Term: quenching https://doi.org/10.1351/goldbook.Q05007 Definition: deactivation of an excited molecular entity intermolecularly by an external environmental influence (such as a quencher) or intramolecularly by a substituent through a non-radiative process. Notes: 0) When the external environmental influence (@Q05006@) interferes with the behaviour of the @E02257@ after its formation, the process is referred to as dynamic quenching. Common mechanisms include energy transfer, @E02011@, etc. 1) When the environmental influence inhibits the @E02257@ formation the process is referred to as static quenching. Related Terms: 1) quencher (http://doi.org/10.1351/goldbook.Q05006). 2) excited state (http://doi.org/10.1351/goldbook.E02257). 3) electron transfer (http://doi.org/10.1351/goldbook.E02011). 4) deactivation (http://doi.org/10.1351/goldbook.D01528). Source: PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 407 (https://doi.org/10.1351/pac200779030293) Citation: 'quenching' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.Q05007 License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.