Electronic coupling for charge transfer in donor–bridge–acceptor systems. Performance of the two-state FCD model

Abstract

Electronic coupling is a key parameter that determines the rate of electron transfer reactions and electrical conductivity of molecular wires. To examine the performance of a two-state approach based on the orthogonal transformation of adiabatic states to diabatic states, we compare the effective donor–acceptor coupling V_DA computed with three different approaches in model donor–bridge–acceptor (D–B–A) systems. It is found that V_DA derived with the two-state method accounts properly for both the direct and superexchange interactions. The approach becomes, however, less accurate with the increasing energy difference of the donor and acceptor states. We suggest a simple diagnostic to identify the situation when the estimated coupling might be inaccurate and consider how to improve the performance of the two-state scheme in such a case.