A highly selective and ratiometric fluorescent sensor for relay recognition of zinc(ii) and sulfide ions based on modulation of excited-state intramolecular proton transfer

Abstract

A new fluorescent 2-(2′-aminophenyl)benzimidazole derivatized sensor BMD was designed and synthesized. In CH₃CN/H₂O (2 : 8, v/v, HEPES 10 mM, pH 7.4) solution, sensor BMD displays two emission bands and exhibits a highly selective and ratiometric response to Zn²⁺ ions with a distinctly longer-wavelength emission blue shifted through the inhibition of the excited-state intramolecular proton transfer (ESIPT) process. BMD can clearly discriminate Zn²⁺ from Cd²⁺ and other metal ions. Moreover, the in situ generated BMD-Zn²⁺ solution exhibits a highly selective and ratiometric response to S²⁻ among various anions and thiol-containing amino acids via Zn²⁺ displacement approach, which results in a revival of the ESIPT phenomenon of free BMD. These results demonstrate that BMD can serve as a ratiometric sensor for sequential recognition of Zn²⁺ and S²⁻ in aqueous solution through inhibition and turn-on of ESIPT process.