GROUND AND EXCITED-STATE CHARACTERIZATION OF SELF-ASSEMBLED RU-II-TRIS-BIPYRIDINE-IRON PORPHYRIN COMPLEXES

The ability to couple the well known excited state redox properties of Ru-II(bpy)(3) (bpy=2,2'-bipyridyl) with the catalytic attributes of m etalloporphyrins is of specific importance in designing efficient ener gy conversion systems. In this study, we report the quenching of the R un(bpy)(3) metal-to-ligand charge transfer excited state ((MLCT)-M-3) by Fe-III-meso-tetra(4-Sulfanatophenyl) porphyrin (Fe(III)4SP) in aque ous solution. Our results indicate that FE(III)4SP forms a 1:1 complex with Ru-II(bpy)(3) under low ionic strength conditions (5 mM HEPES, p H 7) with a binding constant of (1.5+/-0.01) X 10(4) M-1. Complexation leads to extensive quenching of the 3MLCT state of the Ru-II(bpy)(3) with k(q)=5 X 10(9) M-1 s(-1). In contrast, at higher ionic strengths (mu=500 mM) or when the anionic Ru-II(dcbpy)(3) (dcbpy=4,4'-dicarboxy 2,2'-bipyridine) is used the ruthenium excited state quenching is pure ly diffusional and no evidence for complexation is observed. Time reso lved fluorescence data reveals a life time of Ru-II(bpy)(3) within the complex on the order of 10 ps in air saturated solutions. These resul ts demonstrate extremely facile electron transfer within self-assemble d complexes of Ru-II(bpy)(3) and Fe(III)4SP. (C) 1997 Elsevier Science S.A.