Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638391
Title: An experimental and theoretical study of the solvatochromism of 4-pyridiniophanolate dyes
Author: Padfield, J.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2003
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Abstract:
The observed solvatochromism of the betaine 4-(2,4,6-triphenyl-1-pyridinio)phenolate has been assessed both experimentally and theoretically using semi-empirical molecular orbital methods over a larger range of solvent polarity than previously reported. Broad absorption bands are observed in the absorption spectra, suggesting that a number of conformers exist in solution. The large thermochromic shift of the dye in acetone and tetrahydrofuran on cooling from room temperature to ca. - 78°C has been studied, and attributed to a combination of an increase insolvent dielectric constant along with a change in conformer distribution. Calculations were performed at the AM1 and PM3 levels, with the COSMO routine used to model the effect of solvent, and assessed with respect to their ability to reproduce experimental data. The PM3/COSMO method was found to be most applicable to the system being studied, and further conformational studies were carried out. Many conformers very close in energy were found, supporting the idea that many conformers exist in solution. The calculated spectroscopic shifts using a multi-electron configuration interaction treatment show similar trends to those found experimentally in aprotic solvents. In protic solvents, the large negatively solvatochromic shift observed can be divided into two parts, a dielectric component and a hydrogen bonding component. Stable hydrogen bonded structures are predicted to be formed between water, methanol, chloroform and acetonitrile and the exocyclic oxygen of the dye. The overall shifts observed in these solvents show a good correlation with those calculated for the postulated solvates using a version of the CNDO/S method. In addition, the novel betaine 4-(2,4,6-trimethyl-pyridiniophenolate has been synthesised, and the observed solvatochromism has been assessed experimentally and theoretically using semi-empirical molecular orbital methods. The structure and solvatochromism of the betaines 4-(1-pyridinio)phenolate and 10H-pyrido[1,2-a]indolium-2-olate have also been investigated theoretically using semi-empirical molecular orbital methods.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.638391  DOI: Not available
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