Pd-Catalyzed Direct C–H Functionalization/Annulation of BODIPYs with Alkynes to Access Unsymmetrical Benzo[<i>b</i>]‑Fused BODIPYs: Discovery of Lysosome-Targeted Turn-On Fluorescent Probes

A highly efficient palladium-catalyzed direct C–H functionalization/annulation of BODIPYs with alkynes has been developed for the first time to construct a series of unsymmetrical benzo­[b]-fused BODIPYs from readily available starting materials. These unsymmetrical benzo­[b]-fused BODIPYs exhibit remarkably red-shifted emissions and larger Stokes shifts than classical BODIPY dyes. Cell imaging experiments and cytotoxicity assays demonstrate that BODIPYs 4c and 4d have specific lysosome-labeling capacities, turn-on fluorescence emissions in cells, and low cytotoxicity.