An NBD-based two-in-one Cu2+/Ni2+ chemosensor with differential charge transfer processes

Abstract

A new multifunctional NBD-based probe has been developed having high sensitivity and selectivity towards Cu²⁺/Ni²⁺ over other metal ions over a wide pH range. The probe 1 could be used for the simultaneous estimation of Cu²⁺ and Ni²⁺ ions through its visible color change from yellow to blue and light green, respectively, in semi-aqueous systems. The binding mode of probe 1 to Cu²⁺ and Ni²⁺ was determined to be a 1 : 1 complexation stoichiometry using a Job's plot. Ethylenediamine tetraacetate showed high selectivity towards the in situ prepared Cu²⁺ complex over the Ni²⁺ complex, which is applied to distinguish Ni²⁺ and Cu²⁺ ions. The detection limits for Cu²⁺ and Ni²⁺ ions, 1.8 × 10⁻⁷ M and 1.1 × 10⁻⁶ M, respectively, were lower than those recommended by the WHO guidelines for drinking water. Moreover, probe 1 could be used as a practical, visible colorimetric test kit for Cu²⁺ ions. The sensing mechanism of Cu²⁺ and Ni²⁺ ions was supported by DFT-calculations.