Special form of @P04589-1@ in which one or both forms of a @P04589-2@ 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 [Terms] [Paper]