TADF-DLC-OLEDs · Development of highly efficient solution-processable blue organic light-emitting diodes based on liquid-crystalline thermally activated delayed fluorescent emitter materials

Development of highly efficient solution-processable blue organic light-emitting diodes based on liquid-crystalline thermally activated delayed fluorescent emitter materials

This project aimed to develop efficient, stable, and inexpensive blue thermally activated delayed fluorescence (TADF) emitters based on discotic liquid crystalline (DLC) molecules, which will facilitate horizontal alignment of the transition dipole moment in solution-processed films in order to improve the light-outcoupling efficiency and hence the external quantum efficiency (EQE) in solution-processable organic light-emitting diodes (SP-OLEDs). To achieve this horizon, we first explored how to regulate the columnar self-assembly in the liquid crystalline state of the discotic TADF emitters, which had not been investigated in the previous reports. In this project, we proposed the following different design strategies to obtain horizontal alignment in DLCs with TADF emission: i) Strategy 1 is through implication of the central multi-resonant TADF (MR-TADF) moiety attached with peripheral mesogenic unit maintaining the discotic shape of the designed molecule; ii) Strategy 2 regulates the electronic coupling between a donor-acceptor (D-A) TADF, which consists of a small molecular acceptor and a donor-containing mesogenic unit, through molecular conjugation. Objectives Overall assessment: The project has achieved one of its two major objectives and milestones for the period, with relatively minor deviations. Over the period of the fellowship, JD has successfully achieved specific scientific and training objectives as specified in the DoA: Computational calculations: JD has carried out numerous theoretical calculations for TADF emitters and model compounds using density functional theory (DFT) protocols in the group. Organic synthesis: JD has received the opportunity to strengthen his organic synthetic skills by continuing to work on air and moisture-sensitive reactions such as lithiation reactions, C-C, and C-N couplings. Advanced purification techniques: JD received hands-on experience in using purification techniques such as combiflash, gel permeation chromatography (GPC), and gradient temperature sublimation techniques. Analytical skills: JD strengthened his analytical skills through hands-on training on GC-MS, HPLC, and 1D/2D NMR (1H, 13C, 11B, 19F) spectroscopy. Optoelectronic characterization skill: JD expanded his knowledge of spectroscopic instruments such as UV-vis absorption spectrophotometers, electrochemical workstations, fluorimeters, time-resolved fluorescence instruments, and temperature-dependent PL. Device fabrication skill: JD reinforced device fabrication techniques and expanded his device fabrication skills to solution-processed OLEDs. Data management: JD has received training and learned better ways to resource and data management. Communication skills: JD has strengthened his communication and presentation skills by presenting his projects and progress to group meetings and subgroup meetings. JD has received multiple opportunities to discuss his projects with visiting group leaders from other universities and collaborators.

Data: CORDIS, © European Union