Physical world and mathematics

Photocatalytic water splitting

Photocatalytic water splitting uses light-activated semiconductor catalysts to split water into hydrogen and oxygen, storing solar energy as fuel; the record efficiency is 9.2% under concentrated light, and commercialization is thought to require 10%.

Photocatalytic β-scission of alcohols

Photocatalytic β-scission of alcohols is a light-driven reaction in which an alcohol forms an alkoxy radical that cleaves a carbon–carbon bond, yielding a carbonyl compound and a carbon radical.

Photochemical alkene isomerization

Photochemical alkene isomerization is a photochemical process in which light changes a carbon–carbon double bond between E and Z configurations, chiefly to reach the less stable Z isomer.

Photochemical aziridination

Photochemical aziridination is the synthesis of aziridines, three-membered nitrogen-containing heterocycles, by light-driven generation of nitrenes that add to alkenes; a landmark 2016 method used visible light and an iridium photocatalyst.

Photochemical C–H functionalization

Photochemical C–H functionalization uses light-driven chemistry to convert carbon–hydrogen bonds directly into carbon–heteroatom or carbon–carbon bonds, typically via radical intermediates under mild conditions, enabling late-stage modification of drugs and natural products.

Photochemical C–H functionalization of peptides

Photochemical C–H functionalization of peptides is a set of light-driven methods that convert unreactive carbon–hydrogen bonds in peptides into new bonds, without pre-installed functional groups.

Photochemical carbene transfer

Photochemical carbene transfer is a family of metal-free organic reactions in which light generates a carbene from a diazo compound or diazirine, enabling cyclopropanation and C–H or X–H insertion.

Photochemical carboazidation

Photochemical carboazidation is a light-driven alkene difunctionalization reaction that installs a carbon group and an azido group across a carbon–carbon double bond, typically combining alkene, radical precursor, and azide source.

Photochemical fluoroalkylation

Photochemical fluoroalkylation uses light to attach fluoroalkyl groups such as CF₃ to organic molecules, typically through a fluoroalkyl radical; visible-light photocatalysis runs these reactions under mild conditions suited to late-stage drug modification.

Photochemical hydroamidation

Photochemical hydroamidation is the visible-light-driven addition of an amide N-H bond across an alkene, forming a C-N bond and saturated amide under mild conditions without stoichiometric oxidants.

Photochemical nitrogen deletion

Photochemical nitrogen deletion is a skeletal-editing reaction that uses light to remove a nitrogen atom from an organic molecule, forming a new carbon-carbon bond instead.

Photochemical oxidation

Photochemical oxidation is a chemical method that uses light absorbed by a photocatalyst to oxidize organic molecules, applied in selective synthesis and in degrading dyes, pharmaceuticals, and wastewater contaminants.

Photochemical oxidative cleavage

Photochemical oxidative cleavage is the light-driven breaking of an alkene's carbon–carbon double bond, with oxidation, to give carbonyl compounds such as aldehydes, ketones, and carboxylic acids.

Photochemistry

Photochemistry, also called the photochemical effect, is the branch of chemistry concerned with the chemical effects of light, covering reactions inaccessible under ordinary thermal conditions.

Photochromic lens

A photochromic lens is an eyeglass lens that stays clear indoors and darkens automatically in sunlight, blocking UV rays; plastic versions appeared in the 1980s.

Photochromism

Photochromism is the reversible transformation of a chemical species between two states with different absorption, typically colorless to colored under ultraviolet light, underlying self-darkening lenses, smart windows, and anti-counterfeiting inks.

Photoclick chemistry

Photoclick chemistry is a collection of click reactions initiated by light, first applied in 2008 to the tetrazole-alkene cycloaddition and used for protein labeling and bioimaging.

Photoconductivity

Photoconductivity is the increase in a material's electrical conductivity caused by absorbed light, which generates extra charge carriers; it was first observed in selenium in 1873.

Photocontrolled atom transfer radical polymerization

Photocontrolled atom transfer radical polymerization, or photoATRP, is a variant of atom transfer radical polymerization in which light regenerates the active catalyst, allowing polymerization to start and stop with illumination.

Photocurrent spectroscopy

Photocurrent spectroscopy measures the electric current generated in a material as a function of the wavelength of illuminating light, used to determine band gaps and defect states in semiconductors.

Photocycloaddition

Photocycloaddition is a cycloaddition reaction in which light rather than heat drives two unsaturated molecules into a ring, enabling thermally forbidden [2 + 2] alkene additions to cyclobutanes.

Photodarkening

Photodarkening is the pump-induced growth of excess optical loss in rare-earth-doped optical fibers, caused by color centers that degrade the power and efficiency of fiber lasers.

Photodegradable PEG hydrogel

A photodegradable PEG hydrogel is a biocompatible poly(ethylene glycol) hydrogel containing light-cleavable crosslinks, first reported in Science in 2009, that softens, releases molecules, or erodes under precisely controlled irradiation.

Photodesorption

Photodesorption is the release of molecules from an ice into the gas phase after absorption of ultraviolet or X-ray photons, important in cold interstellar regions.

Photodetachment

Photodetachment is the process in which a negative ion absorbs a photon and ejects its excess electron, leaving a neutral atom or molecule; the threshold photon energy equals the electron affinity.

Photodetector

A photodetector, also known as an optical detector or photosensor, is a device that converts absorbed light into a measurable electrical signal, responding directly to photons through photoexcitation rather than heating.

Photodiode

A photodiode is a semiconductor device, usually a p-n junction or PIN structure, that converts light into electric current via the internal photoelectric effect; avalanche photodiodes add carrier multiplication.

Photodiode array detection

Photodiode array detection (PDA), also called diode array detection (DAD), is an optical method using a linear photodiode array to record absorbance across many wavelengths simultaneously.

Photodisintegration

Photodisintegration, also called the photonuclear reaction, is a nuclear process in which a nucleus absorbs a high-energy photon and breaks apart, ejecting protons or neutrons.