构型对芳基桥体分子内电子转移矩阵元影响的理论研究

在HF/6-31G水平上,研究了有机化合物二甲氧基-4-甲苯-四甲苯基桥体-二甲氧基-4-甲苯正离子间的电子转移.用线性反应坐标确定电子转移的过渡态,用两态变分法计算了电子转移矩阵元V_AB,在考虑非平衡态溶剂化效应下,计算了电子转移速率常数.改变桥体与氧化还原中心的二面角,计算了相应的电子转移矩阵元.通过电子结构分析,将电子转移矩阵元分为通过空间的直接耦合和通过键的耦合,提出了将后者进一步分为通过σ键和π键的耦合.得出通过π键的耦合与二面角余弦的平方成正比的结论.

Configuration Effect on Intramolecular Electron Transfer Between Durene-bridged Aromatic Redox Centers

Based on the semi-classical theory of electron transfer,quantum chemical calculation at HF/6-31G level was performed for the study of intramolecular electron transfer between durene-bridged 2,5-dimethoxy-4-methylphenyl and its cation. Two configurations are adopted. After the geometric optimizations of the electron-localized states,a linear reaction coordinate ξ was introduced to determine the transition state. The electronic transfer matrix elementsVABare calculated by variation principle. The non-equilibrium solvation correction was taken into account. The electron transfer rate and reorganization energy obtained by theoretical calculation are consistent well with the experimental values. The electronic transfer matrix elements at different dihedral angles between bridge and redox centers were obtained. In order to show the different contribution to this value,the electronic transfer matrix elements were divided into two parts: through space and through bond. The latter is further divided into σ bond contribution and π bond one. It has been concluded that the through π bond coupling is proportional to the square of cosine of dihedral angle. This conclusion was explained qualitatively.