Special form of photochromism in which one or both forms of a photochromic system are transformed reversibly, either chemically or electrochemically, into a non-photochromic form.
Source:
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 347 (https://doi.org/10.1351/pac200779030293)