Abstract:
A mesomorphic compound represented by the following formula (I): ##STR1## wherein R 1  and R 2  respectively denote an alkyl group having 1-16 carbon atoms optionally substituted; X 1  and X 3  respectively denote a single bond, --O--, ##STR2## X 2  denotes a single bond, ##STR3## A 1  denotes a single bond ##STR4## A 3  denotes ##STR5## A 2  denotes 9, 10-dihydro-2,7-phenanthrenediyl, 2,7-fluorenediyl or 2,7-fluorenonediyl; n is 0 or 1; and X 4  and X 5  respectively denote hydrogen, F, Cl, Br, --CH 3 , --CN or --CF 3 , with proviso that X 1  is a single bond when A 1  is a single bond.

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to a novel mesomorphic compound, a liquid crystal composition a liquid crystal device, a display apparatus and a display method, and more particularly to a novel mesomorphic compound and a liquid crystal composition with improved responsiveness to an electric field, a liquid crystal device using the liquid crystal composition for use in a display device, a liquid crystal-optical shutter, etc., a display apparatus using the device, and a display method using the composition and 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 milli-seconds, 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 so 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. As a result, 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. has been already proposed. However, any method is not sufficient to overcome the above-mentioned drawbacks. As a result, it is the present state that 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, ferroelectric liquid crystal materials developed heretofore cannot be said to satisfy sufficient characteristics required for a liquid crystal device including low-temperature operation characteristic, high-speed responsiveness, etc. 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. 
     Further, 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. 
     As described hereinabove, commercialization of a ferroelectric liquid crystal device requires a liquid crystal composition assuming a chiral smectic phase which has not only a large spontaneous polarization but also a low viscosity, a high-speed responsiveness and a small temperature-dependence of response speed. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a mesomorphic compound, a liquid crystal composition, particularly a chiral smectic liquid crystal composition, containing the mesomorphic compound for providing a practical ferroelectric liquid crystal device, a liquid crystal device using the liquid crystal composition and having a high response speed and a smaller temperature-dependence of the response speed, a display apparatus using the device, and a display method using the composition and device. 
     According to the present invention, there is provided a mesomorphic compound represented by the following formula (I): ##STR6## wherein R 1  and R 2  respectively denote an alkyl group having 1-16 carbon atoms capable of having a substituent; X 1  and X 3  respectively denote a single bond, --O--, ##STR7## X 2  denotes a single bond, ##STR8## A 1  denotes a single bond ##STR9## A 3  denotes ##STR10## A 2  denotes 9, 10-dihydro-2,7-phenanthrenediyl, 2,7-fluorenediyl or 2,7-fluorenonediyl; n is 0 or 1; and X 4  and X 5  respectively denote hydrogen, F, Cl, Br, --CH 3 , CN or CF 3 , with proviso that X 1  is a single bond when A 1  is a single bond. 
     According to the present invention, there is further provided a liquid crystal composition containing at least one species of the mesomorphic compound as described above. 
     The present invention provides 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 comprising the liquid crystal device, and voltage application means for driving 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 switching the alignment direction of liquid crystal molecules by using voltage application means to effect display. 
     Heretofore, mesomorphic compounds having thiadiazole rings have been shown in D. Demus et al., &#34;Flussige Kristalle in Tabellen II&#34;, pp. 359-361 (1984), and disclosed in Japanese Laid-Open Patent Applications (KOKAI) Nos. 51644/1987, 222148/1988 and 61472/1989 and W088/08019. With respect to a thiadiazole derivative having a specific group such as 9,10-dihydro-2,7-phenanthrenediyl, 2,7-fluorenediyl or 2,7-fluorenonediyl represented by the above formula (I) of the present invention, there is no disclosure at all. We found that the thiadiazole derivative having such a group represented by the formula (I) had a wide temperature range of a mesomorphic phase compared with the conventional thiadiazole derivatives. We also found that a liquid crystal device using a ferroelectric chiral smectic liquid crystal composition containing the above thiadiazole derivative of the invention showed an improved low-temperature operation characteristic and a decreased temperature-dependence of response speed. 
     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 display 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 block diagram showing a display apparatus comprising a liquid crystal device utilizing ferroelectricity of a liquid crystal composition and a graphic controller; and 
     FIG. 5 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 
     In the formula (I) as described above, preferred examples of X 1  may includes a single bond, --O-- and ##STR11## 
     Further, X 3  may preferably include a single bond, --O-- and ##STR12## and X 2  may preferably include a single bond and ##STR13## 
     Preferred examples of A 1  may include ##STR14## and a single bond, particularly ##STR15## and a single bond. Further, A 3  may preferably include ##STR16## 
     Further, R 1  and R 2  each may preferably include the following groups (i) to (iv): 
     (i) an n-alkyl group having 1-16 carbon atoms, particularly 3-12 carbon atoms; 
     (ii) ##STR17## wherein m is an integer of 0-6 and n is an integer of 1-8 (optically active or inactive); 
     (iii) ##STR18## wherein r is an integer of 0-6, s is 0 or 1, and t is an integer of 1-12 (optically active or inactive); and 
     (iv) ##STR19## wherein y is 0 or 1 and x is an integer of 1-14. 
     The compounds represented by the general formula (I) may be synthesized through the following reaction schemes A and B. ##STR20## 
     In the above, R 1 , R 2 , X 1 , X 2 , X 3 , A 1 , A 2  and A 3  are the same as defined in the general formula (I). 
     In a case where X 1  and X 3  are respectively --O--, ##STR21## or X 2  is ##STR22## it is also possible to form a group of R 1  -X 1  -A 1  - or R 2  -X 3  -A 3  -X 2 ) n  A 2  - through the following steps (a) to (c): 
     (a) Hydroxyl group or carboxyl group combined with A 1 , A 2  or A 3  is modified with addition of a protective group into a non-reactive or less reactive group such as --OCH 3 , ##STR23## capable of elimination reaction. 
     (b) Ring closure is effected. 
     (c) The protective group is eliminated and modified into the R 1  -X 1  -A 1  - or R 2  -X 3  (A 3  -X 2 ) n  A 2  -structure. 
     Specific examples of the mesomorphic compounds represented by the above-mentioned general formula (I) may include those shown by the following structural formulas. ##STR24## 
     The liquid crystal composition according to the present invention may be obtained by mixing at least one species of the compound represented by the formula (I) and 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 utilizing ferroelectricity, particularly a liquid crystal composition showing a chiral smectic phase. 
     Specific examples of another mesomorphic compound as described above may include those denoted by the following formulas (III) to (XI). ##STR25## 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, ##STR26## and X 3  &#39; and X 4  &#39; respectively denote a single bond, ##STR27## 
     In the formula (III), preferred compounds thereof may include those represented by the following formulas (IIIa) to (IIId): ##STR28## wherein q and h respectively denote 0 or 1 with proviso that g+h=1; i denotes 0 or 1; X 1  &#39; and X 2  &#39; respectively denote a single bond, ##STR29## and X 3  &#39;, X 4  &#39; and X 5  &#39; respectively denote a single bond, ##STR30## --CH 2  O-- or --OCH 2  --. 
     In the formula (IV), preferred compounds thereof may include those represented by the following formulas (IVa) to (IVc): ##STR31## wherein j denote 0 or 1; Y 1  &#39;, Y 2  &#39; and Y 3  &#39; respectively denote H, halogen, CH 3  or CF 3  ; X 1  &#39; and X 2  &#39; respectively denote a single bond, ##STR32## and X 3  &#39; and X 4  &#39; respectively denote a single bond, ##STR33## 
     In the formula (V), preferred compounds thereof may include those represented by the following formulas (Va) to (Vc): ##STR34## wherein k, l and 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, ##STR35## and X 3  &#39; and X 4  &#39; respectively denote a single bond, ##STR36## --CH 2  O-- or --OCH 2  --. 
     In the formula (VI), preferred compounds thereof may include those represented by the following formulas (VIa) to (VIf): ##STR37## 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 two or more non-neighboring 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 --O--, ##STR38## with 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-. 
     Further, preferred examples of R 1  &#39; and R 2  &#39; may respectively include those represented by the following groups (i) to (vii): 
     i) a linear alkyl group having 1-15 carbon atoms; 
     ii) ##STR39## wherein p denotes an integer of 0-5 and q denotes an integer of 1-11 (optically active or inactive); 
     iii) ##STR40## 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); 
     iv) ##STR41## wherein u denotes 0 or 1 and v denotes an integer of 1-16; 
     v) ##STR42## wherein w denotes an integer of 1-15 (optically active or inactive); 
     vi) ##STR43## wherein A denotes an integer of 0-2 and B denotes an integer of 1-15 (optically active or inactive); and 
     vii) ##STR44## wherein C denotes an integer of 0-2 and D denotes an integer of 1-15 (optically active or inactive). 
     In the above-mentioned formula (III), more preferred compounds thereof may include those represented by the formulas (IIIaa) to (IIIdc): ##STR45## 
     In the above-mentioned formula (IV), more preferred compounds thereof may include those represented by the formulas (IVaa) to (IVcd): ##STR46## 
     In the above-mentioned formula (V), more preferred compounds thereof may include those represented by the formulas (Vaa) to (Vbf): ##STR47## 
     In the above-mentioned formula (VI), more preferred compounds thereof may include those represented by the formulas (VIaa) to (VIfa): ##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## --CH 2  O-- or --OCH 2  --. ##STR51## wherein F and G respectively denote 0 or 1; X 1  &#39; and X 2  &#39; respectively denote a single bond, ##STR52## or --O--; and X 3  &#39; and X 4  &#39; respectively denote a single bond, ##STR53## --CH 2  O-- or --OCH 2  --. 
     In the above formula (VII), preferred compounds thereof may include those represented by the following formulas (VIIa) and (VIIb): ##STR54## 
     In the above formula (VIII), preferred compounds thereof may include those represented by the following formulas (VIIIa) and (VIIIb). ##STR55## 
     More preferred compounds of the formula (VIII) may include those represented by the formulas (VIIIaa) to (VIIIbb): ##STR56## 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 two or more non-neighboring 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 --O--, ##STR57## 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; 
     ii) ##STR58## wherein p denotes an integer of 0-5 and q denotes an integer of 1-11 (optically active or inactive); 
     iii) ##STR59## 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); 
     iv) ##STR60## wherein u denotes an integer of 0 or 1 and v denotes an integer of 1-16; 
     v) ##STR61## wherein w denotes an integer of 1-15  (optically active or inactive); 
     vi) ##STR62## wherein A denotes an integer of 0-2 and B denotes an integer of 1-15 (optically active or inactive); and 
     vii) ##STR63## wherein C denotes an integer of 0-2 and D denotes an integer of 1-15 (optically active or inactive). ##STR64## 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, ##STR65## or --O--; A 1  &#39; denotes  and X 3  &#39; and X 4  &#39; respectively denote a single bond, ##STR66## --CH 2  O-- or --OCH 2  --. ##STR67## wherein X 1  &#39; and X 2  &#39; respectively denote a single bond, ##STR68## or --O--; A 2  &#39; denotes ##STR69## and X 3  &#39; and X 4  &#39;respectively denote a single bond, ##STR70## --CH 2  O-- or --OCH 2  --. ##STR71## wherein X 1  &#39; and X 2  &#39; respectively denote a single bond, ##STR72## or --O--; A 3  &#39; denotes ##STR73## and X 3  &#39; respectively denote a single bond, ##STR74## --CH 2  O-- or --OCH 2  --. 
     In the above-mentioned formula (IX), preferred compounds thereof may include those represented by the following formulas (IXa) to (IXc): ##STR75## 
     In the above-mentioned formula (X), preferred compounds thereof may include those represented by the following formulas (Xa) to (Xb): ##STR76## 
     In the above-mentioned formula (IX), more preferred compounds thereof may include those represented by the formulas (IXaa) to (IXcc): ##STR77## 
     In the above-mentioned formula (X), more preferred compounds thereof may include those represented by the formulas (Xaa) to (Xbb): ##STR78## 
     In the above-mentioned formula (XI), preferred compounds thereof may include those represented by the following formulas (XIa) to (XIg): ##STR79## 
     Herein, R 5  &#39; and R 6  &#39; respectively denote a liner or branched alkyl group having 1-18 carbon atoms capable of 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 --O--, ##STR80## 
     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; 
     ii) ##STR81## wherein p denotes an integer of 0-5 and q denotes an integer of 1-11 (optically active or inactive); 
     iii) ##STR82## 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); 
     iv) ##STR83## wherein w denotes an integer of 1-15 (optically active or inactive); 
     v) ##STR84## wherein A denotes an integer of 0-2 and B denotes an integer of 1-15 (optically active or inactive); and 
     vi) ##STR85## 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 a mesomorphic compound represented by the formula (I). 
     Further, when two or more species of the 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 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 assuming a chiral smectic phase 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. 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 O  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 nitride containing hydrogen, silicon carbide, 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 or organic insulating alignment control layer. 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 may have a thickness of ordinarily 30Å-1 micron, preferably 30-3000 Å, further preferably 50-1000 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, 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 assuming a chiral smectic phase is sealed up to provide a liquid crystal layer 1 in a thickness of generally 0.5 to 20 microns, preferably 1 to 5 microns. 
     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. Full lines 23 show liquid crystal molecules. Each liquid crystal molecule 23 has a dipole moment (P⊥) 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⊥) 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. 
     Based on the arrangement 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. 4 and 5, 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. 4, 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 shown in FIGS. 4 and 5. 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 
     2-octyl-7-(5-hexyl-1,3,4-thiadiazole-2-yl)fluorene (Example Compound No. I-13) was synthesized through the following steps i)-vi). ##STR86## 
     Step i) Production of 2-octanoylfluorene 
     To a solution of 10.00 g (60.2 mM) of fluorene in 100 ml of dry carbon disulfide, 9.40 g (70.5 mM) of anhydrous aluminum chloride was added while being cooled on an ice-common salt bath. Under cooling on the bath, 10.3 ml (60.3 mM) of octanoylchloride was gradually added dropwise to the mixture at -2.5° to 1° C., followed by stirring for 2 hours and 50 minutes without cooling on the bath. After the reaction, the reaction mixture was poured into a mixture of 150 g of ice and 50 ml of hydrochloric acid. To the resultant mixture, 100 ml of ethyl acetate was added, followed by stirring at room temperature to precipitate a crystal. The crystal was recovered by filtration and recrystallized from acetone to obtain 3.70 g of 2-octanoylfluorene. The organic layer separated from the filtrate was washed with water, dried with anhydrous sodium sulfate, and condensed into about 100 ml of the resultant solution, followed by cooling on an ice bath to precipitate a crystal. The crystal was recovered by filtration and recrystallized from acetone to obtain 4.09 g of 2-octanoylfluorene. The total amount of 2-octanoylfluorene obtained was 7.79 g (Yield: 44.3%). 
     Step ii) Production of 2-octylfluorene 
     In a 200 ml-three-necked flask, 6.00 g (20.5 mM) of 2-octanoylfluorene, 3.06 ml (50.4 mM) of hydrazine hydrate (80% aqueous solution), 4.20 g (63.6 mM) of potassium hydroxide and 60 ml of diethyleneglycol were placed, followed by heating to about 130° C. to dissolve the mixture. Then, the mixture was gradually heated to 210°-217° C., followed by stirring for 3 hours and 40 minutes under heating. After the reaction, the reaction mixture was cooled and poured into 250 ml of water to precipitate a crystal. The crystal was recovered by filtration and dissolved in toluene, followed by washing with water, drying with anhydrous sodium sulfate and distilling-off of the solvent. The residue was purified by silica gel column chromatography (eluent: toluene/hexane=1/2) to obtain 4.58 g of 2-octylfluorene. 
     Step iii) Production of 2-acetyl-7-octylfluorene 
     To a solution of 4.50 g (16.2 mM) of 2-octylfluorene in 50 ml of dry carbon disulfide, 2.70 g (20.2 mM) of pulverized anhydrous aluminum chloride was added while being cooled on an ice-common salt bath. Under cooling on the bath, 1.20 ml (16.9 mM) of acetyl chloride was added dropwise to the mixture below 7° C., followed by stirring for 1 hour and 50 minutes at 10° C. or below. After the reaction, the reaction mixture was poured into a mixture of 50 g of ice and 15 ml of hydrochloric acid, followed by extraction with ethyl acetate. The organic layer was washed with water, dried with anhydrous sodium sulfate, and condensed, followed by cooling to about -20° C. to precipitate a crystal. The crystal was recovered by filtration to obtain 3.97 g of 2-acetyl-7-octylfluorene (Yield: 76.6%). 
     Step iv) Production of 7-octyl-2-fluorenecarboxylic acid 
     To a solution of 1.30 g (32.5 mM) of sodium hydroxide in 8.8 ml of water, 0.54 ml (10.5 mM) of bromine was added dropwise at -2° to -0.5° C. under cooling on an ice-common salt bath. After the addition, 3.4 ml of dioxane was added to the mixture to prepare a sodium hypobromite solution. The sodium hypobromite solution was added dropwise to a solution of 1.00 g (3.12 mM) of 2-acetyl-7-octylfluorene in a mixture solvent of 28 ml of dioxane and 2 ml of water at about 5.5° C. under cooling on an ice bath. After the addition, the ice bath was removed and 10 ml of dioxane was added to the resultant mixture, followed by stirring for 1 hour and 50 minutes. After the reaction, the reaction mixture was poured into 200 ml of ice water and acidified with 2.3 ml of hydrochloric acid so as to indicate pH=1 to precipitate a crystal. The crystal was recovered by filtration and recrystallized from acetone to obtain 0.80 g of 7-octyl-2-fluorenecarboxylic acid (Yield: 79.5%). 
     Step v) Production of N-heptanoyl-N&#39;-(7-octyl-2-fluorenecarbonyl)hydrazine 
     To 0.70 g (2.17 mM) of 7-octyl-2-fluorenecarboxylic acid, 2.1 ml of thionyl chloride and a drop of N,N-dimethylformamide (DMF) were added, followed by heat-refluxing for 20 minutes under stirring. After the reaction, an excessive thionyl chloride was distilled-off under reduced pressure to obtain 7-octyl-2-fluorenecarbonyl chloride. 
     Then, in a 50 ml-three-necked flask, 0.32 g (2.22 mM) of heptanohydrazide and 15 ml of dioxane were placed. To the mixture, a solution of the above-prepared 7-octyl-2-fluorenecarbonyl chloride in 5 ml of dioxane was added, followed by addition of 0.84 ml of pyridine at about 85° C. under stirring and further stirring for 30 minutes at 85°-88° C. After the reaction, the reaction mixture was cooled and poured into 200 ml of ice water to precipitate a crystal. The crystal was recrystallized from a mixture solvent of toluene-acetone to obtain 0.68 g of N-heptanoyl-N&#39;-(7-octyl-2-fluorenecarbonyl) hydrazine (Yield: 69.8%). 
     Step vi) Production of 2-octyl-7-(5-hexyl-1,3,4-thiadiazole-2-yl)fluorene 
     In a 30 ml-round-bottomed flask, 0.65 g (1.45 mM) of N-heptanoyl-N&#39;-(7-octyl-2-fluorenecarbonyl)hydrazine, 0.62 g (1.53 mM) of Lawesson&#39;s reagent and 10 ml of tetrahydrofuran were placed, followed by heat-refluxing for 1.5 hours. After the reaction, the reaction mixture was poured into a solution of 0.45 g of sodium hydroxide in 100 ml of ice water to precipitate a crystal. The crystal was recovered by filtration, washed with water and dissolved in toluene, followed by washing with water, drying with anhydrous sodium sulfate and distilling-off of the solvent. The residue was purified by silica gel column chromatography (eluent: toluene) and recrystallized two times from a mixture solvent of toluene-methanol to obtain 0.40 g of 2-octyl-7-(5-hexyl-1,3,4-thiadiazole-2-yl)fluorene (Yield: 61.8%). ##STR87## 
     Herein, the respective symbols denote the following phase, Iso.: isotropic phase, SmA: smectic A phase, Sm3: smectic phase of higher order than SmA and SmC (un-identified), and Cryst.: crystal. 
     EXAMPLE 2 
     2-octyl-7-(5-hexyl-1,3,4-thiadiazole-2-yl) fluorenone (Example Compound No. I-109) was synthesized through the following reaction scheme. ##STR88## 
     To a solution of 0.20 g (0.45 mM) of 2-octyl-7-(5-hexyl-1,3,4-thiadiazole-2-yl)fluorene in 20 ml of pyridine, 0.27 ml of 40%-trimethylbenzylammonium hydroxide aqueous solutions as added at 3.5°-4.5° C. under stirring on ice water bath, followed by stirring for 0.5 hour at 3.5°-4.5° C. After the reaction, the reaction mixture was poured into ice water to precipitate a crystal. The crystal was recovered by filtration, washed with water and dissolved in toluene, followed by drying with anhydrous sodium sulfate and distilling-off of the solvent under reduced pressure to obtain a residue. The residue was purified by silica gel column chromatography (eluent: toluene/ethyl acetate=20/1) and recrystallized from a mixture solvent of toluene-acetone to obtain 0.11 g of 2-octyl-7-(5-hexyl-1,3,4-thiadiazole-2-yl)fluorenone (Yield: 53.3%). ##STR89## 
     EXAMPLE 3 
     2-octyl-7-(5-octyl-1,3,4-thiadiazole-2-yl) fluorenone (Example Compound No. I-24) was synthesized in the same manner as in Example 1. ##STR90## 
     SmC: smectic C phase. 
     EXAMPLE 4 
     2-octyl-7-(5-octyl-1,3,4-thiadiazole-2-yl) fluorenone (Example Compound No. I-115) was synthesized in the same manner as in Example 2. ##STR91## 
     EXAMPLE 5 
     2-octyl-7-(5-hexyl-1,3,4-thiadiazole-2-yl)9,10-dihydrophenanthrene (Example Compound No. I-157) was synthesized in the same manner as in Example 1 except that 9,10-dihydrophenanthrene was used instead of fluorene. ##STR92## 
     EXAMPLE 6 
     2-octyl-7-(5-octyl-1,3,4-thiadiazole-2-yl)9,10-dihydrophenanthrene (Example Compound No. I-183) was synthesized in the same manner as in Example 5. ##STR93## 
     EXAMPLE 7 
     2-octyl-7-[5-(1-fluoroheptyl)-1,3,4-thiadiazole-2-yl]-9,10-dihydrophenanthrene was synthesized in the same manner as in Example 5. ##STR94## 
     EXAMPLE 8 
     2-methylbutoxyl-7-(5-decyl-1,3,4-thiadiazole-2-yl)-9,10-dihydrophenanthrene (Example Compound No. I-225) was synthesized through the following steps i) and ii). ##STR95## 
     Step i) Production of 2-hydroxy-9,10-dihydrophenanthrene 
     To a solution of 3.00 g (16.6 mM) of 9,10-dihydrophenanthrene in 40 ml of dry carbon disulfide, 2.73 g (20.5 mM) of anhydrous aluminum chloride was added while being cooled on an ice-common salt bath. Under cooling on the bath, 1.27 ml (17.9 mM) of acetylchloride was gradually added dropwise to the mixture at -4° to -2° C., followed by stirring for 1 hour and 30 minutes at room temperature without cooling on the bath. After the reaction, the reaction mixture was poured into a mixture of 50 g of ice and 15 ml of hydrochloric acid, followed by extraction with ethyl acetate. The organic layer was washed with water, dried with anhydrous sodium sulfate, and distilled-off the solvent under reduced pressure to obtain 3.57 g of oily 2-acetyl-9,10-dihydrophenanthrene (Yield: 96.5%). 
     Then, 2.00 g (11.6 mM) of m-chloroperbenzoic acid was added to a solution of 2.54 g (11.4 mM) of 2-acetyl-9,10-dihydrophenanthrene in 75 ml of dichloromethane at room temperature under stirring to be dissolved therein. To the resultant solution, 1.11 g (11.1 mM) of potassium carbonate was added, followed by heat-refluxing for 2 hours and 10 minutes. After the reaction, the reaction mixture was cooled on an ice bath and poured into 10%-sodium hydrogencarbonate aqueous solution. The resultant organic layer was washed with 5%-sodium hydrogencarbonate aqueous solution, followed by evaporation under reduced pressure to obtain a residue. To the residue, 1.59 g (24.1 mM) of sodium hydride, 25 ml of ethanol and 10 ml of water were added at about 70° C. on a hot water bath, followed by heat-stirring for 0.5 hour. After the reaction, the solvent was distilled-off under reduced pressure from the reaction mixture to obtain a residue. To the residue, 200 ml of water was added and 2.50 ml (28.3 mM) of concentrated hydrochloric acid was further added thereto to precipitate a crystal. The crystal was recovered by filtration and dissolved in ethyl acetate, followed by drying with anhydrous sodium sulfate and distilling-off of the solvent to obtain a crude product. The crude product was purified by silica gel column chromatography (eluent: toluene/ethyl acetate=100/1) to obtain 1.24 g of 2-hydroxy-9,10-dihydrophenanthrene (Yield: 55.3%). 
     Step ii) Production of 2-methylbutoxy-7-(5-decyl-1,3,4-thiadizaol-2-yl)-9,10-dihydrophenanthrene 
     2-methylbutoxy-7-(5-decyl-1,3,4-thiadizaol-2-yl)-9,10-dihydrophenanthrene was synthesized through the above-mentioned reaction schemes from 2-hydroxy-9,10-dihydrophenanthrene. ##STR96## 
     EXAMPLE 9 
     A liquid crystal composition A was prepared by mixing the following compounds in respectively indicated proportions. 
     
         ______________________________________                         wt.Structural formula            parts______________________________________ ##STR97##                    51.57 ##STR98##                    25.79 ##STR99##                    12.89 ##STR100##                   1.19 ##STR101##                   1.19 ##STR102##                   2.37 ##STR103##                   2.50 ##STR104##                   2.50______________________________________ 
    
     The liquid crystal composition A was further mixed with the following Example Compound No. I-24 in the proportions indicated below to provide a liquid crystal composition B. 
     
         ______________________________________Ex.Comp.                             wt.No.   Structural formula          parts______________________________________I-24##STR105##                    10    Composition A                  90______________________________________ 
    
     The liquid crystal composition B showed the following phase transition series. ##STR106## 
     Ch.: cholesteric phase. 
     EXAMPLE 10 
     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 insulting 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 2000 rpm for 15 seconds. Thereafter, the coating film was subjected to heat curing at 300° C. for 60 min. to obtain about 250Å-thick film. The coating film was rubbed with acetate fiber-planted cloth. The thus treated two glass plates were washed with isopropyl alcohol. After alumina 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 each other and heated at 100° C. for 60 min. to form a blank cell. The cell gap was found to be about 2 microns as measured by a Berek compensator. 
     Then, the liquid crystal composition B prepared in Example 9 was heated into an isotropic liquid, and injected into the above prepared cell under vacuum and, after sealing, was gradually cooled at a rate of 20° C./hour to 25° C. to prepare a ferroelectric liquid crystal device. 
     The ferroelectric liquid crystal device was subjected to measurement of the magnitude of spontaneous polarization Ps and 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 are shown below. 
     
         ______________________________________        10° C.                 30° C.                         45° C.______________________________________Response time (μsec)          364        151     62Ps (nC/cm.sup.2)          4.04       2.94    1.61______________________________________ 
    
     EXAMPLE 11 
     A liquid crystal composition C was prepared by mixing the following compounds in respectively indicated proportions. 
     
         ______________________________________                         wt.Structural formula            parts______________________________________ ##STR107##                   46.14 ##STR108##                   23.07 ##STR109##                   11.54 ##STR110##                   3.56 ##STR111##                   3.56 ##STR112##                   7.13 ##STR113##                   2.50 ##STR114##                   2.50______________________________________ 
    
     The liquid crystal composition C was further mixed with the following Example Compound No. I-157 in the proportions indicated below to provide a liquid crystal composition D. 
     
         ______________________________________Ex.Comp.                             wt.No.   Structural formula          parts______________________________________I-157##STR115##                    5    Composition C                  95______________________________________ 
    
     The liquid crystal composition D showed the following phase transition series. ##STR116## 
     EXAMPLE 12 
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 10 except for using the composition D. The ferroelectric liquid crystal device was subjected to measurement of the magnitude of spontaneous polarization Ps and response time in the same manner as in Example 10, whereby the following results were obtained. 
     
         ______________________________________        10° C.                 30° C.                         45° C.______________________________________Response time (μsec)          453        211     148Ps (nC/cm.sup.2)          3.65       2.60    1.30______________________________________ 
    
     EXAMPLE 13 
     A liquid crystal composition E was prepared by mixing the following compounds in respectively indicated proportions. 
     
         __________________________________________________________________________Structural formula                  wt. parts__________________________________________________________________________ ##STR117##                         12 ##STR118##                         10 ##STR119##                         10 ##STR120##                         3 ##STR121##                         8 ##STR122##                         4 ##STR123##                         6 ##STR124##                         2 ##STR125##                         8 ##STR126##                         15 ##STR127##                         7 ##STR128##                         7 ##STR129##                         4 ##STR130##                         2 ##STR131##                         2__________________________________________________________________________ 
    
     The liquid crystal composition E was further mixed with the following Example Compounds in the proportions indicated below to provide a liquid crystal composition F. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula           wt. parts__________________________________________________________________________I-12    ##STR132##                  3I-51    ##STR133##                  2I-79    ##STR134##                  2   Composition E                93__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 10 except for using the composition F. The ferroelectric liquid crystal device was subjected to measurement of response time in the same manner as in Example 10, whereby the following results were obtained. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          698        343     188______________________________________ 
    
     COMPARATIVE EXAMPLE 1 
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 10 except that the liquid crystal composition E prepared in Example 13 was injected into a cell. The measured values of the response time of the device were as follows. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          784        373     197______________________________________ 
    
     EXAMPLE 14 
     A liquid crystal composition G was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition E prepared in Example 13. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula                  wt. parts__________________________________________________________________________I-24    ##STR135##                         4I-92    ##STR136##                         3 I-118    ##STR137##                         2   Composition E                       91__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 10 except that the above liquid crystal composition G 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)          723        355     196______________________________________ 
    
     EXAMPLE 15 
     A liquid crystal composition H was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition E prepared in Example 13. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula                wt. parts__________________________________________________________________________I-83    ##STR138##                       2I-158    ##STR139##                       2I-216    ##STR140##                       4   Composition E                     92__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 10 except that the above liquid crystal composition H 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)          733        360     197______________________________________ 
    
     EXAMPLE 16 
     A liquid crystal composition I was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition E prepared in Example 13. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula                  wt. parts__________________________________________________________________________I-208    ##STR141##                         5I-234    ##STR142##                         3I-264    ##STR143##                         2   Composition E                       90__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 10 except that the above liquid crystal composition I 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)          741        367     208______________________________________ 
    
     EXAMPLE 17 
     A liquid crystal composition J was prepared by mixing the following example in respectively indicated proportions. 
     
         __________________________________________________________________________Structural formula                wt. parts__________________________________________________________________________ ##STR144##                       10 ##STR145##                       5 ##STR146##                       7 ##STR147##                       7 ##STR148##                       6 ##STR149##                       5 ##STR150##                       5 ##STR151##                       8 ##STR152##                       8 ##STR153##                       20 ##STR154##                       5 ##STR155##                       5 ##STR156##                       6 ##STR157##                       3__________________________________________________________________________ 
    
     The liquid crystal composition J was further mixed with the following Example Compounds in the proportions indicated below to provide a liquid crystal composition K. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula             wt. parts__________________________________________________________________________I-40    ##STR158##                    3I-100    ##STR159##                    3I-133    ##STR160##                    2   Composition J                  92__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 10 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)          591        293     151______________________________________ 
    
     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 2 
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 10 except that the liquid crystal composition J prepared in Example 17 was injected into a cell. The measured values of the response time of the device were as follows. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          653        317     159______________________________________ 
    
     EXAMPLE 18 
     A liquid crystal composition L was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition J prepared in Example 17. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula                  wt. parts__________________________________________________________________________I-87    ##STR161##                         2I-98    ##STR162##                         2 I-255    ##STR163##                         4   Composition J                       92__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 10 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)          618        307     160______________________________________ 
    
     EXAMPLE 19 
     A liquid crystal composition M was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition J prepared in Example 17. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula                 wt. parts__________________________________________________________________________I-57    ##STR164##                        3I-173    ##STR165##                        2I-258    ##STR166##                        3   Composition J                      92__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 10 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)          517        263     141______________________________________ 
    
     EXAMPLE 20 
     A liquid crystal composition N was prepared by mixing the following compounds in respectively indicated proportions. 
     
         __________________________________________________________________________Structural formula               wt. parts__________________________________________________________________________ ##STR167##                      6 ##STR168##                      6 ##STR169##                      7 ##STR170##                      14 ##STR171##                      8 ##STR172##                      4 ##STR173##                      2 ##STR174##                      10 ##STR175##                      5 ##STR176##                      10 ##STR177##                      7 ##STR178##                      7 ##STR179##                      5 ##STR180##                      2 ##STR181##                      2 ##STR182##                      2 ##STR183##                      3__________________________________________________________________________ 
    
     The liquid crystal composition N was further mixed with the following Example Compounds in the proportions indicated below to provide a liquid crystal composition O. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula                 wt. parts__________________________________________________________________________I-36    ##STR184##                        4I-254    ##STR185##                        2I-262    ##STR186##                        3   Composition N                      91__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 10 except that the above liquid crystal composition O 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)          481        251     138______________________________________ 
    
     COMPARATIVE EXAMPLE 3 
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 10 except that the liquid crystal composition N prepared in Example 20 was injected into a cell. The measured values of the response time of the device were as follows. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          668        340     182______________________________________ 
    
     EXAMPLE 21 
     A liquid crystal composition P was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition N prepared in Example 20. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula           wt. parts__________________________________________________________________________I-21    ##STR187##                  2I-140    ##STR188##                  2I-227    ##STR189##                  4   Composition N                92__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 10 except that the above liquid crystal composition P 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)          598        311     171______________________________________ 
    
     EXAMPLE 22 
     A liquid crystal composition Q was prepared by mixing the following example compounds in the indicated proportions with the liquid crystal composition N prepared in Example 20. 
     
         __________________________________________________________________________Ex. Comp. No.   Structural formula                    wt. parts__________________________________________________________________________I-33    ##STR190##                           4I-226    ##STR191##                           2I-250    ##STR192##                           2   Composition N                         92__________________________________________________________________________ 
    
     A ferroelectric liquid crystal device was prepared in the same manner as in Example 10 except that the above liquid crystal composition Q 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)          476        248     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. 
     As is apparent from the results shown in the above Examples 13-22, the ferroelectric liquid crystal devices containing the liquid crystal compositions F, G, H, I, K, L, M, O, P and Q showed an improved low-temperature operation characteristic, a high-speed responsiveness, and a decreased temperature dependence of the response speed. 
     EXAMPLE 23 
     A blank cell was prepared in the same manner as in Example 15 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 H prepared in Example 15. The liquid crystal device was subjected to measurement of optical response time in the same manner as in Example 10. The results are shown below. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          676        333     184______________________________________ 
    
     EXAMPLE 24 
     A blank cell was prepared in the same manner as in Example 15 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 the blank cell with the liquid crystal composition H prepared in Example 15. The liquid crystal device was subjected to measurement of optical response time in the same manner as in Example 10. The results are shown below. 
     
         ______________________________________        10° C.                 25° C.                         40° C.______________________________________Response time (μsec)          683        336     190______________________________________ 
    
     As is apparent from the above Examples 23 and 24, also in the cases of different device structures, the devices containing the ferroelectric liquid crystal composition H according to the present invention respectively provided a remarkably improved operation characteristic at a lower temperature and also a decreased temperature-dependence of the response speed similar to those in Example 24. 
     As described hereinabove, according to the present invention, there is provided a mesomorphic compound which can effectively be applied to a liquid crystal device utilizing ferroelectricity when the compound per se assumes a chiral smectic phase. Further, there is also provided a liquid crystal composition containing the compound and assuming a chiral smectic phase, whereby a liquid crystal device comprising the composition can be operated by utilizing ferroelectricity of the composition. The present invention provides a liquid crystal device using such a composition which shows a good switching characteristic, an improved low-temperature operation characteristic and a decreased temperature-dependence of response speed. The present invention further provides a display apparatus and a display method which employ such a device as a display unit, whereby good display characteristics can be obtained in combination with a light source, a drive circuit, etc.