Crystal Engineering-Driven Sunlight Responsiveness and Flexible Waveguide Transmission.

Here, a barbituric acid derivative containing pyrene rings () was successfully synthesized, and two types of crystals were prepared by using crystal engineering methods. Orange sheet-like crystals (, observed in visible light), prepared in a DCM/CHOH solution, exhibited brittleness and weak fluorescence emission, along with sunlight-induced bending and fracturing. Red needle-like crystals (, also observed in visible light), synthesized in a DCM/CHCN solution, demonstrated elastic properties, strong fluorescence emission, and excellent optical waveguide performance (with an optical loss coefficient of 0.23-0.30 dB mm). Single-crystal data analysis revealed that the stacking arrangement of molecules critically influenced the elasticity of the crystals, while the reaction cavity size regulated the photomechanical properties of the crystals. This study achieved effective control over sunlight responsiveness and flexible optical waveguide transmission for the first time, providing innovative insights for the application of homogeneous organic polycrystalline molecular crystals in this field.