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Biothiols, including homocysteine (Hcy), cysteine (Cys) and reduced glutathione (GSH), play various roles in physiological and pathological processes. Because these biothiols possess similar in structures, it is difficult to discriminate Hcy, Cys and GSH from one another. In this work, a novel fluorescent probe, 4-BrCP , based on coumarin as a fluorophore to discriminate GSH from Hcy and Cys was rationally designed and synthesized in three steps with good total yield. The benzothiazol ring played the role of a fluorescent emission wavelength adjuster, while the ester part served as a fluorescent quencher and reactive sites with Hcy, Cys and GSH. The results of responsive experiment indicated that the probe could discriminate GSH from Hcy and Cys distinctly and exhibited a relatively high fluorescence quantum yield (0.84) and low detection limit (9.8 nM). In addition, the probe 4-BrCP also showed good stability and low toxicity. The reaction mechanism of 4-BrCP with GSH was speculated on according to the LC-MS data. Most importantly, because of the length of the skeletons of Hcy, Cys and GSH, different dynamic fluorescent phenomena were observed. Furthermore, imaging experiments suggested that the probe could be used to monitor GSH in living cells and organisms. [Display omitted] • A novel fluorescent probe based on coumarin was rationally designed and synthesized. • The probe could selectively discriminate GSH from Hcy, Cys, or Hcy/Cys/GSH coexisting condition. • The probe showed a good quantum yield (0.84) and low detection limit (9.8 nM). • The probe could trace endogenous GSH in living cells and organisms. [ABSTRACT FROM AUTHOR]