Ferroelectric liquid crystal composition and light switching element comprising the same

A ferroelectric liquid crystal composition, exhibiting an Sc* phase over a wide temperature range including room temperature and having a spontaneous polarization value of 30 nc/cm.sup.2 or less and a quick response time, is provided. An optical switching element, comprising the ferroelectric liquid crystal composition, is also provided. The ferroelectric liquid crystal composition comprises three components A, B and C in respective amount by weight of 75 to 95%, 3 to 9% and 3 to 12% based on the total amount of these components and having a phase sequence series of Iso-N*-Sa-Sc*. Component A is at least one compound selected from the group consisting of the compounds represented by the general formulae: ##STR1## The component B is at least one compound selected from the group consisting of compounds represented by the general formulae: ##STR2## The component C is at least one compound selected from the group consisting of compounds represented by the general formulae: ##STR3## In the above formulae, R.sup.1 to R.sup.10, X, m, n and * are as defined in the claims.

BACKGROUND OF THE INVENTION 1. Field of the Invention 
The present invention relates to a ferroelectric liquid crystal material. 
More particularly, the present invention is concerned with a ferroelectric 
liquid crystal composition having a quick response despite its small 
spontaneous polarization value which comprises a non-chiral smectic liquid 
crystal compound and an optically active compound, and an optical 
switching element comprising the same. 
2. Description of the Prior Art 
Liquid crystal compounds are widely used as a material for display devices. 
Most of these display devices are used in a TN-type display system, and 
liquid crystal materials belonging to a nematic phase are used for this 
purpose. 
Since the TN type display system is a non-emissive display type, it has 
advantages such as freedom from occurrence of eyestrain and very low power 
consumption, but on the other hand it has drawbacks such as slow response 
and difficulty in viewing of display depending upon viewing angle. In 
recent years, this type of system has been converted in such a manner that 
features in the form of a flat display could be utilized. In particular, 
quick response and wide viewing angle have been demanded. 
In order to meet the above demand, an attempt has been made to improve the 
liquid crystal material. However, the TN display system is considerably 
inferior to other emissive types of display (e.g., electroluminescent 
display, plasma display, etc.) in response time and width of viewing 
angle. 
Therefore, development of a novel liquid display system as an alternative 
to the TN type display system is indispensable to attain a combination of 
utilization of the features of a liquid crystal display device, such as 
non-emissive display type and low power consumption, with attainment of 
response characteristics comparable to those of the emissive display. As 
one of such attempts, N. A. Clark and S. T. Lagerwall have proposed a 
display system wherein an optical switching phenomenon of a ferroelectric 
liquid crystal is utilized [see Appl. Phys. Lett., Vol. 36, p. 899 
(1980)]. 
The existence of ferroelectric liquid crystals has been first published in 
1975 by R. B. Mayer [see J. Phys., Vol. 36, p. 69 (1975), and these 
ferroelectric liquid crystals belong respectively to a chiral smectic C 
phase, a chiral smectic I phase, a chiral smectic F phase, a chiral 
smectic G phase, a chiral smectic H phase, a chiral smectic J phase, and a 
chiral smectic K phase (hereinafter simply referred to as "S.sub.C * 
phase", "S.sub.I * phase", "S.sub.F * phase", "S.sub.G * phase", "S.sub.H 
* phase", "S.sub.J * phase" and "S.sub.K * phase", respectively) from the 
viewpoint of the structure of the liquid crystal. 
When the optical switching phenomenon of the ferroelectric liquid crystal 
is applied as a display device, it exhibits two features superior to those 
of the TN-type display system. The first feature is its very quick 
response, and the response speed is one thousand to ten thousands higher 
than that of the TN-type display system. The second feature is the memory 
effect, and this facilitates multiplexing drive through cooperation with 
the above-described quick response. 
Particular attention is now focused on the Sc* phase among the chiral 
smectic phases. 
When the ferroelectric liquid crystal is applied to a display device, it 
should meet the following requirements. 
(1) It should exhibit an Sc* phase over a wide temperature range including 
room temperature (at least 0.degree. to 50.degree. C.). 
(2) A response time of 100 .mu.sec or less is required for a display device 
of 640.times.400 lines or more. 
The response time (.tau.) to the electric field of the ferroelectric liquid 
crystal is expressed by the following equation: 
##EQU1## 
wherein .eta. is the viscosity, Ps is the spontaneous polarization and E 
is the electric field strength. For this reason, in order to realize a 
quick response, it is necessary to have a large spontaneous polarization 
value. 
However, in recent years, occurrence of abnormal phenomena accompanying the 
large spontaneous polarization value has been reported (see, for example, 
Akio Yoshida et al., The 13rd Symposium on Liquid Crystals, 142-143 
(1987); J. Dijon et al., SID 88 DIGEST, 246-249 (1988); or H. R. Dubal et 
al, Jpn. J. Appl. Phys., 27 (1988) L2241-L2244). According to these 
reports, when a commercially available polyimide film is used as an 
insulating layer, the spontaneous polarization value should be 30 
nC/cm.sup.2 or less, preferably 25 nC/cm.sup.2 or less. 
(3) According to N. A. Clark, in order to attain the memory effect, a helix 
should be unwound by making the value of a cell gap (d) smaller than the 
pitch value (P) of the helix (see Appl. Phys. Lett., 36, 899 (1980). For 
this reason, it is necessary to lengthen the pitch of the helix of the 
ferroelectric liquid crystal for the purpose of enabling the use of a cell 
having a large thickness cell gap which can be easily prepared. 
(4) The oriented state of a ferroelectric liquid crystal varies depending 
upon the phase series of the liquid crystal. At the present time, it is 
considered that a liquid crystal having a smectic A phase and a 
cholesteric phase (hereinafter simply referred to as "S.sub.A phase" and 
"N* phase", respectively) on the high temperature side of an Sc* phase 
exhibits the best oriented state through aligning techniques (surface 
treatment processes) currently used in the TN liquid crystal material. In 
other words, it is desired that the ferroelectric liquid crystal have the 
following phase series: isotropic liquid (hereinafter simply referred to 
"Iso").fwdarw.N*.fwdarw.S.sub.A .fwdarw.S.sub.C * (see, for example, 
Japanese Patent Application Laid-Open No. 250086/1986). 
Further, it is considered that among the liquid crystal materials having 
the above-described phase series, those having a larger pitch value in the 
N* phase exhibit a better oriented state (see, for example, Japanese 
Patent Application Laid-Open No. 255323/1986). 
Besides the above-described requirements, there are various requirements 
such as tilt angle (.theta.) of the liquid crystal molecule. 
Even when only the temperature range is taken up, only a few ferroelectric 
liquid materials can be put to practical use. Therefore, at the present 
time, there are few ferroelectric liquid materials which can meet all the 
above-described requirements and can be put to practical use. 
For example, Japanese Patent Application Laid-Open No. 291679/1986 and a 
pamphlet of PCT International Publication No. WO86/06401 each disclose a 
ferroelectric liquid crystal comprising a mixture of a non-chiral phenyl 
pyrimidine compound having a smectic C phase (hereinafter simply referred 
to as "S.sub.C phase") with an optically active compound and describe that 
this ferroelectric liquid material exhibits an S.sub.C * phase over a wide 
temperature range including room temperature and has the phase series 
Iso.fwdarw.N*.fwdarw.S.sub.A .fwdarw.S.sub.C * and has a spontaneous 
polarization value of 30 nC/cm.sup.2 or less. Although the ferroelectric 
liquid crystal composition described in the above-described publications 
satisfies the above-described requirements in respect of the temperature 
range of the S.sub.C * phase, phase series and spontaneous polarization 
value, it cannot be put to practical use because the response time is 300 
to 500 .mu.sec (see, for example, ferroelectric liquid crystal 
compositions described in Examples 1 and 2 of Japanese Patent Application 
Laid-Open No. 29167/1986 or ferroelectric liquid crystal compositions 
described in Examples 45 and 46 of the pamphlet of PCT International 
Publication No. WO86/06401). 
Japanese Patent Application Laid-Open No. 541/1988 discloses a 
ferroelectric liquid crystal composition comprising a mixture of a 
non-chiral phenyl pyrimidine compound with an optically active compound 
represented by the general formula (III), (IV) or (V) of the present 
invention and describes that this ferroelectric liquid crystal composition 
exhibits an S.sub.C * phase over a wide temperature range including room 
temperature and has a response speed as high as 100 .mu.sec or less. 
Although the ferroelectric liquid crystal composition disclosed in the 
above-described patent application satisfies the above-described 
requirements with regard to the temperature range of the S.sub.C * phase 
and response time, it cannot be put to practical use due to the difficulty 
in attaining the excellent orientation attributable to the absence an N* 
phase (see, for example, Examples 1, 3 and 5), and occurrence of an 
abnormal phenomenon when a switching operation is conducted attributable 
to a spontaneous polarization value of 30 nC/cm.sup.2 or more (see, for 
example, Example 2). 
As is apparent from the foregoing description, at the present time, there 
are few ferroelectric liquid crystal materials which can satisfy all the 
above-described requirements and can be immediately applied to a display 
device. 
SUMMARY OF THE INVENTION 
The first object of the present invention is to provide a ferroelectric 
liquid crystal composition which exhibits an S.sub.C * phase over a wide 
temperature range including room temperature and has a spontaneous 
polarization value of 30 nC/cm.sup.2 or less and a quick response, i.e., a 
response time of 100 .mu.sec or less. 
The second object of the present invention is to provide an optical 
switching element having a quick response which comprises such liquid 
crystal composition. 
The present inventors have made extensive and intensive studies with a view 
to solving the above-described problems. As a result, they have found 
that, as will be described below, a combination of a non-chiral phenyl 
pyrimidine compound with an optically active compound having a high 
spontaneous polarization value, the same polarity and an oppositely 
twisted helix enables preparation of a ferroelectric liquid crystal 
composition which exhibits an S.sub.C * phase over a wide temperature 
range including room temperature and easily attains excellent orientation 
and has a spontaneous polarization value of 30 nC/cm.sup.2 or less and a 
quick response, i.e., a response time of 100 .mu.sec or less, which has 
led to the completion of the present invention. 
According to the first aspect of the present invention, there is provided 
the following ferroelectric liquid crystal compositions. 
(1) A ferroelectric liquid crystal composition comprising three components 
A, B and C in respective amounts of 75 to 95% by weight, 3 to 9% by weight 
and 3 to 12% by weight based on the total amount of the components A, B 
and C and having a phase sequence series of an isotropic liquid, a 
cholesteric phase, a smectic A phase and a chiral smectic C phase 
proceeding in that order from the high temperature side and a spontaneous 
polarization value of 30 nC/cm .sup.2 or less, 
said component A being at least one compound selected from the group 
consisting of compounds represented by the general formula (I): 
##STR4## 
wherein R.sup.1 and R.sup.2 which may be the same or different, are each a 
straight-chain or branched alkyl, alkoxy or alkanoyloxy group having 1 to 
18 carbon atoms, and compounds represented by the general formula (II): 
##STR5## 
wherein R.sup.3 and R.sup.4 which may be the same or different are each a 
straight-chain or branched alkyl or alkoxy group having 1 to 18 carbon 
atoms, 
said component B being at least one compound selected from the group 
consisting of compounds represented by the general formula (III): 
##STR6## 
wherein R.sup.5 is a straight-chain or branched alkyl or alkoxy group 
having 1 to 18 carbon atoms, R.sup.6 is a straight-chain or branched alkyl 
group having 2 to 18 carbon atoms or a straight-chain or branched alkoxy 
group having 1 to 18 carbon atoms and * represents an asymmetric carbon 
atom, and compounds represented by the general formula (IV): 
##STR7## 
wherein R.sup.7 is a straight-chain or branched alkyl or alkoxy group 
having 1 to 18 carbon atoms, R.sup.8 is a straight-chain or branched alkyl 
group having 2 to 18 carbon atoms or a straight-chain or branched alkoxy 
group having 1 to 18 carbon atoms and * represents an asymmetric carbon 
atom, 
said component C being at least one compound selected from the group 
consisting of compounds represented by the general formula (V): 
##STR8## 
wherein R.sup.9 is a straight-chain or branched alkyl or alkoxy group 
having 1 to 18 carbon atoms, R.sup.10 is a straight-chain or branched 
alkyl group having 2 to 18 carbon atoms, X is --OCH.sub.2 -- or 
--CH.sub.2)--, m and n are each 1 or 2, provided that m+n=3 and * 
represents an asymmetric carbon atom. 
(2) A ferroelectric liquid crystal composition according to the 
above-described item (1), wherein said component A is at least one 
compound selected from the group consisting of compounds represented by 
the general formula (I) wherein R.sup.1 is a straight-chain alkoxy or 
alkanoyloxy group having 5 to 12 carbon atoms and R.sup.2 is a 
straight-chain alkyl group having 7 to 11 carbon atoms; and compounds 
represented by the general formula (II) wherein R.sup.3 is a 
straight-chain alkyl or alkoxy group having 5 to 10 carbon atoms and 
R.sup.4 is a straight-chain alkyl group having 6 to 10 carbon atoms. 
(3) A ferroelectric liquid crystal composition according to the 
above-described item (1), wherein said component B is at least one 
compound selected from the group consisting of compounds represented by 
the general formula (III) wherein R5 is a straight-chain alkyl or alkoxy 
group having 3 to 10 carbon atoms, R.sup.6 is a straight-chain alkyl or 
alkoxy group having 2 to 10 carbon atoms; and compounds represented by the 
general formula (IV) wherein R.sup.7 is a straight-chain alkyl or alkoxy 
group having 3 to 10 carbon atoms and R.sup.8 is a straight-chain alkyl or 
alkoxy group having 2 to 10 carbon atoms. 
(4) A ferroelectric liquid crystal composition according to the 
above-described item (1), wherein said component C is at least one 
compound selected from the group consisting of compounds represented by 
the general formula (V) wherein R.sup.9 is a straight-chain alkyl or 
alkoxy group having 6 to 12 carbon atoms and R.sup.10 is a straight-chain 
alkyl group having 2 to 10 carbon atoms. 
(5) A ferroelectric liquid crystal composition according to the 
above-described item (1), wherein said component A is at least one 
compound selected from the group consisting of the following compounds: 
##STR9## 
(6) A ferroelectric liquid crystal composition according to the 
above-described item(1), wherein said component B is at least one compound 
selected from the group consisting of the following compounds: 
##STR10## 
(7) A ferroelectric liquid crystal composition according to the 
above-described item (1), wherein said component C is at least one 
compound selected from the group consisting of the following compounds: 
##STR11## 
According to the second aspect of the present invention, there is provided 
the following ferroelectric liquid crystal compositions. 
(8) A ferroelectric liquid crystal composition comprising four components, 
i.e., the above-described three components A, B and C and further 
component D in an amount of 2 to 5% by weight based on the total amount of 
the components A, B and C, and having a phase sequence series of an 
isotropic liquid, a cholesteric phase, a smectic A phase and a chiral 
smectic C phase proceeding in that order from the high temperature side 
and a spontaneous polarization value of 30 nC/cm.sup.2 or less, 
said component D being at least one compound selected from the group 
consisting of compounds represented by the general formula (VI): 
##STR12## 
wherein R.sup.11 is a straight-chain or branched alkyl or alkoxy group 
having 1 to 18 carbon atoms, R.sup.12 is a straight-chain or branched 
alkyl group having 2 to 18 carbon atoms, Y is a cyano group or a halogen 
atom and * represents an asymmetric carbon atom, and compounds represented 
by the general formula (VII): 
##STR13## 
wherein R.sup.13 is a straight-chain or branched alkyl or alkoxy group 
having 1 to 18 carbon atoms, R.sup.14 is a straight-chain or branched 
alkyl group having 2 to 18 carbon atoms and * represents an asymmetric 
carbon atom. 
(9) A ferroelectric liquid crystal composition according to the 
above-described item 8, wherein said component D is at least one compound 
selected from the group consisting of compounds represented by the general 
formula (VI) wherein R.sup.11 is a straight-chain alkyl or alkoxy group 
having 5 to 12 carbon atoms, R.sup.12 is a straight-chain alkyl group 
having 2 to 10 carbon atoms and Y is --CN or --F; and compounds 
represented by the general formula (VII) wherein R.sup.13 is a 
straight-chain alkyl or alkoxy group having 5 to 12 carbon atoms and 
R.sup.14 is a straight-chain alkyl group having 2 to 10 carbon atoms. 
(10) A ferroelectric liquid crystal composition according to the 
above-described item 8, wherein said component D is at least one compound 
selected from the group consisting of the following compounds: 
##STR14## 
(11) According to the third aspect of the present invention, there is 
provided an optical switching element comprising a ferroelectric liquid 
crystal composition according to the above-described item (1) or (8). 
The non-chiral compound represented by the general formula (I) or (II) as 
the component A described in the above-described item (1) is a known 
compound which has an excellent smectic C property and serves as a base 
S.sub.C compound (i.e., exhibits an S.sub.C phase over a wide temperature 
range) in the ferroelectric liquid crystal composition attempted in the 
present invention. The compound represented by the general formula (I) 
exhibits an S.sub.C phase in a relatively low temperature region around 
room temperature, while the compound represented by the general formula 
(II) exhibits an S.sub.C phase in a relatively high temperature region. 
For example, when in the general formula (I) R.sup.1 is C.sub.6 H.sub.13 
O-- and R.sup.2 is --C.sub.8 H.sub.17, the phase transition temperature is 
Cr28S.sub.C 47S.sub.A 58N66I.sub.SO. On the other hand, when in the 
general general formula (II) R.sup.3 is C.sub.7 H.sub.15 -- and R.sup.4 is 
--C.sub.8 H.sub.17, the phase transition temperature is Cr58S.sub.C 
134S.sub.A 144N157I.sub.SO. Therefore, a base S.sub.C mixture having an 
S.sub.C phase over a wide temperature range from a low temperature region 
to a high temperature region can be prepared through a combination of 
compounds represented by the general formula (I) or (II). In view of the 
above, a compound having an S.sub.C phase is preferably used. However, it 
is also possible to use a compound not having an S.sub.C phase in such an 
amount as will bring about no remarkable reduction in the temperature 
range of the S.sub.C * phase. The compound represented by the general 
formula (I) or (II) has an S.sub.A phase and a nematic phase (hereinafter 
simply referred to "N phase") on the high temperature side of the S.sub.C 
phase and plays an important role in the appearance of the phase series 
I.sub.SO --N*--S.sub.A --S.sub.C *. 
Examples of the compound represented by the general formula (I) include 
phenyl pyrimidine compounds wherein R.sup.1 is a straight-chain alkoxy or 
alkanoyloxy group having 5 to 12 carbon atoms and R.sup.2 is a 
straight-chain alkyl group having 7 to 11 carbon atoms, and examples of 
the compound represented by the general formula (II) include biphenyl 
pyrimidine compounds wherein R.sup.3 is a straight-chain alkyl or alkoxy 
group having 5 to 10 carbon atoms and R.sup.4 is a straight-chain alkyl 
group having 6 to 10 carbon atoms. In the present invention, it is 
preferred to use a plurality of the above-described pyrimidine compounds. 
Particularly preferred examples of the pyrimidine compound having an 
S.sub.C phase are shown in the following Tables 1 and 2. 
TABLE 1 
______________________________________ 
Compounds represented by the formula 
##STR15## 
R.sup.1 R.sup.2 R.sup.1 R.sup.2 
______________________________________ 
C.sub.6 H.sub.13 O 
C.sub.8 H.sub.17 
C.sub.7 H.sub.15 O 
C.sub.9 H.sub.19 
C.sub.6 H.sub.13 O 
C.sub.9 H.sub.19 
C.sub.7 H.sub.15 O 
C.sub.10 H.sub.21 
C.sub.6 H.sub.13 O 
C.sub.10 H.sub.21 
C.sub.7 H.sub.15 O 
C.sub.11 H.sub.23 
C.sub.6 H.sub.13 O 
C.sub.11 H.sub.23 
C.sub.8 H.sub.17 O 
C.sub.8 H.sub.17 
C.sub.8 H.sub.17 O 
C.sub.9 H.sub.19 
C.sub.12 H.sub.25 O 
C.sub.7 H.sub.15 
C.sub.8 H.sub.17 O 
C.sub.10 H.sub.21 
C.sub.12 H.sub.25 O 
C.sub.8 H.sub.17 
C.sub.8 H.sub.17 O 
C.sub.11 H.sub.23 
C.sub.5 H.sub.11 COO 
C.sub.8 H.sub.17 
C.sub.9 H.sub.19 O 
C.sub.7 H.sub.15 
C.sub.6 H.sub.13 COO 
C.sub.8 H.sub.17 
C.sub.9 H.sub.19 O 
C.sub.8 H.sub.17 
C.sub.7 H.sub.15 COO 
C.sub.8 H.sub.17 
C.sub.9 H.sub.19 O 
C.sub.9 H.sub.19 
C.sub.8 H.sub.17 COO 
C.sub.8 H.sub.17 
C.sub.9 H.sub.19 O 
C.sub.10 H.sub.21 
C.sub.9 H.sub.19 COO 
C.sub.8 H.sub.17 
C.sub.10 H.sub.21 O 
C.sub.8 H.sub.17 
C.sub.10 H.sub.21 COO 
C.sub.8 H.sub.17 
C.sub.11 H.sub.23 O 
C.sub.7 H.sub.15 
C.sub.11 H.sub.23 COO 
C.sub.8 H.sub.17 
C.sub.11 H.sub.23 O 
C.sub.8 H.sub.17 
______________________________________ 
TABLE 2 
______________________________________ 
Compounds represented by the formula 
##STR16## 
R.sup.3 R.sup.4 R.sup.3 R.sup.4 
______________________________________ 
C.sub.5 H.sub.11 
C.sub.6 H.sub.13 
C.sub.5 H.sub.11 O 
C.sub.6 H.sub.13 
C.sub.5 H.sub.11 
C.sub.7 H.sub.15 
C.sub.5 H.sub.11 O 
C.sub.7 H.sub.15 
C.sub.5 H.sub.11 
C.sub.8 H.sub.17 
C.sub.5 H.sub.11 O 
C.sub.8 H.sub.17 
C.sub.6 H.sub.13 
C.sub.6 H.sub.13 
C.sub.6 H.sub.13 O 
C.sub.6 H.sub.13 
C.sub.6 H.sub.13 
C.sub.7 H.sub.15 
C.sub.6 H.sub.13 O 
C.sub.7 H.sub.15 
C.sub.6 H.sub.13 
C.sub.8 H.sub.17 
C.sub.6 H.sub.13 O 
C.sub.8 H.sub.17 
C.sub.7 H.sub.15 
C.sub.6 H.sub.13 
C.sub.7 H.sub.15 O 
C.sub.6 H.sub.13 
C.sub.7 H.sub.15 
C.sub.7 H.sub.15 
C.sub.7 H.sub.15 O 
C.sub.7 H.sub.15 
C.sub.7 H.sub.15 
C.sub.8 H.sub.17 
C.sub.7 H.sub.15 O 
C.sub.8 H.sub.17 
C.sub.8 H.sub.17 
C.sub.6 H.sub.13 
C.sub.8 H.sub.17 O 
C.sub.6 H.sub.13 
C.sub.8 H.sub.17 
C.sub.7 H.sub.15 
C.sub.8 H.sub.17 O 
C.sub.7 H.sub.15 
C.sub.8 H.sub.17 
C.sub.8 H.sub.17 
C.sub.8 H.sub.17 O 
C.sub.8 H.sub.17 
______________________________________ 
In the ferroelectric liquid crystal compositions according to the present 
invention, the component A serves as a base S.sub.C compound and has the 
function of allowing an I.sub.SO --N*--S.sub.A --S.sub.C * phase series to 
appear. Therefore, it is preferred that the concentration of the component 
A be 75% by weight or more. When the concentration is less than 75% by 
weight, the amount of the optically active compound becomes relatively 
large and the spontaneous polarization value of the liquid crystal 
composition becomes 30 nC/cm.sup.2 or more, which brings about an abnormal 
phenomenon when a switching operation is conducted. 
The optically active compounds represented by the general formula (III) or 
(IV) as the component B described in the above-described item (1) are 
those disclosed in Japanese Patent Application Laid-Open No. 267763/1988 
and Japanese Patent Application Laid-Open No. 63571/1989, and have a large 
spontaneous polarization value and excellent response characteristics. For 
example, when in the general formula (III) R.sup.5 is C.sub.6 H.sub.13 O-- 
and R.sup.6 is --OC.sub.6 H.sub.13, the compound has a phase transition 
temperature of Cr67S.sub.C *96N*107I.sub.SO, a spontaneous polarization 
value of 327 nC/cm.sup.2 (T-T.sub.C =10.degree. C.), a tilt angle of 
45.degree. (T-T.sub.C =10.degree. C.) and a response time of 45 .mu.sec 
(T-T.sub.C =10.degree. C., E=5 V/.mu.m). When in the general formula (IV) 
R.sup.7 is C.sub.9 H.sub.19 -- and R.sup.8 is --OC.sub.3 H.sub.7, the 
compound has a phase transition temperature of Cr70 S.sub.C *103S.sub.A 
108N*110I.sub.SO, a spontaneous polarization value of 243 nC/cm.sup.2 
(T-T.sub.C =10.degree. C.), a tilt angle of 38.degree. (T-T.sub.C 
=10.degree. C.) and a response time of 30 .mu.sec (T-T.sub.C =-10.degree. 
C., E=5 V/.mu.m). Thus, in the ferroelectric liquid crystal composition of 
the present invention, the above-described compounds play an important 
role in the attainment of a quick response. 
Examples of the compound represented by the general formula (III) include 
compounds wherein R.sup.5 is a straight-chain alkyl or alkoxy group having 
3 to 10 carbon atoms and R.sup.6 is a straight-chain alkyl or alkoxy group 
having 2 to 10 carbon atoms, and examples of the compound represented by 
the general formula (IV) include optically active compounds wherein 
R.sup.7 is a straight-chain alkyl or alkoxy group having 3 to 10 carbon 
atoms and R.sup.8 is a straight-chain alkyl or alkoxy group having 2 to 10 
carbon atoms. Examples of the compound represented by the general formula 
(III) or (IV) are shown in the following Tables 3 and 4. 
TABLE 3 
__________________________________________________________________________ 
Compounds represented by the formula 
##STR17## 
R.sup.5 R.sup.6 R.sup.5 R.sup.6 
__________________________________________________________________________ 
C.sub.5 H.sub.11 
C.sub.2 H.sub.5 
C.sub.6 H.sub.13 
OC.sub.5 H.sub.11 
C.sub.5 H.sub.11 
C.sub.6 H.sub.13 
C.sub.3 H.sub.7 
OC.sub.6 H.sub.13 
C.sub.3 H.sub.7 
OC.sub.4 H.sub.9 
C.sub.6 H.sub.13 
OC.sub.6 H.sub.13 
C.sub.5 H.sub.11 
OC.sub.4 H.sub.9 
C.sub.6 H.sub.13 O 
OC.sub.4 H.sub.9 
C.sub.6 H.sub.13 
OC.sub.4 H.sub.9 
C.sub.6 H.sub.13 O 
OC.sub.6 H.sub.13 
C.sub.7 H.sub.15 
OC.sub.4 H.sub.9 
__________________________________________________________________________ 
TABLE 4 
__________________________________________________________________________ 
Compounds represented by the formula 
##STR18## 
R.sup.7 R.sup.8 R.sup.7 R.sup.8 
__________________________________________________________________________ 
C.sub.6 H.sub.13 
C.sub.2 H.sub.5 
C.sub.6 H.sub.13 
OC.sub.3 H.sub.7 
C.sub.7 H.sub.15 
C.sub.2 H.sub.5 
C.sub.7 H.sub.15 
OC.sub.3 H.sub.7 
C.sub.9 H.sub.19 
C.sub.2 H.sub.5 
C.sub.9 H.sub.19 
OC.sub.3 H.sub.7 
C.sub.5 H.sub.11 
OC.sub.3 H.sub.7 
__________________________________________________________________________ 
In the compounds represented by the general formulae (III) and (IV), when 
the absolute configuration of the optically active site is (S, S) or (S, 
R), the polarity of the spontaneous polarization was (-) an the helical 
twist sense was left-handed. On the other hand, when the absolute 
configuration is (R, R) or (R, S), the polarity of the spontaneous 
polarization was (+) and the helical twist sense was right-handed. 
In the ferroelectric liquid crystal composition attempted in the present 
invention, the component B plays an important role in the attainment of a 
quick response. However, when the amount is excessively large, the 
spontaneous polarization value of the liquid crystal composition becomes 
30 nC/cm.sup.2 or more, which brings about an abnormal phenomenon when a 
switching operation is conducted. For this reason, the concentration of 
the component B is preferably 9% by weight or less. 
The optically active compound represented by the general formula (V) as the 
component C described in the above item 1 is a compound disclosed in 
Japanese Patent Application Laid-Open No. 149547/1985. This compound and 
the optically active compound represented by the general formula (III) or 
(IV) are the same in polarity in spontaneous polarization and opposite in 
helical twist sense. Therefore, in the ferroelectric liquid crystal 
composition according to the present invention, it serves as a helical 
pitch modifier and lengthens the helical pitch of the liquid crystal 
composition. Further, it has a large spontaneous polarization value and is 
excellent in response characteristics although the response time is slower 
than that of component B. For example, when in the general formula (V), 
R.sup.9 is C.sub.7 H.sub.15 O--, R.sup.10 is --C.sub.6 H.sub.13, m is 1, n 
is 2 and x is --CH.sub.2 O--, the compound has a phase transition 
temperature of Cr110(S.sub.C *105S.sub.A 108)I.sub.SO, a spontaneous 
polarization value of 142 nC/cm.sup.2 (T-T.sub.C =10.degree. C.), a tilt 
angle of 27.degree. (T-T.sub.C =10.degree. C.) and a response time of 60 
.mu.sec (T-T.sub.C =-10.degree. C., E=5 V/.mu.m). Therefore, a 
ferroelectric liquid crystal composition having a large helical pitch 
length and a quick response can be prepared through a combination of a 
compound corresponding to component C with compounds represented by the 
general formula (III) and (IV) as the component (B). 
Examples of the compound represented by the general formula (V) include 
optically active compounds wherein R.sup.9 is a straight-chain alkyl group 
or alkoxy group having 6 to 12 carbon atoms and R.sup.10 is a 
straight-chain alkyl group having 2 to 10 carbon atoms. Representative 
examples of the compound represented by the general formula (V) are shown 
in the following Tables 5 to 7. 
TABLE 5 
______________________________________ 
Compounds represented by the formula 
##STR19## 
R.sup.9 R.sup.10 R.sup.9 R.sup.10 
______________________________________ 
C.sub.6 H.sub.13 
C.sub.6 H.sub.13 
C.sub.7 H.sub.15 O 
C.sub.6 H.sub.13 
______________________________________ 
TABLE 6 
______________________________________ 
Compounds represented by the formula 
##STR20## 
R.sup.9 R.sup.10 R.sup.9 R.sup.10 
______________________________________ 
C.sub.8 H.sub.17 
C.sub.6 H.sub.13 
C.sub.10 H.sub.21 O 
C.sub.6 H.sub.13 
C.sub.8 H.sub.17 O 
C.sub.6 H.sub.13 
______________________________________ 
TABLE 7 
______________________________________ 
Compounds represented by the formula 
##STR21## 
R.sup.9 R.sup.10 R.sup.9 R.sup.10 
______________________________________ 
C.sub.7 H.sub.15 
C.sub.6 H.sub.13 
C.sub.5 H.sub.11 
C.sub.3 H.sub.7 
C.sub.8 H.sub.17 
C.sub.6 H.sub.13 
C.sub.7 H.sub.15 
C.sub.3 H.sub.7 
C.sub.6 H.sub.13 O 
C.sub.6 H.sub.13 
C.sub.8 H.sub.17 
C.sub.3 H.sub.7 
C.sub.8 H.sub.17 O 
C.sub.6 H.sub.13 
C.sub.5 H.sub.11 O 
C.sub.3 H.sub.7 
C.sub.9 H.sub.19 O 
C.sub.6 H.sub.13 
C.sub.8 H.sub.17 O 
C.sub.3 H.sub.7 
C.sub.10 H.sub.21 O 
C.sub.6 H.sub.13 
C.sub.9 H.sub.19 O 
C.sub.3 H.sub.7 
C.sub.12 H.sub.25 O 
C.sub.6 H.sub.13 
C.sub.10 H.sub.21 O 
C.sub.3 H.sub.7 
______________________________________ 
In the compounds represented by the general formula (V), when the absolute 
configuration of the optically active site is R, the polarity of the 
spontaneous polarization was (-) and the helical twist sense was 
right-handed. On the other hand, when the absolute configuration is S, the 
polarity of the spontaneous polarization was (+) and the helical twist 
sense was left-handed. Therefore, when the absolute configuration of the 
compound as the component B represented by the general formula (III) or 
(IV) is (S, S) or (S, R), it is possible to prepare a ferroelectric liquid 
crystal composition having a large helical pitch through a combination of 
this compound with the compound represented by the general formula (V) as 
component C of which the absolute configuration is R. 
In the ferroelectric liquid crystal composition attempted in the present 
invention, the component C serves mainly as a helical pitch modifier for 
the component B and lengthens the helical pitch without detriment to the 
response characteristics of the liquid crystal composition. However, when 
the amount is excessively large, it has an adverse affect on the response 
characteristics or has an adverse affect on the phase series 
Iso.fwdarw.N*.fwdarw.S.sub.A .fwdarw.S.sub.C * due to its poor N* 
property. Therefore, the concentration of the component C is preferably 
12% by weight or less. 
The ferroelectric liquid crystal composition according to the present 
invention can be prepared mainly through a combination of the 
above-described three components, i.e., components A, B and C. Use of the 
component D as an additional component enables a ferroelectric liquid 
crystal composition having better characteristics to be prepared. 
The optically active compound represented by the general formula (VI) or 
(VII) as the component D described in the above item 8 is a compound 
disclosed in Japanese Patent Application Laid-Open No. 210056/1986, 
48254/1988 or 233966/1988 and is not very quick in the response time. 
However, this compound has a small helical pitch length, and this compound 
and the optically active compound corresponding to component B, 
represented by the general formula (III) or (IV), are the same in polarity 
in spontaneous polarization and opposite in helical twist sense. Thus the 
ferroelectric liquid crystal composition of the present invention, serves 
as a helical pitch modifier, and use thereof as a helical pitch modifier 
in combination with the above-described optically active compound as the 
component C represented by the general formula (V) enables the helical 
pitch of the liquid crystal composition to be further lengthened. 
Examples of the compound represented by the general formula (VI) or (VII) 
include compounds represented by the formula (VI) wherein R.sup.11 is a 
straight-chain alkyl or alkoxy group having 5 to 12 carbon atoms, R.sup.12 
is a straight-chain alkyl group having 2 to 10 carbon atoms and Y is --CN 
or --F, or optically active compounds represented by the formula (VII) 
wherein R.sup.13 is a straight-chain alkyl or alkoxy group having 5 to 12 
carbon atoms and R.sup.14 is a straight-chain alkyl group having 2 to 10 
carbon atoms. Representative examples of the compound represented by the 
general formula (VI) or (VII) are shown in the following Tables 8 to 10. 
TABLE 8 
______________________________________ 
Compounds represented by the formula 
##STR22## 
R.sup.11 R.sup.12 R.sup.11 R.sup.12 
______________________________________ 
C.sub.6 H.sub.13 
C.sub.6 H.sub.13 
C.sub.5 H.sub.11 O 
C.sub.6 H.sub.13 
C.sub.7 H.sub.15 
C.sub.6 H.sub.13 
C.sub.8 H.sub.17 O 
C.sub.6 H.sub.13 
C.sub.8 H.sub.17 
C.sub.6 H.sub.13 
C.sub.10 H.sub.21 O 
C.sub.6 H.sub.13 
______________________________________ 
TABLE 9 
______________________________________ 
Compounds represented by the formula 
##STR23## 
R.sup.11 R.sup.12 R.sup.11 R.sup.12 
______________________________________ 
C.sub.8 H.sub.17 
C.sub.6 H.sub.13 
C.sub.9 H.sub.19 O 
C.sub.6 H.sub.13 
C.sub.6 H.sub.13 O 
C.sub.6 H.sub.13 
C.sub.10 H.sub.21 O 
C.sub.6 H.sub.13 
C.sub.7 H.sub.15 O 
C.sub.6 H.sub.13 
C.sub.12 H.sub.25 O 
C.sub.6 H.sub.13 
C.sub.8 H.sub.17 O 
C.sub.6 H.sub.13 
______________________________________ 
TABLE 10 
______________________________________ 
Compounds represented by the formula 
##STR24## 
R.sup.13 R.sup.14 R.sup.13 R.sup.14 
______________________________________ 
C.sub.5 H.sub.11 
C.sub.2 H.sub.5 
C.sub.7 H.sub.15 O 
C.sub.2 H.sub.5 
C.sub.7 H.sub.15 
C.sub.2 H.sub.5 
C.sub.8 H.sub.17 O 
C.sub.2 H.sub.5 
C.sub.8 H.sub.17 
C.sub.2 H.sub.5 
C.sub.10 H.sub.21 O 
C.sub.2 H.sub.5 
C.sub.10 H.sub.21 
C.sub.2 H.sub.5 
C.sub.12 H.sub.25 O 
C.sub.2 H.sub.5 
______________________________________ 
In the compounds represented by the general formulae (VI) and (VII), when 
the absolute configuration of the optically active site is S, the polarity 
of the spontaneous polarization was (-) and the helical twist sense was 
right-handed. On the other hand, when the absolute configuration is R, the 
polarity of the spontaneous polarization was (+) and the helical twist 
sense was left-handed. 
In the ferroelectric composition of the present invention, the component D 
serves as a helical pitch modifier and plays an important role in 
lengthening the helical pitch of the liquid crystal composition. However, 
this compound is poor in response characteristics, and use thereof in an 
excessive amount deteriorates the response characteristics of the liquid 
crystal composition. In view of the above, the concentration of the 
component D is preferably 5% by weight or less. 
The present inventors have made various studies on proportions of 
components necessary for obtaining a ferroelectric liquid crystal 
composition attempted in the present invention by taking advantage of the 
above-described characteristics of components A, B, C and D and, as a 
result, have found that the proportions of the components A, B, and C are 
75 to 95% by weight, 3 to 9% by weight and 3 to 12% by weight, 
respectively, and the proportion of the component D is preferably 2 to 5% 
by weight, based on the total amount of the three components, i.e., 
components A, B, and C, which has led to the completion of the present 
invention. 
When the amount of a component is less, than the lower limit described 
above, the desired affect of that component can not be attained. 
The present invention provides a ferroelectric liquid crystal composition 
having excellent orientation with no defect also having quick response. 
The invention also provides a liquid crystal element free from occurrence 
of abnormal phenomenon in a switching operation and having excellent 
memory property, very excellent contrast and quick response through the 
use of the above-described liquid crystal composition.

Examples of particular applications for the ferroelectric liquid crystal 
composition of the present invention include high-speed liquid crystal 
shutters and high definition liquid crystal displays. 
EXAMPLES 
The present invention will now be described in more detail by way of the 
following examples. However, the present invention is not limited to these 
examples only. 
In the examples, various measurements were conducted by the following 
methods. 
The spontaneous polarization value (Ps) was measured by the Sawyer-Tower 
method. The tilt angle (.theta.) was determined by applying a sufficiently 
high electric field exceeding a critical electric field to a homogeneously 
aligned cell to bring about disappearance of a helical structure, 
reversing the polarity and measuring the travel angle (corresponding to 
2.theta.) of the extinction position under crossed-nicol prisms. 
The response time was measured by injecting each composition into a cell 
subjected to an aligning treatment and having an electrode-to-electrode 
distance of 2 .mu.m, applying a rectangular wave of 1 kHz having a 
peak-to-peak voltage V.sub.pp of 20 V and measuring a change in the 
transmitted light intensity. 
The Sc* pitch was determined by using a cell of about 200 .mu.m-thickness 
subjected to homogeneous orientation and directly measuring line intervals 
of a striped pattern (dechiralization lines) corresponding to a helical 
pitch under a polarization microscope. 
The N* pitch was indirectly determined by using a wedge-shaped cell, 
measuring intervals (l) of line defections (discrimination lines) and 
calculating the pitch according to the theoretical equation P (pitch)=2 l 
tan .theta. wherein .theta. is the tilt angle of the wedge-shaped cell. 
EXAMPLE 1 
A ferroelectric liquid crystal composition having the following composition 
was prepared by using compounds represented by the general formulae (I), 
(II), (III) and (V). 
##STR25## 
The ferroelectric liquid crystal composition exhibits the following phase 
transition temperature. 
##STR26## 
The spontaneous polarization value, tilt angle and response time each at 
25.degree. C. were 24 nC/cm.sup.2, 20.degree. and 63 .mu.sec, 
respectively. The pitch of the N* phase was 12 .mu.m at 85.degree. C., and 
the pitch of the Sc* phase was 8 .mu.m at 25.degree. C. 
The above liquid crystal composition was injected into a cell equipped with 
a transparent electrode and having a cell gap of 2 .mu.m. The cell was one 
wherein a polyimide as an aligning treatment was applied to the cell and 
the surface of the cell was rubbed for homogeneous aligning. The liquid 
crystal composition was then gradually cooled from the N* phase to Sc* 
phase (cooling rate: 1.degree. C./min), and a pair of polarizers were 
provided in a crossed nicol state for observation under a microscope. As a 
result, it was confirmed that a homogeneous orientation could be attained 
without any defect. The contrast ratio was 1:20. 
As is apparent from the foregoing description, a ferroelectric liquid 
crystal composition exhibiting an Sc* phase over a wide temperature range 
including room temperature, having an I.sub.SO --N*--S.sub.A --S.sub.C * 
phase series, a long helical pitch, a spontaneous polarization value of 30 
nC/cm.sup.2 or less and also quick response can be prepared through a 
combination of compounds of the three components, i.e., components A, B 
and C, respectively represented by the general formulae (I), (II), (III) 
and (V). It is also apparent that a liquid crystal element capable of 
easily attaining good orientation and exhibiting an excellent contrast can 
be prepared through the use of the above-described liquid crystal 
composition. 
EXAMPLE 2 
A ferroelectric liquid crystal composition having the following composition 
was prepared by using compounds represented by the general formulae (I), 
(II), (III), (V) and (VI). 
##STR27## 
The above-described ferroelectric liquid crystal composition exhibits the 
following phase transition temperature. 
##STR28## 
The spontaneous polarization value, tile angle and response time each at 
25.degree. C. were 26 nC/CM.sup.2, 22.degree. and 64 .mu.sec, 
respectively. The pitch of the N* phase was 42 .mu.m at 81.degree. C., and 
the pitch of the Sc* phase was 11 .mu.m at 25.degree. C. 
The above liquid crystal composition was injected into the same cell having 
a cell gap of 2 .mu.m as that used in Example 1, quenched from the N* 
phase to Sc* phase (cooling rate: 10.degree. C./min), and observed under a 
microscope. As a result, it was confirmed that a homogeneous orientation 
could be attained without any defect. The contrast ratio was 1:25. 
As is apparent from the foregoing description, a ferroelectric liquid 
crystal composition having an I.sub.SO --N*--S.sub.A --S.sub.C * phase 
series and a longer helical pitch and a quick response can be prepared 
through a combination of compounds of the three components, i.e., 
components A, B and C, respectively represented by the general formulae 
(I), (II), (III) and (V) with a compound represented by the general 
formula (VI) as component D. It is also apparent that a practicable liquid 
crystal element capable of attaining good orientation even when quenched 
and exhibiting an excellent contrast can be prepared through the use of 
the above-described liquid crystal composition. 
EXAMPLES 3 TO 9 
Ferroelectric liquid crystal compositions having compositions shown in 
Table 11 were prepared and evaluated in the same manner as that of Example 
1 or 2. The characteristics of the liquid crystal compositions of Examples 
3 to 9 are shown in Table 12. 
COMATIVE EXAMPLES 1 AND 2 
The characteristics of a composition falling, outside the composition of 
the present invention with respect to the mixing proportions of the 
components A, B, and C and a composition falling outside the composition 
of the present invention with respect to the mixing proportions of the 
components A, B, C and D are shown in Table 12 respectively as Comparative 
Examples 1 and 2. 
3 TABLE 11 
Ex. No. Comp. Ex. Component Formula Compound 3 4 5 6 7 8 9 1 2 
A I 
##STR29## 
33 30 28 24 28 26 26 24 34 
I 
##STR30## 
10 8 8 7 8 7 7 7 11 
I 
##STR31## 
18 17 16 14 16 15 15 13 18 
II 
##STR32## 
20 17 16 15 16 15 15 15 20 
II 
##STR33## 
-- -- 6 -- 6 5 4 -- -- 
II 
##STR34## 
14 13 12 11 12 12 12 10 14 
II 
##STR35## 
-- -- -- 4 -- -- -- -- 
B III 
##STR36## 
-- -- -- -- -- 4 2 
III 
##STR37## 
3 -- -- -- 3 -- 9 10 
III 
##STR38## 
-- -- -- -- 3 -- -- 
III 
##STR39## 
-- -- -- -- -- 4 -- 
IV 
##STR40## 
-- -- -- 4 -- -- -- 
IV 
##STR41## 
-- -- 3 -- -- -- -- 
IV 
##STR42## 
5 -- -- 5 -- -- -- 
IV 
##STR43## 
-- 7.5 -- -- -- -- -- 
C V 
##STR44## 
-- -- 8 -- -- -- -- 2 -- 
V 
##STR45## 
-- -- -- -- -- 4 -- -- -- 
V 
##STR46## 
3 -- -- 6 4 4 9 -- 13 
V 
##STR47## 
-- 7.5 -- -- -- -- -- -- -- 
V 
##STR48## 
-- -- -- 6 -- -- -- -- -- 
D VI 
##STR49## 
-- -- -- -- -- 5 -- -- -- 
VII 
##STR50## 
-- -- -- -- -- -- 3 -- 
6 
TABLE 12 
__________________________________________________________________________ 
Ex. No. Comp. Ex. 
Characteristics 
3 4 5 6 7 8 9 1 2 
__________________________________________________________________________ 
Phase transition temp. (.degree.C.) 
Cr .fwdarw. Sc* 
-5 -4 -7 -5 -3 -8 -6 -2 -4 
Sc* .fwdarw. S.sub.A 
64 62 62 66 62 63 62 60 61 
S.sub.A .fwdarw. N* 
83 85 88 93 82 80 82 73 85 
N* .fwdarw. I.sub.SO 
93 92 96 95 93 90 90 91 89 
Spontaneous polarization 
14 13 11 23 16 24 25 5 35 
value** (nC/cm.sup.2) 
Tilt angle** (.degree.) 
21 20 20 21 21 24 23 18 25 
Helical pitch (.mu.m) 
N* phase*** 9 10 13 15 9 28 35 8 7 
Sc* phase** 7 6 10 10 8 8 10 4 5 
Response time** (.mu.sec) 
60 75 90 67 73 80 65 350 
100 
__________________________________________________________________________ 
Note: 
**values determined at 25.degree. C. 
***values determined at a temperature of 1.degree. C. higher than the 
phase transfer temperature S.sub.A .fwdarw. N*