The electropolymerisation of a range of 5-substituted indoles results in the formation of redox active films. The redox species present in the film have been characterised as the asymmetric trimer. These films are observed to be extremely photoluminescent and the chief fluorophore has been identified as the trimer. Initial studies have involved electrochemical and photophysical investigation with a view to potential application as fast response potentiometric sensors or as materials for light emitting devices. This thesis extends this work by presenting a computational and electrochemical study of a range of electropolymerised 4-, 5-, 6-, and 7-substituted indoles. This research has employed the powerful combination of computational quantum chemical methods with electrochemical techniques to explore the electronic structure of the 5-substituted indoles. Density Functional Theory and semi-empirical calculations have shown that it is possible to predict oxidation potentials to within ±0.1eV of the experimental values. Calculations of the electronic structure of the monomer radical cation, the species involved in trimer formation, has shown a difference in the calculated p-spin density distribution between indoles with electron withdrawing substituents and indoles with electron donating substituents. For those withdrawing groups the unpaired electron is located at the 3-position which is consistent with the formation of a dimer <i>via</i> 3,3-'linkage in the initial stages of polymerisation. For indoles with electron withdrawing substituents the chief location of the unpaired electron in the radical cation is near the substituent consistent with previous experimental observation that trimerisation of these indoles will only occur on the surface of a preformed trimer film. The electronic structure of the indole radical cation has been probed by studying the effect of the substituent nature and position. The electrooxidation of a various 4-, 6- and 7-substituted indoles result in redox films consisting of novel indole trimers. The monomers and electropolymerised films are photoluminescent and the common fluorophore observed infers that the chief fluorophore in the films are indole trimers. Quantum chemical methods predict oxidation potentials of these indoles in good agreement to experimental values. The transmission of substituent electronic effects through the aromatic system of the indole radical cations is again different for electron withdrawing and electron donating substituents.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:653344 |
| Date | January 2000 |
| Creators | Kettle, Lorna J. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15164 |
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