radicalphotochemical

Radical photochemistry, sometimes written as radicalphotochemical, is the branch of photochemistry that studies reactions initiated by radical species generated upon absorption of light. It also covers photolytic processes that create radicals which then participate in subsequent reaction steps. Core features include homolytic bond cleavage (photolysis) to generate alkyl, acyl, or heteroatom-centered radicals, and photoinduced electron or energy transfer that yields radical intermediates. Common photochemical pathways include Norrish-type reactions of carbonyl compounds, photoredox catalysis that generates radicals under visible light, and radical polymerization initiated by photoinitiators.

Radical intermediates participate in initiation, propagation, and termination steps, enabling bond formations such as C–C, C–N, and C–O through radical coupling, additions, or cyclizations. The field intersects with organic synthesis, materials science, and environmental chemistry, where light-driven radical processes enable polymerizations, degradations, and pollutant transformations. Photoredox systems expand access to otherwise difficult transformations under mild conditions by using photocatalysts to shuttle electrons and generate radical species.

Techniques commonly used to study radical photochemistry include time-resolved spectroscopy, transient absorption, and electron paramagnetic resonance (EPR). Quantum yields, radical lifetimes, and product distributions constrain mechanistic interpretations.

Historically, radical photochemistry has grown from early photolysis studies to the modern integration with catalysis and polymer science. Ongoing challenges include controlling selectivity, managing reactive side paths, and translating laboratory insight to scalable systems.