All articles starting with P

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.

Photocopier

A photocopier, also called a copy machine or Xerox machine, is an office machine that makes paper copies of documents, most commonly by the dry electrostatic xerography process.

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.

Photodissociation

Photodissociation, also known as photolysis, is the breaking of a chemical bond in a molecule caused by absorbing a photon, producing fragments; it governs molecular destruction in interstellar clouds and underpins atmospheric ozone chemistry.

Photodissociation mass spectrometry

Photodissociation mass spectrometry fragments gas-phase ions with laser light, typically ultraviolet, and detects the product ions, yielding rich fragmentation patterns and selective bond cleavage for structural analysis.

Photodissociation region

A photodissociation region, also called a photon-dominated region, is neutral interstellar gas whose heating and chemistry are controlled by far-ultraviolet photons from massive stars at cloud boundaries.

Photodynamic therapy

Photodynamic therapy is a treatment in which a photosensitizing drug activated by light and oxygen generates reactive oxygen species that destroy target cells, with FDA approval for several cancers.

Photoelasticity

Photoelasticity, or the photoelastic effect, is a non-destructive experimental optical method that visualizes stress in transparent materials as fringes via stress-induced birefringence under polarized light.

Photoelectric effect

The photoelectric effect, also called photoelectric emission or the Hertz effect, is the emission of electrons from a material under high-frequency light; Einstein's 1905 explanation helped found quantum theory.

Photoelectrocatalysis

Photoelectrocatalysis (PEC) is a water-treatment method combining photocatalysis with electrochemistry, in which an applied bias separates charge on a semiconductor photoelectrode to degrade organic pollutants.