A mitochondria-targeted colorimetric and NIR ratiometric fluorescent probe for biothiols with large Stokes shift based on thiol–chromene click reaction†

In this study, a carbazole-based mitochondria-targeted colorimetric and NIR ratiometric fluorescent probe for biothiols based on the thiol–chromene click reaction was subtly designed and synthesized. Upon interaction with biothiols (Cys, Hcy and GSH), the absorption of shifted from 496 nm to 388 nm, while its fluorescence spectrum shifted from 650 nm to 530 nm. These transformations were accompanied by a visible color change from pink to colorless under visible light and from red to green when observed under a 365 nm UV lamp, which can be attributed to the click reaction of biothiols with the α,β-unsaturated ketone of the chromene moiety, subsequent pyran ring-opening and phenol formation as well as 1,6-elimination of a p-hydroxybenzyl moiety yielding . These advancements in have allowed us to ratiometrically detect biothiols with high sensitivity (LODs of 97 nM, 94 nM and 93 nM for Cys, GSH and Hcy, respectively), a large Stokes shift (154 nm) and excellent selectivity. In addition, can target mitochondria and image the fluctuation of intracellular biothiols through fluorescence ratiometry. Furthermore, the novel design strategy of modifying chromene to the N atom of quinoline was proposed for the first time.