pi-Complex formation in electron-transfer reactions of porphyrins

it-Complex formation between porphyrins and their radical cations plays an important role in self-exchange electron transfer between neutral porphyrins and the radical cations, leading to negative activation enthalpies when the stabilization energy of the pi-complex is larger than the activation energy for the intracomplex electron transfer in the pi-complex. A number of porphyrin molecules are self-organized on three-dimensional gold nanoclusters to form monolayer-protected gold nanoclusters (MPCs) that act as an efficient photocatalyst for the uphill reduction of HV2+ by BNAH to produce 1-benzylnicotinamidinium ion (BNA(+)) and hexyl viologen radical cation (HV.+). Such three-dimensional architectures of porphyrin MPCs with large surface area allow supramolecular pi-complexation between MPCs and HV2+, resulting in fast electron transfer from the singlet excited state of porphyrin to HV2+ on MPCs. The pi-pi interaction is exploited to develop efficient photovoltaic devices consisting of porphyrin and fullerene assemblies which have an enhanced light-harvesting efficiency throughout the solar spectrum together with a highly efficient conversion of the harvested light into electrical energy. Copyright (c) 2004 Society of Porphyrins & Phthalocyanines.