Department of Chemistry , National Taiwan University , Taipei 10617 , Taiwan.
Institute of Optoelectronic Sciences , National Taiwan Ocean University , Keelung 202 , Taiwan.
ACS Appl Mater Interfaces. 2018 Apr 18;10(15):12930-12936. doi: 10.1021/acsami.8b02766. Epub 2018 Apr 9.
Two isomeric host materials (Sy and Asy) comprising carbazole (donor) and CN-substituted pyrimidine (acceptor) were synthesized, characterized, and utilized as host materials for green and blue thermally activated delayed fluorescence (TADF) organic light emitting diodes (OLEDs). Both molecules have high triplet energy and small energy difference between singlet and triplet states, leading to feasible TADF. The different linking topologies of carbazole and CN groups on the pyrimidine core provide distinct photophysical properties and molecular packing manners, which further influence the efficiency as they served as hosts in TADF OLEDs. As compared to Asy-based cases, the Sy-hosted TADF OLED device gave higher maximum external quantum efficiencies (EQE) of 24.0% (vs 22.5%) for green (4CzIPN as a dopant) and 20.4% (vs 15.0%) for blue (2CzTPN as a dopant) and low efficiency roll-off. The high horizontal dipole ratio (Θ ≈ 88%) for both emitters dispersed in Sy and Asy hosts accounts for the high device efficiency. A clear molecular structure-physical property-device performance relationship has been established to highlight the importance of symmetrical structure in TADF host material design.
两种同分异构的主体材料（Sy 和 Asy），由咔唑（给体）和 CN 取代的嘧啶（受体）组成，进行了合成、表征，并用作绿光和蓝光热激活延迟荧光（TADF）有机发光二极管（OLED）的主体材料。这两种分子都具有高三重态能量和单重态与三重态之间的小能量差，从而实现了可行的 TADF。咔唑和 CN 基团在嘧啶核上的不同连接拓扑结构提供了不同的光物理性质和分子堆积方式，这进一步影响了它们作为 TADF OLED 主体材料的效率。与基于 Asy 的情况相比，基于 Sy 的 TADF OLED 器件为绿光（以 4CzIPN 为掺杂剂）和蓝光（以 2CzTPN 为掺杂剂）分别提供了更高的最大外量子效率（EQE）24.0%（22.5%）和 20.4%（15.0%），并且效率滚降较低。两种发射器在 Sy 和 Asy 主体中分散时的高水平偶极比（Θ≈88%）是器件高效率的原因。已经建立了明确的分子结构-物理性质-器件性能关系，突出了在 TADF 主体材料设计中对称结构的重要性。
