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 Co^III 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 Co^III 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 Co^II complex species reacts slowly with the oxidized species of gelatin. Then a reversible photo-induced redox reaction of Co^III 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 Co^III species, respectively.