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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.
11

New organic semiconductors and crosslinking additives for enhanced device performance and stability

Rumer, Joseph January 2014 (has links)
Organic electronics promises inexpensive devices with diverse applications ranging from grid-scale power generation to disposable packaging. This results principally from compatibility with solution-processed manufacturing methods such as printing with large-scale, flexible and light-weight substrates. Organic solar cells in particular offer an underexploited renewable energy solution to increasing energy demand and global warming. However, for organic photovoltaic (OPV) cells the current goal is now to stabilise commercially viable efficiencies of >10%, for >10 years. As exemplified in this thesis, a structure-properties-fabrication-performance paradigm exists, necessitating judicious molecular design alongside tailored and optimised device manufacturing processes. Structure-property relationships are illustrated in a systematic series of TPD-2T-based copolymers: a C1-branched side-chain promotes increased crystallinity and solid-state packing, compared to C2- or C3-branching. In contrast, fabrication-performance relationships are illustrated with P3EPT, an analogue of P3HT, which exhibits a higher Voc in coarse BHJ blend devices compared to P3HT, most likely due to adopting a different morphology on casting in the absence of PCBM. The total paradigm is explored with a new class of benzodipyrrolidone-derived semiconductors in OPV and OFET applications. The advance from phenyl- to thiophene-flanked units (BPPs to BPTs), with reduced torsional twisting, affords ambipolar charge transport and satisfactory charge carrier mobility. In addition, select dihydropyrroloindoledione (DPID)-based materials afford unencumbered OPV performance when processing with more environmentally benign solvents. Furthermore, enhanced OPV device performance is achieved with DAZH and PDCF3-based small molecule crosslinkers, which convey thermal stability to OPV blends, typically through the frustration of fullerene aggregation. These additives exhibit sufficient shelf-life and ease of handling, with non-invasive and scalable activation by UV light, emitting only inert nitrogen gas. Moreover, our DAZH additive affords an increase in as-cast device efficiency, stemming from its design.
12

EVV 2DIR : a novel approach for protein phosphorylation

Cheung, Michelle January 2014 (has links)
The novel Electron-Vibration-Vibration Two-Dimensional InfraRed (EVV 2DIR) technique is a nonlinear spectroscopic method that measures the vibrational coupling spectrum in a way analogous to the measurement of spin couplings by 2D NMR methods. To date, the main focus of this work has been on the development of EVV 2DIR as a tool for high-throughput, label-free protein identification and absolute quantification. One of the most promising areas where EVV 2DIR technique can provide complementary information not available via other established proteomic methods is for the study of post-translational modifications. This spectroscopy has demonstrated absolute quantification of phosphorylation levels in peptides, something difficult to achieve with other methods. The cyclin-dependent kinase inhibitor p27 is involved in orchestrating a variety of protein interactions in vivo that are key modulators of cell-cycle progression and that are often deregulated in cancer. The regulation of p27 is controlled by phosphorylation on serine, threonine and tyrosine residues thus providing a good model for EVV 2DIR studies.
13

The use of O-(diphenylphosphinyl)hydroxylamines and nitrogen-selenium ylides in transition-metal-free aminations of sp2 carbon centres

Milner, Harry January 2015 (has links)
Due to their abundance in both natural products and synthetic pharmaceuticals, and their diverse and interesting biological properties, nitrogen containing compounds are of great importance to organic chemists. As such, synthetic methodology for the incorporation of nitrogen into organic compounds via the construction of C-N bonds is highly sought after. The research described in this thesis concerns the development of three methodologies for the synthesis of small nitrogen containing compounds via the amination of carbon sp2 centres: 1) Synthesis of N-Boc-aziridines Building upon recent reported methodology utilising O-(diphenylphosphinyl) hydroxylamine (DppONH2) as a nitrogen source for NH-aziridinations, studies were undertaken into the use of N-Boc-O-(diphenylphosphinyl) hydroxylamine (DppONHBoc) in the synthesis of N- Boc-aziridines. Described herein are studies into the use of DppONHBoc as a nucleophilic nitrogen transfer agent (NNTA) for the aziridination of enones and vinyl sulfones under mildly basic conditions. 2) Amination of aromatic C-H centres The use of a N-methyl morpholine (NMM)-derived aminimine as an aminating agent in the vicarious nucleophilic amination (VNA) of electron-deficient (hetero)arenes is also reported. Initial studies which used iodide hydrazinium salts as aminimines precursors in the amination of a range of electron-deficient substrates are described. An alternative reaction system utilising the in situ formation of NMM/DppONH2 hydrazinium salts, in-place of preformed hydrazinium salts, in the vicarious nucleophilic amination reaction was then developed. 3) Synthesis of enantioenriched allylic amines Finally, the NCS-meditated amination/[2,3]-sigmatropic rearrangement of enantioenriched allylic selenides, utilising a range of amino acid derived and aryl amine nucleophiles, is used to access a wide range of novel vinyl glycine derived unnatural peptides and peptidomimetic products.
14

A novel synthetic approach to the fasicularin family of marine alkaloids

Marshall, Joseph January 2014 (has links)
This thesis is divided into four chapters. The first chapter comprises an introduction to the fasicularin family of marine alkaloids, and a review of previous total syntheses of the members of this class of compounds. This chapter also covers the previous work by Craig et al. on the synthesis of (±)-lepadiformine, and how this influenced our initial approach to the enantioselective synthesis of (-)-lepadiformine. The second chapter details the first part of our investigation into the synthesis of these compounds, including short reviews of diastereoselective aziridination protocols developed by Yoon et al. and Sharpless et al. This section includes the results of this investigation, and discusses the successes and failures of this approach. The third chapter concerns our revised second-generation strategy for the synthesis of (-)-lepadiformine, and includes a review of the decarboxylative Claisen rearrangement, and diastereoselective variants thereof. This section also covers our results and discussion for this revised synthesis. The fourth chapter contains experimental details and characterisation data for all compounds synthesised.
15

Optimisation and characterisation of alternative hole transporting media of dye-sensitised solar cells and stability study of perovskite solar cells

Law, Chun Hung January 2014 (has links)
Dye-sensitised solar cells (DSSCs) are regarded as a possible alternative to silicon-based photovoltaics because of their potential for low-cost production. The processing of two alternative hole transport media, one for liquid-state DSSCs and the other for solid-state DSSCs is studied in this thesis. Also, research interest in methyl ammonium lead iodide perovskite solar cells has been increasing quickly. This thesis also reports some preliminary studies on the stability of TiO2/CH3NH3PbI3 perovskite solar cells. Water is not commonly used as a solvent in liquid electrolyte DSSCs, but there are many reasons to re-examine water, ranging from cost advantage to fundamental science. The first part of the thesis addresses the wetting and recombination issues of water-based DSSCs. DSSCs using only water as the solvent and guanidinium iodide/iodine as the redox couple have been fabricated and they operate at 4% energy efficiency under 1-sun illumination. The second part of this thesis studies melt-processing of hole transport materials. This technique overcomes the problem of poor pore filling which is commonly observed in solid-state dye-sensitised solar cells. It is found that the low efficiency of melt-processed DSSCs is due to the heat applied during the melting process which causes a decrease in recombination lifetime. Solid-state DSSCs made with melt-processed spiro-OMeTAD are shown, with a maximum efficiency of 0.45 %. Stability of TiO2/CH3NH3PbI3 perovskite solar cells is examined in the third part of the thesis. Most literature in the perovskite solar cells focuses on the efficiency of devices, with little attention being paid to stability. A TiO2/CH3NH3PbI3 solar cell has been exposed to 40 sun-equivalent constant illumination for 63 hours (which delivers over 2700 hours equivalent of 1 sun photo-excitations). The loss in the cell's Jsc was only 7%, however the loss in Voc was 190 mV (24%) at 1 sun.
16

Metal oxide semiconductors employed as photocatalysts during water splitting

Pesci, Federico M. January 2014 (has links)
Photocatalytic water splitting has attracted significant interest in recent decades as it offers a clean and environmentally friendly route for the production of hydrogen. A key challenge remains the development of systems that employ abundant, non-toxic and inexpensive materials to dissociate water efficiently using sunlight. Titanium dioxide (TiO2), tungsten trioxide (WO3) and hematite (α-Fe2O3) are among the most studied photoanodes employed during water splitting because of the position of their valence band which is suitable for oxidising water to oxygen, and their low costs. However reported efficiencies for these materials are below the reported theoretical maximum values. A good understanding of the factors that are limiting the efficiency of these photoanodes is therefore desirable if improvements in the photocatalytic activity are to be achieved. This thesis is divided in four main sections. Chapters 3 and 4 describe transient absorption spectroscopy (TAS) studies in the microsecond-second timescales carried out on WO3 photoelectrodes and TiO2 nanowires respectively. TAS has been employed to follow the charge carriers dynamics in WO3 highlighting the presence of relatively long-lived holes (30 ms), which have been described as a requirement for the water oxidation reaction to take place. The electrons also appear to be long-lived (0.1 s), and this has been proposed to be due to slow electron transport through the film. TAS measurements have also been carried out on oxygen-deficient hydrogen-treated TiO2 nanowires, highlighting a more efficient suppression of the electron/hole recombination process in comparison with conventional anatase TiO2 photoanodes. Chapter 5 describes TAS and sum frequency generation (SFG) studies on TiO2 films which are designed to investigate the surface mechanisms of water oxidation. The dependence of the hole lifetime on the pH of the electrolytes employed has been examined by TAS and substantially faster decay rates have been found in highly alkaline solutions suggesting a change in the mechanism of water oxidation. Consequently, SFG has been employed in order to detect any possible intermediate at the interface TiO2/water. Initial measurements have provided the evidence of physisorbed and chemisorbed methanol (model probe) on the TiO2 surface and further studies at the TiO2/water interface have been carried out. Chapter 6 describes the development of a hybrid solar fuel reactor coupling a α-Fe2O3 based photoelecrochemical cell with luminescent solar concentrator plates. Initial tests have been carried out on a proof of principle prototype providing encouraging results.
17

The reactivity of hydrogen and carbon dioxide mediated by main group compounds

Herrington, Thomas James January 2014 (has links)
The focus of this thesis has been the design and synthesis of new frustrated Lewis pair (FLP) systems which from structural modifications retain their ability to activate H2/CO2, while displaying differing reactivity modes. Chapter Two describes the first practical synthesis of tris[3,5-bis(trifluoromethyl)phenyl]borane (BArF18). Gutmann-Beckett Lewis acidity measurements reveal that this borane is a more powerful Lewis acid than B(C6F5)3, but it nevertheless is found to bind H2O much more reversibly than B(C6F5)3. The BArF18/2,2,6,6-tetramethylpiperidine (TMP) FLP provides a rare example of H2 activation in Et2O solvent, in which the borohydride salt has been structurally characterised by X-ray crystallography. A novel bridging borohydride [mu-H(BArF18)2]⁻ was revealed, which contrasts to the characteristic terminal borohydrides formed by other borane based mediated FLP systems. Chapter Three details the design of fluorinated trisalkylboranes including B[CH(C6F5)2]3 which has been synthesised for the first time. This borane has been structurally characterised using X-ray crystallography and displays hydrogen bonding interactions between the ortho fluorines on each aryl ring and the adjacent CH proton. Interestingly, and despite this borane showing no Lewis acidity using Gutmann-Beckett and Childs techniques, the B[CH(C6F5)2]3/TMP FLP provides a rare example of H2 activation in THF solvent. Chapter Four details the synthesis of two classical trialkylsilylium-phosphane adducts [R3Si-PtBu3]+[B(C6F5)4]⁻ [R = Et; R = iPr] derived from the sterically unencumbered silylium ions R3Si+ (R = Et, iPr). Both adducts are not found to dissociate at elevated temperature and are appreciably stable towards decomposition. Moreover, adduct formation does not impede archetypal FLP reactivity; admittance of H2 led to heterolysis at elevated temperatures (90-100 °C), while CO2 activation occurs under ambient conditions. The latent stability of the CO2 adducts has allowed for their crystallographic characterisation. Subsequently, the activation parameters for CO2 uptake were investigated and support computational calculations.
18

Ionic liquid thermal stability : implications for cellulose regeneration

Clough, Matthew Thomas January 2015 (has links)
During the course of the past twenty years, the applications of contemporary ionic liquids have become increasingly widespread and varied; as solvents or catalysts for sustainable synthetic processes, as battery electrolytes, and for the dissolution and deconstruction of lignocellulosic biomass. These ionic liquid-assisted procedures frequently operate at high temperatures, therefore a comprehensive understanding of ionic liquid thermal stability is of great practical value. It has been demonstrated that ionic liquids incorporating carboxylate anions are capable of dissolving a substantial quantity of cellulose, the world's most abundant bio-renewable resource. The thermal stabilities of carboxylate ionic liquids are thoroughly characterised in this contribution, employing a broad range of experimental and computational methods. The impact of structural modification of the cation/anion on thermal stability is evaluated, and the prevailing thermal decomposition mechanisms are elucidated. Subsequently, the reactivity and decomposition pathways of cellulose and carbohydrate model compounds, dissolved in carboxylate ionic liquids, are uncovered. Thermal stabilities of carboxylate ionic liquids are found to be highly sensitive to relatively modest changes in the ion chemical structure (e.g. via fluorination or substitution of sulfur into the carboxylate group), and the experimental conditions. Furthermore, the prevailing thermal decomposition mechanisms are dependant on the electronic and steric properties of the ions. Crucially, the prototypical carboxylate ionic liquid 1-ethyl-3-methylimidazolium acetate is susceptible to transient and reversible formation of an N-Heterocyclic Carbene species through abstraction of the ring C2 proton, enabled by the basicity of the anion. This 'non-innocent' behaviour of carboxylate ionic liquids is critical in initiating a sequence of undesirable degradation pathways with dissolved carbohydrates, yielding imidazolium-derived adducts bearing hydroxyalkyl substituents. Strikingly, the analogous ionic liquid 1-butyl-3-methylimidazolium chloride does not initiate the unwanted series of reactions, yet is capable of dissolving a significant quantity of cellulose.
19

Synchronized optical and electrical detection of biomolecules using a low-noise nanopore platform

Pitchford, William January 2015 (has links)
Nanopore biosensors are a relatively new tool for single-molecule detection, whose inception was inspired by molecular transport through transmembrane pores in nature and the operating principle of the Coulter Counter, so-called resistive pulse sensing. In recent years, nanopores have been integrated with alternative detection modes, such as fluorescence spectroscopy, with the goal of increasing structural resolution and analytical throughput. The integration of fluorescence spectroscopy is particularly useful as fluorescent labels can be used to identify different regions of a molecule; discriminate molecules in heterogeneous solutions and probe molecular properties such as distance. This thesis describes the development and application of a unique low-noise nanopore platform, composed of a predominately pyrex substrate and silicon nitride membrane, for synchronized optical and electrical detection of biomolecules. The use of a pyrex substrate was pursued as commonly used Si substrate based nanopore sensors exhibit high ionic current noise with and without laser illumination. This limits their applicability to high-laser-power, high- bandwidth electronic measurements, which in-turn restricts the range of molecules that can be studied and the structural resolution provided by resistive pulse sensing. Proof-of-principle experiments are presented that show a pyrex substrate greatly reduces ionic current noise arising from both platform capacitance and laser illumination. Furthermore, using a confocal microscope and a pyrex based platform with a partially metallic nanopore, thereby acting as a zero mode waveguide, we demonstrate synchronized optical and electrical of dsDNA. The high translocation velocity of biomedically relevant molecules such as proteins and nucleic acids means there is a continual drive for low-noise high-bandwidth measurements within the nanopore community. The use of these low-noise platforms for synchronized measurements increases the sensitivity of resistive pulse sensing and therefore the range of molecules that can be studied and potential applications of the sensor.
20

An automated fluorescence lifetime imaging multiwell plate reader : application to high content imaging of protein interactions and label free readouts of cellular metabolism

Kelly, Douglas James January 2014 (has links)
This thesis reports on work performed in the development and application of an automated plate reading microscope implementing wide field time gated fluorescence lifetime imaging technology. High content analysis (HCA) imaging assays enabled by automated microscopy platforms allow hundreds of conditions to be tested in a single experiment. Though fluorescence lifetime imaging (FLIM) is established in life sciences applications as a method whereby quantitative information may be extracted from time-resolved fluorescence signals, FLIM has not been widely adopted in an HCA context. The FLIM plate reader developed throughout this PhD has been designed to allow HCA-FLIM experiments to be performed and has been demonstrated to be capable of recording multispectral, FLIM and bright field data from 600 fields of view in less than four hours. FLIM is commonly used as a means of reading out Förster resonance energy transfer (FRET) between fluorescent fusion proteins in cells. Using the FLIM plate reader to investigate large populations of cells per experimental condition without significant user input has allowed statistically significant results to be obtained in FRET experiments that present relatively small changes in mean fluorescent lifetime. This capability has been applied to investigations of FOXM1 SUMOylation in response to anthracycline treatment, and to studies of the spatiotemporal activation profiles of small GTPases. Furthermore, the FLIM plate reader allows FLIM-FRET to be applied to protein-protein interaction screening. The application of the instrument to screening RASSF proteins for interaction with MST1 is discussed. The FLIM plate reader was also configured to utilise ultraviolet excitation radiation and optimised for the measurement of autofluorescence lifetime for label-free assays of biological samples. Experiments investigating the autofluorescence lifetime of live cells under the influence of metabolic modulators are presented alongside the design considerations necessary when using UV excitation for HCA-FLIM.

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