Application of Koopmans’ theorem in evaluating electron transfer matrix element of long-range electron transfer

Abstract

This paper has proposed an approach to searching for the minimum of molecular orbital (MO) energy splitting factor, and obtaining the electron transfer (ET) matrix element in long-range electron transfer reactions. This method has been applied to the intramolecular electron transfer reactions between biphenyl anion radical and biphenyl as well as naphthalene, mediated by the 5-α-androstane bridge. The electron transfer matrix element can be determined by the minimum location of the MO energy splitting factor between the lowest unoccupied molecular orbital and the next lowest unoccupied molecular orbital based on Koopmans’ theorem, Such a method is of special interest for asymmetric electron transfer systems in which the excess electron or hole transfers from one site to another. This paper has investigated the orientation dependence of the MO energy splitting factor for the co-axis self-exchange system of biphenyl anion radical and biphenyl. The values of ET matrix elements obtained using Koopmans’ theorem have been discussed in contrast to the state overlap on the basis of two-state model.