子スピン共鳴法(パルスEPR法)を用いて解明することを目的とした。2次元EPR法がピッチ系メソフェース炭素の研究に対する有効性を明かにするものである。該当年度においては以下のような結果を得た。
    2次元EPR法は炭化度の高い炭素にも有効であることが示された。これはアルゴンヌ標準炭からさらにH/C比の低い石炭系ピッチや熱処理石炭系ピッチおよび化学処理石炭系ピッチ試料への測定の展開より明らかになったものであり、得られた結果を赤外分光測定の比較からも検討した。さらにヨウ素添加石炭ピッチの炭化過程の追跡を2次元EPR法を適用して行った結果、電荷移動型相互作用によって生成するイオンラジカルの反応性が重要な役割を果たすことが判明した。
    硝酸処理した石炭ピッチにおいては緻密なメソフェースが得られる過程を2次元EPR法で追跡した。熱処理下でH-,C-によるピークの他にN-によるピークの観測に成功した。このN-原子は加熱処理によってピロール環などのヘテロアトム芳香族化合物としてグラファイト様多環芳香分子に含まれていることが類推された。
    多重層カーボンナノチューブの内部を酸化することによりカルボン酸修飾を行なった。このカルボン酸にアミノ基を含むスピンプローブ剤を結合させ、EPRの線巾、EPR強度のマイクロ波依存性、および緩和時間を測定した。その結果、カーボンナノチューブの内部と外部の分子の運動性に差によるものと思われる現象が、パルス電子スピン共鳴の観測から示唆された。

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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

    Grant number:10740315

    1998 - 1999

    System name:科学研究費助成事業 奨励研究(A)

    Research category:奨励研究(A)

    Awarding organization:日本学術振興会

    生駒 忠昭

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    Grant amount:\2100000 ( Direct Cost: \2100000 )

    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

    Grant number:10137203

    1998

    System name:科学研究費助成事業 特定領域研究(A)

    Research category:特定領域研究(A)

    Awarding organization:日本学術振興会

    伊藤 攻, 生駒 忠昭, 藤塚 守

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    Grant amount:\1700000 ( Direct Cost: \1700000 )

    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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  • High-frequency time-resolved EPR Study on the Short-lived Paramagnetic Species

    Grant number:07404040

    1995 - 1997

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

    Research category:Grant-in-Aid for Scientific Research (A)

    Awarding organization:Japan Society for the Promotion of Science

    TERO Shozo, IKOMA Tadaaki, AKIYAMA Kimio

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    Grant amount:\30200000 ( Direct Cost: \30200000 )

    We built a Q-band time-resolved EPR spectrometer, which works with a pulsed laser. We applied the system to verify the mechanism of the ClDEP spectra due to short-lived radicals and the broadening mechanism of the time-resolved EPR spectra due to short-lived excited triplet states.
    1. Microwave frequency dependence of spin-polarized EPR spectra
    (a) The CIDEP spectra involving triplet mechanism depends on significantly to the observed frequency.
    (b) Time-resolved EPR measurements on the excited triplet states verified that the spectral broadening due to the g-anisotropy is clearly distinguished from the other mechanisms.
    2. The sign of the exchange interaction in the radical ion pairs.
    The present study verified that the exchange interaction is governed by charge transfer interaction rather than covalent bonding interactions, The level crossing between the potential surfaces of the radical ion pair state and ground state is a key factor.
    3. Electronic structure of the excited state of diphenyl carben.
    We successfully observed the short-lived excited state of diphenylmethylene and determined the zero-field splitting constants.
    4. Structure of the dangling bonds in microcrystalline silicon.
    Q-band EPR measurements verified the existence of three kinds of signals due to dangling bonds in microcrystalline silicon.
    5. Eelctronic structure of the excited triplet states having unusually large zero-field splitting constants.

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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

    Grant number:07740449

    1995

    System name:科学研究費助成事業 奨励研究(A)

    Research category:奨励研究(A)

    Awarding organization:日本学術振興会

    生駒 忠昭

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    Grant amount:\1000000 ( Direct Cost: \1000000 )

    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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  • Studies on Energy Transfer with Spin Polarization Conservation in organic Photochemical Reactions

    Grant number:02453002

    1990 - 1991

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for General Scientific Research (B)

    Research category:Grant-in-Aid for General Scientific Research (B)

    Awarding organization:Japan Society for the Promotion of Science

    IKEGAMI Yusaku, IKOMA Tadaaki, AKIYAMA Kimio

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    Grant amount:\6200000 ( Direct Cost: \6200000 )

    The studies have been carried out to clarify the spin polarization conservation during triplet-triplet energy transfer in fluid solution. This phenomenon first demonstrated by us in 1984 for the photochemical cleavage of the dimers of neutral pyridinyl radicals is important to interpret molecular energy transfer mechanism. The following results have been obtained.
    1. Monomer-dimer equilibrium of pyridinyl radicals and its photochemistry. Neutral pyridinyl radicals are substantially in equilibrium with their dimers and the dimers show photochemical cleavage producing the radicals. Time-resolved EPR studies on the initial process disclosed the precursor of photolysis to be the singlet excited state. On the other hand, in the presence of an appropriate triplet sensitizer, triplet-triplet energy transfer with spin polarization conservation occurred leading to the generation of the radical through excited triplet state. Detailed studies on many pyridinyl dimers established a characteristic chemistry of pyridinyl radicals.
    2. Spin polarization conservation during the intramolecular triplet-triplet energy transfer. This phenomenon was successfully demonstrated by the measurements of transient triplet EPR spectra for two types of spiran compounds containing energy-donor and acceptor moieties. Spin alignment is conserved in the molecular frame and high field approximation can not explain the spin polarization pattern of the specatra.
    3. Other photochemical processes. The photochemical initial processes have been clarified for the following titles : (1) CIDEP studies on radicals produced from photochemical reactions of some aromatic carbonyl compounds ; (2) Time-resolved EPR studies on photochemical hydrogen abstraction reactions of 4-substituted pyridines ; (3) Time-resolved EPR study on the excited triplet state of non-phosphorescent tropone.

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