Photochromism of single crystals composed of dioxazolylethene and dithiazolylethene

Although dioxazolylethene 1a did not show any photocoloration in the single crystalline phase, 1a displayed photochromism in the mixed crystal containing both 1a and dithiazolylethene 2a; the mixed crystal changed color from colorless to red, orange, and yellow upon irradiation with light of appropriate wavelengths.