WO1991009008A1

WO1991009008A1 - 3'-fluorinated 4'-cyanosubstituted biphenyls

Info

Publication number: WO1991009008A1
Application number: PCT/GB1990/001946
Authority: WO
Inventors: George William Gray; Kenneth Johnson Toyne; Andrew Ifill; Damien Gerard Mcdonnell; Peter Edward Raynes; Robert Smith
Original assignee: The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland
Priority date: 1989-12-14
Filing date: 1990-12-13
Publication date: 1991-06-27
Also published as: GB8928283D0

Abstract

A 3'-fluorinated 4'-cyanosubstituted biphenyl compound is disclosed, having formula (I), in which R1 is selected from C1-7 alkyl and C2-7 alkoxy and may be straight chain (n), branched (iso) or asymmetrically substituted (chiral).

Description

3 '-FLϋORINATED 4 '-CYAKOSUBSTITϋTED BIPHENYLS

This invention relates to novel 3'-fluorinated 4'-cyanosubstituted biphenyls which show liquid crystalline properties and to liquid crystal materials which incorporate them, in particular such materials which show a nematic phase. Such materials are used industrially in electro-optic displays.

The use in liquid crystal materials of 4-alkyl and 4-alkoxy 4'-cyanobiphenyls is described in GB 1433130 among others. GB 1433130 suggests the possibility of lateral substitution of the phenyl rings with methyl or an unspecified halogen, but no example of such a substituted compound is given.

Mol Cryst Liq Cryst (1985) 123 168-177 describes 2 and 2' fluoro-substituted 4-alkyl-4'-cyanobiphenyls,

where one of the fluorosubstituents (F) is present. WO 89/08102 discloses the compound :

prepared as an intermediate from which the methoxy group is removed to form the phenol, from which esters of formula :

having liquid crystalline properties are prepared. This intermediate is not described as having liquid crystalline properties.

The present invention has identified a class of biphenyls which on the basis of the prior art discussed above appear to be novel and show advantageous properties.

According to this invention, 3'-fluorinated 4'-cyanosubstituted biphenyls are provided, of formula I:

wherein R.. is selected from C., - alkyl and C₂_₇ alkoxy.

R-. may be straight chain (n), branched (iso) or assymetrically substituted (chiral). Preferably R.. is n-alkyl or alkoxy, or if chiral is 2-methylbutyl or 2-methylbutylox .

A suitable method for preparation of compounds of formula I is one in which a boronic acid of formula II :

is coupled with a para-halobenzonitrile of formula III

CN III

wherein X is chlorine, bromine or iodine, preferably bromine. The coupling is conveniently carried out using a tetrakis (triphenylphosphine) palladium (0) catalyst. Methods of preparing compounds of formula II and III, and of performing the coupling are described in WO 89/08102 on pages 9-11 thereof with respect to the known R- = methoxy compound.

Another aspect of this invention is a liquid crystalline material, containing at least two components at least one of which is a compound of formula I. This liquid crystalline material is preferably a nametic or cholesteric liquid crystalline material. Such materials may be used on electro-optic display devices such as watches and calculators etc, and also in thermochromic displays, or in light modulating materials comprising polymer dispersed liquid crystal droplets.

Compounds of formula I, in particular the preferred compounds referred to above, have a number of desirable properties which make them very useful components of liquid crystal materials. They often have higher nematic to isotropic (N-I) clearing point temperatures and lower melting points (C-N) than their unfluorinated counterparts. They generally have a high birefringence. They also generally show a higher solubility in commonly used liquid crystal materials than their unfluorinated counterparts. These advantages are not suggested by the prior art referred to above.

Suitable compounds for the other components of the liquid crystal material will be apparent to those skilled in the field, and will depend upon the properties such as dieletric anisotrophy, birefringence, working temperature range etc required in the material for the application for which the material is intended. Some types of suitable material are discussed briefly below.

Preferably as well as containing one or more formula I compounds the mixture contains one or more compounds of formula IV :

wherein R, is alkyl or alkoxy, preferably containing 1 to 8 carbon atoms, and preferably straight chain, and wherein m is 0 or 1. Such compounds are included in the subject matter of GB 1433130.

Compounds of formula I have a positive dielectric anisotrophy, and the material may for example contain other liquid crystalline compounds which have a positive dielectric anisotrophy, for example as described in EP-A-0132377, particularly in Figure 8 thereof and the related text.

The material may alternatively or also contain liquid crystalline compounds of low dielectric anisotrophy, for example to form a mixture of intermediate dielectric anisotrophy, or a thermochromic mixture. Some examples of such compounds are described in EP-A-0132377, particularly in Figure 9 thereof and the related text.

The material may alternatively or also contain liquid crystalline compounds having a high clearing point, for example to raise the N-I transition temperature. Some examples of such compounds are described in EP-A-0132377, particularly in Figure 10 thereof and the related text.

To cause the material of this aspect of the invention to show a cholesteric (Ch) (or chiral nematic) phase the material must contain at least one compound containing an asymmetric carbon atom. This may be a chiral compound of formula I, or alternatively or also the material may for example contain one or more chiral compound of formula V above, e.g. (+) or (-) _n____ψwt,

PCT/GB90/01946

- 7 -

4-(2-methylbutyl)-4'-cyano biphenyl or 4-(2-methylbutyloxy)-4'-cyano biphenyl.

The material may also contain one or more pleochroic dyes, for example the dyes described in EP-A-82300891.7.

The proportions of these components used in the material of this aspect of the invention will depend upon the intended application, and the material may use fully contain two or more compounds of formula I having different substituents R. on the biphenyl system.

The materials of this aspect of the invention may be used in any of the known forms of liquid crystal display device, for example a twisted nematic effect device, Freedericksz effect device, cholesteric memory mode device, cholesteric to nematic phase change effect device, dynamic scattering effect device, two frequency switching effect device, a "supertwist" effect device, or a thermometer using a thermochromic material. The method of construction and operation of such devices, and characterstics of a liquid crystal material suitable for use therein, are well known in the field. A liquid crystal display device which incorporates as its working fluid a material as described above, constitutes a third aspect of this invention. The invention will now be described by way of example only.

Example 1

4-bromo-2-fluorobenzonitrile was prepared using the method described on page 10-11 of WO 89/08102.

4-alkyl and 4-alkoxy phenylboronic acids of formula II, having R. as n-propyl, n-pentyl and n-heptyloxy were prepared from the corresponding parabromophenyls using the method described on page 9 of WO 89/08102.

The coupling reaction using tetrakis (triphenylphosphine)palladium (0) was carried out analogously to the method described on page 11 of WO 89/08102.

The following compounds were prepared, having properties as indicated. = solid crystal, N = nematic liquid crystal, I = isotropic liquid, = dielelectric anisotrophy.

17.7

Claims

1. A 3 ' -fluorinated 4'-cyanosubstituted biphenyl compound having a formula :-

Formula I

in which R.. is selected from C, ₇ alkyl and C- ₇ alkoxy and may be straight chain (n), branched (iso) or asymmetrically substituted (chiral).

2. A compound according to claim 1, in which R.. is n-alkyl or n-alkoxy.

3. A compound according to claim 1 or claim 2, in which R- is 2-methylbutyl or 2-methylbutyloxy.

4. A nematic or cholesteric liquid crystalline material being a mixture of at least two compounds chracteristed in that at least one compound is a

3 ' -fluorinated 4'-cyanosubstituted biphenyl compound of formula :-

in which R₁ is selected from C. ₇ aklyl and C₂_₇ alkoxy and may be straight chain, branched or asym¬ metrically substituted, or may be n-alkyl or n-alkoxy, and preferably 2-methylbutyl or 2-methylbutyloxy.

5. A material according to claim 4, characterised in that it also contains at least one compound for formula :-

wherein R, is alkyl or alkoxy, containing 1 to 8 carbon atoms and may be straight chain; m is 0 or 1.

6. A liquid crystal electro-optical display device characterised in that it incorporates a material as claimed in claim 4.