A direct fluorescence-on chemo-sensor for selective recognition of Zn(II) by a lower rim 1,3-di-derivative of calix[4]arene possessing bis-{N-(2-hydroxynaphthyl-1-methylimine)} pendants

The bis-{N-(2-hydroxynaphthyl-1-methylimine)} anchored 1,3-di-derivative of lower rim p-tert-butyl-calix4]arene possessing a N₂O₂, N₂O₄ or N₂O₆ binding core was found to be selective for Zn(II) ions even at ?60 ppb by eliciting fluorescence-on behaviour while the other ions, viz., Ti⁴⁺, VO²⁺, Cr³⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Mg²⁺, Cd²⁺ and Hg²⁺ caused no change in the fluorescence. The reaction between 1 and Zn²⁺ was found to be stoichiometric with the formation of a 1:1 complex; while H⁺ quenched the fluorescence of the complex, OH⁻ restored it. The studies of the 1:1 isolated complexes of Zn²⁺, Ni²⁺ and Cu²⁺ augmented the results.