A smart chemosensor with different response mechanisms to multi-analytes: Chromogenic and fluorogenic recognition of Cu2+, Fe3+, and Zn2+

Single-component sensors that can detect multiple analytes have drawn great research attentions. Herein, a smart chemosensor TPBS that can recognize multiple targets was developed by connecting triphenylamine with benzothiazole via an imine link. The N atoms with lone pair electrons on the flexible imine link served as potential coordination sites to allow for variations in charge transfer and molecular configurations. In CH3CN, TPBS simultaneously achieved the recognition of Cu2+ through a chromogenic response (colorless to red) via ligand-metal charge transfer, and the recognition of Fe3+ through a “turn-on” fluorogenic response (non-emission to blue) via the chelation-enhanced fluorescence effect. In aqueous solution, TPBS recognized Zn2+ via a “turn-on” fluorogenic response (non-emission to green) based on the aggregation-induced emission behavior. The detection limits were as low as 0.45 μM, 3.24 μM, and 3.22 μM for Cu2+, Fe3+, and Zn2+, respectively. A 1:1 binding stoichiometry and exact complex modes between TPBS and the target metal ions were deduced using Job's plot and FT-IR analyses. Both experiments and theoretical calculations supported the deduced coordination mechanisms. The ability of TPBS to recognize Cu2+, Fe3+, and Zn2+ was then tested in real-life water samples and through on-site detection of Zn2+ using test strips.