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<p>Two novel <i>N</i>-heterocyclic carbene (NHC)-based ligands featuring rigid boron-oxygen (BO) fused-ring units, named Bpmi and Bpmb, and the two corresponding homoleptic meridianal iridium complexes, namely <i>mer</i>-Ir(Bpmi)<sub>3</sub> and <i>mer</i>-Ir(Bpmb)<sub>3</sub>, were designed and synthesized. The single-crystal structures revealed that both complexes exhibit a meridional coordination geometry. Their shorter Ir–C<sub>carbene</sub> bond lengths and the presence of rigid planar BO-fused ring units contribute to enhanced stability of these complexes. Both complexes exhibit efficient green phosphorescence (<i>λ</i><sub>em</sub> = 536/521 nm in toluene with <i>Φ</i><sub>PL</sub> &gt; 78%) with short lifetimes (<i>τ</i> = 846/1083 ns), leading to high radiative transition rate constants (<i>K</i><sub>r</sub> = 10.04 × 10<sup>5</sup> and 7.29 × 10<sup>5</sup> s<sup>−1</sup>, respectively). Theoretical calculations indicate that both complexes demonstrate a significantly increased metal-to-ligand charge transfer character (<i>mer</i>-Ir(Bpmi)<sub>3</sub>: 21.69%; <i>mer</i>-Ir(Bpmb)<sub>3</sub>: 17.30%) compared to the reference complexes (<i>mer</i>-Ir(pmi)<sub>3</sub>: 13.01%; <i>mer</i>-Ir(pmb)<sub>3</sub>: 15.99%). Furthermore, both complexes exhibit exceptional thermal stability, with decomposition temperatures of 491°C for <i>mer</i>-Ir(Bpmi)<sub>3</sub> and 540°C for <i>mer</i>-Ir(Bpmb)<sub>3</sub>. The organic light-emitting diode devices using <i>mer</i>-Ir(Bpmb)<sub>3</sub> and <i>mer</i>-Ir(Bpmi)<sub>3</sub> as emitters demonstrate good maximum external quantum efficiencies of 20.0% and 15.6%, respectively. This research takes the lead in constructing boron-fused ring-containing NHCs and their phosphorescent iridium(III) complexes, thereby establishing a novel design strategy for developing high-performance NHC-based OLED phosphorescent emitters.</p>

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Rigid oxygen-bridged boron NHC-based homoleptic phosphorescent iridium complexes: structures, photophysics and OLED application

  • 期刊论文

  • 发表日期：

    2026年1月27日

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  • Fuzheng Zhang,
  • Zhenghao Zhang,
  • Jingsheng Miao,
  • Feiyang Li,
  • Jing Zhang,
  • Qiuxia Li,
  • Wenqing Yu,
  • Aihua Yuan,
  • Chao Shi,
  • Chuluo Yang

摘要

Two novel N-heterocyclic carbene (NHC)-based ligands featuring rigid boron-oxygen (BO) fused-ring units, named Bpmi and Bpmb, and the two corresponding homoleptic meridianal iridium complexes, namely mer-Ir(Bpmi)3 and mer-Ir(Bpmb)3, were designed and synthesized. The single-crystal structures revealed that both complexes exhibit a meridional coordination geometry. Their shorter Ir–Ccarbene bond lengths and the presence of rigid planar BO-fused ring units contribute to enhanced stability of these complexes. Both complexes exhibit efficient green phosphorescence (λem = 536/521 nm in toluene with ΦPL > 78%) with short lifetimes (τ = 846/1083 ns), leading to high radiative transition rate constants (Kr = 10.04 × 105 and 7.29 × 105 s−1, respectively). Theoretical calculations indicate that both complexes demonstrate a significantly increased metal-to-ligand charge transfer character (mer-Ir(Bpmi)3: 21.69%; mer-Ir(Bpmb)3: 17.30%) compared to the reference complexes (mer-Ir(pmi)3: 13.01%; mer-Ir(pmb)3: 15.99%). Furthermore, both complexes exhibit exceptional thermal stability, with decomposition temperatures of 491°C for mer-Ir(Bpmi)3 and 540°C for mer-Ir(Bpmb)3. The organic light-emitting diode devices using mer-Ir(Bpmb)3 and mer-Ir(Bpmi)3 as emitters demonstrate good maximum external quantum efficiencies of 20.0% and 15.6%, respectively. This research takes the lead in constructing boron-fused ring-containing NHCs and their phosphorescent iridium(III) complexes, thereby establishing a novel design strategy for developing high-performance NHC-based OLED phosphorescent emitters.