SCIENCE CHINA Materials•2026•DOI: 10.1007/s40843-026-4094-8
Deep-blue multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters with high efficiency, high color purity, and high brightness are critically important for next-generation OLED displays, yet remain challenging due to severe aggregation and host-guest interactions in the solid state. Herein, we report a core-encapsulating molecular design strategy in which bulky and non-conjugated peripheral groups are introduced to sterically encapsulate a blue-emitting MR core, thereby suppressing intermolecular π-π interactions without perturbing its intrinsic electronic structure. Two new emitters, DNa-BN and QNa-BN, featuring half-encapsulated and fully encapsulated MR-core architectures, respectively, were developed. Owing to its fully encapsulated structure, QNa-BN exhibits pronounced aggregation resistance at high doping concentrations, maintaining photoluminescence quantum yields exceeding 96%, radiative decay rate constants on the order of 10^8 s−1, and fast reverse intersystem crossing rates (~10^5 s−1). Consequently, sensitizer-free OLEDs based on QNa-BN deliver narrowband deep-blue emission at 458 nm with a full width at half maximum of 22 nm, CIE coordinates of (0.142, 0.085), a maximum external quantum efficiency (EQE_max) of 34.4%, and a maximum luminance exceeding 20,000 cd m−2. Furthermore, by adopting a hyperfluorescence architecture, the EQE_max is further boosted to 38.7% with significantly suppressed efficiency roll-off. This work demonstrates that steric encapsulation of the MR core provides an effective and general approach to achieving aggregation-resistant, high-efficiency, and high-brightness deep-blue MR-TADF emitters for OLED applications.
SCIENCE CHINA Materials•2026•DOI: 10.1007/s40843-025-3595-7
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 slow radiative decay and fast nonradiative decay. In this study, a linear two-coordinate Cu(I) complex, ICuTMC, was designed and synthesized. By 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 close intramolecular C–H···Cu contacts, providing good steric shielding to the metal center. C–H···π interactions between ligands are also revealed. The complex exhibits highly efficient red TADF with emission maximum at 622 nm, photoluminescence quantum yield of 76%, and short delayed fluorescence lifetime of 0.24 μs. This is enabled by a large oscillator strength from the coplanar donor-Cu-acceptor conformation, a small singlet-triplet energy gap from spatial separation of frontier molecular orbitals, and strong spin-orbit coupling from the metal center. Vacuum-deposited OLEDs based on ICuTMC achieve a peak external quantum efficiency of 25.9% and a significantly small roll-off of 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.
SCIENCE CHINA Materials•2026•DOI: 10.1007/s40843-025-3820-5
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. Single-crystal structures revealed a meridional coordination geometry for both complexes. Shorter Ir–C carbene bond lengths and rigid planar BO-fused ring units contribute to enhanced stability. Both complexes exhibit efficient green phosphorescence (λem = 536/521 nm in toluene, ΦPL > 78%) with short lifetimes (τ = 846/1083 ns), leading to high radiative rate constants (Kr = 10.04 × 10^5 and 7.29 × 10^5 s−1, respectively). Theoretical calculations indicate significantly increased metal-to-ligand charge transfer (MLCT) character (21.69% for mer-Ir(Bpmi)3; 17.30% for mer-Ir(Bpmb)3) compared to reference complexes (13.01% for mer-Ir(pmi)3; 15.99% for mer-Ir(pmb)3). Both complexes exhibit exceptional thermal stability with decomposition temperatures of 491°C (mer-Ir(Bpmi)3) and 540°C (mer-Ir(Bpmb)3). OLED devices using mer-Ir(Bpmb)3 and mer-Ir(Bpmi)3 as emitters demonstrate maximum external quantum efficiencies of 20.0% and 15.6%, respectively. This research pioneers boron-fused ring-containing NHCs and their phosphorescent iridium(III) complexes, establishing a novel design strategy for high-performance NHC-based OLED phosphorescent emitters.