A turn-on AIE active fluorescent sensor for Hg2+ by combination of 1,1-bis(2-pyridyl)ethylene and thiophene/bithiophene fragments

Abstract

Fluorescent sensors for Hg²⁺ that combine aggregation-induced emission (AIE) activity of tetraarylethylenes with metal chelating 1,1-bis(2-pyridylethylene) fragments and thiophene/bithiophene substituents have been prepared and characterized. The sensors exhibit red-shifted and enhanced emission in the presence of Hg²⁺ in aqueous solution while exhibiting little to no change in fluorescence in the presence of other metal ions. Job plot analyses indicate 2 : 1 sensor : Hg²⁺ binding stoichiometries in solution. ¹H-NMR spectroscopy was also employed to investigate solution phase binding interactions between the sensors and Hg(ClO₄)₂, and a chelated HgI₂–bis(pyridyl) complex has been characterized by X-ray crystallography. The limit of detection for Hg²⁺ was determined to be 48 nM. In contrast, the fluorescence of structurally analogous materials possessing quinoline rings in place of pyridine groups is completely quenched in the presence of Hg(ClO₄)₂. The high sensitivity and selectivity displayed by these sensors for Hg²⁺ over other metal ions may enable monitoring of mercury in aqueous environments.