A novel thermally activated delayed fluorescence (TADF) emitter 12,15‐di(10H‐phenoxazin‐10‐yl)dibenzo[a,c]dipyrido[3,2‐h:2′,3′‐j]phenazine (DPXZ‐BPPZ) is developed for a highly efficient red organic light‐emitting diode (OLED). With rigid and planar constituent groups and evident steric hindrance between electron‐donor (D) and electron‐acceptor (A) segments, DPXZ‐BPPZ realizes extremely high rigidity to suppress the internal conversion process. Meanwhile, the highly twisted structure between D and A segments will also lead to an extremely small singlet–triplet energy split to DPXZ‐BPPZ. Therefore, DPXZ‐BPPZ successfully realizes an efficient fluorescent radiation transition and reverse intersystem crossing process, and possesses an extremely high photoluminescence quantum efficiency of 97.1 ± 1.1% under oxygen‐free conditions. The OLED based on DPXZ‐BPPZ shows red emission with a peak at 612 nm and a Commission Internationale de L'Eclairage (CIE) coordinate of (0.60, 0.40), and it achieves high maximum forward‐viewing efficiencies of 20.1 ± 0.2% (external quantum efficiency), 30.2 ± 0.6 cd A⁻¹ (current efficiency), and 30.9 ± 1.3 lm W⁻¹ (power efficiency). The prepared OLED has the best performance among the reported red TADF OLEDs. These results prove that DPXZ‐BPPZ is an ideal candidate for red TADF emitters, and the designing approach is valuable for highly efficient red TADF emitters.

中文翻译：

---

基于新型热激活延迟荧光发射体的外部量子效率超过20％的红色有机发光二极管

一种新型的热活化延迟荧光（TADF）发射体12,15-di（10 H -phenoxazin-10-yl）dibenzo [ a，c ] dipyrido [3,2‐ h：2′，3′‐ j] phenazine（DPXZ-BPPZ）是为高效的红色有机发光二极管（OLED）开发的。DPXZ-BPPZ具有刚性和平面的组成基团，并且在电子给体（D）和电子受体（A）之间存在明显的空间位阻，因此实现了极高的刚性，从而抑制了内部转换过程。同时，D和A段之间的高度扭曲结构也将导致极小的单重态-三重态能量分配给DPXZ-BPPZ。因此，DPXZ-BPPZ成功地实现了有效的荧光辐射跃迁和逆系统间交叉过程，并且在无氧条件下具有97.1±1.1％的极高光致发光量子效率。基于DPXZ-BPPZ的OLED显示红色发射，峰值在612 nm处，并且国际照明委员会（CIE）坐标为（0.60，0。^-1（电流效率）和30.9±1.3 lm W ^-1（功率效率）。所制备的OLED在报道的红色TADF OLED中具有最佳性能。这些结果证明，DPXZ-BPPZ是红色TADF发射器的理想选择，并且该设计方法对于高效红色TADF发射器非常有价值。