Photoinduced electron transfer in a clicked fullerene-porphyrin conjugate

A stable C-60 derivative bearing an azide functional group has been prepared and used as a building block for the preparation of a fullerene-porphyrin conjugate (F-P-F) by reaction with a Zn(II)-porphyrin bearing two terminal alkyne groups under the copper mediated Huisgen 1,3-dipolar cycloaddition conditions. The electrochemical and photophysical properties of the resulting multicomponent system have been investigated in detail. In benzonitrile, F-P-F undergoes photoinduced electron transfer and the resulting charge separated state is relatively long lived (tau = 0.48 mu s). In contrast, intramolecular energy transfer has been evidenced in toluene, with the generation of the fullerene triplet level upon selective excitation of the porphyrin moiety. In this solvent, a CT emission band is observed in the near-infrared region (lambda(max) = 940 nm) as a consequence of a conformational equilibrium causing, to a minor extent, the formation of intramolecular porphyrin-fullerene tight pairs. This finding is supported by measurements of singlet oxygen sensitization and quenching of the long-lived fullerene centered triplet state in the oxygen free solution.