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.