Design and synthesis of blue thermally activated delayed fluorescence emitters for organic light emitting diodes

Abstract

Thermally activated delayed fluorescence (TADF) has emerged as one of the most promising and efficient approaches to realize highly efficient organic light-emitting diodes (OLEDs). It took only several years for OLEDs using organic TADF emitters to reach efficiencies comparable to phosphorescent OLEDs. Chapter 1 presents an overview of the TADF mechanism and focuses more specifically on blue TADF emitter design and their use in OLEDs. There is still room for improvement in terms of highly efficient deep-blue TADF emitters. These include improving exciton lifetime and reducing exciton annihilation in device, and optimizing the orientation of the transition dipole moment of the emitter to enhance light out-coupling. This thesis is focused on blue TADF emitter design and makes efforts to address these issues, and throughout the projects in this thesis, various design strategies are presented to optimize blue TADF materials for OLED applications.

In Chapter 2, three TADF emitters each with a multichromphore structure are presented. In Chapter 3, we explored the use of heteroaromatic bridges between donor and acceptor units for efficient blue TADF emitter design and synthesized four TADF emitters based on different heteroaromatic sulfones as acceptors. In Chapter 4, we synthesized two pyrazine- based emitters bearing a mono and dipyrazine acceptors and di-tert-butylcarbazole as the donor, and in Chapter 5, two pyridine-containing ambipolar hosts were designed and employed as the host for yellow TADF OLEDs. In Chapter 6, to improve and control the orientation of TADF emitters in solution-processed films we explored introducing mesogens onto to TADF emitter. The compound DiKTaLC exhibits both TADF and liquid crystal character. The transition dipole moment of the as-prepared spin-coated neat film of DiKTaLC shows preferential

horizontal orientation. In Chapter 7, we explored the possibility of using nanohoop structures in terms of cycloparaphenylenes (CPPs) for TADF emitter design. The photophysical properties of these materials are investigated, and state-of-the-art OLED performances are demonstrated.