Tetraphenylethylene or naphthalimide-functionalized dendritic carbazole AIEgens: self-assembly visualization, three disparate force-triggered fluorescence responses, and advanced anticounterfeiting applications

Abstract

Three 1,8-naphthalimide-modified donor–π–acceptor-type and three tetraphenylethylene-functionalized fluorogenic dendritic carbazole derivatives are designed and synthesized. These six dendrimer-like carbazole-containing compounds are typical aggregation-induced emission (AIE) luminogens. Specially, the AIE-active 3CzB2Nap possessing trimeric carbazole and two 1,8-naphthalimide groups features aggregation-triggered self-assembly, and the visualization of its intriguing self-assembly process is successfully realized through scanning electron microscopy technology. Notably, three types of contrasting anisotropic mechanical force-induced fluorescence responses from the six prepared dendritic carbazole AIEgens are observed. More specifically, 7CzB2TPE and 3CzB2Nap do not exhibit fluorescence changes after grinding; 1CzB2TPE and 3CzB2TPE display irreversible mechanofluorochromic phenomena; 1CzB2Nap and 7CzB2Nap show reversible mechanofluorochromic characteristics. To deeply elucidate the three distinct types of force-responsive emissive features of the six dendritic AIEgens, powder and single-crystal X-ray diffraction, differential scanning calorimetry experiments, and theoretical simulation calculations of molecular packing structures before and after grinding are carried out. Based on the observed three disparate force-dependent fluorescence phenomena, two advanced information security systems involving multilevel painting anticounterfeiting and multimode information encryption are elaborately constructed.