Photoinduced Single-Crystal to Single-Crystal Transformation via Conformational Change with Turn-On Fluorescence

Single-crystal to single-crystal (SCSC) transformation by phototrigger is presently attracting immense research interest in many fields such as sensors, actuators, artificial muscles, soft robotics, and energy harvesting. However, the only success of rare examples has been achieved by SCSC transformation so far, involving a change in molecular composition based on photocyclization reactions. Here, we show photoinduced SCSC transformation of 3-methylene-2-(quinolin-8-yl) isoindolin-1-one (MQIO) derivatives from monoclinic to triclinic phase via conformational change, just as “small input and big output”. UV light induces a molecular conformation change of MQIO-H with rotation (11.3°) of the carbon–nitrogen single bond. The conformational changes of MQIO-H lead to the slides of molecular packing in crystals, finally resulting in the SCSC transformation from the monoclinic to the triclinic phase. In addition, the SCSC transformation was accompanied by turn-on fluorescence and shape changes of single crystal. The shape changes of single crystals can be clearly observed by UV light triggering under an optical microscope. This work provides a strategy to achieve SCSC transformation via photoinduction.