2,1,3-Benzoxadiazole-based selective chromogenic chemosensor for rapid naked-eye detection of Hg2+ and Cu2+

We report a simple twisted intramolecular charge transfer (TICT) chromogenic chemosensor for rapid and selective detection of Hg2+ and Cu2+. The sensor was composed of an electron-acceptor 4-fluoro moiety and an electron-donor 7-mercapto-2,1,3-benzoxadiazole species where the S together with the 1-N provided the soft binding unit. Upon Hg2+ and Cu2+ complexation, remarkable but different absorbance spectra shifts were obtained in CH3CN–H2O mixed buffer solution at pH 7.6, which can be easily used for naked-eye detection. The sensor formed a stable 2:1 complex with Cu2+, and both 2:1 and 3:1 complexes with Hg2+. While alkali-, alkaline earth- and other heavy and transition metal ions such as Na+, Mg2+, Mn2+, Co2+, Ni2+, Ag+, Zn2+, Pb2+ and Cd2+ did not cause any significant spectral changes of the sensor. This finding is not only a supplement to the detecting methods for Hg2+ and Cu2+, but also adds new merits to the chemistry of 4,7-substituted 2,1,3-benzoxadiazoles.