Ulrich Finkenzeller

Polarized UV spectroscopy of conjugated liquid crystals

Polarized absorption spectra of 13 nematic liquid crystals (LCs) with various conjugations and structures were measured in the spectral range from 185 to 400 nm. These absorption bands represent all the π→π* electronic transitions of these LCs. Resonance wavelength, absorption coefficient, and dichroic ratio of each band were characterized. The contribution of each band to LC birefringence is briefly discussed. Some structural effects on the LC absorption are illustrated. These absorption spectra will also serve as valuable data bases for further theoretical calculations on the band structure of LC molecules.

Physical properties of diphenyldiacetylenic liquid crystals

Optical and electro‐optic properties of two highly conjugated diphenyldiacetylenic liquid crystals (LCs) [1.4‐bis‐(4‐propylphenyl)‐butadiyne, abbreviated as PTTP‐mm] and their eutectic mixture were characterized in the nematic range. These LCs are found to exhibit extraordinarily high birefringence and very low viscoelastic coefficient. Their figure of merit is significantly higher than that of the widely used commercial LC mixture BDH‐E7. Potential application of PTTP‐mm in modulating infrared radiation is addressed.

Liquid-crystalline reference compounds

Abstract A polar (PCH-5) and a non-polar (152) compound are introduced as liquid-crystalline bench-mark compounds. The materials chosen are affordable, stable, easy to handle and possess nematic mesophases between 30–54·9 and 24–103·4°C. All relevant macroscopic physical properties, such as refractive indices n o n e, dielectric permittivities ∥⊊, elastic constants K 11, K 22 and K 33, and bulk and rotational viscosities are given as a function of temperature, wavelength and frequency, when applicable. The reference compounds are available from E. Merck, Darmstadt.

Liquid crystals for active matrix displays

Abstract Active matrix liquid crystal displays belong to one of the fastest growing fields in display research and development. Several pocket TVs using this technology are already available commercially. High quality displays for TV and instrumentation require an understanding and optimization of liquid crystal material parameters. We have, therefore, investigated the influence of the elastic, dielectric and optic properties on the electrical resistance of the liquid crystal as well as on the response times and the viewing angle dependence of active matrix displays. Based on correlations derived from our investigations, we have developed new liquid crystals which have suitable properties and a very high electrical resistivity.

Liquid Crystals with Polar Substituents Containing Fluorine: Synthesis and Physical Properties

Abstract Liquid crystalline compounds with various polar terminal groups containing fluorine have been prepared (see below formula 1 with Z = S‒CHF2, S‒CF3, SO‒CHF2, SO‒CF3, SO2‒CHF2, SO2‒CF3, SO2F, OCH2CF3, CO‒OCH2CF3, CO‒CF3, CO‒CF2Cl, CO‒CF2H, CO‒CF2‒CH3, CO‒CF2‒C3H7). The synthesis of these compounds is outlined here and their physical properties (phase transitions, dielectric anisotropy, birefringence, viscosity) are discussed.

New fluorinated heterocyclic compounds for improved FLC mixtures

New suitable homologues of SmC host materials including different classes of fluorinated and non-fluorinated alkyl-alkyloxy-phenylpyrimidines were developed. Some materials were chosen to develop a new SmC host mixture. Several new chiral dopants have been synthesized. We found an influence of the different ring-systems and various side chains on the physical properties. Chiral dopants with more than one chiral center exhibit interesting properties. One dopant with a fluorine atom at the chiral center and a biphenyl-cyclohexane core showed the best properties and was chosen to introduce, together with the new SmC host mixture, new FLC-mixtures with improved properties. By using low-volt multiplex driving schemes and also high-volt multiplex driving schemes it is shown that these mixtures with an adjustable Ps fulfill the requirements for both methods.

A simple method to estimate and optimize the optical slope of TN-cells and its comparison with experimental results

Abstract It is shown that the initial slope of the mid-plane tilt angle of a nematic TN-cell correlates well with the associated optical slope for a given cell. Upon determination of the mid-plane tilt angle from the physical parameters of the liquid crystal and the cell-specific correlation coefficients it is easily possible to estimate the optical slope for any material. Cell performance can be optimized qualitatively in terms of the elastic constants, the dielectric anisotropy, and the twist angle.