3D visualization of geometries of photoinduced charge-separated states by development of electron spin polarization imaging method

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K19105
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Research Field: Physical chemistry, Functional solid state chemistry, and related fields
• Research Institution: Kobe University
• Principal Investigator: Kobori Yasuhiro 神戸大学, 分子フォトサイエンス研究センター, 教授 (00282038)
• Project Period (FY): 2017-06-30 – 2020-03-31
• Keywords: 光合成 / 光電荷分離 / 電子的相互作用 / 構造解析 / 太陽光エネルギー変換 / 電子スピン共鳴 / タンパク質 / 異方性

Outline of Final Research Achievements

We have developed a novel method of “3D spin polarization imaging” by which the anisotropic spin polarization is mapped to all possible magnetic field directions from the powder-pattern time-resolved electron paramagnetic resonance (EPR) spectra to obtain geometries of the photoinduced primary charge-separated (CS) state of quinone pre-reduced membranes of plant PSII from spinach in frozen solution and in oriented multilayers at 77 K. For this we have observed the primary CS states using an X-band time-resolved EPR method. From the imaging maps, we have characterized cofactor geometries and electronic coupling of the photoinduced primary CS state. It has been revealed that that the electronic coupling between the charges is significantly weak in the CS state separated by 1.5 nm, showing an importance of regulated cofactor-cofactor electronic interaction between a vinyl substituent and an accessory chlorophyll to inhibit the energy-wasting charge-recombination.

Free Research Field

物理化学

Academic Significance and Societal Importance of the Research Achievements

本研究では、初期電荷分離活性種の同定を行うだけでなく、中間体分子の立体的な位置、距離、分子配向および軌道の広がりや重なりによる電子的相互作用を量子論に立脚した全く新しい磁気イメージング法の開発により正確に求めた。これは、試料の結晶化が不可能な複雑系であっても中間体やラジカル対の立体構造をオングストローム領域の高い空間分解能にて三次元映像化する画期的なツールを提供するものであり、磁気共鳴原理をベースとした本技術の開発は太陽電池における効率的電荷生成や新しい光触媒開発への応用や、特定分子をターゲットとする治療への応用など、産業・医療分野の広範囲な応用への可能性を十分に秘めている。