Browsing by Author "Cole, JM"

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    Dye⋯TiO2 interfacial structure of dye-sensitised solar cell working electrodes buried under a solution of I−/I3− redox electrolyte
    (Royal Society of Chemistry, 2017-07-27) McCree-Grey, J; Cole, JM; Holt, SA; Evans, PJ; Gong, Y
    Dye-sensitised solar cells (DSCs) have niche prospects for electricity-generating windows that could equip buildings for energy-sustainable future cities. However, this ‘smart window’ technology is being held back by a lack of understanding in how the dye interacts with its device environment at the molecular level. A better appreciation of the dye⋯TiO2 interfacial structure of the DSC working electrodes would be particularly valuable since associated structure–function relationships could be established; these rules would provide a ‘toolkit’ for the molecular engineering of more suitable DSC dyes via rational design. Previous materials characterisation efforts have been limited to determining this interfacial structure within an environment exposed to air or situated in a solvent medium. This study is the first to reveal the structure of this buried interface within the functional device environment, and represents the first application of in situ neutron reflectometry to DSC research. By incorporating the electrolyte into the structural model of this buried interface, we reveal how lithium cations from the electrolyte constituents influence the dye⋯TiO2 binding configuration of an organic sensitiser, MK-44, via Li+ complexation to the cyanoacrylate group. This dye is the molecular congener of the high-performance MK-2 DSC dye, whose hexa-alkyl chains appear to stabilise it from Li+ complexation. Our in situ neutron reflectometry findings are built up from auxiliary structural models derived from ex situ X-ray reflectometry and corroborated via density functional theory and UV/vis absorption spectroscopy. Significant differences between the in situ and ex situ dye⋯TiO2 interfacial structures are found, highlighting the need to characterise the molecular structure of DSC working electrodes while in a fully assembled device. © Royal Society of Chemistry 2020
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    Molecular origins of the high-performance nonlinear optical susceptibility in a phenolic polyene chromophore: electron density distributions, hydrogen bonding, and ab initio calculations
    (American Chemical Society, 2013-05-09) Lin, TC; Cole, JM; Higginbotham, AP; Edwards, AJ; Piltz, RO; Pérez-Moreno, J; Seo, JY; Lee, SC; Clays, K; Kwon, OP
    The molecular and supramolecular origins of the superior nonlinear optical (NLO) properties observed in the organic phenolic triene material, OH1 (2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile), are presented. The molecular charge-transfer distribution is topographically mapped, demonstrating that a uniformly delocalized passive electronic medium facilitates the charge-transfer between the phenolic electron donor and the cyano electron acceptors which lie at opposite ends of the molecule. Its ability to act as a "push-pull" pi-conjugated molecule is quantified, relative to similar materials, by supporting empirical calculations; these include bond-length alternation and harmonic-oscillator stabilization energy (HOSE) tests. Such tests, together with frontier molecular orbital considerations, reveal that OH1 can exist readily in its aromatic (neutral) or quinoidal (charge-separated) state, thereby overcoming the "nonlinearity-thermal stability trade-off". The HOSE calculation also reveals a correlation between the quinoidal resonance contribution to the overall structure of OH1 and the UV-vis absorption peak wavelength in the wider family of configurationally locked polyene framework materials. Solid-state tensorial coefficients of the molecular dipole, polarizability, and the first hyperpolarizability for OH1 are derived from the first-, second-, and third-order electronic moments of the experimental charge-density distribution. The overall solid-state molecular dipole moment is compared with those from gas-phase calculations, revealing that crystal field effects are very significant in OH1. The solid-state hyperpolarizability derived from this charge-density study affords good agreement with gas-phase calculations as well as optical measurements based on hyper-Rayleigh scattering (HRS) and electric-field-induced second harmonic (EFISH) generation. This lends support to the further use of charge-density studies to calculate solid-state hyperpolarizability coefficients in other organic NLO materials. Finally, this charge-density study is also employed to provide an advanced classification of hydrogen bonds in OH1, which requires more stringent criteria than those from conventional structure analysis. As a result, only the strongest OH center dot center NC interaction is so classified as a true hydrogen bond. Indeed, it is this electrostatic interaction that influences the molecular charge transfer: the other four, weaker, nonbonded contacts nonetheless affect the crystal packing. Overall, the establishment of these structure?property relationships lays a blueprint for designing further, more NLO efficient, materials in this industrially leading organic family of compounds. © 2013, American Chemical Society.
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    Neutron diffraction characterization of C–H···Li interactions in a lithium aluminate polymer
    (ACS Publications, 2014-05-01) Cole, JM; Waddell, PG; Wheatley, AEH; McIntyre, GJ; Peel, AJ; Tate, CW; Linton, DJ
    The reaction of AlMe3 with tBuLi in the presence of trimethylacetonitrile affords the bimetallic complex [tBu(Me)Al(μ-Me)2Li·NC(tBu)]∞ (1). Pseudotetrahedral Al centers form by the nucelophilic addition of tBuLi to AlMe3.The alkali-metal center is stabilized through coordination of the unreacted nitrile and polymer formation via the construction of Al(μ-Me)nLi (n = 1, 2) motifs. Neutron diffraction evidences agostic interactions in the bridging methyl group to give further stabilization. There is only one previous report of a neutron structure of a lithium aluminate compound. This work therefore offers an important structural example of agostic interactions and the precise nature of Al(μ-Me)2Li bridging.© 2014, American Chemical Society.
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    Predicting solar-cell dyes for cosensitization
    (American Chemical Society, 2014-06-03) Bayliss, SL; Cole, JM; Waddell, PG; McKechnie, S; Liu, XGG
    A major limitation of using organic dyes for dye-sensitized solar cells (DSCs) has been their lack of broad optical absorption. Cosensitization, in which two complementary dyes are incorporated into a DSC, offers a route to combat this problem. Here we construct and implement a design route for materials discovery of new dyes for cosensitization, beginning with a chemically compatible series of existing laser dyes which are without an anchor group necessary for DSC use. We determine the crystal structures for this dye series and use their geometries to establish the DSC molecular design prerequisites aided by density-functional theory and time-dependent density-functional theory calculations. Based on insights gained from these existing dyes, modified sensitizers are computationally designed to include a suitable anchor group. A DSC cosensitization strategy for these modified sensitizers is predicted, using the central features of highest-occupied and lowest-unoccupied molecular orbital positioning, optical absorption properties, intramolecular charge-transfer characteristics, and steric effects as selection criteria. Through this molecular engineering of a series of existing non-DSC dyes, we predict new materials for DSC cosensitization. © 2014, American Chemical Society.
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    Reflectometry as a tool for studying dye molecule orientation in dyesensitised solar cells (DSCs)
    (Australian Institute of Physics, 2014-02-06) McCree-Grey, J; Cole, JM
    With world energy demand set to double by 2050, it is imperative that clean, efficient and cost-effective alternatives to fossil fuels are developed. Dye-sensitised Solar Cells (DSCs) are a positive step towards a low-cost, mass-producible source of photovoltaic power, with laboratory devices now capable of reaching efficiencies of up to 15%. Typical DSCs consist of a dye-sensitised semiconductor surrounded by a redox electrolyte and sandwiched between two transparent, conductive substrates. The dye is the principle light adsorber, injecting photo-excited electrons into the semiconductor conduction band and giving rise to the cells electrical characteristics. The electron injection is enabled by the dye’s physical and electrostatic interaction with the semiconductor surface and the nature of this interaction can have a major impact on the cell’s performance. Many dye species have been trialled in DSCs in efforts to improve these characteristics, however, the fundamental properties of dye orientation and molecular packing on the semiconductor surface remain widely unknown. X-ray reflectometry (XRR) has already been successfully applied to this field of DSCs but application of reflectometry to a fully functioning DSC has still yet to be realised. This presentation will discuss results obtained using X-ray reflectometry to study the dye-orientations and packing densities for a number of different dye systems. Further discussion on the development of procedures to then apply neutron reflectometry to study a fully functioning dye-sensitised solar cell will then be examined.