Mitochondria-Targeted NIR Ratiometric and Colorimetric Fluorescent Probe for Biothiols Based on a Thiol–Chromene Click Reaction

In this work, a mitochondria-targeted NIR ratiometric and colorimetric fluorescent probe <b>1</b> was tactfully designed and synthesized by a novel design strategy of modifying chromene to pyridine for the first time. <b>1</b> exhibited a maximum absorption peak at 508 nm and a maximum fluorescence emission peak at 650 nm. Under the stimulus of biothiols (cysteine (Cys), homocysteine (Hcy), and glutathione (GSH)), the maximum absorption and fluorescence emission peaks of <b>1</b> blue-shifted to 448 and 541 nm, respectively, along with color changes from red to yellow under visible light and from red to green under a 365 nm ultraviolet (UV) lamp, which can be ascribed to the click reaction of biothiols with the α,β-unsaturated ketone of the chromene moiety with pyran ring-opening, phenol formation, and 1,6-elimination of the <i>p</i>-hydroxybenzyl moiety. <b>1</b> detected biothiols (Cys, GSH, and Hcy) with high sensitivity (LODs of 29, 23, and 16 nM for Cys, GSH, and Hcy, respectively), excellent selectivity, and fast response. Moreover, <b>1</b> can target mitochondria and image the fluctuation of intracellular biothiols by dual-emission channels.