The secondary donor/acceptor has significant effects on the excited-state properties and efficiencies of thermally activated delayed fluorescent (TADF) emitters. Here, we use two electron-withdrawing units (cyanobenzene and trifluoromethylbenzene) as a secondary acceptor to control the electron-withdrawing ability of the dibenzo[a,c]phenazine (BP) acceptor core based on the BP-triphenylamine (TPA) backbone. The synthesized orange-red TADF emitters (CN-BP-TPA and CF3-BP-TPA) exhibit the singlet-triplet energy splitting (ΔE_ST) values of 0.19 and 0.23 eV, respectively. Both emitters show a high photoluminescence quantum yield up to 92%–98% in the doped films. The organic light-emitting diodes (OLEDs) based on CN-BP-TPA achieve the external quantum efficiency of 26.0%, power efficiency of 76.8 lm/W, and current efficiency of 61.1 cd/A as compared with 16.6%, 59.2 lm/W, and 50.9 cd/A of the CF3-BP-TPA counterpart. In addition, the non-doped OLED involving the non-doped CN-BP-TPA emitter shows an ultralow turn-on voltage of 2.2 V and an external quantum efficiency of 5.0%.

二级供体/受体对热激活延迟荧光 (TADF) 发射体的激发态特性和效率有显着影响。在这里，我们使用两个吸电子单元（氰基苯和三氟甲基苯）作为二级受体来控制基于 BP-三苯胺（TPA）骨架的二苯并[a，c]吩嗪（BP）受体核的吸电子能力。合成的橙红色 TADF 发射器（CN-BP-TPA和CF3-BP-TPA）分别表现出0.19 和 0.23 eV的单线态-三线态能量分裂（ΔE _ST）值。两种发射器在掺杂薄膜中都显示出高达 92%–98% 的高光致发光量子产率。基于CN-BP-TPA的有机发光二极管 (OLED)与CF3-BP-TPA对应物的16.6%、59.2 lm/W 和 50.9 cd/A 相比，实现了 26.0% 的外部量子效率、76.8 lm/W 的功率效率和 61.1 cd/A 的电流效率。此外，涉及非掺杂CN-BP-TPA发射极的非掺杂 OLED显示出 2.2 V 的超低开启电压和 5.0% 的外部量子效率。