A coordination driven deaggregation approach toward Hg2+-specific chemosensors based on thioether linked squaraine-aniline dyads

Herein, we present an effective strategy based on coordination induced deaggregation signaling to create water-soluble fluorescent probes for the detection of mercury ion by introducing the thioether group linkage into squaraine-aniline dyads. Three unsymmetrical squaraine dyes tethered with thiopodand chains in different length were synthesized accordingly. The deaggregation process of the aggregated squaraine dyes triggered by Hg2+ was elucidated in detail. Firstly, the aggregation behavior of squaraine dyes with varying thioether chains in aqueous solutions has been investigated. Secondly, the complexation ability of squaraines with Hg2+ was found to be strengthened by increasing the length of the thioether chain. Additionally, an aggregated squaraine solution was designed by adding trace amount of non-ionic surfactant to solubilize the dye in pure water for the detection of Hg2+. Significantly, the aggregated state of squaraine molecules was selectively broken by Hg2+ ions despite a wide range of other interfering metals in water media. Under optimum conditions, the fluorescence recovery was linearly proportional to the concentration of Hg2+ between 0.03 and 1.8 mu M and the detection limit was as low as 6.6 nM (1.3 ppb). Further study of the mechanism by absorption and emission spectroscopy, MS, H-1 NMR and IR titration showed that a 1: 1 complex was formed between squaraine and Hg2+ ion. (C) 2014 Elsevier B.V. All rights reserved.