Harnessing the orientation of columnar discotic liquid crystals for narrowband blue emission with enhanced out-coupling efficiency toward improvement of SP-OLEDs performance

Controlling the supramolecular alignment of columnar mesogens offers a strategy to optimize charge transport and orientation of the transition dipole moment of emissive solution-processed films, ultimately enabling the fabrication of more efficient solution-processable OLEDs. Here, we report the development of multi-resonant thermally activated delayed fluorescent (MR-TADF) discotic liquid crystals (DLCs) containing a diindolocarbazole emissive core that is decorated with four mesogenic groups that are either branched (DICz-DMOC) or linear (DICz-DOD) in nature. DICz-DMOC adopts a columnar mesophase at room temperature, where the neat film shows homeotropic alignment to the substrate surface. Emission is broad and partially quenched as neat films due to the formation of aggregates, while in toluene and as 10 wt.% doped films in mCP, emission originates mainly from monomolecular species. The DLCs align horizontally, which also orients the transition dipole moment of the emitters preferentially horizontally, reflected in an anisotropy factor, a, of 0.22 for the solution-processed neat films. Solution-processed OLEDs (SP-OLEDs) containing DICz-DMOC as the emitter showed a maximum external quantum efficiency (EQE_max) of 10.0% in doped devices and 5.3% in non-doped devices, representing some of the highest device efficiencies using emitters bearing mesogenic groups.