Design, synthesis and photophysical studies of [60]fullerene hybrids

The synthesis of cis- and trans-stilbene-substituted fulleropyrrolidines are described. Following excitation below 350 nm, cis- and trans-stilbenofulleropyrrolidines afforded a photostationary state that was essentially 100% trans. Conversely, no photoisomerization was observed following irradiation above 400 nm. These results support the notion that the singlet excited state of trans-stilbenofulleropyrrolidine is effectively quenched via intramolecular energy transfer (EnT) to the attached C60 moiety.; The synthesis, electrochemical and photophysical studies of alkyne-linked zinc porphyrin-[60]fullerene dyads are described. Cyclic and differential pulse voltammetry studies confirm that the porphyrin and fullerene moieties are electronically coupled and that the degree of electronic interaction decreases with increasing length of the alkyne chain. In toluene, EnT from the excited zinc porphyrin singlet to the fullerene moiety occurs. These dyads exhibit very rapid photoinduced electron transfer (PET) in THF and PhCN. Slower rates for charge recombination (CR) in THF versus PhCN clearly indicate that CR is occurring in the Marcus inverted region. Exceptionally small attenuation factors beta of 0.06 +/- 0.005 A´-1 demonstrate that the triple bond is an effective mediator of electronic interaction in zinc porphyrin-alkyne-fullerene molecular wires.; In order to further investigate energy transfer and electron transfer (ET) processes in conjugated D-A systems involving porphyrins and fullerenes, a new series of porphyrin-C60 dyads was synthesized. These systems exhibit full conjugation through a butadiynyl bridging element originating from the beta-position of the porphyrin donor and differ only with respect to complexation at the pyrrolic nitrogens in the porphyrin core (Ni, Zn and HZ). Differential pulse voltammetry studies show that the porphyrin and fullerene components are not electronically coupled. In toluene, deactivation of porphyrin singlet excited states occurs via intramolecular EnT to C 60. In THF and PhCN, these dyads exhibit very rapid PET and slightly slower charge recombination dynamics. Increased ET rates with an increase in solvent polarity are consistent with normal Marcus behavior. Slower rates for charge recombination in THF versus PhCN, a more polar solvent that lowers the energy of the charge-separated radical pair state (CSRP) relative to the ground state, is indicative of charge recombination events occurring in the Marcus inverted region.