A Solid‐State Fluorescent Material Based on Carbazole‐Containing Difluoroboron β‐Diketonate: Multiple Chromisms, the Self‐Assembly Behavior, and Optical Waveguides

A carbazole‐containing difluoroboron β‐diketonate complex ( BCZ ), which shows strong fluorescence in both the solid state and in organic solutions, is reported. The crystalline materials of BCZ obtained from different solvents display different emission colors. Single‐crystal analysis reveals that the enhanced overlap between adjacent molecules induces increased excited‐state delocalization and is responsible for the variation of the emission colors from yellow to red. The emission colors of the materials are effectively tuned by external stimuli such as grinding, heating, and solvent vapor. The powder X‐ray diffraction, differential scanning calorimetry, thermogravimetric analysis, and 1 H NMR studies on materials of BCZ reveal that the thermochromic properties of BCZ are closely related to the removal of solvent molecules from the crystalline powders upon heating. Moreover, uniform 1D microstructures of BCZ obtained by solvent exchange in solution exhibit optical waveguide property with low optical loss.