有機高スピン分子スピニクスの化学-直接的スピン同定分光の開発

• 研究課題/領域番号: 12020248
• 研究種目: 特定領域研究(A)
• 配分区分: 補助金
• 研究機関: 大阪市立大学
• 研究代表者: 佐藤 和信 大阪市立大学, 理学部, 講師 (90264796)
• 研究期間 (年度): 2000
• 研究課題ステータス: 完了 (2000年度)
• 配分額: 1,900千円 (直接経費: 1,900千円); 2000年度: 1,900千円 (直接経費: 1,900千円)
• キーワード: パルスESR / 電子スピンニューテーション / フラーレン多価アニオン / スピン格子緩和 / フォノンボトルネック現象 / 共鳴スピントンネル現象 / ヤーンテラー歪み / 遷移モーメント分光

研究概要

有機超伝導や有機強磁性を直接発現した新規な分子性物質として発見されて以来大きな注目を集めてきたフラーレンの多価アニオンの電子構造と分子構造を解明し、その量子的性質の発現機構の解明する手がかりを得ることを目的として、電子スピンニューテーション法とパルスESR法を適用した。カリウム金属ミラーを用いた接触還元法によって、フラーレンジアニオン及びドリアニオンを生成した。スピン状態はそれぞれ三重項、四重項状態になることをcw-ESRおよび二次元電子スピンニューテーション法の測定により同定し、微細構造定数を決定し、分子構造における対称性の低下を明らかにした。また、ESRスペクトルの温度依存性から、サンプルを室温から4.2Kに急冷したときのみ、それぞれ三重項、四重項状態が基底状態となり、10K付近で低スピン状態との逆転が起こり、それぞれ基底一重項、二重項に変化する特異な電子状態をフラーレシ多価アニオン状態がもつことを発見した。パルスESRを用いた緩和時間の測定において、10K以上で観測される熱励起の三重項、四重項状態においてフォノンボトルネック現象が生じ、さらにスピン格子緩和曲線にうねりが生じるスピン格子緩和の異常を初めて観測した。これらの現象をScott-Jeffriesの式、および核の振動を考慮した二重振動子非対称ポテンシャルを用いたシュレデンガー方程式に基づいて考察を行い、ボトルネック現象によってスピン格子緩和速度が遅くなったことと励起スピン状態が近接しているため、すなわちポテンシャル壁の高さが低いためにインコヒーレント共鳴スピントンネル現象がスピン格子緩和曲線のうねりとして観測されたものであると結論した。この共鳴スピントンネル現象は、アルカリ金属をドープしたフラーレン結晶系のhigh-Tc超伝導発現機構を説明する低スピン状態における動的なヤーン・テラー理論を支持する最初の実験的証拠である。

研究成果

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• [文献書誌] Kozo Fukui et al.: "The first non-kekule polynuclear aromatic high-spin hydrocarbon : Generation of a triangulene derivative and band structure calculation of triangulene-based high-spin hydrocarbons"Synthetic Metals. (印刷中). (2001)
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• [文献書誌] Daisuke Shiomi et al.: "Organic molecule-based ferrimagnetism : Magnetic properties of a model compound and numerical calculations of a model spin Hamiltonian"Molecular Crystals and Liquid Crystals. (印刷中). (2001)
• [文献書誌] Suguru Maki et al.: "Hydrogen-bonded open-shell molecules : Synthesis and physical properties of the oxophenalenoxyl-based radical with hydroxyl group"Molecular Crystals and Liquid Crystals. (印刷中). (2001)
• [文献書誌] Nobuyuki Oda et al.: "Molecular and electronic spin structures of high-spin polyphenylene-based oligonitrenes with high symmetry : A semiempirical approach to fine-structure tensors"Molecular Crystals and Liquid Crystals. (印刷中). (2001)
• [文献書誌] Koya Tanaka et al.: "Extremely π-delocalized nature of dianthrylcarbene-based high-spin systems as studied by CW and pulsed 2-D electron-spin transient nutation spectroscopy"Molectular Crystals and Liquid Crystals. (印刷中). (2001)