Photochromic process involving a one-photon mechanism.
In this case, the photoproduct B is formed from the singlet or from the
triplet state
of the thermodynamically-
stable molecular entity A.
Source:
PAC, 2007, 79, 293
(Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006))
on page 377