Liquid crystal compound with a 4-(optically active alkyl)-3-cyanophenyl group

An optically active liquid crystal compound having specific features suitable to a display mode utilizing ferroelectric chiral smectic phases and particularly having a large spontaneous polarization value, and a chiral liquid crystal composition containing the compound are provided, which compound is expressed by the formula ##STR1## wherein R.sup.1 represents an alkyl group of 2 to 18 carbon atoms; R.sup.2 represents an alkyl group or alkoxy group each of 1 to 20 carbon atoms, hydrogen atom, a halogen atom or cyano group; A represents --COO-- or --OCO--; B and C each represent a single bond, ##STR2## wherein X represents hydrogen atom, a halogen atom or cyano group; and l, m and n each represent 0 or 1.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a novel liquid crystalline compound and a liquid 
crystal composition containing the same. More particularly it relates to a 
liquid crystalline compound having an optically active group and a chiral 
liquid crystal composition containing the same. 
2. Description of the Related Art 
At present, TN (Twisted Nematic) display mode has been most broadly 
employed, but it is inferior in the aspect of the response rate to 
emissive type display elements such as electroluminescence, plasma 
display, etc.; hence various improvements in this aspect have been 
attempted, but a possibility of its improvement to a large extent does not 
seem to remain so much. Thus, various devices based on another principle 
in place of that of TN mode display elements have been attempted, and 
among these there is a display mode utilizing ferroelectric liquid 
crystals (N. A. Clark et al; Applied Phys. lett., 36, 899 (1980)). This 
mode utilizes ferroelectric liquid crystal chiral smectic C phase 
(hereinafter abbreviated to SC* phase) or other smectic phases such as SH* 
phase, SF* phase, SG* phase, etc., and has the following three superior 
specific features as compared with TN display mode: 
a first specific feature consists in that the mode affords a very high 
response rate, which amounts to 100 times those of TN mode display 
elements; 
a second specific feature consists in that the mode affords a memory effect 
so that multiplex drive becomes easy in addition to the above-mentioned 
high rate response properties; and 
a third specific feature consists in that it is possible to more easily 
obtain the gray scale than with a TN display mode only by adjusting an 
inverting time of polarity so that the mode has been considered to be 
suitable for graphic display. 
However, in spite of the fact that the mode has the above-mentioned 
superior specific features, currently known ferroelectric liquid crystals 
and compositions have not yet afforded fully satisfactory results in the 
aspect of the response rate; hence the mode appears to have somewhat come 
to a deadlock prior to their practical use. One reason for this can be 
said to consist in that development of a compound having a large 
spontaneous polarization value Ps has been late. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a liquid crystal compound 
having specific features suitable to the above display mode, particularly 
having a large spontaneous polarization value. 
The present inventors have conducted extensive research in order to develop 
an optically active liquid crystal compound suitable to be used for the 
above display mode, and as a result have achieved the present invention. 
The present invention resides in an optically active liquid crystalline 
compound expressed by the formula 
##STR3## 
wherein R.sup.1 represents an alkyl group of 2 to 18 carbon atoms; R.sup.2 
represents an alkyl group or alkoxy group each of 1 to 20 carbon atoms, 
hydrogen atom, a halogen atom or cyano group; A represents --COO-- or 
--OCO--; B and C each represent a single bond, 
##STR4## 
wherein X represents hydrogen atom, a halogen atom or cyano group; and l, 
m and n each represent 0 or 1, and a chiral liquid crystal composition 
containing at least one member of the same.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The phase transition points and spontaneous polarization values Ps of 
representatives of the compound of the formula (I) of the present 
invention are shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
##STR5## 
Sam- 
ple In the above formula Phase transition points (.degree.C.) 
No. m B C R.sup.2 
Cr S.sub.B 
S.sub.C * 
SA Ch I Ps (nC/cm.sup.2) at 
.degree.C. 
__________________________________________________________________________ 
1 0 
##STR6## 
Single bond 
C.sub.8 H.sub.17 
.cndot.22.2 
-- -- -- -- .cndot. 
2 0 
##STR7## 
##STR8## 
C.sub.5 H.sub.11 
.cndot.75.0 
-- -- .cndot.91.1 
.cndot.95.4 
.cndot. 
-28.5.sup.*1 
(25.degree. C.) 
3 0 
##STR9## 
##STR10## 
C.sub.7 H.sub.15 
.cndot.44.4 
(.cndot.40.0) 
-- .cndot.90.0 
.cndot.91.8 
.cndot. 
-30.0.sup.*1 
(25.degree. C.) 
4 0 
##STR11## 
##STR12## 
C.sub.8 H.sub.17 
.cndot.33.0 
(.cndot.11.4) 
.cndot.35.0 
.cndot.89.3 
-- .cndot. 
-15.9 (25.degree. 
C.) 
5 0 
##STR13## 
##STR14## 
OC.sub.4 H.sub.9 
.cndot.128.3 
-- -- .cndot.130.0 
.cndot.136.7 
.cndot. 
6 0 
##STR15## 
##STR16## 
OC.sub.5 H.sub.11 
.cndot.101.8 
-- -- .cndot.121.6 
.cndot.129.0 
.cndot. 
7 0 
##STR17## 
##STR18## 
OC.sub.7 H.sub.15 
.cndot.56.8 
(.cndot.34.5) 
.cndot.81.0 
.cndot.119.5 
.cndot.123.5 
.cndot. 
-34.5 (51.degree. 
C.) 
8 0 
##STR19## 
##STR20## 
OC.sub.8 H.sub.17 
.cndot.47.5 
-- .cndot.85.0 
.cndot.121.3 
.cndot.123.6 
.cndot. 
-37.8 (45.degree. 
C.) 
9 0 
##STR21## 
##STR22## 
OC.sub.10 H.sub.21 
.cndot.52.7 
-- .cndot.86.8 
.cndot.120.8 
-- .cndot. 
-41.5 (46.degree. 
C.) 
10 0 
##STR23## 
##STR24## 
OC.sub.11 H.sub.23 
.cndot.67.2 
-- .cndot.87.5 
.cndot.119.2 
-- .cndot. 
-38.7 (57.5.degree. 
C.) 
11 0 
##STR25## 
##STR26## 
OC.sub.12 H.sub.25 
.cndot.63.7 
-- .cndot.84.7 
.cndot. 119.5 
-- .cndot. 
-34.9 (54.7.degree. 
C.) 
12 0 
##STR27## 
##STR28## 
C.sub.8 H.sub.17 
.cndot.78.3 
-- (.cndot.59.0) 
-- .cndot.84.3 
.cndot. 
-17.5 (49.degree. 
C.) 
13 0 
##STR29## 
##STR30## 
C.sub.8 H.sub.17 
.cndot.61.6 
-- -- -- (.cndot.56.0) 
.cndot. 
14 0 
##STR31## 
##STR32## 
C.sub.8 H.sub.17 
.cndot.62.1 
-- -- (.cndot.56.8) 
.cndot.69.7 
.cndot. 
15 0 
##STR33## 
##STR34## 
C.sub.7 H.sub.15 
.cndot.72.1 
-- -- (.cndot.59.3) 
.cndot.79.5 
.cndot. 
16 0 
##STR35## 
##STR36## 
C.sub.3 H.sub.7 
.cndot.90.5 
-- -- -- (.cndot.82.5) 
.cndot. 
17 1 
##STR37## 
Single bond 
OC.sub.8 H.sub.17 
.cndot.87.4 
-- -- .cndot.106.8 
.cndot.108.7 
.cndot. 
-21.0*.sup.1 
(25.degree. C.) 
__________________________________________________________________________ 
.sup.1 By simple extrapolation from the Ps value of its mixture with 
achiral SC material as exemplifed in Examples 6 and 7. 
.sup.2 Sample numbers 4, 8 and 9 correspond to Examples 3, 1 and 2, 
respectively. 
The first specific feature of the compounds expressed by the formula (I) 
consists in that its spontaneous polarization value is large. As to 
ferroelectric liquid crystals having a large spontaneous value, the 
response rate thereof, i.e., the rate at which molecules are inverted in 
an electric field, has been known to be higher than that of ferroelectric 
liquid crystals having a small spontaneous polarization value. Certain 
compounds of the formula (I) of the present invention have spontaneous 
polarization values exceeding about 40 nC/cm.sup.2. Whereas, in the case 
of compounds corresponding to the compounds of the formula (I) but having 
no cyano group (i.e. having a hydrogen atom in place of the cyano group), 
for example, a compound (A) 
##STR38## 
(a substance disclosed in Japanese patent application laid-open No. Sho 
53-22883/1978) has about plus 1 nC/cm.sup.2 as measured by the present 
inventors. Thus, the larger spontaneous polarization values of the 
compounds of the formula (I) of the present invention have come to be 
presumed to originate from the fact that cyano group is present at the 
ortho-position relative to the optically active group. Namely, it is 
considered that a substituent perpendicular to the major axis of the 
molecule and having a large permanent dipole moment, i.e. the cyano group, 
is present in a position close to the asymmetric carbon atom so that a 
large spontaneous polarization is induced by an interaction between them. 
On the other hand, it has been found that in the case of a compound having 
an asymmetric carbon atom apart from the dipole moment of its substituent 
or a compound having a substituent having a far smaller dipole moment than 
that of a cyano group, such as a fluorine atom, chlorine atom, bromine 
atom, etc., the spontaneous polarization values thereof do not become so 
large. Namely, it has been found by the research of the present inventors 
that for example, in the case of a compound having a fluorine atom in 
place of a cyano group in the formula (I) of the present invention, its 
spontaneous polarization value is almost nil. 
It can be said that the large spontaneous polarization value originates 
from the following cores: 
o-cyano-2-methylalkylphenyl or o-cyano-1-methylalkylphenyl, these groups 
corresponding to the case where l=0 or 1 in the formula (I), 
##STR39## 
and any of liquid crystal compounds containing such cores are superior 
ferroelectric liquid crystal materials having a large spontaneous 
polarization value. 
In particular, the compounds of l=1, i.e., the compounds having an 
o-cyano-2-methylalkylphenyl group, are easier to prepare than those of 
l=0; in this respect, the former compounds are practically more important 
than the latter. Further, compounds having an optically active group whose 
absolute configuration is in S-form are advantageous in view of the fact 
that the raw materials thereof are readily commercially available. 
Comparison of the compounds of the formula (I) with the 
non-cyano-substituted compounds represented by the above formula (A) is 
interesting. When the two series of compounds both having an absolute 
configuration of S-form are compared, 
(i) the compounds of the formula (I) have a spontaneous polarization having 
a sign of minus and a large value, whereas the compounds of the formula 
(A) have a sign of plus and a small value; 
(ii) the compounds of the formula (I) and those of the formula (A) both 
have a right-handed helical twist sense in smectic C phase; and 
(iii) the cholesteric phase induced when the compounds of the formula (I) 
and those of the formula (A) are added to nematic liquid crystals, 
respectively, both have a right-handed helical twist sense. The fact of 
the above paragraph (i) will be explained to be due to the fact that the 
cyano group at the ortho-position on the phenyl ring has a sign reverse to 
that of the spontaneous polarization based on 2-methylalkylphenyl group 
and also has a larger spontaneous polarization value than that of the 
latter. Further, the facts of the above paragraphs (ii) and (iii) will 
exhibit that the handedness of the helix is determined only by the 
absolute configuration of the optically active groups. Such specific 
features of the compounds of the formula (I) result in that the compounds 
are useful as a component of chiral smectic C liquid crystal compositions. 
Namely, when the S-form compounds of the formula (I) wherein l=1 are used 
together with other SC* compounds wherein the sign of the spontaneous 
polarization is minus, the former compounds can afford a large spontaneous 
polarization value without offsetting the spontaneous polarization value 
thereof, unlike the above A type compounds, and also since the handedness 
of the helix thereof is right-handed, the former compounds can make the 
helical pitch of left-handed SC* liquid crystal compositions longer. 
In addition, the compounds of the formula (I) have an optically active 
carbon; hence when they are added to nematic liquid crystals, they have a 
capability of inducing a twisted structure (cholesteric phase) Nematic 
liquid crystals having a twisted structure, i.e. chiral nematic liquid 
crystals, do not form the so-called reverse domain of TN mode display 
elements; hence it is also possible to use the compounds as an agent for 
preventing the reverse domain from forming. 
The compounds of the formula (I) of the present invention have specific 
features of a strong twisting power and a small temperature-dependency of 
the twisting power. Namely, as to the cholesteric pitch of the chiral 
nematic liquid crystals, for example when a compound of Sample No. 8 of 
Table 1 was added in 1% by weight to ZLI-1132 manufactured by Merck 
Company and the pitch of the resulting compositions was measured, the 
pitch was as short as 19 .mu.m; hence they can be said to be very useful 
as a pitch-adjusting agent for chiral nematic liquid crystal compositions. 
Further, the temperature-dependency thereof was so small that the 
temperature specific feature .delta.p expressed by the formula 
##EQU1## 
was as very small as plus 0.212 (at t.sub.1 =20.degree. C. and t.sub.2 
=70.degree. C.). This can be said to be a surprising specific feature as 
compared with the fact that, e.g. (S)-4-(2'-methylbutyl)-4'-cyanobiphenyl 
as a currently known pitch-adjusting agent for chiral nematic liquid 
crystal compositions, has a p.delta. of plus 0.584 as measured under the 
same conditions. 
Next, preparation of the compounds of the formula (I) will be described. 
A compound of the formula (I) wherein A=--COO-- and n=1 may be suitably 
prepared through the following route: 
##STR40## 
In the above equations, R.sup.1, R.sup.2, l, m, B and C are as defined 
above. 
Namely, a 4-(1'-methylalkyl)benzoic acid, 4-(2'-methylalkyl)benzoic acid, 
4-(1'-methylalkyl)biphenyl-4'-carboxylic acid or 
4-(2'-methylalkyl)biphenyl-4'-carboxylic acid (1) is brominated in the 
presence of a catalyst to obtain a 3-bromo-4-(1'-methylalkyl)benzoic acid, 
3-bromo-4-(2'-methylalkyl)benzoic acid, 
3-bromo-4-(1'-methylalkyl)biphenyl-4'-carboxylic acid or 
3-bromo-4-(2'-methylalkyl)biphenyl-4'-carboxylic acid (2), which is 
esterified by reacting a phenolic compound therewith to obtain a compound 
(3), which is reacted with a cyanogenating agent such as cuprous cyanide 
to obtain a compound of the formula (I). 
Further, in the above steps, the order of the cyanogenation and 
esterification may also be reversed. Namely, the compound (2) may be 
cyanogenated to obtain a 3-cyano-4-(1'-methylalkyl)benzoic acid, 
3-cyano-4-(2'-methylalkyl)benzoic acid, 
3-cyano-4-(1'-methylalkyl)biphenyl-4'-carboxylic acid or 
3-cyano-4-(2'-methylalkyl)biphenyl-4'-carboxylic acid, which is then 
esterified to obtain a compound of the formula (I). 
Next, a compound of the formula (I) wherein A=--OCO-- and n=1 may be 
suitably prepared through the following route: 
##STR41## 
In the above equations, R.sup.1, R.sup.2, l, m, B and C are as defined 
above. Further, in the above steps, the order of the cyanogenation and 
esterification may also be reversed. Namely, the compound (7) may be 
cyanogenated to obtain a 3-cyano-4-(1'-methylalkyl)phenol, 
3-cyano-4-(2'-methylalkyl)phenol, 
3-cyano-4-(1'-methylalkyl)-4'-hydroxybiphenyl or 
3-cyano-4-(2'-methylalkyl)-4'-hydroxybiphenyl, which is then esterified to 
obtain the compound of the formula (I). 
Further, a compound of the formula (I) wherein n=0 and B and C each 
represent a single bond may be suitably prepared through the following 
route: 
First, in the case of R.sup.2 =alkoxy: 
##STR42## 
In the above equations, R.sup.1, l and m are as defined above and R 
represents an alkyl group. 
Namely, the compound (7) prepared above is reacted with an alkylating agent 
such as an alkyl bromide to obtain a compound (9), which is then reacted 
with a cyanogenating agent such as cuprous cyanide to obtain the compound 
of the formula (I). 
Next, in the case of R.sup.2 =alkyl: 
##STR43## 
In the above equations, R.sup.1, l and m are as defined above and R 
represents an alkyl group. 
Namely, a 4-(1'-methylalkyl)-alkylbenzene, 4-(2'-methylalkyl)-alkylbenzene, 
4-(1'-methylalkyl)-4'-alkylbiphenyl or 4-(2'-methylalkyl)-4'-alkylbiphenyl 
(10) is brominated in the presence of a catalyst to obtain a compound 
(11), which is then reacted with a cyano-genating agent such as cuprous 
cyanide to obtain the compound of the formula (I). 
The optically active liquid crystal compound of the present invention will 
be described in more detail by way of Examples. 
EXAMPLE 1 
Preparation of (S)-3-cyano-4-(2'-methylbutyl)benzoic acid 
4-octyloxy-4'-biphenylyl ester (a compound of the formula (I) wherein m=0; 
n=1; A=--COO--; R.sup.1 =C.sub.2 H.sub.5 --; R.sup.2 =--OC.sub.8 H.sub.17 
; and 
##STR44## 
A solution of silver nitrate (177 g, 1.1 mol) in water (500 ml) was 
dropwise added to a solution in water (500 ml), of a mixture of 
(S)-4-(2'-methylbutyl)benzoic acid (200 g, 1.0 mol), nitric acid (680 ml) 
and bromine (183 g, 1.1 mol), under ice-cooling, followed by agitating the 
mixture at room temperature for 5 hours, feeding it into ice water, 
filtering deposited crystals, adding a 10% sodium carbonate aqueous 
solution (2 l), sufficiently agitating the mixture, filtering off a 
remaining insoluble substance, acidifying the filtrate with sulfuric acid, 
filtering deposited crystals and recrystallizing from acetic acid (1 l) to 
obtain 3-bromo-4-(2'-methylbutyl)benzoic acid (106.0 g, m.p. 
78.8.degree.-79.7.degree. C.). 
Thionyl chloride (118 g) was added to the 3-bromo-4-(2'-methylbutyl)benzoic 
acid (100 g, 0.37 mol) followed by refluxing the mixture for 2 hours and 
distilling off excess thionyl chloride under reduced pressure to obtain 
3-bromo-4-(2'-methylbutyl)benzoic acid chloride (105.1 g). 
This 3-bromo-4-(2'-methylbutyl)benzoic acid chloride (11.5 g, 0.04 mol) was 
dropwise added to a mixture of 4-hydroxy-4'-octyloxybiphenyl with 
anhydrous pyridine under ice cooling, followed by agitating the resulting 
mixture at 50.degree.-60.degree. C. for 2 hours, adding toluene (100 ml), 
sufficiently agitating the mixture, washing it with 6N-HCl, then with 
2N-NaOH aqueous solution and further with water, further drying over 
anhydrous MgSO.sub.4, distilling off toluene and recrystallizing the 
residue from a mixture of ethanol (100 ml) with ethyl acetate (60 ml) to 
obtain 3-bromo-4-(2'-methylbutyl)benzoic acid 4'-octyloxy-4-biphenylyl 
ester (12.2 g), which exhibited liquid crystalline properties and had the 
following phase transistion points: 
##STR45## 
A mixture of this 3-bromo-4-(2'-methylbutyl)benzoic acid 
4-octyloxy-4'-biphenylyl ester (5.5 g, 0.01 mol), cuprous cyanide (1.1 g, 
0.06 mol) and dimethylformamide (20 ml) was heated to 
145.degree.-147.degree. C., following by agitating it for 6 hours, adding 
a mixture of ferric chloride (4 g), hydrochloric acid (1 ml) and water (7 
ml), keeping the mixture at 60.degree.-70.degree. C. for 15 minutes, 
feeding it into ice water, adding toluene, sufficiently agitating the 
mixture, transferring it into a separating funnel, several times washing 
the resulting organic layer with water, drying it over anhydrous 
MgSO.sub.4, distilling off toluene and recrystallizing the residue from 
ethanol (50 ml) to obtain the objective 3-cyano-4-(2'-methylbutyl)benzoic 
acid 4'-octyloxy-4-biphenylyl ester (1.7 g). The phase transition points 
of this product were as follows: 
##STR46## 
EXAMPLE 2 
Preparation of (S)-3-cyano-4-(2'-methylbutyl)benzoic acid 
4'-decyloxy-4-biphenylyl ester (a compound of the formula (I) wherein m=0; 
n=1; A=--COO--; R.sup.1 =C.sub.2 H.sub.5 ; R.sup.2 =--OC.sub.10 H.sub.21 ; 
and 
##STR47## 
Example 1 was repeated except that 4-hydroxy-4'-octyloxybiphenyl was 
replaced by 4-hydroxy-4'-decyloxybiphenyl, to obtain 
(S)-3-cyano-4-(2'-methylbutyl)benzoic acid 4'-decyloxy-4-biphenylyl ester. 
The phase transition points of this product were as follows: 
##STR48## 
EXAMPLE 3 
Preparation of (S)-3-cyano-4-(2'-methylbutyl)benzoic acid 
4-octyl-4'-biphenylyl ester (a compound of the formula (I) wherein m=0; 
n=1, A=--COO--; R.sup.1 =C.sub.2 H.sub.5 --; R.sup.2 =--C.sub.8 H.sub.17 ; 
and 
##STR49## 
Example 1 was repeated except that 4-hydroxy-4'-octyloxybiphenyl was 
replaced by 4-hydroxy-4'-octylbiphenyl to obtain 
(S)-3-cyano-4'-(2'-methyloctyl)benzoic acid 4'-octyl-4-biphenylyl ester. 
The phase transition points of this product were as follows: 
##STR50## 
Further, as previously described, in the case where the order of the 
cyanogenation and esterification steps may be reversed, Examples 1 to 3 
are changed as follows: 3-bromo-4-(2'-methylbutyl)benzoic acid is first 
cyanogenated to obtain 3-cyano-4-(2'-methylbutyl)benzoic acid (m.p. 
91.2.degree.-92.1.degree. C.), which is then esterified. The physical 
properties of the resulting product were the same as those in the cases of 
Examples 1 to 3. 
EXAMPLE 4 
Preparation of (S)-3-cyano-4-(2'-methylbutyl)biphenyl-4'-carboxylic acid 
4-octyloxyphenyl ester (a compound of the formula (I) wherein m=1; n=1; 
A=--COO--; R.sup.1 =C.sub.2 H.sub.5 --; R.sup.2 =--OC.sub.8 H.sub.17 ; 
##STR51## 
Example was repeated except that (S)-4-(2'-methylbutyl)benzoic acid was 
replaced by (S)-4-(2'-methylbutyl)biphenyl-4'-carboxylic acid to obtain 
(S)-3-cyano-4-(2'-methylbutyl)biphenyl-4'-carboxylic acid 4-octyloxyphenyl 
ester. The phase transition points of this product were as follows: 
##STR52## 
EXAMPLE 5 (USE EXAMPLE 1) 
A liquid crystal mixture consisting of the following proportions of achiral 
smectic liquid crystal compounds was prepared: 
______________________________________ 
##STR53## 30% by weight 
##STR54## 20% by weight 
##STR55## 10% by weight 
##STR56## 10% by weight 
##STR57## 20% by weight 
##STR58## 10% by weight 
______________________________________ 
The above mixture has a m.p. of 4.degree. C. and exhibits SC phase at 
higher temperature than the above, SA phase at 65.degree. C., N phase at 
79.degree. C. and isotropic liquid at 90.degree. C. 
To this liquid crystal mixture (80% by weight) was added compound No. 8 in 
Table 1 (20% by weight) to prepare a chiral smectic liquid crystal 
composition. 
This liquid crystal composition was filled in a cell of 2 .mu.m thick 
provided with transparent electrodes each obtained by coating the surface 
with PVA (polyvinyl alcohol) and rubbing the resulting surface to subject 
it to parallel aligning treatment, followed by placing the resulting 
liquid crystal element between a polarizer and an analyzer crossed to each 
other and impressing a voltage of 15 V. As a result, change in the 
intensity of transmitted light was observed. The response time was sought 
from the change in the intensity of transmitted light at that time to give 
about 125 .mu.sec at 25.degree. C. 
The above composition had a m.p. of 0.degree. C. and exhibited SC* phase at 
higher temperatures than the above, SA phase at 69.2.degree. C., 
cholesteric phase (Ch phase) at 84.5.degree. C. and isotropic liquid at 
92.6.degree. C. The twist senses in the SC* phase and Ch phase were both 
right-handed. 
In addition, its spontaneous polarization value was minus 3 nC/cm.sup.2 at 
25.degree. C. and its tilt angle was 19.degree.. 
As described above, it is seen that when a compound of the formula (I) of 
the present invention is mixed with non-optically active liquid crystal 
compounds, a superior ferroelectric chiral smectic liquid crystal 
composition is obtained. 
EXAMPLE 6 (USE EXAMPLE 2) 
To the same achiral liquid crystal composition as in Example 5 (80% by 
weight) was added compound No. 17 as a compound of the present invention 
(20% by weight). The resulting liquid crystal composition exhibited the 
following transition points: 
C-SC* 3.degree. C.: SC*-SA 70.0.degree. C.: SA-Ch 80.0.degree. C. and Ch-I 
90.6.degree. C. 
This composition also exhibited a spontaneous polarization value of minus 
4.2 nC/cm.sup.2, a tilt angle of 25.degree. and a right-handed SC* twist 
sense, and the response time was 120 .mu.sec under the same conditions as 
in Example 5. 
It was impossible to directly observe the SC* phase of Compound No. 17 by 
itself since it crystallized before it was cooled down to a temperature at 
which SC* phase was exhibited, but as shown in this Example, by mixing 
with a SC liquid crystal composition, it can be used for constituting a 
ferroelectric liquid crystal composition. This fact applies to other 
compounds shown in Table 1 which are not observed to exhibit SC* phase by 
themselves. 
EXAMPLE 7 (USE EXAMPLE 3) 
To the achiral smectic liquid crystal composition described in Example 5 
(80% by weight) was added a compound of Sample No. 3 (in Table 1) (20% by 
weight) to prepare a chiral smectic composition. This composition 
exhibited the following phase transition points: 
C-SC* -11.degree. C.; SC*-SA 62.1.degree. C.; SA-Ch 77.5.degree. C.; and 
Ch-I 86.1.degree. C. 
Its Ps at 25.degree. C. was minus 6.0 nC/cm.sup.2 and its tilt angle was 
18.degree.. 
This liquid crystal composition was made up into a liquid crystal cell as 
described in Example 5 and the response time was measured under the same 
conditions but at an impressed voltage of 20 V to give 90 .mu.sec. 
EXAMPLE 8 (USE EXAMPLE 4) 
A nematic liquid crystal composition consisting of 
______________________________________ 
##STR59## 20% 
##STR60## 40% 
##STR61## 25% 
##STR62## 15% 
______________________________________ 
was filled in a cell having a distance of 10 .mu.m between electrodes to 
prepare a TN mode display cell, which was then observed under a polarizing 
microscope. As a result, a reverse domain was observed to be formed. In 
addition, the cell used was obtained by coating the surface with polyvinyl 
alcohol and rubbing the resulting surface to subject it to parallel 
aligning treatment. 
To the above nematic liquid crystal composition was added compound No. 8 in 
Table 1 in an amount of 0.1% by weight, and a TN mode cell the same as the 
above was prepared. As a result of observing the cell, the reverse domain 
was dissolved and a uniform nematic phase was observed.