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This thesis is concerned primarily with the use of fluorescence spectroscopy and UV-Vis absorption spectroscopy to study the aggregation of phthalocyanine and orthp-hydroxyazo textile dyes in solution. A preliminary investigation of the use of laser irradiation to induce fading of dyed textiles, as a possible method of assessing light fastness of dyes, is also reported. Fluorescence and UV-Vis spectroscopy have been used to investigate the aggregation of a commercial reactive textile dye, a sulphonated copper phthalocyanine dye, known here as turquoise-1. With very few exceptions, phthalocyanine dimers are found to be non-fluorescent. This thesis reports on the observation of a fluorescent dimer of turquoise-1 in ethanol and water. Fluorescence excitation and emission spectra at room temperature and 77K are presented. These are consistent with the conventional model of exciton coupling in a cofacial dimer. The fluorescence arises from a dimer with a particular geometry, while the majority of dimer species present in solution, which give rise to the characteristic hypsochromically shifted absorption spectrum, are non-fluorescent. Theoretical modelling of extinction co-efficients obtained from aqueous solution of turquoise-1 shows that, in salt-free solutions, aggregates higher than dimers exist. However, in solutions containing high salt concentrations the tendency to form the higher aggregates dramatically decreases. The fluorescence spectra of the monomer and dimer species of a typical ortho-hydroxyazo dye, known here as red~l, are shown to be clearly distinguishable, while their absorption spectra overlap strongly and cannot be resolved. Thus, the aggregation of this dye in aqueous and ethanolic solution is not readily apparent from the absorption spectrum, but is revealed by fluorescence spectroscopy. Fluorescence excitation spectra and emission spectra in water and ethanol, at room temperature and 77K are reported. The effect of increasing the temperature of the dye solution on the extent of aggregation has also been investigated. A number of ortho-hyroxyazo reactive dyes related structurally to red~l have also been investigated. These systems show similar behaviour to red~l and fluorescence spectroscopy is again shown to be a valuable probe of aggregation. Initial studies show that laser irradiation of dyed textile fabrics can be used to induce fading of the dye without damage to the textile fibre. The time taken for laser-induced fading of standard samples of blue-dyed wool is consistent with their light fastness values defined by the international dyestuffs industry. The effect of dye strength on laser-induced fading times is in line with results from conventional light fastness measurements. Cotton dyed with turquoise~l exhibits photochromism on laser irradiation, this is attributed to reversible one-electron reduction of the copper (II) phthalocyanine in the presence of free amine groups on the dyed fabric. |
