SPIN-ORBIT-COUPLING CONTROLLED SPIN CHEMISTRY OF RU(BPY)3(2- DETECTION OF STRONG VISCOSITY DEPENDENCE OF IN-CAGE BACKWARD ELECTRON-TRANSFERRATE() PHOTOOXIDATION )

The magnetic field dependence of eta(ce), the cage escape yield of rad icals generated by photoelectron transfer between Ru(bpy)3(2+) and met hylviologen (MV++) was investigated for a series of solvent mixtures o f increasing viscosity, obtained by adding ethylene glycol (EGLY) to H 2O/ACN. From the experimental results the absolute values of the rate parameters characterizing the primary radical ion pair (k(ce) for cage escape, tau(s) for spin relaxation, and k(bet) for spin-allowed backw ard electron transfer) have been obtained. Particularly noteworthy is the strong viscosity dependence of k(bet), which can be assigned to di electric solvent relaxation as the rate limiting step of backward elec tron transfer in the EGLY containing solvents.