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. Based on the intramolecular charge transfer (ICT) effect and the excited‐state intramolecular proton transfer (ESIPT) mechanism, two 2‐(2′‐hydroxyphenyl)benzothiazole‐based fluorescent probes (HNa and HNb) were developed to afford fluorescent turn‐on responses specifically in the present of bisulfite anions. The probes were successfully applied to detect and image bisulfite in living cells.