Novel Benzothiazole-Based Highly Selective Ratiometric Fluorescent Turn-On Sensors for Zn(2+) and Colorimetric Chemosensors for Zn(2+), Cu(2+), and Ni(2+) Ions

[Image: see text] Metal ions play a very important role in environmental as well as biological fields. The detection of specific metal ions at a minute level caught much attention, and hence, several probes are available in the literature. Even though benzothiazole-based molecules have a special place in the medicinal field, only very few chemosensors are reported based on this moiety. The current work describes the design and synthesis of the benzothiazole-based chemosensor for a highly selective and sensitive detection of biologically important metal ions such as Zn(2+), Cu(2+), and Ni(2+). The sensing studies of compound-1 showed a ratiometric as well as colorimetric response toward Zn(2+), Cu(2+), and Ni(2+) ions and color changes from colorless to yellow and is found to be insensitive toward various metal ions (Cd(2+), Cr(3+), Mn(2+), Pb(2+), Ba(2+), Al(3+), Ca(2+), Fe(2+), Fe(3+), Mg(2+), K(+), and Na(+)). Further, compound-1 exhibited ratiometric as well as turn-on-enhanced fluorescence response toward Zn(2+) ions and turn off response for Cu(2+) and Ni(2+) ions. The Job plots revealed that the binding stoichiometry of compound-1 and metal ions is 2:1. The detection limits were found to be 0.25 ppm for Zn(2+), while it was 0.30 ppm and 0.34 ppm for Ni(2+) and Cu(2+), respectively. In addition, density functional theory results strongly support the colorimetric response of metals, and the reversibility studies suggested that compound-1 can be used as a powerful chemosensor for the detection of Zn(2+), Cu(2+), and Ni(2+) ions. The bioimaging data illustrated that compound-1 is a very effective ratiometric sensor for Zn(2+) ions in live cells.