Dual Mode Ratiometric Analysis of Cu²⁺ and Ni²⁺ Ions at Physiological pH: Effect of Signalling Units on Analytical Efficacy

Abstract

Herein, we report the metal ion sensing property of two 2,2’‐bis(pyridylmethyl) amine‐based chromogenic probes at physiological pH in buffered media. The binding of metal ions to the bispicolyl site alters its electronic property, which subsequently influences the optical property of the covalently‐linked signaling unit. The compound experienced a change in the solution color from red to deep and light yellow respectively upon the addition of Cu2+ and Ni2+ ions. Further, it is observed that by modifying the signaling unit, one can tune the mode of metal ion binding and sensitivity. The compound with an electron‐deficient quinolinium unit as the signaling moiety, showed 2:1 stoichiometry of binding with metal ions, while the compound functionalized with a pyrene unit formed complexes with 1:1 stoichiometry. It was conferred that changes in the signaling moiety not only alter the basicity/ nucleophilicity of the pyridine nitrogen ends but also influence their aggregation properties. Such kind of studies will be beneficial for engineering new optical probes with tuneable sensitivity.