Design and synthesis of thermally activated delayed fluorescence emitters for solution-processed organic light-emitting diodes

Thermally activated delayed fluorescence (TADF) emitters have emerged as an important class of materials for organic light-emitting diodes (OLEDs) because they enable the harvesting of both singlet and triplet excitons via reverse intersystem crossing, allowing devices to reach a theoretical internal quantum efficiency of up to 100%. While many efficient TADF emitters have been developed for vacuum-deposited OLEDs, there is increasing interest in developing bespoke materials for solution-processed devices. Solution processing offers attractive advantages for scalable and cost-effective OLED fabrication through techniques such as inkjet printing. However, achieving high performance solution-processed OLEDs remains challenging, as materials must combine good solubility, suitable photophysical, and film-forming properties. This thesis therefore investigates molecular design strategies that produce efficient TADF-based solution-processed OLEDs. Chapter 1 introduces the fundamental photophysical concepts and the operating principles of OLEDs, with particular emphasis on solution-processed devices. It further discusses the molecular design principles of TADF emitters and provides an overview of state-of-the-art solution-processable TADF materials. In Chapter 2 the design of an MR-TADF emitter, Mes-tDABNA, bearing bulky sterically blocking groups, in order to enhance device performance and reduce efficiency roll-off is introduced. Chapter 3 showcases how the use of partially saturated donor moieties in the MR-TADF emitters, DtButHCzB, tButHCzB, SpAc-DtButHCzB and SpAc-tButHCzB, can introduce a blue-shift due to truncated conjugation as well as increased solubility due to the introduction of aliphatic groups. In Chapter 4 and Chapter 5 we discuss the impact of peripheral donor or acceptor decoration of donor dendrons on the photophysical and device properties in the TADF emitters DOBNA-SpAc-DCz, TCzBN-BMes and TCzBN-DBMes Chapter 6 tackles a long-standing challenge of solution-processed OLEDs, severe efficiency roll-off. Here an intramolecular sensitization molecular design in TRZ-SpAc-DBN and DOBNA-SpAc-DBN, paired with a hyperfluorescent device architecture enables SP-OLEDs with minimal efficiency roll-off to high brightnesses. Chapter 7 summarizes the findings of this work and gives an outlook on field of solution-processed OLEDs Chapter 8 documents the general experimental procedures used in this thesis.