This paper presents a series of first-and second-generation click-modified coumarin-based fluorescent probes for thiols.These molecules demonstrate high turn-on fluorescent response and good selectivity towards aromatic thiols over other relevant reactive sulfur species,reactive oxygen species and common nucleophiles.Moreover,probe 1a can detect thiols in the reduced rabbit plasma sample.Therefore,this approach provides a particularly impressive tool for detecting thiol in biological systems. This paper presents a series of first-and second-generation click-modified coumarin-based fluorescent probes for thiols. These letters demonstrate high turn-on fluorescent response and good selectivity to aromatic thiols over other relevant reactive sulfur species, reactive oxygen species and common nucleophiles. Moreover, probe 1a can detect thiols in the reduced rabbit plasma sample. Before this, this example provides an impressive tool for detecting thiol in biological systems.