Stimuli-responsive Enaminitrile Molecular Switches as Tunable AIEgens Covering the Chromaticity Space 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 emission 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. Single-crystal X-ray diffraction measurements and DFT calculations suggested a luminescence mechanism based on restriction of intramolecular rotation and an intramolecular charge transfer effect in the AIE luminogens.