title: A game of rISC – strategic molecular design for high efficiency OLEDs
Creators: name: Riggs, Christopher J.
Publisher: name: University of Glasgow
Year: 2025

description: As society becomes ever more concerned with energy efficiency, the performance of light emitting devices must improve significantly. Organic light emitting diodes (OLEDs) are now a mainstream display technology. Their high brightness and contrast, excellent colour tunability, ultra-fast refresh rates and the ability to be prepared in seemingly limitless form factors, makes them a highly attractive replacement for traditional display methods. Their flexibility makes them attractive to both medical applications and alternative lighting technology as well, and the fact that they can be fabricated from entirely organic materials allows them to be fully biodegradable and recyclable.

Unfortunately, they still suffer from roll-off effects and degradation through prolonged use, particularly for emitter materials utilising higher energy transitions, such as for blue pixels. As such, development of novel deep blue emitter molecules is vital for the more widespread adoption of this technology.

This thesis explores the synthesis and characterisation of novel, entirely organic, emitter molecules for OLED application. A broad review of the current literature of OLED materials is presented, followed by four synthetic themes.

Chapter 1 provides the reader with a history of light emitting devices and organic electronics, before summarising the basic requirements of, and fabrication of OLEDs.

Chapter 2 delves into the physics of semiconductors and introduces the photophysics of excited states and fluorescent and phosphorescent processes. It goes on to summarise the types of photophysical processes observed in emissive organic molecules.

Chapter 3 explores how chemical structure influences TADF in organic molecules and examines the literature, highlighting key developments that have led to our current understanding about the rules governing the fine tuning of the rISC process in state-of-the-art emitter molecules.

Chapter 4 explores a family of simple boron-based D-A type molecules, their photophysics and chemical stability, which helped to inform the design of further compounds in this thesis.

Chapter 5 reports the successful synthesis and photophysical characterisation of a family of six boron-based emitter molecules with varying acceptors and π-bridge structures. The interesting potential for non-covalent interactions between oxygen and the empty p-orbitals of the boron atoms are explored, giving promising results with attractive properties.

Chapter 6 builds upon the non-covalent interactions of Chapter 5 to produce a highly emissive and efficient D-A-D type molecule with a diboron acceptor core. Whilst its stability is poor, it possesses record-breaking emission lifetimes for its colour and demonstrates the highly effective nature of non-covalent interactions in producing HOMO-LUMO decoupling in the excited state.

Chapter 7 takes the interesting, but understudied, dibenzocarbazole donor moiety explored in Chapter 4, and produces a large family of novel emissive molecules. Not only do they mostly possess TADF, but they also all exhibit striking thermochromism and mechanochromism thanks to the quasi-helical nature of the extended carbazole moiety.

All experimental procedures, UV-vis absorption coefficient calculations, NMR and mass spectroscopy data and crystallography data, are collated in the appendices.