Chemo-selective onsite detection of copper ion by crown ether affixed benzothiazole derivatives corroborated with density functional theory

Abstract

A Crown ether and benzothiazole coupled ligands L1 (D-A) and L2 (A-D-A) have been synthesized and characterized through a standard analytical technique. A UV–visible spectrum-based colorimetric analysis has validated the cation-ligand binding affinity. Both L1 and L2 have shown high selectivity towards Cu2+ ion with the distinctive yellow colour from colourless solution without any interference with the competing metal ion, and it was found that the limit of detection for L1 is 5.48 × 10−6 M, and L2 is 8.57 × 10−7 M, also the binding constant for L1 is 6.4 × 101 M−1, and L2 is 3.5 × 102 M−1. The sensing mechanism was elucidated through job’s plot and computational studies where the stoichiometric ratio of 1:1 and 1:2 for L1 and L2 well coordinated with Cu2+ ions. The formation of bonds between the metal and ligand exhibited a reduced band gap compared to the free ligands, which evidenced metal mediated intra ligand charge transfer (ICT) process due to ligand–metal interaction. Test strips and water samples analysis was also performed to determine the efficacy of the probe's ability to detect copper ions in real-time samples. L1 and L2 act efficiently as a Cu2+ ion sensor for the naked eye and it is the work’s key accomplishment.