Mesogenic Groups Control the Emitter Orientation in Multi-Resonance TADF Emitter Films

The use of thermally activated delayed fluorescence (TADF) emitters and emitters that show preferential horizontal orientation of their transition dipole moment (TDM) are two emerging strategies to enhance the efficiency of OLEDs. We present the first example of a liquid crystalline multi-resonance TADF (MR-TADF) emitter, DiKTa-LC. The compound possesses a nematic liquid crystalline phase between 80 degrees C and 110 degrees C. Importantly, the TDM of the spin-coated film shows preferential horizontal orientation, with an anisotropy factor, a, of 0.28, which is preserved in doped poly(vinylcarbazole) films. Green-emitting (lambda(EL)=492 nm) solution-processed OLEDs based on DiKTa-LC showed an EQE(max) of 13.6 %. We thus demonstrate for the first time how self-assembly of a liquid crystalline TADF emitter can lead to the so-far elusive control of the orientation of the transition dipole in solution-processed films, which will be of relevance for high-performance solution-processed OLEDs.

Automated summary

The use of TADF emitters and emitters with preferential horizontal TDM orientation are two emerging strategies to enhance OLED efficiency. In this study, a liquid crystalline MR-TADF emitter, DiKTa-LC, was introduced. The spin-coated film of DiKTa-LC exhibited a preferential horizontal TDM orientation with an anisotropy factor of 0.28. Green-emitting solution-processed OLEDs based on DiKTa-LC achieved an EQE(max) of 13.6%. This study demonstrates how self-assembly of a liquid crystalline TADF emitter can control the orientation of the transition dipole in solution-processed films, which is relevant for high-performance OLEDs.