Flowers of the plant genus Hypericum as versatile photoredox catalysts

Abstract

Photoredox catalysis is a powerful and modern strategy for the synthesis of complex organic molecules. So far, this field has relied on the use of a limited range of metal-based chromophores or artificial organic dyes. Here, we show that the ubiquitous plant genus Hypericum can be used as an efficient photoredox catalyst. The dried flowers efficiently catalyze two typical photoredox reactions, a photoreduction and a photooxidation reaction, with a versatile substrate scope. Constitution analysis of the worldwide available plant genus indicated that naphthodianthrones, namely the compounds of the hypericin family, are crucial for the photocatalytic activity of the dried plant material. In situ UV-vis spectroelectrochemical methods provide insights into the mechanism of the photoreduction reaction where the radical dianion of hypericin (Hyp˙²⁻) is the catalytically active species. Our strategy provides a sustainable, efficient and an easy to handle alternative for a variety of visible light induced photocatalytic reactions.