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Twist Grain Boundary Liquid‐Crystalline Phases under the Effect of the Magnetic Field: A Complete 2 H and 13 C NMR Study
Author(s) -
Domenici Valentina,
Veracini Carlo Alberto,
Novotná Vladimira,
Dong Ronald Y.
Publication year - 2008
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200700647
Subject(s) - supramolecular chemistry , nmr spectra database , crystallography , mesogen , nuclear magnetic resonance spectroscopy , liquid crystal , chemistry , magnetic field , phase (matter) , spectroscopy , paramagnetism , chemical physics , materials science , spectral line , crystal structure , condensed matter physics , stereochemistry , physics , liquid crystalline , organic chemistry , quantum mechanics , astronomy , optoelectronics
A liquid crystal ( HZL 7/* ) containing an ( S )‐2‐methylbutyl‐( S )‐lactate unit in the chiral chain, is investigated by means of 2 H and 13 C NMR spectroscopy in order to obtain information on its orientational order, its molecular structure and the effect of external magnetic fields on the supramolecular structure of its phases. This mesogen presents very peculiar mesomorphic properties and exhibits frustrated TGBA* and TGBC* phases in a wide temperature range up to 60 °C, as well as an additional phase transition from TGBC 1 * to TGBC 2 *. 2 H NMR measurements show, for the first time, a peculiar magnetic field effect in unwinding the supramolecular structure of both the TGBA* and TGBC* phases. This effect is particularly evident at higher magnetic fields, while different behaviour is observed at lower magnetic fields. This indicates that the supramolecular structure is very sensitive to magnetic fields of the order of 1 Tesla. Moreover, the analysis of the 2 H and 13 C NMR spectra of HZL 7/* allow us to obtain several structural properties, such as the tilt angle of the TGBC* phases and the local orientational order parameters referred to the phenyl and biphenyl fragments. This is the first structural characterization of the frustrated phases of these complexes by means of NMR.