Aggregation-enhanced emission enables phenothiazine coumarin as a robust ratiometric fluorescent for rapid and selective detection of HClO.

By taking advantage of phenothiazine moiety as an electron-donating group, a novel donor-acceptor (D-A) type coumarin dye, PTZ-Et, was developed. The introduction of phenothiazine moiety not only caused emission red-shifting and Stokes shift enlarging, but also endowed PTZ-Et with significant aggregation-enhanced emission (AEE) features, thereby enabled PTZ-Et as a robust ratiometric fluorescent probe for HClO detection. Upon oxidation of the sulfur atom on phenothiazine into sulfoxide, PTZ-Et displayed remarkable ratiometric fluorescence response (over 150 folds variations of F/F) toward HClO with rapid response time (<30 s) and ultra-sensitivity (LOD = 15 nM). Additionally, the corresponding sensing mechanism of PTZ-Et for HClO was fully elucidated through the successful purification and well characterization (H NMR, C NMR, HRMS, and single crystal data) of the corresponding reaction product between PTZ-Et and HClO. Significantly, PTZ-Et was capable of monitoring both exogenous and endogenous HClO in living RAW 264.7 cells by ratiometric fluorescence imaging.