Since the cyanide ion is used in a wide range of industries and is harmful to both human health and the environment, a number of research efforts are dedicated to creating fluorescence sensors for the detection of cyanide (CN−). Herein, for the fluorescence detection of CN−, a new highly selective and sensitive sensor 2-(3-(benzo[d]thiazol-2-yl)-4-hydroxybenzylidene)-1H-indene-1,3(2H)-dione (BID) was created by conjugating a benzothiazole moiety with 1H-indene-1,3(2H)-dione. The donor and acceptor components of this hybrid receptor were covalently connected through a double bond. The nucleophilic addition of a cyanide anion to the BID inhibits the intramolecular charge transfer (ICT) transition, resulting in spectral and colour alterations in the receptor. When the solvent polarity was increased from n-hexane to methanol, this molecule exhibited a bathochromic shift in the emission wavelength (610 to 632 nm), suggesting the presence of a solvatochromic action. The sensor BID has shown strong specificity towards CN− by interrupting its internal charge transfer (ICT), resulting in a significant change in the UV-vis spectrum and a notable blue shift in the fluorescence emission spectrum. The cyanide anion (CN−) is responsible for the optical alterations observed by BID, as opposed to the other anions examined. The detection limit was 5.97 nM, significantly less than the WHO's permitted amount of CN− in drinking water. The experimental findings indicate that BID's fluorescence response to CN− is pH insensitive throughout a wide pH range of 6.0 to 12.0. The interaction mechanism between the BID and CN− ions has been studied by HRMS, 1H-NMR titration experiments, FT-IR, and DFT, which confirmed the nucleophilic addition of CN− on vinylidene and subsequent disturbance of ICT. Additionally, we demonstrated the real-time detection application of CN− in environmental water samples and live-cell imaging.
