Yi Rong-Huei, Liu Guan-Yang, Luo Yan-Teng, Wang Wei-Yu, Tsai Han-Yu, Lin Chien-Hsiang, Shen Hsiang-Ling, Chang Chih-Hao, Lu Chin-Wei
Department of Applied Chemistry, Providence University, Taichung, 43301, Taiwan.
Department of Electrical Engineering, Yuan Ze University, Chungli, 32003, Taiwan.
Chemistry. 2021 Sep 9;27(51):12998-13008. doi: 10.1002/chem.202101807. Epub 2021 Aug 5.
A series of dicyano-imidazole-based molecules with thermally activated delayed fluorescence (TADF) properties were synthesized to obtain pure blue-emitting organic light-emitting diodes (OLEDs). The targeted molecules used dicyano-imidazole with a short-conjugated system as the electron acceptor to strong intermolecular π-π interactions, and provide a relatively shallow energy level of the lowest unoccupied molecular orbital (LUMO). The cyano group was selected to improve imidazole as an electron acceptor due to its prominent electron-transporting characteristics. Four different electron donors, that is, 9,9-dimethyl-9,10-dihydroacridine (DMAC), 10H-spiro(acridine-9,9'-fluoren) (SPAC), and 9,9-diphenyl-9,10-dihydroacridine (DPAC), were used to alternate the highest occupied molecular orbital (HOMO) energy level to tune the emission color further. The crowded molecular structure in space makes the electron donor and acceptor almost orthogonal, reducing the energy gap (ΔE ) between the first excited singlet (S ) and the triplet (T ) states and introducing significant TADF property. The efficiencies of the blue-emissive devices with imM-SPAC and imM-DMAC obtained in this work are the highest among the reported imidazole-based TADF-OLEDs, which are 13.8 % and 13.4 %, respectively. Both of Commission Internationale de l'Eclairage (CIE) coordinates are close to the saturated blue region at (0.17, 0.18) and (0.16, 0.19), respectively. Combining these tailor-made TADF compounds with specific device architectures, electroluminescent (EL) emission from sky-blue to deep-blue could be achieved, proving their great potential in EL applications.
合成了一系列具有热激活延迟荧光（TADF）特性的基于二氰基咪唑的分子，以获得纯蓝色发光有机发光二极管（OLED）。目标分子使用具有短共轭体系的二氰基咪唑作为电子受体，以实现强分子间π-π相互作用，并提供相对较浅的最低未占据分子轨道（LUMO）能级。由于氰基突出的电子传输特性，选择氰基来改善咪唑作为电子受体的性能。使用四种不同的电子供体，即9,9-二甲基-9,10-二氢吖啶（DMAC）、10H-螺（吖啶-9,9'-芴）（SPAC）和9,9-二苯基-9,10-二氢吖啶（DPAC），来改变最高占据分子轨道（HOMO）能级，以进一步调节发射颜色。空间中拥挤的分子结构使电子供体和受体几乎正交，减小了第一激发单重态（S）和三重态（T）之间的能隙（ΔE），并引入了显著的TADF特性。在这项工作中获得的含imM-SPAC和imM-DMAC的蓝色发光器件的效率是已报道的基于咪唑的TADF-OLED中最高的，分别为13.8%和13.4%。国际照明委员会（CIE）坐标分别接近饱和蓝色区域，为（0.17, 0.18）和（0.16, 0.19）。将这些定制的TADF化合物与特定的器件结构相结合，可以实现从天蓝色到深蓝色的电致发光（EL）发射，证明了它们在EL应用中的巨大潜力。
