Liquid crystalline (E, E)-butadiene compounds and mixtures and devices containing such compounds

The present invention describes new compounds. In particular it describes 
compounds for use in liquid crystal mixtures and in liquid crystal 
displays (LCDs) or in applications relating to inter alia thermography 
utilising nematic liquid crystal or chiral nematic liquid crystal 
mixtures. 
BACKGROUND OF THE INVENTION 
LCDs, such as multiplexed Twisted Nematic TN-LCDs, Super Twisted Nematic 
STN-LCDs, Super Birefringent SBE-LCDs, Electrically Controlled 
Birefringence ECB-LCDs, or flexoelectric LCDs are currently used or being 
developed for computer monitors, laptop or notebook computers, portable 
telephones, personal digital assistants, etc. The optical, electrical and 
temporal performance, e.g., contrast, threshold and driving voltages, and 
response times, of such displays depends crucially on the ratios of the 
elastic constants (k.sub.33, k.sub.22, k.sub.11) and the cell gap, d. 
Currently commercially available nematic mixtures for sophisticated 
high-information-content LCDs, such as STN-LCDs, incorporate 
trans-1,4-disubstituted-cyclohexyl derivatives with a terminal alkenyl 
chain (i.e., incorporating a carbon--carbon double bond) directly attached 
to the cyclohexane ring in order to produce the necessary elastic constant 
ratios for short response times, high multiplexing rates and low driving 
voltages. Such materials are costly and difficult to synthesise due to the 
requirement for a trans configuration of the 1,4-disubstituted cyclohexane 
ring and the necessity of synthesising the carbon--carbon double bond 
stepwise from this trans-1,4-disubstituted-cyclohexyl intermediate. If the 
carbon--carbon double bond is substituted at both carbon atoms, it must 
have a trans (E) configuration in order to exhibit an advantageous 
combination of elastic constants and to have an acceptably high 
nematic-isotropic transition temperature (N-I). The trans configuration is 
then generally produced by isomerisation of the cis (Z) form generated by 
the preceding Wittig reaction. These materials exhibit low or intermediate 
values of birefringence (.DELTA.n) due to the presence of the saturated 
cyclohexane rings. As the ratio d..DELTA.n determines the optical 
properties of TN-LCDs and is fixed for driving the LCD in the first or 
second minimum, it is clear that higher values of .DELTA.n would allow 
smaller cell gaps. As the response time, t.sub.on of TN-LCDs is inversely 
proportional to d.sup.2, smaller cell gaps have a dramatic effect on 
t.sub.on. Low values of t.sub.on also allow the use of colour or more 
shades of colour due to the shorter frame times. 
Liquid crystals with a (E,E)-butadiene chain are known and are described in 
for example W. Meier and K. Markau Z. Phys. Chem. N. F., (1961), Vol. 28, 
pp 190, Y. Goto and T. Ogawa, EPA 0 280 902 (1988). 
For all the above applications it is not usual for a single compound to 
exhibit all of the properties highlighted, normally mixtures of compounds 
are used which when mixed together induce the desired phases and required 
properties.

DETAILED DESCRIPTION OF THE INVENTION 
According to this invention materials are provided of Formula I: 
##STR2## 
wherein n may be 1-5; 
m may be 1-5; 
p may be 0, 1 or 2; 
q may be 0, 1 or 2; 
p+q is less than or equal to 3; 
A.sub.1, A.sub.2, A.sub.3 are independently chosen from 1,4-disubstituted 
benzene, 2,5-disubstituted pyrimidine, 2,5-disubstituted pyridine, 
2,6-disubstituted naphthalene which may be laterally substituted with F, 
Cl, Br or CN, trans-1,4-disubstituted cyclohexane, 2,5-disubstituted 
dioxane, 2,5-disubstituted thiophene, 2,5-disubstituted furan, 
2,5-disubstituted thiodiazole; 
Z.sub.1 may be COO, OOC, OCH.sub.2, O; 
Z.sub.2, Z.sub.3 are independently chosen from a direct bond, COO, OOC, 
C.sub.2 H.sub.4, CH.sub.2 O, OCH.sub.2, C.sub.4 H.sub.8, C.sub.3 H.sub.6 
O, (E)--CH.dbd.CHC.sub.2 H.sub.4, (E)--CH.dbd.CHCH.sub.2 O, --C.tbd.C--; 
R.sub.1 may be alkyl, alkoxy, alkenyl, alkenyloxy, alkanoyl, alkenoyl, F, 
Cl, Br, CN, OCHF.sub.2, OC.sub.w F.sub.2w+1, NCS or CH.dbd.C(CN).sub.2, 
CH.dbd.CF.sub.2, (E)--CH.dbd.CHCl; R.sub.1 may contain up to 20 carbon 
atoms and may be branched or a straight chain and w may be 1-7. 
The structural and other preferences are expressed below on the basis of 
inter alia desirable liquid crystalline characteristics, in particular an 
advantageous combination of elastic constants and high birefringence in 
the nematic phase, a wide nematic phase, a high nematic-isotropic liquid 
transition temperature and ready synthesis from commercially available 
starting materials already incorporating at least one carbon--carbon 
double bond with the desired configuration and position. 
Preferably n is 1-3; 
Preferably when Z.sub.1 is 0 m is 1 and when Z.sub.1 is COO m is 0; 
Preferably n+m is .ltoreq.5; 
Preferably p is 0 or 1; 
Preferably q is 0 or 1; 
Preferably p+q is 0 or 1; 
Preferably A.sub.1, A.sub.2, A.sub.3, are 1,4-disubstituted benzene or 
trans-1,4-disubstituted cyclohexane; 
Preferably Z.sub.2, Z.sub.3 are direct bonds or C.sub.2 H.sub.4 ; 
Preferably R.sub.1 is nitrile or alkyl or alkoxy. 
Overall preferred structures for formula I are those listed below: 
##STR3## 
Compounds of formula I can be prepared by various routes. Typically the 
ethers can be prepared by the Mitsunobu reaction (Synthesis, (1981) pp 1) 
of a phenol with an alka-2,4-dienol in the presence of triphenyl 
phosphine, a dehydrating agent, such as diethyl azodicarboxylate, and a 
suitable solvent, such as tetrahydrofuran or N,N'-dimethylformamide. 
Alternatively they can be synthesised by alkylation of a secondary alcohol 
or phenol with the tosylate of the appropriate alka-2,4-dienol in the 
presence of a suitable base, such as potassium tert.-butoxide, and a 
suitable solvent, such as tert.-butyl-methyl ether or 1,2-dimethoxyethane 
(J. Mater. Chem., (1994) Vol. 4, pp 1673). The esters can be prepared by 
esterification (Angewandte Chemie (1978) Vol. 90, pp 556) of the 
appropriate phenol or secondary alcohol with an alkenoic acid in the 
presence of 4-(dimethylamino)pyridine, a dehydrating agent, such as 
N,N'-dicyclohexylcarbodiimide, and a suitable solvent, such as 
dichloromethane or N,N'-dimethylformamide. Alternatively they can be 
synthesised by esterification of the appropriate phenol or secondary 
alcohol with an alkenoic acid chloride (produced, for example, from the 
corresponding alkenoic acid by the action of thionyl chloride or oxalyl 
chloride) in the presence of a base, such as pyridine or triethylamine, 
and a suitable solvent, such as toluene or dichloromethane. 
In the following examples C signifies the crystalline state, N the nematic 
phase, I the isotropic phase, S the smectic phase and .DELTA.T.sub.NI the 
temperature range of the nematic phase. 
The invention will now be described, by way of example only, with reference 
to the following examples. 
EXAMPLE 1 
Preparation of 4-cyano-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
Triphenylphosphine (0.95 g, 0.0036 mol) was added in small portions to a 
solution of (E,E)-hexa-2,4-dien-1-ol (0.40 g, 0.0040 mol), 
4-cyano-4'-hydroxybiphenyl (0.71 g, 0.0036 mol), diethylazodicarboxylate 
(0.63 g, 0.0036 mol) in dry diethyl ether (40 cm.sup.3), cooled in an ice 
bath under an atmosphere of nitrogen. The reaction mixture was stirred at 
room temperature overnight. The solvent was removed under reduced pressure 
and the crude product was purified by column chromatography on silica gel 
using a 4:1 petroleum (40-6020 C.) ether/ethyl acetate mixture as eluent, 
followed by recrystallisation from ethanol to yield 0.19 g (19%) of the 
pure ether, K 125.degree. C., N-I 152.degree. C. 
The following compounds could be obtained analogously: 
4-Cyano-4'-[(E,E)-hepta-2,4-dienyloxy]biphenyl. 
4-Cyano-4'-[(E,E)-octa-2,4-dienyloxy]biphenyl. 
4-Cyano-4'-[(E,E)-nona-2,4-dienyloxy]biphenyl. 
4-Cyano-4'-[(E,E)-deca-2,4-dienyloxy]biphenyl. 
4-Fluoro-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Chloro-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Bromo-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
3,4-Difluoro-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
3,4,5-Trifluoro-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Trifluoromethoxy-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Trifluoromethyl-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Trifluoroaceto-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Propyl-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Pentyl-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl, K 119.degree. C., S.sub.A 
-I 136.degree. C. 
4-Heptyl-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Methoxy-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Ethoxy-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Propoxy-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Butoxy-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Pentyloxy-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Hexyloxy-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Heptyloxy-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Octyloxy-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Nonyloxy-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-Decyloxy-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4-[(E)-But-2-enyloxy]-4'-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
4,4'-Di-[(E,E)-hexa-2,4-dienyloxy]biphenyl. 
1-(trans-4-Pentylcyclohexyl)-4-[(E,E)-hexa-2,4-dienyloxy]benzene, K 
71.degree. C., N-I 107.degree. C. 
EXAMPLE 2 
Preparation of 4'-cyanobiphenyl-4-yl(E,E)-hexa-2,4-dienoate 
A solution of N,N'-dicyclohexylcarbodiimide (0.87 g, 0.0042 mol) in 
dichloromethane (10 CM.sup.3) was added to a solution of 
(E,E)-hexa-2,4-dienoic acid (0.47 g, 0.0042 mol), 
4-cyano-4'-hydroxybiphenyl (0.67 g, 0.0035 mol), 4-(dimethylamino)pyridine 
(0.05 g) in dichoromethane (25 cm.sup.3), cooled in an ice bath (0.degree. 
C.) under an atmosphere of nitrogen. The reaction mixture was stirred 
overnight, filtered to remove precipitated material and the filtrate was 
evaporated down under reduced pressure. The crude product was purified by 
column chromatography on silica gel using dichloromethane as eluent, 
followed by recrystallisation from a 1:1 ethanol/ethyl acetate mixture to 
yield 0.76 g (76%). K 160.degree. C., N-I 227.degree. C. 
The following compounds could be obtained analogously: 
4-Cyanophenyl(E,E)-hexa-2,4-dienoate, K 111.degree. C. 
4-Cyanophenyl(E,E)-hepta-2,4-dienoate. 
4-Cyanophenyl(E,E)-octa-2,4-dienoate. 
2-Cyanonaphthyl-6-yl(E,E)-hexa-2,4-dienoate, K 116.degree. C., N-I 
141.degree. C. 
2-Cyanonaphthyl-6-yl(E,E)-hepta-2,4-dienoate. 
2-Cyanonaphthyl-6-yl(E,E)-octa-2,4-dienoate. 
Biphenyl-4-yl(E,E)-hexa-2,4-dienoate, K 110.degree. C., S.sub.A -N 
84.degree. C., N-I 92.degree. C. 
Biphenyl-4-yl(E,E)-hepta-2,4-dienoate. 
Biphenyl-4-yl(E,E)-octa-2,4-dienoate. 
4'-Propylbiphenyl-4-yl(E,E)-hexa-2,4-dienoate. 
4'-Pentylbiphenyl-4-yl(E,E)-hexa-2,4-dienoate, K 86.degree. C., N-I 16820 
C. 
4'-Heptylbiphenyl-4-yl(E,E)-hexa-2,4-dienoate. 
4'-Propyloxybiphenyl-4-yl(E,E)-hexa-2,4-dienoate. 
4'-Butyloxybiphenyl-4-yl(E,E)-hexa-2,4-dienoate. 
4'-Pentyloxybiphenyl-4-yl(E,E)-hexa-2,4-dienoate. 
4'-Hexyloxybiphenyl-4-yl(E,E)-hexa-2,4-dienoate. 
4'-Heptyloxybiphenyl-4-yl(E,E)-hexa-2,4-dienoate. 
4'-Octyloxybiphenyl-4-yl(E,E)-hexa-2,4-dienoate. 
4'-(Trifluoromethoxy)biphenyl-4-yl(E,E)-hexa-2,4-dienoate. 
4'-(Trifluoroaceto)biphenyl-4-yl(E,E)-hexa-2,4-dienoate. 
4'-Fluorobiphenyl-4-yl(E,E)-hexa-2,4-dienoate. 
3',4'-Difluorobiphenyl-4-yl(E,E)-hexa-2,4-dienoate. 
3',4',5'-Trifluorobiphenyl-4-yl(E,E)-hexa-2,4-dienoate. 
trans-4-Cyanocyclohexyl(E,E)-hepta-2,4-dienoate. 
trans-4-Cyanocyclohexyl(E,E)-octa-2,4-dienoate. 
trans-4-(4'-Cyanophenyl)cyclohexyl(E,E)-hexa-2,4-dienoate. 
trans-4-(4'-Fluorophenyl)cyclohexyl(E,E)-hexa-2,4-dienoate. 
trans-4-(4'-Trifluoromethoxyphenyl)cyclohexyl(E,E)-hexa-2,4-dienoate. 
trans-4-(4'-Trifluoroacetophenyl)cyclohexyl(E,E)-hexa-2,4-dienoate. 
4-(trans-4-Cyanocyclohexyl)phenyl(E,E)-hexa-2,4-dienoate. 
trans-4-(trans-4-Cyanocyclohexyl)cyclohexyl(E,E)-hexa-2,4-dienoate. 
4-(trans-4-Pentylcyclohexyl)phenyl(E,E)-hexa-2,4-dienoate, K 86.degree. C., 
N-I 172.degree. C. 
trans-4-(trans-4-Propylcyclohexyl)cyclohexyl(E,E)-hexa-2,4-dienoate. 
trans-4-(trans-4-Pentylcyclohexyl)cyclohexyl(E,E)-hexa-2,4-dienoate, K 
117.degree. C., N-I 180.degree. C. 
trans-4-(trans-4-Heptylcyclohexyl)cyclohexyl(E,E)-hexa-2,4-dienoate. 
trans-4-(trans-4-Propylcyclohexyl)cyclohexyl(E,E)-hepta-2,4-dienoate. 
trans-4-(trans-4-Pentylcyclohexyl)cyclohexyl(E,E)-hepta-2,4-dienoate. 
trans-4-(trans-4-Heptylcyclohexyl)cyclohexyl(E,E)-hepta-2,4-dienoate. 
trans-4-(trans-4-Propylcyclohexyl)cyclohexyl(E,E)-octa-2,4-dienoate. 
trans-4-(trans-4-Pentylcyclohexyl)cyclohexyl(E,E)-octa-2,4-dienoate. 
trans-4-(trans-4-Heptylcyclohexyl)cyclohexyl(E,E)-octa-2,4-dienoate. 
4-(trans-4-Propylcyclohexyl)phenyl(E,E)-hexa-2,4-dienoate. 
4-(trans-4-Heptylcyclohexyl)phenyl(E,E)-hexa-2,4-dienoate. 
4-(trans-4-Propylcyclohexyl)phenyl(E,E)-hepta-2,4-dienoate. 
4-(trans-4-Pentylcyclohexyl)phenyl(E,E)-hepta-2,4-dienoate. 
4-(trans-4-Heptylcyclohexyl)phenyl(E,E)-hepta-2,4-dienoate. 
4-(trans-4-Propylcyclohexyl)phenyl(E,E)-octa-2,4-dienoate. 
4-(trans-4-Pentylcyclohexyl)phenyl(E,E)-octa-2,4-dienoate. 
4-(trans-4-Heptylcyclohexyl)phenyl(E,E)-octa-2,4-dienoate. 
4-(5-Pentylpyrimidin-2-yl)phenyl(E,E)-hexa-2,4-dienoate. 
4-(2-Pentylpyrimidin-5-yl)phenyl(E,E)-hexa-2,4-dienoate. 
4-(5-Cyanopyrimidin-2-yl)phenyl(E,E)-hexa-2,4-dienoate. 
4-(2-Cyanopyrimidin-5-yl)phenyl(E,E)-hexa-2,4-dienoate. 
4-(5-Pentylpyridin-2-yl)phenyl(E,E)-hexa-2,4-dienoate. 
4-(2-Pentylpyridin-5-yl)phenyl(E,E)-hexa-2,4-dienoate. 
4-(5-Cyanopyridin-2-yl)phenyl(E,E)-hexa-2,4-dienoate. 
4-(2-Cyanopyridin-5-yl)phenyl(E,E)-hexa-2,4-dienoate. 
5-(4-Pentylphenyl)pyrimidin-2-yl(E,E)-hexa-2,4-dienoate. 
2-(4-Pentylphenyl)pyrimidin-5-yl(E,E)-hexa-2,4-dienoate. 
5-(4-Cyanophenyl)pyrimidin-2-yl(E,E)-hexa-2,4-dienoate. 
2-(4-Cyanophenyl)pyrimidin-5-yl(E,E)-hexa-2,4-dienoate. 
5-(4-Pentylphenyl)pyridin-2-yl(E,E)-hexa-2,4-dienoate. 
2-(4-Pentylphenyl)pyridin-5-yl(E,E)-hexa-2,4-dienoate. 
5-(4-Cyanophenyl)pyridin-2-yl(E,E)-hexa-2,4-dienoate. 
2-(4-Cyanophenyl)pyridin-5-yl(E,E)-hexa-2,4-dienoate. 
4-[(E,E)-hexa-2,4-dienoyloxy]phenyl(E,E)-hexa-2,4-dienoate, K 183.degree. 
C., N-I 186.degree. C. 
4-[(E,E)-hepta-2,4-dienoyloxy]phenyl(E,E)-hepta-2,4-dienoate. 
4-[(E,E)-octa-2,4-dienoyloxy]phenyl(E,E)-octa-2,4-dienoate. 
4-(5-Cyanothiophen-2-yl)phenyl(E,E)-hexa-2,4-dienoate, K 168.degree. C., 
N-I 18820 C. 
4-(5-Pentylthiophen-2-yl)phenyl(E,E)-hexa-2,4-dienoate, K 76.degree. C., 
N-I 125.degree. C. 
EXAMPLE 3 
Preparation of trans-, 
trans-4-(E,E)-hexa-2,4-dienyloxy-4'-pentyl-1,1'-bicyclohexane 
A mixture of toluene-4-sulfonic acid (E,E)-hexa-2,4-dienyl ester (1.0 g, 
4.0 mmol), trans-, trans-4-hydroxy-4'-pentyl-1,1'-bicyclohexane (0.37 g, 
1.5 mmol), potassium tert-butoxide (0.55 g, 4.5 mmol) and 
1,2-dimethoxyethane (20 cm.sup.3) is stirred at room temperature 
overnight, filtered to remove inorganic material, diluted with water (100 
cm.sup.3) and then extracted into diethyl ether (3.times.25 cm.sup.3). The 
combined organic extracts are washed with water (2.times.200 cm.sup.3), 
dried (MgSO.sub.4), filtered and then evaporated down. The residue is 
purified by column chromatography on silica gel using a 9:1 hexane/ethyl 
acetate mixture as eluent and recrystallisation from ethanol to yield 0.25 
g (51%) of the desired ether. 
The toluene-4-sulfonic acid (E,E)-hexa-2,4-dienyl ester required as 
starting material could be prepared as follows: 
A solution of toluene-4-sulfonyl chloride (0.75 g, 4.0 mmol) in 
dichloromethane (10 cm.sup.3) is added slowly to a solution of 
(E,E)-hexa-2,4-dienol (0.40 g, 4.0 mmol), triethylamine (0.80 g, 8.0 mmol) 
and dichloromethane (50 cm.sup.3) at 0.degree. C. The reaction mixture is 
stirred at 0.degree. C. for 6 h, washed with dilute hydrochloric acid 
(2.times.50 cm.sup.3), water (2.times.50 cm.sup.3) and dilute sodium 
carbonate solution (2.times.50 cm.sup.3), dried (MgSO.sub.4), filtered and 
then evaporated down to yield 1.0 g (99% ) of the desired tosylate, which 
is used without further purification. 
The following compounds could be obtained analogously: 
trans-, trans-4-[(E,E)-Hexa-2,4-dienyloxy]-4'-propyl-1,1'-bicyclohexane. 
trans-, trans-4-[(E,E)-Hexa-2,4-dienyloxy]-4'-pentyl-1,1'-bicyclohexane. 
trans-, trans-4-[(E,E)-Hexa-2,4-dienyloxy]-4'-heptyl-1,1'-bicyclohexane. 
trans-, trans-4-[(E,E)-Hepta-2,4-dienyloxy]-4'-propyl-1,1'-bicyclohexane. 
trans-, trans-4-[(E,E)-Hepta-2,4-dienyloxy]-4'-pentyl-1,1'-bicyclohexane. 
trans-, trans-4-[(E,E)-Hepta-2,4-dienyloxy]-4'-heptyl-1,1 '-bicyclohexane. 
trans-, trans-4-[(E,E)-Octa-2,4-dienyloxy]-4'-propyl-1,1'-bicyclohexane. 
trans-, trans-4-[(E,E)-Octa-2,4-dienyloxy]-4'-pentyl-1,1'-bicyclohexane. 
trans-, trans-4-[(E,E)-Octa-2,4-dienyloxy]-4'-heptyl-1,1'-bicyclohexane. 
trans-1-[(E,E)-Hexa-2,4-dienyloxy]-4-propylcyclohexane. 
trans-1-[(E,E)-Hexa-2,4-dienyloxy]-4-pentylcyclohexane. 
trans-1-[(E,E)-Hexa-2,4-dienyloxy]-4-heptylcyclohexane. 
trans-, trans-4,4'-di-[(E,E)-Hexa-2,4-dienyloxy]-1,1'-bicyclohexane. 
trans-, trans-4,4'-di-[(E,E)-Hepta-2,4-dienyloxy]-1,1'-bicyclohexane. 
trans-, trans-4,4'-di-[(E,E)-Octa-2,4-dienyloxy]-1,1'-bicyclohexane. 
trans-1,4-di-[(E,E)-Hexa-2,4-dienyloxy]cyclohexane. 
trans-1,4-di-[(E,E)-Hepta-2,4-dienyloxy]cyclohexane. 
trans-1,4-di-[(E,E)-Octa-2,4-dienyloxy]cyclohexane. 
4-(trans-4-[E,E)-Hexa-2,4-dienyloxy]cyclohexyl)benzonitrile. 
4-(trans-4-[E,E)-Hepta-2,4-dienyloxy]cyclohexyl)benzonitrile. 
4-(trans-4-[E,E)-Octa-2,4-dienyloxy]cyclohexyl)benzonitrile. 
1-Fluoro-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Chloro-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Bromo-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1,2-Difluoro-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1,2,6-Trifluoro-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Trifluoromethoxy-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Trifluoromethyl-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Trifluoroaceto-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Propyl-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Pentyl-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Heptyl-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Methoxy-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Ethoxy-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Proxy-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Butoxy-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Pentyloxy-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Hexyloxy-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Heptyloxy-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
1-Octyloxy-4-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)benzene. 
4-Cyano-4'-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl. 
4-Fluoro-4'-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl. 
4-Chloro-4'-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl. 
4-Bromo-4'-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl. 
4-Trifluoromethoxy-4'-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl 
. 
4-Trifluoromethyl-4'-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl. 
4-Propyl-4'-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl. 
4-Pentyl-4'-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl. 
4-Heptyl-4'-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl. 
4-Methoxy-4'-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl. 
4-Ethoxy-4'-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl. 
4-Propoxy-4'-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl. 
4-Butoxy-4'-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl. 
4-Pentyloxy-4'-(trans-4-[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl. 
4-Hexyloxy-4'-(trans-4[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl. 
4-Heptyloxy-4'-(trans-4[E,E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl. 
4-[trans-4-(trans-4-[(E,E)-Hexa-2,4-dienyloxy]cyclohexyl)cyclohexyl]benzoni 
trile. 
1-Fluoro-4-[trans-4-(trans-4-[(E,E)-hexa-2,4-dienyloxy]cyclohexyl)cyclohexy 
l]benzene. 
1-Chloro-4-[trans-4-(trans-4-[(E,E)-hexa-2,4-dienyloxy]cyclohexyl)cyclohexy 
l]benzene. 
1-Bromo4-[trans-4-(trans-4-[(E,E)-hexa-2,4-dienyloxy]cyclohexyl)cyclohexyl] 
benzene. 
1-Trifluoromethoxy-4-[trans-4-(trans-4-[(E,E)-hexa-2,4-dienyloxy]cyclohexyl 
)cyclohexyl]benzene. 
1-Trifluoromethyl-4-[trans-4-(trans-4-[(E,E)-hexa-2,4-dienyloxy]cyclohexyl) 
cyclohexyl]benzene. 
1-Trifluoroaceto-4-[trans-4-(trans-4-[(E,E)-hexa-2,4-dienyloxy]cyclohexyl)c 
yclohexyl]benzene 
4-(trans-5-[E,E)-Hexa-2,4-dienyloxy]dioxan-2-yl)benzonitrile. 
4-(trans-5-[E,E)-Hepta-2,4-dienyloxy]dioxan-2-yl)benzonitrile. 
4-(trans-5-[E,E)-Octa-2,4-dienyloxy]dioxan-2-yl)benzonitrile. 
1-Fluoro-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Chloro-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Bromo-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1,2-Difluoro-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1,2,6-Trifluoro-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Trifluoromethoxy-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Trifluoromethyl-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Trifluoroaceto-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Propyl-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Pentyl-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Heptyl-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Methoxy-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Ethoxy-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Proxy-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Butoxy-4-(trans-5[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Pentyloxy-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Hexyloxy-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Heptyloxy-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
1-Octyloxy-4-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene. 
4-Cyano-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl. 
4-Fluoro-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl. 
4-Chloro-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl. 
4-Bromo-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl. 
4-Trifluoromethoxy-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)bipheny 
l. 
4-Trifluoromethyl-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl 
. 
4-Propyl-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl. 
4-Pentyl-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl. 
4-Heptyl-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl. 
4-Methoxy-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl. 
4-Ethoxy-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl. 
4-Propoxy-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl. 
4-Butoxy-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl. 
4-Pentyloxy-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl. 
4-Hexyloxy-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl. 
4-Heptyloxy-4'-(trans-5-[E,E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl. 
4-[trans-4-(trans-5-[(E,E)-Hexa-2,4-dienyloxy]dioxan-2-yl)cyclohexyl]benzon 
itrile. 
TABLE 1 
______________________________________ 
Transition temperatures for the compounds below: 
##STR4## 
Com- C--N/ N--I/ 
.DELTA.T.sub.NI / 
pound R .degree. C. 
.degree. C. 
.degree. C. 
______________________________________ 
##STR5## 58 77 19 
##STR6## 74 82 8 
##STR7## 74 81 7 
##STR8## 125 152 27 
______________________________________ 
TABLE 2 
______________________________________ 
Transition temperatures for the compounds below: 
##STR9## 
Com- C--N/ N--I/ 
.DELTA.T.sub.NI / 
pound R .degree. C. 
.degree. C. 
.degree. C. 
______________________________________ 
##STR10## 53 71 18 
##STR11## 92 131 39 
##STR12## 97 (74) -- 
##STR13## 160 227 67 
______________________________________ 
TABLE 3 
______________________________________ 
Transition temperatures for the compounds below 
##STR14## 
Compound 
X C--N/I.degree. C. 
S.sub.A --N/.degree. C. 
N--I/.degree. C. 
.DELTA.T.sub.NI /.degree. 
______________________________________ 
C. 
H 110 (84) (92) -- 
CN 160 227 67 
______________________________________ 
() Represents a monotropic transition temperature 
TABLE 4 
__________________________________________________________________________ 
Transition temperatures for the compounds below: 
##STR15## 
Compound 
X C--N/I.degree. C. 
N--I/.degree. C. 
.DELTA.T.sub.NI /.degree. C. 
__________________________________________________________________________ 
##STR16## 111 -- -- 
##STR17## 116 141 27 
##STR18## 160 227 67 
__________________________________________________________________________ 
TABLE 5 
______________________________________ 
Transition temperatures for the compounds below 
##STR19## 
Compound Z.sub.1 Z.sub.2 C--N/I/.degree. C. 
N--I .DELTA.T.sub.NI /.degree. C. 
______________________________________ 
OOC COO 86 -- -- 
COO OOC 183 186 3 
______________________________________ 
TABLE 6 
______________________________________ 
Transition temperatures for the compounds 
##STR20## 
##STR21## 
Compound 
##STR22## C--N/.degree. C. 
N--I/.degree. C. 
______________________________________ 
##STR23## 86 172 
##STR24## 117 180 
______________________________________ 
The following birefringence data was obtained: 
##STR25## 
Wt/% in ZLI3086=5 
Ext .DELTA.n 30.degree. C.=0.328 
Ext .DELTA.n 20.degree. C.=0.333 
Ext .DELTA.n T/T.sub.NI =0.8=0.298 wherein Ext .DELTA.n is a linear 
extrapolation in concentration of the birefringence in ZLI3086 which is a 
commercially available (from Mereck UK) apolar nematic host mixture. T is 
the temperature at which the measurement was taken (in Kelvin) and 
T.sub.NI is the phase transition for the nematic-isotropic phase (in 
Kelvin). 
One known device in which the materials of the current invention may be 
incorporated is the twisted nematic device which uses a thin layer of a 
nematic material between glass slides. The slides are unidirectionally 
rubbed and assembled with the rubbing directions orthogonal. The rubbing 
gives a surface alignment to the liquid crystal molecules resulting in a 
progressive 90.degree. twist across the layer. When placed between 
polarisers, with their optical axis perpendicular or parallel to a rubbing 
direction the device rotates the plane of polarised light in its OFF state 
and transmits without rotation in the ON state. Small amounts of 
cholesteric material may be added to the nematic material to ensure the 
90.degree. twist is of the same sense across the whole area of the device 
as explained in UK patents 1,472,247 and 1,478,592. 
An improvement in the performance of large, complex, nematic LCDs occurred 
in 1982 when it was observed that the voltage dependence of the 
transmission of nematic LC layers with twist angles in the range 
180.degree. to 270.degree. could become infinitely steep, see C. M. 
Waters, V. Brimmell and E. P. Raynes, Proc. 3rd Int. Display Res. Conf., 
Kobe, Japan, 1983, 396. The larger twist angles are produced by a 
combination of surface alignment and making the nematic mixture into a 
long pitch cholesteric by the addition of a small amount of a chiral 
twisting agent. The increasing twist angle steepens the 
transmission/voltage curve, until it becomes bistable for 270.degree. 
twist; for a specific twist angle between 225.degree. and 270.degree. the 
curve becomes infinitely steep and well suited to multiplexing. The larger 
twist angles present have resulted in the name supertwisted nematic (STN) 
for these LCDs. 
Liquid Crystal Devices describing the use of STNs may be found in patent 
application GB 8218821 and resulting granted patents including U.S. Pat. 
No. 4,596,446. 
The display of FIGS. 1 and 2 comprises a liquid crystal cell 1 formed by a 
layer 2 of cholesteric liquid crystal material contained between glass 
walls 3,4. A spacer ring 5 maintains the walls typically 6 .mu.m apart. 
Strip like row electrodes 6.sub.1 to 6.sub.m, e.g. of SnO.sub.2 are formed 
on one wall 3 and similar column electrodes 7.sub.1 to 7.sub.n formed on 
the other wall 4. With m-row electrodes and n-column electrodes this forms 
an mxn matrix of addressable elements. Each element is formed by the 
interaction of a row and column electrode. 
A row driver supplies voltage to each row electrode 6. Similarly a column 
drive 9 supplies voltages to each column electrode 7. Control of applied 
voltages is from a control logic 10 which receives power from a voltage 
source 11 and timing from a clock 12. 
An example of the use of a material and device embodying the present 
invention will now be described with reference to FIG. 2. 
The liquid crystal device consists of two transparent plates, 3 and 4, for 
example made from glass. These plates are coated on their internal face 
with transparent conducting electrodes 6 and 7. An alignment layer is 
introduced onto the internal faces of the cell so that a planar 
orientation of the molecules making up the liquid crystalline material 
will be approximately parallel to the glass plates 3 and 4. This is done 
by coating the glass plates 3,4 complete with conducting electrodes so 
that the intersections between each column and row form an x, y matrix of 
addressable elements or pixels. For some types of display the alignment 
directions are orthogonal. Prior to the construction of the cell the 
alignment layers are rubbed with a roller covered in cloth (for example 
made from velvet) in a given direction, the rubbing directions being 
arranged parallel (same or opposite direction) upon construction of the 
cell. A spacer 5 e.g. of polymethyl methacrylate separates the glass 
plates 3 and 4 to a suitable distance e.g. 2 microns. Liquid crystal 
material 2 is introduced between glass plates 3,4 by filling the space in 
between them. This may be done by flow filling the cell using standard 
techniques. The spacer 5 is sealed with an adhesive in a vacuum using an 
existing technique. Polarisers 13 may be arranged in front of and behind 
the cell. 
Alignment layers may be introduced onto one or more of the cell walls by 
one or more of the standard surface treatment techniques such as rubbing, 
oblique evaporation or as described above by the use of polymer aligning 
layers. 
In alternative embodiments the substrates with the aligning layers on them 
are heated and sheared to induce alignment, alternatively the substrates 
with the aligning layers are thermally annealed above the glass transition 
temperature and below the liquid crystal to isotropic phase transition in 
combination with an applied field. Further embodiments may involve a 
combination of these aligning techniques. With some of these combinations 
an alignment layer may not be necessary. 
The device may operate in a transmissive or reflective mode. In the former, 
light passing through the device, e.g. from a tungsten bulb, is 
selectively transmitted or blocked to form the desired display. In the 
reflective mode a mirror, or diffuse reflector, (16) is placed behind the 
second polariser 13 to reflect ambient light back through the cell and two 
polarisers. By making the mirror partly reflecting the device may be 
operated both in a transmissive and reflective mode. 
The alignment layers have two functions, one to align contacting liquid 
crystal molecules in a preferred direction and the other to give a tilt to 
these molecules--a so called surface tilt--of a few degrees typically 
around 4.degree. or 5.degree.. The alignment layers may be formed by 
placing a few drops of the polyimide on to the cell wall and spinning the 
wall until a uniform thickness is obtained. The polyimide is then cured by 
heating to a predetermined temperature for a predetermined time followed 
by unidirectional rubbing with a roller coated with a nylon cloth. 
In an alternative embodiment a single polariser and dye material may be 
combined. 
Cholesteric or chiral nematic liquid crystals possess a twisted helical 
structure which is capable of responding to a temperature change through a 
change in the helical pitch length. Therefore as the temperature is 
changed then the wavelength of the light reflected from the planar 
cholesteric structure will change and if the reflected light covers the 
visible range then distinct changes in colour occur as the temperature 
varies. This means that there are many possible applications including the 
areas of thermography and thermooptics. 
The cholesteric mesophase differs from the nematic phase in that in the 
cholesteric phase the director is not constant in space but undergoes a 
helical distortion. The pitch length for the helix is a measure of the 
distance for the director to turn through 360.degree.. 
By definition, a cholesteric material is chiral material. Cholesteric 
materials may also be used in electro-optical displays as dopants, for 
example in twisted nematic displays where they may be used to remove 
reverse twist defects, they may also be used in cholesteric to nematic 
dyed phase change displays where they may be used to enhance contrast by 
preventing wave-guiding. 
Thermochromic applications of cholesteric liquid crystal materials usually 
use thin film preparations of the cholesterogen which are then viewed 
against a black background. These temperature sensing devices may be 
placed into a number of applications involving thermometry, medical 
thermography, non-destructive testing, radiation sensing and for 
decorative purposes. Examples of these may be found in D G McDonnell in 
Thermotropic Liquid Crystals, Critical Reports on Applied Chemistry, Vol 
22, edited by G W Gray, 1987 pp 120-44; this reference also contains a 
general description of thermochromic cholesteric liquid crystals. 
Generally, commercial thermochromic applications require the formulation of 
mixtures which possess low melting points, short pitch lengths and smectic 
transitions just below the required temperature-sensing region. Preferably 
the mixture or material should retain a low melting point and high 
smectic-cholesteric transition temperatures. 
In general, thermochromic liquid crystal devices have a thin film of 
cholesterogen sandwiched between a transparent supporting substrate and a 
black absorbing layer. One of the fabrication methods involves producing 
an `ink` with the liquid crystal by encapsulating it in a polymer and 
using printing technologies to apply it to the supporting substrate. 
Methods of manufacturing the inks include gelatin microencapsulation, U.S. 
Pat. No. 3,585,318 and polymer dispersion, U.S. Pat. Nos. 1,161,039 and 
3,872,050. One of the ways for preparing well-aligned thin-film structures 
of cholesteric liquid crystals involves laminating the liquid crystal 
between two embossed plastic sheets. This technique is described in UK 
patent 2,143,323. 
For a review of thermochromism in liquid crystals see J G Grabmaier in 
`Applications of Liquid Crystals`, G Meier, E Sackmann and J G Grabmaier, 
Springer-Verlag, Berlin and New York, 1975, pp 83-158. 
The materials of the current invention may be used in many of the known 
devices including those mentioned in the introduction.