Multistimuli-Responsive Enaminitrile Molecular Switches Displaying H⁺-Induced Aggregate Emission, Metal Ion-Induced Turn-On Fluorescence, and Organogelation Properties

Abstract

Multistimuli-responsive enaminitrile-based configurational switches displaying aggregation-induced emission (AIE), fluorescence turn-on effects, and supergelation properties are presented. The E-isomers dominated (>97%) in neutral/basic solution, and the structures underwent precisely controlled switching around the enamine C═C bond upon addition of acid/base. Specific fluorescence output was observed in response to different external input in the solution and solid states. In response to H⁺, configurational switching resulted in complete formation of the nonemissive Z-H⁺-isomers in solution, however displaying deep-blue to blue fluorescence (Φ_F up to 0.41) in the solid state. In response to Cu^II in the solution state, the E-isomers exhibited intense, turn-on, blue-green fluorescence, which could be turned off by addition of competitive coordination. The acid/base-activated switching, together with the induced AIE-effects, further enabled the accomplishment of a responsive superorganogelator. In nonpolar solvents, a blue-fluorescent supramolecular gel was formed upon addition of acid to the E-isomer suspension. The gelation could be reversed by addition of base, and the overall, reversible process could be repeated at least five cycles.