DE2939782A1 - Anisotropic cpds. with three aromatic rings and polarising side gps. - have high negative dielectric constant anisotropy, useful in liquid crystal compsn. - Google Patents

Abstract

New anisotropic cpds. with 3 aromatic rings and polarising side gps. and a negative dielectric constant (DC) anisotropy, have the formula (I) (where independently, R1 and R2 are H, single bonds, carboxyl or oxycarbonyl gps. but if carboxyl and/or oxycarbonyl gps. are present at the same time, the dipole moments are opposed; X1-X6 are H, halogen, CN or nitro gps. but are not all H). (I) are used in liq. crystal compsns. The contribution of the side gps. to the DC perpendicular to the mol. axis is greater than has been possible previously.

Description

Aromatic compounds with negative

DK anisotropy The invention relates to new anisotropic compounds, which contain three aromatic nuclei and have a negative DK anisotropy, as well as liquid crystal (LC) mixtures containing these anisotropic compounds and used as a dielectric for LC displays. The invention also relates to a process for the preparation of anisotropic trinuclear aromatic diester compounds with negative DK anisotropy.

Most of the anisotropic compounds with negative DK anisotropy known to date for LC mixtures are trinuclear aromatic compounds whose aromatic nuclei are linked to one another by carboxyl groups or single bonds and carry polarizing side groups. This z. B. Mol. Cryst. Liqu. Cryst. 42 (1977) 139, and DE-OS 2'240'864, 2'613'293, 2'835'662 and 2'836'086 have the following structural formulas, the meaning of the arrows being explained below: In the above formulas (20) to (24), the wing groups R are usually alkyl or alkoxy groups; the side groups X are polarizing groups, such as halogen atoms, nitro or nitrile groups, where Y can be hydrogen and / or is the same or similar to X, and A = X when X = H; in all cases the side groups X are intended to give the molecule a negative DK anisotropy.

The DK anisotropy (Ag) is known to be defined as the difference value the dielectric constant (g) parallel (l) and perpendicular (1) to the molecular axis, d. H.

= = £ - 6j It is known that polarizing side groups X lead to an increase in El and it is z. B. from DE-OS 2,240,864 also known that when using more than one side group the dipole moments the side groups should work approximately in the same direction.

For different types of LC display cells, especially those of the applicant in the CH-PA No. 7615/78 described FK displays, the so-called Use inverse guest / host effect, but also for some types of dynamic Scatter cells are required LC mixtures with pronounced negative DK anisotropy; this would require anisotropic compounds with very high negative DC anisotropy values as they are with the previously known bonding structures according to the above formulas (20) to (24) cannot be achieved.

The object of the invention is to provide a new group of trinuclear aromatic Connections with polarizing side groups indicate the connections for which the contribution made by the side groups to the dielectric constant perpendicular to the molecular axis is enlarged beyond what was previously possible.

It has been found that the known compounds (20) to (24) den have the common disadvantage that the bridges between the aromatic rings, i. H. the carboxyl groups (-COO-) or oxycarbonyl groups (-OOC-), through the interrelationships provide disadvantageous polarization contributions to one another or to the side groups. In the above formulas (20) to (24) there are arrows to explain this matter drawn showing the direction of the polarization moments of the bridge members or indicate the components of the polarization moments of the side members.

It has been found that these disadvantages with the inventive Allow compounds of the formula (1) given below to be avoided and that this Advantages with regard to higher negative DK anisotropy values and partly also with regard to offers to simplify the synthesis of the compounds (1).

The novel compounds according to the invention correspond to the formula (1) in which R1 and R2 - hereinafter also referred to as wing groups - are identical or different and are hydrogen atoms, alkyl groups with 1-12 carbon atoms or alkoxy groups with 1-12 carbon atoms, Z and Z - also referred to below as bridge members - Single bonds, carboxyl or oxycarbonyl groups with the proviso (a) are that the dipole moments of simultaneously present carboxyl or. Oxycarbonyl groups are directed towards one another and X1 to X6 are hydrogen atoms, halogen atoms, nitrile groups or nitro groups with the proviso (b) that at least two of the groups x1 to x6 are not hydrogen.

While in the known trinuclear compounds of the formulas (20) to (24) given above, the dipole moments of the carboxyl or oxycarbonyl groups serving as bridging members act in the same direction, ie increase the contribution gu to the DC anisotropy of the 4molecules and thus the value of the difference £ 6 } in the direction of positive values, dipole moments of the bridge members that act in the same direction are excluded in the compounds (1) according to the invention by the provision (a). As a result, in compounds (1) according to the invention with a carboxyl / oxycarbonyl or oxycarbonyl / carboxyl bridge structure, the dipole moment of the side groups present comes into full effect and the corresponding compounds according to the invention of the following formulas (2) and (3) have in comparison to known compounds same number of polarizing side groups higher values of the negative DC anisotropy: The formulas (2) and (3) show that, in the case of compounds according to the invention, all positions of the rings ortho to carbonyl groups are preferably occupied by hydrogen atoms.

The reason for this is that the dipole moments of polarizing Due to the bond angle, side groups each also have one parallel to the molecular axis acting components have a moment in the same direction of an adjacent carbonyl group would reinforce; such a gain would in turn reduce the c component of the DK anisotropy increase and thus reduce the targeted highly negative DK anisotropy value.

Accordingly, the compounds (1) according to the invention which have only one carboxyl or carbonyl group as a bridge member differ, ie the compounds according to the invention of the formulas (4) and (5) not only structurally but also functionally of known compounds.

Finally, the invention also includes compounds of the formula (6) which have comparatively lower viscosities than the mono- or diesters of the formulas (2) to (5). With all compounds according to the invention, but especially with those of the formula (6), it is preferred for a given number and type of polarizing side groups that the components of all polarizing side groups present in the molecule that act in the direction of the molecular axis of the compound compensate each other completely or partially .

This can e.g. B. be achieved by paired polarizing side groups with the same or similar dipole moments when the horizontal components of the side groups are in opposite directions, such. B. in the case of compounds of formula (7) which are fully compensated for both the longitudinal polarizing effect of the bridges and the horizontal components of the lateral polarization.

Alternatively, partial co-compensation of the horizontal components can be used of polarizing side groups by using an unpaired number of Side groups with different start dipole moments can be achieved.

The compounds of the formulas (2) and (3) according to the invention represent a particularly preferred group, which is partly surprising simplified synthesis is required, as explained below.

Compounds of the formula (2) in which X3 and X4 are halogen atoms, nitro groups or in particular nitrile groups are preferred. The same applies to X2 and X5 in formula (3), X and X5 in formula (4), and X4 and X6 in formula (5).

Chlorine and / or bromine atoms are usually preferred as halogen atoms.

As wing groups R1, R2, alkyl or alkoxy groups are each with 1-12 carbon atoms preferred. Identical Flagel groups (alkyl / alkyl or alkoxy / alkoxy), especially if the wing groups are each practically the same Contain carbon atoms.

LC mixtures according to the invention contain a compound as a component (1) e.g. B. in proportions of 1-40% by weight, or several different compounds (1) If desired, also a higher total share. FK mixtures that are available as Component contain at least one compound of the above formulas (2) or (3), are particularly preferred.

The other components can be chosen in a similar way to how this z. B. from the above-mentioned DE-OS is known. Because of their comparatively higher negative DK anisotropy, the compounds according to the invention (1) used in correspondingly lower proportions and / or for the production of LC mixtures can be used with an overall higher negative DK anisotropy.

The compounds (1) according to the invention can in principle according to processes analogous to those used for the production of known trinuclear Aromatics with an analogous ring and bridge sequence are described, optionally under Reversal of the hydroxyl and carboxyl functions in the case of esterification based methods.

The compounds of the formulas (2) and (3) according to the invention are preferably prepared in accordance with the scheme given below by condensation of in each case about one molar equivalent of the difunctional 1,4-dihydroxybenzene compound ( Formula 10) or 1,4-dicarboxylbenzene compound (Formula 11), each with about 2 molar equivalents of the monofunctional carboxybenzene compound (Formula 13) or hydroxybenzene compound corresponding to the terminal rings possibly with subsequent modification of X1, X2 to convert into X5, X6.

In the formulas (10) to (13), R3 denotes the hydrogen atom or preferably, alkyl or alkoxy with 1-12 carbon atoms; L1 to L4 are atoms or groups of atoms, those under the condensation conditions to form connections t1-L3 or L2-L4 are capable.

L1 and L can accordingly, for. B. hydrogen or alkali metal atoms, such as Na or K, while L2 and L3 represent hydroxyl groups or halogen atoms are.

The following examples serve to provide further explanation.

Example 1 Preparation of 2,3-dicyano-1,4-hydroquinone bis (4 ', 4 "-dipropyl) benzoate (Formula 7, R1 = R2 = n-propyl) 3.2 g of 2,3-dicyanohydroquinone (20 mM) in 30 ml of 0.5N KOH dissolved and shaken with 11 g of p-n-propylbenzoic acid chloride. That The product which precipitated out was filtered off and washed with water until neutral and after recrystallization from ethanol gave the target product, K 1610C, N 132 ° C I, where "K" means crystalline, "N" means nematic and "I" means isotropic. The connection obtained showed a high negative DK anisotropy.

Examples 2-12 Following the procedure of Example 1 using of the corresponding acid chlorides and the corresponding phenols, the following compounds produced with high negative DK anisotropy: (2) 2, 3 -Dicyano-1,4-hydroquinone-bis (4 ', 4 -dipentyl) benzoate (3) 2,3-dichloro-1,4-hydroquinone bis (4', 4 "-dipropyl) benzoate (4) 2,3-dichloro-1,4-hydroquinone-bis (4 ', 4 "-dipentyl) -benzoate (5) 2,3-dicyano-1,4-hydroquinone-bis (3', 3" - dicyano-4 ', 4 "-dipropyl) benzoate (6) 2,3-Dicyano-1,4-hydroquinone bis (3 ', 3 "-dicyano-4', 4" -dipentyl) benzoate (7) 2,3-dichloro-1,4-hydroquinone to 3' , 3 "-dicyano-4 '4" -dipropyl) benzoate (8) 2,3-dichloro-1'4-hydroquinone bis (3'3 "-dicyano-4'4" -dipentyl) benzoate (9) bis (2,3-dicyano-4-propyl) phenyl terephthalate (10) bis (2,3-dicyano-4-pentyl) phenyl terephthalate (11) bis (2,3-dichloro-4-propyl) phenyl terephthalate (12) bis (2'3-dichloro-4-pentyl) phenyl terephthalate Examples 13-16 From dialkyl terphenylene the corresponding bromine compounds were prepared by conventional bromination and these optionally by reaction with copper (I) cyanide in the corresponding Converted to nitrile compounds.

(13) 3,3 "-dibromo-4,4" -dipropylterphenyl (14) 3,3 "-dibromo-4,4" -dipentylterphenyl (15) 3,3 "-dicyano-4,4" -dipropylterphenyl (16) 3,3 "-dicyano-4,4" -dipentylterphenyl These compounds also showed a strongly negative DK anisotropy.

Claims (28)

Claims t). nisotropic compounds that contain three aromatic nuclei as polarizing side groups and have a negative DK anisotropy, characterized by the formula (1) in which R1 and R2 are identical or different and represent hydrogen atoms, alkyl groups with 1-12 carbon atoms or alkoxy groups with 1-12 carbon atoms, Z1 and z2 are single bonds, carboxyl or oxycarbonyl groups with the proviso that the dipole moments of simultaneously any carboxyl or oxycarbonyl groups present are directed towards one another and x1 to x6 mean hydrogen atoms, halogen atoms, nitrile groups or nitro groups, with the indication that at least two of the groups X1 to x6 do not represent hydrogen atoms. 2. Compound according to claim 1, characterized by the formula (2) in which R1, R2 and x1 to x6 have the meaning given in claim 1. 3. Compound according to claim 1, characterized by the formula (3) in which R1, R2 and x1 to x6 have the meaning given in claim 1. 4. Compound according to claim 1, characterized by the formula (4) in which R1, R2 and X1 to X6 have the meaning given in claim 1. 5. Compound according to claim 1, characterized by the formula (5) in which R1, R2 and X1 to X6 have the meaning given in claim 1. 6. Compound according to claim 1, characterized by the formula (6) in which R1, R2 and X1 to X6 have the meaning given in claim 1. 7. A compound according to claim 2, characterized in that X3 and X4 in the formula (2) are halogen atoms, nitrile or nitro groups. 8. A compound according to claim 3, characterized in that X2 and 5 in the formula (3) are halogen atoms, nitrile or nitro groups, and preferably both mean nitrile groups. 9. A compound according to claim 4, characterized in that X3 and X5 in the formula (4) halogen atoms, nitrile or Nitro groups are and preferably both denote nitrile groups. 10. A compound according to claim 5, characterized in that X4 and X6 in formula (5) are halogen atoms, nitrile or nitro groups and are preferably both mean nitrile groups. 11. Compound according to one of claims 1-10, characterized in that that three or four of the groups X1 to X6 represent hydrogen atoms. 12. Compound according to claim 7, characterized by the formula (7) in which R1 and R2 have the meaning given in claim 1 and preferably represent alkyl or alkoxy groups with 1-12 carbon atoms. 13. A compound according to claim 12, characterized in that R1 and R2 in the formula (7) have the same meaning. 14. A liquid-crystal mixture which contains at least one anisotropic compound with negative DK anisotropy as a component, characterized in that the anisotropic compound with negative DK anisotropy is one of the formula (1) in which R1 and R2 are identical or different and represent hydrogen atoms, alkyl groups with 1-12 carbon atoms or alkoxy groups with 1-12 carbon atoms, Z1 and Z2 are single bonds, carboxyl or oxycarbonyl groups with the proviso that the dipole moments of simultaneously Any carboxyl or oxycarbonyl groups present are directed towards one another and X1 to X6 mean hydrogen atoms, halogen atoms, nitrile groups or nitro groups, with the proviso that at least two of the groups X1 to x6 do not represent hydrogen atoms. 15. LC mixture according to claim 14, characterized in that the compound (1) is one of the formula (2) in which R1, R2 and X1 to X6 have the meaning given in claim 14. 16. LC mixture according to claim 14, characterized in that the compound (1) is one of the formula (3) in which R1, R2 and X1 to X6 have the meaning given in claim 14. 17. LC mixture according to claim 14, characterized in that the compound (1) is one of the formula (4) in which R1, R2 and X1 to X6 have the meaning given in claim 14. 18. LC mixture according to claim 14, characterized in that the compound (1) is one of the formula (5) in which R1, R2 and X1 to X6 have the meaning given in claim 14. 19. LC mixture according to claim 14, characterized in that the compound (1) is one of the formula (6) in which R1, R2 and X1 to X6 have the meaning given in claim 14. 20. LC mixture according to claim 15, characterized in that X3 and X4 in the formula (2) are halogen atoms, nitrile or nitro groups. 21. LC mixture according to claim 16, characterized in that X2 and X5 in the formula (3) are halogen atoms, nitrile or nitro groups, and preferably both mean nitrile groups. 22. LC mixture according to claim 17, characterized in that X3 and X5 in the formula (4) are halogen atoms, nitrile or nitro groups, and preferably both mean nitrile groups. 23. LC mixture according to claim 18, characterized in that X4 and X6 of formula (5) are halogen atoms, nitrile or nitro groups and are preferably both mean nitrile groups. 24. LC mixture according to one of the claims 14-23, characterized in that that three or four of the groups X1 to X6 represent hydrogen atoms. 25. LC mixture according to claim 20, characterized in that the compound (2) is one of the formula (7) in which R1 and R2 have the meaning given in claim 14 and preferably represent alkyl or alkoxy groups with 1-12 carbon atoms. 26. LC mixture according to claim 25, characterized in that R1 and R2 in the formula (7) have the same meaning. 27. Process for the preparation of anisotropic compounds of the formulas (8) or (9) in which R3 denotes hydrogen atoms, alkyl groups with 1-12 carbon atoms or alkoxy groups with 1-12 carbon atoms, and X1 to X4 are hydrogen atoms, halogen atoms, nitrile groups or nitro groups, characterized by the condensation of approximately 1 molar equivalent of corresponding bifunctional compounds of the formulas ( 10) or (11) with approximately 2 molar equivalents of corresponding monofunctional compounds of the formulas (12) or (13) in which L1, L2, L3 and L4 are atoms or groups of atoms which, under the condensation conditions, form compounds of the formulas L1-L3 or L -L. 28. The method according to claim 27, characterized in that L1 or L hydrogen or alkali metal atoms and L or L3 hydroxyl groups or Are halogen atoms.