Fullerenes linked to photosynthetic pigments

The synthesis and photochemical characterization of two porphyrin-fullerene dyads, two zinc porphyrin-fullerene dyads, and a carotenobuckminsterfullerene are reviewed. In these molecules, the fullerene first excited singlet state may be formed by direct excitation or by singlet-singlet energy transfer from the attached pigment. In polar solvents, the dominant singlet-state decay pathway is photoinduced electron transfer to yield the pigment radical cation and fullerene radical anion. This charge-separated state has a long lifetime relative to the time constant for charge separation. In toluene, in cases where photoinduced electron transfer is slow for thermodynamic reasons, the fullerene singlet state decays by intersystem crossing, and the resulting triplet energy is partitioned between the components of the dyad according to their triplet energies. The results suggest that fullerenes can be valuable components of photochemically active multicomponent molecular systems.