Liu Qinglin, Deng Yun, Ren Baoyi, Lan Xia, Zhang Yuehong, Guo Runda, Li Chensheng, Xiong Gang, Sun Yaguang, Zhao Zujin
College of Science, Key Laboratory of Inorganic Molecule-Based Chemistry of Liaoning Province, Shenyang University of Chemical Technology, Shenyang 110142, China.
Frontiers Science Center for Flexible Electronics, Xi'an Institute of Flexible Electronics and Xi'an Institute of Biomedical Materials & Engineering, Northwestern Polytechnical University, Xi'an 710072, China.
Nanomaterials (Basel). 2023 Sep 8;13(18):2517. doi: 10.3390/nano13182517.
For developing high-performance organic light-emitting diodes (OLEDs) with thermally activated delayed fluorescent (TADF) emitters, the diphenyltriazine (TRZ) unit was introduced onto the 2'- and 3'-positions of xanthene moiety of spiro[fluorene-9,9'-xanthene] (SFX) to construct n-type host molecules, namely 2'-TRZSFX and 3'-TRZSFX. The outward extension of the TRZ unit, induced by the -linkage, resulted in a higher planarity between the TRZ unit and xanthene moiety in the corresponding 3'-TRZSFX. Additionally, this extension led to a perched level, as well as a lower unoccupied molecular orbital (LUMO) level when compared with 2'-TRZSFX. Meanwhile, the 3'-TRZSFX molecules in the crystalline state presented coherent packing along with the interaction between TRZ units; the similar packing motif was spaced apart from xanthene moieties in the 2'-TRZSFX crystal. These endowed 3'-TRZSFX superior electron transport capacity in single-carrier devices relative to the 2'-TRZSFX-based device. Hence, the 3'-TRZSFX-based TADF-OLED showed remarkable electroluminescent (EL) performance under the operating luminance from turn-on to ca. 1000 cd·m with a maximum external quantum efficiency () of 23.0%, thanks to its matched LUMO level with 4CzIPN emitter and better electron transport capacity. Interestingly, the 2'-TRZSFX-based device, with an of 18.8%, possessed relatively low roll-off and higher efficiency when the operating luminance exceeded 1000 cd·m, which was attributed to the more balanced carrier transport under high operating voltage. These results were elucidated by the analysis of single-crystal structures and the measurements of single-carrier devices, combined with EL performance. The revealed position effect of the TRZ unit on xanthene moiety provides a more informed strategy to develop SFX-based hosts for highly efficient TADF-OLEDs.
为了开发具有热激活延迟荧光（TADF）发光体的高性能有机发光二极管（OLED），将二苯基三嗪（TRZ）单元引入到螺[芴-9,9'-呫吨]（SFX）的呫吨部分的2'-和3'-位，以构建n型主体分子，即2'-TRZSFX和3'-TRZSFX。由 - 键诱导的TRZ单元向外延伸，导致相应的3'-TRZSFX中TRZ单元与呫吨部分之间具有更高的平面度。此外，与2'-TRZSFX相比，这种延伸导致了一个更高的占据能级以及更低的未占据分子轨道（LUMO）能级。同时，结晶态的3'-TRZSFX分子呈现出与TRZ单元之间相互作用的相干堆积；在2'-TRZSFX晶体中，类似的堆积模式与呫吨部分间隔开。相对于基于2'-TRZSFX的器件，这些赋予了3'-TRZSFX在单载流子器件中优异的电子传输能力。因此，基于3'-TRZSFX的TADF-OLED在从开启到约1000 cd·m-2的工作亮度下表现出显著的电致发光（EL）性能，最大外量子效率（）为23.0%，这得益于其与4CzIPN发光体匹配的LUMO能级和更好的电子传输能力。有趣的是，基于2'-TRZSFX的器件，外量子效率为18.8%，当工作亮度超过1000 cd·m-2时具有相对较低的效率滚降和更高的效率，这归因于在高工作电压下更平衡的载流子传输。通过单晶结构分析、单载流子器件测量以及EL性能相结合，阐明了这些结果。TRZ单元在呫吨部分上揭示的位置效应为开发用于高效TADF-OLED的基于SFX的主体提供了更明智的策略。
