Encapsulation of indigoid dyes

Thesis

This thesis describes approaches towards the synthesis of encapsulated indigo-based systems. The chemistry and application of indigo has been widely investigated, but its use as an emitter is restricted by its low fluorescence, which is caused by the ultrafast proton transfer in the excited state. Substitution of the N-positions prevents this process, making indigo accessible for photonic applications. This thesis focuses on the synthesis and properties of indigo-derived materials. The aim is to make new encapsulated indigo-derived materials for photonic applications (e.g. OLEDs). Encapsulation is a common tool to prevent interactions (e.g. π-stacking) between molecules which can lead to a decreased emission in the solid state. Focus is set on two encapsulation methods, i.e. self- encapsulation by a metathesis reaction, and encapsulation under formation of hydrogen bonds between a tetralactam macrocycle (hydrogen bond donor) and several guest systems (hydrogen bond acceptor). The concept of increasing binding strengths in hydrogen bonding systems by electrochemically reducing the guest (hydrogen bond acceptor) has also been introduced and investigated.

Chapter 1 reviews encapsulation as a tool to enhance the emissive properties of host-guest systems. Focus is mainly on self-encapsulation and encapsulation with hydrogen bonding macrocycles. Additionally, the chemistry of indigo and its use in devices is explained.

Chapter 2 explores the N-substitution and the bay-annulation of indigo including a study of their photophysical properties. Analysis of several crystal structures shows the impact of substitution resulting in increased emissive properties.

Chapter 3 describes the synthesis of a self-encapsulated bay-annulated indigo derivative and its photophysical properties in solution and solid state.

Chapter 4 focuses on the binding between tetralactam macrocycles and hydrogen bond acceptors. Also, binding enhancement with electrochemical methods is investigated. Simulations of the binding processes are shown and their results compared to the common tools for calculating the binding constants in the reduced state.

Chapter 5 summarises the results in this thesis and contains proposals for future work in this research area.

Authors: Weidlich, S

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford