Theoretical Treatment of Magnetic Field Dependent In-cage Backward Electron Transfer During Photooxidation of Ru(II) Complexes

Abstract

A theoretical treatment is presented of the magnetic field dependence of in-cage backward electron transfer within the primary redox pair originating from electron transfer between photoexcited Ru(II)-trisbipyridyl [Ru(bpy)~+] and methylviologen (MV2+). The treatment is based on the numerical solution of a stochastic Liouville equation for a density matrix represented in the basis of an explicitly given set of spin-orbit states of the redox pair [Ru(bpyH + ... MV'']. Calculations with various sets of model parameter values were performed in order to obtain the best fit to the experimentally observed magnetic field dependence of the efficiency ofcage escape. A reasonable simulation required the assumption of substantial initial singlet character of the primary redox pair and a very high rate of relaxation within the set of its four lowest spin-orbit states. A rate constant of about 1011 s-1 for a hypothetically spin-allowed backward electron transfer was evaluated.