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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

The synthesis and single-molecule conductance of conjugated molecular wires

Zhao, Xiaotao January 2014 (has links)
The past decades have seen the fast development of electronic devices in the industrial sector. There is increasingly rapid growth in the demand for alternative electronic building blocks to compliment, and possibly replace, the conventional silicon-based products. Electronic devices based on organic molecules, especially those based on single molecules, receive intense studies both theoretically and experimentally. In this presented work, a new family of oligo(aryleneethenylene)s (OAE)s with molecular lengths (N…N distance) of ca. 2-6 nm were designed to investigate the length dependence of conductance at the single molecule level. X-ray molecular structures of OAEs with a molecular length up to 5.3 nm were successfully analysed and presented. Secondly, four groups of pyridyl terminated oligo(phenyleneethylene) (OPE) derivatives were studied for the quantum interference effects. A dramatic destructive quantum interference effect was observed which decreased the single molecule conductance by several orders of magnitude. Unsymmetrical molecules with only one anchor group were noticed to form π-π stacking between two molecules. Thirdly, amino terminated OPEs bearing various substituents on the central phenyl rings were explored to present the robustness of the central OPE backbone towards various functionalising substituents. Fourthly, diaryloligoynes with different anchor groups were synthesised and the single-molecule conductances were studied. The stability of the tetrayne compounds is discussed and X-ray crystal structures of the stable tetraynes are presented. Finally, pyridyl terminated OAE derivatives bearing an anthraquinone core were synthesised to investigate the charge transport through the central anthraquinone core, with special purpose of investigating quantum interference effects and the switching process of the central anthraquinone core.

TIR-Raman spectroscopy of model supported lipid bilayers

Churchwell, John Hampilton January 2014 (has links)
In this thesis the technique of total internal reflection (TIR) Raman spectroscopy was applied to study the properties and interactions of supported lipid bilayers (SLBs) at the silica-water interface, both kinetically and at equilibrium. First, the formation kinetics of SLB systems from lipid aggregate suspensions was investigated. The lipid systems comprised POPC, POPE, egg-SM and a 1:1:1 mixture of POPE, egg-SM and cholesterol, all in tris buffer with and without added NaCl and CaCl2. Vesicle/aggregate suspensions were prepared by bath sonication and their size distributions were quantified with nanoparticle tracking analysis (NTA). The additional group I and group II salts altered the size distribution of the lipid vesicle/aggregate suspensions produced and played large role in the kinetics observed. For POPC, by changing the buffer conditions the adsorption of extraneous vesicles on the SLB could be tuned. For POPE, a previously unknown formation pathway was observed, whereby larger aggregates spread following adsorption to the interface. For the mixed system, the final ratio of components was found to be the same as that in the initial suspension. Second, the physical transformations of SLBs composed of DMPC, egg-SM and POPE were examined and the role of NaCl and CaCl2 upon these phase transitions was investigated. Raman spectra were obtained as a function of temperature and quantified using order parameter analysis. The resulting data were interpreted using the Zimm and Bragg model, which yielded the cooperativity of each phase transition. Cooperativity was controlled by the interfacial energy between regions of Lβ/Pβ and Lα phase. The presence or absence of the above salts altered the number of molecules within the cooperative unit for each of the species listed and controlled the interfacial energy. The most striking result was that of the POPE main phase transition with added CaCl2, for which cooperativity was massively reduced yielding a structural transition over a broad temper- ature range; AFM images confirmed the nature of this transition, showing domain like structures over a matching broad temperature range. Third, the interaction of SDS with SLBs composed of POPE, POPC, egg-SM and the 1:1:1 mixture of POPE, egg-SM and cholesterol was explored. Partitioning isotherms were constructed from equilibrium data and interpreted with a non-ideal partitioning model previously applied to vesicular systems. Accounting for the theoretical build-up of surface charge was found to be unnecessary probably owing to counterion binding. Kinetic data of the partitioning process for the different SLBs were obtained and qualitatively interpreted. For POPC at low dSDS concentrations dSDS translocation or flip-flop from the distal to proximal bilayer leaflets did not occur. At higher concentrations a period of rapid uptake lasting for approximately 100 s was followed by a slower increase lasting on the order of 10 minutes thus indicating that translocation was occurring. Upon subsequent rinsing, there was an initial rapid decrease in dSDS followed by a slower protracted decrease indicating that reverse flip-flop was occurring. The most intriguing result was that of the overall lipid signal upon rinsing, often it was observed to recover to levels equal to those prior to dSDS addition. These data suggest the formation of blebs or tubules as a result of dSDS induced spontaneous curvature; kinetic data from the CH region provided further evidence. Comparable data was obtained for POPE and egg-SM which showed very similar dSDS partitioning and rinsing kinetics, although the equilibrium behaviour differed in the strength of the dSDS lipid interaction. Less dSDS partitioned into the 1:1:1 mixture of POPE, egg-SM and cholesterol than any of the other species studied indicating its detergent resistance. Partial removal of this SLB from the interface left the contour of the CH region unchanged.

Crossing bridges : synthetic and charge transfer studies of linear and cross-conjugated systems

Vincent, Kevin Barry January 2014 (has links)
This thesis sets out to explore the electronic structure and properties of organometallic complexes. The mixed valence states generated on one-electron oxidation are investigated based on the theory developed in Chapter 1, which provides an introduction to the general area and electron transfer. Further Chapters in this thesis set out to explore the communication between redox states spanning linear and branched architectures and draw on the ideas presented in Chapter 1 to draw conclusions as to the degree of communication between the sites. To this extent a series of platinum-acetylide complexes bearing the unusual triarylamine ligand, containing one to four redox centres, were prepared and the electronic properties probed with IR and UV-vis NIR spectroelectrochemistry. The results show that there is only very weak communication between the centres. In Chapter 3 the work looks at symmetrical analogues of these compounds and builds on previously published work to explore in more detail the electronic structure of a series of trans-[Pt(C≡CC6H4NAr’2)2(PR3)2] complexes to explore the effect of the triarylamine and ancillary phosphine ligands. The results show modest communication between the centres and little effect of the phosphine ligand. The later chapters in this thesis focus on developing synthetic routes and analyses of branched-conjugated materials. Chapter 4 develops the synthesis of a range of compounds based on the FcCH=C(CCR)2 with organic R groups. The results show that, despite proposals of such systems being able to act as transistors, the ferrocene moiety is electronically isolated. Chapter 5 builds on this work and develops the synthesis of FcCH=C(CCC6H4CCMLn)2, MLn= Ru(PPh3)2Cp or Ru(dppe)Cp*. Spectroelectrochemical analysis has shown weak communication between the –Ru-(CC)- centres. Finally, Chapter 6 addresses the interactions within multi-ferrocenyl compounds. Analysis by IR SEC studies have shown that in compounds bearing either 2, 3 or 4 ferrocene groups that each centre is essentially electronically isolated despite electrochemical studies highlighting that in the right conditions a degree of through-space communication can be observed.

The aqueous phosphorylation and ligation of nucleoside analogues and aqueous azide reduction methodology

Conway, Louis Patrick January 2014 (has links)
The research within this thesis is primarily concerned with the synthesis of modified nucleosides, their oxyphosphorylation and thiophosphorylation to form analogues of nucleoside monophosphates and phosphodiester linkages, and the chemistry of the thiophosphoryl group. These families of compounds may have potential in the areas of antisense oligonucleotide agents or nuclease inhibition. The work described here may also provide routes to new glycosyltransferase inhibitors. This work builds upon previous work in the Hodgson research group, principally the thiophosphorylation and subsequent alkylation of organic amine fragments as a ligation strategy, and the optimisation of the thiophosphorylation procedure as applied to 5$'$\hyp{}amino\hyp{}5$'$\hyp{}deoxyguanosine. My role was to extend these techniques to the thiophosphorylation of other nucleoside derivatives and to use the thiophosphorylation procedure to produce potentially biologically active compounds. This thesis is divided into a number of chapters and appendices, and commences by providing a review of the synthesis, properties, and applications of natural and unnatural phosphodiester compounds in the first chapter. The second chapter details the work which has already been carried out within this research group on the synthesis, oxyphosphorylation, and thiophosphorylation of aminodeoxynucleosides; this forms the foundation to my own work on optimisation of the oxyphosphorylation procedure, and the application of both the oxyphosphorylation and the thiophosphorylation methodology to other aminodeoxynucleosides. The third chapter describes the application of the thiophosphorylation procedure to the synthesis of a thiophosphoramidate mimic of a dinucleoside. The following chapter concerns the investigations into the hydrolytic stability of the thiophosphoramidate group, using the dinucleoside thiophosphoramidate analogue as a model. The fifth chapter is on an aqueous method for the reduction of organic azides using the thiophosphate ion as the reducing agent. The reaction was tested on a number of alkyl and aryl susbstrates, and the mechanism of the reduction was investigated. Appended to this thesis are some chapters on work related to the main project in their application of modified nucleosides and nucleotides; in the first appendix, modifications were made to the phosphate group of guanosine monophosphate to allow the role of the phosphate group in the formation of G-quadruplex structures to be studied. The second appendix concerns work done in support of a project to incorporate 5$'$-deoxy-5$'$-hydrazinoguanosine into the 5$'$- terminus of RNA strands, which allowed the termini to be labelled with fluorescein isothiocyanate (FITC). Using 5$'$-deoxy-5$'$-hydrazinoguanosine as a model for the modified RNA strands, it was shown that within the limits of detection, each hydrazine group reacts with only one molecule of FITC.

Drying inkjet droplets : internal flows and deposit structure

Talbot, Emma Louise January 2014 (has links)
Inkjet printing delivers droplets with picolitre volumes onto a substrate. This thesis focuses on improving the quality of inkjet prints by controlling the particle distribution in the deposit. To this end, the internal flows in evaporating droplets were compared on purpose-built imaging rigs. Formulations were developed for deposit control based on the results of this analysis. Initial studies of pure solvents determined the influence of the substrate wettability and thermal conductivity on evaporation. It was demonstrated that an isothermal model accurately predicted the drying times of picolitre droplets, provided that evaporative cooling was insignificant. Evaporation of simplified model inks (two solvents + latex particles) was then considered. Marangoni flows transported particles along streamlines, with a circulating region that switched from the droplet centre to the edge on reversing the flow direction. Particles also migrated across streamlines towards the centre of the droplet, independent of the Marangoni flow direction. Large particles migrated faster than smaller particles, forming a tighter central group. Migration mechanisms were considered: Thermophoresis was ruled out due to particle migration in droplets with negligible thermal effects. Chemophoresis was not consistent with all observations of particle migration, though chemophoretic velocities are large enough to contribute. Shear-induced migration to regions of low shear rate is a promising potential migration mechanism. The deposit macro/microstructures were investigated for pure and binary mixtures. In pure solvents, evaporation-driven radial flow built up a ring stain at the contact line. This stain was inhibited for some binary solvent mixtures. However, in most cases, a ring stain developed after the Marangoni flow period ended. Hence, alternative routes of deposit control were investigated. Two strategies were developed to control the deposit structure: i) a sol-gel transition in a suspension of a nano-particulate clay (laponite), or ii) depletion flocculation induced by a free polymer (PSS). The latter strategy was the most successful for ethanol/water mixtures, producing a printed dot smaller than the droplet contact area. In water droplets, the sol-gel transition proved a successful method for obtaining a uniform particle distribution in the deposit.

A combined experimental and theoretical study into the excited states of luminescent platinum complexes

Freeman, Gemma Rachel January 2014 (has links)
Luminescent transition metal complexes have attracted much attention in recent years due to their potential as phosphors in organic light-emitting devices, their use in sensory systems and their applications in bioimaging. It is often desirable to predict the photophysical properties of such compounds to allow tailored design, accentuating certain characteristics. This combined experimental and theoretical study of the excited states of platinum complexes outlines synthesis, photophysical measurements and theoretical consideration of some such compounds, giving insight into the theoretical techniques applied. Reproduction of absorption spectra is described for a series of previously reported Pt(II) complexes, using different basis sets, functionals and solvent models, the techniques then applied to a novel set of related Pt(IV) complexes. Understanding of these parameters was then used for more complicated modelling of the emissive process in thiolate-substituted derivatives of Pt(dpyb)Cl. These were studied experimentally and theoretically, showing a change in excitation character upon coordination of the thiolate ligand. TD-DFT showed the importance of modelling solvent for the prediction of the correct excitation character, alongside a consideration of techniques and mathematical parameters for the correct calculation of emission energies. Bis-imine, bis-ketimine and bis-oxime ligands have been synthesised by Schiff base condensation chemistry and their corresponding N∧C∧N-coordinated Pt(II) complexes prepared. A wide range in quantum yields was observed and attributed to varying rates of non-radiative decay. Consideration of the S0 and T1 geometries by DFT and their distortion relative to one another showed the origin of this decay. Methyl-substituted benzenes were investigated for similar properties. Those derivatives for which the calculations predict significant distortion do show emission properties typical of triplet state distortion. However, due to “triplet instabilities”, TDA geometries appear to be more reliable than those calculated by DFT, showing better consistency with the experimental trends. Techniques described above were also applied to other classes of Pt(II) complexes. The rate of radiative decay was considered for these compounds by taking into account both the orbital overlap and the degree to which the metal atom was involved in the excitation.

Holographic particle image velocimetry of ink jet streams

McKeague, Thomas Anderson January 2015 (has links)
Ink jet technology is a rapidly growing and diverse field of research. Ink jets are used to deliver very precise and small (picolitre) volumes of fluid to a surface. Recent advances in ink jet technology demand a better understanding of the dynamics of the fluid during jetting. The aim of this project was to design a method capable of measuring the flow velocities inside ink jet streams. This objective has been achieved by the use of digital holographic particle image velocimetry. The difficulty with measuring flows inside tightly curved samples is that the refractive index change over the boundary leads to an optical distortion and therefore particles cannot be viewed or tracked reliably. Optical distortion is compensated for by taking advantage of the ability to replay a holographically recorded wave. The light scattered by particles is propagated numerically back through the sample’s surface, to form a three-dimensional image in which all refractions at the interface have been accounted for. Three dimensional particle fields are then analysed using custom particle detection and correlation code to extract the displacement of individual particles between exposures, which facilitates the construction of full flow profiles. Holograms were recorded with a simple off-axis holographic microscope, comprising two point sources of divergent light, formed from the same objective lens, acting as the source of illumination and reference light, respectively. Experiments were conducted on continuous ink jet streams of water issuing from a nozzle with 100 µm diameter. For a few millimetres after the nozzle exit, the jet is cylindrical, it then starts to form swells and necks; the swells continue to grow at the expense of the necks until the jet breaks up into a stream of droplets. Measurements of the stream wise component of velocity have been successful in the cylindrical parts of the jet, in swells and in necks greater than 20 µm in diameter. To my knowledge measurements of particle velocities on fluid jets at this scale have not been accomplished previously.

Structural, electronic and magnetic properties of fulleride materials

Zadik, Ruth Helen January 2015 (has links)
This thesis outlines new research findings into the solid-state properties of selected alkali- and alkaline-earth-intercalated fullerides, focusing on their structural, electronic and magnetic properties at ambient and non-ambient temperatures and pressures, primarily employing synchrotron X-ray powder diffraction and SQUID magnetometry. Understanding the relationship between superconducting, neighbouring insulating and normal metallic states above Tc in unconventional superconductors is fundamentally important. Highly expanded fcc Cs3C60 behaves very differently to underexpanded A3C60 alkali fullerides such as K3C60 and Rb3C60. Whilst superconductivity in the latter seems well described by conventional Bardeen-Cooper-Schrieffer (BCS) theory, Cs3C60, a Mott-Jahn-Teller insulator under ambient pressure, exhibits distinctly non-BCS type superconductivity upon pressurisation. The intermediate regime adjacent to the Mott boundary, where strong electronic correlations are prominent, was hitherto only studied through physical pressurisation of Cs3C60 to tune the intermolecular spacing. This thesis reports the solid-state synthesis of fcc-rich RbxCs3−xC60 (0.25 ≤ x ≤ 2) bulk superconducting materials, with excellent stoichiometry control, and the effects on the electronic properties in situ of tuning intermolecular separation by varying temperature, physical and chemical pressurisation via adjusting the cation dopant ratio. It is shown that the Mott boundary can be traversed at ambient pressure upon cooling, and the metal-insulator crossover temperature tuned by chemical and physical pressurisation. A15 Cs3C60 orders antiferromagnetically below 46 K. Previous studies found no evidence of symmetry lowering or discontinuous structural changes upon magnetic ordering, despite theoretical predictions to the contrary. This issue is addressed with the first systematic ultrahigh-resolution investigation of its structural evolution with temperature, evidencing a transition to a rhombohedral phase below TN. The structural properties of A15 Cs3C60 and Ba3C60 in situ upon pressurisation are described, extending previous work on A15 Cs3C60. This first study of the effects of compression on the latter system reveals a pressure-induced structural transition to a hitherto unreported monoclinic phase.

Ultracold scattering of alkali-metal atoms in magnetic fields

Blackley, Caroline Laura-Anne January 2015 (has links)
This thesis reports on calculations of the scattering properties of a variety of ultracold alkali-metal mixtures. In particular, we have calculated the scattering properties of homonuclear mixtures of 85Rb, in a variety of incoming channels, and we have calculated the properties of heteronuclear mixtures of the isotopologues of Rb and Cs, and K and Cs. In general, we are interested in the location and character of Feshbach resonances in these mixtures with a view towards ultracold molecule formation. In 85Rb there is a rich Feshbach structure and potential uses for the resonances that we find, in the scattering lengths of the various incoming channels, are discussed. In 85RbCs there is a rich Feshbach structure and the prospects for ultracold molecule formation using this system are detailed. Similarly, we detail the Feshbach resonances of 87RbCs and discuss our results in the context of the successful formation of ultracold ground-state molecules. In the isotopologues of KCs each system has a rich Feshbach structure and we detail the location and width of the resonances, as well as the potential for ultracold molecule formation using each of the isotopes of potassium. In addition to scattering calculations, we have also calculated the location and character of the highest-lying bound states of each system. We have investigated the energy dependence of the scattering length using accurate coupled-channel calculations on 6Li, 39K and 133Cs to explore the behaviour of the effective range in the vicinity of both broad and narrow Feshbach resonances. We present an alternative parametrization of the effective range and further demonstrate that an analytical form of an energy and magnetic field-dependent phase shift, based on multichannel quantum defect theory, gives accurate results for the energy-dependent scattering length. Lastly, we examine the effect of additional external fields on alkali-metal collisions and discuss how external fields can be used to manipulate the interaction properties of a system.

Highly luminescent lanthanide chirality probes

Neil, Emily Rose January 2015 (has links)
The chirality of biological systems can be probed using highly emissive lanthanide complexes with the aid of circularly polarised luminescence and emission spectroscopy. Such chirality probes can be synthesised through the incorporation of a remote chiral centre within the ligand framework, which can preferentially stabilise a particular stereoisomer giving an enantiopure complex of well-defined helicity. Alternatively, lanthanide chirality probes can be derived from achiral or dynamically racemic ligands, where the selective induction of a CPL signal can be monitored as a function of the nature and concentration of a selected chiral analyte. A series of chiral lanthanide complexes has been synthesised. Each complex is based on an amide substituted 1,4,7-triazacyclononane system derived from either R-(+) or S-(-)-α-methylbenzyl amine. The stereochemistry of the amide moiety controls the helicity of the complex, and one major diastereoisomer is formed for each lanthanide metal. The absolute stereochemistry of the major diastereoisomer was determined by X-ray crystallography (S-Δ-λλλ and R-Λ-δδδ). Inclusion of an aryl-alkynyl chromophore generated complexes that exhibited large extinction coefficients (up to 55,000 M-1 cm-1) and high quantum yields (up to 37%) in water. A second set of bright Eu (III) complexes has been prepared based on an achiral heptadentate ligand system, which vary in the nature of the pyridyl donor (phosphinate, carboxylate and amide). The binding of a number of chiral acids including lactate, mandelate and cyclohexylhydroxyacetate was monitored by a change in the emission spectrum and the induction of strong CPL. Empirical analysis of the ΔJ = 4 region of each of the Eu (III) complexes allows an assignment of the complex-anion adducts as R-Δ and S-Λ. Furthermore, variations in the sign and magnitude of CPL allow the enantiomeric purity of samples with unknown enantiomeric composition to be assessed. Finally, several dynamically racemic lanthanide chirality probes have been synthesised and characterised. Induced CPL has been assessed, which arises as a result of the change in complex constitution upon binding to important chiral biomolecules such as, sialic acid, O-phosphono-amino acids and peptides and oleoyl-L-lysophosphatidic acid (LPA). This work presents the first example of induced CPL in the detection of cancer biomarkers, sialic acid and LPA, and demonstrates the utility of this class of dynamically racemic Eu (III) complexes as chirality probes.

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