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

Abstract

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(9 H -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.

High Triplet Energy Phosphine Sulfide Host Materials with Selectively Modulated Electrical Performance for Blue Electrophosphorescence

“…Moreover, the molecular conformation and intra-/intermolecular packing arrangement of DBFSPS , DBTSPS , DBFDPS , and DBTDPS (Figure b,c, Figure S13, and Table S1) were evaluated by single-crystal X-ray diffraction analysis. Notably, DBTSPS exhibits interlaced molecular packing mode and large crystal density, potentially facilitating the establishment of charge-transporting network and suppressing the aggregation of emissive phosphors, which could probably strengthen the charge carrier flux and recombination performance and reduce the concentration quenching of triplet excitons for significantly improving electroluminescent (EL) properties. − …”

Asymmetric Host Molecule Bearing Pyridine Core for Highly Efficient Blue Thermally Activated Delayed Fluorescence OLEDs

“…As shown in Scheme 1, the structural difference between the two host materials pCzBzbCz and pCzPybCz lies in the core (i.e.,p henyl and pyridine), whichd emonstratest he same 2,5substitution positiono ft he carbazole and9 H-3,9'-bicarbazole units. The two host materials were modifiedf rom the known CCP [30,31] and PyDCz [34] molecules by including the 9H-3,9'-bicarbazole unit instead of as ingle carbazole unit.…”

A Si-Substituted Spirobifluorene Hole-Transporting Material for Perovskite Solar Cells

“…The bandgap of small molecular organic semiconductors tends to decrease as the size of the molecule or the conjugated system increases, as larger molecules have more closely spaced energy levels, which results in a small energy difference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) . However, the HOMO–LUMO gap of organic materials is more complex than that of inorganic semiconductors due to their molecular conformation and packing structure . The optical red-shift can be further discussed in conjunction with the molecular structure.…”

“…29 However, the HOMO−LUMO gap of organic materials is more complex than that of inorganic semiconductors due to their molecular conformation and packing structure. 30 The optical red-shift can be further discussed in conjunction with the molecular structure.…”