29 results on '"Dowland S"'
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2. Seahorse brood pouch morphology and control of male parturition in Hippocampus abdominalis
- Author
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Dudley, J.S., Paul, J.W., Teh, V., Mackenzie, T.E., Butler, T.A., Tolosa, J.M., Smith, R., Foley, M., Dowland, S., Thompson, M.B., and Whittington, C.M.
- Published
- 2022
- Full Text
- View/download PDF
3. Ontology of language, with applications to demographic data
- Author
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Dowland, S. Clint, primary, Smith, Barry, additional, Diller, Matthew A., additional, Landgrebe, Jobst, additional, and Hogan, William R., additional
- Published
- 2023
- Full Text
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4. Embodied mind sparsism
- Author
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Dowland, S. Clint
- Published
- 2016
5. Linking microscale morphologies to localised performance in singlet fission quantum dot photon multiplier thin films
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Toolan, D.T.W., Weir, M.P., Dowland, S., Winkel, J.F., Willmott, J.R., Zhang, Z., Gray, V., Xiao, J., Petty, A.J., Anthony, J.E., Greenham, N.C., Friend, R.H., Rao, A., Jones, R.A.L., and Ryan, A.J.
- Abstract
Hybrid small-molecule/quantum dot films have the potential to reduce thermalization losses in single-junction photovoltaics as photon multiplication devices. Here grazing incidence X-ray scattering, optical microscopy and IR fluorescence microscopy (probing materials at two distinct wavelengths), provide new insight into highly complex morphologies across nm and μm lengthscales to provide direct links between morphologies and photon multiplication performance. Results show that within the small molecule crystallites three different QD morphologies may be identified; (i) large quantum dot aggregates at the crystallite nucleus, (ii) relatively well-dispersed quantum dots and (iii) as aggregated quantum dots “swept” from the growing crystallite and that regions containing aggregate quantum dot features lead to relatively poor photon multiplication performance. These results establish how combinations of scattering and microscopy may be employed to reveal new insights into the structure and function of small molecule:quantum dot blends.
- Published
- 2022
6. Zinc as a non-hormonal contraceptive: an alternative to the copper intrauterine device (IUD).
- Author
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Shankie-Williams, K. N., Lindsay, L. A., Murphy, C. R., and Dowland, S. N.
- Subjects
COPPER intrauterine contraceptives ,LONG-acting reversible contraceptives ,ZINC ,INTRAUTERINE contraceptives ,ENDOMETRITIS - Abstract
Long-acting and reversible contraceptives (LARC) are the most widely used form of female contraception worldwide; however, they have significant side effects that often result in early removal. Most LARCs are hormonal, but the use of exogenous hormones is not suitable for all women and causes side effects in many others. The copper IUD (CuIUD) is the only non-hormonal LARC, but a large proportion of users suffer severe side effects. This study proposes the use of zinc as a suitable alternative to the CuIUD. A rat intrauterine device (IUD) model was established to test the efficacy of a zinc IUD (ZnIUD) against a CuIUD. The IUD was surgically implanted into one uterine horn while the other remained untreated. Both the ZnIUD and CuIUD resulted in zero implantation sites which were significantly fewer compared to non-treated horns. Histological assessment revealed damage and inflammation in the endometrium of CuIUD-treated horns but only minor epithelial changes in ZnIUD-treated horns. This suggests ZnIUDs may not share the side effect profile of the CuIUD. To test the long-term efficacy of the ZnIUD, rats had a ZnIUD surgically implanted into both horns and cohoused with males for 3 months. These rats mated regularly but did not get pregnant, confirming long-term effectiveness. Reversibility of the ZnIUD was also established, as removal of the ZnIUD after 3 months resulted in no significant difference in the number of implantation sites between treated and untreated horns. This study demonstrated the contraceptive efficacy of zinc and its potential as a LARC. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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7. Embodied mind sparsism.
- Author
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Clint Dowland, S.
- Subjects
- *
SUBSTANCE (Philosophy) , *ONTOLOGY , *SELF -- Social aspects , *NECESSITY (Philosophy) , *PHILOSOPHICAL anthropology , *PERSONALITY (Theory of knowledge) ,SOCIAL aspects - Abstract
If we are physical things with parts, then accounts of what we are and accounts of when composition occurs have important implications for one another. Defenders of restricted composition tend to endorse a sparse ontology in taking an eliminativist stance toward composite objects that are not organisms, while claiming that we are organisms. However, these arguments do not entail that we are organisms, for they rely on the premise that we are organisms. Thus, sparsist reasoning need not be paired with animalism, but could instead be paired with other accounts according to which we are composites. The embodied mind account-a version of the brain view-is one such account. Replacing the premise that we are organisms with the premise that we are embodied minds, in arguments that otherwise parallel those supporting animalist sparsism, yields an account according to which composite objects include thinkers, but perhaps nothing else. Since animalism has implausible implications about scenarios which are handled better by the embodied mind account, this approach is preferable to animalist sparsism. Furthermore, the role of mental features in sparsism makes embodied mind sparsism the more reasonable conclusion. Meanwhile, adopting sparsism allows the embodied mind account to dodge objections that may not be as easily avoided by it or other versions of the brain view if not paired with sparsism. These include objections about brains that are not persons, inorganic part replacement, and another form of part replacement that might seem to allow one to get a new brain. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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8. 312. THE DISTRIBUTION OF PROMININ-1 IN THE RAT UTERUS DURING EARLY PREGNANCY
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Dowland, S. N., primary, Lindsay, L. A., additional, and Murphy, C. R., additional
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- 2010
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9. Religion and the American Presidency: George Washington to George W. Bush, with Commentary and Primary Sources
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Dowland, S., primary
- Published
- 2009
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10. Ligand-Directed Self-Assembly of Organic-Semiconductor/Quantum-Dot Blend Films Enables Efficient Triplet Exciton-Photon Conversion.
- Author
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Gray V, Toolan DTW, Dowland S, Allardice JR, Weir MP, Zhang Z, Xiao J, Klimash A, Winkel JF, Holland EK, Fregoso GM, Anthony JE, Bronstein H, Friend R, Ryan AJ, Jones RAL, Greenham NC, and Rao A
- Abstract
Blends comprising organic semiconductors and inorganic quantum dots (QDs) are relevant for many optoelectronic applications and devices. However, the individual components in organic-QD blends have a strong tendency to aggregate and phase-separate during film processing, compromising both their structural and electronic properties. Here, we demonstrate a QD surface engineering approach using electronically active, highly soluble semiconductor ligands that are matched to the organic semiconductor host material to achieve well-dispersed inorganic-organic blend films, as characterized by X-ray and neutron scattering, and electron microscopies. This approach preserves the electronic properties of the organic and QD phases and also creates an optimized interface between them. We exemplify this in two emerging applications, singlet-fission-based photon multiplication (SF-PM) and triplet-triplet annihilation-based photon upconversion (TTA-UC). Steady-state and time-resolved optical spectroscopy shows that triplet excitons can be transferred with near unity efficiently across the organic-inorganic interface, while the organic films maintain efficient SF (190% yield) in the organic phase. By changing the relative energy between organic and inorganic components, yellow upconverted emission is observed upon 790 nm NIR excitation. Overall, we provide a highly versatile approach to overcome longstanding challenges in the blending of organic semiconductors with QDs that have relevance for many optical and optoelectronic applications.
- Published
- 2024
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11. Quantitative Singlet Fission in Solution-Processable Dithienohexatrienes.
- Author
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Fallon KJ, Sawhney N, Toolan DTW, Sharma A, Zeng W, Montanaro S, Leventis A, Dowland S, Millington O, Congrave D, Bond A, Friend R, Rao A, and Bronstein H
- Abstract
Singlet fission (SF) is a promising strategy to overcome thermalization losses and enhance the efficiency of single junction photovoltaics (PVs). The development of this field has been strongly material-limited, with a paucity of materials able to undergo SF. Rarer still are examples that can produce excitons of sufficient energy to be coupled to silicon PVs (>1.1 eV). Herein, we examine a series of a short-chain polyene, dithienohexatriene (DTH), with tailored material properties and triplet (T
1 ) energy levels greater than 1.1 eV. We find that these highly soluble materials can be easily spin-cast to create thin films of high crystallinity that exhibit ultrafast singlet fission with near perfect triplet yields of up to 192%. We believe that these materials are the first solution-processable singlet fission materials with quantitative triplet formation and energy levels appropriate for use in conjunction with silicon PVs.- Published
- 2022
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12. Porosomes in uterine epithelial cells: Ultrastructural identification and characterization during early pregnancy.
- Author
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Kalam SN, Dowland S, Lindsay L, and Murphy CR
- Subjects
- Pregnancy, Female, Animals, Rats, Cell Membrane metabolism, Cholesterol metabolism, SNARE Proteins metabolism, Exocytosis, Epithelial Cells
- Abstract
Porosomes are plasma membrane structures in secretory cells that allow transient docking and/or partial fusion of vesicles during which they release their content then disengage. This is referred to as "kiss and run" exocytosis. During early pregnancy, at the time of receptivity, there is a high level of vesicle activity in uterine epithelial cells (UECs). One of the secretory pathways for these vesicles could be via porosomes, which have yet to be identified in UECs. This study identified porosomes in the apical plasma membrane of UECs for the first time. These structures were present on days 1, 5.5, and 6 of early pregnancy, where they likely facilitate partial secretion via "kiss and run" exocytosis. The porosomes were measured and quantified on days 1, 5.5, and 6, which showed there are significantly more porosomes on day 5.5 (receptive) compared to day 1 (nonreceptive) of pregnancy. This increase in porosome numbers may reflect major morphological and molecular changes in the apical plasma membrane at this time such as increased cholesterol and soluble NSF attachment protein receptor proteins, as these are structural and functional components of the porosome complex assembly. Porosomes were observed in both resting (inactive) and dilated (active) states on days 1, 5.5, and 6 of early pregnancy. Porosomes on day 5.5 are significantly more active than on day 1 as demonstrated by the dilation of their base diameter. Further two-way ANOVA analysis of base diameter in resting and dilated states found a significant increase in porosome activity in day 5.5 compared to day 1. This study therefore indicates an increase in the number and activity of porosomes at the time of uterine receptivity in the rat, revealing a mechanism by which the UECs modify the uterine luminal environment at this time., (© 2022 The Authors. Journal of Morphology published by Wiley Periodicals LLC.)
- Published
- 2022
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13. Triplet transfer from PbS quantum dots to tetracene ligands: is faster always better?
- Author
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Gray V, Drake W, Allardice JR, Zhang Z, Xiao J, Congrave DG, Royakkers J, Zeng W, Dowland S, Greenham NC, Bronstein H, Anthony JE, and Rao A
- Abstract
Quantum dot-organic semiconductor hybrid materials are gaining increasing attention as spin mixers for applications ranging from solar harvesting to spin memories. Triplet energy transfer between the inorganic quantum dot (QD) and organic semiconductor is a key step to understand in order to develop these applications. Here we report on the triplet energy transfer from PbS QDs to four energetically and structurally similar tetracene ligands. Even with similar ligands we find that the triplet energy transfer dynamics can vary significantly. For TIPS-tetracene derivatives with carboxylic acid, acetic acid and methanethiol anchoring groups on the short pro- cata side we find that triplet transfer occurs through a stepwise process, mediated via a surface state, whereas for monosubstituted TIPS-tetracene derivative 5-(4-benzoic acid)-12-triisopropylsilylethynyl tetracene (BAT) triplet transfer occurs directly, albeit slower, via a Dexter exchange mechanism. Even though triplet transfer is slower with BAT the overall yield is greater, as determined from upconverted emission using rubrene emitters. This work highlights that the surface-mediated transfer mechanism is plagued with parasitic loss pathways and that materials with direct Dexter-like triplet transfer are preferred for high-efficiency applications., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)
- Published
- 2022
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14. Ultrafast exciton transport at early times in quantum dot solids.
- Author
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Zhang Z, Sung J, Toolan DTW, Han S, Pandya R, Weir MP, Xiao J, Dowland S, Liu M, Ryan AJ, Jones RAL, Huang S, and Rao A
- Subjects
- Quantum Dots, Selenium Compounds
- Abstract
Quantum dot (QD) solids are an emerging platform for developing a range of optoelectronic devices. Thus, understanding exciton dynamics is essential towards developing and optimizing QD devices. Here, using transient absorption microscopy, we reveal the initial exciton dynamics in QDs with femtosecond timescales. We observe high exciton diffusivity (~10
2 cm2 s-1 ) in lead chalcogenide QDs within the first few hundred femtoseconds after photoexcitation followed by a transition to a slower regime (~10-1 -1 cm2 s-1 ). QD solids with larger interdot distances exhibit higher initial diffusivity and a delayed transition to the slower regime, while higher QD packing density and heterogeneity accelerate this transition. The fast transport regime occurs only in materials with exciton Bohr radii much larger than the QD sizes, suggesting the transport of delocalized excitons in this regime and a transition to slower transport governed by exciton localization. These findings suggest routes to control the optoelectronic properties of QD solids., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)- Published
- 2022
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15. Deoxyribonucleic Acid Encoded and Size-Defined π-Stacking of Perylene Diimides.
- Author
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Gorman J, Orsborne SRE, Sridhar A, Pandya R, Budden P, Ohmann A, Panjwani NA, Liu Y, Greenfield JL, Dowland S, Gray V, Ryan STJ, De Ornellas S, El-Sagheer AH, Brown T, Nitschke JR, Behrends J, Keyser UF, Rao A, Collepardo-Guevara R, Stulz E, Friend RH, and Auras F
- Subjects
- Semiconductors, Perylene chemistry, Perylene analogs & derivatives, DNA chemistry, Imides chemistry
- Abstract
Natural photosystems use protein scaffolds to control intermolecular interactions that enable exciton flow, charge generation, and long-range charge separation. In contrast, there is limited structural control in current organic electronic devices such as OLEDs and solar cells. We report here the DNA-encoded assembly of π-conjugated perylene diimides (PDIs) with deterministic control over the number of electronically coupled molecules. The PDIs are integrated within DNA chains using phosphoramidite coupling chemistry, allowing selection of the DNA sequence to either side, and specification of intermolecular DNA hybridization. In this way, we have developed a "toolbox" for construction of any stacking sequence of these semiconducting molecules. We have discovered that we need to use a full hierarchy of interactions: DNA guides the semiconductors into specified close proximity, hydrophobic-hydrophilic differentiation drives aggregation of the semiconductor moieties, and local geometry and electrostatic interactions define intermolecular positioning. As a result, the PDIs pack to give substantial intermolecular π wave function overlap, leading to an evolution of singlet excited states from localized excitons in the PDI monomer to excimers with wave functions delocalized over all five PDIs in the pentamer. This is accompanied by a change in the dominant triplet forming mechanism from localized spin-orbit charge transfer mediated intersystem crossing for the monomer toward a delocalized excimer process for the pentamer. Our modular DNA-based assembly reveals real opportunities for the rapid development of bespoke semiconductor architectures with molecule-by-molecule precision.
- Published
- 2022
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16. Structural changes to the brood pouch of male pregnant seahorses (Hippocampus abdominalis) facilitate exchange between father and embryos.
- Author
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Dudley JS, Hannaford P, Dowland SN, Lindsay LA, Thompson MB, Murphy CR, Van Dyke JU, and Whittington CM
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- Animals, Male, Smegmamorpha embryology, Oviparity physiology, Smegmamorpha anatomy & histology
- Abstract
Introduction: Embryonic growth and development require efficient respiratory gas exchange. Internal incubation of developing young thus presents a significant physiological challenge, because respiratory gas diffusion to embryos is impeded by the additional barrier of parental tissue between the embryo and the environment. Therefore, live-bearing species exhibit a variety of adaptations facilitating respiratory gas exchange between the parent (usually the mother) and embryos. Syngnathid fishes are the only vertebrates to exhibit male pregnancy, allowing comparative studies of the biology and evolution of internal incubation of embryos, independent of the female reproductive tract. Here, we examine the fleshy, sealed, seahorse brood pouch, and provide the first quantification of structural changes to this gestational organ across pregnancy., Methods: We used histological analysis and morphometrics to quantify the surface area for exchange across the brood pouch epithelium, and the structure of the vascular bed of the brood pouch., Results: We show dramatic remodelling of gestational tissues as pregnancy progresses, including an increase in tortuosity of the gestational epithelium, an increase in capillary density, and a decrease in diffusion distance between capillaries and the pouch lumen., Discussion: These changes produce an increased surface area and expansion of the vascular bed of the placenta that likely facilitates respiratory gas exchange. These changes mirror the remodelling of gestational tissue in viviparous amniotes and elasmobranchs, and provide further evidence of the convergence of adaptations to support pregnancy in live-bearing animals., (Copyright © 2021 Elsevier Ltd. All rights reserved.)
- Published
- 2021
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17. Singlet exciton fission in a modified acene with improved stability and high photoluminescence yield.
- Author
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Budden PJ, Weiss LR, Müller M, Panjwani NA, Dowland S, Allardice JR, Ganschow M, Freudenberg J, Behrends J, Bunz UHF, and Friend RH
- Abstract
We report a fully efficient singlet exciton fission material with high ambient chemical stability. 10,21-Bis(triisopropylsilylethynyl)tetrabenzo[a,c,l,n]pentacene (TTBP) combines an acene core with triphenylene wings that protect the formal pentacene from chemical degradation. The electronic energy levels position singlet exciton fission to be endothermic, similar to tetracene despite the triphenylenes. TTBP exhibits rapid early time singlet fission with quantitative yield of triplet pairs within 100 ps followed by thermally activated separation to free triplet excitons over 65 ns. TTBP exhibits high photoluminescence quantum efficiency, close to 100% when dilute and 20% for solid films, arising from triplet-triplet annihilation. In using such a system for exciton multiplication in a solar cell, maximum thermodynamic performance requires radiative decay of the triplet population, observed here as emission from the singlet formed by recombination of triplet pairs. Combining chemical stabilisation with efficient endothermic fission provides a promising avenue towards singlet fission materials for use in photovoltaics.
- Published
- 2021
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18. Thiol-Anchored TIPS-Tetracene Ligands with Quantitative Triplet Energy Transfer to PbS Quantum Dots and Improved Thermal Stability.
- Author
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Gray V, Zhang Z, Dowland S, Allardice JR, Alvertis AM, Xiao J, Greenham NC, Anthony JE, and Rao A
- Abstract
Triplet energy transfer between inorganic quantum dots (QDs) and organic materials plays a fundamental role in many optoelectronic applications based on these nanocomposites. Attaching organic molecules to the QD as transmitter ligands has been shown to facilitate transfer both to and from QDs. Here we show that the often disregarded thiol anchoring group can achieve quantitative triplet energy transfer yields in a PbS QD system with 6,11-bis[(triisopropylsilyl)ethynyl]tetracene-2-methylthiol (TET-SH) ligands. We demonstrate efficient triplet transfer in a singlet fission-based photon multiplication system with 5,12-bis[(triisopropylsilyl)ethynyl]tetracene generating triplets in solution that transfer to the PbS QDs via the thiol ligand TET-SH. Importantly, we demonstrate the increased thermal stability of the PbS/TET-SH system, compared to the traditional carboxylic acid counterpart, allowing for higher photoluminescence quantum yields.
- Published
- 2020
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19. Correction to Direct vs Delayed Triplet Energy Transfer from Organic Semiconductors to Quantum Dots and Implications for Luminescent Harvesting of Triplet Excitons.
- Author
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Gray V, Allardice JR, Zhang Z, Dowland S, Xiao J, Petty A 2nd, Anthony JE, Greenham NC, and Rao A
- Published
- 2020
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20. Direct vs Delayed Triplet Energy Transfer from Organic Semiconductors to Quantum Dots and Implications for Luminescent Harvesting of Triplet Excitons.
- Author
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Gray V, Allardice JR, Zhang Z, Dowland S, Xiao J, Petty AJ 2nd, Anthony JE, Greenham NC, and Rao A
- Abstract
Hybrid inorganic-organic materials such as quantum dots (QDs) coupled with organic semiconductors have a wide range of optoelectronic applications, taking advantage of the respective materials' strengths. A key area of investigation in such systems is the transfer of triplet exciton states to and from QDs, which has potential applications in the luminescent harvesting of triplet excitons generated by singlet fission, in photocatalysis and photochemical upconversion. While the transfer of energy from QDs to the triplet state of organic semiconductors has been intensely studied in recent years, the mechanism and materials parameters controlling the reverse process, triplet transfer to QDs, have not been well investigated. Here, through a combination of steady-state and time-resolved optical spectroscopy we study the mechanism and energetic dependence of triplet energy transfer from an organic ligand (TIPS-tetracene carboxylic acid) to PbS QDs. Over an energetic range spanning from exothermic (-0.3 eV) to endothermic (+0.1 eV) triplet energy transfer we find that the triplet energy transfer to the QD occurs through a single step process with a clear energy dependence that is consistent with an electron exchange mechanism as described by Marcus-Hush theory. In contrast, the reverse process, energy transfer from the QD to the triplet state of the ligand, does not show any energy dependence in the studied energy range; interestingly, a delayed formation of the triplet state occurs relative to the quantum dots' decay. Based on the energetic dependence of triplet energy transfer we also suggest design criteria for future materials systems where triplet excitons from organic semiconductors are harvested via QDs, for instance in light emitting structures or the harvesting of triplet excitons generated via singlet fission.
- Published
- 2020
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21. Correction to "Engineering Molecular Ligand Shells on Quantum Dots for Quantitative Harvesting of Triplet Excitons Generated by Singlet Fission".
- Author
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Allardice JR, Thampi A, Dowland S, Xiao J, Gray V, Zhang Z, Budden P, Petty AJ 2nd, Davis NJLK, Greenham NC, Anthony JE, and Rao A
- Published
- 2019
- Full Text
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22. Exploiting Excited-State Aromaticity To Design Highly Stable Singlet Fission Materials.
- Author
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Fallon KJ, Budden P, Salvadori E, Ganose AM, Savory CN, Eyre L, Dowland S, Ai Q, Goodlett S, Risko C, Scanlon DO, Kay CWM, Rao A, Friend RH, Musser AJ, and Bronstein H
- Abstract
Singlet fission, the process of forming two triplet excitons from one singlet exciton, is a characteristic reserved for only a handful of organic molecules due to the atypical energetic requirement for low energy excited triplet states. The predominant strategy for achieving such a trait is by increasing ground state diradical character; however, this greatly reduces ambient stability. Herein, we exploit Baird's rule of excited state aromaticity to manipulate the singlet-triplet energy gap and create novel singlet fission candidates. We achieve this through the inclusion of a [4n] 5-membered heterocycle, whose electronic resonance promotes aromaticity in the triplet state, stabilizing its energy relative to the singlet excited state. Using this theory, we design a family of derivatives of indolonaphthyridine thiophene (INDT) with highly tunable excited state energies. Not only do we access novel singlet fission materials, they also exhibit excellent ambient stability, imparted due to the delocalized nature of the triplet excited state. Spin-coated films retained up to 85% activity after several weeks of exposure to oxygen and light, while analogous films of TIPS-pentacene showed full degradation after 4 days, showcasing the excellent stability of this class of singlet fission scaffold. Extension of our theoretical analysis to almost ten thousand candidates reveals an unprecedented degree of tunability and several thousand potential fission-capable candidates, while clearly demonstrating the relationship between triplet aromaticity and singlet-triplet energy gap, confirming this novel strategy for manipulating the exchange energy in organic materials.
- Published
- 2019
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23. Ligand Shell Structure in Lead Sulfide-Oleic Acid Colloidal Quantum Dots Revealed by Small-Angle Scattering.
- Author
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Weir MP, Toolan DTW, Kilbride RC, Penfold NJW, Washington AL, King SM, Xiao J, Zhang Z, Gray V, Dowland S, Winkel J, Greenham NC, Friend RH, Rao A, Ryan AJ, and Jones RAL
- Abstract
Nanocrystal quantum dots are generally coated with an organic ligand layer. These layers are a necessary consequence of their chemical synthesis, and in addition they play a key role in controlling the optical and electronic properties of the system. Here we describe a method for quantitative measurement of the ligand layer in 3 nm diameter lead sulfide-oleic acid quantum dots. Complementary small-angle X-ray and neutron scattering (SAXS and SANS) studies give a complete and quantitative picture of the nanoparticle structure. We find greater-than-monolayer coverage of oleic acid and a significant proportion of ligand remaining in solution, and we demonstrate reversible thermal cycling of the oleic acid coverage. We outline the effectiveness of simple purification procedures with applications in preparing dots for efficient ligand exchange. Our method is transferrable to a wide range of colloidal nanocrystals and ligand chemistries, providing the quantitative means to enable the rational design of ligand-exchange procedures.
- Published
- 2019
- Full Text
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24. Engineering Molecular Ligand Shells on Quantum Dots for Quantitative Harvesting of Triplet Excitons Generated by Singlet Fission.
- Author
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Allardice JR, Thampi A, Dowland S, Xiao J, Gray V, Zhang Z, Budden P, Petty AJ 2nd, Davis NJLK, Greenham NC, Anthony JE, and Rao A
- Abstract
Singlet fission is an exciton multiplication process in organic molecules in which a photogenerated spin-singlet exciton is rapidly and efficiently converted to two spin-triplet excitons. This process offers a mechanism to break the Shockley-Queisser limit by overcoming the thermalization losses inherent to all single-junction photovoltaics. One of the most promising methods to harness the singlet fission process is via the efficient extraction of the dark triplet excitons into quantum dots (QDs) where they can recombine radiatively, thereby converting high-energy photons to pairs of low-energy photons, which can then be captured in traditional inorganic PVs such as Si. Such a singlet fission photon multiplication (SF-PM) process could increase the efficiency of the best Si cells from 26.7% to 32.5%, breaking the Shockley-Queisser limit. However, there has been no demonstration of such a singlet fission photon multiplication (SF-PM) process in a bulk system to date. Here, we demonstrate a solution-based bulk SF-PM system based on the singlet fission material TIPS-Tc combined with PbS QDs. Using a range of steady-state and time-resolved measurements combined with analytical modeling we study the dynamics and mechanism of the triplet harvesting process. We show that the system absorbs >95% of incident photons within the singlet fission material to form singlet excitons, which then undergo efficient singlet fission in the solution phase (135 ± 5%) before quantitative harvesting of the triplet excitons (95 ± 5%) via a low concentration of QD acceptors, followed by the emission of IR photons. We find that in order to achieve efficient triplet harvesting it is critical to engineer the surface of the QD with a triplet transfer ligand and that bimolecular decay of triplets is potentially a major loss pathway which can be controlled via tuning the concentration of QD acceptors. We demonstrate that the photon multiplication efficiency is maintained up to solar fluence. Our results establish the solution-based SF-PM system as a simple and highly tunable platform to understand the dynamics of a triplet energy transfer process between organic semiconductors and QDs, one that can provide clear design rules for new materials.
- Published
- 2019
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25. Microtubules are reorganised and fragmented for uterine receptivity.
- Author
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Kalam SN, Dowland S, Lindsay L, and Murphy CR
- Subjects
- Animals, Cell Separation, Epithelial Cells metabolism, Female, Microtubules ultrastructure, Pregnancy, Rats, Wistar, Tubulin metabolism, Uterus cytology, Microtubules metabolism, Uterus metabolism
- Abstract
For the development of uterine receptivity, many morphological and molecular changes occur in the apical surface of luminal uterine epithelial cells (UECs) including an increase in vesicular activity. Vesicular movements for exocytosis and endocytosis are dependent on microtubules; however, changes in microtubules in UECs during early pregnancy have received little attention. β-tubulin, one of the main component of microtubules, is distributed throughout the cytoplasm of UECs on day 1 (non-receptive) of pregnancy in the rat. On day 5.5, β-tubulin is concentrated above the nuclei and by day 6 (receptive), β-tubulin is concentrated in a band-like fashion above the nucleus. Western blot analysis of isolated UECs found two bands (50 and 34 kDa) for β-tubulin in UECs during early pregnancy. The intensity of the 34 kDa band was significantly higher on day 6 compared to day 1. The increase in the 34 kDa band may be due to higher proteolytic activity associated with microtubule polymerisation during the receptive state. Transmission electron microscopy showed fragmented microtubules at the time of receptivity in UECs. This is the first study to show that microtubules are reorganised during uterine receptivity. This re-organisation likely facilitates vesicular movement and promotes the reorganisation of the apical plasma membrane for uterine receptivity.
- Published
- 2018
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26. Sterically controlled azomethine ylide cycloaddition polymerization of phenyl-C61-butyric acid methyl ester.
- Author
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Stephen M, Ramanitra HH, Santos Silva H, Dowland S, Bégué D, Genevičius K, Arlauskas K, Juška G, Morse GE, Distler A, and Hiorns RC
- Abstract
Phenyl-C61-butyric acid methyl ester (PCBM) is polymerized simply using a one-pot reaction to yield soluble, high molecular weight polymers. The sterically controlled azomethine ylide cycloaddition polymerization (SACAP) is demonstrated to be highly adaptable and yields polymers with probable Mn≈ 24 600 g mol(-1) and Mw≈ 73 800 g mol(-1). Products are metal-free and of possible benefit to organic and hybrid photovoltaics and electronics as they form thin films from solution and have raised LUMOs. The promising electronic properties of this new polymer are discussed.
- Published
- 2016
- Full Text
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27. Caveolins redistribute in uterine epithelial cells during early pregnancy in the rat: an epithelial polarisation strategy?
- Author
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Madawala RJ, Dowland S, Poon CE, Lindsay LA, and Murphy CR
- Subjects
- Animals, Cell Membrane metabolism, Female, Microscopy, Fluorescence, Pregnancy, Protein Transport, Rats, Rats, Wistar, Uterus metabolism, Caveolin 1 metabolism, Caveolin 2 metabolism, Cell Polarity, Epithelial Cells metabolism, Uterus cytology
- Abstract
At the time of implantation, uterine luminal epithelial cells undergo a dramatic change in all plasma membrane domains. Changes in the basolateral plasma membrane at the time of implantation include progression from smooth to highly tortuous, as well as a loss of integrin-based focal adhesions. Another aspect of the basolateral plasma membrane that has not been studied in uterine epithelial cells are caveolae, which are omega-shaped invaginations of the plasma membrane known to be involved in endocytosis and contribute to membrane curvature. The current study investigated caveolin, a major protein of caveolae, to explore the possible roles that they play in the remodelling of the basolateral plasma membrane of uterine epithelial cells during early pregnancy in the rat. Morphological caveolae were found at the time of implantation and were significantly increased compared to day 1 of pregnancy. Caveolins 1 and 2 were found to shift to the basolateral plasma membrane of uterine epithelial cells at the time of implantation as well as when treated with progesterone alone, and in combination with oestrogen. A statistically significant increase in the amount of caveolin-1 and a decrease in caveolin-2 protein in uterine epithelial cells was observed at the time of implantation. Caveolin-1 also co-immunoprecipitated with integrin β1 on day 1 of pregnancy, which is a protein that has been reported to be found in integrin-based focal adhesions at the basolateral membrane on day 1 of pregnancy. The localisation and expression of caveolin-1 at the time of implantation is consistent with the presence and increase of morphological caveolae seen at this time. The localisation and expression of caveolins 1 and 2 in luminal uterine epithelium at the time of implantation suggest a role in trafficking proteins and the maintenance of a polarised epithelium.
- Published
- 2014
- Full Text
- View/download PDF
28. Charge photogeneration in hybrid solar cells: a comparison between quantum dots and in situ grown CdS.
- Author
-
Reynolds LX, Lutz T, Dowland S, MacLachlan A, King S, and Haque SA
- Subjects
- Nanoparticles chemistry, Oleic Acid chemistry, Thiophenes chemistry, Cadmium Compounds chemistry, Quantum Dots, Solar Energy, Sulfides chemistry
- Abstract
We demonstrate that blend films containing poly(3-hexylthiophene-2,5-diyl) and in situ grown CdS display a greater yield of photogenerated charges than a blend containing an equivalent amount of pre-synthesised CdS quantum dots. Moreover, we show that the greater charge yield in the in situ grown films leads to an improvement in device efficiency. The present findings also appear to suggest that charge photogeneration at the CdS/polymer heterojunction is facilitated by the formation of nanoparticle networks as a result of CdS aggregation.
- Published
- 2012
- Full Text
- View/download PDF
29. Direct growth of metal sulfide nanoparticle networks in solid-state polymer films for hybrid inorganic-organic solar cells.
- Author
-
Dowland S, Lutz T, Ward A, King SP, Sudlow A, Hill MS, Molloy KC, and Haque SA
- Subjects
- Cadmium Compounds chemistry, Electric Power Supplies, Metal Nanoparticles ultrastructure, Temperature, Thiones chemistry, Metal Nanoparticles chemistry, Polymers chemistry, Solar Energy, Sulfides chemistry
- Published
- 2011
- Full Text
- View/download PDF
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