Multiplicity-driven photochromism controls three-state fulgimide photoswitches.

Fulgimide photoswitches display three-state photoswitching between isomeric forms Z, E and C. Fulgimides have therefore access to both large steric change of double bond isomerization and the large spectral change induced by electrocyclization. By controlling the multiplicity and photoisomerization conditions, we achieved precise and near-quantitative control over both isomerization modes.