PHOTOINDUCED ELECTRON-TRANSFER IN A TRIS(2,2'-BIPYRIDINE)-C-60-RUTHENIUM(II) DYAD - EVIDENCE OF CHARGE RECOMBINATION TO A FULLERENE EXCITED-STATE

A 1,3-dipolar cycloaddition reaction of azomethine ylides to C-60 has been used to prepare a fulleropyrrolidine covalently linked to a subst ituted tris(2,2'-bipyridine)ruthenium(II) chromophore. Electrochemical studies revealed a single one-electron reversible oxidation of the ru thenium center and ten one-electron reversible reductions, five of the m occurring at the C-60 core and five at the bipyridine (bpy) ligands. Steady-state fluorescence and time-resolved flash-photolytic investig ations of dyad 6 are reported in solvents of different polarity. The e mission in toluene/CH2Cl2, CH2Cl2, and CH3CN was substantially quenche d, relative to model complex 8. suggesting intramolecular quenching of the ruthenium MLCT excited state. Picosecond-resolved photolysis of 6 showed light-induced formation of the photoexcited ruthenium center, which undergoes rapid intramolecular electron transfer. Nanosecond-res olved photolysis revealed a charge-separated state (tau(1/2) = 210 ns in CH2Cl2 and tau(1/2) = 100 ns in CH3CN) that decays to the ground st ate by regeneration of the ruthenium MLCT excited state in CH2Cl2 or t hrough the formation of the C-60 triplet excited state in CH3CN.