Design and investigation of de Vries liquid crystals based on 5-phenyl-pyrimidine and ( R,R )-2,3-epoxyhexoxy backbone

Abstract

Calamitic liquid crystals based on 5-phenyl-pyrimidine derivatives have been designed, synthesized, and characterized. The 5-phenyl pyrimidine core was functionalized with a chiral (R,R)-2,3-epoxyhexoxy chain on one side and either siloxane or perfluoro terminated chains on the opposite side. The one involving a perfluorinated chain shows SmA^{*} phase over a wide temperature range of 82 °C, whereas the siloxane analog exhibits both SmA^{*} and SmC^{*} phases over a broad range of temperatures, and a weak first-order SmA^{*}-SmC^{*} transition is observed. For the siloxane analog, the reduction factor for the layer shrinkage R (relative to its thickness at the SmA^{*}-SmC^{*} transition temperature, T_{AC}) is ∼0.373, and layer shrinkage is 1.7% at a temperature of 13 °C below the T_{AC}. This compound is considered to have "de Vries smectic" characteristics with the de Vries coefficient C_{deVries} of ∼0.86 on the scale of zero (maximum-layer shrinkage) to 1 (zero-layer shrinkage). A three-parameter mean-field model is introduced for the orientational distribution function (ODF) to reproduce the electro-optic properties. This model explains the experimental results and leads to the ODF, which exhibits a crossover from the sugar-loaf to diffuse-cone ODF some 3 °C above T_{AC}.

Fluorenone imidazolium salts as novel de Vries materials

“…[26][27][28][29] De Vries materials have created much interest recently, because ferroelectric displays based on de Vries materials might overcome limitations of current nematic LC displays such as limited resolution and low optical efficiency. [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] One of the characteristic features of de Vries materials is their tilting transition without defect generation. These materials show no or only very low layer contraction upon the SmA to SmC phase transition, enabling ferroelectric displays without zig-zag defects caused by the chevron-like arrangement of the molecules in the mesophase.…”

Considerations in the determination of orientational order parameters from X-ray scattering experiments

“…The behaviour of typical nematic phases has been shown to be broadly consistent with Maier-Saupe theory [13], for which the different order parameters have a consistent relationship, enabling the distribution function f(β) (peaked at β = 0) to be inferred reliably from a single value of hP 2 i. However, some phases do not exhibit behaviour consistent with such distribution functions, such as the twist-bend (TB) phase, which is reported to exhibit a heliconical structure [14,15], and the de Vries smectic A phase, which is proposed to exhibit a sugar-loaf or diffuse-cone (volcano) distribution function [16][17][18][19], in which the maximum probability of molecular orientations is not necessarily at β = 0. Measurements of hP L i values for L ≥ 2 are required to study systems with such distribution functions, and reliable techniques for determining these values are highly desirable since a maximum entropy argument [3,13] can be used to infer an orientational distribution function from measured values of hP n i.…”

Fast Ferroelectric Liquid Crystal Based Optical Switch: Simulation and Experiments

“…The RN-1175 polymer (Nissan Chemicals, Tokyo, Japan) is used to obtain perfect homogeneous alignment. This thermo aligning polymer aligns nematic [30][31][32] and ferroelectric [33][34][35][36] LC molecules homogenously in cells. The spin coated (3000 rpm, 30 s) Indium Tin Oxide (ITO) glass substrates were baked at 250 °C for an hour to generate planar alignment by evaporating excess solvent.…”