Rational Design of a Two-Photon Ratiometric Fluorescent Probe for Hypochlorous Acid with a Large Stokes Shift.

By introducing the tetrahydroquinoxaline group as the electron donor to enhance intramolecular charge transfer effect, we deliberately designed a coumarin derivative, TQC-HClO, to serve as a two-photon ratiometric fluorescent probe for imaging hypochlorous acid in cells and zebra fish with good sensitivity and high selectivity. TQC-HClO displayed an obvious two-photon absorbance cross-section (over 100 GM in 800-840 nm), large Stokes shifts (159 to 173 nm), and a ratiometric fluorescence change from orange (λmaxem = 583 nm) to red (λmaxem = 650 nm) in response to hypochlorous acid.