Polymorphs of a diarylethene that exhibits strong emission and direct visualization of polymorphic phase transition process by fluorescence color change

Luminescent solid-state materials with high fluorescence quantum yield have attracted much attention in application to organic optoelectronics. In the course of study of photochromic diarylethene crystals, we found that two polymorphic forms of a diarylethene are obtained by recrystallization from acetone and n-hexane solutions. Surprisingly, both polymorphic crystals exhibited strong emission whose fluorescence quantum yield (>0.5) is much higher than that in n-hexane solution (0.017). Furthermore, the thermodynamic solid-state polymorphic phase transition was found and the process was directly visualized by a fluorescence color change.