Rational Design of High‐Brightness Aza‐ BODIPY ‐Based NIR ‐ II Fluorophore with Aggregation‐Induced Emission for In Vivo Imaging

Comprehensive Summary Fluorescence imaging in the second near‐infrared (NIR‐II) window has emerged as a powerful tool for noninvasive in vivo and in situ visualization in both fundamental research and clinical applications. However, the development of high‐brightness NIR‐II fluorophores for in vivo imaging remains challenging. Herein, we report novel Aza‐BODIPY‐based NIR‐II organic fluorophores featuring pronounced aggregation‐induced emission (AIE) feature. In this molecular design, triphenylamine (TPA) units were incorporated as strong electron donors to red‐shift the emission into the NIR‐II region, while methylphenyl and tetraphenylethylene (TPE) moieties were introduced as sterically hindered structures to suppress detrimental intermolecular interactions. The resulting TAB‐5 nanoparticles (NPs), encapsulated with DSPE‐mPEG 2000 , exhibited bright NIR‐II fluorescence with a quantum yield of 0.52% and a molar absorption coefficient of 5.5×10 4 M −1 ·cm −1 . Benefiting from these superior optical properties, high‐contrast in vivo NIR‐II imaging with high signal‐to‐background ratios (SBR) was achieved for both vascular and skeletal imaging in mice. This molecular design strategy could be extended to Aza‐BODIPY derivatives and other NIR‐II emissive conjugated systems to achieve high NIR‐II brightness for in vivo visualization.