Synthesis, Crystal Structure, and the Deep Near-Infrared Absorption/Emission of Bright AzaBODIPY-Based Organic Fluorophores

Abstract

Annularly fused azaBODIPY-based organic fluorophores (HBPs 2) containing up to 13 aromatic ring fusions were synthesized by a Suzuki coupling reaction with bromoazadipyrromethenes and a subsequent regioselective oxidative ring-fusion reaction. X-ray analysis indicates almost planar dipyrrin cores for all crystals but overall curved or "wave" conformations for those HBP dyes. These molecules exhibit unique structural and physical properties including excellent spectral selectivity (negligible absorption between 300 and 700 nm), sharp near-infrared (NIR) absorption (up to 878 nm) and emission (up to 907 nm), large extinction coefficient (up to 4.5 × 10⁵ M^-1 cm^-1), and excellent photostabilities.