Photochemistry of manganese porphyrins. Part 9. Redox reactions photosensitised by diamagnetic metalloporphyrins

Abstract

Photoredox processes employing diamagnetic metalloporphyrins as photosensitisers have been used to generate both oxidising and reducing radicals in aqueous solution. The reducing radicals reduce manganese(III) porphyrins to the corresponding manganese(II) porphyrins with high efficiency. Incorporating the manganese(III) porphyrin in a negatively charged micelle, vesicle, or microemulsion leads to a decrease in the efficiency of the reaction but reduction still occurs. Oxidation of either manganese-(II) or -(III) porphyrins by the oxidising radicals was not observed. The lifetime of the oxidising radical was kept short by primary reverse electron transfer and by reduction with impurities. The use of microheterogeneous media gave no real benefits for the oxidative cycle.