In this article we investigate the complexity of the molecular architectures of liquid crystals based on rod-like mesogens. Starting from simple monomeric systems founded on fluoroterphenyls, we first examine the effects of aromatic core structure on mesophase formation from the viewpoint of allowable polar interactions, and then we model these interactions as a function of terminal aliphatic chain length. By incorporating a functional group at the end of one, or both, of the aliphatic chains we study the effects caused by intermolecular interfacial interactions in lamellar phases, and in particular the formation of synclinic or anticlinic modifications. We then develop these ideas with respect to dimers, trimers, tetramers, etc. We show, for dendritic systems, that at a certain level of molecular complexity the local mesogenic interactions become irrelevant, and it is gross molecular shape that determines mesophase stability. The outcome of these studies is to link the complexity of the molecular interac...

Molecular complexity and the control of self-organising processes

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

The effect of fluorine substitution into a mesogenic system depends critically on the manner in which it is introduced. The relative stabilities of smectic and nematic phases may be inverted by altering the site of substitution, and lateral fluorination is particularly interesting for the strong suppression of smectic phase stability which can result. This effect has been applied to hydrocarbon mesogens to obtain new series of wide range, room temperature nematics of low viscosity and moderately high birefringence. These properties are readily conferred on mixtures, and the technical utility of fluorinated LC's is illustrated by reference to wide nematic range, fast switching mixtures having high birefringence, and suitable for static or multiplex drive.

Fluorination in Nematic Systems

The elastic constants k11, k22, k33 , the bulk and rotational viscosities, the birefringence, the static dielectric and electro-optical properties in TN-LCDs of new, positive dielectric and electro...

Polar Alkenyls: Physical Properties and Correlations with Molecular Structure of New Nematic Liquid Crystalsf

(R)-Binaphthyl derivatives as chiral dopants: substituent position controlled circularly polarized luminescence in liquid crystals.

A number of esters and other compounds containing a trans-1,4-substituted cyclohexane ring system-have been prepared, and the liquid crystal thermal stabilities of these new mesogens are discussed in relation to those of their analogues containing the 1,4-phenylene ring. The observed effects are discussed in terms of a possible thermal energy absorption by the cyclohexane ring in causing minor conformational changes. Other physical properties of these new mesogens are also discussed with particular reference to their potential in applications. In relation to electro-optical display devices, such properties as birefringence, dielectric anistropy, viscosity etc., are important parameters, and the new materials have been assessed in this context as possible additives to the 4-n-alkyl- and 4-n-alkyloxy-4′-cyanobiphenyls for producing a favorable combination of physical parameters. Also reported is a liquid crystal mixture which has a 100°C nematic range and which contains only materials which are ali...

Liquid Crystal Compounds Incorporating the Trans-1,4-Substituted Cyclohexane Ring System

The synthesis and some important properties of the l-(trans-4′-n-alkylcyclohexyl)-2-(4”-cyanophenyl)ethanes—where n-alkyl = C 1 to C 7—are described. These stable low melting materials have excellent properties comparable in many ways with those of the PCH materials wherein the cyclohexyl and phenyl rings are directly linked. The properties of the new series of materials, which we propose should be called the PECH compounds, are further elaborated in a companion paper by Raynes, et al, also presented at the Bangalore conference. In that paper it is made clear that the PECH materials have in fact higher order parameters and give superior order parameters for dissolved dyes compared with the PCH materials. The PECH compounds are therefore significant new nematogens to be considered for use in both twisted nematic and cholesteric-nematic dyed phase change displays.

D. G. Mcdonnell

Papers

Liquid Crystal Compounds Incorporating the Trans-1,4-Substituted Cyclohexane Ring System

The 1-(trans-4′-n-Alkylcyclohexyl)-2-(4”-cyanophenyl)ethanes— A New Series of Stable Nematogens of Positive Dielectric Anisotropy