39 research outputs found

    Simulations of absorption spectra of conjugated oligomers: role of planar conformation and aggregation in condensed phase

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    <p>This Review highlights the structure/property relationship underlying the morphology modulation through various factors towards the exploration of light-absorbing materials for efficient utilisation of solar power. Theoretical study using a combination of molecular dynamics imulations and the time-dependent density functional theory demonstrated that the planarity plays an important role in tuning spectral properties of oligomer aggregates. The aggregation-induced blue-shift in absorption spectra of oligothiophenes and the red-shift for oligofluorenols were rationalised in a unified way from the reduced (and increased) content of planar conformations in molecular aggregates. The planarity versus non-planarity of oligomers can be modulated by introduction of alkyl side chain or steric bulky substituents. The substitution with various groups in the ortho-position of azobenzene leads to the distorted backbone, breaking symmetry, and hence the red-shift in spectra, expanding the application in biological systems with visible light absorption. The donor–acceptor substituent groups in conjugated oligomers can increase the degree of planarity, electron delocalisation and polarisation, and charge separation, giving rise to the red-shift in spectra and enhancement in polarisability and charge mobility for device applications. The solvent dependent and pH-sensitive properties and intramolecular hydrogen bonds also caused the shift of absorption spectra with the appearance of planar conformers.</p

    Unconventional O–H···C Hydrogen Bonding and Effects of Conformational Changes on Infrared Spectroscopy of <i>o</i>‑Cresol in Solutions

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    The unconventional O–H···C intramolecular hydrogen bonding and the effect of conformational changes on IR spectra of <i>o</i>-cresol in aqueous solutions were investigated by using molecular dynamics (MD) simulations, density functional theory (DFT), and experiments. A facial rotational isomerization between global minimum with <i>trans</i> conformation and the <i>cis</i> isomer is predicted to take place in gas phase with a low barrier of about 3.7 kcal/mol through a <i>vertical</i>-like transition state. Upon solvation in aqueous solution, the contents of energetically high–lying <i>vertical</i> and <i>cis</i> conformations of neutral <i>o</i>-cresol are increased to 19% and 57%, respectively, in comparison with those (<i>vertical</i>, 0%; <i>cis</i>, 27%) in vacuum. The IR spectra of aqueous solution are closely related to the relative population of the different conformations, especially for the <i>cis</i> conformation with hydroxyl group facing to alkyl group. The appearance of <i>cis</i> conformations and unconventional O–H···C intramolecular hydrogen bond (HB) caused the low-frequency shift in OH stretching vibration of the IR spectra, which was also correlated with cation-like charge distribution and the decrease in <i>s</i>-component of oxygen hybridization orbital. However, the intermolecular HB between the <i>o</i>-cresol and surrounding water (<i>o</i>-cresol) molecules gave rise to more evident shifts in IR spectra than that caused by the intramolecular HB contributions in <i>cis</i> isomer. Further identification of intramolecular HB effect is performed through the comparison of spectrum changes that occurs on passing from aqueous solution to less interacting (carbon tetrachloride and cyclohexane) solvents. The absence of the intermolecular HB interaction between <i>o</i>-cresol and carbon tetrachloride (and cyclohexane) solvents leads to the weaker intensity and narrower width of OH stretching vibration region (around 3407 cm<sup>–1</sup>) in the IR spectra than that in aqueous solution

    Spectroscopic Compositional Analysis of Electrolyte during Initial SEI Layer Formation

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    The energy density of an electrochemical capacitor can be significantly improved by utilizing a lithiated negative electrode and a high surface area positive electrode. During lithiation of the negative carbon electrode, the electrolyte reacts with the electrode surface and undergoes decomposition to form a solid electrolyte interphase (SEI) layer that passivates the surface of the carbon electrode from further reactions between Li and the electrolyte. The reduction reactions that the solvent undergoes not only form insoluble and gaseous byproducts but also electrolyte-soluble products. In this work, those liquid-phase products generated by reductive decomposition of a carbonate-based electrolyte, 1.2 M LiPF<sub>6</sub> in EC/PC/DEC (3:1:4), were analyzed at different stages during the lithiation process of an amorphous carbon electrode. An LCMS analysis of the electrolyte during the initial lithiation process was correlated to a DRIFTS analysis of the carbon electrode surface and the results from the EIS and gas-phase analysis previously reported. It was concluded that the formation reactions of the electrolyte-soluble reduction products are dependent on electrochemical processes but are independent of those reactions that directly lead to the generation of the decomposition gases. This is the first time that the composition of the electrolyte during the initial stages of formation of the SEI layer was systematically determined through the use of an <i>in situ</i> electrochemical-MS analysis. The results presented in this work are focused on the initial analysis, elucidation of the empirical formulas, and determining possible structures for these compounds through a detailed analysis of the spectra from each of these unknowns

    Results of subgroups analyses of pooled ORs (95% CIs).

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    <p>NCC, nest case-control study; CS, cross-sectional study; CC, case-control study; NA, not available; ABL, alveolar bone loss; OHI, oral health index; PI, periodontal index; CAL, clinical attachment loss; FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; GOLD criteria, Global Initiative for Chronic Obstructive Lung Disease spirometry guidelines; PFT, pulmonary function test, that means the article just mentioned but did not give what measurement have been used.</p

    Study characteristics of included studies.

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    <p>NCC, nest case-control study; CS, cross-sectional study; CC, case-control study; NA, not available; ABL, alveolar bone loss; OHI, oral health index; PI, periodontal index; CAL, clinical attachment loss; FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; GOLD criteria, Global Initiative for Chronic Obstructive Lung Disease spirometry guidelines; PFT, pulmonary function test, that means the article just mentioned but did not give what measurement have been used.</p

    Forst plot of sensitivity analysis by removing each study in each turn.

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    <p>The pooled OR was represented by a diamond of standard height, with the width indicating the 95% CI. PD, periodontal dsease; COPD, chronic obstructive pulmonary disease; OR, odds ratio; CI, confidence interval; NCC, nest case-control study; CC, case-control study; CS, cross-sectional study.</p

    Filled funnel plot with pseudo-95% CIs of results of 14 studies.

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    <p>Log of OR represents the natural logarithm of the OR of individual studies; Standard Error by Log odds ratio represents the standard error in the natural logarithm of the OR of individual studies. A circle in the figure represents a study, while a black spot represents an unpublished study that would have to exist to negate the results of the meta-analysis.</p

    Direct Synthesis of Unilamellar MgAl-LDH Nanosheets and Stacking in Aqueous Solution

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    Two-dimensional (2D) materials, such as graphene, inorganic oxides, and hydroxides, are one of the most extensively studied classes of materials due to their unilamellar crystallites or nanosheet structures. In this study, instead of using the universal exfoliation method of the bulky crystal precursor, 2D crystals/nanosheets of MgAl-layered double hydroxides (LDHs) were synthesized in formamide. We propose that the obtained crystals are unilamellar according to the XRD, TEM, and AFM observations. The HRTEM and fast Fourier transform images confirm that the crystal structures are the same as those of the exfoliated MgAl-LDH nanosheets. The directly synthesized sheets can stack into a 3D crystal structure, which is the same as that of typical LDHs except for the disordered orientation of the <i>a</i>-/<i>b</i>- crystal axis of each sheet. This result provides not only a novel approach to the preparation of 2D crystals but also insight into the formation mechanism of LDHs

    Colloidal Synthesis of Lettuce-like Copper Sulfide for Light-Gating Heterogeneous Nanochannels

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    Lettuce-like Cu<sub><i>x</i></sub>S micron particles were successfully prepared by a colloidal hot-injection method, and the preliminary evaluation of the light-gating artificial ionic nanochannels designed using these particles was also demonstrated. A likely underlying mechanism behind the formation of the lettuce architecture was tentatively proposed <i>via</i> monitoring the evolution process. These particles are hydrophobic and possess a high surface area that can readily absorb the light-responsive 1,3,3-trimethylindolino-6′-nitrobenzopyrylospiran (Spiro) molecules. Finally, the heterogeneous nanochannels were constructed by spin-coating the preprepared Cu<sub><i>x</i></sub>S particles loaded with Spiro onto the commercially available anodic alumina (AAO) substrate. The AAO-Cu<sub><i>x</i></sub>S/Spiro heterogeneous nanochannels “close” under illumination of ultraviolet light (365 nm) and then “open” by visible light irradiation, which exhibits a regulated ionic transport property with good responsive switchability and stability
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