Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka 819-0395, Japan.
ACS Nano. 2011 Feb 22;5(2):1165-78. doi: 10.1021/nn102806z. Epub 2011 Jan 4.
A combined theoretical and experimental study was performed on diarylethenes and diarylethene-capped sexithiophenes aiming at an improved understanding of the electrochemical and photochemical ring-opening and ring-closing mechanisms. Theoretical calculations, based on DFT and TDDFT, suggested that the spatial distribution and the occupancy of the frontier orbitals determine and control the diarylethenes' ring-opening and ring-closing upon photoirradiation and electrochemical oxidation. Optimized geometries, potential energy surfaces, and activation energies between the open-ring and closed-ring forms were calculated for diarylethenes in the neutral ground state, excited states, and mono- and dicationic states. Analysis of the frontier orbitals was employed to understand the cyclization and cycloreversion of diarylethenes and to predict and explain the switching properties of diarylethene-capped sexithiophene molecular wires. The TDDFT data were verified with experimentally measured UV/vis spectra. The DFT calculations estimated open-shell ground states of diarylethene-capped sexithiophene dications, which were verified with EPR spectroscopy, and the broadening of the peaks in the EPR spectra were explained with the calculated singlet-triplet splitting. The good agreement of experiment and theory allows for the understanding of switching behavior of diarylethenes in solutions, in metal break junctions, in monolayers on metal surfaces, and as a part of complex organic molecular wires.
本文对二噻烯和二噻烯封端的六噻吩进行了理论和实验研究，旨在深入了解电化学和光化学开环和闭环机理。基于密度泛函理论（DFT）和含时密度泛函理论（TDDFT）的理论计算表明，前线轨道的空间分布和占据决定并控制了二噻烯在光辐照和电化学氧化下的开环和闭环。计算了中性基态、激发态、单阳离子和二阳离子态中二噻烯的开环和闭环形式的优化几何形状、势能面和活化能。通过分析前线轨道，研究了二噻烯的环化和环反转，并预测和解释了二噻烯封端六噻吩分子线的开关性能。用实验测量的紫外/可见光谱验证了 TDDFT 数据。DFT 计算估计了二噻烯封端六噻吩二阳离子的开壳基态，并用电子顺磁共振（EPR）光谱进行了验证，并解释了 EPR 光谱中峰的展宽与计算得到的单重态-三重态分裂有关。实验和理论的良好一致性允许理解二噻烯在溶液、金属断裂结、金属表面单层以及作为复杂有机分子线的一部分中的开关行为。
