Construction and Application of Fluorescent Probes with Imine Protective Groups for Hypochlorite Detection.

Several fluorescent probes have been designed to detect ClO in biological systems based on the isomerization mechanism of C = N bonds. Particularly, fluorescein has emerged as an important fluorophore for detecting ClO because of its unique properties. Previously, we introduced the fluorescein analog F-1 with an active aldehyde group. In this study, two ClO fluorescent sensors (F-2 and F-3) with imine groups were designed and synthesized using diaminomaleonitrile and 2-hydrazylbenzothiazole as amines. The electron cloud distribution of F-2 and F-3 in ground and excited states was explored via Gaussian calculations, reasonably explaining their photophysical properties. The fluorescence detection of ClO in solution using the two probes (F-2 and F-3) was realized based on the mechanism of imine deprotection with ClO. NaClO concentration titration demonstrated that the colorimetric detection of ClO with the naked eye could be achieved using both F-2 and F-3. However, after adding ClO, the fluorescence intensity of probe F-2 increased, whereas that of probe F-3 first decreased and then increased. Probes F-2 and F-3 exhibited good selectivity, anti-interference capability, and sensitivity, with the detection limits of 169.95 and 37.30 µM, respectively. Owing to their low cell toxicity, probes F-2 and F-3 can be applied to detect ClO in vivo. The design approach adopted in this study will further advance the future development of ClO chemical probes through the removal of C = N bond isomerization.