The structure and conformation of a mesogenic compound between almost zero and almost complete orientational order

Abstract

The conformational distributions in molecules that form liquid crystalline phases are predicted to depend strongly on orientational order. Results are presented here to test this hypothesis. The mesogen 4-hexyloxy-49-cyanobiphenyl (6OCB) has been studied by NMR spectroscopy in the isotropic phase and in the nematic phase. In the isotropic phase the fieldinduced orientational ordering produces small dipolar couplings between 13 C and 1 H nuclei, which were determined from the 13 C spectra. Couplings between 1 H nuclei were also obtained using 2D selective refocusing experiments. In the nematic phase, both 1 H-1 H dipolar couplings and quadrupolar splittings for deuterium nuclei were measured for partiallydeuterated samples. Both proton and deuterium spectra were also obtained for 6OCB in an equimolar mixture with 4-(ethoxybenzylidene)-49-butylaniline (EBBA). This mixture exhibits SmA and SmB phases. The data obtained from these experiments has been analysed to yield the probability distribution of the conformations in this molecule generated by rotations about bonds. It is found that there is a substantial influence of the orientational order of the molecules on these distributions.

C13 NMR study of the director distribution adopted by the modulated nematic phases formed by liquid-crystal dimers with odd numbers of atoms in their spacers

“…Studies on other mesogens containing these groups [15,[27][28][29][30][31][32] suggest that to a good approximation only the term involving S zz is of appreciable magnitude for carbon atoms, which are on the z axis, and so i and S zz for these sites are linearly related:…”

Sulfur-linked cyanobiphenyl-based liquid crystal dimers and the twist-bend nematic phase

“…In order to establish the geometric parameters of the dimers, quantum mechanical density functional theory was used [36]. Geometry optimization for sulfur-linked dimers with the spacer in the all-trans conformation was performed using Gaussian between the calculated ground state and all-trans conformations is small, typically around 1 kJ mol -1 , and is likely to be substantially different in an ordered liquid crystal phase which will preferentially select more linear conformations [41]. Thus, we consider the all-trans conformation to be a better representation of the average molecular shape in discussing the transitional properties of the dimers containing ether links.…”

Change of Polarizability of Molecules at the Isotropic Liquid – Nematic – Smectic A – Crystal B Phase Transitions of the Liquid Crystal 4O.8

“…Уплотнение молекул в немати-ческой и смектической-А фазах с ростом анизотропии их координационного окружения и ≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡ параметров порядка S, || ведет к росту величины Q 2 относительно значения Q 2i в изотропной фазе согласно зависимости [15] [15,16] и вносит вклад в изменение параметров ().…”

“…11 ≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡ В соответствии с формулами (10), (16) …”