High Figure-of-Merit Laterally Fluorinated Biphenyltolane-Isothiocyanates

Abstract

We have designed, synthesized, and evaluated the physical properties of some high birefringence (Dn) isothiocyanato biphenyl-tolane liquid crystals. These compounds exhibit Dn $ 0.48-0.52 at room temperature and wavelength k ¼ 633 nm. Laterally substituted short alkyl chains and fluorine atom eliminate smectic phase and lower the melting temperature. The moderate melting temperature and very high clearing temperature make those compounds attractive for eutectic mixture formulation. A eutectic mixture based on those compounds was formulated and its physical properties evaluated.

Determination of ordinary and extraordinary refractive indices of nematic liquid crystals by using wedge cells

“…The errors dV, dN, dE, and dO were found as empirical mean deviations and from them the errors dn o , dn e , and dDn were estimated. These results are in good agreement with those taken from the literature [14][15][16][17][18][19][20][21] …”

“…The second one was filled with the 4−trans−4'−n−hexylcyclohexyl isothiocyanatobenzene (6CHBT), the well−known NLC [13]. The third and fourth ones were filled with two NLC mixtures, LCJ 1650 and LCJ 1791A, of large optical aniso− tropy, recently produced in our university [16][17][18][19][20][21].…”

High Birefringence Liquid Crystals

“…They have a birefringence reaching up to 0.45 at room temperature in the case of isothiocyanates for pentyl terminal chain, and furthermore, they also reach Δn values up to 0.6 for the ethyl chain [110,111]. Their FoM 1 values are about 40 at room temperature and reach maximum value ~240 at 150 °C .…”

“…Many such mixtures with Δn values in the range 0.3-0.7 have been demonstrated so far [49,50,91,93,94,101,111,122,124,128]. Mixtures with a broad range of nematic phases and birefringence values of Δn = 0.3-0.45 are now available with an acceptable level of viscosity (γ < 300 mPa· s), see example Mixtures 1791 and 1825 composed of fluoro-substituted alkyltolane and alkylphenyl tolane isothiocyanates have the highest birefringence among those presented in Table 17.…”

Highly birefringent, low-loss liquid crystals for terahertz applications

“…Over the past few years, different isothiocyanato compounds were investigated, for example, by Catanescu and Chien 17 as well as by our group. [18][19][20][21][22][23][24] These studies led to the selection of the following, particularly promising compounds, see Figure 1.…”