Near-infrared absorbing (>700 nm) aza-BODIPYs by freezing the rotation of the aryl groups

The typical aza-BODIPYs in the dye family are known for bright fluorescence, excellent stability, and tunable absorption wavelengths. Hence, these dyes are attracting the increasing attention. Aza-BODIPYs having the maxima absorption in the near-infrared (NIR) region (650–900 nm) are very favorable for bioimaging in vivo due to the less photo-damage, deeper tissue penetration, and less interference from background auto-fluorescence by biomolecules in the living systems. Many strategies have been employed to modify the structures of the aza-BODIPY core to provide the NIR absorbing dyes. Among these, the most effective method is the fusion of the aromatic rings in aza-BODIPY system. This review allsidedly summarizes the recent development of ring-fused aza-BODIPY dyes (λ_abs > 700 nm) focusing on the design, synthesis, and potential applications in the NIR region since 2002.