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As fossil fuels, the major source of energy used today, create the greenhouse gas carbon dioxide which causes global warming, alternative energy sources are necessary in the future. There is a need for different types of renewable energy sources such as hydropower, windpower, wave- power and photovoltaics since different parts of the world have different possibilities. The sun is a never ending energy source. Photovoltaics use the energy of the sun and converts it into electricity. There are different types of photovoltaics and a combination of them could provide humankind with energy in a sustainable way. In this thesis dye-sensitized solar cells are investigated. Materials for the counter electrode have been investigated and resulting in a polymer based cathode outperforming the traditionally used platinized counter electrode in a cobalt-based redox mediator system (paper I). The sensitizer of the TiO2 was investigated, in this study by modifications of the π-linker unit in an organic donor-linker-acceptor based dye. Four new dyes were synthesized, all four showing extended absorption spectra compared to the reference dye. However, it was found that increasing the absorption spectrum does not neces- sarily increase the power conversion efficiency of the solar cell (paper II). In the last part of this thesis, water-based electrolyte dye-sensitized solar cells were investigated. A hydrophilic dye with glycolic chains close to the center of regeneration was synthesized. The results show increased wettability by water-based electrolyte for the sensitized surface, increased regenera- tion and performance for the hydrophilic dye compared to a hydrophobic dye (paper III). The glycolic chains complex with small cations such as Na+ and K+ in the electrolyte, this proba- bly facilitate the regeneration of the hydrophilic dye even further (paper IV). In this thesis new materials for a more environmentally friendly dye-sensitized solar cell are investigated.

Efficiency of particulate semiconductors for driving photocatalytic reactions is impractically low due to the recombination of excited carriers and intermediate species at the interface. In the literature it has been demonstrated internal depolarisation fields in ferroelectric materials separate electron and hole carriers, this gives rise to spatially distinct reduction and oxidation processes. It is hypothesised this property can supress the rate of back reactions and carrier recombination to improve photocatalytic efficiency. In this thesis the properties of ferroelectric particulates for driving photocatalytic reactions are investigated. Lithium niobate and barium titanate powders were suspended in aqueous solutions of acid black 1 or rhodamine b dye. Adsorption studies compared retention of dye in the double layer by the different powders. Under UV or simulated solar illumination barium titanate or lithium niobate powders photocatalytically decolourised the dye solutions. Powders of lithium niobate powder doped with magnesium or iron showed altered reaction rates and structural selectivity of decolourisation reactions. Photochemical deposition of silver nanoparticles at the surface of the barium titanate or lithium niobate powders increased the rate of photocatalytic decolourisation of rhodamine b solutions under UV or simulated solar illumination. Photochemical reduction of carbon dioxide to form formic acid and formaldehyde over lithium niobate powder was studied under UV illumination. Solid-liquid phase reactions were carried out using aqueous suspensions of powder bubbled with carbon dioxide gas. Solid-gas phase reactions were investigated using a purpose built reaction vessels loaded with carbon dioxide gas and water vapour. Under solid-gas phase conditions the rate of formation of products over lithium niobate powder was greater than over titanium dioxide powder.

Ruthenium (II) complexes are used extensively in photoelectrochemical and photophysical devices, such as Dye-Sensitized Solar Cells (DSSCs). The use of Cu(I) as a possible replacement for Ru(II) has to date had limited exploration, but has obvious advantages in terms of low cost and high abundance. However, Cu(I) typically undergoes conformational change from tetrahedral towards square planar upon oxidation or MLCT excitation, often leading to reduced stability, reduced electron transfer rates and reduced excited state lifetime, thus impairing useful function. Typically, steric constraints are used to prevent this; however these can often be synthetically intensive, involving multi-step and low yielding synthetic pathways. In this work, we explore “blocking” functionality using two different ligands combined with a range of bipyridyl ligands with varying substituent groups. The study has looked into the synthesis of heteroleptic Cu(I) complexes of the general formula: [Cu(POP)(bipyridyl)][BF4], where POP = bis[2-(diphenylphosphanyl)phenyl] ether, and [Cu(pmppE)(bipyridyl)], where pmppE = hydrazono pyrazol-5-thiones(one). The work presented in this thesis focuses on the synthesis, and subsequent photoelectrochemical and photophysical characterisation of Cu(I) complexes, yielding results that open new avenues for design of functional Cu(I) systems. Solar cell testing also revealed photovoltages comparable to those of existing Cu(I) DSSC sensitisers. An extensive spectroscopic study of [Cu(POP)(dmbpy)]+ and [Cu(POP)(tmbpy)]+ has revealed the latter to have the significantly larger quantum yield: 65 % and 4% respectively in PMMA at 300 K. A complimentary computational investigation was carried out in order to gain a better understanding of how structural rigidity affects emission properties.

Nile red and Nile blue are intensely colored fluorescent dyes from the benzophenoxazine family. Modification of the donor amine with varying alkyl substituents was achieved with the principle aim being to investigate differences, both optical and physical, between dye scaffolds outfitted with secondary amines versus tertiary amines. These changes to the dyes’ architectural framework gave holistic effects to the bulk molecule by modulating hydrophobicity, optical properties, and protein binding constants to human serum albumin.

The problem with which this study was concerned was that of developing wood stain formulas from a small supply of materials. These formulas should produce a wide variety of colors from which to select, the use of which should be suited to the school or home laboratory.

Both the challenges and rewards of pattern dyeing motivated an examination of resist materials, the subject of this study. The first part of the problem was to investigate new materials and those not previously used for dye resists. The second part was to test some of the traditional resisting agents in non-traditional ways. The selected materials were evaluated for their effectiveness as dye resists and for their usefulness to the artist-craftsman. They were also compared to traditional techniques to determine any advantages they may or may not have over previous resist materials.

As interações entre as moléculas de corante e as partículas de argila em suspensão podem envolver diferentes processos dependendo da argila e da maneira pela qual as suspensões corante/argila são preparadas. Os processos que ocorrem são: a adsorção de moléculas de nas superfícies externas das partículas de argila seguidas de migração para as regiões interlamelares, outro processo é devido a interações partícula-partícula, onde as moléculas de corante ficam envoltas em aglomerados de partículas de argila e um terceiro processo é devido a migração das moléculas de corante entre partículas de argila. No presente trabalho foi estudada a influência de diferentes metodologias nos processos de migração de moléculas do corante azul de metileno (AM) entre partículas de argilas em suspensão aquosa. Experimentos adicionando-se partículas de argila nas suspensões corante/argila foram realizados com acompanhamento das variações espectrais em função do tempo. Foi possível detectar variações espectrais nas suspensões corante/argila atribuídas a processos de migração de moléculas de corante adsorvidas em partículas de argila para outras partículas na suspensão. Os resultados indicaram que o processo de migração entre diferentes partículas de argila depende da razão corante/argila. Em outro tipo de experimento, utilizando diferentes formas de adição do corante à suspensão de argila (lenta, rápida e diálise) constatou-se que o modo de adição do corante pode afetar os processos de adsorção, para alguns sistemas corante/argila é muito importante considerar a forma de adição do corante à suspensão de argila, para que se tenham suspensões corante/argila com propriedades desejáveis. / Interactions between dye molecules and suspended clay particles may follow different processes depending on how the dye/clay suspensions are prepared. The processes that occur are: adsorption of molecules on the external surfaces of clay followed by migration to the interlamelar areas, another process is due to particle-particle interactions, in which the dye molecules are wrapped in clay particle agglomerates and a third process due to the migration of the dye molecules between clay particles. In the presente work the influence of different metodologies on the migration processes for the methylene blue dye between clay particles in aqueous suspension was studied. Experiments adding clay particles to the system dye/clay were done monitoring following the spectral changes in function of time. It was possible to detect spectral variations in the dye/clay suspensions attributed to the migration of adsorbed dye molecules to other particles in the suspension dye molecules adsorbed in clay particles migration process. The results indicated that the migration process between different clay particles depend on the nature of the clay and on the dye/clay ratio. In another type of experiment, using different forms for adding dye to the clay suspension (slow, fast and dialysis) it was seen that the adding way for the dye can affect the adsorption processes, for some dye/clay systems it is very important to consider the adding way of the dye to the clay suspension, so that dye/clay suspensions with desirable properties are obtained.

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