Photoreversible interference color modulation to multicolor in photochromic molecular crystals

Abstract

Functional molecular crystals responsive to external stimuli represent a new frontier for material chemistry and crystal engineering. Here, we report on the photoreversible interference color change in single crystals composed of a photochromic diarylethene derivative, 1,2-bis(2-ethyl-5-phenyl-3-thienyl)-perfluorocyclopentene (1a). When crystal 1a was observed by rotating the sample stage at 45° from the extinction position under crossed Nicols, it showed an interference color. Upon irradiation with ultraviolet (UV) light, the interference color changed dramatically and instantaneously in response to photo-irradiation due to the photocyclization reaction from the open-ring form to the closed-ring form. The change was quite sensitive to the photochromic reaction. It is attributable to the large decrease in retardation induced by the photocyclization reaction in crystals. These results might provide new opportunities for application of photochromic crystals.