4-Arylethynyl-5-fluorobenzoyl-1-methylimidazole Exhibiting Self-Recovering Mechanofluorochromism and Forming Fluorescence Molecular Glass

4-Arylethynyl-5-fluorobenzoyl-1-methyl-1H-imidazoles exhibited self-recovering mechanofluorochromism and formed a glass state. Although the solid sample of the anisyl-substituted 1a and dimethoxyphenyl-substituted 1b exhibited no and blue fluorescence, respectively, they exhibited bluish-green fluorescence after grinding. These compounds recovered the color of their fluorescence after approximately 20 s and after 20 h, respectively. Both compounds exhibited non-crystalline samples after melting and rapid cooling to room temperature. Based on thermal analysis, it was found 1a and 1b were supercooling liquid and glass, respectively, at room temperature. Both non-crystalline samples exhibited fluorescence at a wavelength longer than that of the solid state. DFT calculations indicated that the bluish-green fluorescence of the ground and non-crystalline samples was derived from the twisted intramolecular charge transfer excitation state.