Photoinduced energy and electron transfer in a giant zinc porphyrin-bridge-C60 system

Photoinduced electronic energy transfer (EET) and electron transfer (PET) have been investigated in a multichromophoric system 2, that comprises zinc porphyrin (ZnP), dimethoxynaphthalene, and [60]fullerene (C-60) chromophores separated by norbornylogous bridge sections of six and five bond lengths, respectively. In toluene as solvent, EET from ZnP to C-60 occurs in folded and extended conformations of the molecule with rate constants of 1.3 x 10(10) and 8.1 x 10(8) s(-1), respectively. Evidence is presented for the existence of a third collapsed conformation of 2 which can undergo PET with a rate constant of 1.1 X 10(12) s(-1). In benzonitrile solvent, PET can also occur in the folded and extended geometries leading to a charge separated lifetime of 460 ns. The mechanisms for the unusually complex solvent and conformationally dependent excited-state processes in this molecule are discussed.