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

We report the first examples of Sb(III) and Bi(III) compounds that exhibit phosphorescence in the near-infrared region-II (NIR-II, 1000–1700 nm) in solution at room temperature. Geometric constraint of the pnictogen centers by a redox-active NNN pincer ligand enables ligand-to-metal charge transfer (LMCT) upon visible-light excitation. Significant structural reorganization upon photoexcitation leads to the largest Stokes shift ever reported for Sb and Bi compounds to emit in the NIR region (>6000 cm⁻¹), 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 abundant, low-toxicity main group elements.