Konidena Rajendra Kumar, Lee Kyung Hyung, Lee Jun Yeob, Hong Wan Pyo
School of Chemical Engineering, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon, Gyeonggi, 440-746, Korea.
LG Chem, Ltd, LG Science Park, 30, Magokjungang 10-ro, Gangseo-gu, Seoul, 07796, Republic of Korea.
Chem Asian J. 2019 Jul 1;14(13):2251-2258. doi: 10.1002/asia.201900388. Epub 2019 Jun 5.
Establishment of the structure-property relationships of thermally activated delayed fluorescence (TADF) materials has become a significant quest for the scientific community. Herein, two new donors, 10H-benzofuro[3,2-b]indole (BFI) and 10H-benzo[4,5]thieno[3,2-b]indole (BTI), have been developed and integrated with a aryltriazine acceptor to design the green TADF emitters benzofuro[3,2-b]indol-10-yl)-5-(4,6-diphenyl-1,3,5-triazin-2-yl)benzonitrile (BFICNTrz) and 2-(10H-benzo[4,5]thieno[3,2-b]indol-10-yl)-5-(4,6-diphenyl-1,3,5-triazin-2-yl)benzonitrile (BTICNTrz), respectively. The physicochemical and electroluminescence properties of the compounds were tuned by exchanging the heteroatom in the donor scaffold. Intriguingly, the electronegativity of the heteroatom and the ionization potential of the donor unit played vital roles in control of the singlet-triplet energy splitting and TADF mechanism of the compounds. Both compounds showed similar singlet excited states that originated from the charge transfer (CT) states ( CT), whereas the triplet excited states were tuned by the heteroatom in the donor unit. The origin of phosphorescence in the BTICNTrz emitter was CT emission from the triplet state ( CT), whereas that in the BFICNTrz emitter stemmed from the local triplet excited state ( LE). Consequently, BTICNTrz showed a small singlet-triplet energy splitting of 0.08 eV, compared with 0.26 eV for BFICNTrz. Thus, BTICNTrz showed efficient delayed fluorescence with a high quantum yield and a short delayed exciton lifetime, whereas BFICNTrz displayed weak delayed fluorescence with a relatively long lifetime. Furthermore, a BTICNTrz-based device exhibited a maximum external quantum efficiency (EQE) of 15.2 % and reduced efficiency roll-off (12 %) compared with its BFICNTrz-based counterpart, which showed a maximum EQE of 6.4 % and severe efficiency roll-off (55 %) at a practical brightness range of 1000 cd m . These results demonstrate that the choice of subunit plays a vital role in the design of efficient TADF emitters.
建立热激活延迟荧光（TADF）材料的结构-性能关系已成为科学界的一项重要探索。在此，开发了两种新型供体，10H-苯并呋喃并[3,2-b]吲哚（BFI）和10H-苯并[4,5]噻吩并[3,2-b]吲哚（BTI），并将它们与芳基三嗪受体整合，分别设计出绿色TADF发射体苯并呋喃并[3,2-b]吲哚-10-基)-5-(4,6-二苯基-1,3,5-三嗪-2-基)苯甲腈（BFICNTrz）和2-(10H-苯并[4,5]噻吩并[3,2-b]吲哚-10-基)-5-(4,6-二苯基-1,3,5-三嗪-2-基)苯甲腈（BTICNTrz）。通过交换供体骨架中的杂原子来调节化合物的物理化学和电致发光性能。有趣的是，杂原子的电负性和供体单元的电离势在控制化合物的单重态-三重态能量分裂和TADF机制中起着至关重要的作用。两种化合物都表现出源于电荷转移（CT）态（ CT）的相似单重激发态，而三重激发态则由供体单元中的杂原子调节。BTICNTrz发射体中磷光的起源是三重态（ CT）的CT发射，而BFICNTrz发射体中的磷光则源于局域三重激发态（ LE）。因此，BTICNTrz的单重态-三重态能量分裂较小，为0.08 eV，而BFICNTrz为0.26 eV。因此，BTICNTrz表现出高效的延迟荧光，具有高量子产率和短延迟激子寿命，而BFICNTrz则表现出较弱的延迟荧光，寿命相对较长。此外，基于BTICNTrz的器件在实际亮度范围为1000 cd m 时，最大外量子效率（EQE）为15.2%，效率滚降降低（12%），而基于BFICNTrz的器件在该亮度范围内最大EQE为6.4%，且效率滚降严重（55%）。这些结果表明，亚基的选择在高效TADF发射体的设计中起着至关重要的作用。
