A benzimidazole-derived fluorescent chemosensor for Cu(ii)-selective turn-off and Zn(ii)-selective ratiometric turn-on detection in aqueous solutions

Abstract

A 2,6-dibenzoimidazolyl-4-methoxyphenol conjugate (BBMP) was designed and synthesized to develop a novel fluorescent chemosensor for Cu²⁺ and Zn²⁺. The as-fabricated BBMP showed an excited-state intramolecular proton-transfer (ESIPT) fluorescence emission at 542 nm that was selectively and efficiently quenched by Cu²⁺ in a Tris-HCl solution (70% THF, pH = 7.4) due to the inhibition of ESIPT upon binding to metal ions. In contrast, the addition of Zn²⁺ not only resulted in a substantial decline in the original ESIPT fluorescence of BBMP but was also accompanied by the appearance of a new blue fluorescence emission at 462 nm. This indicated the potential for the present BBMP as a novel fluorescent probe for Cu²⁺ (turn-off) and Zn²⁺ (ratiometric turn-on) detection in aqueous solutions. The linear range and detection limit were found to be 0–5 μM and 0.16 μM for Cu²⁺, as well as 0–10 μM and 0.1 μM for Zn²⁺, respectively. A 2 : 1/1 : 1 coordination mode between BBMP and Cu²⁺/Zn²⁺ was confirmed by Job plots and mass analysis. Potential practical applications were also demonstrated by the analysis of real water samples and living cell imaging.