JP7501163B2 - Liquid crystal composition and liquid crystal display device - Google Patents

Description

This invention relates to a cholesteric liquid crystal composition useful as a material for display elements and a display element using the same.

Liquid crystal display elements using cholesteric (chiral nematic) liquid crystal compositions in which an optically active compound is added to give the liquid crystal phase a twisted alignment are used in electronic books, electronic price tags, presentation panels, and other applications that require particularly low power consumption, due to their bistability. Bistability in cholesteric liquid crystals is achieved by switching between a planar state and a focal conic state by applying a pulse voltage, and since both the planar and focal conic states are maintained even when the voltage is turned off, this bistability is sometimes referred to as memory properties.

A liquid crystal display element using cholesteric liquid crystal shows a specific selective reflection wavelength that depends on the chiral pitch when the helical axis of the cholesteric liquid crystal is perpendicular to the substrate (planar state). The selective reflection wavelength (λ) is determined by the product of the average refractive index (n) of the liquid crystal composition and the chiral pitch (P), so when the refractive index of the liquid crystal composition is fixed, the desired selective reflection wavelength can be obtained by adjusting the chiral pitch P by adjusting the concentration of the chiral compound. The half-width (Δλ) of the selective reflection light at this time is proportional to the product of the refractive index anisotropy (Δn = ne - no) of the liquid crystal and the chiral pitch, but a liquid crystal composition with a large Δn must be used because a relatively wide half-width is required for a bright display. In this case, the average refractive index of the liquid crystal composition also becomes large, so in order to adjust to the desired λ, it is necessary to add more chiral to shorten P, but if the amount of chiral compound added is too large, problems such as a deterioration in the liquid crystal temperature range of the host liquid crystal and an increase in viscosity occur. That is, designing cholesteric liquid crystals requires chiral compounds that have a high liquid crystal twisting power that induces chiral pitch and have little effect on the host liquid crystal, and a host liquid crystal composition that has excellent compatibility with such compounds and a high Δn is required. Furthermore, a sufficiently large dielectric anisotropy (Δε) that enables low-voltage operation as a liquid crystal display element and good storage stability that does not cause precipitation even in low-temperature environments are required. For example, Patent Document 1 discloses several cholesteric liquid crystal compositions to solve these problems.

The chiral pitch length of cholesteric liquid crystal depends on the type and concentration of the chiral compound, and can be expressed as P = 1/(β·c). Here, c is the concentration of the chiral compound in the cholesteric liquid crystal composition, and β is the power with which the chiral compound twists the liquid crystal composition, called the Helical Twisting Power (HTP), which can be calculated using the formula HTP = n/(λ x 0.01 x c). Here, n is the average refractive index of the liquid crystal composition. Using this HTP, the desired pitch can be given to the liquid crystal composition.

Chiral compounds generally narrow the temperature range of the liquid crystal phase and increase the viscosity. Furthermore, it is known that the chiral pitch length generated by adding a chiral compound has temperature dependence. For example, when a compound represented by formula (Chiral-1), which is a chiral compound having an asymmetric carbon, is added to a general liquid crystal composition, the pitch length increases as the temperature changes from room temperature to high temperatures, and this change differs greatly depending on the host liquid crystal composition.

Due to the temperature dependency of the chiral pitch of cholesteric liquid crystals, cholesteric liquid crystal compositions have the drawback that the selective reflection wavelength λ shifts and the color changes due to changes in the environmental temperature when they are operated as an element. In other words, the chiral compound and host liquid crystal composition must be selected so as to minimize the occurrence of such drawbacks, taking into consideration the effects on the physical properties and stability of the host liquid crystal composition and the environmental temperature in which it is used. However, no specific host liquid crystal composition is known that can resolve these drawbacks while satisfying the various requirements required of cholesteric liquid crystal compositions, namely, large dielectric anisotropy, wide operating temperature range, stability at low temperatures, the desired selective reflection wavelength, high reliability against external light, etc.

JP 2010-275463 A

The problem that the present invention aims to solve is to provide a cholesteric liquid crystal composition that has high dielectric anisotropy (Δε) and refractive index anisotropy (Δn), a wide cholesteric liquid crystal temperature range, is stable at low temperatures, has high reliability against external stimuli such as heat and light, and has small temperature change in the selective reflection wavelength. Furthermore, the object is to provide a liquid crystal display element that uses such cholesteric liquid crystal and has small color change with temperature, sufficient brightness, a wide operating temperature range, low driving voltage, and high reliability.

As a result of intensive research by the present inventors, it has been found that the present invention is a composition comprising a dielectrically positive first component, a dielectrically neutral second component, and a third component containing at least two optically active substances having temperature dependencies of chiral pitch length different from each other,
The inventors have found that the above-mentioned problems can be solved by a cholesteric liquid crystal composition having positive dielectric anisotropy, which contains one or more compounds represented by general formula (1-1) as a first component, one or more compounds represented by general formula (1-2) as a first component, and one or more compounds represented by general formula (2-1) as a second component. This has led to the completion of the present invention.

( ^R1 and ^R2 each independently represent an alkyl group having 1 to 7 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, or an alkenyl group having 2 to 7 carbon atoms; ring A represents a 1,4-cyclohexylene group or a 1,4-phenylene group; and ^Y1 to ^Y5 each independently represent a hydrogen atom or a fluorine atom.
R ³ and R ⁴ each independently represent an alkenyl group having 2 to 7 carbon atoms or an alkenyloxy group; Y ⁶ to Y ¹¹ each independently represent a hydrogen atom, a fluorine atom or a methyl group; Z ¹ represents a single bond, -COO- or -CH ₂ CH ₂ -; and a, b and c each independently represent 0 or 1.

The present invention provides a cholesteric liquid crystal composition having superior properties to conventional cholesteric liquid crystals in terms of achieving multiple physical properties. That is, it is possible to provide a cholesteric liquid crystal composition having superior physical properties in terms of temperature change of selective reflection wavelength, dielectric anisotropy (Δε) and refractive index anisotropy (Δn), cholesteric liquid crystal temperature range, low temperature stability, stability against external stimuli such as heat and light, etc. Furthermore, since the chiral pitch of the liquid crystal composition of the present invention hardly changes, particularly in the practical temperature range of 0°C to 50°C, the selective reflection wavelength dependent on the chiral pitch also does not change. This makes it possible to provide a high-quality cholesteric liquid crystal display element that satisfies the various properties of cholesteric liquid crystal display elements that have been conventionally required, and further, the color of the reflection state does not change substantially.

The present invention is described in detail below.

A liquid crystal compound is "dielectrically positive" means that the Δε of the compound is +3.0 or more, and "dielectrically neutral" means that the Δε of the compound is -1.5 to +1.5. The Δε of each compound can be calculated by extrapolating the Δε value obtained when a certain amount of each compound is added to a liquid crystal composition. In the present invention, "%" means mass % unless otherwise specified.

The liquid crystal composition of the present invention contains a dielectrically positive compound as the first component.

In the general formula (1-1), ^Y1 and ^Y2 each represent a hydrogen atom or a fluorine atom, and preferably both are hydrogen atoms. ^Y3 represents a hydrogen atom or a fluorine atom, and preferably a hydrogen atom. a represents 0 or 1, and it is also preferable to use a bicyclic compound in which a is 0 in combination with a tricyclic compound in which a is 1.

In the general formula (1-2), ^Y4 and ^Y5 represent a hydrogen atom or a fluorine atom, and b represents 0 or 1. It is preferable that b is 0 and ^Y4 and ^Y5 are both fluorine atoms, or that b is 1 and ^Y4 and ^Y5 are both hydrogen atoms. It is also preferable to use a bicyclic compound in which b is 0 and a tricyclic compound in which b is 1 in combination.

In the general formulae (1-1) and (1-2), R ¹ and R ² each independently represent preferably an alkyl group having 1 to 7 carbon atoms, and more preferably an alkyl group having 1 to 5 carbon atoms.

The preferred content of the compounds represented by general formula (1-1) and general formula (1-2) is 40 to 75%, more preferably 45 to 70%, and particularly preferably 48 to 68%. The compound represented by general formula (1-1) has a large Δε and a moderate Δn, and the compound represented by general formula (1-2) has a large Δε and a high Δn. By using these in combination, it is possible to impart very large Δε and Δn to the composition while maintaining the liquid crystal temperature range and low-temperature stability, etc.

In addition, a compound represented by general formula (1-3) may be added to further increase Δε and Δn.

(R ⁷ represents an alkyl group having 1 to 7 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, or an alkenyl group having 2 to 7 carbon atoms; Y ¹² to Y ²³ each independently represent a hydrogen atom or a fluorine atom; X ¹ represents a fluorine atom, a chlorine atom, -CN, -NCS, -CF ₃ , or -OCF ₃ ; Z ³ and Z ⁴ each independently represent a single bond, -CH ₂ CH ₂ -, -COO-, -OCO-, -CH ₂ O-, -OCH ₂ -, -CF ₂ O-, -OCF ₂ -, or -C≡C-.)
When the liquid crystal composition contains the compound represented by formula (1-3), the content of the compound represented by formula (1-3) is preferably 1% or more, and more preferably 5% or more.

Furthermore, a compound represented by general formula (1-4) may be added. The compound represented by general formula (1-4) has a medium Δε and a medium Δn, and by using these in combination, the liquid crystal temperature range and low temperature stability can be improved.

(R ⁹ represents an alkyl group having 1 to 7 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, or an alkenyl group having 2 to 7 carbon atoms; X ² represents a fluorine atom, a chlorine atom, -CN, -NCS, -CF ₃ , or -OCF ₃ ; rings B and C each independently represent a 1,4-cyclohexylene group or a 1,4-phenylene group in which a hydrogen atom may be substituted with a fluorine atom; Z ⁵ represents a single bond, -COO-, -CH ₂ CH ₂ -, -CH=CH-, -FC=CF-, or -C=N-N=C-; d represents 1, 2, or 3, and when a plurality of rings B and Z ⁵ are present, they may be the same or different, but in general formula (1-4), the compounds represented by general formulas (1-1) and (1-3) are excluded.)
Ring C in formula (1-4) is preferably a 1,4-phenylene group in which a hydrogen atom may be substituted with a fluorine atom, and is preferably a 3-fluoro-1,4-phenylene group or a 3,5-difluoro-1,4-phenylene group.

At least one of the rings B in the general formula (1-4) is preferably a 1,4-cyclohexylene group, and the group directly bonded to R ⁹ is preferably a 1,4-cyclohexylene group.

The preferred total content of the first component is 40-80%, more preferably 45-75%, and most preferably 50-70%.

Preferred examples of the compounds represented by general formula (1-1), formula (1-2), formula (1-3) and formula (1-4) are the compounds represented by the following general formulas (1-1-a) to (1-1-d), general formulas (1-2-a) to (1-2-d), general formulas (1-3-a) to (1-3-f) and general formulas (1-4-a) to (1-4-i).

(In the formula, R ¹ has the same meaning as R ¹ in formula (1-1), R ² has the same meaning as R ² in formula (1-2), and R ⁷ has the same meaning as R ⁷ in formula (1-3).)

(In the formula, R ⁹ represents an alkyl group having 1 to 7 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, or an alkenyl group having 2 to 7 carbon atoms.)
The liquid crystal composition of the present invention contains a dielectrically neutral compound as the second component.

In general formula (2-1), c is 0 or 1, preferably 0. Y ⁶ to Y ¹¹ are all preferably hydrogen atoms. R ³ and R ⁴ each independently represent an alkenyl group or an alkenyloxy group having 2 to 7 carbon atoms, preferably an alkenyl group having 2 to 7 carbon atoms, and more preferably a group represented by any one of the following formulae (R1) to (R5). (The black dots in each formula are bonding points and represent the carbon atoms in the present ring A or the optionally substituted 1,4-phenylene group in the formula.)

The content of the compound represented by general formula (2-1) is preferably 1 to 35%, more preferably 2 to 30%, and particularly preferably 3 to 25%. The compound represented by general formula (2-1) has the effect of suppressing the viscosity of the liquid crystal composition low, and can impart a high Δn to the composition while adjusting the upper limit temperature of the liquid crystal phase, and also exhibits extremely good solubility with the first component.

By using a large amount of a compound in which ^Y6 to ^Y11 in general formula (2-1) are hydrogen atoms, the viscosity of the composition can be kept low, and by using a compound in which at least one is substituted with a methyl group or a fluorine atom, the stability of the liquid crystal phase can be further increased.

Preferred examples of the compound represented by general formula (2-1) are the following general formulas (2-1-a) to (2-1-e):

(In the formula, R ³ has the same meaning as R ³ in formula (2-1), and R ⁴ has the same meaning as R ⁴ in formula (2-1).)
Furthermore, a compound represented by the general formula (2-2) may be added as a second component for the purpose of reducing viscosity and expanding the liquid crystal temperature range.

( ^R5 and ^R6 each independently represent an alkyl group having 1 to 7 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, or an alkenyl group having 2 to 7 carbon atoms; rings B and C each independently represent a 1,4-cyclohexylene group or a 1,4-phenylene group in which a hydrogen atom may be substituted with a fluorine atom; ^Z2 represents a single bond, -COO-, _-CH2CH2- , -CH= _CH- , -FC=CF-, or -C=N-N=C-; d represents 1, 2, or 3, but when a plurality of rings B and ^Z2 are present, they may be the same or different.)
Preferred examples of the compound represented by formula (2-2) are the following formulae (2-2-a) to (2-2-k).

(In the formula, R ⁵ has the same meaning as R ⁵ in formula (2-2), and R ⁶ has the same meaning as R ⁶ in formula (2-2).)
More preferred examples of the compound represented by general formula (2-2) are compounds represented by formula (2-2-a), formula (2-2-b), formula (2-2-c) or formula (2-2-d), and it is particularly preferred to contain a compound selected from the group of compounds represented by formula (2-2-a) and/or (2-2-d) in which R ⁵ is an alkenyl group.

The content of the compound represented by general formula (2-2) is preferably 3% or more, more preferably 5% or more, and particularly preferably 7% or more.

In addition, the compound represented by general formula (2-3) as the second component can not only impart a high Δn to the liquid crystal composition while adjusting the viscosity and the upper limit temperature of the liquid crystal phase, but also exhibits extremely good solubility with the first component.

By using a large amount of a compound in which Y ^{to Y} in general formula (2-3) are hydrogen atoms, the viscosity of the composition can be kept low, and by using a compound in which at least one is substituted with a methyl group or a fluorine atom, the stability of the liquid crystal phase can be further increased.

(When c is 0, R ⁷ and R ⁸ each independently represent an alkyl group having 1 to 7 carbon atoms or an alkoxy group having 1 to 7 carbon atoms; when c is 1, R ⁷ and R ⁸ each independently represent an alkyl group having 1 to 7 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, or an alkenyl group or an alkenyloxy group having 2 to 7 carbon atoms; ring A represents a 1,4-cyclohexylene group or a 1,4-phenylene group in which a hydrogen atom may be substituted with a fluorine atom or a methyl group; Y ²⁴ to Y ²⁹ each independently represent a hydrogen atom, a fluorine atom, or a methyl group; Z ¹ represents a single bond, -COO-, or -CH ₂ CH ₂ -; and c represents 0 or 1.)
Preferred examples of the compound represented by formula (2-3) are the following formulae (2-3-a) to (2-3-e).

(In the formula, R ⁷ has the same meaning as R ⁷ in formula (2-3), and R ⁸ has the same meaning as R ⁸ in formula (2-3).)
The total content of the compounds represented by formula (2-3) is preferably 10 to 50%, more preferably 15 to 45%, and particularly preferably 20 to 40%.

The preferred total content of the second component is 20 to 55%, more preferably 25 to 50%, and particularly preferably 30 to 45%.

The liquid crystal composition of the present invention contains at least two optically active substances (chiral compounds) as a third component, which have different temperature dependencies of chiral pitch length. It is preferable that one of these compounds has a positive chiral pitch temperature dependency and the other has a negative chiral pitch temperature dependency at the normal temperature of the liquid crystal display element, i.e., preferably in the range of 0 to 50°C. The total content of the third component varies depending on the intended selective reflection wavelength, but is preferably 10% or less, more preferably 8% or less, and particularly preferably 6% or less. There is no particular restriction on the preferable lower limit, but when the liquid crystal twisting force is extremely large, the amount of the third component added in the composition becomes very small, and a slight deviation in the mixing ratio may cause deviations in the selective reflection wavelength and its temperature dependency. Although it is also affected by the weighing accuracy of the manufacturing equipment, as long as the concentration of the third component is approximately 0.1% or more, the composition can be manufactured with high accuracy regardless of the manufacturing scale.

The chiral compound preferably contains one or more compounds represented by general formula (3).

( ^R8 and ^R9 each independently represent an alkyl group having 1 to 7 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, or an alkenyl group having 2 to 7 carbon atoms; rings D, E, F, and G each independently represent a 1,4-cyclohexylene group or a 1,4-phenylene group; ^Z5 and ^Z6 each independently represent a single bond, -OCO-, or -COO-; and e and f each independently represent 0, 1, or 2. When a plurality of rings D, G, ^Z5 , and ^Z6 are present, they may be the same or different.)
Preferred examples of the compound represented by formula (3) are the compounds represented by the following formulas (3-1) to (3-4).

The compounds represented by formulas (3-1) and (3-2) generally have a positive temperature dependence of the chiral pitch length. The compounds represented by formulas (3-3) and (3-4) generally have a negative temperature dependence of the chiral pitch length. In addition, the compounds represented by formulas (3-1) and (3-3) are dextrorotatory substances, and the compounds represented by formulas (3-2) and (3-4) are levorotatory substances. A suitable combination of chiral compounds in the present invention is given in the table below. The dextrorotatory and levorotatory properties can be appropriately selected according to the required specifications of the display element, but when cholesteric liquid crystal regions adjusted to different selective reflection wavelengths are adjacent to each other, it is preferable to reverse the optical rotation of each to avoid color mixing.

Preferable physical properties of the cholesteric liquid crystal composition of the present invention are described below. Note that Δn and Δε are the values of the host liquid crystal composition before the chiral compound is added.

The preferred range of Δn is 0.10 to 0.40, more preferably 0.15 to 0.35, and particularly preferably 0.20 to 0.30. The preferred range of Δε is 10 to 50, more preferably 15 to 45, and particularly preferably 20 to 40. The preferred range of Tni is 60 to 120°C, more preferably 70 to 110°C, and particularly preferably 80 to 110°C.

The smaller the flow viscosity, the more preferable, and there is no particular lower limit, but if it is 100 mPa·s or less, a response speed sufficient for practical use can be achieved.

The cholesteric liquid crystal composition of the present invention may further contain additives as necessary. For example, UV absorbers, antioxidants, HALS, etc. may be added to enhance stability against external stimuli. Although the structure is not particularly limited, various compounds that are generally known to be added to liquid crystal compositions, such as benzotriazole-based UV absorbers and hindered phenol-based oxidation inhibitors, may be used. Furthermore, various polymerizable compounds may also be included for the purpose of fixing the cholesteric liquid crystal phase. In this case, the polymerizable compound is preferably a substance that exhibits liquid crystallinity before curing. This can also be polymerized and cured by ultraviolet irradiation or heating, etc., to form a layer that has no fluidity and is changed to a state in which the alignment form does not change due to external forces.

Among the compounds described in the examples, compounds other than the optically active substance as the third component were prepared, and nematic liquid crystal compositions serving as host liquid crystals were produced, and various physical properties were measured.
We then prepared a compound containing a third component to produce a cholesteric liquid crystal.
To measure the selective reflection wavelength, a cell with a gap of 3 μm was prepared using a substrate with a horizontal alignment film, and after injecting liquid crystal, it was heated to above Tni and slowly cooled to room temperature. Then, the cell surface was pressed with a finger to change it to a planar alignment. Using this cell, the temperature dependence of the selective reflection wavelength was measured.

For the measurements, an LCD-5200 (manufactured by Otsuka Electronics) was used, with incident light coming from a direction tilted 30° from the normal to the cell, and selectively reflected light in the normal direction was received.

The compositions in the following examples and comparative examples contain each compound in the proportions shown in the table, and the content is listed in "mass %." The following abbreviations are used to describe the compounds in the examples.

(Ring structure)

Unless otherwise specified, this refers to the trans form.

(Side Chain Structure and Linking Structure)

(Physical properties)
Clearing point (°C): the temperature at which the composition transitions to an isotropic phase (Tni)
Melting point (°C): temperature at which the composition returns to the nematic phase from the solid phase, etc. Δn: refractive index anisotropy of the host liquid crystal composition at 25°C and 589 nm Δε: dielectric constant anisotropy of the host liquid crystal composition at 25°C and 1 kHz η (mPa·s): flow viscosity of the host liquid crystal composition at 20°C

Example 1
The compositions of Example 1 and Comparative Example 1 are shown in Table 3.
Nematic liquid crystal compositions (host liquid crystal compositions) were prepared by adjusting compositions excluding the third component in the table below, and their physical properties were measured. In addition, a third component compound was added to each of the host liquid crystal compositions as a chiral compound to prepare cholesteric liquid crystal compositions with a selective reflection wavelength of about 560 nm at 25°C.

The physical properties of each composition and the temperature dependence of the selective reflection wavelength are shown below.

The host liquid crystal composition of Example 1, excluding the third component, had the same Tni point, a lower melting point (= wider liquid crystal temperature range), a smaller viscosity (η), a larger dielectric anisotropy (Δε), and was capable of lower voltage operation, compared to Comparative Example 1.

In addition, cells made of cholesteric liquid crystal compositions containing a third component have a small temperature dependence of the selective reflection wavelength, making them more suitable as cholesteric materials for display elements.

Here, the cells using the cholesteric liquid crystal compositions of Example 1 and Comparative Example 1 were visually observed for color change as the temperature was changed from 0°C to 50°C. The cell into which the composition of Example 1 was injected showed no change, whereas the cell into which the composition of Comparative Example 1 was injected showed a change in color as the temperature increased. Furthermore, when the low-temperature storage stability of the compositions of Example 1 and Comparative Example 1 was compared, precipitation was observed after 48 hours at -20°C for the composition of Comparative Example 1, whereas the composition of Example 1 maintained its liquid crystal phase even after 240 hours, demonstrating excellent storage stability.

(Examples 2 to 5)
The compositions of Examples 2 to 5 are shown in Table 5.

As in Example 1, a host composition was prepared excluding the third component in the table below, a nematic liquid crystal composition (host liquid crystal composition) was produced, and the physical properties were measured. In addition, a third component compound was added to the host liquid crystal composition as a chiral compound to prepare a cholesteric liquid crystal composition with a selective reflection wavelength at 25°C of approximately 560 nm.

Compared to the host liquid crystal composition of Comparative Example 1, the host liquid crystal compositions of Examples 2 to 5 excluding the third component have a lower melting point (= wider liquid crystal temperature range), a smaller viscosity (η), a slightly larger dielectric anisotropy (Δε), and can be driven at a low voltage. Furthermore, the temperature dependence of the selective reflection wavelength of the cell of the cholesteric liquid crystal composition containing the third component is smaller, and it is found to be more suitable as a cholesteric material for display elements.

The temperature of the cholesteric liquid crystal composition cells of Examples 2 to 5 was changed from 0°C to 50°C, and the color change was visually observed. There was no change in the cells into which the compositions of Examples 2 to 5 were injected.

Furthermore, the compositions of Examples 2 to 5 maintained the liquid crystal phase even after 240 hours had passed, demonstrating excellent storage stability.

Claims (11)

A cholesteric liquid crystal composition having positive dielectric anisotropy, comprising a dielectrically positive first component, a dielectrically neutral second component, and a third component containing at least two optically active substances having temperature dependencies of chiral pitch length different from each other, comprising one or more compounds represented by general formula (1-1) as the first component, one or more compounds represented by general formula (1-2) as the first component, and one or more compounds represented by general formula (2-1) as the second component.

(R ¹ and R ² each independently represent an alkyl group having 1 to 7 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, or an alkenyl group having 2 to 7 carbon atoms; ring A represents a 1,4-cyclohexylene group or a 1,4-phenylene group; and Y ¹ to Y ⁵ each independently represent a hydrogen atom or a fluorine atom.
R ³ and R ⁴ each independently represent an alkenyl group having 2 to 7 carbon atoms or an alkenyloxy group; Y ⁶ to Y ¹¹ each independently represent a hydrogen atom, a fluorine atom or a methyl group; Z ¹ represents a single bond, -COO- or -CH ₂ CH ₂ -; and a, b and c each independently represent 0 or 1. 2. The cholesteric liquid crystal composition according to claim 1, further comprising, as a second component, one or more compounds represented by general formula (2-2):

( ^R5 and ^R6 each independently represent an alkyl group having 1 to 7 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, or an alkenyl group having 2 to 7 carbon atoms; rings B and C each independently represent a 1,4-cyclohexylene group or a 1,4-phenylene group in which a hydrogen atom may be substituted with a fluorine atom; ^Z2 represents a single bond, -COO-, _-CH2CH2- , -CH= _CH- , -FC=CF-, or -C=N-N=C-; d represents 1, 2, or 3, but when a plurality of rings B and ^Z2 are present, they may be the same or different.) 3. The cholesteric liquid crystal composition according to claim 1, further comprising, as the first component, one or more compounds represented by general formula (1-3):

(R ⁷ represents an alkyl group having 1 to 7 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, or an alkenyl group having 2 to 7 carbon atoms; Y ¹² to Y ²³ each independently represent a hydrogen atom or a fluorine atom; X ¹ represents a fluorine atom, a chlorine atom, -CN, -NCS, -CF ₃ , or -OCF ₃ ; Z ³ and Z ⁴ each independently represent a single bond, -CH ₂ CH ₂ -, -COO-, -OCO-, -CH ₂ O-, -OCH ₂ -, -CF ₂ O-, -OCF ₂ -, or -C≡C-.) The cholesteric liquid crystal composition according to any one of claims 1 to 3, comprising one or more compounds represented by general formula (1-1) below:

( ^R1 has the same meaning as ^R1 in claim 1.) The cholesteric liquid crystal composition according to any one of claims 1 to 4, comprising, as the compound represented by general formula (1-2), one or more compounds selected from the group of compounds represented by general formulas (1-2-a) and (1-2-b):

( ^R2 has the same meaning as ^R2 in claim 1.) 6. The cholesteric liquid crystal composition according to claim 1, comprising one or more compounds selected from the compounds represented by formula (2-3):

(R ⁷ and R ⁸ each independently represent an alkyl group having 1 to 7 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, or an alkenyl group or alkenyloxy group having 2 to 7 carbon atoms; ring A represents a 1,4-cyclohexylene group or a 1,4-phenylene group in which a hydrogen atom may be substituted with a fluorine atom or a methyl group; Y ²⁴ to Y ²⁹ each independently represent a hydrogen atom, a fluorine atom, or a methyl group; Z ¹ represents a single bond, -COO-, or -CH ₂ CH ₂ -; and c represents 0 or 1, except for the compound represented by general formula (2-1) in general formula (2-3).) 7. The cholesteric liquid crystal composition according to claim 1, further comprising, as a first component, one or more compounds selected from the group consisting of compounds represented by formula (1-4):

(R ⁹ represents an alkyl group having 1 to 7 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, or an alkenyl group having 2 to 7 carbon atoms; X ² represents a fluorine atom, a chlorine atom, -CN, -NCS, -CF ₃ , or -OCF ₃ ; rings B and C each independently represent a 1,4-cyclohexylene group or a 1,4-phenylene group in which a hydrogen atom may be substituted with a fluorine atom; Z ⁵ represents a single bond or a single bond, -COO-, -CH ₂ CH ₂ -, -CH=CH-, -FC=CF-, or -C=N-N=C-; d represents 1, 2, or 3, and when a plurality of rings B and Z ² are present, they may be the same or different, but in general formula (1-4), the compounds represented by general formulas (1-1) and (1-3) are excluded.) The cholesteric liquid crystal composition according to any one of claims 1 to 7, which contains, as a third component, one or more chiral compounds whose chiral pitch length has a positive temperature dependency, and one or more chiral compounds whose chiral pitch length has a negative temperature dependency. 9. The cholesteric liquid crystal composition according to claim 8, further comprising, as a third component, one or more compounds represented by general formula (3):

(R ¹¹ and R ¹² each independently represent an alkyl group having 1 to 7 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, or an alkenyl group having 2 to 7 carbon atoms; rings D, E, F, and G each independently represent a 1,4-cyclohexylene group or a 1,4-phenylene group; Z ⁶ and Z ⁷ each independently represent a single bond or -COO-; and e and f each independently represent 0, 1, or 2.) The cholesteric liquid crystal composition according to any one of claims 1 to 9, in which the temperature change in chiral pitch length in the range of 0 to 50°C is -1 nm/°C or more and +1 nm/°C or less. A liquid crystal display device using the cholesteric liquid crystal composition according to any one of claims 1 to 10.