α-Cyanostilbene-based sensor with “AIE and ESIPT” features emitting long-wavelength intense red-fluorescence for highly selective and sensitive detection of Cu2+

Through Schiff base reaction of the salicylaldehyde-like α-cyanostilbene derivative with benzophenone hydrazone, a novel fluorophore has been successfully obtained in high yield of 89% and fully characterized by standard spectroscopic techniques. Depending upon the synchronic function of aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) mechanisms, this fluorophore emitted the fascinating red-fluorescence at 602 nm with a large Stokes' shift of 287 nm in aggregation state. This fluorophore as a sensor showed the highly selective and sensitive chelating ability towards Cu2+ in THF/water system (fw = 90%, pH = 7.4), which was confirmed by a prominent attenuation of red-fluorescence at 602 nm with the limit of detection (LOD) of 2.34 × 10-8 M due to the complexation of the sensor and Cu2+ with 2: 1 binding stoichiometry. The proposed recognition mechanism was supported by SEM images, HR-MS analysis, FT-IR and 1H NMR spectra. For applications, this sensor was successfully utilized to determine Cu2+ in environmental water samples. The silica gel test strip impregnated with this fluorophore was also employed for the on-site monitoring of Cu2+ under UV365nm illumination, indicating its potential utility for visual detection of Cu2+ in solid state. Hence, this work provided a feasible strategy to construct long-wavelength intense fluorescence sensor for effective measurement of Cu2+ level in aggregation state as well as visual detection of Cu2+ in solid state.