Redox Control Recombination in Axially Linked “Donor – Aluminum(III) Porphyrin – Fullerene” Reaction Center Models

Abstract

Aluminum(III) porphyrins (AlPor) are well suited for the construction of axially linked multicomponent donor-acceptor systems. The axial hydroxide reacts with carboxylic acids or alcohols to form covalent ester or ether linkage, respectively. Moreover, they bind Lewis bases such as imidazole or pyridine to form a coordination bond with the Al center. They hold high fluorescence quantum yields with adequate singlet and triplet state lifetimes, as well as rich redox chemistry with two reversible oxidation and reduction processes. They can act as either a photosensitizing electron acceptor or donor with a wide variety of redox and optically active compounds. By exploiting these unique properties, we have designed several donor-AlPor-acceptor systems to mimic the reaction center complex of natural photosynthesis. In these systems, we have studied the electron transfer processes in perpendicular to the porphyrin plane. The optical studies showed that the excitation of AlPor results in a sequential electron transfer between redox-active units to generate long-lived radical pairs. I will discuss some of these systems to show how the recombination dynamics depend on the redox potentials.