The magnetic field influence on bridge-assisted electron transfer

Abstract

The influence of an external magnetic field on the rate of electron transfer is studied theoretically for the case of a donor-acceptor complex with paramagnetic ions as bridging sites. We demonstrate for a bridge with a single and with two paramagnetic ions that the applied magnetic field causes a blocking effect of the electron transfer. Each paramagnetic ion staying in its electronic ground state is assumed to reduce its spin from S to S − 1 2 if the transferred electron is coupled to it. Such a spin reduction determines the magnetic field dependence of the transfer rate in a specific manner. The magnetic field dependence is derived at low temperatures in utilizing the Wigner 6 j-symbols method. For the case of two paramagnetic ions per bridge the exchange interaction between them has been additionally included into the calculations. It is responsible for the step-like dependence of the rate constant on the magnetic field, as well as for the creation of a rather narrow field-strength region where the rate constant drops to zero.