Oxygen-containing chromophores

This chapter covers the photochemistry of carbonyl compounds and their application as reagents, catalysts or promoters of metal-free photochemical transformations reported in the mid-2020 to the mid-2022 period. The carbonyl chromophore can absorb UV–visible light and thereby generate new C–C and C–heteroatom bonds and perform complex chemical transformations through different mechanisms: Hydrogen Atom Transfer (HAT), Single Electron Transfer (SET), and Triplet Energy Transfer (ET). This chapter is mostly organized according to reaction types (Norrish type I, Norrish type II, Aza-Yang reaction, Paterno–Büchi reactions, acyl radical addition, intramolecular cyclization, photoredox-mediated Giese reaction), but also by the type of bonds generated (C–C, C–heteroatom bonds) by either a photocatalytic or a non-photocatalytic reaction. Mechanistic information available by means of steady-state and time-resolved studies, as well as the information derived from theoretical calculations, or control studies are briefly commented on.