[<i>a</i>]‑Phenanthrene-Fused BF₂ Azadipyrromethene (AzaBODIPY) Dyes as Bright Near-Infrared Fluorophores

A new substitution pattern of BF2 azadipyrromethene (azaBODIPY) dyes was obtained by phenanthrene fusion through a key palladium-catalyzed intramolecular C–H activation reaction. These [a]-phenanthrene-fused azaBODIPYs have a near planar structure of the phenanthrene-fused azadipyrromethene core in the crystalline state. The chromophore absorbs (log ε > 5) and fluoresces (ϕ = 0.32–0.38) strongly above 700 nm with excellent photostability and may be used as an attractive bright NIR bioimaging agent.