Phenanthro[b]-Fused BODIPYs through Tandem Suzuki and Oxidative Aromatic Couplings: Synthesis and Photophysical Properties

A new synthetic method to build phenanthrene-fused boron dipyrromethenes (BODIPYs) through tandem Suzuki couplings on readily available 2,3,5,6-tetrabromoBODIPYs, followed by an intramolecular oxidative aromatic coupling mediated by iron(III) chloride is reported. This efficient synthesis allows a very straightforward approach for tuning the absorption and emission of BODIPYs in the red/near-infrared (NIR) range. These resulting phenanthrene-fused BODIPYs exhibit strong absorption (extinction coefficients up to 2.2 × 105 M–1 cm–1) and emission in the near-infrared (NIR) range (688–754 nm). Substituents on the resulting phenanthrene rings have a significant impact on the photophysical properties of these phenanthrene-fused BODIPYs.