fotoredoxcatalyse

Fotoredoxcatalyse, more commonly called photoredox catalysis, is a branch of catalysis in which light-activated catalysts mediate redox transformations via excited-state electron transfer. Photocatalysts absorb visible or near-UV light to generate reactive radical or ionic intermediates under mild conditions, enabling bond-forming and bond-breaking processes that complement thermal methods.

Mechanistically, a photocatalytic cycle begins with photoexcitation of a catalyst to a long-lived excited state with altered redox properties. The excited catalyst can either oxidize or reduce substrates, generating radical intermediates that participate in subsequent bond-forming steps. Redox-neutral and redox-driven variants exist, with oxidative or reductive quenching cycles regenerating the ground-state catalyst. In some systems energy transfer rather than electron transfer drives reactivity.

Common photocatalysts include transition-metal complexes such as Ru(bpy)3^2+ and Ir(ppy)3, which enable catalytic redox processes, as well as organic dyes like eosin Y and rose bengal for metal-free routes. Inorganic and heterogeneous systems are also explored. Light sources predominantly involve LEDs, and reactions are frequently conducted in polar solvents at ambient temperatures, contributing to milder conditions compared with traditional methods.

Applications span C–C and C–heteroatom bond formations, decarboxylative couplings, hydrofunctionalization, and cross-electrophile couplings. Mechanistic approaches incorporate single-electron transfer and energy-transfer pathways, with diverse substrates including arenes, alkenes, and carbonyl compounds. The field has expanded to continuous-flow photochemistry and greener, metal-free catalysts. Ongoing challenges include light penetration in complex media, catalyst stability, and substrate scope, with ongoing work aimed at broader reactivity and sustainability.