Highly Selective and Sensitive 2-(2 '-Hydroxyphenyl)benzothiazole-Based Turn-On Fluorescent Probes for Detecting and Imaging Bisulfite in Living Cells

Bisulfite (HSO3-) is one of the main forms of sulfur dioxide in physiological systems. Two 2-(2'-hydroxyphenyl)benzothiazole-derived fluorescent probes bearing a nitroolefin moiety were designed based on the intramolecular charge transfer (ICT) effect and excited-state intramolecular proton transfer (ESIPT) mechanism to afford a fluorescent turn-on response specifically in the present of HSO3- ions. Owing to the remarkable ICT effect from hydroxy group to the nitro group, the probes exhibit extremely weak fluorescence. Upon the conjugate addition reaction with HSO3- at the nitroolefin moiety of the probes, the ICT character is weakened and the absorption spectra of the products are blueshifted. A pronounced fluorescence enhancement based on ESIPT was also observed. The two probes exhibited good sensitivity, high selectivity and an excellent anti-interference properties of their large Stokes shifts, indicating that the probes are highly suitable for biological systems. Furthermore, they were successfully applied to the imaging of HSO3- in living cells.