Ligand dependence of magnetic spin effects on photooxidation of [Ru(bpy)3−n(CN)2n](+2−2n) type complexes

Photoinduced electron transfer reaction from the series of [Ru(bpy)(3−n)(CN)2n](2+−2n) complexes (n=0, 1, 2) to methylviologen has been investigated using external magnetic field modulation in order to obtain relevant kinetic parameters for spin relaxation, backward electron transfer and cage escape of the geminate radical pair. The replacement of one bpy by two cyanide ligands results in an increase of the quenching rate constant and a decrease of the cage escape efficiency. The latter is decreased in a magnetic field and the sensitivity of this effect is weakened by introducing CN− ligands. From the analysis of the magnetic field dependence it can be inferred that with increasing number of CN− ligands, backward electron transfer rate and spin relaxation time in the geminate radical pair exhibit a moderate decrease but that the rate constant of cage escape decreases very strongly.