Ruthenium/fullerene dyads from rapid intramolecular electron/energy transfer to the generation of long-lived radical pairs

摘要

Excited states properties of a dinuclear [Ru(II)]_2-androstane-C_(60) donor-bridge-acceptor dyad were studied under various conditions and compared with those of a mononuclear Ru(II)-androstane-C_(60) dyad. In light of extending the ground-state absorption to the red region of the visible spectrum and, in turn, improving the light sensitization, the design of a dinuclear ruthenium chromophore proofs to be a conceptional success. While the steady-state luminescence quantum yield of the mononuclear dyad is substantially quenched relative to a ruthenium model complex, the respective dinuclear dyad is, however, subject to a very inefficient intramolecular quenching reaction. Picosecond and nanosecond resolved photolysis show that the photoexcited MLCT states transform, in the case of the mononuclear dyad, rapidly into the charge separated state, while the dinuclear dyad reveals a relative slow formation of the fullerene's triplet excited state. The difference in reactivity has been related to substantial different MLCT excited state energies of the corresponding antenna molecule in the mono- and dinuclear ruthenium dyad, respectively.