Mechanoresponsive Fluorescence of 2-Aminobenzophenone Derivatives Based on Amorphous Phase to Crystalline Transformation with High “Off–On” Contrast Ratio

In this paper, mechanoresponsive fluorescent molecules with high “off–on” contrast ratios that undergo molecular packing transformation from amorphous phase to crystalline by scratching are first reported. Three 2-aminobenzophenone derivatives 1, 2, and 3, which possess crystallization-induced fluorescence characteristics, exhibited bright cyan, blue, and green fluorescence colors with “off–on” contrast ratios as high as 175-fold by scratching. The scratching induced transformation from amorphous phase to crystalline of 1, 2, and 3were directly observed by XRD and SEM studies. In addition, the fluorescence of the scratched sample can readily convert back into the initial nonfluorescent state by fuming in ethanol or heating. Letters with three fluorescence emission colors of 1, 2, and 3in ethanol solution smeared on a glass surface can be easily written by scratching and erased by fumigation, demonstrating the potential value as reversible mechanoresponsive fluorescent materials.