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<p>Cu(I) complexes exhibiting thermally activated delayed fluorescence (TADF) have emerged as promising alternatives to noble-metal-based emitters for organic light-emitting diodes (OLEDs). However, the development of red-emitting Cu(I) complexes has been hindered by the slow radiative decay and fast nonradiative decay rate. In this study, a linear two-coordinate Cu(I) complex, namely ICuTMC, was designed and synthesized. Through pairing a pyrazine-fused <i>N</i>-heterocyclic carbene and a <i>tetra</i>-methylcarbazolyl ligand, a strong ligand-to-ligand charge transfer excited state is generated. Single crystal structure authenticates the presence of close intramolecular C–H⋯Cu contacts, providing a good steric shielding environment to the metal center. The C–H⋯<i>π</i> interactions between the ligands are also revealed. The Cu(I) complex exhibits highly efficient red TADF with an emission maximum of 622 nm, a photoluminescence quantum yield of 76% and a short delayed fluorescence lifetime of 0.24 µs. This is conceived to be enabled by a large oscillator strength associated with the coplanar donor-Cu-acceptor conformation, a small singlet-triplet excited states energy gap resulting from the spatial separation of the frontier molecular orbitals, and a strong spin-orbit coupling effect brought about by the metal center. Vacuum-deposited OLEDs based on ICuTMC exhibit a peak external quantum efficiency of 25.9% and a significantly small roll-off (1.9%) at 10,000 cd m<sup>−2</sup>. These performances demonstrate a way to overcome the energy gap law for linear coinage metal complexes toward red OLEDs.</p>

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Short-lived TADF-Cu(I) complex for red OLEDs with EQEmax of 25.9% and <2% roll-off at 10,000 cd m−2

  • 期刊论文

  • 发表日期：

    2025年12月4日

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  • Yi Zhang,
  • Qizheng Zhang,
  • Xintong Wan,
  • Rongfang Zeng,
  • Nengquan Li,
  • Jingsheng Miao,
  • Xiu-Fang Song,
  • Xiaojun Yin,
  • Chuluo Yang,
  • Kai Li

摘要

Cu(I) complexes exhibiting thermally activated delayed fluorescence (TADF) have emerged as promising alternatives to noble-metal-based emitters for organic light-emitting diodes (OLEDs). However, the development of red-emitting Cu(I) complexes has been hindered by the slow radiative decay and fast nonradiative decay rate. In this study, a linear two-coordinate Cu(I) complex, namely ICuTMC, was designed and synthesized. Through pairing a pyrazine-fused N-heterocyclic carbene and a tetra-methylcarbazolyl ligand, a strong ligand-to-ligand charge transfer excited state is generated. Single crystal structure authenticates the presence of close intramolecular C–H⋯Cu contacts, providing a good steric shielding environment to the metal center. The C–H⋯π interactions between the ligands are also revealed. The Cu(I) complex exhibits highly efficient red TADF with an emission maximum of 622 nm, a photoluminescence quantum yield of 76% and a short delayed fluorescence lifetime of 0.24 µs. This is conceived to be enabled by a large oscillator strength associated with the coplanar donor-Cu-acceptor conformation, a small singlet-triplet excited states energy gap resulting from the spatial separation of the frontier molecular orbitals, and a strong spin-orbit coupling effect brought about by the metal center. Vacuum-deposited OLEDs based on ICuTMC exhibit a peak external quantum efficiency of 25.9% and a significantly small roll-off (1.9%) at 10,000 cd m−2. These performances demonstrate a way to overcome the energy gap law for linear coinage metal complexes toward red OLEDs.