D–π–A-type tetraphenylethylene-based AIEgen: multi-stimuli-responsive behavior and multilevel anti-counterfeiting applications

Abstract

Multi-stimuli-responsive luminescent materials, as a type of smart materials, have gained considerable research interest in numerous fields, including optical sensing, anti-counterfeiting and information storage. Herein, a novel AIE-active molecule, (E)-5-(pyridin-4-yl)-2-(4-(1,2,2-triphenylvinyl)styryl)quinolin-8-ol (HL), is synthesized and shown to exhibit multi-stimuli-responsive PL behavior based on its electron donor (D)–π–electron acceptor (A) structure. Within this molecule, tetraphenylethylene (TPE) acts as the D group and 5-(4-pyridyl)-8-hydroxyquinoline acts as the A moiety. HL can not only be applied as a fluorescence sensor for Zn²⁺ with a detection limit of 7.10 × 10⁻⁸ M in aqueous media but also exhibit reversible acidochromism and mechano-responsive luminescence (MRL) behaviors. The combined results of X-ray photoelectron spectroscopy, ¹H NMR spectroscopy and PXRD demonstrate that its reversible acidochromism is ascribed to the protonation/deprotonation of its pyridine N atoms. DFT calculation results further manifest a decrease in its HOMO–LUMO energy gap upon protonation, which is responsible for the intensification and red shift in its emission following acid vapor fumigation. The weak intermolecular interactions within HL crystals give rise to the facile interconversion between crystalline and amorphous states, thereby leading to its MRL property. Moreover, a multi-level anti-counterfeiting strategy is developed on account of the photoresponsive behavior of HL to multiple stimuli.