Patrick W. Fowler
Department of Chemistry University of Sheffield
Aromaticity: Attribution of aromaticity to a molecule is associated with a loose cluster of criteria based on geometric, energetic and reactivity properties, but one persuasive definition is based on magnetic properties: ability to sustain an induced diatropic ring current. Using modern ipsocentric methods it is possible to perform calculations that map the currents, giving a direct quantitative visualisation of aromaticity and anti-aromaticity, but also explaining the patterns of current in terms of orbitals, energies, nodes and symmetry the standard toolkit of qualitative chemical theory. Our most recent work includes a qualitative `band theory´ of the currents in giant graphite-flake molecules. Two new projects investigate the magnetic response of `exotic carbon nanostructures´, including toroidal and Möbius-twisted carbon (PhD research project of David Bean) and the connection between induced currents and the ballistic currents in single-molecule devices (PhD research project of Tsanka Todorova). We are working on ring-current aspects of the many proposed types of aromaticity, aiming to supply symmetry/topological criteria for each. We have strong collaborations in this area with Physical Organic and Theoretical Chemistry groups in Utrecht, Warsaw, Modena, Salerno and Toulouse.