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

Abstract

Multi-stimulus responsive luminescent materials, as a type of smart materials, have gained considerable interests 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 exhibits multi-stimuli responsive PL behavior based on the structure of electron donor (D)-π-electron acceptor (A). Within this molecule, tetraphenylethylene (TPE) acts as the D group, 5-(4-pyridyl)-8-hydroxyquinoline plays the role of A moiety. HL not only can be applied as fluorescence sensor for Zn 2+ with a detection limit of 7.10 × 10 -8 M in aqueous media, but also exhibits reversible acidochromism and mechano-responsive luminescence (MRL) behaviors. The combined results of X-ray photoelectron spectroscopy, 1 H NMR and PXRD patterns demonstrate that the reversible acidochromism is ascribed to protonation/deprotonation of pyridine N atoms. DFT calculation results further manifested a decrease in the HOMO-LUMO energy gap upon protonation, which is responsible for the intensification and red shift in emission following acid vapor fumigation. Weak intermolecular interactions within HL crystals give rise to the facile interconversion between the crystalline and amorphous states, thereby leading to the MRL property. Moreover, a multi-level anti-counterfeiting strategy is developed on account of the photoresponsive behavior of HL to multiple stimuli.