A new chromogenic and fluorogenic chemosensor for Hg(II) with high selectivity based on the Hg2+-promoted deprotection of thioacetals

In this paper, a thioacetal chemosensor 1 incorporating simultaneously a carbazole moiety and an azobenzene moiety was synthesized. Among other metal ions, Hg2+ proved to be able to selectively induce both color and fluorescence changes of 1. The mechanism of Hg2+-promoted cleavage of thioacetal was confirmed by 1H NMR experiments. Upon the addition of Hg2+ into the yellow CH3CN/H2O solution of 1, the resultant azobenzene-containing thioglycolamide was precipitated from the solution as a mercuric salt, leading to a colorless solution. Therefore, a novel color change pattern was developed.