α-Cyanostilbene Containing -NH ₂ Unit: Facile Preparation, Characterization, Solvatochromism, Acidichromism, Water Detection in Hygroscopic Organic Solvents

α-Cyanostilbene, as a key Aggregation-Induced Emission (AIE) fluorophore, has garnered considerable attention in the fields of biology, chemistry, and materials science for diverse applications. Herein, α-cyanostilbene luminogen with π-electron acceptor-π-electron donor (π-A-π-D) architecture was easily synthesized in a high yield of 86% via Knoevenagel condensation of 4- aminophenylacetonitrile and benzaldehyde in the presence of NaOH. The relationship between the structure and photophysical properties was studied via spectroscopic analysis and Density Functional Theory (DFT) calculations. Interestingly, it demonstrated the solvatochromism in the solution state. With an increasing polarity of the solvent, the Stokes shift was increased, and a significant change in fluorescence from blue to green was observed; however the fluorescence emission intensity decayed due to the Twisted Intramolecular Charge Transfer (TICT) effect. Moreover, it expressed solid green fluorescence and underwent noticeable acidichromism. The periodic HCl/NH<sub>3</sub> vapor stimulated changes in fluorescence from green to faint yellow, suggesting that it could be utilized for reusable encryption technology. Furthermore, it displayed apparent fluorescence quenching upon the addition of different amounts of water in hygroscopic organic solvents. The Limits Of Detection (LODs) of it in THF, MeCN, EtOH, and DMF for water detection were 0.0023%, 0.0018%, 0.0015%, and 0.003%, respectively.