A Novel Ratiometric Fluorescent Probe For Hydrogen Sulfide Based On Excited-state Intramolecular Proton Transfer Mechanism

With further research on the significant physiological role of hydrogen sulfide（H2S） in recent years, it has been established that H₂S acts as an essential physiological mediator and cellular signalling species, and H₂S has been identified as the third gasotransmitter following nitric oxide and carbon monoxide. However, our understanding of the far-ranging contributions of H₂S to physiology and pathology is still in its infancy, one key reason for which is that the specific and accurate detection of physiological H₂S hasn’t been reached due to the interference of surrounding biological thiols with high concentrations and the imperfection of traditional methods for H₂S detection. Therefore, the accurate analysis of H₂S in biological systems is crucial for studying the fundamental problems unsolved, such as the mechanism of H₂S action and the modulation of its production and degradation. Compared to the turn-on/of fluorescent probes which can be easily influenced by environmental factors, the ratiometric fluorescent probes provide greater precision for the quantitative determination based on self-calibration by modulating the ratio of fluorescence intensities at two emission bands. In this study, we designed and synthesized a novel ratiometric fluorescent probe A for H₂S based on modulating the excited-state intramolecular proton transfer（ESIPT） process of 2-（2’-hydroxy-3’-methoxyphenyl） benzothiazole（HMBT）. By H2S-induced reduction of azides and tandem cyclization reaction, the protecting group of the hydroxyl was removed, and the ESIPT process of HMBT was retrieved. The emission wavelengths were changed from the only enol emission（372 nm） of the probe A to the new keto emission（487 nm） with a remarkable red shift. There was a linear correlation between the ratio of intensities at two wavelengths and the concentrations of H₂S, by which the accurate quantitative measurements of H₂S in aqueous solution and fetal bovine serum were both achieved. And the probe A exhibited high selectivity for H₂S.