Photochemistry

Photochemistry studies chemical reactions initiated when molecules absorb light. It connects the energy and wavelength of absorbed photons to changes in molecular structure and chemical composition.

Photophysical processes: Molecular events after light absorption that do not produce a lasting chemical change. These competing pathways can return an excited molecule to its original state before it reacts.
Photon: A quantum of electromagnetic radiation that carries energy and momentum. Its energy sets which molecular transitions can be initiated by light.
Photoredox catalysis: Catalysis in which light-excited catalysts transfer single electrons to or from substrates. It uses excited-state redox power to construct molecules under mild conditions.
Haber–Weiss reaction: A reaction involving superoxide and hydrogen peroxide that can generate hydroxyl radicals. Photochemical routes can generate the reactive oxygen species involved in this chemistry.
Solar water splitting: The use of sunlight to drive water oxidation and reduction into oxygen and hydrogen. Making this conversion efficient and durable remains a major challenge in light-driven chemistry.
Jablonski diagram: A diagram of electronic states and radiative or nonradiative transitions in a molecule. It maps the excited-state pathways that precede or compete with chemical reactions.
Absorption spectroscopy: The measurement of how a substance absorbs radiation across wavelengths. Absorption spectra identify the wavelengths capable of exciting a molecule.
Photopolymerization: Polymer formation initiated or controlled by light-induced chemical reactions. Light can trigger polymer growth precisely in selected regions and at selected times.
Norrish reaction: A family of light-induced reactions of carbonyl compounds involving bond cleavage or rearrangement. Its named pathways show how excited carbonyl states produce distinct products.
Singlet fission: A process in which one excited singlet state produces two lower-energy triplet excitations. Its use in solar-energy conversion depends on controlling competing excited-state pathways.

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