A benzothiazole-based semisquarylium dye suitable for highly selective Hg2+ sensing in aqueous media

A novel semisquarylium dye was synthesized by the reaction between 3,4-dibutoxy-3-cyclobutene-1,2-dione and a benzothiazolium salt and its metal ion sensing properties were investigated using absorption and emission spectroscopy. These misquarylium exhibited high selectivity for Hg2+ ions, as compared with Ca2+, Pb2+, Al3+, Ce2+, Ba2+, Ni2+, Cd2+, Zn2+ and Mg2+ ions in DMSO/H2O (9:1, v/v), which was attributed to the formation of a 2:1 BSQ:Hg2+ coordination complex, the formation of which was supported by the calculated geometry of the complex.