The invention relates to a liquid-crystalline medium based on a mixture of polar compounds having negative dielectric anisotropy (Δe), which contains at least one compound selected from the group of compounds of the formula I, II A and II B and at least one compound of the formula I* in which R0, R1, R2, R1*, X1, X2, A1, A1*, A2*, Z1, Z1*, Z2*, L1*, L2*, p, q, v, m and m* are as defined in Claim 1, and to the use thereof for an active-matrix display based on the ECB, VA, PS-VA, FFS, PALC or IPS effect.

Liquid Crystalline Medium

This critical review begins with a brief, but essential, introduction to the special nature of liquid crystal materials, their peculiar properties, and their commercial applications, followed by an introductory insight into the remarkable nature of the fluoro substituent, and its fascinating influence on the properties of organic compounds. However, the main focus of the review is to discuss the enormous amount of exciting research on fluorinated liquid crystals that has been reported. The small size of the fluoro substituent enables its incorporation into all types of liquid crystal, including calamitic, discotic, banana, lyotropic, and polymers, without ruining the liquid crystalline nature of the material. However the fluoro substituent is larger than hydrogen, and hence causes a significant steric effect, which combined with the high polarity, confers many fascinating, and often remarkable, modifications to melting point, mesophase morphology and transition temperatures, and the many other very important physical properties, such as dielectric anisotropy, optical anisotropy, and visco-elastic properties. There are many different positions within a liquid crystal structure where a fluoro substituent can be located, including (i) a terminal position, (ii) within a terminal chain, as a semi-fluorinated or as a perfluorinated chain, or as one fluoro substituent at a chiral centre, (iii) as part of a linking group, and (iv) a lateral position in the core section. Such variety enables the interesting and advantageous tailoring of properties, both for the fundamental purposes of establishing structure–property relationships, and for materials targeted towards commercially-successful liquid crystal display applications.

Fluorinated liquid crystals – properties and applications

Substances forming calamitic mesophases have been known for more than 100 years but only the recent, rapid advance in active matrix liquid crystal display (AM-LCD) technology helped these materials to achieve the crucial position in flat panel display technology they hold today. Due to their high contrast, large viewing angle, and rapid switching times, modern AM-LCDs offer a superior picture quality even compared to conventional cathode ray tubes. Their flatness, low weight, and low energy consumption render them the technology of choice for all kinds of portable devices. Some of the future promises of AM-LCD technology are centered around the development of liquid crystalline materials for the different subtypes of active matrix applications. This development is aimed, on the one hand, towards improved electrooptical and viscoelastic properties; on the other hand, the increasing performance of LCDs leads to extremely stringent reliability demands on the liquid crystals. Responding to these high standards of performance and quality, most liquid crystals for contemporary AM-LCD applications are multiply fluorinated compounds with very high purities, as is typical for materials used in the electronics industry. The synthesis of these superfluorinated materials (SFMs) often requires specialized methods, which, in several cases, had to be introduced for the first time into the canon of industrial production. The immense market pressure, as well as the rapid advance of AM-LCD technology on the side of the display manufacturers, urges an increasing pace of the materials development. This demand for new materials can no longer be fulfilled by conventional trial-and-error approaches. As in the pharmaceutical industry, in the search for new, superior liquid crystals, the purely empirical methods are increasingly supported by a rational design based on computational methods.

Nematic Liquid Crystals for Active Matrix Displays: Molecular Design and Synthesis.

This article describes the use of nematic liquid crystals in the Twisted Nematic Liquid Crystal Display (TN-LCD) since the large majority of instruments manufactured currently incorporating a liquid crystal display (LCD) utilise this type of device. The correlation between the electro-optical performance of these devices and the invention and synthesis of nematic liquid crystals with a continually improved property spectrum in order to meet constantly changing specifications is illustrated using the TN-LCD as an example of general trends and relationships.

Liquid crystals for twisted nematic display devices

Induction of smectic layering in nematic liquid crystals using immiscible components. 1. laterally attached side-chain liquid crystalline poly(norborn ene)s and their low molar mass analogs with hydrocarbon/fluorocarbon substi tuents

Mesomorphic derivatives of 2-substituted 5-p-alkyl(alkoxy or cyano)phenylpyridines, 1,4-disubstituted piperidines, and ethyl 5-p-alkylphenylthiophene-2-carboxylates have been synthesised and their liquid crystal properties compared with those of analogous benzene and cyclohexane derivatives. Intermediates in the pyridine derivative synthesis 2-thienyl- and 2-furylpyridines-have been found to be mesomorphic too. Some piperidine compounds containing the cyano group in the benzene ring exhibit a large (over + 30) positive dielectric anisotropy.

New Heterocyclic Liquid Crystalline Compounds

The paper reports synthesis of LC derivatives of different chemical classes containing terminal groups ‒OCHF2, ‒OCF3, ‒SCHF2, ‒OCnF2n +1 and ‒CnF2n + 1 and indicates their phase transition points and physico-chemical properties.

Synthesis and Properties of Liquid Crystals with Fluorinated Terminal Substituents

The liquid crystalline 6-alkoxynicotinic acids were prepared, and their transition temperatures measured. The isomeric 5-alkoxypicolinic acids are not mesomorphic. A series of 2, 6- and 2,5-disubstituted benzazoles were also synthesized. The effects of a molecule geometry, central linkages and a heteroatom on the mesomorphic properties of these compounds are discussed.

Nematic Liquid Crystals Containing Pyridine and Benzazole Rings

This paper presents a review of the work on the molecular design of liquid crystalline 2,5-disubstituted pyridine derivatives for the twisted nematic (TN) and super twisted nematic (STN) liquid crystal displays (LCDs) and examines in some detail the correlations between the molecular structure of pyridine derivatives and their physico-chemical properties.

Liquid crystalline 2,5-disubstituted pyridine derivatives

Liquid crystalline 2-(4-alkoxyphenyl)-5-alkylpyridines have been synthesized. They exhibit more smectogeneous properties than analogous pyrimidine derivatives but their melting and clearing points are comparable with those of the latter. A liquid crystalline phase formed by 2-alkyl-5-(4-alkyl- or alkoxyphenyl)pyridines has a higher thermal stability than the same of isomeric 2-arylpyridines. These pyridine derivatives form exclusively smectic mesophases. A formation of pyridinic ring in synthesized compounds was accomplished by heteroatom exchange in pyrilium salts. A series of intermediate compounds, 2-(5-alkylthienyl-2)-5-arylpyridines in particular, form liquid crystals also.

A. I. Pavluchenko

Papers

New Heterocyclic Liquid Crystalline Compounds

Synthesis and Properties of Liquid Crystals with Fluorinated Terminal Substituents

Nematic Liquid Crystals Containing Pyridine and Benzazole Rings

Liquid crystalline 2,5-disubstituted pyridine derivatives

New Liquid Crystalline Pyridine Derivatives