Efficient charge separation in porphyrin-fullerene-ligand complexes

Photoprocesses associated with the complexation of a pyridine-functionalize d C-60 fullerene derivative to ruthenium- and zinc-tetraphenylporphyrins (t pp) have been studied by time-resolved optical and transient EPR spectrosco pies. It has been found that upon irradiation in toluene, a highly efficien t triplet-triplet energy transfer governs the deactivation of the photoexci ted [Ru(tpp)], while electron transfer (ET) from the porphyrin to the fulle rene prevails in polar solvents. Complexation of [Zn(tpp)] by the fullerene derivative is reversible and, following excitation of the [Zn(tpp)], gives rise to very efficient charge separation. In fluid polar solvents such as THF and benzonitrile. radical-ion pairs (RPs) are generated both by intramo lecular ET inside the complex and by intermolecular ET in the uncomplexed f orm. Charge-separated states have lifetimes of about 10 mus in THF and seve ral hundred of microseconds in benzonitrile at room temperature.