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.

Date of Award	15 Jun 2022
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Eli Zysman-Colman (Supervisor)