ENERGY AND PHOTOINDUCED ELECTRON-TRANSFER IN PORPHYRIN-FULLERENE DYADS

Time-resolved fluorescence and absorption techniques have been used to investigate energy and photoinduced electron transfer in a covalently linked free-base porphyrin-fullerene dyad and its zinc analog. In tol uene the porphyrin first excited singlet states decay in about 20 ps b y singlet-singlet energy transfer to the fullerene. The fullerene firs t excited singlet state is not quenched and undergoes intersystem cros sing to the tripler, which exists in equilibrium with the porphyrin tr ipler state. In benzonitrile, photoinduced electron transfer from the porphyrin first excited singlet state to the fullerene competes with e nergy transfer. The fullerene excited singlet state is also quenched b y electron transfer from the porphyrin. Overall, the charge-separated state is produced with a quantum yield approaching unity. This state l ives for 290 ps in the free-base dyad and 50 ps in the zinc analog. Th ese long lifetimes suggest that such dyads may be useful as components of more complex light-harvesting systems.