Two bipolar host materials were designed and synthesized for blue thermally activated delayed fluorescence (TADF) OLEDs. Both bipolar materials, 5-(4-(dibenzo[b,d]furan-2-yl)-pyridin-2-yl)-5H-benzo[d]benzo-[4,5]imidazo[1,2-a]imidazole (4-DBFBI) and 5-(5-(dibenzo[b,d]furan-2-yl)-pyridin-2-yl)-5H-benzo[d]benzo-[4,5]imidazo[1,2-a]imidazole (5-DBFBI), were constructed with a hole-transporting type of benzimidazole moiety and an electron-transporting type of dibenzofuran moiety, and these derivatives exhibit high triplet energy over 3.10 eV. To achieve a high triplet energy level, a pyridine linker was placed between the benzimidazole and dibenzofuran moieties. As a result, 4-DBFBI and 5-DBFBI showed a high triplet energy level of 3.06 eV and 2.96 eV, respectively. Further, blue TADF devices were fabricated with our synthesized bipolar host materials. For our current study, we adopted 5,10-diphenyl-15-(10-(2,4,6-triisopropylphenyl)-10H-dibenzo[b,e][1,4]oxaborinin-3-yl)-10,15-dihydro-5H-diindolo[3,2-a:3′,2′-c]carbazole (PXB-DI) as the blue TADF dopant. The maximum external quantum efficiencies of the 20 wt% blue TADF devices were 31.8 and 32.5% for 4-DBFBI and 5-DBFBI, respectively. Moreover, the 4-DBFBI based host device exhibited a very low efficiency roll-off of 0.93 up to 1000 cd m⁻², which is attributed to its well-balanced charge transporting ability.

中文翻译：

---

高三重态能量双极主体材料，结合二苯并呋喃和苯并咪唑并苯并咪唑部分，用于蓝色热激活的延迟荧光发射体

设计并合成了两种双极性主体材料，用于蓝色热激活延迟荧光（TADF）OLED。两种双极材料，5-（4-（二苯并[ b，d ]呋喃-2-基）-吡啶-2-基）-5 H-苯并[ d ]苯并-[4，5]咪唑[1,2- a ]咪唑（4-DBFBI）和5-（5-（二苯并[ b，d ]呋喃-2-基）-吡啶-2-基）-5 H-苯并[ d ]苯并-[4,5]咪唑[1,2- a用咪唑（5-DBFBI）空穴传输型苯并咪唑部分和电子传输型二苯并呋喃部分构建，这些衍生物在3.10 eV以上显示出高三重态能量。为了获得高的三线态能量水平，将吡啶连接基置于苯并咪唑和二苯并呋喃部分之间。结果，4-DBFBI和5-DBFBI分别显示出3.06 eV和2.96 eV的高三重态能级。此外，蓝色TADF器件是用我们合成的双极主体材料制造的。在我们当前的研究中，我们采用了5,10-二苯基-15-（10-（2,4,6-三异丙基苯基）-10 H-二苯并[ b，e ] [1,4] oxaborinin-3-yl）-10 ，15-dihydro-5 H -diindolo [3,2- a：3'，2'- c]咔唑（PXB-DI）作为蓝色TADF掺杂剂。对于4-DBFBI和5-DBFBI，20 wt％蓝色TADF器件的最大外部量子效率分别为31.8和32.5％。此外，基于4-DBFBI的主机设备在1000 cd m ^-2时表现出0.93的非常低的效率下降，这归因于其良好平衡的电荷传输能力。