Abstract:
An optically inactive mesomorphic compound of the formula (I) according to claim 1 characterized by having a terminal group of: --A 3  --C r  F 2r+1 , where A 3  is a specific cyclic group and r is 2-18, is suitable as a component for a liquid crystal composition providing improved response characteristics and a high contrast. A liquid crystal device is constituted by disposing the liquid crystal composition between a pair of electrode plates. The liquid crystal device is used as a display panel constituting a display apparatus (or display method) providing good display characteristics.

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to a mesomorphic compound, a liquid crystal composition, a liquid crystal device, a display apparatus and a display method, and more particularly to an optically inactive compound, a liquid crystal composition containing the compound with improved responsiveness to an electric field, a liquid crystal device using the composition for use in a display device, a liquid crystal-optical shutter, etc., a display apparatus using the device, and a display method of using the composition or device. 
     Hitherto, liquid crystal devices have been used as an electro-optical device in various fields. Most liquid crystal devices which have been put into practice use TN (twisted nematic) type liquid crystals, as shown in &#34;Voltage-Dependent Optical Activity of a Twisted Nematic Liquid Crystal&#34; by M. Schadt and W. Helfrich &#34;Applied Physics Letters&#34; Vol. 18, No. 4 (Feb. 15, 1971) pp. 127-128. 
     These devices are based on the dielectric alignment effect of a liquid crystal and utilize an effect that the average molecular axis direction is directed to a specific direction in response to an applied electric field because of the dielectric anisotropy of liquid crystal molecules. It is said that the limit of response speed is on the order of μsec, which is too slow for many uses. On the other hand, a simple matrix system of driving is most promising for application to a large-area flat display in view of cost, productivity, etc., in combination. In the simple matrix system, an electrode arrangement wherein scanning electrodes and signal electrodes are arranged in a matrix, and for driving, a multiplex driving scheme is adopted wherein an address signal is sequentially, periodically and selectively applied to the scanning electrodes and prescribed data signals are selectively applied in parallel to the signal electrodes in synchronism with the address signal. 
     When the above-mentioned TN-type liquid crystal is used in a device of such a driving system, a certain electric field is applied to regions where a scanning electrode is selected and signal electrodes are not selected (or regions where a scanning electrode is not selected and a signal electrode is selected), which regions are called &#34;half-selected points&#34;. If the difference between a voltage applied to the selected points and a voltage applied to the half-selected points is sufficiently large, and a voltage threshold level required for allowing liquid crystal molecules to be aligned or oriented perpendicular to an electric field is set to a value therebetween, display devices normally operate. However, in fact, as the number (N) of scanning lines increases, a time (duty ratio) during which an effective electric field is applied to one selected point when a whole image area (corresponding to one frame) is scanned decreases with a ratio of 1/N. Accordingly, the larger the number of scanning lines are, the smaller is the voltage difference of an effective value applied to a selected point and non-selected points when scanning is repeatedly effected. This leads to unavoidable drawbacks of lowering of image contrast or occurrence of interference or crosstalk. These phenomena are regarded as essentially unavoidable problems appearing when a liquid crystal having no bistability (i.e. liquid crystal molecules are horizontally oriented with respect to the electrode surface as stable state and is vertically oriented with respect to the electrode surface only when an electric field is effectively applied) is driven (i.e. repeatedly scanned) by making use of a time storage effect. To overcome these drawbacks, the voltage averaging method, the two-frequency driving method, the multiple matrix method, etc. have been already proposed. However, any method is not sufficient to overcome the above-mentioned drawbacks. As a result, the development of large image area or high packaging density in respect to display elements is delayed because it is difficult to sufficiently increase the number of scanning lines. 
     To overcome drawbacks with such prior art liquid crystal devices, the use of liquid crystal devices having bistability has been proposed by Clark and Lagerwall (e.g. Japanese Laid-Open Patent Appln. No. 56-107216; U.S. Pat. No. 4,367,924, etc.). In this instance, as the liquid crystals having bistability, ferroelectric liquid crystals having chiral smectic C-phase (SmC*) or H-phase (SmH*) are generally used. These liquid crystals have bistable states of first and second stable states with respect to an electric field applied thereto. Accordingly, as different from optical modulation devices in which the above-mentioned TN-type liquid crystals are used, the bistable liquid crystal molecules are oriented to first and second optically stable states with respect to one and the other electric field vectors, respectively. Further, this type of liquid crystal has a property (bistability) of assuming either one of the two stable states in response to an applied electric and retaining the resultant state in the absence of an electric field. 
     In addition to the above-described characteristic of showing bistability, such a ferroelectric liquid crystal (hereinafter sometimes abbreviated as &#34;FLC&#34;) has an excellent property, i.e., a high-speed responsiveness. This is because the spontaneous polarization of the ferroelectric liquid crystal and an applied electric field directly interact with each other to induce transition of orientation states. The resultant response speed is faster than the response speed due to the interaction between dielectric anisotropy and an electric field by 3 to 4 digits. 
     Thus, a ferroelectric liquid crystal potentially has very excellent characteristics, and by making use of these properties, it is possible to provide essential improvements to many of the above-mentioned problems with the conventional TN-type devices. Particularly, the application to a high-speed optical shutter and a display of a high density and a large picture is expected. For this reason, there has been made extensive research with respect to liquid crystal materials showing ferroelectricity. However, previous ferroelectric liquid crystal materials do not sufficiently satisfy characteristics required for a liquid crystal device including low-temperature operation characteristic, high-speed responsiveness, high contrast, etc. 
     More specifically, among a response time τ, the magnitude of spontaneous polarization Ps and viscosity η, the following relationship exists: τ=η/(Ps·E), where E is an applied voltage. Accordingly, a high response speed can be obtained by (a) increasing the spontaneous polarization Ps, (b) lowering the viscosity η, or (c) increasing the applied voltage E. However, the driving voltage has a certain upper limit in view of driving with IC, etc., and should desirably be as low as possible. Accordingly, it is actually necessary to lower the viscosity or increase the spontaneous polarization. 
     A ferroelectric chiral smectic liquid crystal having a large spontaneous polarization generally provides a large internal electric field in a cell given by the spontaneous polarization and is liable to pose many constraints on the device construction giving bistability. Further, an excessively large spontaneous polarization is liable to accompany an increase in viscosity, so that remarkable increase in response speed may not be attained as a result. 
     Moreover, if it is assumed that the operation temperature of an actual display device is 5°-40° C., the response speed changes by a factor of about 20, so that it actually exceeds the range controllable by driving voltage and frequency. 
     In general, in a liquid crystal device utilizing birefringence of a liquid crystal, the transmittance under right angle cross nicols is given by the following equation: 
     
         I/I.sub.0 =sin.sup.2 4θ·sin.sup.2 (Δnd/λ)π, 
    
     wherein 
     I 0  : incident light intensity, 
     I: transmitted light intensity, 
     θ: tilt angle, 
     Δn: refractive index anisotropy, 
     d: thickness of the liquid crystal layer, 
     λ: wavelength of the incident light. 
     Tilt angle θ in a ferroelectric liquid crystal with non-helical structure is recognized as a half of an angle between the average molecular axis directions of liquid crystal molecules in a twisted alignment in a first orientation state and a second orientation state. According to the above equation, it is shown that a tilt angle θ of 22.5 degrees provides a maximum transmittance and the tilt angle θ in a non-helical structure for realizing bistability should desirably be as close as possible to 22.5 degrees in order to provide a high transmittance and a high contrast. 
     However, when a birefringence of a liquid crystal is utilized in a liquid crystal device using a ferroelectric liquid crystal in a non-helical structure exhibiting bistability reported by Clark and Lagerwall, the following problems are encountered, thus leading to a decrease in contrast 
     First, a tilt angle θ in a ferroelectric liquid crystal with a non-helical structure obtained by alignment with a polyimide film treated by rubbing of the prior art has become smaller as compared with a tilt angle  H (the angle  H is a half of the apex angle of the cone shown in FIG. 4 as described below) in the ferroelectric liquid crystal having a helical structure, thus resulting in a lower transmittance. 
     Secondly, even if the device provides a high contrast in a static state, i.e., under no electric field application, liquid crystal molecules fluctuate due to a slight electric field at a non-selection period of time in a matrix drive scheme in the case of applying a voltage to the liquid crystal molecules for providing a display image, thus resulting in the display image including a light (or pale) black display state, i.e., a decrease in a contrast. 
     Thus, as described hereinabove, commercialization of a ferroelectric liquid crystal device requires a liquid crystal composition assuming a chiral smectic phase which provides a high contrast, a high-speed responsiveness and a small temperature-dependence of response speed. 
     In order to afford uniform switching characteristics at display, a good view-angle characteristic, a good storage stability at a low temperature, a decrease in a load to a driving IC (integrated circuit), etc. to the above-mentioned ferroelectric liquid crystal device or a display apparatus including the ferroelectric liquid crystal device, the above-mentioned liquid crystal composition is required to optimize its properties such as spontaneous polarization, a chiral smectic C (SmC*) pitch, a cholesteric (Ch) pitch, a temperature range showing a mesomorphic phase, optical anisotropy, a tilt angle and dielectric anisotropy. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a mesomorphic compound providing a high speed responsiveness, a high contrast and a decreased temperature-dependence of response speed; a liquid crystal composition, particularly a chiral smectic liquid crystal composition containing the mesomorphic compound for providing a practical ferroelectric liquid crystal device as described above; a liquid crystal device including the liquid crystal composition and affording good display performances; a display apparatus including the device; and a display method using the composition or device. 
     According to the present invention, there is provided an optically inactive mesomorphic compound represented by the following formula (I): ##STR1## in which R 1  denotes hydrogen; halogen; --CN; --X 3  .paren open-st.CH 2  .paren close-st. p  C t  F 2t+1  where p is an integer of 0-18, t is an integer of 1-18, and X 3  denotes a single bond, --O--, --CO--O-- or --O--CO--; or a linear, branched or cyclized alkyl group having 1-18 carbon atoms capable of including at least one methylene group which can be replaced with --O--; --S--; --CO--; --CHW-- where W is halogen, --CN or --CF 3  ; --CH═CH-- or --C.tbd.C-- provided that heteroatoms are not connected with each other; 
     A 3  denotes ##STR2##  and A 1  and A 2  independently denote A 3 , ##STR3##  wherein Y 1  and Y 2  independently denote hydrogen, halogen, --CH 3 , --CF 3  or --CN; R 2 , R 3 , R 4 , R 5 , R 6  and R 7  independently denote hydrogen, or a linear or branched alkyl group having 1-18 carbon atoms; and Z 1  is O or S; 
     X 1  and X 2  independently denote a single bond, --Z 2  --, --CO--, --COZ 2  --, --Z 2  CO--, --CH 2  O--, --OCH 2  --, --OCOO--, --CH 2  CH 2  --, --CH═CH-- or --C.tbd.C-- wherein Z 2  is O or S; 
     m is 0 or 1; 
     r is an integer of 2-18; and 
     with the proviso that when m=0, A 2  is ##STR4##  and A 3  is ##STR5##  then X 2  cannot be a single bond, and that when m=0, A 2  and A 3  are ##STR6##  and X 2  is --OCO--, then R 1  denotes hydrogen; halogen; --X 3  .paren open-st.CH 2  .paren close-st. p  C t  F 2t+1  where p is an integer of 0-18, t is an integer of 1-18, and X 3  denotes a single bond, --O--, --CO--O-- or --O--CO--; or a linear, branched or cyclized alkyl group having 1-18 carbon atoms capable of including at least one methylene group which can be replaced with --S--, --CO--, --COO--, --OCO--, --CH═CH-- or --C.tbd.C-- provided that heteroatoms are not connected with each other. Heretofore, there have been known mesomorphic compounds having a perfluoroalkyl group including those disclosed in Japanese Laid-Open Patent Application Nos. 63-27451, 2-142753, 1-230548 and 2-69443. These compounds have a linkage between a terminal perfluoroalkyl group and an inner mesogen skeleton. The linkage is ether group or ester group respectively containing methylene group or ethylene group. Thus, these compounds are distinguished from the above-mentioned mesomorphic compound of the formula (I) containing a mesogen skeleton (A 3 ) and a perfluoroalkyl group (C r  F 2r+1 ) directly connected to the mesogen skeleton (i.e., --A 3  --C r  F 2r+1 ). 
     JP-A (Kokai) 3-93748 discloses compounds capable of containing a mesogen skeleton and a perfluoroalkyl group directly connected to each other. However, the compounds are limited to an optically active compound, thus being different from the optically inactive mesomorphic compound of the formula (I) according to the present invention. JP-A (Kohyo) 1-501945 discloses compounds containing a cyclohexane ring ##STR7## and a perfluoroalkyl group directly connected to the cyclohexane ring. On the other hand, the mesomorphic compound of the formula (I) has the mesogen skeleton (A 3 ) containing no cyclohexane ring, thus being different from the compounds of JP-A 1-501945. 
     According to the present invention, there is further provided a liquid crystal composition containing at least one species of the above-mentioned mesomorphic compound. 
     The present invention provides a liquid crystal device including the liquid crystal composition, particularly a liquid crystal device comprising a pair of electrode plates and the liquid crystal composition described above disposed between the electrode plates. 
     The present invention further provides a display apparatus including a display panel comprising the liquid crystal device. 
     The present invention still further provides a display method using the liquid crystal composition or the liquid crystal device described above and controlling the alignment direction of liquid crystal molecules in accordance with image data thereby to obtain a desired display image. 
     We have found that an optically inactive mesomorphic compound represented by the formula (I) is suitable as a component of a liquid crystal composition, particularly a ferroelectric chiral smectic liquid crystal composition, and a liquid crystal device including the liquid crystal composition which provides good display characteristics based on improvements in various characteristics such as an alignment characteristic, switching characteristic, responsiveness, a temperature-dependence of response speed, and a contrast. As the mesomorphic compound of the formula (I) according to the present invention has good compatibility with another (mesomorphic) compound used herein, it is possible to use the mesomorphic compound of the formula (I) for controlling various properties such as spontaneous polarization, SmC* pitch, Ch pitch, a temperature range showing a mesomorphic phase, optical anisotropy, a tilt angle and dielectric anisotropy, with respect to a liquid crystal mixture or composition. 
    
    
     These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic sectional view of a liquid crystal device using a liquid crystal composition assuming a chiral smectic phase; 
     FIGS. 2 and 3 are schematic perspective views of a device cell embodiment for illustrating the operation principle of a liquid crystal device utilizing ferroelectricity of a liquid crystal composition; 
     FIG. 4 is a schematic view for illustrating a tilt angle H in a ferroelectric liquid crystal with a helical structure. 
     FIG. 5A shows unit driving waveforms used in an embodiment of the present invention; FIG. 5B is time-serial waveforms comprising a succession of such unit waveforms; 
     FIG. 6 is an illustration of a display pattern obtained by an actual drive using the time-serial waveforms shown in FIG. 5B; 
     FIG. 7 is a block diagram showing a display apparatus comprising a liquid crystal device utilizing ferroelectricity of a liquid crystal composition and a graphic controller; and 
     FIG. 8 is a time chart of image data communication showing time correlation between signal transfer and driving with respect to a liquid crystal display apparatus and a graphic controller. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred examples of the optically inactive mesomorphic compound of the formula (I) may include mesomorphic compounds containing no or one linkage group between mesogen groups since a linkage group comprising a polar group (e.g., --CO--O--) generally increases a viscosity of a mesomorphic compound having the linkage group. More specifically, the mesomorphic compound of the formula (I) may preferably include compounds represented by the following formulae (II), (III) and (IV): 
     
         R.sub.1 --A.sub.2 --X.sub.2 --A.sub.3 --C.sub.r F.sub.2r+1 (II), 
    
     
         R.sub.1 --A.sub.1 --A.sub.2 --X.sub.2 --A.sub.3 --C.sub.r F.sub.2r+1 (III), 
    
     and 
     
         R.sub.1 --A.sub.1 --X.sub.1 --A.sub.2 --X.sub.2 --A.sub.3 --C.sub.r F.sub.2r+1                                                (IV). 
    
     In the above, R 1 , A 1 , A 2 , A 3 , X 1 , X 2  and r are the same as those in the above-mentioned formula (I). 
     In view of some properties such as a wider mesomorphic temperature range, a good compatibility, a lower viscosity, a good alignment characteristic, etc.; the above mesomorphic compounds represented by the formulae (II), (III) and (IV) may preferably be mesomorphic compounds represented by the following formulae (IIa) to (IIg), (IIIa) to (IIIg) and (IVa) to (IVf), respectively. 
     
         R.sub.1 --A.sub.2 --A.sub.3 --C.sub.r F.sub.2r+1           (IIa) 
    
     
         R.sub.1 --A.sub.2 --OOC--A.sub.3 --C.sub.r F.sub.2r+1      (IIb) 
    
     
         R.sub.1 --A.sub.2 --COO--A.sub.3 --C.sub.r F.sub.2r+1      (IIc) 
    
     
         R.sub.1 --A.sub.2 --OCH.sub.2 --A.sub.3 --C.sub.r F.sub.2r+1 (IId) 
    
     
         R.sub.1 --A.sub.2 --CH.sub.2 O--A.sub.3 --C.sub.r F.sub.2r+1 (IIe) 
    
     
         R.sub.1 --A.sub.2 --CH.sub.2 CH.sub.2 --A.sub.3 --C.sub.r F.sub.2r+1 (IIf) 
    
     
         R.sub.1 --A.sub.2 --C.tbd.C--A.sub.3 --C.sub.r F.sub.2r+1  (IIg) 
    
     in which 
     R 1  denotes hydrogen; halogen; --CN; --X 3  .paren open-st.CH 2  .paren close-st. p  C t  F 2t+1  where p is an integer of 0-18, t is an integer of 1-18, and X 3  denotes a single bond, --O--, --CO--O-- or --O--CO--; or a linear, branched or cyclized alkyl group having 1-18 carbon atoms capable of including at least one methylene group which can be replaced with --O--; --S--; --CO--; --CHW-- where W is halogen, --CN or --CF 3  ; --CH═CH-- or --C.tbd.C-- provided that heteroatoms are not connected with each other; 
     A 3  denotes ##STR8##  and A 2  denotes A 3 , ##STR9##  wherein Y 1  and Y 2  independently denote hydrogen, halogen, --CH 3 , --CF 3  or --CN; R 2 , R 3  and R 4  independently denote hydrogen, or a linear or branched alkyl group having 1-18 carbon atoms; and Z 1  is O or S; 
     r is an integer of 2-18; and 
     with the proviso that when A 2  is ##STR10##  in the formula (IIa), then A 3  cannot be ##STR11##  and that when A 2  and A 3  are ##STR12##  in the formula (IIb), then R 1  denotes hydrogen; halogen; --X 3  .paren open-st.CH 2  .paren close-st. p  C t  F 2t+1  where p is an integer of 0-18, t is an integer of 1-18, and X 3  denotes a single bond, --O--, --CO--O-- or --O--CO--; or a linear, branched or cyclized alkyl group having 1-18 carbon atoms capable of including at least one methylene group which can be replaced with --S--, --CO--, --COO--, --OCO--, --CH═CH-- or --C.tbd.C-- provided that heteroatoms are not connected with each other. 
     
         R.sub.1 --A.sub.1 --A.sub.2 --A.sub.3 --C.sub.r F.sub.2r+1 (IIIa) 
    
     
         R.sub.1 --A.sub.1 --A.sub.2 --OOC--A.sub.3 --C.sub.r F.sub.2r+1 (IIIb) 
    
     
         R.sub.1 --A.sub.1 --A.sub.2 --COO--A.sub.3 --C.sub.r F.sub.2r+1 (IIIc) 
    
     
         R.sub.1 --A.sub.1 --A.sub.2 --OCH.sub.2 --A.sub.3 --C.sub.r F.sub.2r+1 (IIId) 
    
     
         R.sub.1 --A.sub.1 --A.sub.2 --CH.sub.2 O--A.sub.3 --C.sub.r F.sub.2r+1 (IIIe) 
    
     
         R.sub.1 --A.sub.1 --A.sub.2 --CH.sub.2 CH.sub.2 --A.sub.3 --C.sub.r F.sub.2r+1                                                (IIIf) 
    
     
         R.sub.1 --A.sub.1 --A.sub.2 --C.tbd.C--A.sub.3 --C.sub.r F.sub.2r+1 (IIIg) 
    
     in which 
     R 1  denotes hydrogen; halogen; --CN; --X 3  .paren open-st.CH 2  .paren close-st. p  C t  F 2t+1  where p is an integer of 0-18, t is an integer of 1-18, and X 3  denotes a single bond, --O--, --CO--O-- or --O--CO--; or a linear, branched or cyclized alkyl group having 1-18 carbon atoms capable of including at least one methylene group which can be replaced with --O--; --S--; --CO--; --CHW-- where W is halogen, --CN or --CF 3  ; --CH═CH-- or --C.tbd.C-- provided that heteroatoms are not connected with each other; 
     A 3  denotes ##STR13##  and A 1  and A 2  independently denote A 3 , ##STR14##  wherein Y 1  and Y 2  independently denote hydrogen, halogen, --CH 3 , --CF 3  or --CN; R 2 , R 3  and R 4  independently denote hydrogen, or a linear or branched alkyl group having 1-18 carbon atoms; and Z 1  is O or S; and 
     r is an integer of 2-18. 
     
         R.sub.1 --A.sub.1 --OCC--A.sub.2 --A.sub.3 --C.sub.r F.sub.2r+1 (IVa) 
    
     
         R.sub.1 --A.sub.1 --COO--A.sub.2 --A.sub.3 --C.sub.r F.sub.2r+1 (IVb) 
    
     
         R.sub.1 --A.sub.1 --OCH.sub.2 --A.sub.2 --A.sub.3 --C.sub.r F.sub.2r+1 (IVc) 
    
     
         R.sub.1 --A.sub.1 --CH.sub.2 O--A.sub.2 --A.sub.3 --C.sub.r F.sub.2r+1 (IVd) 
    
     
         R.sub.1 --A.sub.1 --CH.sub.2 CH.sub.2 --A.sub.2 --A.sub.3 --C.sub.r F.sub.2r+1                                                (IVe) 
    
     
         R.sub.1 --A.sub.1 --C.tbd.C--A.sub.2 --A.sub.3 --C.sub.r F.sub.2r+1 (IVf) 
    
     in which 
     R 1  denotes hydrogen; halogen; --CN; --X 3  .paren open-st.CH 2  .paren close-st. p  C t  F 2t+1  where p is an integer of 0-18, t is an integer of 1-18, and X 3  denotes a single bond, --O--, --CO--O-- or --O--CO--; or a linear, branched or cyclized alkyl group having 1-18 carbon atoms capable of including at least one methylene group which can be replaced with --O--; --S--; --CO--; --CHW-- where W is halogen, --CN or --CF 3  ; --CH═CH-- or --C.tbd.C-- provided that heteroatoms are not connected with each other; 
     A 3  denotes ##STR15##  and A 1  and A 2  independently denote A 3 , ##STR16##  wherein Y 1  and Y 2  independently denote hydrogen, halogen, --CH 3 , --CF 3  or --CN; R 2 , R 3  and R 4  independently denote hydrogen, or a linear or branched alkyl group having 1-18 carbon atoms; and Z 1  is O or S; and 
     r is an integer of 2-18. 
     Further, the mesomorphic compounds of the formulae (II), (III) and (IV) may more preferably be mesomorphic compounds of the following formulae (IIaa) to (IIgc), (IIIaa) to (IIIga) and (IVaa) to (IVfc), respectively. ##STR17## 
     In the above formulae (IIaa) to (IVfc), R 1  denotes hydrogen; halogen; --CN; --X 3  .paren open-st.CH 2  .paren close-st. p  C t  F 2t+1  where p is an integer of 0-18, t is an integer of 1-18, and X 3  denotes a single bond, --O--, --CO--O-- or --O--CO--; or a linear, branched or cyclized alkyl group having 1-18 carbon atoms capable of including at least one methylene group which can be replaced with --O--, --S--, --CO--, --CH═CH-- or --C.tbd.C-- provided that heteroatoms are not connected with each other; 
     Y 1 , Y 2 , Y 1  &#39; and Y 2  &#39; independently denote hydrogen, halogen, --CH 3 , --CF 3  or --CN; and 
     r is an integer of 2-18. 
     Y 1 , Y 2 , Y 1  &#39; and Y 2  &#39; in the above formulae (IIaa) to (IVfc) may preferably be hydrogen, halogen or CF 3 , particularly hydrogen or fluorine. 
     R 1  in the formula (I) may preferably be selected from the following groups (i) to (vi): ##STR18## wherein a is an integer of 1-16; d, g and p are an integer of 0-7; b, e and t are an integer of 1-10, f is 0 or 1; X 3  denotes a single bond, --O--, --O--CO-- or --CO--O--; and the groups (ii) and (iii) are optically inactive. R 1  having the above group (i) having 3-12 carton atoms may preferably be used. X 3  in the above groups (i) to (iv) may preferably be a single bond or --O--. 
     In the above formula (I) (including formulae (II) to (IV), (IIa) to (IVf) and (IIaa) to (IVfc), Y 1  and Y 2  may more preferably be hydrogen, halogen or --CF 3 , particularly hydrogen or fluorine. 
     Similarly, in the formula (I), r preferably is an integer of 3 to 12. 
     The mesomorphic compound of the formula (I) may generally be synthesized through, e.g., the following reaction scheme. ##STR19## 
     In the above, R 1 , A 1 , A 2 , A 3 , X 1 , X 2 , m and r have the same meanings as those described above. In a case where X 2  is not a single bond, E 1  and E 2  are appropriate group for forming X 2 , such as --COOH, --OH or --CH 2  OH, respectively. 
     In a case where X 1  and X 2  are a single bond, it is possible to adopt the following reaction scheme. ##STR20## 
     Specific examples of the optically inactive mesomorphic compounds represented by the formula (I) (inclusive of compounds of the formulae (II)-(IV), (IIa)-(IVf) and (IIaa)-(IVfc)) may include those shown by the following structural formulae. ##STR21## 
     The liquid crystal composition according to the present invention may be obtained by mixing at least one species of the mesomorphic compound represented by the formula (I) and at least one species of another mesomorphic compound in appropriate proportions. 
     The liquid crystal composition according to the present invention may preferably be formulated as a liquid crystal composition capable of showing ferroelectricity, particularly a liquid crystal composition showing a chiral smectic phase. 
     Specific examples of another mesomorphic compound described above may include those denoted by the following formulae (V) to (XV). ##STR22## wherein e denotes 0 or 1 and f denotes 0 or 1 with proviso that e+f=0 or 1; Y&#39; denotes H, halogen, CH 3  or CF 3  ; X 1  &#39; and X 2  &#39; respectively denote a single bond, ##STR23## X 3  &#39; and X 4  &#39; respectively denote a single bond ##STR24## and A 1  &#39; denotes ##STR25## 
     In the formula (V), preferred compounds thereof may include those represented by the following formulas (Va) to (Ve): ##STR26## wherein g and h respectively denote 0 or 1 with the proviso that g+h=0 or 1; i denotes 0 or 1; X 1  &#39; and X 2  &#39; respectively denote a single bond, ##STR27## and X 3  &#39;, X 4  &#39; and X 5  &#39; respectively denote a single bond ##STR28## 
     In the formula (VI), preferred compounds thereof may include those represented by the following formulas (VIa) to (VIc): ##STR29## wherein j denotes 0 or 1; Y 1  &#34;, Y 2  &#34; and Y 3  &#34; respectively denote H, halogen, CH 3  or CF 3  ; X 1  &#39; and X 2  &#39; respectively denote a single bond ##STR30## and X 3  &#39; and X 4  &#39; respectively denote a single bond ##STR31## 
     In the formula (VII), preferred compounds thereof may include those represented by the following formulas (VIIa) and (VIIb): ##STR32## wherein k, l and m respectively denote 0 or 1 with proviso that k+l+m=0, 1 or 2; X 1  &#39; and X 2  &#39; respectively denote a single bond ##STR33## and X 3  &#39; and X 4  &#39; respectively denote a single bond, ##STR34## 
     In the formula (VIII), preferred compounds thereof may include those represented by the following formulas (VIIIa) to (VIIIf): ##STR35## 
     Herein, R 1  &#39; and R 2  &#39; respectively denote a linear or branched alkyl group having 1-18 carbon atoms capable of including one or non-neighboring two or more methylene groups which can be replaced with --CH halogen-- and capable of further including one or two or more non-neighboring methylene groups other than those directly connected to X 1  &#39; or X 2  &#39; which can be replaced with at least one species of ##STR36## with the proviso that R 1  &#39; and R 2  &#39; respectively do not connect to a ring structure by a single bond when R 1  &#39; and R 2  &#39; respectively denote a halogenated alkyl group containing one methylene group replaced with --CH(halogen)-- or --CH(CF 3 )--. 
     Further, preferred examples of R 1  &#39; and R 2  &#39; may respectively include those represented by the following groups (i) to (xi): 
     i) a linear alkyl group having 1-15 carbon atoms; ##STR37##  wherein p denotes an integer of 0-5 and q denotes an integer of 2-11 (optically active or inactive); ##STR38##  wherein r denotes an integer of 0-6, s denotes 0 or 1, and t denotes an integer of 1-14 (optically active or inactive); ##STR39##  wherein u denotes 0 or 1 and v denotes an integer of 1-16; ##STR40##  wherein w denotes an integer of 1-15 (optically active or inactive); ##STR41##  wherein x denotes an integer of 0-2 and y denotes an integer of 1-15; ##STR42##  wherein z denotes an integer of 1-15; ##STR43##  wherein A denotes an integer of 0-2 and B denotes an integer of 1-15 (optically active or inactive); ##STR44##  wherein C denotes an integer of 0-2 and D denotes an integer of 1-15 (optically active or inactive); 
     x) H; and 
     xi) F. 
     In the above-mentioned formulas (Va) to (Vd), more preferred compounds thereof may include those represented by the formulas (Vaa) to (Vdc): ##STR45## 
     In the above-mentioned formulas (VIa) to (VIc), more preferred compounds thereof may include those represented by the formulas (VIaa) to (VIcb): ##STR46## 
     In the above-mentioned formulas (VIIa) and (VIIb), more preferred compounds thereof may include those represented by the formulas (VIIaa) to (VIIbf): ##STR47## 
     In the above-mentioned formulas (VIIIa) to (VIIIf), more preferred compounds thereof may include those represented by the formulas (VIIIaa) to (VIIIfa): ##STR48## wherein E denotes 0 or 1; X 1  &#39; and X 2  &#39; respectively denote a single bond, ##STR49## and X 3  &#39; denotes a single bond, ##STR50## wherein F and G respectively denote 0 or 1; X 1  &#39; and X 2  &#39; respectively denote a single bond, ##STR51## and X 3  &#39; and X 4  &#39; respectively denote a single bond, ##STR52## 
     In the above formula (IX), preferred compounds thereof may include those represented by the following formulas (IXa) and (IXb): ##STR53## 
     In the above formula (X), preferred compounds thereof may include those represented by the follwoing formulas (Xa) and (Xb). ##STR54## 
     More preferred compounds of the formula (Xb) may include those represented by the formulas (Xba) to (Xbb): ##STR55## 
     Herein, R 3  &#39; and R 4  &#39; respectively denote a linear or branched alkyl group having 1-18 carbon atoms capable of including one or non-neighboring two or more methylene groups which can be replaced with --CH halogen-- and capable of further including one or two or more non-neighboring methylene groups other than those directly connected to X 1  &#39; or X 2  &#39; which can be replaced with at least one species of ##STR56## with proviso that R 3  &#39; and R 4  &#39; respectively do not connect to a ring structure by a single bond when R 3  &#39; and R 4  &#39; respectively denote a halogenated alkyl group containing one methylene group replaced with --CH(halogen)--. 
     Further, preferred examples of R 3  &#39; and R 4  &#39; may respectively include those represented by the following groups (i) to (vii): 
     i) a linear alkyl group having 1-15 carbon atoms; ##STR57##  wherein p denotes an integer of 0-5 and q denotes an integer of 2-11 (optically active or inactive); ##STR58##  wherein r denotes an integer of 0-6, s denotes 0 or 1, and t denotes an integer of 1-14 (optically active or inactive); ##STR59##  wherein u denotes an integer of 0 or 1 and v denotes an integer of 1-16; ##STR60##  wherein w denotes an integer of 1-15 (optically active or inactive); ##STR61##  wherein A denotes an integer of 0-2 and B denotes an integer of 1-15 (optically active or inactive); and ##STR62##  wherein C denotes an integer of 0-2 and D denotes an integer of 1-15 (optically active or inactive). ##STR63## wherein H and J respectively denote 0 or 1 with proviso that H+J=0 or 1; ; X 1  &#39; and X 2  &#39; respectively denote a single bond ##STR64## A 2  &#39; denotes ##STR65## and X 3  &#39; and X 4  &#39; respectively denote a single bond, ##STR66## wherein X 1  &#39; and X 2  &#39; respectively denote a single bond, ##STR67## A 3  &#39; denotes ##STR68## and X 3  &#39; and X 4  &#39; respectively denote a single bond, ##STR69## wherein X 1  &#39; and X 2  &#39; respectively denote a single bond, ##STR70## A 4  &#39; denotes ##STR71## and X 3  &#39; respectively denotes a single bond, ##STR72## wherein K, L and M respectively denote 0 or 1 with the proviso that K+L+M=0 or 1; X 1  &#39; denotes a single bond, ##STR73## X 3  &#39; denotes a single bond, ##STR74## Y 4  &#39;, Y 5  &#39; and Y 6  &#39; respectively denote H or F; and Z 1  &#39; is CH or N. ##STR75## wherein Z 2  &#39; denotes --O-- or --S--; A 5  &#39; denotes ##STR76## and X 1  &#39; denotes a single bond, --CO--O--, --O--CO-- or --O--. 
     In the above formula (XI), preferred compounds thereof may include those represented by the following formulas (XIa) to (XIc): ##STR77## 
     In the above formula (XII), preferred compounds thereof may include those represented by the following formulas (XIIa) and (XIIb): ##STR78## 
     In the above formula (XIV), preferred compounds thereof may include those represented by the following formulas (XIVa) and (XIVf): ##STR79## 
     In the above formula (XI), preferred compounds thereof may include those represented by the following formulas (XVa) to (XVe): ##STR80## 
     In the above-mentioned formulas (XIa) to (XIc), more preferred compounds thereof may include those represented by the formulas (XIaa) to (XIcc): ##STR81## 
     In the above-mentioned formulas (XIIa) to (XIIb), more preferred compounds thereof may include those represented by the formulas (XIIaa) to (XIIbb): ##STR82## 
     In the above formula (XIII), preferred compounds thereof may include those represented by the following formulas (XIIIa) to (XIIIg): ##STR83## 
     In the above-mentioned formulas (XIVa) to (XIVd), more preferred compounds thereof may include those represented by the formula (XIVaa) to (XIVdb): ##STR84## 
     Herein, R 5  &#39; and R 6  &#39; respectively denote a linear or branched alkyl group having 1-18 carbon atoms capable of including one non-neighboring two or more methylene groups other than those directly connected to X 1  &#39; or X 2  &#39; which can be replaced with at least one species of ##STR85## 
     Further, preferred examples of R 5  &#39; and R 6  &#39; may respectively include those represented by the following groups (i) to (vi): 
     i) a linear alkyl group having 1-15 carbon atoms ##STR86##  wherein p denotes an integer of 0-5 and q denotes an integer of 2-11 (optically active or inactive); ##STR87##  wherein r denotes an integer of 0-6, s denotes 0 or 1, and t denotes an integer of 1-14 (optically active or inactive); ##STR88##  wherein w denotes an integer of 1-15 (optically active or inactive); ##STR89##  wherein A denotes an integer of 0-2 and B denotes an integer of 1-15 (optically active or inactive); and ##STR90##  wherein C denotes an integer of 0-2 and D denotes an integer of 1-15 (optically active or inactive). 
     In formulating the liquid crystal composition according to the present invention, the liquid crystal composition may desirably contain 1-80 wt. %, preferably 1-60 wt. %, more preferably 1-40 wt. % of the optically inactive mesomorphic compound represented by the formula (I). 
     Further, when two or more species of the mesomorphic compounds represented by the formula (I) are used, the liquid crystal composition may desirably contain 1-80 wt. %, preferably 1-60 wt. %, more preferably 1-40 wt. %, of the two or more species of the mesomorphic compounds represented by the formula (I). 
     The liquid crystal device according to the present invention may preferably be prepared by heating the liquid crystal composition prepared as described above into an isotropic liquid under vacuum, filling a blank cell comprising a pair of oppositely spaced electrode plates with the composition, gradually cooling the cell to form a liquid crystal layer and restoring the normal pressure. 
     FIG. 1 is a schematic sectional view of an embodiment of the liquid crystal device utilizing ferroelectricity prepared as described above for explanation of the structure thereof. 
     Referring to FIG. 1, the liquid crystal device includes a liquid crystal layer 1 assuming a chiral smectic phase disposed between a pair of glass substrates 2 each having thereon a transparent electrode 3 and an insulating alignment control layer 4. The glass substrates 2 are placed or arranged opposite each other. Lead wires 6 are connected to the electrodes so as to apply a driving voltage to the liquid crystal layer 1 from a power supply 7. Outside the substrates 2, a pair of polarizers 8 are disposed so as to modulate incident light I 0  from a light source 9 in cooperation with the liquid crystal 1 to provide modulated light I. 
     Each of two glass substrates 2 is coated with a transparent electrode 3 comprising a film of In 2  O 3 , SnO 2  or ITO (indium-tin-oxide) to form an electrode plate. Further thereon, an insulating alignment control layer 4 is formed by rubbing a film of a polymer such as polyimide with gauze or acetate fiber-planted cloth so as to align the liquid crystal molecules in the rubbing direction. Further, it is also possible to compose the alignment control layer of two layers, e.g., by first forming an insulating layer of an inorganic material, such as silicon nitride, silicon carbide containing hydrogen, silicon oxide, boron nitride, boron nitride containing hydrogen, cerium oxide, aluminum oxide, zirconium oxide, titanium oxide, or magnesium fluoride, and forming thereon an alignment control layer of an organic insulating material, such as polyvinyl alcohol, polyimide, polyamide-imide, polyester-imide, polyparaxylylene, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyvinyl acetate, polyamide, polystyrene, cellulose resin, melamine resin, urea resin, acrylic resin, or photoresist resin. Alternatively, it is also possible to use a single layer of inorganic insulating alignment control layer comprising the above-mentioned inorganic material or organic insulating alignment control layer comprising the above-mentioned organic material. An inorganic insulating alignment control layer may be formed by vapor deposition, while an organic insulating alignment control layer may be formed by applying a solution of an organic insulating material or a precursor thereof in a concentration of 0.1 to 20 wt. %, preferably 0.2-10 wt. %, by spinner coating, dip coating, screen printing, spray coating or roller coating, followed by curing or hardening under prescribed hardening condition (e.g., by heating). The insulating alignment control layer 4 may have a thickness of ordinarily 10 Å-1 micron, preferably 10-3000 Å, further preferably 10-1000 Å. The two glass substrates 2 with transparent electrodes 3 (which may be inclusively referred to herein as &#34;electrode plates&#34;) and further with insulating alignment control layers 4 thereof are held to have a prescribed (but arbitrary) gap with a spacer 5. For example, such a cell structure with a prescribed gap may be formed by sandwiching spacers of silica beads or alumina beads having a prescribed diameter with two glass plates, and then sealing the periphery thereof with, a sealing material comprising, e.g., an epoxy adhesive. Alternatively, a polymer film or glass fiber may also be used as a spacer. Between the two glass plates a liquid crystal composition assuming a chiral smectic phase is sealed up to provide a liquid crystal layer 1 in a thickness of generally 0.5 to 20 μm, preferably 1 to 5 μm. 
     The transparent electrodes 3 are connected to the external power supply 7 through the lead wires 6. Further, outside the glass substrates 2, polarizers 8 are applied. The device shown in FIG. 1 is of a transmission type and is provided with a light source 9. 
     FIG. 2 is a schematic illustration of a liquid crystal cell (device) utilizing ferroelectricity for explaining operation thereof. Reference numerals 21a and 21b denote substrates (glass plates) on which a transparent electrode of, e.g., In 2  O 3 , SnO 2 , ITO (indium-tin-oxide), etc., is disposed, respectively. A liquid crystal of an SmC*-phase (chiral smectic C phase) or SmH*-phase (chiral smectic H phase) in which liquid crystal molecular layers 22 are aligned perpendicular to surfaces of the glass plates is hermetically disposed therebetween. Lines 23 show liquid crystal molecules. Each liquid crystal molecule 23 has a dipole moment (P.sub.⊥) 24 in a direction perpendicular to the axis thereof. The liquid crystal molecules 23 continuously form a helical structure in the direction of extension of the substrates. When a voltage higher than a certain threshold level is applied between electrodes formed on the substrates 21a and 21b, a helical structure of the liquid crystal molecule 23 is unwound or released to change the alignment direction of respective liquid crystal molecules 23 so that the dipole moments (P.sub.⊥) 24 are all directed in the direction of the electric field. The liquid crystal molecules 23 have an elongated shape and show refractive anisotropy between the long axis and the short axis thereof. Accordingly, it is easily understood that when, for instance, polarizers arranged in a cross nicol relationship, i.e., with their polarizing directions crossing each other, are disposed on the upper and the lower surfaces of the glass plates, the liquid crystal cell thus arranged functions as a liquid crystal optical modulation device of which optical characteristics vary depending upon the polarity of an applied voltage. 
     Further, when the liquid crystal cell is made sufficiently thin (e.g., less than about 10 microns), the helical structure of the liquid crystal molecules is unwound to provide a non-helical structure even in the absence of an electric field, whereby the dipole moment assumes either of the two states, i.e., Pa in an upper direction 34a or Pb in a lower direction 34b as shown in FIG. 3, thus providing a bistable condition. When an electric field Ea or Eb higher than a certain threshold level and different from each other in polarity as shown in FIG. 3 is applied to a cell having the above-mentioned characteristics by using voltage application means 31a and 31b, the dipole moment is directed either in the upper direction 34a or in the lower direction 34b depending on the vector of the electric field Ea or Eb. In correspondence with this, the liquid crystal molecules are oriented in either of a first stable state 33a and a second stable state 33b. 
     When the above-mentioned ferroelectric liquid crystal is used as an optical modulation element, it is possible to obtain two advantages. First is that the response speed is quite fast. Second is that the orientation of the liquid crystal shows bistability. The second advantage will be further explained, e.g., with reference to FIG. 3. When the electric field Ea is applied to the liquid crystal molecules, they are oriented in the first stable state 33a. This state is stably retained even if the electric field is removed. On the other hand, when the electric field Eb of which direction is opposite to that of the electric field Ea is applied thereto, the liquid crystal molecules are oriented to the second stable state 33b, whereby the directions of molecules are changed. This state is similarly stably retained even if the electric field is removed. Further, as long as the magnitude of the electric field Ea or Eb being applied is not above a certain threshold value, the liquid crystal molecules are placed in the respective orientation states. 
     FIGS. 5A and 5B are waveform diagrams showing driving voltage waveforms adopted in driving a ferroelectric liquid crystal panel as an embodiment of the liquid crystal device according to the present invention. 
     Referring to FIG. 5A, at S S  is shown a selection scanning signal waveform applied to a selected scanning line, at S N  is shown a non-selection scanning signal waveform applied to a non-selected scanning line, at I S  is shown a selection data signal waveform (providing a black display state) applied to a selected data line, and at I N  is shown a non-selection data signal waveform (providing a white display state) applied to a non-selected data line. Further, at (I S  -S S ) and (I N  -S S ) in the figure are shown voltage waveforms applied to pixels on a selected scanning line, whereby a pixel supplied with the voltage (I S  -S S ) assumes a black display state and a pixel supplied with the voltage (I N  -S S ) assumes a white display state. FIG. 5B shows a time-serial waveform used for providing a display state as shown in FIG. 6. 
     In the driving embodiment shown in FIGS. 5A and 5B, a minimum duration Δt of a single polarity voltage applied to a pixel on a selected scanning line corresponds to the period of a writing phase t 2 , and the period of a one-line clearing phase t 1  is set to 2Δt. 
     The parameters V S , V I  and Δt in the driving waveforms shown in FIGS. 5A and 5B are determined depending on switching characteristics of a ferroelectric liquid crystal material used. In this embodiment, the parameters are fixed at a constant value of a bias ratio V I  /(V I  +V S )=1/3. It is of course possible to increase a range of a driving voltage allowing an appropriate matrix drive by increasing the bias ratio. However, a large bias ratio corresponds to a large amplitude of a data signal and leads to an increase in flickering and a lower contrast, thus being undesirable in respect of image quality. According to our study, a bias ratio of about 1/3-1/4 was practical. 
     Based on an arrangement appearing hereinbelow and data format comprising image data accompanied with scanning line address data and by adopting communication synchronization using a SYNC signal as shown in FIGS. 7 and 8, there is provided a liquid crystal display apparatus of the present invention which uses the liquid crystal device according to the present invention as a display panel portion. 
     Referring to FIG. 7, the ferroelectric liquid crystal display apparatus 101 includes a graphic controller 102, a display panel 103, a scanning line drive circuit 104, a data line drive circuit 105, a decoder 106, a scanning signal generator 107, a shift resistor 108, a line memory 109, a data signal generator 110, a drive control circuit 111, a graphic central processing unit (GCPU) 112, a host central processing unit (host CPU) 113, and an image data storage memory (VRAM) 114. 
     Image data are generated in the graphic controller 102 in an apparatus body and transferred to a display panel 103 by signal transfer means. The graphic controller 102 principally comprises a CPU (central processing unit, hereinafter referred to as &#34;GCPU&#34;) 112 and a VRAM (video-RAM, image data storage memory) 114 and is in charge of management and communication of image data between a host CPU 113 and the liquid crystal display apparatus (FLCD) 101. The control of the display apparatus is principally realized in the graphic controller 102. A light source is disposed at the back of the display panel 103. 
     Hereinbelow, the present invention will be explained more specifically with reference to examples. It is however to be understood that the present invention is not restricted to these examples. 
     EXAMPLE 1 
     Production of 6-octyl-2-(4-perfluorooctylphenyl) benzothiazole (Example Compound No. 47) 
     6-octyl-2-(4-perfluorooctylphenyl)benzothiazole was synthesized through the following steps i) and ii). ##STR91## Step i) Production of 4-perfluorooctylbenzoic Acid 
     230.1 g (422 mM) of perfluorooctyl iodide, 94.9 g (383 mM) of 4-iodobenzoic acid, 121 g of copper powder and 770 ml of dimethyl sulfoxide (DMSO) were placed in a round-bottomed flask, followed by stirring for 7 hours at 120° C. under argon atmosphere. After the reaction, the reaction mixture was cooled and poured into 2 liters of water to precipitate a crystal. The crystal was recovered by filtration, successively washed with water and methanol, and subjected to extraction with 6 liters of ethyl acetate under heating, followed by filtration under heating. The filtrate was treated with activated carbon and subjected to recrystallization from ethyl acetate two times to obtain 63.6 g (118 mM) of 4-perfluorooctylbenzoic acid (Yield: 31%). 
     Step ii) Production of 6-octyl-2-(4-perfluorooctylphenyl)benzothiazole 
     To 1.2 g (2.24 mM) of 4-perfluorooctylbenzoic acid, 5 ml of thionyl chloride was added, followed by heat-refluxing for 1 hours. After the refluxing, an excessive thionyl chloride was distilled off to obtain 4-perfluorooctylbenzoic acid chloride. 
     To this acid chloride, 0.5 g (1.12 mM) of 5-octyl-2-zinc aminobenzenethiol was added, followed by stirring for 30 minutes at 200° C. After the reaction, the reaction mixture was left standing. An appropriate amount of diluted sodium hydroxide aqueous solution was added to the reaction mixture and then subjected to extraction with toluene. The organic layer was washed with water and dried with anhydrous sodium sulfate, followed by distilling-off of the solvent and purification by silica gel column chromatography (eluent: toluene). The purified product was treated with activated carbon and recrystallized from a mixture solvent (toluene/methanol) to obtain 0.5 g of 6-octyl-2-(4-perfluorooctylphenyl)benzothiazole (Yield: 30%). 
     Phase transition temperature (°C.) ##STR92## 
     Herein, the respective symbols denote the following phase; Iso: isotropic phase; Ch: cholesteric phase; S A  or SmA: smectic A phase; SmC*: chiral smectic C phase; Sx: smectic phase (un-identified); and Cry.: crystal. 
     EXAMPLE 2 
     Production of 5-dodecyl-2-(4-perfluorooctylphenyl)-1,3,4-thiadiazole (Ex. Comp. No. 26) 
     5-dodecyl-2-(4-perfluorooctylphenyl)-1,3,4-thiadiazole was synthesized through the following steps i) and ii). ##STR93## Step i) Production of N-4-perfluorooctylphenyl-N&#39;-undecyl Hydrazide 
     A solution of 1.0 g of 4-perfluorooctylbenzoic acid chloride in 5 mo of dry benzene was added dropwise to a solution of 0.23 g of dodecyl hydrazide in 2 ml of pyridine at 40° C., followed by stirring for 16 hours at 40° C. The benzene was distilled off to obtain an objective crude product. 
     Step ii) Production of 5-dodecyl-2-(4-perfluorooctylphenyl)-1,3,4-thiadiazole 
     To the above crude product (N-4-perfluorooctylphenyl-N&#39;-undecyl hydrazide), 0.4 g (1 mM) of Lawesson&#39;s reagent and 5 ml of tetrahydrofuran (THF) were added, followed by heat-refluxing for 2 hours. After the reaction, the reaction mixture was cooled. To the reaction mixture, 20 ml of water was added thereby to precipitate a crystal. The crystal was recovered by filtration to obtain a crude product. The crude product was purified by silica gel column chromatography (eluent: toluene) and recrystallized from a mixture solvent (toluene/methanol) to obtain 0.44 g of 5-dodecyl-2-(4-perfluorooctylphenyl)-1,3,4-thiadiazole (Yield: 61%; melting point (m.p.): 111° C.). 
     EXAMPLE 3 
     Production of 4-(5-decylpyrimidine-2-yl)-4-perfluorooctyl benzoate (Ex. Comp. No. 182) ##STR94## 
     A mixture of 0.40 g (1.0 mM) of 4-perfluorooctylbenzoic acid chloride, 0.30 g (1.0 mM) of 5-decyl-2-(4-hydroxyphenyl)pyrimidine, 0.24 g (3 mM) of pyridine and 5 ml of benzene was stirred for 1 hour at 50° C. After the reaction, the reaction mixture was neutralized by 3N-HCl and subjected to extraction with ether. The extract was dried, followed by distilling-off of the solvent to obtain a crude product. The crude product was purified by silica gel column chromatography (eluent: toluene) and recrystallized from a mixture solvent (toluene/methanol) to obtain 0.60 g of 4-(5-decylpyrimidine-2-yl)-4-perfluorooctyl benzoate (Yield: 73%). 
     Phase Transition Temperature (°C.) ##STR95## 
     EXAMPLE 4 
     Production of 2-fluoro-4-(5-decylpyrimidine-2-yl)phenyl-4-perfluorooctyl Benzoate (Ex. Comp. No. 202) ##STR96## 
     An objective product was prepared in the same manner as in Example 3 except that 5-decyl-2-(3-fluoro-4-hydroxyphenyl)pyrimidine was used instead of 5-decyl-2-(4-hydroxyphenyl)pyrimidine used in Example 3 (Yield: 71%). 
     Phase Transition Temperature (°C.) ##STR97## 
     EXAMPLE 5 
     Production of 4-(2-decyl-1,3-thiazole-2-yl)phenyl-4-perfluorooctyl Benzoate (Ex. Comp. No. 241) ##STR98## 
     An objective product was prepared in the same manner as in Example 3 except that 2-decyl-5-(4-hydroxyphenyl)-1,3-thiazole was used instead of 5-decyl-2-(4-hydroxyphenyl)pyrimidine used in Example 3 (Yield: 68%). 
     Phase Transition Temperature (°C.) ##STR99## 
     EXAMPLE 6 
     Production of 4-perfluorohexyl-4&#39;-pentyltolan (Ex. Comp. No. 107) 
     4-perfluorohexyl-4&#39;-pentyltolan was synthesized through the following steps i) and ii). ##STR100## Step i) Production of 4-perfluorohexylphenyl Iodide 
     202.5 g (455 mM) of perfluorohexyl iodide, 150.0 g (455 mM) of diiodobenzene, 36 g of copper powder and 450 ml of dimethyl sulfoxide (DMSO) were stirred for 9 hours at 120° C. under argon atmosphere. After the reaction, the reaction mixture was cooled to precipitate a crystal, The crystal was recovered by filtration and the filtrate was poured into 1.5 liters of water, followed by extraction with dichloromethane. The organic layer was washed with water and dried with anhydrous magnesium sulfate, followed by distilling-off of the solvent to obtain a crude product. The crude product was purified by vacuum distillation to obtain 57.1 g (109 mM) of 4-perfluorohexylphenyl iodine (Yield: 24%; boiling point (b.p.): 95° C./6 torr). 
     Step ii) Production of 4-perfluorohexyl-4&#39;-pentyltolan 
     A mixture of 0.17 g (0.99 mM) of 4-pentylphenylacetylene, 0.50 g (0.96 mM) of 4-perfluorohexylphenyl iodide, 0.03 g of tetrakis (triphenylphosphine)palladium (O), 0.02 g of copper iodide and 10 ml of triethylamine was heat-refluxed for 90 minutes. After the reaction, 50 ml of cooled water was added to the reaction mixture and subjected to extraction with ethyl acetate. The extract was dried, followed by distilling-off of the solvent to obtain a crude product. The crude product was purified by silica gel column chromatography (hexane) and recrystallized once from a mixture solvent (acetone/methanol) and once from acetone to obtain 0.34 g of 4-perfluorohexyl-4&#39;-pentyltolan (Yield: 63%). 
     Phase Transition Temperature (°C.) ##STR101## 
     EXAMPLE 7 
     Production of 2-decyl-5-(4-perfluorohexylphenyl)indan ##STR102## 
     A mixture of 0.40 g (1.32 mM) of 2-decylindan-5-boronic acid (dihydroxyborane), 0.72 g (1.38 mM) of 4-perfluorohexylphenyl iodide, 0.08 g of tetrakis (triphenylphosphine)palladium (O), 2.2 ml of 2M-sodium carbonate aqueous solution, 1,1 ml of ethanol and 2.2 ml of toluene was heat-refluxed for 6 hours. After the reaction, the reaction mixture was poured into ice water and subjected to extraction with a mixture solvent (toluene/ethyl acetate). The extract was dried, followed by distilling-off of the solvent to obtain a crude product. The crude product was purified by silica gel column chromatography (toluene/hexane=1/1) and recrystallized from a mixture solvent (toluene/methanol) to obtain 0.70 g of 2-decyl-5-(4-perfluorohexylphenyl)indan (Yield: 81%; m.p.: 68° C.). 
     EXAMPLE 8 
     A liquid crystal composition A was prepared by mixing the following compounds in the indicated proportions. 
     
         __________________________________________________________________________Structural formula            wt. parts__________________________________________________________________________ ##STR103##                   4.0 ##STR104##                   8.0 ##STR105##                   8.0 ##STR106##                   4.0 ##STR107##                   26.0 ##STR108##                   15.0 ##STR109##                   5.0 ##STR110##                   5.0 ##STR111##                   6.7 ##STR112##                   3.3 ##STR113##                   10.0 ##STR114##                   5.0__________________________________________________________________________ 
    
     The liquid crystal composition A showed the following phase transition series. 
     Phase Transition Temperature (°C.) ##STR115## 
     EXAMPLE 9 
     Two 0.7 mm-thick glass plates were provided and respectively coated with an ITO film to form an electrode for voltage application, which was further coated with an insulating layer of vapor-deposited SiO 2 . On the insulating layer, a 0.2%-solution of silane coupling agent (KBM-602, available from Shinetsu Kagaku K.K.) in isopropyl alcohol was applied by spinner coating at a speed of 2000 rpm for 15 second and subjected to hot curing treatment at 120° C. for 20 min. 
     Further, each glass plate was provided with an ITO film and treated in the above described manner was coated with a 1.5%-solution of polyimide resin precursor (SP-510, available from Toray K.K.) in dimethylacetoamide by a spinner coater rotating at 2000 rpm for 15 seconds. Thereafter, the coating film was subjected to heat curing at 300° C. for 60 min. to obtain about 250 Å-thick film. The coating film was rubbed with acetate fiber-planted cloth. The thus treated two glass plates were washed with isopropyl alcohol. After silica beads with an average particle size of 2.0 microns were dispersed on one of the glass plates, the two glass plates were applied to each other with a bonding sealing agent (Lixon Bond, available from Chisso K.K.) so that their rubbed directions were parallel to and identical to each other and heated at 100° C. for 60 min. to form a blank cell. 
     Then, the liquid crystal composition A prepared in Example 8 was heated into an isotropic liquid, and injected into the above prepared cell under vacuum and, after sealing, was gradually cooled to 25° C. at a rate of 20° C./hour to prepare a ferroelectric liquid crystal device. The cell gap was found to be about 2 microns as measured by a Berek compensator. 
     The ferroelectric liquid crystal device was subjected to measurement of a magnitude of spontaneous polarization Ps and an optical response time (time from voltage application until the transmittance change reaches 90% of the maximum under the application of a peak-to-peak voltage Vpp of 20 V in combination with right-angle cross-nicol polarizers). The results of the measurement are shown below. 
     
         ______________________________________        20° C.                 30° C.                         40° C.______________________________________Response time (μsec)          105        71      50Ps (nC/cm.sup.2)          7.9        5.7     3.9______________________________________ 
    
     EXAMPLE 10 
     A liquid crystal composition B was prepared by mixing the following compounds in the indicated proportions. 
     
         __________________________________________________________________________Structural formula                wt. parts__________________________________________________________________________ ##STR116##                       6 ##STR117##                       6 ##STR118##                       7 ##STR119##                       14 ##STR120##                       8 ##STR121##                       4 ##STR122##                       2 ##STR123##                       10 ##STR124##                       5 ##STR125##                       10 ##STR126##                       7 ##STR127##                       7 ##STR128##                       5 ##STR129##                       2 ##STR130##                       2 ##STR131##                       2 ##STR132##                       3__________________________________________________________________________ 
    
     The liquid crystal composition B was further mixed with the following example compounds in the indicated proportions to provide a liquid crystal composition C. 
     
         ______________________________________Ex.                              wt.Comp. No.   Structural formula       parts______________________________________ 2    ##STR133##              241    ##STR134##              3   Composition B            95______________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 9 except that the above liquid crystal composition C was used, and the device was subjected to measurement of an optical response time and observation of switching states. In the device, a monodomain with a good and uniform alignment characteristic was observed. The results of the measurement of response time are shown below. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          560        299     166______________________________________ 
    
     COMPARATIVE EXAMPLE 1 
     A ferroelectric liquid crystal device was prepared and subjected to measurement of response time in the same manner as in Example 10 except for injecting the composition B alone into a blank cell, whereby the following results were obtained. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          668        340     182______________________________________ 
    
     EXAMPLE 11 
     A liquid crystal composition D was prepared by mixing the following Example Compounds instead of those of (2) and (41) used in Example 10 in the indicated proportions with the liquid crystal composition B. 
     
         ______________________________________Ex.Comp.                            wt.No.   Structural formula         parts______________________________________35  ##STR135##                373  ##STR136##                2 Composition B              95______________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 9 except that the above liquid crystal composition D was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          561        302     168______________________________________ 
    
     EXAMPLE 12 
     A liquid crystal composition E was prepared by mixing the following Example Compounds instead of those of (2) and (41) used in Example 10 in the indicated proportions with the liquid crystal composition B. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula          wt. parts__________________________________________________________________________ 30    ##STR137##                 3132    ##STR138##                 2   Composition B               95__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 9 except that the above liquid crystal composition E was used, and the device was subjected to measurement of optical response time. The results of the measurement are shown below. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          565        305     169______________________________________ 
    
     EXAMPLE 13 
     A liquid crystal composition F was prepared by mixing the following compounds in the indicated proportions. 
     
         __________________________________________________________________________Structural formula                  wt. parts__________________________________________________________________________ ##STR139##                         12 ##STR140##                         10 ##STR141##                         10 ##STR142##                         3 ##STR143##                         8 ##STR144##                         4 ##STR145##                         6 ##STR146##                         2 ##STR147##                         8 ##STR148##                         15 ##STR149##                         7 ##STR150##                         7 ##STR151##                         4 ##STR152##                         2 ##STR153##                         2__________________________________________________________________________ 
    
     The liquid crystal composition F was further mixed with the following compounds in the proportions indicated below to provide a liquid crystal composition G. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural Formula             wt. parts__________________________________________________________________________122    ##STR154##                    1198    ##STR155##                    1232    ##STR156##                    3   Composition F                  95__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 9 except that the above liquid crystal composition G was used, and the device was subjected to measurement of optical response time. The results are shown below. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          625        322     175______________________________________ 
    
     COMPARATIVE EXAMPLE 2 
     A ferroelectric liquid crystal device was prepared and subjected to measurement of response time in the same manner as in Example 9 except for injecting the composition F alone used in Example 13 into a blank cell, whereby the following results were obtained. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          784        373     197______________________________________ 
    
     EXAMPLE 14 
     A liquid crystal composition H was prepared by mixing the following Example Compounds instead of those of (122), (198) and (232) used in Example 13 in the indicated proportions with the liquid crystal composition F. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula          wt. parts__________________________________________________________________________20    ##STR157##                 367    ##STR158##                 3   Composition F               94__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 9 except that the above liquid crystal composition H was used, and the device was subjected to measurement of optical response time. The results are shown below. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          620        316     174______________________________________ 
    
     EXAMPLE 15 
     A liquid crystal composition I was prepared by mixing the following Example Compounds instead of those of (122), (198) and (232) used in Example 13 in the indicated proportions with the liquid crystal composition F. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula          wt. parts__________________________________________________________________________ 57    ##STR159##                 3109    ##STR160##                 2   Composition F               95__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 9 except that the above liquid crystal composition I was used, and the device was subjected to measurement of optical response time. The results are shown below. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          621        318     174______________________________________ 
    
     EXAMPLE 16 
     A liquid crystal composition J was prepared by mixing the following compounds in the indicated proportions. 
     
         __________________________________________________________________________Structural formula                wt. parts__________________________________________________________________________ ##STR161##                       10 ##STR162##                       5 ##STR163##                       7 ##STR164##                       7 ##STR165##                       6 ##STR166##                       5 ##STR167##                       5 ##STR168##                       8 ##STR169##                       8 ##STR170##                       20 ##STR171##                       5 ##STR172##                       5 ##STR173##                       6 ##STR174##                       3__________________________________________________________________________ 
    
     The liquid crystal composition J was further mixed with the following compounds in the proportions indicated below to provide a liquid crystal composition K. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula             wt. parts__________________________________________________________________________128    ##STR175##                    3139    ##STR176##                    2   Composition J                  95__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 9 except that the above liquid crystal composition K was used, and the device was subjected to measurement of optical response time and observation of switching states. In the device, a monodomain with a good and uniform alignment characteristic was observed. The results of the measurement are shown below. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          539        272     141______________________________________ 
    
     Further, when the device was driven, a clear switching action was observed, and good bistability was shown after the termination of the voltage application. 
     COMPARATIVE EXAMPLE 3 
     A ferroelectric liquid crystal device was prepared and subjected to measurement of response time in the same manner as in Example 9 except for injecting the composition J alone used in Example 6 into the cell, whereby the following results were obtained. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          653        317     159______________________________________ 
    
     EXAMPLE 17 
     A liquid crystal composition L was prepared by mixing the following Example Compounds instead of those of (128) and (139) used in Example 16 in the indicated proportions with the liquid crystal composition J. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula              wt. parts__________________________________________________________________________190    ##STR177##                     2222    ##STR178##                     2204    ##STR179##                     2   Composition J                   94__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 9 except that the above liquid crystal composition L was used, and the device was subjected to measurement of optical response time and observation of switching states. In the device, a monodomain with a good and uniform alignment characteristic was observed. The results of the measurement are shown below. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          545        274     142______________________________________ 
    
     EXAMPLE 18 
     A liquid crystal composition M was prepared by mixing the following Example Compounds instead of those of (128) and (139) used in Example 16 in the indicated proportions with the liquid crystal composition J. 
     
         __________________________________________________________________________Ex. Comp.No.   Structural formula        wt. parts__________________________________________________________________________23  ##STR180##               259  ##STR181##               1120  ##STR182##               2 Composition J             95__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 9 except that the above liquid crystal composition M was used, and the device was subjected to measurement of optical response time and observation of switching states. In the device, a monodomain with a good and uniform alignment characteristic was observed. The results of the measurement are shown below. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          535        272     143______________________________________ 
    
     As apparent from the above Examples 10 to 18, the ferroelectric liquid crystal device including the liquid crystal compositions C, D, E, G, H, I, K, L and M, i.e., compositions containing an optically inactive compound of the formula (I) according to the present invention, provided improved operation characteristic at a lower temperature, high speed responsiveness and a decreased temperature dependence of response speed. 
     EXAMPLE 19 
     A blank cell was prepared in the same manner as in Example 9 by using a 2% aqueous solution of polyvinyl alcohol resin (PVA-117, available from Kuraray K.K.) instead of the 1.5%-solution of polyimide resin precursor in dimethylacetoamide on each electrode plate. A ferroelectric liquid crystal device was prepared by filling the blank cell with the liquid crystal composition C prepared in Example 10. The liquid crystal device was subjected to measurement response time in the same manner as in Example 10. The results are shown below. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          558        298     165______________________________________ 
    
     EXAMPLE 20 
     A blank cell was prepared in the same manner as in Example 9 except for omitting the SiO 2  layer to form an alignment control layer composed of the polyimide resin layer alone on each electrode plate. A ferroelectric liquid crystal device was prepared by filling such a blank cell with liquid crystal composition C used in Example 10. The liquid crystal device was subjected to measurement of response time in the same manner as in Example 10. The results are shown below. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          551        295     162______________________________________ 
    
     As is apparent from the above Examples 19 and 20, also in the case of a different device structure, the device containing the ferroelectric liquid crystal composition C according to the present invention provided an improved low-temperature operation characteristic and a decreased temperature dependence of response speed similarly as in Example 10. 
     EXAMPLE 21 
     A liquid crystal composition N was prepared by mixing the following compounds in the indicated proportions. 
     
         __________________________________________________________________________Structural formula               wt. parts__________________________________________________________________________ ##STR183##                      5 ##STR184##                      10 ##STR185##                      5 ##STR186##                      10 ##STR187##                      7 ##STR188##                      15 ##STR189##                      5 ##STR190##                      5 ##STR191##                      5 ##STR192##                      2 ##STR193##                      5 ##STR194##                      2 ##STR195##                      6 ##STR196##                      2 ##STR197##                      3 ##STR198##                      3 ##STR199##                      10__________________________________________________________________________ 
    
     The liquid crystal composition N was further mixed with the following example compounds in the indicated proportions to provide a liquid crystal composition O. 
     
         ______________________________________Ex.Comp.No.   Structural formula        wt. parts______________________________________ 1  ##STR200##               218  ##STR201##               3 Composition N             95______________________________________ 
    
     Two 0.7 mm-thick glass plates were provided and respectively coated with an ITO film to form an electrode for voltage application, which was further coated with an insulating layer of vapor-deposited SiO 2 . On the insulating layer, a 0.2%-solution of silane coupling agent (KBM-602, available from Shinetsu Kagaku K.K.) in isopropyl alcohol was applied by spinner coating at a speed of 2000 rpm for 15 second and subjected to hot curing treatment at 120° C. for 20 min. 
     Further, each glass plate provided with an ITO film and treated in the above described manner was coated with a 1.5%-solution of polyimide resin precursor (SP-510, available from Toray K.K.) in dimethylacetoamide by a spinner coater rotating at 3000 rpm for 15 seconds. Thereafter, the coating film was subjected to heat curing at 300° C. for 60 min. to obtain about 120 Å-thick film. The coating film was rubbed with acetate fiber-planted cloth. The thus treated two glass plates were washed with isopropyl alcohol. After silica beads with an average particle size of 1.5 microns were dispersed on one of the glass plates, the two glass plates were applied to each other with a bonding sealing agent (Lixon Bond, available from Chisso K.K.) so that their rubbed directions were parallel to and identical to each other and heated at 100° C. for 60 min. to form a blank cell. The cell gap was found to be about 1.5 microns as measured by a Berek compensator. 
     Then, the liquid crystal composition O prepared above was heated into an isotropic liquid, and injected into the above prepared cell under vacuum and, after sealing, was gradually cooled to 25° C. at a rate of 20° C./hour to prepare a ferroelectric liquid crystal device. 
     The ferroelectric liquid crystal device was subjected to measurement of a contrast ratio at 30° C. when the device was driven by applying a driving voltage waveform shown in FIGS. 5A and 5B (bias ratio=1/3), whereby a contrast ratio of 14.2 was obtained. 
     COMPARATIVE EXAMPLE 4 
     A ferroelectric liquid crystal device was prepared and subjected to measurement of a contrast ratio in the same manner as in Example 21 except for injecting the composition N alone used in Example 21 into a blank cell, whereby a contrast ratio (at 30° C.) of 6.7 was obtained. 
     EXAMPLE 22 
     A liquid crystal composition P was prepared by mixing the following Example Compounds instead of those of (1) and (18) used in Example 21 in the indicated proportions with the liquid crystal composition N. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula              wt. parts__________________________________________________________________________ 31    ##STR202##                     2136    ##STR203##                     2190    ##STR204##                     1   Composition N                   95__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 21 except that the above liquid crystal composition P was used, and the device was subjected to measurement of a contrast ratio, whereby a contrast ratio (at 30° C.) of 15.1 was obtained. 
     EXAMPLE 23 
     A liquid crystal composition Q was prepared by mixing the following Example Compounds instead of those of (1) and (18) used in Example 21 in the indicated proportions with the liquid crystal composition N. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula          wt. parts__________________________________________________________________________ 3    ##STR205##                 154    ##STR206##                 295    ##STR207##                 1   Composition N               96__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 21 except that the above liquid crystal composition Q was used, and the device was subjected to measurement of a contrast ratio, whereby a contrast ratio (at 30° C.) of 16.0 was obtained. 
     EXAMPLE 24 
     A liquid crystal composition R was prepared by mixing the following Example Compounds instead of those of (1) and (18) used in Example 21 in the indicated proportions with the liquid crystal composition N. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula             wt. parts__________________________________________________________________________ 3    ##STR208##                    2195    ##STR209##                    1244    ##STR210##                    1   Composition N                  96__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 21 except that the above liquid crystal composition R was used, and the device was subjected to measurement of a contrast ratio, whereby a contrast ratio (at 30° C.) of 14.8 was obtained. 
     As apparent from the above Examples 21 to 24, the ferroelectric liquid crystal device including the liquid crystal compositions O, P, Q and R, i.e., compositions containing a mesomorphic compound of the formula (I) according to the present invention, provided improved a higher contrast ratio when driven. 
     EXAMPLE 25 
     A blank cell was prepared in the same manner as in Example 21 by using a 2% aqueous solution of polyvinyl alcohol resin (PVA-117, available from Kuraray K.K.) instead of the 1.0%-solution of polyimide resin precursor in dimethylacetoamide on each electrode plate. A ferroelectric liquid crystal device was prepared by filling the blank cell with the liquid crystal composition O used in Example 21. The liquid crystal device was subjected to measurement a contrast ratio in the same manner as in Example 21, whereby a contrast ratio (at 30° C.) of 21.1 was obtained. 
     EXAMPLE 26 
     A blank cell was prepared in the same manner as in Example 21 except for omitting the SiO 2  layer to form an alignment control layer composed of the polyimide resin layer alone on each electrode plate. A ferroelectric liquid crystal device was prepared by filling such a blank cell with liquid crystal composition O used in Example 21. The liquid crystal device was subjected to measurement of response time in the same manner as in Example 21, whereby a contrast ratio (at 30° C.) of 13.8 was obtained. 
     EXAMPLE 27 
     A blank cell was prepared in the same manner as in Example 21 except that a 1.0%-solution of polyamide acid (LQ-1802, available from Hitachi Kasei K.K.) in NMP (N-methylpyrrolidone) was formed instead of the 1.5%-solution of polyimide resin precursor in dimethylacetoamide on each electrode plate and that the hot curing treatment thereof was effected at 270° C. for 1 hour. A ferroelectric liquid crystal device was prepared by filling the blank cell with the liquid crystal composition O used in Example 21. The liquid crystal device was subjected to measurement a contrast ratio in the same manner as in Example 21, whereby a contrast ratio (at 30° C.) of 29.8 was obtained. 
     As is apparent from the above Examples 25, 26 and 27, also in the case of a different device structure, the device containing the ferroelectric liquid crystal composition O according to the present invention provided a higher contrast ratio similarly as in Example 21. 
     Further, in the case of a driving voltage waveform different from that used in Example 21, a liquid crystal device using the liquid crystal composition according to the present invention provided a higher contrast ratio compared with a liquid crystal device using a liquid crystal composition containing no mesomorphic compound of the formula (I) of the present invention. 
     As described hereinabove, according to the present invention, it is possible to drive a liquid crystal device including a liquid crystal composition containing at least one mesomorphic compound of the formula (I) by utilizing ferroelectricity of the liquid crystal composition. Such a liquid crystal device provides improved characteristics such as a good alignment characteristic, a good switching property, high-speed responsiveness, a decreased temperature-dependence of response speed, and a high contrast ratio. 
     Further, a display apparatus using the liquid crystal device according to the present invention as a display device such as a display panel can realize good display characteristics in combination with a light source, a drive circuit, etc.