A triple pH-responsive AIEgen: Synthesis, optical properties and applications

Abstract Stimuli-responsive luminogens with aggregation-induced emission (AIE) properties have attracted more and more attention for their intense emission in the aggregated state and tunable physicochemical performances. Nevertheless, it still remains challenging to design multifunctional AIE luminogens (AIEgens) with multi-responsive moieties and tunable fluorescence and morphologies. Here, a novel multifunctional AIEgen (DAS-BA) is elaborately designed based on the synergistic effect of twisted intramolecular charge-transfer (TICT), restriction of intramolecular motions (RIM), and excited-state intramolecular proton transfer (ESIPT). DAS-BA not only possesses triple pH-responsivenesses and long-wavelength emission, but also shows corresponding transition in its fluorescence and self-assembled morphologies. Under strong alkaline conditions, owing to the deprotonation of phenolic hydroxyl group, the red emission of DAS-BA is quenched and the molecular assemblies change from micro-rods to nano-rods. However, under weak acidic conditions, the red fluorescence dramatically shifts to yellow-green and the assemblies strikingly transform from micro-rods to nano-spheres due to the protonation of diethylamino moieties. Further acidification can hydrolyze the Schiff base, resulting in fluorescence quenching and destruction of the nano-spheres. Based on the reversible protonation process of diethylamino moiety, DAS-BA exhibits CO2-activated reversible fluorescence switching. Furthermore, DAS-BA has been successfully applied in anti-counterfeit and dual encryption, photo-patterning and molecular logic gates.