The electropolymerisation of a range of 5-substituted indoles has been shown previously to result in the formation of redox-active films. The oxidation potentials of both the indole monomers and their polymers can be altered by substitution of the monomer with different electron-withdrawing groups. Both the indole monomers and polymers also have high fluorescence quantum yields. However the fluorescence wavelengths of the indole polymers are not tuneable by substitution. In this thesis the work on the electropolymerisation of indole(s) is extended to two monomers which have larger conjugated systems than the indoles; indolo{3,2,1-jk}carbazole (IC) and pyrrolo{3,2,1-jk} carbazole (PC). A combination of computational, electrochemical and spectroscopic techniques have been employed to investigate both these monomers and their polymers. Computational confidence tests have been performed on a range of small organic molecules to assess methods of calculating oxidation potentials, radical cation spin density distributions and excited states using the software Gaussian 98. Calculations have predicted the oxidation potentials of such molecules to within 0.19 V of their experimental values. These calculated oxidation potentials are systematically underestimated. Gaussian 98 has been used to calculate the radical cation spin density distribution of indole and has been found to reproduce the results of previous calculations performed using the software DMol<sup>3</sup>. Configuration interaction singles (CIS) calculations incorrectly predicted the energetic ordering of the two lowest singlet excited states of indole and carbazole. However CIS correctly predicted the dipole moment of the <sup>I</sup>L<sub>a</sub> state to be larger than the dipole moment of the <sup>I</sup>L<sub>b</sub> state of indole. The oxidation potentials of IC and PC have been measured experimentally and calculated. IC and PC have both been electropolymerised to form redox-active polymers. IC forms a conducting film which has been shown to contain two different dimers by mass spectrometry and NMR. Although successful in predicting the ring positions at which indole(s) link during electropolymerisation, radical cation spin density calculations have been shown to be unsuccessful in predicting the linkage sites for IC. The mechanism of electropolymerisation of IC has been shown to be similar to the mechanism of electropolymerisation of indole(s) with initial film formation occurring in solution, followed by linkage of IC radical cations which are adsorbed on the electrode surface. The diffusion coefficient has been measured from Koutecky-Levich plots as 5.9 x 10<sup>-5</sup> cm<sup>2</sup> s<sup>-1</sup> (±2.0 x 10<sup>-3</sup>). The rate of film formation for IC has been shown to be approximately 0.8 times that of indole-5-carboxylic acid and 0.7 times that of 5-cyanoindole. Steady-state fluorescence spectroscopy in solution at room temperature has shown both the IC and PC monomers and their polymers to be highly fluorescent. There is no significant difference between the equilibrium geometries and potential energy surfaces of the IC monomer in the ground and first singlet excited states. However such a difference does not exist between the ground and first singlet excited states of the PC monomer. The electropolymerisation of each monomer produces a number of emitting species which have more extensive p-electron delocalisation than the monomers. The emission from the IC dimer peaks at 408 nm. IC electropolymerisation has been shown to proceed in a similar manner to indole electropolymerisation, with the first step the formation of dimer followed by the linkage of dimer units to form longer polymer species. The IC polymer has been found to be fluorescent in the solid state.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:642747 |
| Date | January 2004 |
| Creators | Chapman, Madelaine A. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13360 |
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