ChemInform Abstract: Fullerenes as Novel Acceptors in Photosynthetic Electron Transfer

Abstract

We propose a novel strategy using fullerenes for the construction of solar energy conversion systems that mimic the primary electron transfer events in photosynthesis. Redox-active fullerenes such as C60 and C70 were covalently bound to a porphyrin and the photophysical properties of the resulting compounds were investigated. Regardless of solvent and linkage, the charge-separated state is produced efficiently in zincporphyrin–fullerene dyads, showing that fullerenes are good electron acceptors. The most intriguing characteristic of fullerenes in electron transfer is that they accelerate photoinduced charge separation as well as charge shift and slow down charge recombination, properties that are in sharp contrast with those of conventional two-dimensional aromatic acceptors such as quinones and imides. The peculiar electron transfer properties of fullerenes can be explained by the small reorganization energies, which make it possible to optimize artificial photosynthetic multistep charge separation. A combination of the two strategies, multistep electron transfer and small reorganization energy of fullerenes, has been applied to light energy conversion systems as well as the more complex molecular systems such as triads. Highly efficient photosynthetic multistep electron transfer has been realized at gold electrodes modified with self-assembled monolayers of fullerene-containing molecules. These results will provide new principles and concepts to develop artificial photosynthetic materials as well as molecular devices.