The photochemistry of molecules can be investigated computationally, and this provides great insight into the underlying chemistry and physics. Such computational approaches are challenging and can pose many difficulties compared to ground state methodologies. Care must be taken to accurately describe these systems, as some lowlevel approximate methods can fail. The geometrical and electronic structures (TiO2)n clusters (n=1-4) have been investigated. These are of enormous technological interest as wide band-gap semiconductors yet the nature of electronic transitions in nano-sized clusters has yet to be fully elucidated. Structures of the neutral closed-shell, radical cationic and radical anionic clusters at each size are described and rationalised in terms of the pseudo-Jahn- Teller effect. We have used high-level response theory to set benchmarks for such systems. The TiO2 monomer is the simplest of the clusters studied yet proves a stern test for many lower order ab-initio methods. It is shown that high-level methods are required to properly describe this simple molecule. The Monte Carlo Configuration Interaction method attempts to combine the power of Full CI with a scalability that allows it to be used to study much larger systems. It can be systematically improved and can approach the accuracy of the Full CI method. This method is applied here to investigate potential energy surfaces and multipole moments of a range of small but challenging systems.

This thesis describes the photochemistry and ultraviolet (UV) spectroscopy of cyclic aromatic hydrocarbons such as benzene and naphthalene, along with small water clusters and crystalline water ice clusters. Firstly, benzene and naphthalene interactions with small water hexamer (W6) clusters, and then benzene interactions with crystalline water ice clusters are investigated. This thesis primarily focuses on the applications of a range of computational chemistry techniques to investigate and characterize excited states of these complex systems, which are generated following one-photon absorption. Benzene and naphthalene, as prototypical polycyclic aromatic hydrocarbons (PAHs), and water and crystalline ice clusters, taken as representative of interstellar ices, could also be considered as useful model systems to replicate polycyclic aromatic hydrocarbons (PAHs) in interstellar ices, and to study their behaviour under UV processing. From coupled cluster (CC) benchmark studies on small water clusters up to water the pentamer, it is shown that that highly correlated linear-response coupled cluster methods such as CCSD and CC3 are important to consider while studying electronic excitations, as electron correlation effects play an important role in such systems, with double excitations playing a dominant role. However, triple excitations contributions calculated are negligible with CCSD and CC3 methods converging monotonically to similar results. The aggregation effect on water at CCSD level has shown a blue shift of ~ 0.7 eV in the central water molecule of water pentamer (C2v) relative to water monomer (C2v), and is in good agreement with the experimental blue shift of ~ 1 eV in condensed phase. For both benzene- and naphthalene-bound water W6 clusters, we have calculated interesting features of benzene- and naphthalene-mediated electronic excitations of the water W6 cluster at wavelengths where photon absorption cross section of water is negligible i.e., above 170 nm. These excitations were originally absent in the isolated water W6 cluster. Similar features are calculated for benzene-bound crystalline ice clusters, which also illustrate the effect of cyclic aromatic hydrocarbons on electronic excitations of ice clusters, and are also observed experimentally. The brightest π → π* electronic transition of benzene and naphthalene is calculated to be red-shifted in wavelength and occurs with lower intensities after interacting with the water W6 and ice clusters. The degeneracy of this transition is also slightly broken in benzene. We have observed new electronic transition features such as charge transfer (CT), and locally diffuse Rydberg type excitation in these complexes. We have found a good performance of hybrid DFT functionals i.e. M06-2X and CAM-B3LYP in calculating vertical excitation energies of these complexes using time dependent density functional theory (TD-DFT). Further, diffusion studies of the deuterium (D) atom have shown the importance of surface morphology in generating different potential sites and hopping characteristics of the D atom on crystalline and amorphous ice surfaces. D2 formation is found to be efficient on the amorphous ice surface, with longer residence times of the D atom indicating a possibility of the deuterium atom getting trapped in such sites. There is then a further possibility of the diffusing D atom to recombine with the trapped D atom to form a D2 molecule. However, such D atom trapping is a rare possibility on crystalline surface, as hopping is fast and thus the recombination process is not efficient on crystalline ice surface.

The enthalpy of transfer (DeltaHt°) of uranyl nitrate hexahydrate from 0.492 M nitric acid and 0.5 M tri-n-butyl phosphate (TBP) in cyclohexane solutions has been measured by (i) direct calorimetric, and (ii) temperature coefficient methods. The present work applies the calorimetric measurements to aqueous and organic phases separately, in order to obtain DeltaHt° (uranyl nitrate hexahydrate) from an aqueous to an organic phase. In the calorimetric method the aqueous phase contained nitric acid and was presaturated with the organic phase, and the organic phase had itself the composition derived from presaturation with aqueous nitric acid in order that conditions for the determination of DeltaHt°should be those prevailing in determinations by the temperature coefficient method. The composition of presaturated aqueous and organic phases has been obtained by analytical measurements. The standard state was that of infinite dilution of uranyl nitrate in the specified aqueous phase and infinite dilution of uranyl nitrate in the specified organic phase. In order to obtain DeltaHt° by the temperature coefficient method, the variation of the distribution coefficient of uranyl nitrate hexahydrate in the nitric acid-TBP system, as a function of temperature (25-60°C) has been studied employing cyclohexane as a diluent, at four concentrations of TBP (0.25, 0.50, 0.75 and 1.00 mol l-1) and at four concentrations of aqueous nitric acid (0.492, 1.5, 2.5 and 4.0 mol l-1). All the data obtained showed that the extraction of U(VI) from nitric acid into TBP-cyclohexane is exothermic in nature. The thermodynamic functions for the extraction reaction: have been calculated. It is clearly seen from the data in the table that the DeltaHt° values are similar, within the experimental error. Variation of the heat of solution of UO2(NO3)26H2O at different concentrations in different concentrations of nitric acid has also been measured, and the percentage of nitrate complex UO2NO3+ at different nitric acid concentrations has been calculated. The standard heat of solution of UO2(NO3)26H2O in water has been calculated (DeltaHs° = 4995 +/- 80 cal mol-1) from these measurements. A critical evaluation of thermodynamic quantities in this and closely related systems is offered.

Electrowetting, the manipulation of surface wettability with an electric field, is an emerging technology used in next generation displays and cameras. This has been made possible by the development of 'electrowetting -on- die lectric' by Berge in 1993. Howev er, such a system operates on large voltages poorly suited to portable devices. In recent years, theoretical and experimental results have suggested that electrowetting using the interface between two immiscible electrolyte solutions (ITIES) may provide a solution to this problem. By applying less than 1 V to such a system, it is possible to induce substantial changes in the wettability - and hence the shape - of liquid droplets. However, there is a large degree of hysteresis in such a system meaning that there is a poor correlation between droplet shape and applied potential. Furthermore, the stability of the ITIES over long periods is of concern. This thesis attempts to address the current problems with ITIES electrowetting highlighted above. By moving to smoother and more lubricated surfaces, a substantial reduction in hysteresis was seen. These surfaces were produced by template stripping. In addition, several other surfaces were prepared as potential electrowetting substrates. These involved surface functionalisation by plasma treatment or the reduction of diazonium compounds; preparation of ultra smooth glassy carbon and preparation of a hydrophobic conducting polymer. The potential range over which an ITIES is stable was also improved with the use of a novel mixed organic solvent phase. By optimising the electrode and electrolyte compositions, an electrowetting system operating on less than 1 V with a contact angle range of 53 o and a gap of only 100 mV between forward and reverse scans was possible. Other electrowetting systems with no hysteresis were also developed, although these did not operate within the potential limits defined by the onset of Faradaic processes.

The remarkable properties of single-walled carbon nanotubes (SWNTs) and potential applications are hindered by current solution-phase processing strategies. The initial dissolution of SWNTs remains a fundamental challenge, reliant on aggressive chemistry or ultrasonication and lengthy ultracentrifugation. In this thesis, a simple non-aqueous electrochemical reduction process that leads to spontaneous dissolution of individualised SWNTs from raw, unprocessed powders is outlined. The intrinsic electrochemical stability and conductivity of these nanoparticles allows their electrochemical dissolution from a pure SWNT cathode to form solutions of well-defined nanoparticle anions with characteristic charge density. Other than a reversible change in redox/solvation state, there is no obvious chemical functionalisation of the structure, suggesting an analogy to conventional atomic electrochemical dissolution. The heterogeneity of as-synthesised SWNT samples leads to the sequential dissolution of distinct fractions over time. Initial preferential dissolution of defective nanotubes and carbonaceous debris provides a simple, non-destructive means to purify raw materials without recourse to the usual, damaging, competitive oxidation reactions. During early stage developments, the process showed remarkable affinity for dissolving metallic SWNTs, providing a potentially scalable route for separation by electronic character, vital for many applications. However, selectivity was lost with significantly increased process yields (complete dissolution) following several optimisations. Subsequently, the electrochemical deposition of SWNTs is proposed as a new route to selectively plate specific SWNT species and avoid unwanted functionalisations that occur when exposing reduced SWNTs to different atmospheres. Finally, the extension of electrochemical processing to related materials including activated and graphitic nanocarbons, metallic and metal chalcogenide nanomaterials was also investigated, with great promise for the development of new applications.

Helicenes are ortho-fused aromatic molecules rendered chiral due their unique helical topology. These fascinating molecules with their extended electronic conjugation have vast potential in a variety of applications. Indeed, their applicability has been highlighted in the fields of catalysis1 and molecular recognition2 amongst others. Current methods employed to synthesise helicenes offer little means of stereocontrol. Our group aims to develop a unified, general strategy to enable the asymmetric synthesis of unfunctionalised carbo- and hetero- helicenes. Two chiral relay protocols to control the sense of helical chirality have been investigated: (i) axial chirality to helical chirality and (ii) planar chirality to helical chirality (Figure A1). The use of tricarbonyl chromium moieties as the planar chiral source and probing the conformation of hindered axially chiral compounds is described. In the synthetic route towards [6]helicene, the 1,8-diarylnaphthalene motif represents a key intermediate. Such motifs were prepared by a double Suzuki-Miyaura cross coupling reactions using two different substrates: employing diboronic acid i and bis-iodide iii. The latter substrate afforded dimethoxy v in excellent yield. Subsequent treatment with Cr(CO)6 provided an efficient route to access compound vi which exhibits both axial and planar chirality. These 1,8-diarylnaphthalene motifs exist as atropisomers: syn (meso)- and anti (chiral)- isomers (FigureA2). Further dynamic onformational studies, employing NMR techniques, on these compounds successfully determined the barriers to isomerisation (Table A1), in addition to investigating the solvent dependency on the anti:syn ratio. In the synthetic route towards aza[6]helicene, the development of a C-H activation/arylation reaction of tricarbonyl chromium complexed 2-phenylpyridines has been accomplished. Optimisation of the conditions for the two-step process involving C-H activation by the formation of a isolable palladacycle ix followed by an arylation using various aryl boronic acids furnished triaryl products xii and xiii in moderate to excellent yields (Scheme A3). This methodology was developed into a one-pot activation/arylation process resulting in key intermediate arylated products for the synthesis of aza[6]helicene. The ability of [7]helicene to function as a chiral molecular tweezer of certain metallic cations is described. Formation of a 1:1 Ag:[7]helicene complex was monitored by NMR spectroscopy and its structure was determined by X-ray crystallography (Figure A3).

This thesis is concerned with measuring the short-range structural changes that are induced when electrochromic transition metal oxide films are electrochemically oxidised and reduced. Three systems are studied: electrochemically-deposited nickel hydroxide, sol-gel-derived niobium oxide and oxide films anodically-grown on tungsten. Structural changes are measured using extended X-ray absorption fine structure (EXAFS), a technique that is sensitive to atomic structure up to about 5A, providing interatomic distances, and the number and identity of neighbouring atoms. Standard and quick transmission, energy dispersive, fluorescence and reflection modes are utilised. Additionally, the crystal impedance technique is used to study rheological changes during the sol-gel conversion of niobium oxide, and the X-ray reflectivity of the tungsten oxide films is measured at several stages of growth. For the nickel hydroxide system, a distorted first Ni-O shell is observed in the anodically charged electrode, which reverts to a regular octahedral form as charge density decreases. An antagonistic movement is observed in the first Ni-Ni shell. For the niobium oxide system, the structures of both uncharged and cathodically charged electrodes are determined. The initially distorted first Nb-O shell of the uncharged Nb2O5 film is replaced by a regular octahedral Nb-O shell when charged. Again, a reversed effect is displayed by the first Nb-Nb shell. Also, the rheological development taking place during the sol-gel transformation is characterised. For the tungsten oxide films, a separation of W-O and W-W shells initially occurs during formation, reaching a maximum of 1.3A, then diminishes with a further increase of electrode charge density. Shell separation coincides with cation insertion during the formation of HWO3; the subsequent shell convergence results from cation expulsion when WO3 is being formed.

The spatial distributions of polymer and solvent within three types of polymer modified electrode have been investigated using the technique of neutron reflectivity. The overall aim of this research is to rationalise electrochemical behaviour of polymer modified electrodes through improved knowledge of in situ electrode structure. This may in future assist the design and fabrication of modified electrodes of desired function. The permselectivity failure of poly(vinylferrocene) has been investigated, with neutron reflectivity used to quantify mobile species transfer which occurs during redox cycling. Short time scale reflectivity studies have allowed observation of the changes in spatial distributions which occur within such films during oxidation and reduction, and rate limiting species transfers have been proposed. The reaction of the polymer poly(pentafluorophenyl 3-(pyrrol-1-yl)propanoate) with the nucleophile ferrocene-ethylamine has been followed and in particular the progress of the nucleophile's reaction front through the polymer monitored as a function of time. Definite regional differences in polymer structure were identified, which had an effect on the reaction progress. Studies on a third system looked at the effect of electrolyte pH on the structure of poly(orthotoluidine) films. At high acid concentration films are observed to swell, with the species responsible dependent on acid concentration. Neutron reflectivity was also used to rationalise combined EQCM/PBD responses obtained during redox cycling of poly(orthotoluidine).

This thesis is concerned with two studies of kinetics in aqueous solutions; (i) salt-effects on kinetics in water, (ii) oscillating reactions. The first-order rate constants for the aquation of tris (5-nitro-1,10-phen) iron (II) in water and in aqueous salt solutions were measured using a Unicam SP 1800 A spectrophotometer. The effects of the added electrolytes on the magnitude of the rate constants are discussed in the light of past work, classical expressions and a treatment involving the effects of added salt on the initial and transition states. The first-order rate constants for the aquation of sulphur trioxide trimethylamine in water and in aqueous salt solutions were also measured, by titrating the acid produced against a solution of sodium hydroxide. The effects of added electrolytes on the magnitude of the rate constants proved strikingly similar to those, observed for the aquation of tris (5-nitro-1,10-phen) iron (II). The results are discussed in the light of this similarity. The change in the redox potential and the bromide ion concentration with time, during the Belousov reaction, one of the few known oscillating reactions, were measured using a platinum electrode and a bromide sensitive electrode respectively. Under specified sets of conditions, the induction period (the period prior to oscillation) and the frequency of oscillation were obtained. Experiments to determine the effects of temperature, added t-butyl alcohol and added sodium dodecyl sulphate, on both the induction period and frequency of oscillation are described. Also described is an experiment to determine the decay of oscillations with time. The results of these experiments are discussed with respect to the mechanism of this reaction. Chemical kinetic models, simulating the oscillatory behaviour of experimentally observed reactions are described. The results of a computer analysis on the Oregonator, a model based on the Belousov reaction, are discussed.

Chromium electrodeposition is important for the production of anti-wear and anti-corrosion coatings. It has been carried out for over 50 years in a multi-billion dollars industry using essentially the same technology based on chromic acid. The toxicity of the electrolyte makes the search for an alternative process an environmental imputative. In this study a variety of novel formulations of deep eutectic solvents are produced and tested to determine their efficacy for chromium deposition. The study concentrates on using urea as a complexing agent with a variety of trivalent chromium salts. In the first results chapter complexes of CrCl3·6H2O with urea are formed. It is shown that this system displays high conductivities, despite relatively high viscosities compared with the previously reported chromium based deep eutectic solvents. Thick, adherent, non-cracked black chromium could be deposited and produce relatively hard chromium coatings. EXAFS suggests that there are a variety of chromium species but they are probably cationic with a variety of oxygen donors as ligands. In the next section [Cr(en)3]3+ species was produced as the cationic species and this had a higher conductivity than any similar system previously described. Bright, adherent, hard chromium was obtained by electroreduction with constant speciation. A novel solvatochromic shift, that we are unaware of in the literature, demonstrates the charge transfer complex results in an unexpected colour change. In an endeavour the remove of Cl- from the formation chrome-alum (KCr(SO4)2·12H2O) was used as the metal salt. This produced unprecedented high conductivity for this type of medium with a low viscosity. It was proposed that unlike most ionic liquids mass transport is not limited by hole transport and instead it is proposed that these liquids function more like very concentrated electrolytes where ion paring becomes important. In the final result section a variety of additives are tested. Some are shown to have a significant effect on the morphology and hardness of the deposit. Ultimately bright metallic chromium films could be reproducibly produced with a hardness of 800±10 HV. This is the first process based on Cr(III) to be able to achieve these rigorous requirements and suggests the first real alternative to hexavalent chromium for hard chrome.