Amide/urea-based simple fluorometric receptors for iodide and Hg2+ ions in aqueous medium: Aggregation induced emission and DFT studies

Abstract

Herein, we report pyrene-tagged amide and urea-basedsugar derivatives 1and2in a simple synthetic pathway to recognize I− and Hg2+ ions. Both molecules showed absorbance and fluorescence selectivity towards iodide ions in THF/H2O (7/3, v/v) medium. The selectivity and sensitivity of2 for iodide ions are superior to 1due to more H-bond donors in2. Interestingly, fluorometric receptor2exhibited aggregation-induced emission (AIE) at higher pH with a remarkable fluorometric color change. The AIE phenomenon might be explained by the self-association of2 after forming imine functionality in the alkali medium. The Stern-Volmer plot showed the fluorescence quenching constant of each receptor with an iodide ion and indicated the quenching pathway. The LODs of 1and2for iodide ions were evaluated as 0.84 and 0.17 µM, respectively. The 1:1 binding stoichiometry of1or2 with iodide was found from the Job plot and verified by measuring the complex mass.Further, the complexes of each receptor with I− ions can detect Hg2+ ions selectively by fluorescence turn-on method with low sensitivities (LODs: 0.008 µM for 1 and 0.01 µM for 2). DFT results were used to understand the binding mode of receptors 1 and 2 with iodide ions and the quenching process in the aqueous THF medium. The real application of the receptors was established for the recovery of iodide and Hg2+ ions from natural water samples.