Determination of relative positions and localizations of paramagnetic probe molecules in liquid crystal by analysis of concentration broadening of EPR spectra

Pomogailo, Daria A.; Paramonov, N. A.; Chumakova, Natalia A.; Vorobiev, Andrey Kh.

doi:10.1016/j.cplett.2016.05.051

Cited by 3 publications

(2 citation statements)

References 36 publications

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“…Obviously, the two states of the probe correspond to different positions in the spatially inhomogeneous SmA structure. This result is in accordance with the previously published conclusion …”

Section: Resultssupporting

confidence: 94%

Spin Probe Determination of Molecular Orientation Distribution and Rotational Mobility in Liquid Crystals: Model-Free Approach

et al. 2019

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A model-free approach for simulation of EPR spectra of nitroxide spin probes in liquid-crystalline materials was suggested and used to obtain parameters of molecular orientation and rotational mobility. The developed method is based on experimental recording and numerical simulation of the angular dependence of EPR spectra, which is shown to be much more informative in comparison with a single EPR spectrum. Quantitative spectral simulations considering both local orientational ordering and distribution of local directors in the sample were used for discrimination of models of rotational mobility and orientational alignment. The method was applied for detailed quantitative characterization of axial, orthorhombic, and low-symmetry non-orthorhombic molecular orientation distributions. It is shown that the ordinarily used model of rotational diffusion in a mean-field potential is suitable for the description of molecular mobility and orientational ordering only for relatively low sample temperatures and low-mobility probe molecules with large sizes. In cases of high molecular mobility, the more realistic jump mechanism of molecular moves can be approximately described as quasi-librations. For ordered liquid crystals it was found that mostly the order parameters up to rank 12–14 are essential and easily determined. When well-aligned materials are described, the order parameters up to 18th rank or even higher become meaningful. Both molecular and sample biaxiality is analyzed and quantitatively characterized. The local molecular ordering and sample orientational alignment are quantitatively characterized separately.

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Section: Resultssupporting

confidence: 94%

Spin Probe Determination of Molecular Orientation Distribution and Rotational Mobility in Liquid Crystals: Model-Free Approach

et al. 2019

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“…The quantitative theory of the EPR spectra linewidth of LC-forming nitroxyls was developed by our group earlier. , It was shown that the presented angular dependencies can be quantitatively described based on the assumption that the closest neighbors are characterized by a “head-to-tail” packing, which is characteristic of nematics . The radius vector between adjacent nitroxyls has the components parallel and perpendicular to the LC directors b m and a m , correspondingly.…”

Section: Epr Spectra Of the H-bonded Complexmentioning

confidence: 99%

Photo-orientation and Electron Paramagnetic Resonance Spectra of a Nitroxide and Azobenzene-Containing Hydrogen-Bonded Complex

2022

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Photochromism and light-induced orientation of a hydrogen-bonded paramagnetic mesogenic complex were investigated. The azopyridine chromophore included in the chemical structure of the complex is capable of reversible trans-to-cis photoisomerization with the lifetime of the cis-isomer being on the order of seconds. The action of polarized light on the solid film of the complex results in its in-plane photo-orientation, wherein the azopyridine chromophores become preferentially aligned perpendicular to the electric vector of the incident light. The photoorientation kinetics strongly depends on the morphological properties and thermal history of the film and has an unusual Sshaped form due to the topochemical nature of the process (Avrami kinetics). The observed peculiarities of the photoinduced alignment of the complex corroborate the mechanism of photoorientation by means of microscopic structure rearrangement. The polarized optical absorbance and electron paramagnetic resonance spectra of the photoaligned film of the material prove that the sample is characterized by macroscopic biaxiality due to the presence of two competing orienting forces, namely, the polarized light and the orienting influence of the surface. Electron paramagnetic resonance spectra of the complex in aligned crystalline and nematic samples are interpreted in terms of the macroscopic order of the material and intermolecular spin−spin interactions of the nitroxyl fragments.

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Novel nitroxide biradical probe with spiro-fused rigid core for EPR determination of rotational mobility and orientational order of soft materials

Bogdanov

Tamura

Vorobiev

2020

Chemical Physics Letters

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Determination of relative positions and localizations of paramagnetic probe molecules in liquid crystal by analysis of concentration broadening of EPR spectra

Cited by 3 publications

References 36 publications

Spin Probe Determination of Molecular Orientation Distribution and Rotational Mobility in Liquid Crystals: Model-Free Approach

Spin Probe Determination of Molecular Orientation Distribution and Rotational Mobility in Liquid Crystals: Model-Free Approach

Photo-orientation and Electron Paramagnetic Resonance Spectra of a Nitroxide and Azobenzene-Containing Hydrogen-Bonded Complex

Novel nitroxide biradical probe with spiro-fused rigid core for EPR determination of rotational mobility and orientational order of soft materials

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