First N‑Borylated Emitters Displaying Highly Efficient Thermally Activated Delayed Fluorescence and High-Performance OLEDs

Despite the fast boom of thermally activated delayed fluorescence (TADF) emitters bearing borane-based acceptor, so far, no TADF emitter with a direct B–N linkage between N-donor and boryl acceptor has been reported. The latter should simplify the molecular architecture and hence facilitate the synthetic design and versatility. We report here the preparation and characterization of a new series of N-borylated compounds with functional acridine donor unit; namely: ACBM, PACBM, and SACBM. Spectroscopic studies were performed to explore their photophysical properties that exhibited prominent solvatochromism and thermally activated delayed fluorescence. The time-dependent DFT calculation indicated the involvement of substantial intramolecular charge transfer character for which HOMO and LUMO are spatially separated. For compound SACBM, fabrication of green emitting OLED gave CIE chromaticity of (0.22, 0.59) and maximum external quantum efficiency, luminance efficiency and power efficiency of 19.1%, 60.9 cd/A, and 43.6 lm/W, respectively, demonstrating for the first time the highly efficient OLEDs using N-borylated TADF emitters.尽管带有硼基受体的热激活延迟荧光（TADF）发光体研究发展迅猛，但迄今为止，尚未有报道过在N给体与硼基受体之间存在直接B-N键的TADF发光体。此类结构本可简化分子架构，进而助力合成设计与应用通用性的提升。本文报道了一类带有官能化吖啶给体单元的新型N-硼基化化合物，即ACBM、PACBM与SACBM的制备与表征。通过光谱研究对其光物理性质展开探究，结果显示这些化合物均表现出显著的溶剂致变色效应与热激活延迟荧光特性。含时DFT计算结果表明，此类化合物具有显著的分子内电荷转移特征，其最高占据分子轨道（HOMO）与最低未占据分子轨道（LUMO）在空间上相互分离。针对化合物SACBM，制备的绿色发光有机发光二极管（OLED）的CIE色度坐标为(0.22, 0.59)，最大外量子效率、亮度效率与功率效率分别可达19.1%、60.9 cd/A及43.6 lm/W，首次证实了采用N-硼基化TADF发光体可制备高效OLED器件。