A highly selective colorimetric chemosensor based on Salicylaldehyde Schiff base for Cu+2 and F− ions detection with a turn-off response for copper (II) ion: Experimental and theoretical studies

•Salicylaldehyde Schiff base containing pyridine-2-carboxamidine moiety was synthesized via convenient and simple method.•Detection of important copper ion was established using UV–visible spectroscopy as well as fluorescent “turn-off” mechanism.•The synthesized sensor was successfully used for the selective detection of fluoride ion in organic medium with the detection limit of 1.94 × 10−4 M.•The detection limits of Cu+2 were found to be 1.7 × 10−5 m and 6.6 × 10−6 m using the absorption spectral changes and fluorescence analysis, respectively.•The experimental results were supported by theoretical density functional theory studies. A salicylaldehyde-Schiff base ligand (SS) containing a pyridine-2-carboxamidine group was synthesized via a simple and convenient method to facilitate the highly selective colorimetric detection of Cu+2 and F− ions. Employing colorimetric, UV–visible, and fluorescence techniques, as well as 1H NMR titration experiments, we assessed the sensing capabilities of the synthesized sensor SS towards Cu+2 and F− ions. The developed sensor showed remarkable selectivity in the presence of competing ions, with a color transition from colorless to yellow and orange in the presence of Cu+2 and F− ions respectively. The detection limits for Cu+2 and F− ions were determined to be 1.7 × 10−5 M and 1.94×10−4 M, respectively, using UV-visible analysis. Notably, the fluorescence experiment displayed a significantly lower detection limit for Cu+2 ion, approximately 6.6 μM. Analysis of the spectroscopic data using Job's plot revealed a 1:2 binding stoichiometry between Cu+2 and SS, while 1:1 complex formation was observed between SS and F− ions. Density functional theory (DFT) calculations enabled us to explore the optimized structures, electronic properties, and binding mechanisms of the SS, SS-F− adduct, and SS-Cu+2 complexes. These computations revealed a reduction in the HOMO-LUMO energy gap for SS upon its interaction with fluoride and copper species, consistent with the experimental observations. [Display omitted]