The photochemistry of mixed-ligand complexes (ArS)2ZnPhen with the lowest ligand—ligand charge transfer excited states

Abstract

Abstract Flash photolysis and spin-trapping experiments were performed to investigate the photochemistry of the mixed-ligand zinc complexes (4—XC 6 H 4 S) 2 Zn(Phen) (XH, MeO or Me 2 N) in liquid solutions. The lowest ligand—ligand charge transfer excited state of these complexes was shown to dissociate, yielding arylthiyl radicals and a reduced zinc-phenanthroline moiety. Back electron transfer with nearly diffusion-controlled rates was found to be a predominant process in the case of MeO- and Me 2 N-substituted arylthiolate complexes while the recombination of unsubstituted phenylthiyl radicals is also significant. The reductive dissociation product may be trapped by oxygen or methyl viologen (MV 2+ ) cations, leading to the photo-oxidation of complexes in aerated solutions or production of MV + radical cations. The latter decays via diffusion-controlled electron transfer to arylthiyl radicals. Steady state illumination produces MV + only in solutions of phenylthiolate complex where its oxidation by phenylthiyl radicals competes with recombination of the latter.