Tuning Intramolecular Conformation and Packing Mode of Host Materials through Noncovalent Interactions for High-Efficiency Blue Electrophosphorescence

Molecular conformation plays an important role in tuning the packing modes of organic optoelectronic materials to achieve enhanced and/or balanced charge transport. Here, we introduce the noncovalent intramolecular interactions to the host materials of phosphorescent organic light-emitting diodes (PhOLEDs). Different numbers and/or positions of intramolecular CH···N noncovalent interactions were constructed by using different N-heterocycles of pyridine, pyrimidine, and pyrazine as acceptor units and carbazole as the donor unit in a donor-acceptor-donor (D-A-D) motif. Thus, designed D-A-D molecules were synthesized facilely through a one-step Ullmann reaction in high yields, showing varied intramolecular interactions to regulate the molecular conformation significantly. Impressively, owing to the quasi-parallel molecular conformation, which is beneficial for forming facile transporting channels of both holes and electrons, the newly designed host material of 9,9′-(pyridine-2,5-diyl)­bis­(9H-carbazole) exhibits good device performance of blue PhOLEDs with current, power, and external quantum efficiencies up to 33.0 cd A–1, 32.1 lm W–1, and 16.3%, respectively. This work highlights the significant importance of the noncovalent interactions in designing advanced organic semiconductors for high-performance optoelectronic devices.

分子构象在调控有机光电材料的堆积模式以实现电荷传输性能增强与/或平衡方面具有重要作用。本研究将非共价分子内相互作用引入磷光有机发光二极管（PhOLEDs）的主体材料体系。通过在给体-受体-给体（D-A-D）结构基元中，以吡啶、嘧啶、吡嗪等不同氮杂环作为受体单元、咔唑作为给体单元，我们构建了不同数目与/或位置的分子内CH···N非共价相互作用。所设计的D-A-D型分子可通过一步乌尔曼反应以高产率便捷合成，且存在差异化的分子内相互作用，可显著调控其分子构象。值得关注的是，得益于有利于形成空穴与电子高效传输通道的准平行分子构象，主体材料9,9′-(吡啶-2,5-二基)双(9H-咔唑)展现出优异的蓝色PhOLED器件性能：其电流效率、功率效率及外量子效率最高分别可达33.0 cd A⁻¹、32.1 lm W⁻¹及16.3%。本研究凸显了非共价相互作用在设计用于高性能光电器件的先进有机半导体材料中的关键意义。