A Carbazole Acrylonitrile Substituted Turn-On Fluorescence Chemosensors for Cyanide Ion and its Application to Real...

An efficient probe (E)-2-(benzo[d]thiazol-2-yl)-3-(9-ethyl-9 H-carbazol-3-yl)acrylonitrile (CZ-BTZ) for selective fluorescence "turn-on" response with cyanide (CN^-) ion sensor was developed by simple Knoevenagel condensation of 9-ethyl-9 H carbazole-3-carbaldehyde with 2-(benzo[d]thiazol-2-yl) acetonitrile. The sensing ability of probe CZ-BTZ was tested with different inorganic anions through spectrophotometric and spectrofluorimetric methods. The UV-vis and fluorescence spectral studies show the formation of a new adduct between CZ-BTZ and CN^- by appearing with a new absorbance band at 350 nm and "turn-on" fluorescence at 535 nm in CH₃CN: H₂O (8:2, v/v, pH 7.2). The absorbance and fluorescence study reveals the formation of 1:1 (CZ-BTZ: CN^-) stoichiometry adducts with an estimated association constant of 2.04 × 10⁵ M^-1. The probe CZ-BTZ could detect CN^- down to 4.19 nM without much interference, much lower than the WHO limit (1.9 µM) in drinking water. The sensing mechanism of CZ-BTZ with CN^- ions was studied using FTIR, ESI mass analysis, and DFT calculation. Further, the probe was applied to analyse CN^- ions' real-time food sample analysis.