School of Chemistry - Research Publications
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ItemSelenoproteins in Health(MDPI, 2024-01)Selenium (Se) is a naturally occurring essential micronutrient that is required for human health. The existing form of Se includes inorganic and organic. In contrast to the inorganic Se, which has low bioavailability and high cytotoxicity, organic Se exhibits higher bioavailability, lower toxicity, and has a more diverse composition and structure. This review presents the nutritional benefits of Se by listing and linking selenoprotein (SeP) functions to evidence of health benefits. The research status of SeP from foods in recent years is introduced systematically, particularly the sources, biochemical transformation and speciation, and the bioactivities. These aspects are elaborated with references for further research and utilization of organic Se compounds in the field of health.
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ItemPredicting valence tautomerism in diverse cobalt-dioxolene complexes: elucidation of the role of ligands and solvent(ROYAL SOC CHEMISTRY, 2024-04-17)The ability of molecular switches to reversibly interconvert between different forms promises potential applications at the scale of single molecules up to bulk materials. One type of molecular switch comprises cobalt-dioxolene compounds that exhibit thermally-induced valence tautomerism (VT) interconversions between low spin Co(iii)-catecholate (LS-CoIII-cat) and high spin Co(ii)-semiquinonate (HS-CoII-sq) forms. Two families of these compounds have been investigated for decades but have generally been considered separately: neutral [Co(diox)(sq)(N2L)] and cationic [Co(diox)(N4L)]+ complexes (diox = generic dioxolene, N2L/N4L = bidentate/tetradentate N-donor ancillary ligand). Computational identification of promising new candidate compounds prior to experimental exploration is beneficial for environmental and cost considerations but requires a thorough understanding of the underlying thermochemical parameters that influence the switching. Herein, we report a robust approach for the analysis of both cobalt-dioxolene families, which involved a quantitative density functional theory-based study benchmarked with reliable quasi-experimental references. The best-performing M06L-D4/def2-TZVPP level of theory has subsequently been verified by the synthesis and experimental investigation of three new complexes, two of which exhibit thermally-induced VT, while the third remains in the LS-CoIII-cat form across all temperatures, in agreement with prediction. Valence tautomerism in solution is markedly solvent-dependent, but the origin of this has not been definitively established. We have extended our computational approach to elucidate the correlation of VT transition temperature with solvent stabilisation energy and change in dipole moment. This new understanding may inform the development of VT compounds for applications in soft materials including films, gels, and polymers.
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ItemAb initio-based determination of lanthanoid-radical exchange as visualised by inelastic neutron scattering(ROYAL SOC CHEMISTRY, 2024-03-20)Magnetic exchange coupling can modulate the slow magnetic relaxation in single-molecule magnets. Despite this, elucidation of exchange coupling remains a significant challenge for the lanthanoid(iii) ions, both experimentally and computationally. In this work, the crystal field splitting and 4f-π exchange coupling in the erbium-semiquinonate complex [ErTp2dbsq] (Er-dbsq; Tp- = hydro-tris(1-pyrazolyl)borate, dbsqH2 = 3,5-di-tert-butyl-1,2-semiquinone) have been determined by inelastic neutron scattering (INS), magnetometry, and CASSCF-SO ab initio calculations. A related complex with a diamagnetic ligand, [ErTp2trop] (Er-trop; tropH = tropolone), has been used as a model for the crystal field splitting in the absence of coupling. Magnetic and INS data indicate antiferromagnetic exchange for Er-dbsq with a coupling constant of Jex = -0.23 meV (-1.8 cm-1) (-2Jex formalism) and good agreement is found between theory and experiment, with the low energy magnetic and spectroscopic properties well modelled. Most notable is the ability of the ab initio modelling to reproduce the signature of interference between localised 4f states and delocalised π-radical states that is evident in the Q-dependence of the exchange excitation. This work highlights the power of combining INS with EPR and magnetometry for determination of ground state properties, as well as the enhanced capability of CASSCF-SO ab initio calculations and purposely developed ab initio-based theoretical models. We deliver an unprecedentedly detailed representation of the entangled character of 4f-π exchange states, which is obtained via an accurate image of the spin-orbital transition density between the 4f-π exchange coupled wavefunctions.
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ItemJohn Atherton Young 1936–2004(CSIRO Publishing, 2024)John Atherton Young (1936–2004) graduated in medicine at the University of Queensland and undertook research in physiology at the Kanematsu Institute in Sydney for which he was awarded his PhD. After postdoctoral studies in Germany, he joined the department of physiology at the University of Sydney, rising to professor, then Dean of the Faculty of Medicine and finally Pro-Vice-Chancellor for Health Sciences. His research on the physiology of epithelial ducts, beginning with those of the kidney but later centring on salivary glands and the pancreas, brought him international recognition as a leader in the field. He made significant contributions to professional societies and was recognised with international and national awards including membership of the Order of Australia. A bronze portrait head of Young by sculptor Dan Lake is displayed in the foyer of the Edward Ford building at the University of Sydney. He was a man of great culture, a witty conversationalist and a great scientist.
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ItemNo Preview AvailableResolving conjugated polymer film morphology with polarised transmission and time-resolved emission microscopy(IOP Publishing, 2024-07-01)The alignment of chromophores plays a crucial role in determining the optoelectronic properties of materials. Such alignment can make interpretation of fluorescence anisotropy microscopy (FAM) images somewhat ambiguous. The time-resolved emission behaviour can also influence the fluorescence anisotropy. This is particularly the case when probing excitation energy migration between chromophores in a condensed phase. Ideally information concerning the chromophoric alignment, emission decay kinetics and fluorescence anisotropy can be recorded and correlated. We report on the use of polarised transmission imaging (PTI) coupled with both steady-state and time-resolved FAM to enable accurate identification of chromophoric alignment and morphology in thin films of a conjugated polydiarylfluorene. We show that the combination of these three imaging modes presents a comprehensive methodology for investigating the alignment and morphology of chromophores in thin films, particularly for accurately mapping the distribution of amorphous and crystalline phases within the thin films, offering valuable insights for the design and optimization of materials with enhanced optoelectronic performance.
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ItemPhotophysical Identification of Three Kinds of Low-Energy Green Band Defects in Wide-Bandgap Polyfluorenes(AMER CHEMICAL SOC, 2019-04-04)Blue-light-emitting semiconductors based on polyfluorenes often exhibit an undesired green emission band. In this report, three well-defined oligofluorenes corresponding to three types of "defects" attributed to aggregation, keto formation, and chain entanglement, respectively, are systemically investigated to unveil the origins of the green emission band in fluorene-based materials. First, the optical properties of defect molecules in different states are studied. The defect associated with aggregation is absent in dilute solutions and in films doped at 0.01 wt % with poly(methyl methacrylate). Second, the dependence of the emission spectra on the solvent was monitored to compare the effects of the "keto-" and "chain-entanglement defect" molecules. The green emission of keto defects exhibited a strong dependence on solvent polarity, whereas this cannot be observed in case of chain-entanglement defect. Third, energy transfer between poly[4-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]- co-[5-(octyloxy)-9,9-diphenyl-fluoren-2,7-diyl] and the keto or chain-entanglement defect molecules is illustrated. Compared to those of the chain-entanglement defect, the spectra of the keto defect molecule (1:10-3) show signs of defect emission at lower proportions. These investigations not only provide insight into the photophysics of oligofluorenes but also supply a new strategy to explore defects in semiconductor polymers, which will aid in the development of effective approaches to obtain stable, pure blue organic light-emitting diodes based on polyfluorenes.
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ItemChemical vapor deposition growth of phase-selective inorganic lead halide perovskite films for sensitive photodetectors(ELSEVIER SCIENCE INC, 2021-01)Inorganic lead halide perovskites are attractive optoelectronic materials owing to their relative stability compared to organic cation alternatives. The chemical vapor deposition (CVD) method offers potential for high quality perovskite film growth. The deposition temperature is a critical parameter determining the film quality owing to the melting difference between the precursors. Here, perovskite films were deposited by the CVD method at various temperatures between 500−800 °C. The perovskite phase converts from CsPb2Br5 to CsPbBr3 gradually as the deposition temperature is increased. The grain size of the perovskite films also increases with temperature. The phase transition mechanism was clarified. The photoexcited state dynamics were investigated by spatially and temporally resolved fluorescence measurements. The perovskite film deposited under 750 °C condition is of the CsPbBr3 phase, showing low trap-state density and large crystalline grain size. A photodetector based on perovskite films shows high photocurrent and an on/off ratio of ∼2.5 × 104.
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ItemTime-resolved emission microscopy of light-induced aggregation of luminescent polymers(IOP Publishing, 2019-12-23)Photon pressure has been used to induce the aggregation from solution of a series of photoluminescent conjugated polyelectrolytes containing tetraphenylethene units. These polymers show steady-state and time-resolved emission properties that are dependent on the local chromophore environment that can be influenced by the degree of intra- and inter-molecular interactions, which enables the photoaggregation process to be monitored by time-resolved fluorescence imaging techniques. Structural differences in the polymer lead to variations in the photo-induced aggregation behaviour.
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ItemLight losses from scattering in luminescent solar concentrator waveguides(OPTICAL SOC AMER, 2017-04-01)The reductions in the transmission of emission originating from a fluorophore dissolved in a polymer matrix due to light scattering were compared in two forms of planar waveguides used as luminescent solar concentrators: a thin film of poly(methylmethacrylate) (PMMA) spin-coated on a glass plate and a solid PMMA plate of the same dimensions. The losses attributable to light scattering encountered in the waveguide consisting of the thin film of polymer coated on a glass plate were not detectable within experimental uncertainty, whereas the losses in the solid polymer plate were significant. The losses in the solid plate are interpreted as arising from light-scattering centers comprising minute bubbles of vapor/gas, incomplete polymerization or water clusters that are introduced during or after the thermally induced polymerization process.
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ItemExcitonic Processes in a Conjugated Polyelectrolyte Complex(CSIRO Publishing, 2020)In aqueous solution, a di-sulfonated phenylenevinylene polymer (DPS-PPV) forms a complex with non-ionic poly(vinyl alcohol) (PVA) leading to absorption spectroscopic shifts and a dramatic (6-fold) increase in DPS-PPV fluorescence intensity. Spectroscopic investigations demonstrate that the complexation with PVA and other neutral polymers results in conformational changes in the DPS-PPV chains that lead to the removal of non-fluorescent energy traps and results in the observed increase in fluorescence in the bulk solution. Single molecule fluorescence measurements of DPS-PPV chains dispersed on glass and in PVA films confirm that efficient exciton energy transfer occurs within each photo-excited DPS-PPV chain and that the observed increase in fluorescence intensity in the PVA film environment is also associated with fewer quenching sites. The results highlight the importance of conjugated polyelectrolyte conformation on exciton relaxation pathways.