JP6006038B2 - Liquid crystal composition - Google Patents

Description

  The present invention relates to a liquid crystal material and a liquid crystal composition for reducing deterioration of basic characteristics due to ultraviolet rays.

  Liquid crystal elements include mobile devices such as mobile phones and PDAs, display devices for office automation equipment such as copiers and personal computer monitors, display devices for home appliances such as liquid crystal televisions, clocks, calculators, measuring instruments, automotive meters, It is used for applications such as cameras, and various performances such as a wide operating temperature range, a low operating voltage, high-speed response, and chemical stability are required.

  In such a liquid crystal element, a material exhibiting a liquid crystal phase is used, but conventionally, there is no compound that satisfies all of the above characteristics alone, and a plurality of liquid crystal compounds and non-liquid crystal compounds are mixed. Thus, a liquid crystal composition satisfying the required performance was obtained. Therefore, it is desired to develop a liquid crystal or non-liquid crystal material excellent in one or more characteristics, not all of the various characteristics.

  Recently, there has been a demand for further faster response of the display. For this purpose, several improvement methods are conceivable. One of them is a low-viscosity liquid crystal composition. That is, if the viscosity of the liquid crystal composition is lowered, the response speed is improved, and display at a practical speed is possible even at a low temperature.

  For this purpose, difluorostilbene compounds have been proposed (see Patent Documents 1 and 2).

  Difluorostilbene has improved light stability compared to stilbene compounds in which fluorine is not substituted at the double bond site. However, as compared with generally used liquid crystal compounds, there is still a problem in light stability, and difluorostilbene compounds have been employed only in situations where some use environments are limited.

  In order to solve such problems, it has been proposed to change the alignment film from aromatic polyimide to aliphatic polyimide (see Patent Document 3).

  According to Patent Document 3, it is described that the structure of polyimide used for the alignment film is greatly related to the photoisomerization of difluorostilbene.

  However, since an aromatic polyimide is often used as an alignment film of a liquid crystal display, the application of Patent Document 3 has been difficult.

  Therefore, a liquid crystal material having low viscosity and high stability to light has been desired.

JP-A-6-329566 JP-A-7-133241 JP 2005-206617 A

  The present invention suppresses photoisomerization by using a compound represented by the formula (a) among difluorostilbene derivatives, and is compatible by containing a specific compound represented by the formula (b-1) and the like. An object of the present invention is to provide a liquid crystal composition in which the above is improved. Another object of the present invention is to provide a liquid crystal electro-optical element using the liquid crystal composition.

The present invention relates to a compound represented by the following formula (a), the following formula (b-1), formula (b-2), formula (b-3), formula (b-4), formula (b-5). ), At least one compound represented by formula (b) selected from the group consisting of formula (b-6) and formula (b-7).
The symbols in the formula have the following meanings.
X ¹ and X ² : independently of each other, a hydrogen atom, an alkyl or alkenyl group having 1 to 10 carbon atoms, or an electron withdrawing group.
However, the electron-withdrawing group has a Hammett's substituent constant para-effect greater than or equal to a fluorine atom.
L ¹ , L ² , L ⁷ and L ⁸ : independently of each other, a hydrogen atom, a methyl group, a fluorine atom or a chlorine atom.
L ³ , L ⁴ , L ⁵ and L ⁶ : hydrogen atom.
m and n: both are 0.
In the compound represented by the formula (a), a sum ρ1 of Hammett's substituent constants of L ¹ , L ² , L ³ , L ⁴ and X ¹ is obtained, and further, L ⁵ , L ⁶ , L ⁷ , L ⁸ and When the sum ρ2 of Hammett's substituent constants of X ² is obtained, the absolute value of the difference between ρ1 and ρ2 is 0.2 or less,
However, Formula (a) satisfies the following conditions 1 and 2.
Condition 1: X ¹ is an electron withdrawing group, or,, L ^1, and L ² of at least one of a fluorine atom or a chlorine atom.
Condition 2: At least one is a fluorine atom or a chlorine atom X ² is an electron withdrawing group, or,, L ^7, and L ^8.

The symbols in the formula have the following meanings.
R ¹ and R ² : each independently an alkyl group having 1 to 10 carbon atoms or an alkenyl group.
R ³ and R ⁴ : each independently an alkyl group having 1 to 10 carbon atoms, an alkenyl group, or an alkoxy group.

Compounds represented by the before following formula (a) are those also preferred X ¹ and X ² is an electron-attracting group.
Further, the compound represented by the formula (a) ^{is, L 1 = L 8, L} 2 = L 7, L 3 = L 6, L 4 = L 5, it shall be preferably one One X ¹ = X ^2.
In the compound represented by the formula (a), the electron withdrawing group is a fluorine atom, a chlorine atom, or a group represented by —OCF ₂ R (where R is a hydrogen atom, a fluorine atom, a carbon number of 1 to 5). An alkyl group or an alkenyl group having 2 to 5 carbon atoms.) Or a cyano group is also preferable.

  The liquid crystal composition contains 3 to 40% by mass of the compound represented by the formula (a), the formula (b-1), the formula (b-2), the formula (b-3), and the formula (b- 4) containing at least one compound represented by formula (b) selected from the group consisting of formula (b-5), formula (b-6) and formula (b-7) in an amount of 3 to 40% by mass. Those are also preferred.

  The present invention also provides a liquid crystal electro-optical element formed by sealing any one of the above liquid crystal compositions between two substrates provided with electrodes.

  The liquid crystal composition of the present invention can suppress photoisomerization by using the compound represented by the formula (a), and further contains a specific compound represented by the formula (b-1) or the like. , Compatibility, particularly compatibility at low temperatures can be improved. For this reason, the liquid crystal composition of the present invention has a very low viscosity, good light resistance, and good low-temperature storage stability.

The present invention will be described in more detail below.
In the present specification, the compound represented by the formula (a) is referred to as a compound (a), and the compounds represented by other formulas are also described in the same manner.
In this specification, the formula (b-1), the formula (b-2), the formula (b-3), the formula (b-4), the formula (b-5), the formula (b-6), and the formula (b The respective compounds represented by -7) are collectively referred to as a compound (b).
In this specification, a liquid crystal compound means a compound that exhibits a liquid crystal phase and a compound that does not exhibit a liquid crystal phase but is useful as a constituent of a liquid crystal composition.

In the compound (a), X ¹ and X ² are as described above.
Examples of the alkyl group include methyl group, ethyl group, propyl group, isopropyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group and the like.
Examples of the alkenyl group include a vinyl group, 1-propenyl group, 1-butenyl group, 1-pentenyl group, 3-butenyl group, and 3-pentenyl group.

In the present invention, the electron-withdrawing group means that the Hammett's substituent constant para-effect has a value greater than or equal to the fluorine atom, as described above.
Specific examples include a halogen atom such as a fluorine atom or a chlorine atom, a cyano group, or a group represented by —OCF ₂ R. (R is a hydrogen atom, a fluorine atom, an alkyl group having 1 to 5 carbon atoms, or an alkenyl group having 2 to 5 carbon atoms.)

X ¹ and X ² are preferably electron withdrawing groups because of good light resistance, and among them, a group represented by a fluorine atom, a chlorine atom, or —OCF ₂ R (R is a hydrogen atom, a fluorine atom) , An alkyl group having 1 to 5 carbon atoms, or an alkenyl group having 2 to 5 carbon atoms.) Or a cyano group. Among them, a fluorine atom, a chlorine atom, —OCF ₃ or —OCHF ₂ is particularly preferable because of low viscosity and easy synthesis.

In the compound (a), L ¹ , L ² , L ³ , L ⁴ , L ⁵ , L ⁶ , L ⁷ , L ⁸ , L ⁹ , L ¹⁰ , L ¹¹ , L ¹² , L ¹³ , L ¹⁴ , L ¹⁵ And L ¹⁶ are as described above.
Note that “existing L ¹ , L ² , L ³ , L ⁴ , L ⁹ , L ¹⁰ , L ¹¹ , L ¹² ” means that when m is 0, “L ¹ , L ² , L ³ , L ⁴ ”means that when m is 1, it means“ L ¹ , L ² , L ³ , L ⁴ , L ⁹ , L ¹⁰ , L ¹¹ , L ¹² ”.
Similarly, “existing L ⁵ , L ⁶ , L ⁷ , L ⁸ , L ¹³ , L ¹⁴ , L ¹⁵ , L ¹⁶ ” means “L ⁵ , L ⁶ , L ⁷ ” when n is 0. , L ⁸ ”and when n is 1, it means“ L ⁵ , L ⁶ , L ⁷ , L ⁸ , L ¹³ , L ¹⁴ , L ¹⁵ , L ¹⁶ ”.

L ¹ , L ² , L ³ , L ⁴ , L ⁵ , L ⁶ , L ⁷ , L ⁸ , L ⁹ , L ¹⁰ , L ¹¹ , L ¹² , L ¹³ , L ¹⁴ , L ¹⁵ and L ¹⁶ are In view of high light resistance and low viscosity, a hydrogen atom or a fluorine atom is preferred.
L ³ , L ⁴ , L ⁵ and L ⁶ are particularly preferably hydrogen atoms because of their low viscosity.

  In the compound (a), m and n are as described above. As m and n, those in which both m and n are 0 or those in which both are 1 are preferable, and those in which both m and n are 0 are particularly preferable because of low viscosity.

The compound (a) satisfies the above conditions 1 and 2. This means that both ends of —CF═CF— of the compound (a) are electron withdrawing groups.
In addition, the compound (a) is “existing L ¹ , L ² , L ³ , L ⁴ , L ⁹ , L ¹⁰ , L ¹¹ , L ¹² and X ¹ ”, that is, Hammett on the left side of —CF═CF—. The sum ρ1 of substituent constants and “existing L ⁵ , L ⁶ , L ⁷ , L ⁸ , L ¹³ , L ¹⁴ , L ¹⁵ , L ¹⁶ and X ² ”, that is, Hammett on the right side of —CF═CF— The absolute value of the difference of the sum of substituent constants ρ2 is preferably 0.2 or less, more preferably 0.15 or less, and particularly preferably 0.1 or less. This is because when the difference between the sums of Hammett's substituent constants on the left and right of -CF = CF- is small, light resistance is improved.
Among them, L ¹ = L ⁸ , L ² = L ⁷ , L ³ = L ⁶ , L ⁴ = L ⁵ , L ⁹ = L ¹⁶ , L ¹⁰ = L ¹⁵ , L ¹¹ = L ¹⁴ , L ¹² = A structure in which L ¹³ and X ¹ = X ² have a point-symmetric structure with respect to —CF═CF— is preferable from the viewpoint of light resistance since the difference in the sum is zero.

In the compound (b), R ¹ , R ² , R ³ and R ⁴ are as described above.
Examples of the alkyl group and alkenyl group are the same as those exemplified for the compound (a).
Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentoxy group, a heptyloxy group, and an octyloxy group.

R ¹ and R ² are preferably an alkyl group having 1 to 5 carbon atoms or an alkenyl group having 2 to 5 carbon atoms.
R ³ and R ⁴ are preferably an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an alkoxy group having 1 to 5 carbon atoms.

  As the compound (b), since the solubility of the compound (a) is improved and the compatibility of the composition is improved, the compound (b-1), the compound (b-2), and the compound (b-3) Compound (b-5) and Compound (b-6) are preferable, and Compound (b-1) is particularly preferable.

Compound (a) can be synthesized with reference to known documents such as Patent Document 1. In addition, for example, when the compound (a) is symmetrical, more specifically, m and n are both 0, L ^{1 to} L ⁸ are all hydrogen atoms, and X ¹ and X ^When both compounds are fluorine atoms, the compound (1) is reacted with a metal reagent such as butyllithium to give a compound (2) which is a lithiated compound, and this is combined with tetrafluoroethylene as follows. It can also be synthesized by reacting.
However, Ph in the formula is a 1,4-phenylene group.

  The mechanism of reversible geometric isomerization reaction by light stimulation of difluorostilbene is shown below. Assuming that there is a reversible photoisomerization reaction between trans-difluorostilbene, which is one of the geometric isomers, and cis-difluorostilbene, which is the other geometric isomer, by photosensitization from the polyimide alignment film. Yes. That is, each of the difluorostilbene geometric isomers can be converted into the triplet state by receiving triplet energy from the polyimide excited triplet state generated through intersystem crossing when the polyimide is excited by external light stimulation. Excited. Since the triplet state usually has a longer lifetime than the singlet state, it is considered that each of the trans and cis difluorostilbenes in the excited triplet state shifts to a metastable twisted structure. Thereafter, the ground state is changed to the ground state while returning to the ground state trans-form or cis-form difluorostilbene.

  Apart from the above-mentioned concept, difluorostilbene may be photoexcited by a light stimulus that has entered from the outside. Also in this case, each of the trans and cis difluorostilbenes absorbs light and enters an excited singlet state, then crosses into the triplet state, and then difluorostilbene has a metastable twisted structure. The excited triplet state is considered. After that, the ground state is changed to the ground state while returning to the ground state trans-form or cis-form difluorostilbene.

  As described above, the difluorostilbene derivative undergoes a light stimulus intrinsically or extrinsically, and a reversible photoisomerization reaction occurs between the trans form and the cis form.

  Since difluorostilbene derivatives have different liquid crystal properties in the trans form and cis form, if a reversible photoisomerization reaction between the trans form and the cis form by light stimulation proceeds, the liquid crystal composition will not be in an equilibrium state. Since the physical property value is changed, it is necessary to suppress the photoisomerization reaction as much as possible.

  There are several methods for suppressing the reversible photoisomerization reaction of the difluorostilbene derivative under the above-mentioned environment. However, it is most effective to find a derivative structure in which photoisomerization hardly occurs.

  In the present invention, the light stability can be improved by using the compound (a) and the compound (b) in combination as a liquid crystal composition. Furthermore, compatibility at low temperatures is improved, and storage stability at low temperatures can be improved. In this case, the stability against ultraviolet light can be more effectively improved by using an ultraviolet cut filter, a triplet quencher, or a photoisomerization inhibitor in combination.

Examples of the triplet quencher include 1,3,5-triene or a derivative thereof and a compound represented by the following formula (c).

Examples of the photoisomerization inhibitor include pyrene and derivatives thereof, and examples thereof include compounds represented by the following formula (d).
R ^d1 , R ^d2 and R ^d3 in the formula are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

  The liquid crystal composition of the present invention is obtained by mixing the compound (a) and the compound (b) with another liquid crystal compound or a non-liquid crystal compound (collectively referred to as “other compounds”). Configure.

The liquid crystal composition of the present invention can contain one or more compounds (a), and can contain one or more compounds (b). In the present specification, the content of the compound (a) in the composition is the content as the compound (a). Therefore, the term “total” is used particularly when two or more compounds (a) are contained. Even if not, it is the total amount of two or more compounds (a), and the same applies to compound (b).
The content of the compound (a) in the liquid crystal composition of the present invention can be appropriately changed depending on the use, purpose of use, the type of other compounds, etc., but is preferably 3 to 40% by mass with respect to the total amount of the liquid crystal composition. 3-30 mass% is preferable. Moreover, 3-40 mass% is preferable and, as for content of a compound (b), 3-30 mass% is especially preferable.

  Other compounds used in combination with compound (a) and compound (b) include components that adjust the refractive index anisotropy value, components that lower viscosity, components that exhibit liquid crystallinity at low temperatures, and improved dielectric anisotropy Components that impart cholesteric properties, components that exhibit dichroism, components that impart electrical conductivity, and other various additives. These are appropriately selected depending on the application, required performance, and the like. Usually, those composed of a liquid crystal compound, a main component having a similar structure to the liquid crystal compound, and an additive component added as necessary are preferable.

In the liquid crystal composition of the present invention, examples of the other compound include those represented by the following formulae. In the following formulae, R ⁵ and R ⁶ represent a group such as an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, a halogen atom or a cyano group. R ⁵ and R ⁶ may be the same or different.
In the following formulas, -Cy- represents a trans-1,4-cyclohexylene group, -Ph- represents a 1,4-phenylene group, and -PhFF- represents a difluorophenylene group.

R ⁵ -Cy-PhFF-CN
R ⁵ —Ph—C≡C—Ph—R ⁶
R ⁵ -Cy-COO-Ph-R ⁶
R ⁵ -Cy-COO-PhFF-CN
R ⁵ -Ph-COO-Ph-R ⁶
R ⁵ -Ph-COO-PhFF-CN
R ⁵ —Cy—CH═CH—Ph—R ⁶
R ⁵ —Ph—CH═CH—Ph—R ⁶
R ⁵ —Cy—CF═CF—Ph—R ⁶
R ⁵ —Cy—CF═CF—Cy—R ^{6
R 5 -Cy-Ph-CF =} CF-Cy-R 6

R ⁵ —Ph—Cy—CF═CF—Cy—R ⁶
R ⁵ —Cy—Cy—CF═CF—Ph—R ⁶
R ⁵ —Cy—CH ₂ CH ₂ —Ph—R ^{6
_{R 5 -Cy-Ph-CH 2}} CH 2 -Ph-R 6
_{^{R 5 -Cy-Ph-CH 2}} CH 2 -Cy-R 6
_{^{R 5 -Cy-Cy-CH 2}} CH 2 -Ph-R 6
_{^{R 5 -Ph-CH 2 CH 2}} -Ph-R 6
_{^{R 5 -Ph-Ph-CH 2}} CH 2 -Ph-R 6
_{^{R 5 -Ph-Ph-CH 2}} CH 2 -Cy-R 6
R ⁵ -Cy-Ph-PhFF-CN
R ⁵ -Cy-Ph-C≡C-Ph-R ⁶
R ⁵ -Cy-Ph-C≡C-PhFF-CN
R ⁵ -Cy-Ph-C≡C-Ph-Cy-R ⁶
R ⁵ —Cy—CH ₂ CH ₂ —Ph—C≡C—Ph—R ⁶

R ⁵ —Cy—CH ₂ CH ₂ —Ph—C≡C—Ph—Cy—R ⁶
R ⁵ -Cy-Ph-Ph-Cy-R ⁶
R ⁵ -Ph-Ph-Ph-R ⁶
R ⁵ -Ph-Ph-C≡C-Ph-R ⁶
R ⁵ —Ph—CH ₂ CH ₂ —Ph—C≡C—Ph—R ⁶
R ⁵ —Ph—CH ₂ CH ₂ —Ph—C≡C—Ph—Cy—R ^{6
R 5 -Cy-COO-Ph-} Ph-R 6
R ⁵ -Cy-COO-Ph-PhFF-CN
R ⁵ -Cy-Ph-COO-Ph-R ^{6
R 5 -Cy-Ph-COO-} PhFF-CN
^{R 5 -Cy-COO-Ph-} COO-Ph-R 6
^{R 5 -Cy-COO-Ph-} COO-PhFF-CN
^{R 5 -Ph-COO-Ph-} COO-Ph-R 6
^{R 5 -Ph-COO-Ph-} OCO-Ph-R 6
R ⁵ —Ph—CF ₂ O—Ph—R ⁶

_{^{R 5 -Cy-CF 2 O-}} Ph-R 6
R ⁵ —Ph—CF ₂ O—Cy—R ^{6
_{R 5 -Cy-Ph-CF 2}} O-Ph-R 6
_{^{R 5 -Cy-Ph-CF 2}} O-Cy-R 6
_{^{R 5 -Cy-Cy-CF 2}} O-Ph-R 6
_{^{R 5 -Ph-Ph-CF 2}} O-Ph-R 6
_{^{R 5 -Ph-Ph-CF 2}} O-Cy-R 6
_{^{R 5 -Cy-Ph-CF 2}} O-PhFF-R 6
_{^{R 5 -Cy-PhFF-CF 2}} O-PhFF-R 6
R ⁵ -Ph-Ph-CF ₂ O-PhFF-R ^{6
_{R 5 -Ph-PhFF-CF 2}} O-PhFF-R 6
^{_{R 5 -Ph-CF 2 CF 2}} -Ph-R 6

^{_{R 5 -Cy-CF 2 CF 2}} -Ph-R 6
R ⁵ -Cy-CF ₂ CF ₂ -Cy-R ^{6
_{R 5 -Cy-Ph-CF 2}} CF 2 -Ph-R 6
_{^{R 5 -Cy-Ph-CF 2}} CF 2 -Cy-R 6
_{^{R 5 -Cy-Cy-CF 2}} CF 2 -Ph-R 6
_{^{R 5 -Ph-Ph-CF 2}} CF 2 -Ph-R 6
_{^{R 5 -Ph-Ph-CF 2}} CF 2 -Cy-R 6

These compounds are merely representative examples, and a hydrogen atom present in a ring structure or a terminal group in the compound may be substituted with a halogen atom, a cyano group, a methyl group, or the like. In addition, the cyclohexane ring or the benzene ring may be substituted with another 6-membered ring or 5-membered ring, for example, a pyrimidine ring or a dioxane ring. Changed to a divalent linking group such as —CH ₂ O—, —CH═CH—, —N═N—, —CH═N—, —COOCH ₂ —, —OCOCH ₂ — or —COCH ₂ —, etc. It can be selected according to the desired performance.

  Furthermore, the present invention provides a liquid crystal electro-optical element that uses the liquid crystal composition as a constituent material of a liquid crystal layer. In this specification, the liquid crystal electro-optical element is not limited to a display element, but various functional elements that use the electrical or optical characteristics of liquid crystal, for example, a liquid crystal display element, a light control window, an optical shutter, and a polarization It includes elements used for applications such as conversion elements and variable focus lenses. For example, a liquid crystal electro-optical element having an electro-optical element portion formed by sandwiching a liquid crystal layer formed by, for example, injecting the liquid crystal composition of the present invention into a liquid crystal cell between two substrates having electrodes. I will provide a. This liquid crystal electro-optic element is a twisted nematic (TN) method, a super twisted nematic (STN) method, an ECB mode, a VA mode, a guest host method, a dynamic scattering method, a phase change method, a DAP method, a dual frequency drive method, a strong Examples include those driven in various modes such as a dielectric liquid crystal display system.

A typical liquid crystal electro-optic element includes a twisted nematic (TN) type liquid crystal display element. The twisted nematic (TN) type liquid crystal display device, first, plastics, onto a substrate such as glass, of SiO _2, Al ₂ O undercoat layer or a color filter layer, such as ₃ to form optionally, an In ₂ O _A film made of _3- SnO ₂ (ITO), SnO ₂ or the like is formed, and an electrode having a required pattern is formed by photolithography or the like. Next, if necessary, an overcoat layer of polyimide, polyamide, SiO ₂ , Al ₂ O ₃ or the like is formed and oriented. A sealing material is printed on this, it arrange | positions so that an electrode surface may mutually oppose, a periphery is sealed, a sealing material is hardened, and an empty cell is formed.

  Furthermore, the composition of the present invention is injected into an empty cell, and the injection port is sealed with a sealant to form a liquid crystal cell. If necessary, this liquid crystal cell is laminated with a polarizing plate, a color polarizing plate, a light source, a color filter, a transflective plate, a reflecting plate, a light guide plate, an ultraviolet cut filter, etc., printing characters, figures, etc., non-glare processing, etc. Thus, a liquid crystal electro-optical element can be obtained.

  Note that the above description describes the basic configuration and manufacturing method of the liquid crystal electro-optical element, and other configurations can be employed. For example, a substrate using a two-layer electrode, a two-layer liquid crystal cell having a two-layer liquid crystal layer, a substrate using a reflective electrode, an active matrix device using an active matrix substrate having an active element such as a TFT or MIM, etc. Various configurations can be employed.

  Furthermore, the composition of the present invention is a mode other than the TN type, that is, a high twist angle STN type liquid crystal electro-optical element, a guest-host (GH) type liquid crystal electro-optical element using a pleochroic dye, In-plane switching (IPS) type liquid crystal electro-optical element that drives liquid crystal molecules parallel to the substrate by a direction electric field, VA type liquid crystal electro-optical element that aligns liquid crystal molecules vertically with respect to the substrate, ferroelectric liquid crystal electro-optics It can be used in various ways such as an element. Further, it can be used not only in a method of electrically writing but also in a method of writing by heat.

  Hereinafter, the present invention will be described more specifically with reference to examples. The following examples are intended to illustrate the present invention without limiting the present invention.

The liquid crystal clearing point (Tc) was measured under the following conditions.
[Measurement of liquid crystal clearing point (Tc)]
By placing the liquid crystal composition on the hot plate of a melting point measuring apparatus equipped with a polarizing microscope, raising the temperature at 1 ° C./min, observing the phase change, measuring the Tc of the liquid crystal composition, and extrapolating the measured value The extrapolated value of Tc of the compound was calculated.

The light resistance test method is described below.
Liquid crystal composition prepared by mixing Merck's liquid crystal composition ZLI-4792 and compounds (a-1) to (a-6) shown in Table 1 synthesized in the same manner as in a known method at a mass ratio shown in Table 2. The composition was sealed in a glass cell, placed in a xenon weather meter (XT1-15, manufactured by Suga Test Instruments Co., Ltd.) and irradiated with light. The integrated light intensity is measured using an ultraviolet integrated light meter (main body: UIT-250, light receiver: UVD-S365, manufactured by USHIO INC.), And integrated light quantity (J) = illuminance (W / cm ² ) × irradiation time. (Seconds). ΔTc was calculated by measuring the liquid crystal clearing point (Tc) when irradiated with about 32 J as the integrated light quantity. ΔTc was determined from ΔTc = Tc1−Tc0 by measuring Tc0 when not irradiated and Tc1 after irradiation. These results are shown in Table 2.

Moreover, also about the compound (e-1) and (e-2) synthesize | combined by the well-known method, the composition was produced by the method similar to the said method, and the light resistance test was done. These results are shown in Table 2. Table 3 shows the results of calculating Hammett's substituent constant of each compound.

  From this result, compared with the compound (e-1) which does not have an electron withdrawing group, the compound (e-2) and the compound (a) having an electron withdrawing group have lower Tc in the light resistance test. There were few favorable results. In addition, when the absolute value of the difference between the left and right sums of substituent constants is 0.2 or less starting from the double bond of fluoroethylene, the decrease in Tc after the light resistance test may be further reduced. I understood. Furthermore, it has been found that it is more preferable to arrange an electron withdrawing group at the para position.

A liquid crystal composition obtained by adding the compound (a) synthesized in the same manner as a known method to a liquid crystal composition ZLI-4792 manufactured by Merck Ltd. was allowed to stand at −25 ° C. for 72 hours, and then the low-temperature stability of the liquid crystal composition was confirmed. Table 4 shows the results.
In the table, ◯ means a nematic phase, and × means that crystals are precipitated.

  Usually, a liquid crystal composition is mixed with 10 to 20 kinds of compounds, and the effect on the properties of the composition is small unless at least 3% by mass, preferably 5% by mass or more is added. Although it is desired to add as many materials having good characteristics as possible, the compound (a) has a problem in solubility at a low temperature with respect to addition as a simple substance, and there is a problem that compatibility in the liquid crystal composition is low.

Here, 90% by mass of ZLI-4792 was added to 5% by mass of the compound (a-2), and 5% by mass of the compounds (b-11) to (b-62) shown in Table 5 were similarly added. Table 6 shows the results of confirming the low temperature stability after standing at 72 ° C. for 72 hours.

In the table, ◯ means nematic phase.

  From this result, it was found that the low temperature stability of the compound (a-2) was improved by combining with the compound (b) rather than using alone.

The liquid crystal composition of the present invention was able to improve the stability of the compound (a) by light stimulation by disposing electron withdrawing groups on both sides of —CF═CF— of the compound (a). In particular, the sum of Hammett's substituent constants is calculated on both sides of -CF = CF- of compound (a), and the absolute value of the difference between the left and right sums is made 0.2 or less. ) Was able to improve the light stability.
Furthermore, the low temperature stability of the composition was improved by improving the solubility of the compound (a) at a low temperature and improving the compatibility of the composition at a low temperature by combining with the compound (b).
It has been clarified that by using such a compound for a liquid crystal composition, a composition having various performances required for a liquid crystal electro-optical element can be prepared.

Claims (6)

The compound represented by the following formula (a), the following formula (b-1), formula (b-2), formula (b-3), formula (b-4), formula (b-5), formula ( A liquid crystal composition comprising at least one compound represented by formula (b) selected from the group consisting of b-6) and formula (b-7).
The symbols in the formula have the following meanings.
X ¹ and X ² : independently of each other, a hydrogen atom, an alkyl or alkenyl group having 1 to 10 carbon atoms, or an electron withdrawing group.
However, the electron-withdrawing group has a Hammett's substituent constant para-effect greater than or equal to a fluorine atom.
L ¹ , L ² , L ⁷ and L ⁸ : independently of each other, a hydrogen atom, a methyl group, a fluorine atom or a chlorine atom.
L ³ , L ⁴ , L ⁵ and L ⁶ : hydrogen atom.
m and n: both are 0.
In the compound represented by the formula (a), a sum ρ1 of Hammett's substituent constants of L ¹ , L ² , L ³ , L ⁴ and X ¹ is obtained, and further, L ⁵ , L ⁶ , L ⁷ , L ⁸ and When the sum ρ2 of Hammett's substituent constants of X ² is obtained, the absolute value of the difference between ρ1 and ρ2 is 0.2 or less,
However, Formula (a) satisfies the following conditions 1 and 2.
Condition 1: X ¹ is an electron withdrawing group, or,, L ^1, and L ² of at least one of a fluorine atom or a chlorine atom.
Condition 2: At least one is a fluorine atom or a chlorine atom X ² is an electron withdrawing group, or,, L ^7, and L ^8.
The symbols in the formula have the following meanings.
R ¹ and R ² : each independently an alkyl group having 1 to 10 carbon atoms or an alkenyl group.
R ³ and R ⁴ : each independently an alkyl group having 1 to 10 carbon atoms, an alkenyl group, or an alkoxy group. The liquid crystal composition according to claim 1, wherein in the compound represented by the formula (a), X ¹ and X ² are electron withdrawing groups. In the compound represented by the formula (a), is ^{L 1 = L 8, L 2} = L 7, L 3 = L 6, L 4 = L 5, or One X ¹ = X ^2, claim 1 or 2 the liquid crystal composition according to. In the compound represented by the formula (a), the electron-withdrawing group is a fluorine atom, a chlorine atom, or a group represented by —OCF ₂ R (where R is a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 5 carbon atoms). , or an alkenyl group having 2 to 5 carbon atoms.) or a cyano group, a liquid crystal composition according to any one of claims 1-3. 3 to 40% by weight of compounds represented by formula (a), the formula contains 3 to 40 wt% of the compound represented by (b), the liquid crystal composition according to any one of claims 1-4 . Any liquid crystal composition according to item 1, the liquid crystal electro-optical device formed by sealing the two substrates on which electrodes are arranged in claims 1-5.