Selective fluorometric detection of F− and Zn(ii) ions by a N, O coordinating sensor and naked eye detection of Cu(ii) ions in mixed-aqueous solution

Abstract

Through click chemistry, salicylaldehyde and fluorene groups have been explored to recognize anions through O–H⋯A– hydrogen-bonding complexation followed by an ESIPT mechanism and cation sensing via CHEF and CHEQ mechanisms for Zn²⁺ and Cu²⁺ metal ions respectively. Herein, we demonstrate evidence of the interactions between the O–H bond and F⁻ which were studied by fluorescence spectroscopic, UV-Vis spectroscopic, lifetime spectroscopic, ¹H NMR spectroscopic titrations and theoretical treatment. This sensor could simultaneously detect two biologically important metal ions (Cu²⁺ and Zn²⁺) through colorimetric methods in mixed aqueous solution. The 2 : 1 binding stoichiometry ratio of the ligand and metal in the complexes was established by UV-Vis, fluorescence, ¹H NMR and ESI-MS spectroscopy, and their corresponding association constants, K_assoc observed at 8.13 × 10⁴ and 5.12 × 10⁶ M⁻¹ corresponds to Zn²⁺ and Cu²⁺ metal ions in aqueous buffer–CH₃OH (2 : 1, v/v) at pH 7.2. In addition, the electronic structures and photo physical properties of the ligand and complexes were calculated by DFT and time-dependent DFT (TDDFT) methods.