Review -- Two different multiple photosynthetic reaction centers using either zinc porphyrinic oligopeptide-fulleropyrrolidine or free-base porphyrinic polypeptide-Li+@C60supramolecular complexes

Abstract

An overview of two successful examples of photosynthetic reaction center models combined with light-capturing antenna chromophores is presented. In the first example, supramolecular complexes are formed between flexible zinc porphyrinic oligopeptides and fulleropyrrolidine bearing either a pyridine or imidazole functionalized C60 via a coordination bond plus π-π interactions. The excited energy migration occurs between porphyrin units followed by charge separation. The charge separation (CS) lifetimes of the supramolecular oligopeptide complexes have been elongated by increasing the generation of the porphyrins, enabling us to attain the longest lifetime (0.84 ms) for the P(ZnP)8-ImC60 supramolecular system in PhCN solution at 298 K, ever reported for supramolecular complexes. In the second example, free-base porphyrin polypeptides (P(H2P)n; n = 4 and 8) form supramolecular complexes with Li+@C60 in PhCN, in which the binding is much stronger than C60. Efficient energy migration occurs between porphyrins in P(H2P)n. The triplet CS states derived from 3Li+@C60 had long lifetimes due to spin-forbidden back electron transfer. The triplet CS lifetime becomes longer upon increasing the number of H2P due to the charge migration among porphyrins. The present study provides valuable insight into the energy and electron transfer processes leading to long-lived charge separated states in artificial photosynthetic antenna-reaction center models.