Orientational properties of liquid-crystalline 4-<i>n</i>-alkyloxybenzilidene-4′-fluoroanilines

Catalano, Donata; Gandolfo, C.; Shilstone, G. N.; Veracini, Carlo Alberto

doi:10.1080/02678299208028979

Cited by 9 publications

(53 citation statements)

References 5 publications

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“…A second difference between the deuterium results for FAB-OC6 and the present method is that the former shows that the order parameter suddenly decreases at the smectic A to smectic B transition, so that S,, for the smectic B phase is less than that for the smectic A, which is a very perplexing result. The order parameter S,, determined from the deuterium results of the smectic B phase then quickly increases linearly to a maximum value of the smectic B phase [2]. By contrast, figure 2 shows that the order parameter S,, determined in this work does not have this anomaly; it has a sudden increase at the transition from the smectic A phase to the smectic B phase, and then stays constant within experimental error.…”

Section: Resultscontrasting

confidence: 54%

“…The transition temperatures between the phases, C (47.7"C) SR (550°C) S, (61.5"C) N (63.0"C) I, were determined by polarizing microscopy. The values were somewhat higher than those reported in previous studies of this compound [2,4], and the smectic A range was slightly wider. The microscope temperatures were calibrated with a standard, and the sharp transitions indicated a high purity for our sample.…”

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confidence: 68%

“…There are two commonly used NMR techniques for determining the order parameters of liquid crystals. The first one calculates the order parameters for the quadrupolar and deuterium-proton dipolar splittings observed in the deuterium NMR spectrum [2,. This technique has proven t o be very effective, but requires the synthesis of deuteriated liquid crystals.…”

Section: Introductionmentioning

confidence: 99%

“…Several members of the homologous series incorporating 4-n-hexyloxybenzilidene-4-fluoroaniline (FAB-OCn) have been the object of studies by polarizing microscopy, Xray diffraction [4], and deuterium and fluorine NMR spectroscopy [ 2 ] . These studies revealed a surprising and interesting physical property, namely some of the highest measured order parameters for the smectic liquid crystalline phases.…”

Section: Introductionmentioning

confidence: 99%

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Determination of order parameters from carbon–fluorine dipolar coupling

1994

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A convenient NMR method for the determination of the order parameters for liquid crystals containing a fluorinated phenyl ring is described. The technique consists of measuring the carbon-fluorine dipolar coupling constants in the onedimensional C-13 spectrum of the molecule. The order parameters may then be calculated for the fluorine-containing ring with a high degree of precision because of the excellent resolution afforded by the 1-D C-13 spectra. The method is used to determine the core order parameters for 4-n-hexyloxybenzilidene-4'-fluoroaniline (FAB-OC6). The results of the carbon-fluorine dipolar coupling method are compared with two established methods for determining the core order parameters of phenyl rings, namely deuterium NMR spectroscopy and SLF/VAS, a twodimensional (2-13 NMR spectroscopy. Some comments about the orientational properties of the fluorinated liquid crystal FAB-OC6 are made.

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Section: Resultscontrasting

confidence: 54%

contrasting

confidence: 68%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Determination of order parameters from carbon–fluorine dipolar coupling

1994

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“…Isotopomers deuteriated in meta positions respect to fluorine (FABOCn‐d 2 in Table ) have been investigated by Catalano et al . for the homologues with n = 6 and n = 7 and by Calucci et al . for the compounds with n = 4, 5, and 8 .…”

Section: Applicationsmentioning

confidence: 99%

Orientational ordering studies of fluorinated thermotropic liquid crystals by NMR spectroscopy

Calucci

Geppi

Urban

2014

Magnetic Reson in Chemistry

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Fluorinated calamitic thermotropic liquid crystals represent an important class of materials for high-tech applications, especially in the field of liquid crystal displays. The investigation of orientational ordering in these systems is fundamental owing to the dependence of their applications on the anisotropic nature of macroscopic optical, dielectric, and visco-elastic properties. NMR spectroscopy is the most powerful technique for studying orientational order in liquid crystalline systems at a molecular level thanks to the possibility of exploiting different anisotropic observables (chemical shift, dipolar couplings, and quadrupolar coupling) and nuclei ((2)H, (13)C, and (19)F). In this paper, the basic theory and NMR experiments useful for the investigation of orientational order on fluorinated calamitic liquid crystals are reported, and a review of the literature published on this subject is given. Finally, orientational order parameters determined by NMR data are discussed in comparison to those obtained by optical and dielectric anisotropy measurements.

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Orientational Order Properties in Fluorinated Liquid Crystals from an Optical, Dielectric, and ¹³C NMR Combined Approach

et al. 2007

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Orientational order properties of two fluorinated nematogens, exhibiting a wide nematic range, have been investigated by means of optical methods, dielectric spectroscopy, and 13C NMR. 13C NMR spectra have been recorded by 1H-SPINAL decoupling CP techniques under both static and magic angle spinning conditions. The order parameters of the fluorinated aromatic fragments have been calculated by analyzing the 13C−19F dipolar couplings at different levels of approximations by means of a least-squares fitting procedure using geometrical parameters determined by DFT methods, eventually including empirical corrections for vibrations and anisotropic scalar couplings. The nematic order parameters determined from optical birefringence data, dielectric anisotropy, and NMR have been compared: their trends with temperature, analyzed by the Haller model and by more sophisticated ones, are very similar, even if the order parameters from optical birefringence are shifted to slightly higher values. The differences among the results obtained by the three methods can be related to the different anisotropic properties monitored, described by tensors whose principal or “long” axes can be located at slightly different places on the molecule. The assumptions and approximations used in each case are discussed in detail.

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Orientational properties of liquid-crystalline 4-n-alkyloxybenzilidene-4′-fluoroanilines

Cited by 9 publications

References 5 publications

Determination of order parameters from carbon–fluorine dipolar coupling

Determination of order parameters from carbon–fluorine dipolar coupling

Orientational ordering studies of fluorinated thermotropic liquid crystals by NMR spectroscopy

Orientational Order Properties in Fluorinated Liquid Crystals from an Optical, Dielectric, and ¹³C NMR Combined Approach

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Orientational properties of liquid-crystalline 4-n-alkyloxybenzilidene-4′-fluoroanilines

Cited by 9 publications

References 5 publications

Determination of order parameters from carbon–fluorine dipolar coupling

Determination of order parameters from carbon–fluorine dipolar coupling

Orientational ordering studies of fluorinated thermotropic liquid crystals by NMR spectroscopy

Orientational Order Properties in Fluorinated Liquid Crystals from an Optical, Dielectric, and 13C NMR Combined Approach

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Orientational Order Properties in Fluorinated Liquid Crystals from an Optical, Dielectric, and ¹³C NMR Combined Approach