Visual light photoswitches derived from bindone: Toward stabilization of colored photo-isomers

Condensation of bindone and cinnamaldehydes afforded five cyclic products instead of the expected merocyanines. The structures of all products were confirmed by the X-ray data. In solution, the weakly colored cyclic isomers form deeply colored (orange to red shades) open isomers upon irradiation in the UV and visible range (up to 530 nm). The colored isomers are very stable and undergo thermal discoloration with the half-life times between 13 h and 128 h, depending on the substituent and solvent at room temperature. Heating their solutions above 130 °C gives rise to rapid discoloration. High fatigue resistance was demonstrated by repeating the irradiation/heating cycles.