Redox Photosensitizers Used for Photocatalytic CO₂ Reduction

Abstract

Redox photosensitizers, which absorb visible light and initiate an electron transfer, play a critical role in various photocatalytic reactions including CO₂ reduction, water splitting, and organic synthesis. In this review, the recent advance of redox photosensitizers used for photocatalytic CO₂ reduction was summarized. To function as an efficient photosensitizer, a long lifetime in its excited state is necessary for photo-induced electron transfer process. In addition to the most widely used ruthenium(II) tris-diimine complexes, osmium(II) complexes with S-T absorption and ring-shaped rhenium(I) multinuclear complexes also functioned as a photosensitizer. Recently, from the strategic point to use abundant elements, copper(I) and zinc(II) complexes and purely organic compounds have been used as a photosensitizer. In these systems, the method to obtain triplet excited states with long lifetimes is a key in the absence of heavy metal effects of 4d and 5d elements accelerating inter-system crossing.