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.