School of Chemistry - Research Publications
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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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ItemSpatially Resolved Photophysical Dynamics in Perovskite Microplates Fabricated Using an Antisolvent Treatment(American Chemical Society, 2017-11-30)Perovskite microplates have important implications in the fields of functional electronics and optoelectronics. We report a facile strategy, antisolvent treatment for the growth of perovskite microplates. The morphology and crystalline quality of the microplates could be controlled by the amount of the chlorobenzene antisolvent used. An appropriate amount of antisolvent facilitates the formation of high-quality perovskite microplates with no residual precursor remaining. Spatially and temporally resolved fluorescence measurements demonstrate the heterogeneity of defect-state density and recombination processes in various perovskite microplate regions. The body center shows higher defect state density when compared with that at the edge or the corner of the microplate. Excessive antisolvent degrades the microplates into smaller particles. The results of this study reveal the factors that influence the crystallization process and photophysical dynamics of perovskite microplates.
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ItemPoly(3-hexylthiophene) coated graphene oxide for improved performance of bulk heterojunction polymer solar cells(Elsevier, 2017-05-01)An effective method for preparing poly(3-hexylthiophene) (P3HT) coated graphene oxide (GO), (P-GO), based on an ethanol mediated mixing and solvent evaporation method is described. P-GO exhibits good dispersibility in the non-polar solvent o-dichlorobenzene (DCB) allowing the preparation of polymer blend composites. P-GO was doped into P3HT: PCBM blends by solution mixing and shown to facilitate phase separation of P3HT and PCBM in P3HT: PCBM blend films to achieve a more optimum morphology for polymer photovoltaic cells. Bulk heterojunction P3HT: PCBM solar cells exhibit ∼18% power conversion efficiency enhancement in the presence of P-GO.
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ItemContinuous Flow Synthesis of Conjugated Polymers and Carbon Materials(WILEY-V C H VERLAG GMBH, 2017)The basic equipment associated with the synthesis of chemicals in the laboratory has remained essentially unchanged since the establishment of chemistry as a scientific discipline. Most techniques and apparatus are optimized for batch-by-batch processes. These traditional batch techniques have the benefit of familiar and time-tested methodology and low up-front cost, and therefore the shift to more modern apparatus requires some additional motivating factors. Continuous flow processing is a technique which involves a nontrivial initial investment of both time and finances, but which offers significant benefits to synthetic chemists. Continuous flow processing has been increasing in prominence in the research laboratory setting in the last decade, and a number of research groups now specialize in the development of methods for flow processing. This progress is buoyed by the commercial availability of the associated equipment, which can now be purchased from several vendors.
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ItemIntegrated activities of two alternative sigma factors coordinate iron acquisition and uptake by Pseudomonas aeruginosa(WILEY, 2017-12)Alternative sigma (σ) factors govern expression of bacterial genes in response to diverse environmental signals. In Pseudomonas aeruginosa σPvdS directs expression of genes for production of a siderophore, pyoverdine, as well as a toxin and a protease. σFpvI directs expression of a receptor for ferripyoverdine import. Expression of the genes encoding σPvdS and σFpvI is iron-regulated and an antisigma protein, FpvR20 , post-translationally controls the activities of the sigma factors in response to the amount of ferripyoverdine present. Here we show that iron represses synthesis of σPvdS to a far greater extent than σFpvI . In contrast ferripyoverdine exerts similar effects on the activities of both sigma factors. Using a combination of in vivo and in vitro assays we show that σFpvI and σPvdS have comparable affinities for, and are equally inhibited by, FpvR20 . Importantly, in the absence of ferripyoverdine the amount of FpvR20 per cell is lower than the amount of σFpvI and σPvdS , allowing basal expression of target genes that is required to activate the signalling pathway when ferripyoverdine is present. This complex interplay of transcriptional and post-translational regulation enables a co-ordinated response to ferripyoverdine but distinct responses to iron.
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ItemHigh Reversible Pseudocapacity in Mesoporous Yolk-Shell Anatase TiO2/TiO2(B) Microspheres Used as Anodes for Li-Ion Batteries(WILEY-V C H VERLAG GMBH, 2017-12-08)Abstract As an anode material for lithium‐ion batteries, titanium dioxide (TiO2) shows good gravimetric performance (336 mAh g−1 for LiTiO2) and excellent cyclability. To address the poor rate behavior, slow lithium‐ion (Li+) diffusion, and high irreversible capacity decay, TiO2 nanomaterials with tuned phase compositions and morphologies are being investigated. Here, a promising material is prepared that comprises a mesoporous “yolk–shell” spherical morphology in which the core is anatase TiO2 and the shell is TiO2(B). The preparation employs a NaCl‐assisted solvothermal process and the electrochemical results indicate that the mesoporous yolk–shell microspheres have high specific reversible capacity at moderate current (330.0 mAh g−1 at C/5), excellent rate performance (181.8 mAh g−1 at 40C), and impressive cyclability (98% capacity retention after 500 cycles). The superior properties are attributed to the TiO2(B) nanosheet shell, which provides additional active area to stabilize the pseudocapacity. In addition, the open mesoporous morphology improves diffusion of electrolyte throughout the electrode, thereby contributing directly to greatly improved rate capacity.
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ItemAuxiliary-Directed C(sp3)-H Arylation by Synergistic Photoredox and Palladium Catalysis(WILEY-V C H VERLAG GMBH, 2017-10-17)Herein we describe the auxiliary-directed arylation of unactivated C(sp3 )-H bonds with aryldiazonium salts, which proceeds under synergistic photoredox and palladium catalysis. The site-selective arylation of aliphatic amides with α-quaternary centres is achieved with high selectivity for β-methyl C(sp3 )-H bonds. This operationally simple method is compatible with carbocyclic amides, a range of aryldiazonium salts and proceeds at ambient conditions.
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ItemTriggered and Tunable Hydrogen Sulfide Release from Photogenerated Thiobenzaldehydes(WILEY-V C H VERLAG GMBH, 2017-08-22)Hydrogen sulfide (H2 S) has been identified as an important cell-signaling mediator and has a number of biological functions, such as vascular smooth muscle relaxation, neurotransmission, and regulation of inflammation. A facile and versatile approach for H2 S production initiated by light irradiation and controlled by reaction with an amine or an amino acid was developed. The donor was synthesized in a one-pot reaction, and simple crystallization led to a yield of approximately 90 %. The synthetic strategy is scalable and versatile, and the H2 S donors can be expressed ina number of different molecular and macromolecular forms, including crystalline small-molecule compounds, water-soluble polymers, polystyrene films, and hydrogels. The H2 S donors based on polystyrene film and hydrogel were used as cell-culture scaffolds. The H2 S donor based on water-soluble polymer was applied in photocontrolled inhibition of P-selectin expression on human platelets and subsequent regulation of platelet aggregation. This study provides the simplest controllable H2 S source to study its biological functions. The developed materials are also new therapeutic platforms to deliver H2 S, as there is no accumulation of toxic byproducts, and the donor materials from polystyrene films and hydrogels can be readily removed after releasing H2 S.
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ItemSolid-State Gas Adsorption Studies with Discrete Palladium(II) [Pd-2(L)(4)](4+) Cages(Wiley, 2017-08-04)The need for effective CO2 capture systems remains high, and due to their tunability, metallosupramolecular architectures are an attractive option for gas sorption. While the use of extended metal organic frameworks for gas adsorption has been extensively explored, the exploitation of discrete metallocage architectures to bind gases remains in its infancy. Herein the solid state gas adsorption properties of a series of [Pd2(L)4]4+ lantern shaped coordination cages (L = variants of 2,6‐bis(pyridin‐3‐ylethynyl)pyridine), which had solvent accessible internal cavities suitable for gas binding, have been investigated. The cages showed little interaction with dinitrogen gas but were able to take up CO2. The best performing cage reversibly sorbed 1.4 mol CO2 per mol cage at 298 K, and 2.3 mol CO2 per mol cage at 258 K (1 bar). The enthalpy of binding was calculated to be 25–35 kJ mol−1, across the number of equivalents bound, while DFT calculations on the CO2 binding in the cage gave ΔE for the cage–CO2 interaction of 23–28 kJ mol−1, across the same range. DFT modelling suggested that the binding mode is a hydrogen bond between the carbonyl oxygen of CO2 and the internally directed hydrogen atoms of the cage.