DE2802588A1 - LIQUID CRYSTAL MIXTURE - Google Patents

Description

The invention relates to a liquid crystal (LC) display liquid crystal mixture suitable with twisted nematic phase.

LC displays with twisted nematic phase (so-called Twisted Nematic Displays or nematic rotary cells) belong to the state of the art (see M. Schadt and W. HeIfrieh, Applied Physics Letters 18/1971/127) and have been used for a number of years on a large scale for digital displays, e.g. B. in clocks, small computers and the like.

The dielectric, the "liquid crystal", arranged between the two electrodes of a conventional display cell of this type,

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is generally a mixture of several liquid crystalline compounds (LC compounds), i. H. Fabrics that are used in solid / liquid transition form a liquid phase in which orient the molecules, d. H. are available in an orderly manner. This order leads to the fact that a liquid crystalline phase, the "mesophase", shows electrical and optical anisotropy phenomena.

LC displays with a twisted nematic phase require liquid crystals with a nematic orientation of the molecules and with a positive DK anisotropy in the sense that the dielectric constant (DK) of the liquid crystal parallel to the molecular axis {£ ") is greater than the dielectric constant perpendicular to the molecular axis (£ _A ). These dielectric constants are z. B. measured according to the method described in Z. Naturforschung 29a (1974) 905 and the size of the difference Δ £ = € "-6 _x is the measure of the size of the positive DK anisotropy.

Furthermore, it is for more practical reasons, namely the functionality of a wristwatch, for example used LC display with nematic rotary cell, important that the nematic anisotropic state of order of the liquid crystal is maintained under the ambient conditions normally to be expected, d. H. at temperatures in the range from zero ° C or less to 65 ° C or more, and the mesophase a corresponding width of the temperature range between the crystalline / nematic-liquid-crystalline transition temperature K / N on the one hand and the nematic-liquid-crystalline / isotropic-liquid transformation temperature N / I, d. H. the so-called Clearing point, on the other hand.

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Finally, the liquid crystal or the LC mixture should no particularly high viscosity in the anisotropic liquid range and cause neither chemical nor undesired physical changes. Regarding the latter criterion In addition to the chemical stability of the components, this also includes the physical characteristics of the mixing system under the operating conditions of the cell, including the behavior of the LC mixture in the form of a thin layer of approx. 10 micrometers thick, which should normally be practically colorless.

These properties can be influenced by the selection and concentration of the components of the LC mixture, however many of the previously known main components or additives that have one of the parameters mentioned, e.g. B. the width of the mesophase, have an adverse effect on another parameter, e.g. B. the positive DK anisotropy or / and the viscosity and / or the chemical stability.

In practice, it is also important that the complexity increases with the number of components in the mixture the mixture on the one hand to practically irreversible changes during use, z. B. Crystallization of Components with brief hypothermia, and on the other hand to chromatography-like segregation phenomena, in particular in filling the cells.

An ideal solution to these problems has not yet been found and the search is still being carried out for LC mixtures and components which the desired contribution to the effect can be achieved with as few and accordingly active compounds as possible, without these connections affecting other parameters

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gen. Well-known FK Misehungen are z. B. in DE-OS 2'321'632, 2'45O ¹ 088 and 2'502'904 as well as US-PS 3,951,846.

All of the technical LC mixtures suitable for nematic rotary cells for use as displays in wristwatches or other small electrical or electronic devices are made up of so many components that the mixtures tend to separate due to chromatographic effects and the desirable eutectic effects when they are poured into the display cells Compositions are usually poorly defined and can hardly be achieved in practice. For example, one of the best LC mixtures currently available for technical purposes (Hoffmann-La Roche, Switzerland, mixture type RO-TN 403) consists of six components and accordingly has the disadvantages of complex mixtures, albeit the positive dielectric anisotropy for many purposes sufficiently high and the colorless mixture is nematic at least in the temperature range from zero to 65 ° C. In contrast, a technically available LC mixture (product "E7" from British Drug House, England), which consists of only four components, has a clearing point of only 60 ° C, while another commercial LC mixture consists of four components (product ZL I 1132 from Merck, Germany) has too low an anisotropy of the light breakage index (^ n). This value, which is determined analogously to the above £ as the difference between the refractive index T ^ parallel (n _e ) to the molecular axis to the refractive index perpendicular (n_) to the molecular axis, has a practically important function: is this value for a given LC mixture too small, an LC display cell produced with it tends to form colored interference images (Newton ¹ see rings) even with a layer thickness of the nematic phase in the range of 10 micrometers. Since such or even lower dik-

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2Ö02588

ken. are required, these relationships were examined in more detail and explained below Criterion of the required minimum value of Δ η developed «

Surprisingly, it was found that with corresponding Selection of the components of nematic LC mixtures allow ternary systems to form which are free from the above mentioned disadvantages and offer a considerable advance for the production and operation of LC displays.

The LC mixture according to the invention, suitable for LC displays with a twisted nematic phase, has a positive and
preferably highly positive dielectric anisotropy of Δ £ at least about 8jy \ i5 is at least in the temperature range of
Zero to 65 ° C, preferably from -10 to +70 ⁰ G or more,

z. B. up to about 100 ° C, nematic and is chemically stable and colorless. An LC mixture is referred to here as chemically stable which, under operational conditions, does not show any significant changes during the normal period of use
shows the chemical structure of the components. The color solubility criterion includes both the absence of structure-related color in the mixture and the absence of interference color formation in the case of layer thicknesses in the range of 10
Micrometers.

The LC mixture according to the invention is characterized by
a ternary system

(a) a first compound of the formulas (1) or (2)

(D

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in which R is an alkyl group with 1 to 10 carbon atoms in

2
practical straight chain, R is an alkyl or alkoxy group

pe with 1 to 10 carbon atoms in a practically straight chain and m are two or three,
(b) a second compound of the formula (3)

(3)

in which R has the meaning of R and η the meaning of m, and

(c) a third compound of the formulas (1), (2) or (3), which differs from both the first connection (a) and the second connection (b),

Compounds of formula (1) are known per se, e.g. B. off the CH-PS 565 * 234 or DE-AS 2'306'739 or can analogously how to obtain the specifically described compounds (1).

Compounds of the formula (2) can either of the formula (2a)

(2a)

or the formula (2b)

(2 B)

0 α 9V * 0

correspond, in which R and R are those mentioned for R.

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have interpretations. The compounds of the formulas (2a), (2b) are known, e.g. B. from DE-OS 2'356'085, or can analogously how to obtain the compounds specifically described.

The compounds of the formula (3) can either be of the formula (3a)

or the formula (3b)

correspond, in which R ^a and R have the meanings given for R, and are z. B. in Angewandte Chemie, Volume 89, Issue No. 2 (1977), page 103, or can be obtained analogously to the compounds specifically described.

An LC mixture according to the invention must therefore have at least one Contain compound of formula (3), but can also contain two compounds of formula (3). If the FK mix two Contains compounds of the formula (3), at least one of them - or both - is generally one of the formula (3a). LC mixtures which contain a compound of the formula (3b) and optionally one of the formula (3a) represent a preferred embodiment of the invention. The LC mixture usually contains at least no more than about 25 mol% of compound (3) when it is one of the formula (3b). It contains one or two compounds of the formula (3a) and none

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Compound of the formula (3b), so about 35 to 65 mol% a compound (3a) or up to about 95 mol% of two different Compounds of formula (3a) be present.

According to a preferred embodiment, mixtures according to the invention contain either a compound of the formulas (1) and (2) or

10 two compounds of formula (2). Compounds of the formula

(1) can generally in proportions of about zero to 30 mol%, preferably 15 to 25 mole percent, while compounds of the formula (2), subject to the criteria according to the invention with regard to the ternary system, zero to 85 mol% of

15 represent mixture, the proportion of compounds of the

Formula (2a) preferably between 22 and 85 mol%, that of compounds of the formula (2b) preferably between 8 and 25 mole percent.

Some general examples of the preferred range values of the component proportions (in mol%) of LC mixtures according to the invention are compiled in Table I below. Specific examples are given below.

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TABLE I.

General examples of proportion ranges (mol%)
of the components according to the invention LC mixtures

CC O CO CO NJ σ>

cn OI to

A. B. - C. 15-18 - D. - E. F. 50-78 G - 90-92 Formula 1) 0-30 15-30 - 18-24 15-18 - 14-17 - 37-61 - 8-10 (49/54) ^ -
(36 / 43Γ Formula (2) 0-85 - 70-85 64-66 83-86 48-57 22-50 13-17 8-10 Formula (2a) 0-85 59-65 64-66 (64/75) * +
(11 / 22Γ 39-55 22-50 Formula (2b) 0-25 11-20 - 0-12 0-12 - Formula (3) 0-92 14-17 43-52 Formula (3a) 0-92 30-52 Formula (3b) 0-25 0-13

I:

Ul ¹ I.

Bern .:)) Lower and upper limit of a compound mixed with another
Compound of the same formula

CX) CD

OI OO OD

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Additional criteria for the selection of components or proportions within or outside the specified areas result from the following information on the specific effect of the components.

The compounds (1) have an advantageous, i. H. high Δ £ value but a relatively high * _

Viscosity and relatively low clearing points.

The compounds (2a) have an average ^ S value, a relatively low clearing point and an advantageously low viscosity. "

The compounds (2b) advantageously have high clearing points but relatively low Δί values and are viscous.

The compounds (3) · have relatively low ΔG values, where the compounds (3a) have an advantageously low viscosity but relatively low clearing points, whereas the compounds (3b) show advantageous high clearing points and a medium viscosity.

Since the minimum width of the liquid-crystalline range up to 65 ^f is zero, and the ^ E value is preferably in the high positive loading ^(rich are of at least 8 and is in particular approximately be 15, can be inventive LC mixtures based on these general criteria together with relatively simple Try to optimize it for a given purpose without difficulty.

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The above-mentioned criterion of the value of Λ η can also be used here. It has been found that if the product of the Λ η value of the LC mixture and the layer thickness in micrometers has a value of at least 2, no interference colors (Newton's rings) occur in the layer thicknesses that are practically in question and that the inventive LC mixtures generally have such a minimum value. For a layer thickness of the LC mixtures according to the invention of, for example, 10 micrometers in a customary nematic rotating cell, the Δη value of the mixture is therefore at least 0.2 in order to rule out the formation of interference colors.

It should be emphasized that this advantage is not lost if the LC mixture is a system of the type mentioned above and additionally contains a fourth compound which corresponds to one of the formulas (1), (2) or (3) and is different from the three different connections. If the minimum

o * anisotropy range from zero to 65 C and preferably also a highly positive ^ ζ value is given - which can be achieved without difficulty using the above criteria, one also obtains an LC mixture that is still very advantageous from the prior art differs.

For the preparation of the LC mixtures according to the invention described in the following examples, the in compounds characterized in Table II below are used. The components of the mixtures can be in any Mixing in the order and according to conventional methods and in the conventional manner for LC mixtures Cells are filled. The proportions of the components are all based on mol%; H. the percentage Molar fractions of a given mixture must be

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Add 100, which latter sum is then one mole of the total mixture is equivalent to.

TABLE II

Compounds of formula (1)

C-O-V V-CN

(D

Meaning of R: ~ ^C 4 ^H g ~ ^C 5 ^H n " ^C 6 ^H 13"" ^C 7 ^H 15 ~ ^C 8 ^H 17 Compound number: 101 102 103 104 105

Compounds of the formula (2a)

CN

(2a)

meaning
from R ^a :

Connection number:

-CH ₁ . -CH ₁ _ -CH ₁₁ . -OC.H. "OC-H ₁₁

D JLJ. O XJ / ID j / D XX

-OC ₇ H ₁₅

202 203 204 205 207 208 209

Compounds of formula (2b)

(2 B)

.2 B

Meaning of R
Connection number: 211

- ^C 5 ^H 11

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IT TABLE (continued)

Compounds of formula (3a)

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.3a:

Meaning of R connection number: 301

(3a)

" ^C 3 ^H 7" ^C 4 ^H 9 " ^C 5 ^H 11" ^C 6 ^H 13

302

303

305

Compounds of formula (3b)

-3b

- ^C 5 ^H 11

Meaning of R connection number: 311

(3b)

10 Examples 1-13

Ternary LC mixtures according to the invention were obtained by mixing compounds of the formulas (1) and (3b) given in Table II as the first or second compound and a compound of the formulas (2a) or (3a) as the third compound in the proportions given in Table III (in mol%). The clearing points of the mixtures (N / I) are in ⁰ C.
also given in Table III. All mixtures of Examples 1-13
Layers 1Ό micrometers thick were not frozen even after seven days of storage at -20 ° C.

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All of these mixtures were found to be liquid crystal when used (Layer thickness 1 ° micrometer) in a conventional Display with twisted nematic phase as extremely useful.

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TABLE III

formula 101 102 (D 105 (2a) (3a) 59.4 60.8 60.2 60.8 (3b) FK / FI
(° C) Connecting
application no. 103 104 202 301 303 60.1 311 example
No. 21.2 59.7 75 1 20.3
23.0 61.4 17.4 73
77 to
σ 2
3 23.5 64.5 60.1 15.2
16.8 84 co
co 4th 17.1 66 OT 5 18.5 66.0 15.5 76 CD 6th 22.0 17.1 82
68 553 7th
8th 22.5
19.0 65.6 17.3
15.4 77 9 22.5 60.5 17.0 84 10 23.0 18.7 17.2 67 11 22.1 65.8 15.5 77 12th 22.6 17.1 83 13th 17.3

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All the mixtures of Examples 1 to 13 are chemically stable, colorless and, as layers 10 micrometers thick between plane-parallel glass panes, show no Newton's rings. The refractive index anisotropy Δη is at least ° j2. The positive dielectric anisotropy (Δζ) of each of the mixtures rfar greater than 8.

Examples 14-17

LC mixtures according to the invention were each made up of two compounds of formula (2a) and a compound of formula (3b). Components (Table II), proportions and clearing points the LC mixtures obtained are listed in Table IV .

TABLE IV

Connect
dung the
formula 202 (2a) 19.2 208 I. (3b) FK / FI
C ° c> Connect
application no. 205 207 209 311 example
No. 64.7 69 14th 65.4 20.1 15.2 70 15th 69.2 14.5 15.4 71 16 67.3 16.3 71 17th 16.8 15.9

The LC mixtures of Examples 14-17 otherwise have similar properties to those of Examples 1-13.

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Example 18

By mixing 71.8 mol% of compound no. 202 (formula 2a, R ^2a = n-pentyl), 11.2 mol% of compound no. 211 (formula 2b, R = n-pentyl) and 17.0 mol % of compound no. 311 (formula 3b, R = n-pentyl) was a ternary LC mixture according to the invention with a clearing point N / I of 99.degree

and a Δη greater than ° j2. the This low-viscosity, colorless and chemically stable LC mixture showed a 10 micrometer thick layer between two flat

rallelen cell plates no Newtonian rings and did not solidify even after seven days at -20 ⁰ C "

This mixture proved itself in use

as liquid crystal (layer thickness 10 micrometers) in a standard Display cell with twisted nematic phase as

15 extremely useful.

Examples 19 and 20

LC mixtures according to the invention were each formed from

(19) 55.2 mole% Compound No. 202, 31.9 mole% Compound No. 305 and

20 12.9 mole percent Compound No. 311

respectively.

(20) 74.5 mole% Compound No. 203, 10.1 mole% Compound No. 211 and 15.4 mole percent Compound No. 311.

The clearing points were 69 ° C (for 19) and 78 ° C (for 20). Otherwise, the properties of the LC mixtures were similar to those of the LC mixture of Example 18.

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Examples. 21-26

There were LC mixed breeds according to the invention from the following Table V prepared components in the indicated proportions. The temperatures of the N / I conversion (Clearing point) are also given in Table V. Otherwise, the properties of the LC mixtures were similar to those of the previous examples.

TABLE V

10 For
mel (2a) (2 B) (3a) 43.9 52.0 36.3 48.7 41.5 (3b) FK / FI
(C) Connect
application no. 204 211 301 302 303 305 311 example
No. 68 15th 21 39.6 9.7 50.7 70 22nd 45.5 10.6 67 23 34.7 13.3 71 24 47.2 16.5 73 25th 37.3 14.0 76 20th 26th 43.0 15.5

Examples 27-30

With these LC mixtures according to the invention from the in table VT specified components or proportions with the clarification points also mentioned in Table VI were each relatively low.

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ge proportions of compound (2a) with alkoxy groups used as R ^a in a mixture with the compounds (3a) and (3b). The properties of the LC mixtures obtained and their usability in nematic rotating cells are similar to those of the preceding examples.

TABLE VI

formula 205 (2a) 207 301 (3a) 303 (3b) FK / FI
(° c) Connect
application no. 311 example
No. 22.6 60.4 79 27 23.0 59.8 17.0 85 28 22.5 60.5 17.2 80 29 23.0 59.8 17.0 88 30th 17.2

Examples 31-33

LC mixtures according to the invention with similar properties as described in the preceding examples, each with one component of the formula (2b) and two different ones Compounds of the formula (3a) prepared as the second or third component of the ternary system. The components, The proportions and clearing points of these LC mixtures are listed in Table VII.

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TABLE VII

formula (2 B) 301 (3a) 305 FK / FI
(° C) Connect
application no. 211 303 example
No. 49.3 65 31 8.2 54.0 42.5 68 32 9.4 51.4 36.6 74 33 9.8 38.9

As already indicated above, the mixtures described in Examples 1-33 can be modified by adding a further component of the formulas (1), (2) or (3). While you lose the advantage of simplicity of the ternary system with respect to the determination of the eutectic, but still gaining significant advantages over the known quaternary systems, particularly with regard to increased clearing point (65 ° C to about 100 ⁰ C) increased Δί and lack of interference colors in thin layers. The proportion of the fourth component can be kept relatively small.

20 th, z. B. below about 20 mol%.

In addition, numerous modifications based on the above information within the scope of the invention are apparent to the person skilled in the art. This also applies in particular to variations in the chain length in the alkyl parts of the substituents R according to the formein (1), (2) and (3). Alkyl or alkoxy chains with 3 to 8 carbon atoms are preferred for many purposes, but this is the case not critical and the entire range of 1 to 10 carbon atoms is considered operable. It should be noted that the above-mentioned alkyl or alkoxy groups, n-alkyl or n-alkoxy groups are, as generally stretched for LC substances

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; ~ "~~ 28Q2588

Molecular shapes are preferred. A relatively small branch at the free end of a relatively long molecular chain is regarded as practically straight-chain. Finally, it should be noted that the R-substituted rings of the formulas (3), (3a) and (3b) are cyclohexane rings, which is usually indicated by the
Notation "H" is emphasized in these rings.

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Claims (22)

Claims 1. For liquid crystal displays with twisted nematic Phase-suitable liquid-crystal mixture, which has a positive dielectric anisotropy, at least im Temperature range from zero to 65 C is nematic and chemically stable as well as colorless, characterized in that that the mixture is a ternary system of (a) a first compound of the formulas (1) or (2) R " ■ / Λ ic (D in which R is an alkyl group with 1 to 10 carbon atoms in 2
practically straight chain, R is an alkyl or alkoxy group with 1 to 10 carbon atoms in a practically straight chain and m Two or three means (b) a second compound of the formula (3) (3) in which R is an alkyl group with 1 to 10 carbon atoms in a practically straight chain and η is one or two, and (c) a third compound of formulas (1), (2) or (3), which differs from both the first and the second compound of the mixture differs. 909826/0553 ORlGJNAL INSPECTED BBC Baden 124/77 802588 2. LC mixture according to claim 1, characterized / that the proportion of compounds of the formula (1) is at most 30 mol%, the proportion of compounds of the formula (2) at most 85 mol% and the proportion of compounds of the formula (3) makes up at most 92 mol% of the ternary system. 3. LC mixture according to claim 1 or 2, characterized in that that the first compound of the formula (1), the second compound of the formula (3b) (3b) and the third compound is one of the formulas (2a) or (3a) (2a) where R, R and R have the meanings given for R and R in each case. 4. LC mixture according to claim 3, characterized in that that the compound of the formula (1) in a proportion of 15 to 30 mol%, the compound of the formula (3b) in one Proportion of 10 to 20 mol% and the third compound forms the remainder of the mixture. 909826/0553 BBC Baden 124/77 5. LC mixture according to claim 4, characterized in that that the third compound is one of the formula (2a). 6. LC mixture according to claim 4, characterized in that the third compound is one of the formula (3a). 7. LC mixture according to claim 1, characterized in that that the first compound is one of the formulas (2a) or (2b) (2a) (2 B) the second compound is one of the formulas (3a) or (3b) (3a) (3b) wherein R ^a , R, R ^a and R have the meanings given for R and R, respectively, and the third compound is a compound of the formulas (2a), (2b), (3a) or which is different from the second and third compounds (3b) is. 8. LC mixture according to claim 7, characterized in that it consists of a total of 83 to 86 mol% of two different Compounds of formula (2) and consists of 14 to 17 mol% of a compound of formula (3b). 909826/055 3 BBC Baden '124/77 9. LC mixture according to claim 8, characterized in that that both compounds of the formula (2) are those of the formula (2a). 10. LC mixture according to claim 9, characterized in that that a compound of the formula (2a) as R ^{a is} an alkyl group and the other compound of the formula (2a) as R carries an alkoxy group. 11. LC mixture according to claim 8, characterized in that the one compound of the formula (2) is one of the Formula (2b) in a proportion of 8 to 12 mol% and the other is that of Formula (2a). 12. LC mixture according to claim 7, characterized in that it consists of about 72 mol% of a compound of the formula (2a), about 17 mol% of a compound of formula (3b) and about 11 mol% of a compound of formula (2b). 13. LC mixture according to claim 7, characterized in that that it consists of about 55 mol% of a compound of the formula (2a), about 32 mol% of a compound of the formula (3a) and about 13 mol% of a compound of formula (3b) consists. 14. LC mixture according to claim 7, characterized in that it consists of about 75 mol% of a compound of the formula (2a), about 15 mol% of a compound of formula (3b) and about 10 mol% of a compound of formula (2b). 15. LC mixture according to claim 7, characterized in that it consists of 39 to 46 mol% of a compound of the formula (2a), 9 to 11 mol% of a compound of the formula (2b) and 43 to 52 mol% of a compound of the formula (3a). 909826/0553 BBC Baden 124/77 16. LC mixture according to claim 7, characterized in that that they consist of 22 to 50% of a compound of the formula (2a), 37 to 61 mol% of a compound of the formula (3a) and 13 to 17 mol% of a compound of formula (3b). 17. LC mixture according to claim 7, characterized in that it consists of 8 to 10 mol% of a compound of the formula (2b), 49 to 54 mol% of a compound of the formula (3a) and 36 to 43 mol% of another compound of the formula (3a). 18. LC mixture according to one of the claims 1-17, characterized characterized in that R and R or R and R, respectively 2 2a Are alkyl groups with 3 to 8 carbon atoms and R or R and R are alkyl or alkoxy groups with 3 to 8 carbon atoms. 19. LC mixture according to one of claims 1-18, characterized in that the three compounds and their proportions are chosen so that the mixture has a positive dielectric anisotropy Δ ^ νοη at least about 8. ■ 20. LC mixture according to one of claims 1-19, characterized in that the three compounds and their proportions are chosen so that the mixture has a refractive index anisotropy Δη of at least about 0.2. 21. Liquid-crystal mixture suitable for liquid-crystal displays with a twisted nematic phase, which has a positive exhibits dielectric anisotropy, nematic at least in the temperature range from zero to 65 C, chemically stable and are colorless and have a Δη of at least 0.2, characterized in that the mixture consists of 909826 / 0E53 BBC Baden 124/77 2802S88 (a) a first compound of the formulas (1) or (2) πι (2) in which R is an alkyl group with 1 to 10 carbon atoms in 2
practically straight chain, R is an alkyl or alkoxy group with 1 to 10 carbon atoms in a practically straight chain and m Two or three means (b) a second compound of the formula (3) (3) in which R is an alkyl group with 1 to 10 carbon atoms in
practically straight chain and η is one dder two, (c) a third compound of the formulas (1), (2) or (3), which is different from both the first and the second compound the mix is different, and (d) a fourth compound of the formulas (1), (2) or (3), which is different from all compounds contained in the mixture (a), (b) and (c) differ. 22. LC mixture according to claim 21, characterized in that the fourth compound is less than 20 mol% of the mixture matters. 903826/0553