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.