Dye-Sensitised Solar Cells (DSSC) were first reported in the early 1990’s and function by the sensitisation of a semiconductor using a dye molecule such as organic and transition metal organometallic dyes. This thesis reports the synthesis and characterisation of transition metal dyes with applications as sensitisers in DSSC. Complexes of Ni, Pd and Pt were investigated for use in standard liquid electrolyte cells and Donor-Acceptor type solid-state solar cells. A family of [Pt(II)(diimine)(dithiolate)] complexes of general formula [Pt{X,X’(CO₂R)₂-bpy}(mnt)] (where X=3, 4 or 5; R=H or Et, bpy = 2,2’-bipyridyl and mnt = maleonitriledithiolate), have been synthesised, spectroscopically and electrochemically characterised and attached to a TiO₂ substrate to be tested as solar cell sensitisers. A single crystal X-ray structure showing a large torsion angle between the bipyridyl rings was determined for [Pt{3,3’(CO₂Et)₂-2,2’-bpy}(mnt)].MeCN. The effect of changing the position of the bpy substituents from 3,3’ to 4,4’ and 5,5’ is discussed with reference to structural and electronic changes seen within the different members of the family of molecules. The UV/Vis/NIR and <i>in-situ</i> EPR spectroelectrochemical studies of the family and its related precursor molecules are discussed. All three complexes (where R=H) were tested as solar cell sensitisers with the 3,3’-disubstituted bpy complex giving an intermediate dye loading value but superior photovoltaic performance to those of the other two. The performance of this sensitiser is then compared with that of a well known Ru(polypyridyl) sensitiser. A family of unsymmetrical [Ni(II)(dithione)(dithiolate)] complexes of general formula, [Ni(R₁R₂pipdt)(dmit)], where R = Me, Bz and Prⁱ, pipdt = 1,4-disbustituted-piperazine-3,2-dithione and dmit = 1,3-dithiole-2-thione-4,5-dithiolate, have been synthesised and characterised and investigated for use in solid-state solar cells. electrochemistry and UV/Visible spectroscopy results show that the reduction potential of a complex is related to the number of aromatic substituents on the pipdt ligand. The dibenzyl substituted complex shows the largest absorption wavelength in the NIR which is attributed to it having the smallest HOMO-LUMO gap of the complexes studied. <i>In-situ</i> EPR results show the reduction electron to be located on the R₁R₂pipdt ligand which confirms previous proposals that the LUMO is in part located on this part of the complex. Raman spectroscopy confirms the dmit ligand to be formally dianionic with the R₁R₂pipdt having a formally neutral charge.

The results of preparative eleotrolyses in aoetonitrile containing tetrealkylammonium salts have confirmed that the hydrodimerisation of cinnamonitrile, benzaldehyde and aorylonitrile by electroreduotion at low current densities can be used to initiate the nuoleophilic cyanomethylation of these compounds. The cyanomethylated adducts, once formed, are capable of regenerating -CH2CN by further proton abstraction. Compounds such as benzophenone and 3-phenyloinnamonitrile which have stable radical-anions cannot be cyanomethylated in this way in pure acetonitrile. The effects on the yield of cyanomethylated products of temperature, concentration of the electroactive species, the presence of acids, water and alkali metal cations, and the use of an undivided cell have been investigated. The results of linear sweep voltammetries (LSV) have shown that the presence of azopyridines in solutions of benzophenone, benzaldehyde or acrylonitrile decreases the peak current of each of these substrates, whereas no significant decrease is obtained for cinnamonitrile or 3-phenyloinnamonitrile. Using ISV, it was found that electroreduced azo compounds in super-dry acetonitrile deprotonate the solvent in a reversible reaction; cyanomethylation of the substrates explains the decreases in peak current. Computer simulation of the voltammetric experiment revealed that the chemical stability of the radical-anion of the substrate has only a small effect on the peak current while the decrease in the peak current is much larger if regeneration of the nucleophilic species occurs. Working curves were produced from which could be estimated the 2nd-order rate constant, k2, for the reaction of an electrochemically generated nucleophilic species with the electroactive substrates k2 for cyanomethylation of benzophenone - 600 lmol-i8 1. Preparative electrolyses of benzenesulphonylacetonitrile in DMF in the presence of acrylonitrile yielded glutaronitrile, adiponitrile and propionitrile; possible mechanisms have been discussed. Cyanomethylated products were not detected in the electroreduction in DMF of benzenesulphonylacetonitrile in the presence of either acetophenone or 3-methylcinnamonitrile. ISV indicated that alkyl aryl ketones undergo nucleophilic addition by a species formed during the electroreduction of benzenesulphonylacetonitrile in DMF.

The electropolymerisation of a range of 5-substituted indoles results in the formation of redox active films. The redox species present in the film have been characterised as the asymmetric trimer. These films are observed to be extremely photoluminescent and the chief fluorophore has been identified as the trimer. Initial studies have involved electrochemical and photophysical investigation with a view to potential application as fast response potentiometric sensors or as materials for light emitting devices. This thesis extends this work by presenting a computational and electrochemical study of a range of electropolymerised 4-, 5-, 6-, and 7-substituted indoles. This research has employed the powerful combination of computational quantum chemical methods with electrochemical techniques to explore the electronic structure of the 5-substituted indoles. Density Functional Theory and semi-empirical calculations have shown that it is possible to predict oxidation potentials to within ±0.1eV of the experimental values. Calculations of the electronic structure of the monomer radical cation, the species involved in trimer formation, has shown a difference in the calculated p-spin density distribution between indoles with electron withdrawing substituents and indoles with electron donating substituents. For those withdrawing groups the unpaired electron is located at the 3-position which is consistent with the formation of a dimer <i>via</i> 3,3-'linkage in the initial stages of polymerisation. For indoles with electron withdrawing substituents the chief location of the unpaired electron in the radical cation is near the substituent consistent with previous experimental observation that trimerisation of these indoles will only occur on the surface of a preformed trimer film. The electronic structure of the indole radical cation has been probed by studying the effect of the substituent nature and position. The electrooxidation of a various 4-, 6- and 7-substituted indoles result in redox films consisting of novel indole trimers. The monomers and electropolymerised films are photoluminescent and the common fluorophore observed infers that the chief fluorophore in the films are indole trimers. Quantum chemical methods predict oxidation potentials of these indoles in good agreement to experimental values. The transmission of substituent electronic effects through the aromatic system of the indole radical cations is again different for electron withdrawing and electron donating substituents.

In this thesis electropolymerised samples of the 5-cyanoindole and 5-bromoindole were studied. Steady state fluorescence and Time Correlated Single Photon Counting experiments were performed on solutions in ethanol of both types of polymer, and potentiometric experiments to ascertain the pH sensing ability of 5-cyanoindole solid films were carried out. The potential of rotating disc electrodes modified with thick (1.37μm) and thin (0.49μm) films 5-cyanoindole polymer were found to respond to changes in electrolyte pH linearly with a near-Nernstian slope, which is indicative of a promising pH sensing material. The response was independent of direction of pH change and sustainable over a time period of at least a week. The thin film shored promise as a good fast response pH sensor. Steady State (SS) fluorescence spectroscopy experiments carried out on solutions of electropolymerised 5-cyanoindole in ethanol at room temperature have shown that, when exciting at short wavelength the trimer chromophore gives the most intense emission at short wavelength, with no emission seen at longer wavelengths, and no noticeable difference between samples produced to produce trimer-rich and more extensively linked films. Exciting at longer wavelength a slight difference between the emission intensities of higher polymer and higher trimer content films was observed. Time Correlated Single Photon Counting (TCSPC) experiments were carried out at excitation wavelengths 360nm and 450nm and it was seen that the free trimer chromophore was the dominant contributor to the excited state population at all wavelengths. SS experiments were carried out on solutions of electropolymerised 5-bromoindole in ethanol and, consistent with previous work, it was seen that higher intensity of emission was seen in the polymeric region at longer emission wavelength. Additionally a marked difference was seen between higher and lower polymer content films.

This thesis is devoted to the photoelectrochemical characterisation of the interface between two immiscible electrolyte solutions. A number of new phenomena are reported and analysed. These include photoinitiated ion transfer, photosensitised ion transfer, interfacial photoanation of the [Ru(bpy)<SUB>3</SUB>]<SUP>2</SUP>+ ion and photoinitiated electron transfer. This last phenomenon takes place between the luminescent state of the [Ru(bpy)<SUB>3</SUB>]<SUP>2</SUP>+ ion and 7,7,8,8-tetracyanoquinodimethane, across the water/1,2-dichloroethane interface. A novel technique is presented to examine the ion transfer reactions of electrogenerated species, and data resulting from this technique are brought to bear on heterogeneous electron transfer reactions.

Three different types of mixed-valence complexes are studied in this thesis, namely, homonuclear d⁴/d⁵, heteronuclear d⁵/d⁶ and homonuclear d⁵/d⁶ binuclear metallic species. The electrochemical syntheses of the mononuclear complexes [OsC1₅(N-cypy)]^-/2- (N = 2,3, 4; cypy = cyanopyridine), and the asymmetrical homonuclear complexes, [C1₅Os(N-cypy)OsC1₅]^n- (N = 3, 4; n = 4, 5, 6) are reported. The mononuclear cyanopyridine complexes produce two isomeric forms, the cyanopyridine can be bound through either the pyridine nitrogen or the cyano nitrogen. Electrochemical investigations confirm that the isomer bound through the pyridine nitrogen is most stable. The X-ray crystal structure of this isomer for 3- and 4-copy is reported. The complexes have also been investigated using UV/Vis spectroelectrochemistry. The mononuclear complexes have been found to be very similar electronically. That is, the exact position of the cyano moiety has little effect on the overall electronic nature of the complex. This is in accordance with these ligands been principally s-donating ligands. The binuclear complexes of 3- and 4-cypy have also been synthesised and investigated electrochemically. The redox chemistry of the binuclear complex differs from the monoclear compounds. This is indicative of some communication between the two metal centres, K_c for the 4-cypy complex was found to be 17000 and for 3-cypy to be 1100. Thus the degree of communication is larger for 4-cypy compared to 3-cypy, in agreement with results published previously using these ligands, with different metal fragments. These complexes are described as class II mixed-valence complexes.

A series of binary ligand complexes [ReCl<SUB>6-n</SUB>(py)<SUB>n</SUB>]<SUP>z</SUP> (where n=0 to 6, z is the charge on the complex and py=pyridine) have been chemically and electrochemically synthesised <I>via</I> reduction-induced substitution reactions from [ReCl<SUB>6</SUB>]<SUP>2-</SUP>. These complexes have been characterised using electrochemical and spectroelectrochemical techniques. Seven members of the series, namely, [ReCl<SUB>5</SUB>py]<SUP>1-</SUP>, <I>trans-, cis- </I>[ReCl<SUB>4</SUB>(py)<SUB>2</SUB>]<SUP>0,-1</SUP>, <I>mer-</I>[ReCl<SUB>3</SUB>(py)<SUB>3</SUB>], <I>trans</I>[ReCl<SUB>2</SUB>(py)<SUB>4</SUB>]<SUP>1+</SUP>, [ReCl(py)<SUB>5</SUB>]<SUP>2+</SUP> and [Re(py)<SUB>6</SUB>]<SUP>2+</SUP>, have been structurally characterised by single crystal X-ray diffraction studies. Extended Hückel Molecular Orbital calculations have been performed on the complexes to elucidate which orientation of the pyridine ring(s) gives rise to the most stable structure. The theoretically and experimentally determined structures agree well. The complexes exhibit a wide range of redox processes spanning from Re<SUP>II/I</SUP> to Re<SUP>V/IV</SUP> based couples. The electrochemical data obtained from these complexes have been used to fit two ligand additivity models, those of Bursten and Lever. Practically, Lever's model is more convenient to use than Bursten's model while the latter is more successful in correcting for isomer effects. The linear relationship between the half-wave potentials for the redox couples of the series and either stoichiommetry, n, or the sum of Lever's ligand parameters ΣE<SUB>L</SUB> indicates that the six ligands around the metal centre individually influence the electronic character of the metal centre. Comparison of the UV/Vis/NIR spectra of [ReCl<SUB>6-n</SUB>(py)<SUB>n</SUB>]<SUP>z</SUP> complexes, varying n and z, has resulted in detailed assignments of the charge transfer bands to electronic transitions, including the elucidation of d–d transitions within the non-degenerate t<SUB>2g</SUB> orbitals. To explore how a ligand alters the stability and reactivity of a complex and hence probe the influence of ligand substitution on the electronic structure of the metal centre in the complex, three monosubstituted chlororhenium complexes, [ReCl<SUB>5</SUB>L]<SUP>1-</SUP> (L=benzonitrile, acetonitrile and pyridine), have been electrochemically and spectroelectrochemically studied. The structure of the complex [ReCl<SUB>5</SUB>(NCPh)]<SUP>1-</SUP> has been determined by single crystal X-ray diffraction studies. The three complexes undergo reduction induced substitution reactions which have been fully investigated using several electrochemical techniques.

Electrochemical machining is a process that has the potential to machine complex full-form shapes at high production rates. The economic utilisation of this process, however, has been impeded by the iterative trial and error approach that is often required to generate process specifications for any one machining set-up. This approach arises due to the incompleteness of models used to describe the complex physical, chemical and hydrodynamic parameter interdependencies. Such interdependence results in non-ideal effects that distort the transfer geometry between the tool shape and the required workpiece form. In this thesis a semi-empirical characterisation strategy, aimed at mapping out parameter interdependence through a single characterisation trial is proposed. This approach has been realised through the development of a segmented tooling assembly that enables the probing of spatial parameters sensitivities and through the development of distributed gap measurement system. The combined use of these systems, in the form of the characterisation cell assembly, has enabled detail parameter mappings to be carried out within a procedure taking only a few minutes to complete. The concept of the C-function expression is introduced as a means of representing parameter independence generated by the characterisation trials. This expression represents non-ideal effects as a spatial series, descretized along intervals of flow path length, with coefficients representing the sensitivity of gap size to primary process variables. Characterisation trials have been carried out using both titanium and nickel based alloys machined using chloride and nitrate based electrolytes. The method has also been applied to an analysis of one of the recently developed titanium aluminide alloys. These trials have identified a range of parameter interdependencies. Most significantly these have included an observation of the previously unknown phenomenon which has been termed electrochemical hysteresis, and a range of spatial characteristics in the dependencies between current density, flow velocity and gap size. The use of the C-function as a means of representing these characteristics is demonstrated by extrapolating planar characterisation data to shape prediction for a 2-D double-cosine profile.

This thesis concerns the reduction induced substitution reactions of three families of transition metal salts: (i) [MX₆]^2-, where M = Ir, Os, Re and X = Cl^-, Cr^-, l^-, (ii) OsX₃Y₃], where X = Cl^- or Br^- and Y = a tertiary alkyl phosphine or arsine, and (iii) techniques, in particular double-step chronoamperometry, to elucidate the mechanisms involved and the factors influencing the rate of reaction and the activation energy for the process. On one-electron reduction, [MX₆]^2- undergoes a substitution reaction of one halide, X, for a ligand, L, of less electron donating character. The rate constant and activation energy are largely independent of the nature or the concentration of the entering group, L, and inhibited by an increased concentration of the leaving group in solution. The rate limiting step is the loss of halide. The rate increases Cl^- < Br^- < I^-, reflecting leaving group ability and ease of solvation in the organic solvent. On changing the metal centre, the rate of reaction decreases Re>>Os>Ir, rationalised in terms of the nuclear charge of the metal centre: Re(III) is less able to support the electron density from the halides than Os(III) and Ir(III). The activation energy is understood to be the energy required to break the metal-halide bond and represents the extent of orbital overlap between the metal and halide. The nephelauxetic parameter, b, indicates strongly covalent character of the iridium-halide bond reflecting a high overlap of the iridium and halide orbitals. Overall, a Dissociative mechanism has been assigned to the halide loss with the exception of [OsCl₆]^2- which can be more adequately described by a dissociative Interchange mechanism with the formation of a pre-equilibrium complex, {[OsCl₆]^3-,L}. Digital simulation of the mechanisms supports these findings.

This work details the simulation of charge transfer at ultramicrointerfaces. A novel algorithm is presented for the simulation of electrochemical techniques applied to both ultramicrodisc and ultramicropipette electrodes. <i>Numerical Method</i>. The simulations employ the Crank-Nicolson finite differences or the Alternating Direction Implicit (ADI) method extended to include expansion of the space grid in two dimensions, a n-point current calculation and implicit determination of boundary conditions. The effects are determined of; point separation, choice of grid expansion equation, boundary conditions and relative number of points on electrode and in solution. Also, diffusion geometry, time increment, and the stability of the algorithm are considered in detail. The various methods currently available to model electrochemical response at ultramicrointerfaces are discussed, together with their limitations and a suggested protocol for their use. <i>Computing</i>. All programs are written in FORTRAN and all calculations performed in double precision. Source codes were compiled and run on the Edinburgh Multi-Access System (EMAS). <i>Electrochemical techniques</i>. Techniques simulated include cyclic voltammetry and chronoamperometry at macro, ultramicrodisc and ultramicropipette electrodes, including asymmetric sweep voltammetry at ultramicropipette electrodes. Results are presented for both reversible and quasi-reversible charge transfer. Effects of sweep rate, electrode radius, charge transfer coefficient and rate of charge transfer are studied. Disc and pipette electrochemical responses are compared over a range of experimental parameters. The simulation method presented is fast, accurate and stable over a wide range of experimental parameters and is easily adapted to different electrode geometries and experimental techniques.