Carbonyl compounds are very interesting chromophores which can lead to a rich variety of photochemical reactions. Relevant photoreactions of carbonyl compounds are the reduction of carbonyl compounds by hydrogen abstraction, fragmentations, including the Norrish type cleavages, cycloaddition to alkenes (such as the Paterno–Büchi reaction), and rearrangement reactions, among others (Fig. 1A).

The development of novel photocatalytic reactions promoted by visible-light irradiation has encouraged the renaissance of the photochemistry field, focused on the preparation of simple and complex organic molecules, including natural products, for the pharmaceutical industry. Photoorganocatalysis is considered an important part of photochemistry and is based on the use of small organic molecules that act as photocatalysts (PCs) to promote photochemical transformations and they are deemed to be the greenest chemical. Several mechanisms have been proposed to be responsible for these transformations, such as hydrogen atom transfer (HAT), single electron transfer (SET), and energy transfer (ET) processes.