THEORETICAL TREATMENT OF MAGNETIC-FIELD DEPENDENT IN-CAGE BACKWARD ELECTRON-TRANSFER DURING PHOTOOXIDATION OF RU(II) COMPLEXES

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)3/2+] 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 explicity given set of spin-orbit states of the redox pair [Ru(bpy)3/3+ ... 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 of cage 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 10(11) s-1 for a hypothetically spin-allowed backward electron transfer was evaluated.