Study of the Orientational Order and Dynamics in the Nematic and Smectic Phases ofp′-Hexyloxybenzyliden-p-Fluoroaniline by Means of2H-NMR

Orientational ordering studies of fluorinated thermotropic liquid crystals by NMR spectroscopy

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.

The SPORT-NMR software: a tool for determining relaxation times in unresolved NMR spectra

A software package which allows the correct determination of individual relaxation times for all the nonequivalent nuclei in poorly resolved NMR spectra is described. The procedure used, based on the fitting of each spectrum in the series recorded in the relaxation experiment, should improve the analysis of relaxation data in terms of quantitative dynamic information, especially in anisotropic phases. Tests on simulated data and experimental examples concerning 1H and 13C T1rho measurement in a solid copolymer and 2H T1Z and T1Q measurement in a liquid crystal are shown and discussed.