Distinctive Photomechanical Shape Change of <i>p</i>‐Phenylenediacrylic Acid Dimethyl Ester Single Crystals Induced by a Spatially Heterogeneous Photoreaction

Understanding photoreaction dynamics in crystals is important for predicting the dynamic property changes accompanying these photoreactions. In this work, we investigate the photoreaction dynamics of p-phenylenediacrylic acid dimethyl ester (p-PDAMe) in single crystals that show reaction front propagation, in which the photoreaction proceeds heterogeneously from the edge to the center of the crystal. Moreover, we find that p-PDAMe single crystals exhibit a distinctive crystal shape change from a parallelogram to a distorted shape resembling a fluttering flag, then to a rectangle as the photoreaction proceeds. Density functional theory calculations predict the crystal structure after the photoreaction, providing a reasonable explanation of the distinctive crystal shape change that results from the spatially heterogeneous photoreaction. These results prove that the spatially heterogeneous photoreaction dynamics have the ability to induce novel crystal shape changes beyond what would be expected based on the equilibrium reactant and product crystal shapes.