Polymorphism-dependent and piezochromic luminescence based on molecular packing of a conjugated molecule

Different luminescent single crystals of 2-(anthracen-9-yl)-4,5-diphenyl-1H-imidazole (ADPI) were obtained through the construction of different stacking modes with the aid of intermolecular interactions. Both the fluorescence and the stacking mode of the crystals can be reversibly tuned by mechanical and thermal forces to render ADPI piezochromic, which represents a unique example of reversibly controlled solid emission. The regulation of pi-pi stacking between the anthracene planes by mechanical and thermal forces is suggested to be the main driving force for the piezochromic character of ADPI.