Synthesis of functional polyaromatic heterocycles and their material and medicinal applications

Abstract

Polyaromatic heterocycles can be found in almost all areas of chemistry being a highly versatile class of compounds. From materials to therapeutic agents, the extensive applications make them the targets of many research pursuits. Carbazole derived compounds have seen applications in OLEDs and LECs in the form of highly novel TADF emitters, then also appear in the anti-cancer and anti-fungal research centred around the indolocarbazole alkaloids.
Chapters 1 and 2 of this thesis describe the synthetic approaches utilised to access novel ionic salts combining fluorescent heterocyclic cations with polyoxometalate anions. A series of 7 novel polyoxometalate containing salts are isolated and their physical and optical properties examined. In this work we demonstrate the ability of polyoxometalate anions to enhance the solid-state photoluminescence of associated emissive heterocyclic cations. Furthermore, we have investigated the potential of these salts in the active layer of LECs, demonstrating the limited hole transporting ability of the materials.
Chapter 3 of this research endeavour displays the synthetic advances towards carbazole-based TADF emitters. The ability to control sequential SNAr reactions on polyfluorinated aromatic systems, hexafluorobenzene and tetrafluoroisophthalonitrile, is explored. The capability to limit the substitution of carbazole to 2 positions with hexafluorobenzene and 3 positions with tetrafluoroisophthalonitrile was determined and further substitution with derivatised carbazole compounds scrutinised. The inability to substitute these final positions efficiently leads to a new approach targeting a difluoro-diiodo aromatic system that provides orthogonal opportunities for functionalisation. This system was successfully accessed in 2 steps with a 22% yield.
The final part of this thesis, Chapters 4 and 5, outline the refinement of the Brown group’s approach to a reduced form of the staurosporine aglycone which presents as an indole-indoline system then investigates its regioselective functionalisation. Successful selective glycosylation of the indoline moiety allowed for the total synthesis of K252d as well as its β-anomer in a 4% yield over 6 steps. Furthermore, glycosylation with D-glucose and D-galactose yielded two previously unknown glycosidic analogues. The nature of the glycosylation step is studied, and the limitations of this approach made clear in the form of an equilibrium that limits the conversion to the initial glycosylated intermediate to approximately 40%.

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Identifiers

ORCID for Ashley Shiels: orcid.org/0009-0006-5101-077X

ORCID for Richard Brown: orcid.org/0000-0003-0156-7087

ORCID for Lynda Brown: orcid.org/0000-0002-5678-0814

ORCID for David Harrowven: orcid.org/0000-0001-6730-3573

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