A highly sensitive pyridine-dicarbohydrazide based chemosensor for colorimetric recognition of Cu2+, AMP2-, F- and AcO- ions

A new pyridine-dicarbohydrazide based colorimetric chemosensor L1 is designed and synthesized for the detection of anions and cations. The chemosensor allows the naked-eye' recognition of toxic cation Cu2+ and biologically relevant anions AMP(2-), F- and AcO- in DMSO/H2O (8/2, v/v) solution with a fast response time (approximate to 5 s). The selectivity, sensitivity and binding stoichiometry of L1 for the aforementioned ions are investigated using colorimetric, UV-Vis spectroscopic and H-1 NMR studies. The binding mode is analyzed by UV-Vis and H-1 NMR studies, which are supported by density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. The optimized geometries indicate that the carbohydrazide moiety provides the binding site for the cation and anions. The HOMO-LUMO energy gap for the complex of AMP(2-) with L1 is least among all the complexes, possibly due to the charge-transfer effect. The detection limits of L1 for Cu2+ and AMP(2-) were determined to be 0.12 M and 0.08 M, respectively. Furthermore, the potential application of the sensor for the detection of fluoride ion in commercially available toothpaste was demonstrated successfully.