Fotochemi

Fotochemi, or photochemistry, is the branch of chemistry that studies chemical reactions initiated by light. It examines how photons interact with molecules to promote electronic excitation, leading to chemical transformations that can differ from those driven by heat alone. The field encompasses the fundamental steps of light absorption, the formation and evolution of excited states, and the pathways by which excited molecules return to the ground state or undergo chemical change.

Key concepts in fotochemi include absorption of light, creation of excited singlet and triplet states, and relaxation processes such as internal conversion and intersystem crossing. Photochemical reactions compete with thermal pathways, and the outcome is governed by quantum yield, wavelength of light, solvent effects, and the presence of quenchers or sensitizers. Common processes include photoisomerization (change of geometric arrangement), photocyclization, photodimerization, and photodissociation. Photosensitized reactions and energy or electron transfer from excited species expand the repertoire of possible transformations.

Techniques used in fotochemi range from actinometry, which measures light intensity, to various spectroscopic methods such as UV–Vis, fluorescence, and time-resolved spectroscopy. Experimental approaches often involve controlled light sources, inert or oxygenated environments, and specialized reactors to manage exposure and heat.

Applications span organic synthesis, polymerization and materials processing, photolithography and microfabrication, solar energy conversion and dye-sensitized devices, sensors, and photodynamic therapy. Fotochemi provides tools for building light-driven processes and for understanding fundamental light–matter interactions that underpin many natural and technological phenomena.