In this paper,a novel fluorescence probe was designed and synthesized for the detection of HClO based on phenanthroimidazole.The probe 2-(4-(methylthio)phenyl) 1H-phenanthro［9,10-d］imidazole(MPI) was prepared through one step reaction with commercial reagents 9,10-phenanthroquinone and 4 (methylthio)benzaldehyde,and obtained in good yield(85%) by simple filtration and washing.The free MPI displayed relatively weak fluorescence due to the heavy atom effect of sulfur atom.However,addition of HClO into the MPI solution triggered a strong fluorescence at 445 nm as the HClO promoted oxidation of sulfide into sulfoxide reduced the heavy atom effect and strengthened the intramolecular charge transfer(ICT) process.The reaction mechanism of MPI and HClO was confirmed using high resolution mass spectrometry.In PBS buffer(DMF∶H2O=2 ∶8,by volume,pH 7.4),the probe MPI could be used for quantitative detection of HClO in the range of 0-100 μmol/L with a detection limit of 0.26 μmol/L as it has high sensitivity and selectivity to HClO other than other analytes.More importantly,with good biocompatibility and cell membrane permeability,the probe MPI could be applied in the visual imaging of HClO in living cells.Therefore,The probe MPI provides a reliable and effective tool for detection and tracing of HClO in biological systems.