Lee Ha Lim, Kang Jihoon, Lim Junseop, Kim Seung Chan, Jeon Soon Ok, Lee Jun Yeob
School of Chemical Engineering, Sungkyunkwan University 2066, Seobu-ro, Jangan-gu, Suwon-si, Gyeonggi-do, 16419, Korea.
Samsung Advanced Institute of Technology, Samsung Electronics, 130 Samsung-ro, Suwon, Gyeonggi, 16678, Republic of Korea.
Nat Commun. 2023 Aug 9;14(1):4818. doi: 10.1038/s41467-023-40481-w.
Multiple resonance (MR) thermally activated delayed fluorescence emitters have been actively studied as pure blue dopants for organic light-emitting diodes (OLEDs) because of excellent color purity and high efficiency. However, the reported MR emitter, 2,5,13,16-tetra-tert-butylindolo[3,2,1-jk]indolo[1',2',3':1,7]indolo[2,3-b]carbazole (tDIDCz) based on bis-fused indolocarbazole framework could not demonstrate efficient triplet-to-singlet spin crossover. In this work, we report two isomeric MR emitters designed to promote triplet exciton harvesting by reconstructing the electronic structure of tDIDCz. To manage excited states, strong electron donors were introduced at the 2,5-/1,6-position of tDIDCz. As a result, 2,5-positions managed tDIDCz shows long-range charge transfer characteristics while preserving the MR nature. Quantum chemical calculation demonstrates direct spin-orbit coupling by long-range charge transfer and spin-vibronic coupling assisted reverse intersystem crossing by short-range charge transfer simultaneously contribute to triplet-to-singlet spin crossover. Consequently, high performance blue OLED recorded a high external quantum efficiency of 30.8% at a color coordinate of (0.13, 0.13).
由于具有出色的色纯度和高效率，多共振（MR）热激活延迟荧光发射体作为有机发光二极管（OLED）的纯蓝色掺杂剂受到了广泛研究。然而，报道的基于双稠合吲哚咔唑骨架的MR发射体2,5,13,16-四叔丁基吲哚并[3,2,1-jk]吲哚并[1',2',3':1,7]吲哚并[2,3-b]咔唑（tDIDCz）无法实现有效的三重态到单重态自旋交叉。在这项工作中，我们报道了两种异构体MR发射体，它们通过重构tDIDCz的电子结构来促进三重态激子的捕获。为了控制激发态，在tDIDCz的2,5-/1,6-位引入了强电子供体。结果，2,5-位修饰的tDIDCz在保持MR性质的同时表现出长程电荷转移特性。量子化学计算表明，长程电荷转移引起的直接自旋-轨道耦合和短程电荷转移辅助的自旋-振动耦合反向系间窜越同时促成了三重态到单重态的自旋交叉。因此，高性能蓝色OLED在色坐标（0.13, 0.13）下实现了30.8%的高外量子效率。
