Smart Colorimetric Chemosensors for Multi‐Analyte Signaling: Recognition of Heavy Metal Ions in an Aqueous Medium and DFT Studies

A Schiff's base colorimetric chemosensors R1–R3 consist of carbohydrazide, and heterocyclic aldehydes have been designed and synthesized for sensing of heavy metal ions. Synthesized receptors were well characterized by various standard spectroscopic techniques. The receptor R1 exhibited multi‐ion selectivity for Cd2+, Hg2+, Pb2+, Cu2+ ions and showed lowest detection limit of 1.9 ppb, for Cd2+ & Hg2+ ions. The receptors R2 and R3 displayed dual ion selectivity (R2 for Hg2+, Cu2+, and R3 for Cu2+, AsO2– ions) in an aqueous medium at ppb levels. The UV–Vis and colorimetric studies confirmed the selectivity and sensitivity of chemosensors R1–R3 in the presence of other interfering metal ions. Further, using the B–H plot, FT‐IR, and mass analysis data, the binding modes, stoichiometric ratios of receptors R1–R3 with the metal ions were investigated. The estimated association constant values were found to be 104 to 105 M–1/M–2. The experimental results are well concordant with that of calculated theoretical DFT results. The receptors R1–R3 exhibited good sensitivity and selectivity compared to literature reports and successfully demonstrated for test strip applications. New receptors R1–R3 have developed for the heavy metal ions detection at trace levels. R1 displayed sensitivity at ppb levels for multi‐ions (Cd2+, Hg2+, Pb2+, Cu2+). The R2 and R3 displayed dual ion selectivity (i.e,. R2 for Cu2+, Hg2+ and R3 for Cu2+, AsO2– ions). The R1–R3 displayed good results in test strips/colorimetric application. The sensing mechanism was explained by experimental and theoretical studies. Among the reported receptors, R1 has a low detection limit of 1.9 ppb for Hg2+.