Novel Benzothiazole-Based Highly Selective Ratiometric Fluorescent Turn-On Sensors for Zn²⁺and Colorimetric Chemosensors for Zn²⁺, Cu²⁺, and Ni²⁺Ions

Abstract

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 Zn²⁺, Cu²⁺, and Ni²⁺. The sensing studies of <b>compound-1</b> showed a ratiometric as well as colorimetric response toward Zn²⁺, Cu²⁺, and Ni²⁺ ions and color changes from colorless to yellow and is found to be insensitive toward various metal ions (Cd²⁺, Cr³⁺, Mn²⁺, Pb²⁺, Ba²⁺, Al³⁺, Ca²⁺, Fe²⁺, Fe³⁺, Mg²⁺, K⁺, and Na⁺). Further, <b>compound-1</b> exhibited ratiometric as well as <i>turn-on</i>-enhanced fluorescence response toward Zn²⁺ ions and <i>turn off</i> response for Cu²⁺ and Ni²⁺ ions. The Job plots revealed that the binding stoichiometry of <b>compound-1</b> and metal ions is 2:1. The detection limits were found to be 0.25 ppm for Zn²⁺, while it was 0.30 ppm and 0.34 ppm for Ni²⁺ and Cu²⁺, respectively. In addition, density functional theory results strongly support the colorimetric response of metals, and the reversibility studies suggested that <b>compound-1</b> can be used as a powerful chemosensor for the detection of Zn²⁺, Cu²⁺, and Ni²⁺ ions. The bioimaging data illustrated that <b>compound-1</b> is a very effective ratiometric sensor for Zn²⁺ ions in live cells.