Fotokemi

Fotokemi is the branch of chemistry that studies chemical processes initiated by light. It deals with reactions that occur when molecules absorb photons, leading to electronic excitation and subsequent chemical transformations. Photochemical reactions can proceed through excited singlet or triplet states and may involve energy transfer, electron transfer, or bond cleavage and formation. Key concepts include the quantum yield, which measures the efficiency of a photochemical step, and the dependence of reaction outcomes on wavelength and light intensity. The same molecule can undergo different reaction pathways when irradiated at different wavelengths.

Common mechanisms in fotokemi include photosensitized reactions where a sensitizer absorbs light and transfers energy to the substrate; photodissociation where bonds break; isomerization and cycloadditions such as [2+2] cycloadditions; and photocatalytic reactions enabling redox steps under light. The field also covers energy- or electron-transfer processes and the design of light-driven reaction networks.

Techniques used in fotokemi include actinometry for calibrating light sources, UV-Vis spectroscopy to monitor absorption, and time-resolved spectroscopic methods to study fast excited-state processes. Photoinitiation is widely used in polymerization and organic synthesis, including photoredox catalysis that enables selective bond formation under light. In environmental chemistry, photochemical reactions drive degradation of pollutants; in atmospheric chemistry, photochemistry governs the fate of many trace species. Applications span synthesis, materials science, energy conversion, and environmental remediation, with safety considerations for ultraviolet exposure requiring shielding and appropriate protection.