Currents in Carbon and Heterocyclic Networks

Current density maps are calculated within the ipsocentric approach for a variety of systems, to determine the nature of their aromatic magnetic response, and to probe the underlying principles governing ring current aromaticity. The first chapter briefly discusses the history of the term aromaticity, from the discovery of benzene, to ring current theory, the modern quantum mechanical ipsocentric approach, and the simple but powerful selection rules that are derived from it. Examples of systems displaying aromatic, antiaromatic and localised, non aromatic responses are provided in Chapter 2 to demonstrate the utility of the method, and the in depth analysis of aromaticity that it permits. Chapter 3 explores the possibility of designing tailored ring current responses on finite nanographene flakes via functionalisation by examining a variety of nanographene/nanographane hybrids derived from coronene and ovalene. This idea is extended in Chapter 4, by consideration of substitution of C6 cycles for borazine like B3N3 cycles, creating benzenoid/borazinoid hybrids. Chapter 5 investigates how BN heteroannulenes can be successfully aromatised by alteration of electronic charge. The approaches for altering current response introduced in Chapters 3 to 5 are unified in Chapter 6 in a case study of pyrene and structures derived from it by variation of charge, substitution, and functionalisation. Chapter 7 further examines how changing the electronic environment by substitution of carbon centres for heteroatoms alters ring current patterns, using linear polyacenes as the example systems. Chapter 8 moves away from the methods of controlling ring current by chemical manipulation and considers the effects of geometric change on aromaticity of the homotropenylium cation and the extended family of N homoannulenes. A brief discussion of the possibilities of designing aromatic systems using extended non standard ring architectures concludes the thesis.