fotokemian

Fotokemian is the branch of chemistry that studies chemical reactions initiated by light. It examines how photons promote molecules from their ground electronic state to excited states and how these excited species drive chemical transformations. The field intersects with photophysics and spectroscopy and is distinguished by the central role of light in initiating reactions. The concept has evolved with advances in spectroscopy and light sources, including lasers.

A core principle is the Grotthuss–Draper law: only light absorbed by a substance can produce photochemical change. After absorption, molecules may access singlet or triplet excited states and follow diverse pathways, including bond cleavage, energy transfer, or electron transfer. The efficiency of a photochemical reaction is described by its quantum yield, the fraction of absorbed photons that lead to product formation.

Common mechanisms include homolytic bond breaking, photosensitized reactions, and photoinduced electron transfer. Photochemical processes often occur under milder conditions than thermal reactions and can be highly selective due to state-specific pathways. Reaction outcomes depend on factors such as light wavelength, intensity, solvent environment, and the presence of catalysts or sensitizers.

Applications span photography, photolithography, and polymerization; photocatalysis and solar energy conversion; and atmospheric chemistry, where light-driven reactions affect ozone and radical formation. Analytical and materials techniques, such as time-resolved spectroscopy and quantum yield measurements, are used to study these processes and guide the design of new photochemical systems. The field continues to contribute to green chemistry, renewable energy, and advanced materials.