A photosensitizer dinuclear ruthenium complex: Intramolecular energy transfer to a covalently linked fullerene acceptor

A fullerene derivative (5) in which a dinuclear ruthenium complex is covale ntly linked to a fulleropyrrolidine (FP) through a rigid spacer has been pr epared through azomethine ylide cycloaddition to C-60 Electrochemical and p hotophysical studies revealed that ground-state electronic interactions bet ween the bimetallic ruthenium chromophore and the FP moiety are small. The absorption spectrum of 5 displays a metal-to-ligand charge transfer (MLCT) transition at about 620 nm in CH2Cl2 which is shifted by nearly 160 nm rela tive to that of a previously reported mononuclear dyad (8). The photophysic al investigations have also shown that both in dichloromethane and acetonit rile the photoexcited MLCT state of dyad 5 transforms into the fullerene tr iplet excited state with a quantum yield of 0.19 and that, contrary to mono nuclear dyad 8, electron transfer, if any under the applied conditions, is negligible relative to energy transfer.