Crystalline solid responsive to mechanical and acidic stimuli: Boron–fluorine derivative with TICT characteristic

Abstract Mechanochromism is found for a novel Boron-fluorine derivative bearing dimethylamino moieties (BOPIM-dma). The title compound shows weak or no fluorescence in organic solvents due to twisted intramolecular charge transfer (TICT), which induces energy lost via non-irradiation decay. However, intense fluorescence was observed in crystalline solid, obtained by recrystallization from organic solvents. Grinding the polycrystals of BOPIM-dma into amorphous solid induces red-shift of absorption and fluorescence quenching, which could be recovered by recrystallization. Moreover, the absorption and fluorescence of the crystalline solid could also be reversibly tuned by acidic and basic vapor.