Multi-responsive smart fluorophores from pyrazole-functionalized tetraphenylethene AIEgens in response to Hg(II) ion, temperature, and mechanical force

Five tetraphenylethene (TPE) derivatives 1a, 1b, 2, 3, and 4 with adjustable stimuli-responsive characteristics were designed and synthesized in this study. Using single-crystal X-ray diffraction, the effects of substitution positions and pyrazolyl numbers on molecular packing were examined in the solid state. The findings indicate that as the pyrazolyl numbers increased, the molecular packing of the compound progressively changed from the C−H···π stacked compact mode in 1 − 3 to the X-crossing stacked loose mode in 4, which results in the origin of various stimuli-responsive phenomena in compound 4. This approach facilitates the preparation of multi-stimuli-responsive (thermochromism, mechanochromism, and metal ion fluorescence switch) smart fluorophores with tunable emission color. Moreover, compound 4, with an excellent fluorescence performance, exhibited three different colors when reversible mechanochromism was selected as the candidate for an optical recording material and security ink. This study proposes an effective method to guide the design of stimuli-responsive materials, which, in turn, would facilitate the development of high-contrast MC molecules, and the optical information anticounterfeiting based on grinding was proven by utilizing the grind-responsive luminescence capabilities.