Mitochondria-Targeted\nNIR Ratiometric and Colorimetric\nFluorescent Probe for Biothiols Based on a Thiol–Chromene Click\nReaction

In this work, a mitochondria-targeted NIR ratiometric\nand colorimetric\nfluorescent probe <b>1</b> was tactfully designed and synthesized\nby a novel design strategy of modifying chromene to pyridine for the\nfirst time. <b>1</b> exhibited a maximum absorption peak at\n508 nm and a maximum fluorescence emission peak at 650 nm. Under the\nstimulus of biothiols (cysteine (Cys), homocysteine (Hcy), and glutathione\n(GSH)), the maximum absorption and fluorescence emission peaks of <b>1</b> blue-shifted to 448 and 541 nm, respectively, along with\ncolor changes from red to yellow under visible light and from red\nto green under a 365 nm ultraviolet (UV) lamp, which can be ascribed\nto the click reaction of biothiols with the α,β-unsaturated\nketone of the chromene moiety with pyran ring-opening, phenol formation,\nand 1,6-elimination of the <i>p</i>-hydroxybenzyl moiety. <b>1</b> detected biothiols (Cys, GSH, and Hcy) with high sensitivity\n(LODs of 29, 23, and 16 nM for Cys, GSH, and Hcy, respectively), excellent\nselectivity, and fast response. Moreover, <b>1</b> can target\nmitochondria and image the fluctuation of intracellular biothiols\nby dual-emission channels.