有机共轭体系电子转移反应的溶剂重组能

应用Marcus双球模型计算溶剂重组能λs时,在AM1法优化给受体几何构型基础上,提出了共轭体系电子云分布的扁球模型,并用统计的方法求出了rD/A.同时依照Miller等的处理办法,结合其他理论及实验证据将电子转移交叉反应中联苯分子的扭转能计入溶剂重组能λs中,从而用实验速率常数拟合出含扭转能的λs值.此实验拟合值与扁球法得到的λs计算值吻合得很好.通过比较理论值与实验值,发现了给受体间距的大小、受体分子的变化、溶剂的不同对λs计算值相对λs实验值的偏差的影响,直接证实了电子给受体的耦合作用,溶剂分子参与的超交换电子转移及溶质溶剂分子表面相互作用等量子因素造成的实际反应体系对溶剂经典连续介质模型的偏离.

Solvent Reorganization Energy of Organic Conjugated Systems in Electron Transfer Reactions

In the calculation of solvent reorganization energy by Marcus′s two sphere model,we presented a flat sphere model based on benzene solvent system′s exact geometry structure to describe the electron cloud of conjugated systems.We figured out the radii of electron donors and acceptors by using statistics method,after AM1 geometry optimization,and then calculated λs.Besides,according to Miller′s experiment and consulting McHale and other researchers′ Raman Spectrometry results,we supposed that the solute molecular low frequency torsion gave no contribution to λv when the frequency was too small and the λs obtained from flat sphere model had contained low frequency contribution.This revised λs was in agreement with the value figured out by subtracting revised λv from experimental λ value.By comparing them,we found that the distance between donor and acceptor,the alteration of acceptor and solvent affected the deviation of calculated λs from experiment values.Finally,we confirmed that the D A coupling,super exchange mediated by solvent molecule,surface interaction of solvent solute molecules and other similar quantum effects would reduce the classical value of λs,thus contribute to ET reaction.Our results proved the deviation of practical reaction systems to the continuum dielectric theory and reflected the necessity of describing the behaviors of solvent and solute molecules using molecular model.