A Columnar Liquid Crystalline Self-Assembly of a Donor–Acceptor TADF Emitter Design for Solution-Processed OLEDs

Abstract

The self-assembly of π-conjugated molecules into supramolecular columnar structures has become as an effective strategy for the creation of soft, durable, and adaptable materials with immense potential for application in organic optoelectronic devices. In this regard, the columnar organization of discotic liquid crystals (DLCs) is well-studied in terms of a quasi-1D charge transport medium, which can be exploited across a range of organic electronic device applications. There are relatively few examples of room temperature columnar DLCs emitting thermally activated delayed fluorescent (TADF). Herein, we demonstrate a molecular design strategy to deliver a material that simultaneously shows bright and efficient TADF and self-organizes into columnar DLCs at room temperature. The compound TCzTRZ-DLC contains three dendrimeric carbazole-based donors with mesogenic units decorating a central 1,3,5-triphenyltriazine acceptor. Notably, the system exhibited a desired homeotropic alignment resulting in preferential aromatic p-stacking among disc-like molecules, which is beneficial to boost the light out-coupling efficiency in solution-processed organic light-emitting diodes (OLEDs). The resulting green-emitting SP-OLEDs emitted at l_EL of 488 nm and showed a maximum external quantum efficiency, EQE_max of 15.5%. This represents a significant improvement in OLED efficiency compared to other solution-processed devices using TADF emitters bearing mesogenic groups.