Nematic liquid crystals exhibiting high birefringence

Abstract

Two fluorinated isothiocyanato nematic liquid crystalline compounds, 4 0 -butylcyclohexyl-3, 5-difluoro-4-isothiocyanatobiphenyl and 4 0 -pentylcyclohexyl-3, 5-difluoro-4-isothiocynatobiphenyl are studied in detail to obtain their different physical parameters. Optical polarizing microscopy, differential scanning calorimetry, density and dielectric studies have been carried out for the two samples. Both the samples were found to have high clearing temperature ([100°C) and exhibit small enthalpy of transition. The two samples exhibit high optical birefringence (Dn [ 0.2). The values of order parameters for the two samples were obtained using different approaches, namely, Vuks', Neugebauer's, modified Vuks' and direct extrapolation method from birefringence data. Experimentally obtained values of order parameters have also been compared with theoretical Maier-Saupe values. The parallel and perpendicular components of dielectric permittivity values of the two compounds were also calculated and their anisotropy values were found to be small. The effect of temperature on the molecular dipole moment l and the angle of inclination b of the dipole axis with the director have also been investigated in this work.

A comparative DFT analysis of chiral laterally semi-fluorinated liquid crystals

“…They are 1 3 ,1 5 -difluoro-1 4 -isothiocyanato-3 4 -propyl-1 1 ,2 1 :2 4 ,3 1 -terphenyl and 1 3 ,2 2 -difluoro-1 4 -isothiocyanato-3 4 -propyl-1 1 ,2 1 :2 4 ,3 1 -terphenyl. LC compounds with isothiocyanate group are subjects of great interest for study due to properties like high polarity, low viscosity, high optical birefringence and broad temperature range for the nematic phase are good criteria for device application [17,29,30]. The main focus of our work is to explore the molecular properties of these materials by density functional theory (DFT).…”

Optical and Geometrical Characterizations of Non-Linear Supramolecular Liquid Crystal Complexes

“…Yildiz et al used Abbe refractometer and rotating-analyzer techniques for measuring ordinary (n o ) and extraordinary (n e ) refractive indices and birefringence (∆n) [5,9]. In addition, the dependence of birefringence on temperature was studied for LCs [10][11][12][13][14][15][16][17][18]. The factors of the birefringence, of thermal stability and order parameter were also reported [19,20].…”

“…Among the self-assembly method LCs is H-bonding intermolecular interactions with noncovalent bonds [32][33][34][35][36]. Among the H-bond acceptors studied for LCs [10][11][12][13][14][15][16][17][18]. The factors of the birefringence, of thermal stability and order parameter were also reported [19,20].…”