A General Strategy for Development of Near-Infrared Fluorescent Probes for Bioimaging

Near-infrared (NIR) fluorescent dyes with favorable photophysical properties are highly useful for bioimaging, but such dyes are still rare. The development of a unique class of NIR dyes via modifying the rhodol scaffold with fused tetrahydroquinoxaline rings is described. These new dyes showed large Stokes shifts (>110 nm). Among them, WR3, WR4, WR5, and WR6 displayed high fluorescence quantum yields and excellent photostability in aqueous solutions. Moreover, their fluorescence properties were tunable by easy modifications on the phenolic hydroxy group. Based on WR6, two NIR fluorescent turn-on probes, WSP-NIR and SeSP-NIR, were devised for the detection of H₂ S. The probe SeSP-NIR was applied in visualizing intracellular H₂ S. These dyes are expected to be useful fluorophore scaffolds in the development of new NIR probes for bioimaging.