Title: Kasha rule
Long Title: IUPAC Gold Book - Kasha rule
DOI: 10.1351/goldbook.K03370
Status: current

Definition
Polyatomic molecular entities luminesce with appreciable yield only from the lowest excited state of a given multiplicity. There are exceptions to this rule.

Note
The concept has been extended to the reaction of excited species, i.e., polyatomic molecular entities react with appreciable yield only from the lowest excited state of a given multiplicity.

Related Terms
- excited state: https://goldbook.iupac.org//terms/view/E02257
- molecular entities: https://goldbook.iupac.org//terms/view/M03986

Source
- PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 360 (https://doi.org/10.1351/pac200779030293)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/K03370/html
- json: https://goldbook.iupac.org/terms/view/K03370/json
- xml: https://goldbook.iupac.org/terms/view/K03370/xml

Citation: Citation: 'Kasha rule' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.K03370
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Accessed: 2026-04-19T05:41:37+00:00