Photophysics of ruthenium(II) complexes carrying amino acids in the ligand 2,2′-bipyridine and intramolecular electron transfer from methionine to photogenerated Ru(III)

Abstract

New ruthenium(II) complexes carrying methionine and phenylalanine in the bipyridine ligand, [Ru(bpy) 2(4-Me-4′-(CONH- l-methionine methyl ester)-2,2′-bipyridine)](PF 6) 2 ( IV) and [Ru(bpy) 2(4-Me-4′-(CONH- l-phenylalanine ethyl ester)-2,2′-bpy)](PF 6) 2 (V) have been synthesized and characterized and their photophysical properties studied. Flash photolysis measurements of complex IV, in the presence of an electron acceptor, methyl viologen (MV 2+) show that an intermolecular electron transfer from the excited state of Ru(II) in complex IV, to MV 2+ takes place, forming Ru(III) and the methyl viologen cation radical, MV + . The formation of MV + in this system is confirmed using time-resolved transient absorption spectroscopy. This intermolecular electron transfer is followed by intramolecular electron transfer from the thioether moiety (methionine) to the photogenerated Ru(III), regenerating Ru(II).