School of Chemistry - Theses

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    Toward the synthesis and analysis of selenium-containing glucocorticoid prodrugs
    Macdougall, Phoebe Eleanor. (University of Melbourne, 2007)
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    NMR studies of amyloid ab-peptide in membranes
    Lau, Tong Lay (Crystal) (University of Melbourne, 2006)
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    Synthesis and Testing of diaryl sulphide based Fluorine-18 Radiotracers for Positron Emission Tomography of Hypoxic Tumours
    Chong, Lee Wenn ( 2019)
    Hypoxia is a critical physiological marker demonstrated in a variety of cancers, imaging it will provide valuable insight into prognosis and treatment. However, the slow kinetics of [18F]FMISO(1.2) means that there is a 2 hour delay between injection and imaging for patients. Fluorine-18 labelled Chloroethyl sulfoxides [18F]SO101 and [18F]SO201 were shown to have both faster kinetics and higher contrast compared to [18F]FMISO(1.2) in a rat model of ischemic stroke. Perceived toxicity from the nitrogen mustard analogues in [18F]SO101 and [18F]SO201 lead to structural changes resulting in [18F]SO501. [18F]SO501 demonstrated good uptake into hypoxic SK-RC-52 tumours while also clearing from muscle, giving good contrast and therefore high-quality images, however it had a low radiochemical yield of 2.5% making it impractical for routine clinical application. Structural changes were made to the base compound [18F]SO501 in order to adapt it to a different method of radiolabelling in an attempt to increase the RCY while maintaining its selectivity for hypoxic tissue. The modifications made included the introduction of a propargyl group for click chemistry, variable length PEG groups and alterations to the ester group from an ethyl ester to an isopropyl ester and in one case doing away with it entirely. Six different diaryl-sulfoxide radiolabelled compounds were synthesised for this project [18F]2.16, [18F]2.26, [18F]2.36, [18F]2.43, [18F]2.53 and [18F]2.63 from their respective diaryl-sulfoxide precursors 2.15, 2.25, 2.35, 2.42, 2.52 and 2.62. After in-vivo imaging in SK-RC-52 tumours xenografted onto BALB/c nude mice the most promising tracer [18F]2.16, which had the best tumour to muscle ratio of 1.6 at 60 minutes and 2.1 at 110min, underwent metabolism studies involving Rat S9 liver fractions.
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    Designing New Singlet Fission Materials for High Performance Organic Solar Cells
    Masoomigodarzi, Saghar ( 2019)
    Singlet fission (SF) is the photophysical process of splitting one singlet state into two triplet states. The first requirement for SF is that the first excited singlet state of the chromophore should be at least twice the energy of the first triplet state. In the last decade, SF has received a lot of attention as a way of converting high energy photon above the semiconductor bandgap to two lower energy excitons closer to the bandgap and so overcoming the Shockley-Quiesser limit (maximum theoretical efficiency of photovoltaic cells) of single-junction solar cells. However, the number of SF materials that can be included in photovoltaic devices is limited because of strict materials requirements. This is the main reason why only a small increase in the efficiency of photovoltaic devices by including SF materials has been reported so there is a need to design, synthesis and study new class of material for SF. A new strategy to design a class of intramolecular SF (iSF) material is reported to be coupling two strong acceptors with low triplet energy level with a strong donor (A-D-A). This model not only takes the advantage of providing an excited electronic state with significant charge-transfer character that facilitate SF but also allows us to choose units based on the energy level requirement. Using this strategy, I have designed and synthesized the small molecule (BDT(DPP)2) and polymer (p-BDT-DPP) systems by coupling benzodithiophene (BDT) as electron donor and bisthiophene-pyrrolopyrrole-dione (TDPP) as electron acceptor with low lying triplet energy level. Various steady state and time-resolved spectroscopic techniques such as ultrafast and nanosecond transient absorption (TA) spectroscopy were used to study the excited state mechanism in the candidate compounds. In most of highly efficient SF systems, a large degree of crystallinity is required, and the SF yield is highly sensitive to the crystal packing and intermolecular nearest-neighbour coupling. The first set of A-D-A material revealed that a stronger self-association is needed to drive SF in this class of material. To address this issue, a self-organizing core such as hexa-peri-hexabenzocoronene (HBC) is used as electron donor and is attached to TDPP as an electron acceptor and the results show a significant increase in the efficiency of triplet yield. It has been demonstrated that the chromophore packing has a significant impact on the SF parameters such as yield and rate and understanding this relationship will help us to understand SF mechanism better. To investigate this relationship, four perylenediimide (PDI) derivatives were studied for SF comprising the same PDI core but with different substituents at their imide positions, 4-butylphenyl, butyl-terphenyl, diisopropylphenyl and mesityl which display distinct molecular geometries with varied intermolecular pi-pi interactions. The results demonstrate that SF occurs with different rates and yields in the PDI derivatives. Also, the results show that both decay rate and SF rate are sensitive to intermolecular packing.
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    Incorporation of Quantum Dots into Optoelectronic Devices: Ligands as Charge Brigands
    Blauth, Christian ( 2019)
    With their tunable and almost monochromatic emission over the whole visible spectrum, colloidal II-VI semiconductor quantum dots (QDs) are attracting significant interest as novel electroluminescent materials in light-emitting diodes (LEDs). Being processable in solution allows the deposition of large-scale films at low cost and brings QDs in a competitive position to their organic counterparts. Organic ligands capping QDs are used to maintain colloidal stability during synthesis and provide passivation in solution. While ligands remain invisible under optical characterisation, this thesis provides insights into the mechanisms by which ligands impact charge carrier dynamics within a light-emitting diode. In doing so, robust and bright QDs emitting at 410 nm are synthesized, passivated with ligands of various lengths and electrical conductivity and incorporated into an LED architecture. Based on Impedance Spectroscopy measurements ligands have been identified as a major obstacle for charges transiting to the QD to produce light: ligands act as brigands in trapping charges and prevent efficient charge recombination. A novel capacitance behaviour is described and attributed to the accumulation of charge carriers within the ligands during operation. Together with an inductive response in the impedance plane changes in capacitance can be used as a diagnostic tool to determine the recombination efficiency in a quantum dot light-emitting diode (QLED). By driving a QLED with a rectangular pulse accumulated charges lead to a delayed luminescence peak when the bias is turned off and can thereby be visualised. When a 5 nm thick aluminium layer is added into the hole transport layers, trapped charges can open a memory window and add a new device functionality to a QLED. This thesis concludes with ideas to overcome the ligand-dependent charge accumulation and suggests a novel type of QDs for a more efficient device performance.
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    Development of novel cross-linked polymer inclusion membranes (PIMs) for the separation of metallic and non-metallic species
    Hoque, Bosirul ( 2019)
    Separation based on polymer inclusion membranes (PIMs) has gained significant interest in recent years as an environmentally friendly separation technique. PIMs are generally classified as a type of liquid membrane in which the membrane organic phase (containing the extractant and in some cases a plasticizer or modifier) is immobilized within the entangled chains of a polymer. The majority of the extractants used in PIMs are liquids, although solid extractants such as trioctylphosphine oxide (TOPO) can also be used when liquified because of the presence of impurities (e.g., solvents). Different base polymers, such as poly(vinyl chloride) (PVC), cellulose triacetate (CTA), and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), have been used as the polymeric support of PIMs. Although the extractants are the active PIM components, the nature of the polymeric support also plays a vital role in the performance of these membranes. In the research described in this thesis the structure of the PIM polymeric support has been altered using different cross-linking agents (i.e., polymer of monomers) and their effect on PIM extraction and separation performance has been studied.
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    Investigation of optically transparent non-wetting coatings
    Wang, Chang ( 2019)
    Surfaces that exhibit extreme non-wettability are the result of the combination of surface chemistry and a high degree of roughness. Typically, such materials are visibly opaque, predominantly due to the enhanced light-scattering from the rough interfaces. In the present study, particle-based coatings with carefully controlled surface and bulk roughness parameters are investigated in multiple length scales to identify conditions under which extreme surface-phobicity and visible transparency can coexist. Visibly transparent micron-thick fumed silica nanoparticle (7–40nm) seeded sol-gel coatings were fabricated. Nano-scale surface and bulk features with varying degrees of water-repellency (hydrophobicity) were correlated with visible optical transparency. Furthermore, alternative tuneable hollow silica spheres in the sub- micron scale range were utilised to create a finely detailed range of roughness, which simultaneously changes both the refractive index through lowering relative optical permittivity and film density, and the surface wettability. Surface morphology and roughness of individual samples were examined in detail using atomic force microscopy, non-contact optical profilometry, scanning electron microscopy and synchrotron-based small-angle X-ray scattering (SAXS) in transmission mode. The latter was employed to investigate the nano-scaled common length scale (repeating) features in the coating. Coatings consisted of hierarchically ordered structures similar to fractals, with nano-scale (12–30nm) features superimposed on top of larger (200–400nm) sub-micron features displaying coexistence of optical transparency and water repellency. Extended surface studies were achieved by sputtering a thin (8–15nm) layer of sputter-coated Cr metal, which enhanced the surface X-ray scattering. Coatings fabricated using colloidal fractals with enrichment of both nano (20–30nm) and sub-micron (50–270nm) length scale on its surface structure displayed an enhancement to the roughness-induced water-repellency behaviour. Analysis of the bulk features alone was performed through the cross-sectional imaging under dual- beam FIB/SEM. Visible optical transparency in the film required nanoparticle cluster size to be between 130–180nm in length, to minimise the scattering of visible light. Alternatively, through the manipulation of the size of hollow core and silica shell thickness, the optical transparency at specific wavelengths of visible light correlated to the size of hollow silica spheres is enhanced without the loss of roughness. Hollow silica spheres within the sub-micron length scale (300–700nm) provide an alternative system for fabricating roughness-induced optically transparent non-wettable coating.
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    Supramolecular Assemblies of Cyclotricatechylene
    Holmes, Jessica Louise ( 2019)
    This thesis presents the results of synthetic and structural investigations of novel cyclotricatechylene-based supramolecular assemblies. Cyclotricatechylene is a bowl-shaped tris-catechol that has been shown to associate with other chemical species through hydrogen bonding and metal coordination. The research focuses on the synthesis and characterisation of novel crystalline supramolecular assemblies of cyclotricatechylene. The compounds described in the four experimental chapters include assemblies of cyclotricatechylene and its related anions with s, p, d and f-block elements of the periodic table. The compounds have been characterised X-ray crystallography. Synthetic and structural investigations of compounds formed from the combination of cyclotricatechylene with s-block metal cations reveal a diverse array of network materials, with cyclotricatechylene in various protonation states. The s-block cations are commonly found to associate with the oxygen atoms of the ligand, however Rb+ and Cs+ also exhibit an affinity for the inner and outer aromatic surfaces of the ligand. Two compounds containing cyclotricatechylene ‘clams’, H[Cs(ctcH5)(ctcH5)] and [Cs(ctcH6)2]+ are reported, in which cyclotricatechylene is found in different protonation states. In these compounds, the large group 1 metal cation Cs+ associates with the electron-rich aromatic surfaces of the cyclotricatechylene bowls, an interaction present in many structures described in this thesis. Metal-cyclotricatechylene polymeric structures are reported, in which s-block metal cations are chelated by catechol(ate) oxygen atoms. These structures include 2D sheets containing Ca2+, Sr2+ and Ba2+ cations, [Cs2Li4(ctcH3)4]6- metallocycles that hydrogen bond to each other to form a 3D network that has the topology of diamond, undulating ‘honeycomb’ networks with Cs+ or Rb+, and a 3D network with the topology of the (10,3)-a net, containing Cs+ in cyclotricatechylene bowls and Sr2+ chelated by catecholate units. Four high-symmetry cubic structures formed from the specific combination of cyclotricatechylene with Cs+ or Rb+, K+, acetone, water and an oxyanion contain metallocubes of formula [K4(ctcH6)4(H2O)8]4+. The assemblies are arranged in a symmetrical manner, which reflects high level of complementarity in these crystalline supramolecular assemblies. The combination of cyclotricatechylene with vanadyl or uranyl units leads to the formation several large, anionic coordination ‘cage’ assemblies with fully deprotonated cyclotricatechylene. An aesthetically pleasing example is an assembly with trigonal prismatic geometry, of formula [(VO)9Cs6(ctc)6]18-, in which vanadyl oxo groups are directed both into and out of the cage. Systems containing the uranyl cation (UO22+) were found to exhibit considerable structural diversity that can be attributed to the formation small clusters of uranyl cations with oxo, hydroxo, peroxo and aqua ligands. The co-precipitation of uranyl-based side products provides significant challenges with respect to the characteristion of these materials. A robust tetrahedral assembly of cyclotricatechylene with silicon, [(PhSi)6(ctc)4]6-, was found to be identical in topology to, but much easier to characterise than, its d-block metal analogues. Unlike geometrically similar metal-based cages, all bonds within the anionic assembly are covalent. The cage has been shown to persist in the gas phase and also when crystals of the compound are boiled in water. The crystalline material can also uptake Cs+ cation guests, which occupy the bowls of the tetrahedra.
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    Development and application of theoretical models for molecular magnetism
    Rao, Shashank Vittal ( 2019)
    My thesis consists of two projects. In the first, I have worked on the development of scalar relativistic and spin-orbit coupling methods within the ab-initio framework of the package CERES, developed in our group. In the other project, I have explored for the possibility of attaining toroidal moments in magnetic rings with weak or zero spin-orbit coupling. I managed to theoretically identify entirely new families of molecules that have a degenerate ground state where it is possible to prepare a purely toroidal quantum state. In Project 1, I have implemented the Douglas Kroll Hess method of 2nd order in the quantum chemistry code CERES to incorporate the scalar relativistic effects. I have also explored approximations to the Breit-Pauli Hamiltonian and found that the bare one-electron operator is often sufficient to obtain reasonably good crystal field energy levels within the lowest spin-orbit multiplet. I also present a comparison between different mean-field approximations for incorporating the two-electron terms. In Project 2, I have theoretically investigated new spin-frustrated molecular triangles that show the first known example of a toroidal quartet, composed of two degenerate toroidal doublets, solely as a consequence of spin-frustration, and despite having no spin-orbit coupling. Finally, I have generalized these findings to extended odd-membered ring and managed to identify infinite families of molecular rings that show a ground multiplet composed of one or more toroidal doublets.