JPH0971578A - Optically active compound and liquid crystal composition containing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a new optically active compound which is excellent in responsiveness and memory, shows ferroelectricity, and is useful as an electrooptic switching element. SOLUTION: This optically active compound is represented by formula I [R1 is a 1-18C alkyl(oxy); R2 is a 1-18C alkyl, a 3-18C alkenyl; R1 and R2 may contain each an asymmetric carbon; A is 2-1 group of formula II (X" is H, a halogen, cyano or methyl) or of formula III; n is 0, 1]. For example, a compound of' formula IV. The compound of formula I is obtained by reaction of an optically active glycidyl ether of formula V(X' is X") with a malonic diester of formula VI in the presence of a base in an organic solvent.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention provides a novel optically active compound and a liquid crystal composition containing the same.
The optically active compound provided by the present invention is a compound which exhibits ferroelectricity (chiral smectic C phase) excellent in responsiveness and memory property by itself or when mixed with another liquid crystal compound, It is used as an optical switching element.

[0002]

2. Description of the Related Art TN (twisted nematic) is one of the widely used display systems for liquid crystal display devices.
There is a mold. This is a liquid crystal display device containing a liquid crystal compound called a nematic liquid crystal as a main component, but one of its disadvantages is that the response speed is slow and only a maximum response speed of the order of several milliseconds can be obtained. This is one of the factors that limit the increase in size of display devices using nematic liquid crystals. As a solution to the drawbacks of the conventional liquid crystal display device, a liquid crystal display device using a bistable liquid crystal proposed by Clark and Laguerre has been receiving attention (see Japanese Patent Laid-Open No. 56-107216). ).

This bistable liquid crystal is called a ferroelectric liquid crystal, and is most promising because of its memory property, high-speed response, wide viewing angle, and good contrast. Not only for displays, but also in the field of optoelectronics such as optical printer heads, light valves, optical computer elements,
There is an urgent need for development toward its practical application.

Generally, a ferroelectric liquid crystal is a compound having an optically active site, and is expressed in a series of smectic phases having a molecular orientation in which the molecular long axis is tilted from the normal direction of the layer. Among them, chiral smectic C (hereinafter, S
The phase (abbreviated as c ^* ) has a low viscosity and is relatively superior in low voltage operability, and thus is practically superior. As such a ferroelectric liquid crystal, 1975, RB Meyer
4- (4-n-decyloxybenzylideneamino) cinnamic acid-2-methylbutyl ester (hereinafter abbreviated as DOBAMBC), which is synthesized by J. et al., Is known (J. Physique 36 L-69 (1975).
reference). However, since this DOBAMBC contains a Schiff base as a structure, it is difficult to be stable against water and light, so that it is physically and chemically stable as a ferroelectric liquid crystal material, and in the temperature range showing the Sc ^* phase. However, the emergence of a wide range of materials is strongly expected.

The response speed (τ) of the ferroelectric liquid crystal is expressed as τ = η / (Ps · E) (Ps: spontaneous polarization, η: viscosity, E: applied electric field), and the spontaneous polarization (Ps) Is larger, τ is smaller, that is, the response speed is faster. Therefore, in order to obtain a ferroelectric liquid crystal having a high response speed, it is necessary to develop a material having a large spontaneous polarization. Actually, a connector (spacer part) between the core skeleton containing a cyclic molecule (benzene ring, pyrimidine ring, cyclohexane ring, etc.) and the chiral skeleton aiming at increasing spontaneous polarization.
Is actively studied (Japanese Patent Laid-Open No. 1-238557).

However, although they exhibit large spontaneous polarization, on the contrary, in many cases, the viscosity is increased, the response speed is slowed, and the temperature range of the liquid crystal phase or Sc ^* phase is narrowed. It could not be said to be an effective molecular design guide. Therefore, it has been desired to develop a ferroelectric liquid crystal having a wider temperature range of Sc ^* phase and a larger spontaneous polarization than the known ferroelectric liquid crystal. Recently, JP-A-2-138274
Japanese Patent Application Laid-Open No. 3-58981 discloses a combination of structures of γ-butyrolactone and a 2- or 3-ring phenylpyrimidine ring, but it is within a very limited range and a sufficient effect can be obtained. Not not. When these are blended with the base liquid crystal, the magnitude of response speed and the magnitude of tilt angle are not sufficient. Further, regarding the phase transition temperature, the chiral smectic C phase-smectic A phase-
A cholesteric-isotropic phase sequence cannot be shown.

[0007]

DISCLOSURE OF THE INVENTION The object of the present invention is to provide a novel optically active substance and a liquid crystal compound used for a ferroelectric liquid crystal material. A structurally physically and chemically stable compound 1. 2. A compound which exhibits ferroelectricity by mixing with another liquid crystal compound or by itself, and which exhibits a Sc ^* phase in a wide temperature range. 3. A compound having a large induced spontaneous polarization derived from a permanent dipole moment. 4. A compound showing a fast response to an applied voltage. 5. Compounds in which the cholesteric phase and the chiral smectic C phase each have a sufficiently long helical pitch and a large tilt angle. 7. A compound showing a high-speed response by preparing a low-viscosity liquid crystal composition by adding a small amount thereof. By adding a small amount, a compound that improves the threshold value of memory characteristics and obtains a sufficiently high contrast ratio was found, and a compound containing at least one of these compounds was actually used to display the liquid crystal of a display device. It is to provide a compound that can be used as.

[0008]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have used a naphthalene skeleton for a core part and have two side chain parts sandwiching it.
One of the side chains is a group having a lactone ring having at least two chiral carbon atoms in the ring, and the other side chain has an optically active compound having a group which may contain a chiral carbon atom. I arrived.

That is, the present invention relates to the following contents. (1) An optically active compound represented by formula (I).

[0010]

Embedded image (In the formula, R ₁ is a linear or branched alkyl group having 1 to 18 carbon atoms, a linear or branched alkyloxy group having 1 to 18 carbon atoms, a linear or branched alkenyl group having 3 to 18 carbon atoms. A group, a linear or branched alkynyl group having 3 to 18 carbon atoms or a linear or branched alkoxyalkyl group having 1 to 3 carbon atoms in the alkoxy portion and an alkyl portion having 1 to 18 carbon atoms, or these R ₂ may be substituted with one or more halogens; R ₂ is a linear or branched alkyl group having 1 to 18 carbon atoms, a linear or branched alkenyl group having 3 to 18 carbon atoms, or carbon. A linear or branched alkynyl group of the number 3 to 18 is shown; R ₁ and R ₂ may contain an asymmetric carbon atom; A
Is selected from the group of formula (A); n is 0 or 1
X, X ′, X ″ and X ′ ″ each independently represent a hydrogen atom, a halogen atom, a cyano group, a methyl group, a methoxy group or a trihalomethyl group; the symbol * indicates an asymmetric carbon atom. Represent )

(2) The optically active compound as described in (1) above, wherein each of the two asymmetric carbon atoms of the lactone ring is (S) coordinated. (3) The two asymmetric carbon atoms of the lactone ring are each (R)
The optically active compound according to (1) above, which is coordinated. (4) A liquid crystal composition comprising at least one kind of the optically active compound described in (1) to (3) above. (5) A ferroelectric characterized by adding a chiral dopant containing the optically active compound described in (1) to (3) to a liquid crystal compound or composition showing a smectic C phase and a chiral smectic C phase. Chiral smectic liquid crystal composition. The present invention also discloses a liquid crystal display device using the liquid crystal composition described in (5) above.

Hereinafter, the present invention will be described in detail. The above novel optically active compound according to the present invention has a carbonyl group having a permanent dipole moment fixed to the inside of a 5-membered ring in order to exhibit ferroelectricity, and 2 or 3 in this ring.
Preferably having 2 asymmetric carbon atoms.
By having asymmetric carbon atoms, the free rotation of this part is suppressed, and by making the direction of the permanent dipole constant as a whole, an unprecedented large induced spontaneous polarization is exhibited, and the response speed It is possible to obtain higher speed. However, from the results of molecular dynamics calculation, the selection of the core skeleton is very important because the π electron of naphthalene and the nitrogen atom such as pyrimidine greatly contribute to the intermolecular interaction as the core skeleton. is there. Furthermore, the bookshelf layer structure commonly obtained with the naphthalene-based liquid crystal composition can be easily obtained, and a sufficiently high contrast ratio can be obtained by having a sufficient threshold value of the memory characteristic. It was also found that the tilt angle increases, which increases spontaneous polarization. In this way, a large spontaneous polarization could be expressed by combining the core portion of pyrimidine or the like with naphthalene and the lactone ring. Further, the compound of the present invention has two types of diastereomers by having two asymmetric carbon atoms in the lactone ring, and each of them has the result of meeting the purpose of suppressing the free rotation of the permanent dipole moiety. Become.
Further, they are useful as liquid crystal compounds either individually or as a mixture of each. Further, in the present invention, among the above-mentioned optically active compounds, there is a great feature that a liquid crystal phase is observed alone, and even if the liquid crystal phase itself does not show, induced spontaneous polarization by mixing with a liquid crystal composition. Indicates.

In the above general formula, the alkyl group for R ₁ and R ₂ is, for example, methyl, ethyl, n-propyl,
n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, isopropyl, t-butyl,
2-methylpropyl, 1-methylpropyl, 3-methylbutyl, 2-methylbutyl, 1-methylbutyl, 4-methylpentyl, 3-methylpentyl, 2-methylpentyl, 1-methylpentyl, 5-methylhexyl, 4-methyl Hexyl, 3-methylhexyl, 2-methylhexyl, 1-methylhexyl, 6-methylheptyl, 5-methylheptyl, 4-methylheptyl, 3-methylheptyl, 2-methylheptyl, 1-methylheptyl, 7-methyl Octyl, 6-methyloctyl, 5-methyloctyl, 4-methyloctyl, 3-methyloctyl, 2-methyloctyl, 1-methyloctyl, 8-methylnonyl, 7-methylnonyl, 6-methylnonyl, 5-methylnonyl, 4- Methylnonyl, 3-methylnonyl, 2-methylnonyl, 1-me Runoniru, 3,7-dimethyl octyl, groups such as 3,7,11-trimethyl-dodecyl used. Further, as an example of the alkenyl group, for example, 2
Straight-chain such as -propenyl, 3-butenyl, 4-pentenyl, 5-hexenyl, 6-heptenyl, 7-octenyl, 8-nonenyl, 9-decenyl, 10-undecenyl, 11-dodecenyl, 12-tridecenyl, 1-
Examples include branched alkenyl groups such as methyl-2-propenyl and 3-methyl-3-butenyl.

Further, examples of the alkynyl group include, for example, 2-propynyl, 3-butynyl, 5-hexynyl, 2-
Examples include straight-chain ones such as octynyl and branched alkynyl groups such as 1-methyl-2-propynyl.
The compound represented by formula (I) according to the present invention can be produced by the following method.

[0015]

Embedded image That is, the symbols of optically active glycidyl ether represented by the general formula (II) and A, n, R ₁ , R ₂ , R ₃ and * in the general formula (III) (formulas (II) and (III) are as follows: As described above, R ₃ represents a lower alkyl group.) And a malonic acid diester derivative represented by the formula ( ₃ ) can be synthesized by reacting them in an organic solvent in the presence of a base.

Regarding the production of the compound of the above formula (I), the compound of the formula (II) and 1 to 5 equivalents of the formula (III) are refluxed for 2 to 24 hours in the presence of 1 to 5 equivalents of a base in an organic solvent. Can be obtained. As the base used at this time, potassium t-butoxide, sodium methoxide, sodium ethoxide, sodium hydride, calcium hydride, potassium hydride, lithium hydride, n-butyllithium, lithium diisopropylamide or the like is preferable, and As the organic solvent, alcohols such as t-butanol, ethers such as tetrahydrofuran and diethyl ether, aprotic organic solvents such as dimethylformamide, and mixed solvents of the above organic solvents are preferable.

The above formula (II) compound, which is the starting material compound, is
It can be manufactured by the following method.

[0018]

Embedded image It can be produced by reacting the phenol derivative represented by the above formula (IV) with optically active epichlorohydrin in the presence of a base. That is, regarding the production of the compound of the formula (II), the phenol derivative of the compound of the formula (IV) and 1 to 10 equivalents of optically active epichlorohydrin in the presence of 1 to 5 equivalents of a base in an organic solvent at 40 to 80 ° C. It can be obtained by stirring for 1 to 6 hours. As the base used at this time, potassium t-butoxide,
Sodium hydroxide, potassium hydroxide, sodium carbonate,
Potassium carbonate, cesium carbonate and the like are preferable, and as the organic solvent, alcohols such as t-butanol and aprotic polar solvents such as dimethylformamide are preferable. Also, a phase transfer catalyst can be used in place of the base. For example, benzyltriethylammonium bromide and the like.

A commercially available reagent was used as the optically active epichlorohydrin. The compound of the formula (IV), which is the above-mentioned raw material compound, can be produced, for example, by the following method. That is, a 6-alkyloxy-2-hydrooxynaphthalene derivative can be produced according to the following synthetic route.

Embedded image Further, a 6-alkyl-2-hydroxynaphthalene derivative can be produced according to the following synthetic route.

[0020]

[Chemical 6] Furthermore, 6- [5-alkyloxy-2-pyrimidinyl]
The 2-hydroxynaphthalene derivative and the 6- [5-alkyl-2-pyrimidinyl] -2-hydroxynaphthalene derivative can be produced according to the following synthetic route.

[0021]

[Chemical 7] Furthermore, a 6- [4-alkyloxyphenyl] -2-hydroxynaphthalene derivative and a 6- [4-alkylphenyl] -2-hydroxynaphthalene derivative can be produced according to the following synthetic route.

[0022]

Embedded image As one of the excellent characteristics of the compound represented by the general formula (I), it is possible to induce a sufficiently large spontaneous polarization even when added in a small amount. For example, as shown in Example 3 below, only 4% by weight of the compound obtained in Example 1 and S
In the Sc ^* liquid crystal composition containing 96% by weight of the host liquid crystal (abbreviated as host liquid crystal) showing the c phase, the spontaneous polarization value at 25 ° C. is −13.9 nC / cm ^2, which is very large. . For this reason, 0.1
If it is added in an amount of about wt% or more, it becomes possible to induce spontaneous polarization sufficient for high-speed response. Furthermore, by adding a small amount, it becomes possible to prevent the viscosity of the host liquid crystal from increasing. Furthermore, the bookshelf layer structure commonly obtained with the naphthalene-based liquid crystal composition can be easily adopted, and a sufficiently high contrast ratio can be obtained by having a sufficient threshold value of the memory characteristic.

Further, the compound represented by the general formula (I) of the present invention has asymmetric carbon atoms at the 2-position and 4-position of the lactone ring. Of these, the factor that determines the polarity of the induced spontaneous polarization, which is a major feature of the chiral dopant, is the absolute configuration of the asymmetric carbon atom at the 4-position, and the absolute configuration of the asymmetric carbon atom at the 2-position is its size. Have a great influence on. In addition, the absolute configuration of the asymmetric carbon atom at the 2-position is
When the absolute configuration of the asymmetric carbon atom at the 4-position is the same, the lactone ring has a cis configuration, and when different, it has a trans configuration. Therefore, in these cis and trans forms,
Although there is no difference in the polarity of the induced spontaneous polarization, the size of the cis body is generally 1.5 to 10 times larger than that of the cis body. However, since the cis form and the trans form of the present invention can be separated, a low viscosity and high-speed response can be obtained by adding a small amount.

As described above, the compound represented by the general formula (I) of the present invention is preferably added as a liquid crystal composition rather than used alone. This liquid crystal composition,
A smectic C phase-nematic phase-isotropic phase or a smectic C phase-smectic A, containing at least one kind of the optically active compound represented by the general formula (I) and, if necessary, one or more kinds of suitable chiral dopants. Phase-nematic phase-
Ferroelectricity (chiral smectic C phase) which exhibits a phase sequence of chiral smectic C phase-smectic A phase-cholesteric phase-isotropic phase when added to a non-chiral liquid crystal or liquid crystal composition showing a phase sequence such as isotropic phase ) Is induced.
Therefore, the optically active substance of the present invention showing no liquid crystal phase is useful as an additive for inducing ferroelectricity. Particularly when used as a liquid crystal display device, a composition containing a host liquid crystal as a main component is desirable. The compound represented by the general formula (I) is capable of inducing a sufficiently large spontaneous polarization, and is 0.1 to 20% by weight in the host liquid crystal.
If added to some extent, a ferroelectric Sc ^* composition capable of high-speed response can be obtained. Many of the compounds represented by the general formula (I) do not exhibit a liquid crystal phase by themselves, but the addition of a small amount of them does not often narrow the temperature range of the liquid crystal phase of the liquid crystal composition, especially the Sc ^* phase. Absent. The host liquid crystal to which the optically active compound of the present invention is added is not particularly limited, but compounds known as host liquid crystals can be used. For example, the following is exemplified.

[0025]

Embedded image (In the formula, R ₄ and R ₅ represent a C3 to C18 alkyl group or an alkoxy group.), A phenylpyrimidine-based liquid crystal,

Embedded image (Wherein R ₆ and R ₇ represent a C3 to C18 alkyl group or an alkoxy group), when added to a host liquid crystal composed of a single or a mixture of phenylbenzoate liquid crystals.
The characteristics such as high-speed response and retention of the Sc phase temperature range of the host liquid crystal become remarkable.

[0026]

EXAMPLES The compounds of the present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples. Hereinafter, the symbols K, N, Ch, S _A ,
Sc, Sc ^* , and I are crystals, nematic phase, cholesteric phase, smectic A phase, and smectic C, respectively.
Phase, a chiral smectic C phase, and an isotropic phase, and S _X represents a higher-order structure of the smectic phase. The compound was purified by silica gel column chromatography and recrystallization. The measurement of the phase transition point shown below may be slightly affected by the purity of the substance.

Example 1 6- [5-nonyl-2-pyrimidinyl] -2-naphthol 1.20 g (0.33 mmol), R-(-)-epichlorohydrin 3.05 g, potassium t-butoxide 1.13 g, and Mix 10 ml of t-butanol and mix 4
Stirred at 5 ° C for 6 hours. After the reaction, the temperature is returned to room temperature, cooling water is added, and the product is extracted with ethyl acetate. The extract was purified by silica gel column chromatography to obtain 1.1 g of S-form glycidyl ether form represented by the following structural formula.

[0028]

Embedded image 312 m of the optically active glycidyl ether body obtained above
g, diethyl n-butylmalonate 862 mg, potassium t-butoxide 209 mg, and t-butanol 10 m
1 was mixed and stirred under reflux for 12 hours. The reaction solution is returned to room temperature, neutralized with 4N-hydrochloric acid, and then the product is extracted with dichloromethane. The extract was purified by silica gel column chromatography to obtain 130 mg of trans form (2R, 4S) and cis form (2S, 4) of γ-lactone form shown in the following structural formula.
S) 160 mg was obtained. 1-1) (2R, 4S) body

[0029]

[Chemical 12]

[0030]

Embedded image

Example 2 1.79 g of 6-octyloxy-2-naphthol (0.
66 mmol), R-(-)-epichlorohydrin 7.
10 g, potassium t-butoxide 2.26 g, and t-
20 ml of butanol was mixed and stirred at 45 ° C. for 6 hours. After the reaction, the temperature is returned to room temperature, cooling water is added, and the product is extracted with ethyl acetate. The extract was purified by silica gel column chromatography to obtain 1.57 g of S-form glycidyl ether form represented by the following structural formula.

[0032]

Embedded image Optically Active Glycidyl Ether Body 329m Obtained Above
g, diethyl n-butylmalonate 1.15 g, potassium t-butoxide 279 mg, and t-butanol 15 m
1 was mixed and stirred under reflux for 12 hours. The reaction solution is returned to room temperature, neutralized with 4N-hydrochloric acid, and then the product is extracted with dichloromethane. The extract was purified by silica gel column chromatography to obtain 140 mg of trans form (2R, 4S) of γ-lactone form and cis form (2S, 4) of the following structural formula.
S) 180 mg was obtained. 2-1) (2R, 4S) body

[0033]

[Chemical 15] 2-2) (2S, 4S) body

[0034]

Embedded image

Typical structural formulas obtained by the similar method are shown below. (In the chemical formula, (O) represents O or a single bond, and C ₆ represents C ₆ H _13. )

[0036]

Embedded image

[0037]

Embedded image

[0038]

Embedded image

[0039]

Embedded image

[0040]

[Chemical 21]

[0041]

Embedded image

[0042]

Embedded image

[0043]

Embedded image

[0044]

Embedded image

[0045]

[Chemical formula 26]

[0046]

Embedded image

[0047]

Embedded image

[0048]

[Chemical 29]

[0049]

Embedded image

[0050]

[Chemical 31]

[0051]

Embedded image

[0052]

[Chemical 33]

[0053]

Embedded image

[0054]

Embedded image

[0055]

Embedded image

[0056]

Embedded image

[0057]

Embedded image

Example 3 (Preparation of Ferroelectric Liquid Crystal Composition) The compound (2%) represented by the formula (X) synthesized in Example 1 was
Compounded in the non-optically active pyrimidine-based liquid crystal (A) having the following Sc phase,

[0059]

Embedded image

A liquid crystal composition was prepared. At this time, the phase transition temperature of the liquid crystal composition is And shows a chiral smectic C phase at room temperature.

(Measurement of Spontaneous Polarization, Viscosity, Response Speed, and Inclination Angle) The obtained liquid crystal composition containing the lactone derivative was heated to form an isotropic liquid, and then polyimide was applied and rubbing treatment was performed. It was injected into a thin cell with a transparent electrode (2.4 microns). After that, the cell was cooled, and a uniform Sc ^* phase monodomain in which the helical structure disappeared was obtained. At 25 ° C, 48Vpp, 5
A spontaneous polarization was measured by applying a triangular wave voltage of 0 Hz. Similarly, a rectangular wave voltage of 24 Vpp and 50 Hz was applied to this cell, and the response speed and viscosity at 25 ° C. were measured. A rectangular wave voltage of 48 Vpp and 0.1 Hz was applied to the same cell, and the angular difference between the extinction positions corresponding to the two switching states was measured.

2% or 4 of the lactone derivative synthesized this time
Table 1 shows the measurement results of the spontaneous polarization, the viscosity, the response speed, and the tilt angle when 100% was added to the liquid crystal composition. The results of comparison of existing lactone derivatives are also shown in Tables 2 and 3.

[0063]

[Table 1]

[0064]

[Table 2]

[0065]

[Table 3]

[0066]

INDUSTRIAL APPLICABILITY As described above, the optically active compound of the present invention is a novel compound represented by the general formula (I),
When the compound is added to a liquid crystal composition having no ferroelectric property, the compound exhibits the ferroelectric property of the entire composition and can induce a larger spontaneous polarization, and as a result,
High-speed response was obtained. In addition, the uniform orientation was good, the monodomain state was confirmed, and the memory property was obtained. From the above, a very excellent ferroelectric liquid crystal material could be provided.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area // C07M 7:00

Claims (5)

[Claims] 1. An optically active compound represented by formula (I). Embedded image (In the formula, R ₁ is a linear or branched alkyl group having 1 to 18 carbon atoms, a linear or branched alkyloxy group having 1 to 18 carbon atoms, or a linear or branched chain having 3 to 18 carbon atoms. An alkenyl group, a straight-chain or branched-chain alkynyl group having 3 to 18 carbon atoms, or a straight-chain or branched-chain alkoxyalkyl group having 1 to 18 carbon atoms in the alkyl moiety and 1 to 18 carbon atoms in the alkoxy moiety, or these May be substituted with one or more halogens; R ₂ is a linear or branched alkyl group having 1 to 18 carbon atoms, a linear or branched alkenyl group having 3 to 18 carbon atoms, or A linear or branched alkynyl group having 3 to 18 carbon atoms is shown; R ₁ and R ₂ may contain an asymmetric carbon atom; A
Is selected from the group of formula (A); n is 0 or 1
X, X ′, X ″ and X ′ ″ each independently represent a hydrogen atom, a halogen atom, a cyano group, a methyl group, a methoxy group or a trihalomethyl group; the symbol * indicates an asymmetric carbon atom. Represent ) 2. The optically active compound according to claim 1 or 2, wherein the two asymmetric carbon atoms of the lactone ring each have (S) coordination. 3. The optically active compound according to claim 1, wherein the two asymmetric carbon atoms of the lactone ring each have (R) coordination. 4. A liquid crystal composition comprising at least one kind of the optically active compound according to claim 1. 5. A ferroelectric composition comprising a liquid crystal compound or composition exhibiting a smectic C phase and a chiral smectic C phase, to which a chiral dopant containing the optically active compound according to claim 1 is added. Chiral smectic liquid crystal composition.