Mechanism of the tris(bipyridine)ruthenium(II) photosensitized reversible redox reaction of a macrocyclic cobalt(III) complex in gelatin hydrogel and hydrosol

Abstract

The Ru(bpy)2+3 photosensitized reduction of a macrocyclic CoIII complex, Co(N4)(OH2)3+2(N4= 5, 7, 7, 12, 14, 14-hexamethyl-1, 4, 8, 11-tetraazacyclotetradeca-4, 11-diene), has been investigated in the networks of gelatin hydrogel and hydrosol. In these systems, a net charge separation proceeds due to reduction of the CoIII complex by the excited state of Ru(bpy)2+3 and the scavenging of the oxidized species of Ru(bpy)2+3 by a gelatin molecule. The photochemically generated CoII complex species reacts slowly with the oxidized species of gelatin. Then a reversible photo-induced redox reaction of CoIII takes place repeatedly in these systems. The results indicate that the tyrosine residue in gelatin and the corresponding oxidized species in the oxidized form of gelatin act as a reducing agent for the oxidized form of the photosensitizer and an oxidizing agent for the reduced CoIII species, respectively.