A coumarin–dihydroperimidine dye as a fluorescent chemosensor for hypochlorite in 99% water

The hypochlorite anion (OCl(−)), a reactive oxygen species (ROS), is an important microbicidal agent in the immune system. Accurate and selective detection of OCl(−) in environmental and biological samples by a fluorescent molecular sensor is an important subject. All previously reported sensors, however, have suffered from tedious multi-step synthesis for the sensors and the use of large amounts of organic solvents for the analysis. Herein, we report that a coumarin–dihydroperimidine dye prepared by facile condensation behaves as a fluorescent sensor for OCl(−) in 99% water. The sensor exhibits weak fluorescence, but OCl(−)-selective dehydrogenation of its dihydroperimidine unit creates a strong blue fluorescence. This turn-on fluorescence response facilitates selective and sensitive detection of OCl(−) in the physiological pH range. Ab initio calculation revealed that the fluorescence enhancement by OCl(−) is triggered by intramolecular proton transfer from the coumarin –OH to the imine nitrogen of the formed perimidine moiety.