Photoinduced Bending and Curling Motions in Molecular Microcrystals of Naphthyl Meldrum’s Acid Derivative Based on E-to-Z Photoisomerization

Dynamic photoresponsive molecular crystals are promising candidates for making intelligent devices and materials in the future. Here, we synthesized a new photoactive molecule (E)-2,2-dimethyl-5-[3-(naphthalen-1-yl)allylide]-1,3-dioxane-4,6-dione [(E)-DNADD] that undergoes an E-to-Z photoisomerization in both liquid solution and solids when exposed to visible light (405 nm). Compared to the bulk crystals, the photoresponsive behavior in microcrystals was profoundly improved. Highly crystalline (E)-DNADD microplate crystals exhibit robust motions, including bending, curling, and coiling under light irradiation. The photoproduct conversion of the photochemical reaction in the microplate is no more than 20%, while the large bending curvature of the coiled illuminated samples was estimated at approximately 150–300 mm⁻¹, comparable to some photoactive nanowires. Our results indicate that shrinking crystal dimensions can boost the photoresponses in molecular crystals and provide a facile strategy for developing dynamic molecular crystals at the microscopic scale.