Stimuli-responsive enaminitrile molecular switches as tunable AIEgens covering the chromaticity space, operating out-of-equilibrium, and acting as vapor sensors

A family of responsive enaminitrile molecular switches showing tunable turn-on fluorescence upon switching and aggregation is reported. When activated by the addition of acid/base, isomerization around the C═C bond could be effectuated, resulting in complete and reversible switching to the E- or Z-isomers. Typical aggregation-induced emission (AIE) could be recorded for one specific state of the different switches. By subtle tailoring of the parent structure, a series of compounds with emissions covering almost the full visible color range were obtained. The switchable AIE features of the enaminitrile structures enabled their demonstration as solid-state chemosensors to detect acidic and basic vapors, where the emission displayed an “off-on-off” effect. Furthermore, switching to the Z-configuration could be driven out-of-equilibrium through transient changes in acidity while giving rise to fluorescence. Single-crystal X-ray diffraction measurements suggested a luminescence mechanism based on restriction of intramolecular rotation and an intramolecular charge transfer effect in the AIE luminogens.