Solute orientation behavior in nematic solutions: Trichlorobenzene in MBBA

Lee, Y. P.; Gilson, D. F. R.

doi:10.1063/1.437622

Cited by 5 publications

(1 citation statement)

References 9 publications

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“…An early approach to calculating the molecular alignment of solute molecules suggested that the minimum moment of inertia (MOI) axis gave a good description of the principal molecular axis for a range of substituted benzenes, including some of low symmetry, in a nematic host. 15 Subsequent NMR studies have applied this approach to analyse a range of different solutes with varying degrees of success: some reports have noted slight deviations of the principal molecular axis from the minimum MOI axis that were attributable to steric effects, 16,17 whereas others have suggested that the approach does not apply to some systems, 18 and that shape-based approaches are more appropriate to cover a wide range of solute molecules. 19,20 However, in the limiting case of a rod-like molecule of high symmetry, the minimum MOI axis will match the principal symmetry axis, and hence its principal molecular axis.…”

Section: Introductionmentioning

confidence: 99%

Principal molecular axis and transition dipole moment orientations in liquid crystal systems: an assessment based on studies of guest anthraquinone dyes in a nematic host

Sims

Abbott

Cowling

et al. 2017

Phys. Chem. Chem. Phys.

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An assessment of five different definitions of the principal molecular axis along which molecules align in a nematic liquid crystal system has been made by analysing fully atomistic molecular dynamics (MD) simulations of a set of anthraquinone dyes in the cyanobiphenyl-based nematic host mixture E7. Principal molecular axes of the dyes defined by minimum moment of inertia, minimum circumference, minimum area, maximum aspect ratio, and surface tensor models were tested, and the surface tensor model was found to give the best description. Analyses of MD simulations of E7 alone showed that the surface tensor model also gave a good description of the principal molecular axes of the host molecules, suggesting that this model may be applicable more generally. Calculated dichroic order parameters of the guest-host systems were obtained by combining the surface tensor analysis with fixed transition dipole moment (TDM) orientations from time-dependent density functional theory (TD-DFT) calculations on optimised structures of the dyes, and the trend between the dyes generally matched the trend in the experimental values. Additional analyses of the guest-host simulations identified the range of conformers explored by the flexible chromophores within the dyes, and TD-DFT calculations on corresponding model structures showed that this flexibility has a significant effect on the TDM orientations within the molecular frames. Calculated dichroic order parameters that included the effects of this flexibility gave a significantly improved match with the experimental values for the more flexible dyes. Overall, the surface tensor model has been shown to provide a rationale for the experimental alignment trends that is based on molecular shape, and molecular flexibility within the chromophores has been shown to be significant for the guest-host systems: the computational approaches reported here may be used as a general aid in the predictive design of dyes with appropriate molecular shapes and flexibilities for guest-host applications.

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Section: Introductionmentioning

confidence: 99%

Principal molecular axis and transition dipole moment orientations in liquid crystal systems: an assessment based on studies of guest anthraquinone dyes in a nematic host

Sims

Abbott

Cowling

et al. 2017

Phys. Chem. Chem. Phys.

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Optical Activity of Oriented Molecules. 10.Analysis of the n‐π Transition of 4‐en‐3‐one Steroids and Comparison of the Order Parameters of Host and Guest in a Compensated Nematic Phase

Altschuh

Weiland

Kosack

et al. 1984

Ber Bunsenges Phys Chem

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Anisotropic sample / Liquid Crystals / Order parameters / Spectroscopy, CD-ORD / Spectroscopy, UltravioletWhile different substitution in the 17 p-position of 4-en-3-one steroids (testosterones, progesterones) does not influence the CD spectra, the CD of the anisotropic solutions (ACD) undergoes a drastic variation of the band shape connected with a change from negative to positive curves. From this variation and the wavelength dependence of the degree of polarization of the UV spectra results that at least two progressions of vibrations (iim + nii, and Vo0 + 1, + n 1 , ) are responsible for the band structure of the n-A* transition of the 4-en-3-one chromophore where the totally symmetric (Y1) and the non-totally symmetric vibration (V,) are about 1200 and 600 cm-', respectively. Furthermore, this variation of the ACD spectra for constant temperature and solute (guest) to solvent (host: cholesteryl chloride/cholesteryl laurate) ratio is a consequence of a change of the order parameter of the guest and the host which have been determined in the same solution by ACD and AORD, respectively. Most variation of the guest order can be understood by the proportionality to the anisotropy of the polarizability 2a33-a22-a,, or the length to width ratio 2/3-/2-/, if no hydroxy group is present. Here a very high order exists. For some compounds the high order of the guest is connected with a strong decrease of the host order. In general, the alteration of the host order is not a function of the order of the guest i.e. at least one molecular property responsible for the ordering of the guest should be different from those properties of the guest which alterate the order of the host.

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The Orientational Behaviour of Some Fluorinated Molecules in Nematic Liquid Crystal Solvents

Gilson

1984

Molecular Crystals and Liquid Crystals

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Solute orientation behavior in nematic solutions: Trichlorobenzene in MBBA

Abstract: 1,3,5-trichlorobenzene is used as a probe to study the order parameters in MBBA. The NMR spectrum of 1,3,5-trichlorobenzene in MBBA is reported. (AIP)

Cited by 5 publications

References 9 publications

Principal molecular axis and transition dipole moment orientations in liquid crystal systems: an assessment based on studies of guest anthraquinone dyes in a nematic host

Principal molecular axis and transition dipole moment orientations in liquid crystal systems: an assessment based on studies of guest anthraquinone dyes in a nematic host

Optical Activity of Oriented Molecules. 10.Analysis of the n‐π Transition of 4‐en‐3‐one Steroids and Comparison of the Order Parameters of Host and Guest in a Compensated Nematic Phase

The Orientational Behaviour of Some Fluorinated Molecules in Nematic Liquid Crystal Solvents

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