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 ratio that undergo molecular packing transformation from amorphous phase to crystalline by scratching is firstly reported. Three 2-aminobenzophenone derivatives 1, 2 and 3, which possess crystallization-induced fluorescence (CIF) characteristics, exhibited bright cyan, blue and green fluorescence colors with “off-on” contrast ratio as high as 175 fold by scratching. The scratching induced transformation from amorphous phase to crystalline of 1, 2 and 3 were directly observed by XRD and SEM studies. In addition, the fluorescence of the scratched sample can readily convert back into the initial non-fluorescent state by fuming in ethanol. Letters with three fluorescence emission colors of 1, 2 and 3 in 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.