A quinoline based Schiff base as a turn-on fluorescence chemosensor for selective and robust detection of Cd2+ ion in semi-aqueous medium

A new quinoline based Schiff base receptor L was designed and synthesized by reacting 2-hydroxy-1-naphthaldehyde with 2-hydrazino quinoline. The metal recognition ability of L was investigated with various cations by colorimetry, UV–vis absorption spectroscopic, and fluorescence spectroscopic techniques in ACN:H2O (8:2, v/v). The probe L exhibits a noticeable color change from colorless to crimson yellow under visible light and turn-on yellow fluorescence under UV light selective to Cd2+ over the other metal ions. Further, the L-Cd2+ complex shows new UV–Vis absorbance band at 440 nm and emission band at 510 nm upon the excitation at 380 nm. The ligand could form a 2:1 stoichiometry complex with Cd2+ and the calculated binding constant of 1.77 × 105 M−1 by BH plot method. Besides, the LOD and LOQ of Cd2+ by L was found to be 14.8 nM and 49.5 nM respectively. The sensing ability of L with Cd2+ was investigated by 1H NMR and density functional theory (DFT) calculation. Furthermore, the probe was successfully used for the quantification of Cd2+ in a different water sample.