Phosphorescence of Heavy, T-Shaped Pnictogen Trisamides in Solution at Room Temperature in the Near-Infrared II...

We report T-shaped Sb(III) and Bi(III) trisamides that exhibit phosphorescence in the near-infrared-II region (NIR-II, 1000-1700 nm) in solution at 25 °C. Geometric constraint of the pnictogen(III) centers by an NNN pincer ligand enables ligand-to-metal charge transfer upon visible-light excitation. Significant structural reorganization upon photoexcitation leads to the largest Stokes shifts (> 6000 cm^-1) ever reported for Sb and Bi compounds to emit in the NIR region, reminiscent of precious metal photosensitizers. The emissive triplet states exhibit lifetimes up to the microsecond range, offering a new design principle for NIR emitters based on main group elements.