Manipulating Dynamic Light‐Driven Solid‐Liquid Transition and Static Reversible Photochromism by an Organic Cocrystal Strategy

Abstract Developing of molecular crystalline materials with light‐induced multiple dynamic deformation in space dimension and photochromism on time scales has attracted much attention for its potential applications in actuators, sensoring and information storage. Nevertheless, organic crystals capable of both photoinduced dynamic effects and static color change are rare, particularly for multi‐component cocrystal system. In this study, we first report the construction of charge transfer cocrystal allows their light‐induced solid‐to‐liquid transition and photochromic behaviors to be controlled by trans‐stilbene (TSB) as an electron donor and 3,4,5,6‐tetrafluorophthalonitrile (TFP) as an electron acceptor. In this case, the dynamic photo‐responsive solid‐to‐liquid phase transition is due to the photoisomerization of TSB under UV light irradiation, while the accumulation of melted droplets during solid‐state photochemical process causes mechanical deformation of TSB‐TFP cocrystals. The subsequent reversible photochromic behavior is attributed to the emergence of free radicals through a photo‐induced electron transfer. Moreover, TSB‐TFP microcrystals present typical excitation wavelength dependent emission (EWDE) fluorescence by surfactant‐mediated method. This work realizes the dynamic‐static photochemical cascade processes in response to UV light irradiation in an organic cocrystal system, providing the effective method for a new type of smart photo‐responsive materials.