Photoredox processes in metalloporphyrin–crown ether systems

Abstract

Metalloporphyrins have been prepared with benzo-crown-ether groups attached at each of the four meso positions. Cations can be inserted into the crown-ether void, and the photophysical properties of the resultant complexes depend upon the nature of the cation. With Eu³⁺ as cation, intramolecular electron transfer occurs from the triplet excited state of the metalloporphyrin to Eu³⁺, but the large Eu²⁺ ion so formed is displaced from the crown-ether void so that reverse electron transfer is bimolecular. In the presence of an electron donor, irradiation of the metalloporphyrin forms the π-radical anion which transfers its extra electron to the Eu³⁺ ion housed in the crown-ether void.