Phenothiazine-coumarin-pyridine hybrid as an efficient fluorescent probe for ratiometric sensing hypochlorous acid

• A new ratiometric fluorescent probe (1) was developed for hypochlorous acid. • Probe 1 displays a distinct ratiometric response without spectral cross-talk (Δλ em = 130 nm). • Probe 1 features high sensitivity and selectivity to hypochlorous acid. • Probe 1 has the capability for ratiometric imaging of hypochlorous acid both in vitro and in vivo. Hypochlorous acid (HOCl) is one of the most potent reactive oxygen species and plays a vital role in many biological processes. Chemical probes for HOCl have proven to be valuable tools in understanding its contributions to healthy and disease states. Herein, a new ratiometric fluorescent probe ( 1 ), which composed of a coumarin scaffold bearing a phenothiazine moiety as the electron-donating group and a pyridine unit as the electron-accepting group, was rationally designed and synthesized for sensing HOCl. Probe 1 exhibited a distinct deep-red emission (∼630 nm), while displayed a completely different emission in the cyan region (∼500 nm) upon the addition of HOCl, thereby allowing the ratiometric detection of HOCl without spectral crosstalk interference. In addition, the presented probe has several other advantages for HOCl detection, including rapid response, high signal to noise ratio, excellent selectivity and sensitivity. Furthermore, the probe has shown the utility for visualizing HOCl in cells and organisms.