Photo-induced charge separation by ruthenium (II) photosensitizers

Abstract

The values of the cage escape yields of redox products (ηce) were determined for the reductive quenching of the excited states of homo- and heteroleptic complexes of Ru(II) and 2,2′-bipyridine (bpy), 2,2′-bipyrimidine (bpm), and 2,2′-bipyrazine (bpz) by triethanolamine (TEOA) as a sacrificial reductive quencher in aqueous, acetonitrile, and propylene carbonate solutions. In aqueous solution, ηce varies with the standard reduction potential (E0) of the complex, describing a weak dependence. The values of ηce are independent of E0 in propylene carbonate, but exhibit an inverted dependence in acetonitrile; the values of ηce in acetonitrile are generally higher than those in aqueous and propylene carbonate solutions, due to the higher diffusional rate constant for cage escape of the redox geminate pair in acetonitrile. The variable dependencies of ηce in the different solvents on the driving force of back electron transfer require that the conventional model be modified to account for the reorientation of the geminate pair within the solvent cage. © 1993 Indian Academy of Sciences.