A thiocoumarin-based turn-on fluorescent probe for hypochlorite detection and its application to live-cell imaging

A thiocoumarin-based turn-on fluorescence probe for the detection of hypochlorite anion (ClO⁻) was prepared and characterized. Coumarin dye (CZCN-O) exhibited intense fluorescence with good quantum yields (Φ_PL = 0.98) in acetonitrile. Contrastingly, the fluorescence of thiocoumarin dye (CZCN-S) was almost completely quenched (Φ_PL < 0.01) because of the efficient intersystem crossing from the emissive singlet excited state to the non-emissive triplet state. The addition of ClO⁻ to the PBS buffer (pH = 7.4, containing 50% ACN) of thiocoumarin resulted in a remarkable fluorescence enhancement with an emission maximum at 486 nm, indicating the sensitive OFF–ON fluorescence sensing of ClO⁻. The calculated detection limit of ClO⁻ in 50% aqueous ACN was 0.17 μM. An investigation of the sensing behavior to various analytes revealed that thiocoumarin dye had an excellent selectivity for ClO⁻. The recognition mechanism was attributed to the ClO⁻-induced conversion of thiocarbonyl coumarin into its oxo analogue through oxidative desulfurization. In particular, cell studies demonstrated that thiocoumarin dye could be used as an effective fluorescent probe for the detection of ClO⁻ in living cells.