Extended Fused Carbazole‐BODIPY, High Brightness NIR Organic Dyes

Abstract

ABSTRACT Fluorescence‐based bioimaging enables noninvasive visualization of molecular and cellular processes with high sensitivity and without ionizing radiation. However, conventional fluorophores emitting in the visible or near‐red infrared I (NIR‐I) (650–800 nm) regions suffer from limited tissue penetration and scattering. Extending fluorescence emission into the deeper NIR region represents a promising strategy to overcome these drawbacks, yet achieving high brightness and stability in organic dyes remains a major challenge. We report an original family of hetero‐substituted‐fused boron‐dipyrromethene (BODIPY) dyes bearing carbazole and thienyl donors that exhibit record brightness and emission maxima up to 852 nm in toluene. The synthetic route combines successive Stille couplings from a 2,6‐dibromo‐3,5‐diiodo‐BODIPY precursor and an unprecedented silver(I)‐mediated oxidative cyclization, affording high yields and suppressing undesired chlorination. The resulting dyes display intense absorption ( ε = 1.8–2.5 × 10 5 M − 1 cm − 1 ) and exceptional fluorescence quantum yields ( Φ up to 0.73). Encapsulation in silica nanoparticles (NPs) preserves their photophysical properties and enables efficient NIR‐II in vivo imaging in mice, allowing tumor detection at doses as low as 0.2 nmol with tumor‐to‐muscle ratios > 4. These fused BODIPY derivatives rank among the brightest NIR fluorophores reported to date and open new avenues for high‐contrast deep‐tissue imaging and image‐guided surgery.