Liquid crystalline esters

Compounds of the formula ##STR1## wherein m represents is the number 0 or 1; A is a single covalent bond, --CH.sub.2 --CH.sub.2 --, --OCH.sub.2 --, --COO-- or --OOC--; rings B, C and D are 1,4-phenylene optionally substituted with cyano, halogen or lower alkyl; Y.sup.1 and Y.sup.2 are hydrogen or one of them also is cyano; and R.sup.1 and R.sup.2 each represents C.sub.1 -C.sub.18 -alkyl or C.sub.2 -C.sub.18 alkenyl, either of which is optionally halogen-substituted, in which one CH.sub.2 group or two non-adjacent CH.sub.2 groups is/are optionally replaced by oxygen; with the provisos that at least one of R.sup.1 and R.sup.2 has a chiral carbon atom or a C--C double bond or both when A is --COO-- and at least one of R.sup.1 and R.sup.2 has a C--C double bond when A is a single covalent bond, their preparation, liquid crystalline mixtures containing these compounds and their use for electro-optical purposes are described.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to liquid crystalline compounds and mixtures 
as well as electro-optical devices. 
2. Description of the Art 
Liquid crystals are used primarily as dielectrics in indicating devices, 
since the optical properties of such substances can be influenced by an 
applied voltage. Electro-optical devices based on liquid crystals are 
well-known to the person skilled in the art and can be based on various 
effects such as, for example, dynamic scattering, the deformation of 
aligned phases (DAP cells), the SchadtHelfrich effect (TN cells, i.e, 
twisted-nematic, and STN cells i.e, super twisted-nematic), the guest/host 
effect (guest/host cells), a cholesteric-nematic phase transition 
(phase-change cells) or the SBE effect (super birefringence effect). 
Cholesteric liquid crystals are used, for example, in the above-mentioned 
phase-change cells. Further, cholesteric additives or other chiral 
substances with suitable choice of the concentration can also be used to 
improve the electro-optical properties of liquid crystals for TN cell 
indicators. Mematic liquid crystal components can be used in all of the 
aforementioned applications. 
The aforementioned indicating devices generally have response times in the 
order of several milliseconds or more. In order to improve the response 
times of indicating devices, liquid crystals with ferroelectric properties 
have recently also been used. In this application there are used chiral 
smectic phases, for example, smectic C, F or I phases, mainly smectic C 
phases. Hitherto, however, relatively few of such liquid crystals have 
become known and their stability is often inadequate. 
In order to be suitable for use in indicating devices liquid crystals 
should have a good chemical and thermal stability and a good stability 
towards electrical fields and electromagnetic radiation. Further, they 
should be colorless and have low viscosities and should give short 
response times and a high contrast in indicating devices. Furthermore, the 
liquid crystals should have a suitable mesophase, for example, a 
cholesteric or a suitable chiral smectic phase, at the usual operating 
temperatures. Because liquid crystals are usually employed in mixtures, it 
is important that the components have a good miscibility with one another. 
Other properties such as, for example, the threshold potential, the 
dielectric anisotropy and the optical anisotropy, must fulfill different 
conditions depending on the type of cell used. Liquid crystals with 
ferroelectric properties preferably have a negative dielectric anisotropy 
or a small absolute value of the dielectric anisotropies. 
SUMMARY 
The present invention provides tricyclic and tetracyclic esters of the 
formula 
##STR2## 
wherein m is for the number 0 or 1; A is a single covalent bond, 
--CH.sub.2 --CH.sub.2 --, --OCH.sub.2 --, --COO-- or --OOC--; rings B, C 
and D are 1,4-phenylene unsubstituted or substituted with cyano, halogen 
or lower alkyl; Y.sup.1 and Y.sup.2 are hydrogen or one of these 
substituents Y.sup.1 and Y.sup.2 also is cyano; and R.sup.1 and R.sup.2 
each individually represents C.sub.1 -C.sub.18 alkyl or C.sub.2 -C.sub.18 
alkenyl, either of which is optionally halogen-substituted, in which one 
CH.sub.2 group or two non-adjacent CH.sub.2 groups is/are optionally 
replaced by oxygen; with the provisos that at least one of R.sup.1 and 
R.sup.2 has a chiral carbon atom or a C--C double bond or both when A is 
--COO-- and at least one of R.sup.1 and R.sup.2 has a C--C double bond 
when A stands for a single covalent bond. 
DETAILED DESCRIPTION OF THE PRESENT INVENTION 
The compounds in accordance with the invention are suitable components for 
ferroelectric liquid crystals and themselves have, for the most part, a 
chiral smectic phase. They are, however, also suitable for cholesteric or 
nematic mixtures. They are optically active or optically inactive and have 
the requisite properties referred to above. 
The above term "halogen" embraces fluorine, chlorine or bromine. 
The term "lower alkyl" embraces alkyl groups with 1-5 carbon atoms such as 
methyl, ethyl, propyl and isopropyl, preferably methyl. 
The terminology "1,4-phenylene optionally substituted with cyano, halogen 
or lower alkyl" embraces groups such as 1,4-phenylene, 
2-cyano-1,4-phenylene, 2,3-dicyano-1,4-phenylene, 2-fluoro-1,4-phenylene, 
2,3-difluoro-1,4-phenylene, 2-chloro-1,4-phenylene, 2-bromo-1,4-phenylene, 
2-methyl-1,4-phenylene, and the like. The compound 1,4-phenylene is 
generally preferred. However, the transition temperatures, solubility, 
dielectric anisotropy, and the like, can be modified and higher ordered 
phases can be suppressed by using substituted groups. 
The terminology "alkyl or alkenyl in which optionally one CH.sub.2 group or 
two non-adjacent CH.sub.2 groups is/are replaced by oxygen" embraces 
straight-chain and branched groups such as alkyl, alkoxy, alkoxyalkyl, 
alkoxyalkoxy, alkenyl, alkenyloxy, alkoxyalkenyl, alkenyloxyalkyl, 
alkoxyalkenyloxy, and the like. Corresponding halogen-substituted groups 
are, for example, halogenoalkyl, halogenoalkoxy, halogenoalkenyl, 
halogenoalkenyloxy, and the like. 
Compounds of formula I in which Y.sup.1 or Y.sup.2 signifies cyano have a 
negative anisotropy of the dielectric constants. In general, however, 
Y.sup.1 and Y.sup.2 preferably are hydrogen. In many instances, C--C 
double bonds in R.sup.1 or R.sup.2, or both, lead to an improvement of the 
chiral smectic properties. 
A preferred group of compounds in accordance with the invention comprises 
those in which Y.sup.1 and Y.sup.2 are hydrogen and ring C and optionally 
present ring D are 1,4-phenylene. Ring B preferably denotes 1,4-phenylene, 
2-cyano-1,4-phenylene, 2,3-dicyano-1,4-phenylene, 2-halogeno-1,4-phenylene 
or 2,3-dihalogeno-1,4-phenylene. 
A further group of preferred compounds of formula I comprises those in 
which A is --CH.sub.2 CH.sub.2 --, --OCH.sub.2 -- or --OOC--, especially 
--CH.sub.2 CH.sub.2 -- or --OCH.sub.2 --. 
In formula I, above, m preferably is zero. 
A further preferred aspect is concerned with optically active compounds of 
formula I which have a chiral carbon atom in R.sup.1 and/or R.sup.2, or 
both. 
Preferred groups R.sup.1 or R.sup.2 having chiral carbon atoms are those 
groups of the general formulae 
##STR3## 
wherein n, p and q are whole numbers and n is zero or 1, p is zero to 6 
and q is 2 to 6; R.sup.3 is alkyl and R.sup.4 is halogen, alkoxy, alkenyl, 
alkenyloxy or alkyl different from R.sup.3 ; or R.sup.3 is alkenyl and 
R.sup.4 is alkoxy; R.sup.5 denotes alkyl; R.sup.6 denotes halogen, alkoxy 
or alkyl different from R.sup.5 ; and C* is the chiral carbon atom. 
Groups of formula II in which R.sup.3 is methyl and R.sup.4 is alkyl 
different from methyl, preferably ethyl, are especially preferred. 
In the case of optically active compounds of formula I, R.sup.1 preferably 
has a chiral carbon atom. Those compounds of formula I in which R.sup.1 is 
a group of formula II or III are, therefore, especially preferred. 
Alkyl, alkenyl, alkoxyalkenyl and alkenyloxyalkyl are preferred for 
R.sup.2. When R.sup.1 has a chiral carbon atom, R.sup.2 preferably is a 
straight-chain residue. 
In general, particularly preferred are those compounds of formula I in 
which R.sup.1 is a chiral or achiral alkoxy or alkenyloxy group and 
R.sup.2 is a chiral or achiral alkyl or alkenyl group. R.sup.2 is 
preferably achiral. 
A double bond optionally present in R.sup.1 or R.sup.2, or both, is 
preferably situated in position 1, 3 or 4 (including oxygen atoms which 
may be present) or in the terminal position of the side-chain R.sup.1 or 
R.sup.2, especially in position 4. Especially preferred unsaturated groups 
are, therefore, groups such as 1E-alkenyl, 3E-alkenyl, 4-alkenyl, 
2E-alkenyloxy, 3-alkenyloxy, alkoxy-3E-al-kenyl, alkoxy-4-alkenyl, 
alkoxy-3-alkenyloxy, 5-hexenyl, 4-pentenyloxy, 6-heptenyl, 5-hexenyloxy, 
7-octenyl, 6-hep-tenyloxy, 8-nonenyl, 7-octenyloxy, 9-decenyl, 
8-nonenyloxy, and the like. 
The groups R.sup.1 and R.sup.2 conveniently have a maximum of 18 carbon 
atoms in each case. The group or groups with a chiral carbon atom 
preferably have from 4 to 18, particularly 4 to 15, carbon atoms. An 
optionally present group R.sup.1 or R.sup.2 without a chiral carbon atoms 
preferably has a maximum of 12, particularly a maximum of 7, carbon atoms. 
For chiral smectic applications there are, however, generally preferred 
compounds of formula I which have in R.sup.1 and R.sup.2 together at least 
7, especially at least 10, carbon atoms. 
The compounds of formula I can be prepared in accordance with the invention 
by 
(a) esterifying a compound of the general formula 
##STR4## 
and a compound of the general formula 
##STR5## 
wherein A, R.sup.1, R.sup.2, Y.sup.1, Y.sup.2, m and rings B, C and D are 
as defined above, or reactive derivatives of these compounds and, if 
desired, reacting a compound of formula I in which ring B, C or D is 
1,4-phenylene substituted with chlorine or bromine, with copper(I) 
cyanide, sodium cyanide or potassium cyanide, or 
(b) for the manufacture of compounds of formula I in which A is an ester 
group --COO-- or --OOC--, esterifying a compound of the general formula 
##STR6## 
and a compound of the general formula 
##STR7## 
wherein one of Z.sup.1 and Z.sup.2 denotes the carboxyl group and the 
other denotes the hydroxy group and R.sup.1, R.sup.2, Y.sup.1, Y.sup.2, m 
and rings B, C and D are as defined above, or reactive derivatives of 
these compounds and, if desired, reacting a compound of formula I obtained 
in which ring B, C or D is 1,4-phenylene substituted with chlorine or 
bromine, with copper(I) cyanide, sodium cyanide or potassium cyanide. 
The reaction of the compounds of formulae IV and V or of the compounds of 
formulae VI and VII can be carried out in a known manner by esterifying 
the carboxylic acid or a reactive derivative thereof (e.g., acid chloride, 
bromide or anhydride) with the hydroxy compound or a suitable salt (e.g., 
the sodium salt). A preferred method comprises reacting the acid chloride 
(which is obtainable from the carboxylic acid, such as by heating with 
thionyl chloride) with the hydroxy compound. This reaction is conveniently 
carried out in an inert organic solvent, for example, one of which is 
diethyl ether, tetrahydrofuran, dimethylformamide, benzene, toluene, 
cyclohexane, carbon tetrachloride, and the like. In order to bind the 
hydrogen chloride liberated during the reaction, an acid-binding agent, 
for example, a tertiary amine, pyridine, and the like, is conveniently 
used. The acid-binding agent can also simultaneously serve as the solvent. 
Further preferred methods comprise reacting the carboxylic acid with the 
hydroxy compound in the presence of 4-(dimethylamino)pyridine and 
N,N'-dicyclohexylcarbodiimide or in the presence of oxalyl chloride and 
dimethylformamide. The temperature and pressure at which the above 
esterification reactions are carried out are not critical and, in general, 
are carried out at atmospheric pressure and a temperature between 
-30.degree. C. and the boiling temperature of the reaction mixture. 
The reaction of a compound of formula I in which ring B, C or D is 
1,4-phenylene substituted with chlorine or bromine to give the 
corresponding cyano-substituted compound is conveniently carried out with 
copper(I) cyanide, sodium cyanide or potassium cyanide, in an inert 
organic solvent such as ethylene glycol, tetrahydrofuran, 
dimethylformamide, dimethyl sulphoxide, pyridine or acetonitrile. The 
temperature and pressure are not critical. Atmospheric pressure and a 
temperature between room temperature and the boiling temperature of the 
reaction mixture are conveniently used. 
The starting materials of formulae IV-VII are known compounds or analogs of 
known compounds and can be prepared according to known methods. 
The compounds in accordance with the invention can be used in the form of 
mixtures with one another and/or with other liquid crystal components. 
They are especially suitable for the manufacture of chiral smectic 
mixtures, primarily for mixtures with a smectic C phase. However, they can 
also be used as additives for nematic mixtures (in the case of optically 
inactive compounds) or cholesteric mixtures. The mixtures in accordance 
with the invention contain at least 2 components, of which at least one 
component is a compound of formula I. The amount of compounds of formula I 
in the mixtures in accordance with the invention can vary over a wide 
range depending on the use and, for example, from about 1% to 100%. In 
general, the mixtures in accordance with the invention with a nematic, 
cholesteric or chiral smectic phase contain about 1-80 wt.%, preferably 
about 5-50 wt.%, of compounds of formula I. An especially preferred range 
for chiral smectic mixtures amounts to about 10-70 wt.%, particularly 
about 30-50 wt.%. When optically active compounds of formula I are used as 
additives in mixtures for TN cell applications, the amount thereof can 
also be smaller and can, for example, amount to about 0.2-10 wt.% 
depending on the pitch and the cell thickness. 
The liquid crystal mixtures in accordance with the invention with nematic 
or cholestric properties and the mixtures for TN cell indicators 
preferably contain, in addition to one or more compounds of formula I, one 
or more of the compounds of the following formulae 
##STR8## 
wherein R.sup.7, R.sup.8, R.sup.9 and R.sup.10 each independently are 
alkyl, alkoxy, alkenyl or alkenyloxy with a maximum of 7 carbon atoms in 
each case, or R.sup.8 on a benzene ring also can be cyano or --NCS, or 
R.sup.9 on a benzene ring also can be cyano; ring E represents 
trans-1,4-cyclohexylene or 1,4-phenylene; X denotes hydrogen or fluorine; 
and t is 0 or 1. 
The liquid crystal mixtures in accordance with the invention with chiral 
smectic phases can contain, in addition to one or more compounds of 
formula I, usual components for chiral smectic mixtures. They preferably 
contain one or more compounds of the formula 
##STR9## 
wherein R.sup.11 and R.sup.12 are alkyl, alkoxy, alkanoyl, alkanoyloxy, 
alkoxycarbonyl or alkoxycarbonyloxy with up to 18 carbon atoms; r and s 
are 1 or 2; R.sup.13 and R.sup.14 are alkyl or alkoxy with 1 to 18 carbon 
atoms; X.sup.1 is CH and X.sup.2 is N, or X.sup.1 is N and X.sup.2 is CH; 
G is a single covalent bond, trans-1,4-cyclohexylene, 
cis-4-cyano-trans-1,4-cyclohexylene or 1,4-phenylene optionally 
substituted with halogen or methyl; ring F is trans-1,4-cyclohexylene, 
1,4-phenylene optionally substituted with halogen or methyl, or, when G is 
a single covalent bond, also cis-4-cyano-trans-1,4-cyclohexylene; R.sup.15 
and R.sup.16 each denotes an optionally halogen-substituted alkyl or 
alkenyl group in which optionally one CH.sub.2 group or two non-adjacent 
CH.sub.2 groups is/are replaced by --O--, --COO-- and/or --OOC--; m, 
Y.sup.1, Y.sup.2 and rings B, C and D have the meanings given in formula 
I; and R.sup.17 and R.sup.18 are C.sub.1 -C.sub.18 alkyl in which 
optionally one CH.sub.2 group or two non-adjacent CH.sub.2 groups is/are 
replaced by oxygen. 
The chiral smectic mixtures in accordance with the invention can consist of 
optically inactive compounds. However, they preferably contain one or more 
optically active compounds in order to produce a spontaneous polarization, 
i.e., they preferably contain at least one optically active compound of 
formula I with a chiral carbon atom in R.sup.1 and/or R.sup.2 and/or at 
least one optically active additive. Preferred chiral smectic mixtures 
with at least 2 components are, accordingly, those in which at least one 
component is an optically active compound of formula I and a second 
component can be optically active or optically inactive, as well as those 
in which at least one component is an optically inactive, preferably 
achiral, compound of formula I and a second component is optically active. 
The second component is preferably a further compound of formula I or a 
compound of formulae XVII-XX. 
The optically active compounds of formula XX which are 
laterally-substituted on B, C and/or D and/or which are 
axially-substituted on the cyclohexane ring are novel. They can be 
manufactured in a manner an analogous to the compounds of formula I. 
The mixtures in accordance with the invention can also contain dichroic 
coloring substances, for example, azo, azoxy or anthraquinone coloring 
substances. The amount of coloring substance is determined by the 
solubility and the desired color, extinction, and the like, and generally 
amounts to a maximum of about 10 wt.% in the total mixture. 
A practical application of the compound of this invention is in an 
electro-optical cell, which comprises 
(a) two-plate means; 
(b) a liquid crystal disposed between the plate means and which includes a 
dielectric of the formula: 
##STR10## 
wherein m is the number 0 or 1; A is a single covalent bond, --CH.sub.2 
--CH.sub.2 --, --OCH.sub.2 ', --COO-- or --OOC--; rings B, C and D are 
1,4-phenylene optionally substituted with cyano, halogen or lower alkyl; 
Y.sup.1 and Y.sup.2 are hydrogen or one of these substituents also is 
cyano; and R.sup.1 and R.sup.2 each represents C.sub.1 -C.sub.18 -alkyl or 
C.sub.2 -C.sub.18 alkenyl, either of which is optionally 
halogen-substituted, in which one CH.sub.2 group or two non-adjacent 
CH.sub.2 group is/are optionally replaced by oxygen; with the provisos 
that at least one of R.sup.1 and R.sup.2 has a chiral carbon atom and/or a 
C--C double bond when A is --COO-- and at least one of R.sup.1 and R.sup.2 
has a C--C double bond when A is a single covalent bond; and 
(c) a means for applying an electrical potential to said plate means. 
The preparation of the mixtures and electro-optical devices of this 
invention can be affected using known ways. 
The preparation of the compounds in accordance with the invention, of the 
novel compounds of formula XX and of the starting materials as well as 
mixtures in accordance with the invention are illustrated in greater 
detail in the following Examples. The phases are denoted by the following 
symbols: C is crystalline, S is smectic, S.sub.A is smectic A, S.sub.B is 
smectic B, S.sub.C is smectic C, S*.sub.C is chiral smectic C, Ch is 
cholesteric, N is nematic and I is isotropic.