TD-DFT study on the fluorescent chemosensor for Hg2+, 2-(Benzo-d-thiazol-2-yl)quinoline

2-(Benzo-d-thiazol-2-yl)quinoline (BTQ) was synthesized and tested for its use as a fluorescent chemosensor for Hg2+. The metal-ion recognition of BTQ was investigated by adding several metal ions (M2+) to a solution of BTQ in acetonitrile. The shape and intensity of the fluorescence spectra did not change upon addition of several metal ions, except for Hg2+ and Cu2+. The time-dependent density functional calculations were carried out on BTQ and BTQ–M2+ complexes (M = Zn, Cd, and Hg) to clarify their spectroscopic properties. The results of the calculation showed that the energy levels of the excited singlet and triplet states are similar in Zn2+ and Cd2+ complexes, whereas the Hg2+ complex has lower transition energy. The character of their excited states was also different between zinc and cadmium complexes with the mercury complex.