Benzimidazole-based optical probe for selective detection of multiple-cations via dual-channel analysis

A benzimidazole-based optical probe having pendant carboxyl, amine, and imine groups as ionophore has been prepared for screening various metal ions. The 4-(1H-benzod]imidazol-2-yl)-1H-imidazole-5-carboxylic acid (1) has been obtained in good yield and characterized by full battery of complementary physico-chemical techniques including ¹H NMR, UV-Vis, fluorescence spectroscopy, and single crystal X-ray crystallography. Metal ion-binding properties of 1 have been studied using ppm level concentration of representative alkali metal (Na⁺, K⁺), alkaline earth metal (Mg²⁺, Ca²⁺), and transition metal (Zn²⁺, Co²⁺, Fe³⁺, Cd²⁺, Hg²⁺, Pb²⁺, Cu²⁺, Ag⁺) ions and the output signal was monitored via two different channels viz chromogenically and fluorogenically. Selective recognition of Hg²⁺ has been explored with absorption spectra whereas emission spectra of 1 display differential response for multiple cations at parts-per-million (ppm) level concentration that allow selective detection of Ca²⁺, Mg²⁺, and Na⁺ ions. The results have been discussed in light of selectivity, sensitivity, response time, mode of binding/interactions, and sensing properties.