Photoinduced Energy and Electron Transfer in a Giant Zinc Porphyrin−Bridge−C60 System

Abstract

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 (C60) chromophores separated by norbornylogous bridge sections of six and five bond lengths, respectively. In toluene as solvent, EET from ZnP to C60 occurs in folded and extended conformations of the molecule with rate constants of 1.3 × 1010 and 8.1 × 108 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 × 1012 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.