MECHANISM OF THE TRIS(BIPYRIDINE)RUTHENIUM(II) PHOTOSENSITIZED REVERSIBLE REDOX REACTION OF A MACROCYCLIC COBALT(III) COMPLEX IN GELATIN HYDROGEL AND HYDROSOL

The Ru(bpy)3(2+) photosensitized reduction of a macrocyclic Co(III) complex, Co(N4)(OH2)23+ (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)3(2+) and the scavenging of the oxidized species of Ru(bpy)3(2+) 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.