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Understanding the interactions between dye molecules and their constituent moieties will lead to an improvement in the design of new molecules with the appropriate properties. Here, we use computational methods to investigate the relative stability of the three tautomers of hydroxy-triazine, and how they interact with themselves in the gas phase, in aqueous solution and in the solid state. <i>Ab initio</i> and density functional theory (DFT) methods were used to establish the relative gas phase stability of the tautomers, showing two of the tautomers to be significantly more stable than the third. Thermodynamic cycles were calculated using <i>ab initio</i> free energies of salvation and gas phase energies. The crystal phase investigation involved data mining of the Cambridge Structural Database and generating hypothetical crystal structures which were subjected to lattice energy minimisations. The interactions were investigated in the gas phase by minimising small clusters of the tautomers, treated as rigid molecules, from a number of random starting conformations. Molecule dynamics simulations looked at the behaviour in solution, while the lattice energy minimisations and the CSD were again used to look at solid phase interactions. The above methods were also incorporated into further investigations of the interactions between these tautomers and another important dye-related molecule, morpholine, both as an additive and as a covalently bonded fraction. Whole dye molecules containing these substructures, were then studied using the above methods, as well as UV-Vis spectroscopic analysis to calculate dimerisation equilibrium constants. Finally the computational methods were applied to look at the effects of substituents on the interactions of zinc phthalocyanine.

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This thesis is concerned with the photophysics of organic materials and intermolecular order of guest dyes in self-assembled protein structures. Photophysical processes in polyfluorenes and iridium-containing polyfluorenes copolymer complexes were investigated. Interchain singlet energy transfer processes were investigated by studying the copolymers in various concentrations in a polystyrene matrix. The amount of polyfluorenes in the co-polymers was also varied so that intrachain energy transfer processes could be studied. The singlet exciton decays were fitted to a stretched exponential function to obtain a value for the dimensionality of the system. It was found that although intersystem crossing is an important decay channel, a significant proportion of excitons must still undergo singlet diffusion before decaying back to the ground state. The binding of dye molecules to amyloid fibrils was investigated through a study of their morphology and chemical interaction. Native protein with dye was compared to fibrils with dye by various spectroscopic techniques, which illuminated a significant morphological difference. Possible binding sites between the dye an fibril were suggested. The excited-state dynamics of the dye bound fibrils was also investigated and were found to be considerably different from native protein with dye. The order of the system was investigated through polarisation anisotropy measurements. A new excited state species was found to exist in the fibrillised protein with dye, which also gave a negative anisotropy indicating a particular order in the system. The fibrils themselves are highly ordered and stable structures and the eventual aim is to utilise them as templates for optoelectronic devices.

Poly(dialkylfluorene)s are one of the most important classes of blue-light emitting conjugated polymers for use in polymer light-emitting diodes. Despite their advantages of ready synthetic accessibility, and high luminance, they suffer a major problem in colour stability with an emission band in the green about 530 nm appearing very rapidly upon operation of a device. The primary source of these defects is thought to be the oxidation of monoalkylfluorenes to the corresponding fluorenone, the former being present as impurities in the dialkylfluorene monomers. (Fig. 16660) The synthesis and properties of monoalkylfluorene derivatives are described in Chapter 2. The degradation pathways of monoalkylfluorene derivatives in air were investigated using GC-MS. The thermal degradation of 9-<i>tert</i>-butylfluorene was also investigated. Fluorenone formation was suppressed and 2,7-disubstituted-9-tert-butyl-9H-fluorene derivatives exhibited enhanced thermal stability. A new synthetic route to 9,9-dioctyl-9<i>H</i>-fluorene without monoalkylfluorene defects is described in Chapter 3. Light emitting devices of polyfluorenes, prepared by Yamamoto and Suzuki polymerisation of the defect-free monomers, exhibited minimal green emission attributable to fluorenone formation. Incorporation of as little as 0.06 mol% of 9-octyl-9<i>H-</i>fluorene comonomer in polyfluorene led to evolution of green fluorescence in the PL and EL emission spectra. The 3-dimensional configuration of oligomeric polyfluorenes carrying twisted biphenyl comonomers is studied in Chapter 4. A study of the X-ray crystal structures of the model oligomers provided useful insight into how the twisted biphenyls effectively modify the planarity of polyfluorene backbone and suppress potential interchain interactions.

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