A phthalazine-based two-in-one chromogenic receptor for detecting Co²⁺ and Cu²⁺ in an aqueous environment

A new multifunctional and highly selective chemosensor 1 for Co²⁺ and Cu²⁺ was designed and synthesized. 1 could simultaneously detect both Co²⁺ and Cu²⁺ by changing its color from pale yellow to pink and to orange in a near-perfect aqueous solution. The binding modes of 1 to Co²⁺ and Cu²⁺ were determined to be a 2 : 1 complexation stoichiometry through Job's plot, ESI-mass spectrometry analysis and ¹H NMR titration. The detection limits (1.5 and 2.1 μM) of 1 for Co²⁺ and Cu²⁺ were lower than the DEP guidelines (1.7 μM for Co²⁺) and the WHO guidelines (31.5 μM for Cu²⁺) for drinking water. The chemosensor 1 could be used to quantify Co²⁺ and Cu²⁺ in water samples. Moreover, 1 could be used as a practical, visible colorimetric test kit for both Co²⁺ and Cu²⁺. The sensing mechanisms of Co²⁺ and Cu²⁺ by 1 were supported by theoretical calculations.