Liquid crystal medium and liquid crystal display

Abstract

Dielectrically positive liquid-crystalline media comprising a compound of the formula TINUVIN 770 and optionally one or more compounds of formula I, ##STR00001##
in which the parameters have the respective meanings indicated in the specification, and optionally one or more further dielectrically positive compounds and optionally one or more further dielectrically neutral compounds, and to liquid-crystal displays, especially active-matrix displays and in particular TN, IPS and FFS displays, containing these media.

Claims

1. A liquid-crystal medium having positive dielectric anisotropy (Δε) in the range from 12 to 17 at 20° C. and 1 kHz, comprising a) a compound of the formula below, ##STR00313## and b) a liquid crystal mixture comprising one or more compounds of formula II in a concentration of 33% to 60% by weight based on the weight of the liquid crystal mixture as a whole and one or more compounds of formula II-2; ##STR00314## in which R.sup.2 denotes alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, or alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms, ##STR00315## on each appearance, independently of one another, denote ##STR00316## L.sup.21 L.sup.22, L.sup.23 and L24 independently of one another, denote H or F, X.sup.2 denotes halogen, halogenated alkyl or alkoxy having 1 to 3 C atoms or halogenated alkenyl or alkenyloxy having 2 or 3 C atoms, and m denotes 0, 1, 2 or 3 wherein the total concentration of the compound of the following formula ##STR00317## in the medium is in the range from 1 ppm to 2000 ppm.

2. The liquid-crystal medium according to claim 1, which additionally comprises one or more compounds of formula III ##STR00318## in which R.sup.3 denotes alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, or alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms, ##STR00319## on each appearance, independently of one another, denote ##STR00320## L.sup.31 and L.sup.32 independently of one another, denote H or F, X.sup.3 denotes halogen, halogenated alkyl or alkoxy having 1 to 3 C atoms or halogenated alkenyl or alkenyloxy having 2 or 3 C atoms, Z.sup.3 denotes —CH.sub.2CH.sub.2—, —CF.sub.2CF.sub.2—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH.sub.2O— or a single bond, and N denotes 0, 1, 2 or 3.

3. The liquid-crystal medium according to claim 1, which additionally comprises one or more compounds of formula IV ##STR00321## in which R.sup.41 and R.sup.42 independently of one another, denote alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, or alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms, ##STR00322## independently of one another and, if ##STR00323## occurs twice, also these independently of one another, denote ##STR00324## Z.sup.41 and Z.sup.42 independently of one another and, if Z.sup.41 occurs twice, also these independently of one another, denote —CH.sub.2CH.sub.2—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH.sub.2O—, —CF.sub.2O—, —C≡C— or a single bond, and p denotes 0, 1 or 2.

4. The liquid-crystal medium according to claim 2, which additionally comprises one or more compounds of formula IV ##STR00325## in which R.sup.41 and R.sup.42 independently of one another, denote alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, or alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms, ##STR00326## independently of one another and, if ##STR00327## occurs twice, also these independently of one another, denote ##STR00328## Z.sup.41 and Z.sup.42 independently of one another and, if Z.sup.41 occurs twice, also these independently of one another, denote —CH.sub.2CH.sub.2—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH.sub.2O—, —CF.sub.2O—, —C≡C— or a single bond, and p denotes 0, 1 or 2.

5. The liquid-crystal medium according to claim 1, further comprising a stabilizer compound that is a di-ortho-(tert-butyl)phenol compound, which contains a structural element of the following formula ##STR00329##

6. The liquid-crystal medium according to claim 1, further comprising a stabilizer compound of the following formula ##STR00330## wherein n is 1-7.

7. The liquid-crystal medium according to claim 1, which additionally comprises one or more compounds of formula I, ##STR00331## in which n denotes an integer from 1 to 4, m denotes (4−n), ##STR00332## denotes an organic radical having 4 bonding sites, in which, in addition to the m groups R.sup.12 present in the molecule, but independently thereof, a further H atom may be replaced by R.sup.12 or a plurality of further H atoms may be replaced by R.sup.12, in which one —CH.sub.2— group or a plurality of —CH.sub.2— groups may be replaced by —O— or —(C═O)— in such a way that two O atoms are not bonded directly to one another, or denotes a substituted or unsubstituted aromatic or heteroaromatic hydrocarbon radical having 1 to 4 valences, in which, in addition to the m groups R.sup.12 present in the molecule, but independently thereof, a further H atom may be replaced by R.sup.12 or a plurality of further H atoms may be replaced by R.sup.12, Z.sup.11 and Z.sup.12 independently of one another, denote —O—, —(C═O)—, —(N—R.sup.14)— or a single bond, but do not both simultaneously denote —O—, r and s independently of one another, denote 0 or 1, Y.sup.11 to Y.sup.14 each, independently of one another, denote alkyl having 1 to 4 C atoms and alternatively, independently of one another, one or both of the pairs Y.sup.11 and Y.sup.12 and/or Y.sup.13 and Y.sup.14 together also denote a divalent group having 3 to 6 C atoms, R.sup.11 denotes O., R.sup.12 on each occurrence, independently of one another, denotes H, F, OR.sup.14, NR.sup.14R.sup.15, a straight-chain alkyl having 1-20 C atoms or branched alkyl chain having 3-20 C atoms, in which one —CH.sub.2— group or a plurality of —CH.sub.2— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH.sub.2— groups cannot be replaced by —O—, or denotes a hydrocarbon radical which contains a cycloalkyl having 3 to 10 C atoms or alkylcycloalkyl unit having 4 to 10 C atoms, and in which one —CH.sub.2— group or a plurality of —CH.sub.2— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH.sub.2— groups cannot be replaced by —O—, and in which one H atom or a plurality of H atoms may be replaced by OR.sup.14, N(R.sup.14)(R.sup.15) or R.sup.16, or denotes an aromatic or heteroaromatic hydrocarbon radical, in which one H atom or a plurality of H atoms may be replaced by OR.sup.14, N(R.sup.14)(R.sup.15) or R.sup.16, R.sup.13 on each occurrence, independently of one another, denotes a straight-chain alkyl having 1-20 C atoms or branched alkyl chain having 3-20 C atoms, in which one —CH.sub.2— group or a plurality of —CH.sub.2— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH.sub.2— groups cannot be replaced by —O—, or denotes a hydrocarbon radical which contains a cycloalkyl having 3 to 10 C atoms or alkylcycloalkyl unit having 4 to 10 C atoms, and in which one —CH.sub.2— group or a plurality of —CH.sub.2— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH.sub.2— groups cannot be replaced by —O—, and in which one H atom or a plurality of H atoms may be replaced by OR.sup.14, N(R.sup.14)(R.sup.15) or R.sup.16, or denotes an aromatic or heteroaromatic hydrocarbon radical, in which one H atom or a plurality of H atoms may be replaced by OR.sup.14, N(R.sup.14)(R.sup.15) or R.sup.16, or can be 1,4-cyclohexylene of the following formula ##STR00333## in which one or more —CH.sub.2— groups may be replaced by —O—, —CO— or —NR.sup.14—, or an acetophenyl, isopropyl or 3-heptyl radical, R.sup.14 on each occurrence, independently of one another, denotes a straight-chain alkyl having 1 to 10 C atoms or branched-chain alkyl having 3 to 10 C atoms or acyl group having 1 to 10 C atoms or an aromatic hydrocarbon or carboxyl radical having 6-12 C atoms, R.sup.15 on each occurrence, independently of one another, denotes a straight-chain alkyl having 1 to 10 C atoms or branched-chain alkyl having 3 to 10 C atoms or acyl group having 1 to 10 C atoms or an aromatic hydrocarbon or carboxyl radical having 6-12 C atoms, R.sup.16 on each occurrence, independently of one another, denotes a straight-chain alkyl having 1 to 10 C atoms or branched-chain alkyl group having 3 to 10 C atoms, in which one —CH.sub.2— group or a plurality of —CH.sub.2— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH.sub.2— groups cannot be replaced by —O—, with the provisos that, in the case where n=1, and —[Z.sup.11—].sub.r—[Z.sup.12—].sub.s—═—O—, —(CO)—O—, —O—(CO)—, —O—(CO)—O—, —NR.sup.14 or —NR.sup.14—(CO)—, ##STR00334## does not denote straight-chain alkyl having 1 to 10 C atoms or branched-chain alkyl having 3 to 10 C atoms, also cycloalkyl having 3 to 10 C atoms, cycloalkylalkyl having 4 to 10 C atoms or alkylcycloalkyl having 1 to 10 C atoms, where in all these groups one or more —CH.sub.2— groups may be replaced by —O— in such a way that no two O atoms in the molecule are bonded directly to one another, in the case where n=2, ##STR00335## does not denote ##STR00336##

8. The medium according to claim 7, comprising one or more compounds of formula III ##STR00337## in which R.sup.3 denotes alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, or alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms, ##STR00338## on each appearance, independently of one another, denote ##STR00339## L.sup.31 and L.sup.32 independently of one another, denote H or F, X.sup.3 denotes halogen, halogenated alkyl or alkoxy having 1 to 3 C atoms or halogenated alkenyl or alkenyloxy having 2 or 3 C atoms, Z.sup.3 denotes —CH.sub.2CH.sub.2—, —CF.sub.2CF.sub.2—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH.sub.2O— or a single bond, and n denotes 0, 1, 2 or 3.

9. The medium according to claim 8, which comprises more than one compound of the formula II and one or more compounds of formula II-2.

10. The medium according to claim 8, which comprises more than one compound of the formula III.

11. The liquid-crystal medium according to claim 8, which additionally comprises one or more compounds of formula IV ##STR00340## in which R.sup.41 and R.sup.42 independently of one another, denote alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, or alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms, ##STR00341## independently of one another and, if ##STR00342## occurs twice, also these independently of one another, denote ##STR00343## Z.sup.41 and Z.sup.42 independently of one another and, if Z.sup.41 occurs twice, also these independently of one another, denote —CH.sub.2CH.sub.2—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH.sub.2O—, —CF.sub.2O—, —C≡C— or a single bond, and p denotes 0, 1 or 2.

12. The liquid-crystal medium according to claim 8, wherein joint concentration of the compounds of formulae II and III within the liquid crystal medium ranges from 49% to 60% by weight based on the weight of the whole liquid crystal medium.

13. The medium according to claim 7, comprising one or more compounds of formula IV ##STR00344## in which R.sup.41 and R.sup.42 independently of one another, denote alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 carbon atoms, or alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 carbon atoms, ##STR00345## independently of one another and, if ##STR00346## occurs twice, also these independently of one another, denote ##STR00347## Z.sup.41 and Z.sup.42 independently of one another and, if Z.sup.41 occurs twice, also these independently of one another, denote —CH.sub.2CH.sub.2—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH.sub.2O—, —CF.sub.2O—, —C≡C— or a single bond, and p denotes 0, 1 or 2.

14. The medium according to claim 7, wherein the total concentration of the compounds of formula I and the compound of the following formula ##STR00348## in the medium combined is in the range from 1 ppm to 2000 ppm.

15. The medium according to claim 7, wherein the compounds of the formula I are compounds selected from the group of the compounds of the formulae I-1 to I-9 ##STR00349## ##STR00350## t denotes an integer from 1 to 12, R.sup.17 denotes a straight-chain alkyl having 1 to 12 C atoms or branched alkyl chain having 3-12 C atoms, in which one —CH.sub.2— group or a plurality of —CH.sub.2— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH.sub.2— groups cannot be replaced by —O—, or denotes an aromatic or heteroaromatic hydrocarbon radical, in which one H atom or a plurality of H atoms may be replaced by OR.sup.14, N(R.sup.14)(R.sup.15) or R.sup.16.

16. The medium according to claim 7, comprising one or more dielectrically neutral compounds of formula V ##STR00351## in which R.sup.51 and R.sup.52 independently of one another, denote alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 carbon atoms, or alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 carbon atoms, ##STR00352## on each occurrence, independently of one another, denotes ##STR00353## Z.sup.51 and Z.sup.52 independently of one another and, if Z.sup.51 occurs twice, also these independently of one another, denote —CH.sub.2CH.sub.2—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH.sub.2O—, —CF.sub.2O— or a single bond, and r denotes 0, 1 or 2.

17. A liquid-crystal display, containing the medium according to claim 7.

18. The display according to claim 17, which is addressed by an active matrix.

19. A method of using a medium according to claim 7, comprising operating said medium in a liquid-crystal display to generate an image in said display.

20. A process for the preparation of the medium according to claim 7, wherein the compound of the following formula ##STR00354## is mixed with one or more compounds of formula I, one or more compounds of formula II, one or more compounds of formula II-2 and with i) one or more compounds of formula III, ii) one or more compounds of formula IV, iii) one or more further mesogenic compounds, or iv) one or more additives or a combination thereof, ##STR00355## in which R.sup.2 and R.sup.3 independently of one another, denote alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, or alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms, ##STR00356## on each appearance, independently of one another, denote ##STR00357## L.sup.21, L.sup.22, L.sup.31 and L.sup.32 independently of one another, denote H or F, X.sup.2 and X.sup.3 independently of one another, denote halogen, halogenated alkyl or alkoxy having 1 to 3 C atoms or halogenated alkenyl or alkenyloxy having 2 or 3 C atoms, Z.sup.3 denotes —CH.sub.2CH.sub.2—, —CF.sub.2CF.sub.2—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH.sub.2O— or a single bond, and m and n independently of one another, denote 0, 1, 2 or 3, ##STR00358## in which R.sup.41 and R.sup.42 independently of one another, denote alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 carbon atoms, or alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 carbon atoms, ##STR00359## independently of one another and, if ##STR00360## occurs twice, also these independently of one another, denote ##STR00361## Z.sup.41 and Z.sup.42 independently of one another and, if Z.sup.41 occurs twice, also these independently of one another, denote —CH.sub.2CH.sub.2—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH.sub.2O—, —CF.sub.2O—, —C≡C— or a single bond, and p denotes 0, 1 or 2.

Description

EXAMPLES

(1) The examples below illustrate the present invention without limiting it in any way.

(2) However, the physical properties show the person skilled in the art what properties can be achieved and in what ranges they can be modified. In particular, the combination of the various properties which can preferably be achieved is thus well defined for the person skilled in the art.

(3) Liquid-crystal mixtures having the composition and properties as indicated in the following tables are prepared.

SUBSTANCE EXAMPLES

(4) The following substances are substances of the formula I preferably to be employed in accordance with the present application.

(5) ##STR00300## ##STR00301## ##STR00302## ##STR00303## ##STR00304##

Synthesis Example 1

Synthesis of bis(2,2,6,6-tetramethyl-4-piperidyl)-N,N.SUP.1.-dioxyl succinate (Substance Example 1

(6) ##STR00305##

(7) 2.15 g (12.26 mmol) of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 40 mg (0.33 mmol) of 4-(dimethylamino)pyridine and 1 ml (12.4 mmol) of dried pyridine are initially introduced in 20 ml of dry dichloromethane. 4 Ångström activated molecular sieve is subsequently added, and the mixture is stirred at room temperature (RT for short; about 22° C.) for 90 min. The reaction solution is cooled to a temperature in the range from 7 to 10° C., and 0.71 ml (6.13 mmol) of succinyl dichloride is slowly added, and the mixture is stirred at RT for 18 h. Sufficient sat. NaHCO.sub.3 solution and dichloromethane are added to the reaction solution, and the organic phase is separated off, washed with water and sat. NaCl solution, dried over Na.sub.2SO.sub.4, filtered and evaporated. The crude product is purified over silica gel with dichloromethane/methyl tert-butyl ether (95:5), giving the product as a white solid having a purity of >99.5%.

Synthesis Example 2

Synthesis of bis(2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl) decanedioate (Substance Example 4

(8) ##STR00306##

(9) 28.5 g (166 mmol) of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (free radical) and 250 mg (2.05 mmol) of 4-(dimethylamino)pyridine are dissolved in 300 ml of degassed dichloromethane, and 50.0 ml (361 mmol) of triethylamine are added. The mixture is subsequently degassed and cooled to 0° C., and 10 g (41.4 mmol) of sebacoyl chloride dissolved in 100 ml of degassed dichloromethane are added dropwise at 0-5° C., and the mixture is stirred at room temperature for 18 h. When the reaction is complete, water and HCl (pH=4-5) are added with ice-cooling, and the mixture is stirred for a further 30 min. The organic phase is separated off, and the water phase is subsequently extracted with dichloromethane, and the combined phases are washed with saturated NaCl solution and dried over Na.sub.2SO.sub.4, filtered and evaporated, giving 24.4 g of a red liquid, which together are passed through 100 g of basic Al.sub.2O.sub.3 and 500 g of silica gel on a frit with dichloromethane/methyl tert-butyl ether (95/5), giving orange crystals, which are dissolved in degassed acetonitrile at 50° C. and crystallised at −25° C., giving the product as orange crystals having an HPLC purity of 99.9%.

Synthesis Example 3

Synthesis of bis(2,2,6,6-tetramethyl-4-piperidyl)-N,N′-dioxylbutanediol (Substance Example 7

(10) ##STR00307##

(11) Sufficient pentane is added to 15.0 g (60% in mineral oil, 375 mmol) of NaH under a protective gas, and the mixture is allowed to settle. The pentane supernatant is pipetted off and carefully quenched with isopropanol with cooling. 100 ml of THF are then carefully added to the washed NaH. The reaction mixture is heated to 55° C., and a solution of 50.0 g (284 mmol) of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl in 400 ml of THF is carefully added dropwise. The hydrogen formed is discharged directly. When the addition of the solution is complete, stirring is continued at 60° C. overnight (16 h). The reaction mixture is subsequently cooled to 5° C., and 1,4-butanediol dimethylsulfonate is added in portions. The mixture is subsequently slowly heated to 60° C. and stirred at this temperature for 16 h. When the reaction is complete, the mixture is cooled to RT, and 200 ml of 6% ammonia solution in water are added with cooling, and the mixture is stirred for 1 h. The organic phase is subsequently separated off, the aqueous phase is rinsed with methyl tert-butyl ether, the combined organic phases are washed with sat. NaCl solution, dried and evaporated. The crude product is purified over silica gel with dichloromethane/methyl tert-butyl ether (8:2) and crystallised from acetonitrile at −20° C., giving the product as a pink crystalline solid having a purity of >99.5%.

Synthesis Example 4

Synthesis of bis[2,2,6,6-tetramethyl-1-(1-phenyl-ethoxy)piperidin-4-yl] succinate (Substance Example 24

(12) ##STR00308##

Step 4.1: Synthesis of 2,2,6,6-tetramethyl-1-(1-phenylethoxy)piperidin-4-ol

(13) ##STR00309##

(14) 5.0 g (29.03 mmol) of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 7.80 g (58.1 mmol) of 2-phenylpropionaldehyde and 100.6 mg (1.02 mmol) of copper(I) chloride are initially introduced in 20 ml of tert-butanol. 6.45 ml (58.06 mmol) of 35% hydrogen peroxide solution are then carefully and slowly added dropwise at such a rate that the internal temperature does not exceed 30° C. The mixture is therefore cooled by means of ice-cooling during the dropwise addition. Oxygen is formed in the reaction and would spontaneously be released in large quantities if the addition were too fast and the temperature too high. When the addition is complete, the reaction solution is stirred at RT for a further 16 h, and sufficient water/methyl tert-butyl ether is subsequently added, and the organic phase is separated off. The organic phase is washed with 10% ascorbic acid until peroxide-free, and the peroxide content is checked. The mixture is subsequently washed with 10% NaOH solution, water and sat. NaCl solution, dried over Na.sub.2SO.sub.4, filtered and evaporated. The crude product obtained is purified over silica gel with heptane/methyl tert-butyl ether (1:1), giving the product as colourless crystals.

Step 4.2: Synthesis of bis[2,2,6,6-tetramethyl-1-(1-phenylethoxyl)piperidin-4-yl] succinate

(15) 1.52 g (5.5 mmol) of the product from the preceding step, the compound 2,2,6,6-tetramethyl-1-(1-phenylethoxyl)piperidin-4-ol, 15.3 mg (0.125 mmol) of dimethylaminopyridine and 1.02 ml (12.6 mmol) of dried pyridine are initially introduced in 10 ml of dichloromethane and cooled to a temperature in the range from 7 to 10° C. 0.255 ml (2.199 mmol) of succinoyl dichloride is then added dropwise as such and if necessary topped up if hydroxyl compound is still present. When the reaction is complete, the reaction mixture is filtered directly through silica gel with dichloromethane and subsequently eluted with heptane/methyl tert-butyl ether (1:1) and pure methyl tert-butyl ether. The product obtained is dissolved in acetonitrile and purified by means of preparative HPLC (2 Chromolith columns with 50 ml/min of acetonitrile), giving the product as a yellow oil having a purity of >99.9%.

Synthesis Example 5

Synthesis of 2,2,6,6-tetramethyl-1-(1-phenyl-ethoxy)piperidin-4-yl pentanoate (Substance Example 31

(16) ##STR00310##

(17) 2.5 g (9.01 mmol) of the compound 2,2,6,6-tetramethyl-1-(1-phenyl-ethoxy)piperidin-4-ol from step 3.1 and 55.1 mg (0.45 mmol) of (4-dimethylaminopyridine) are dissolved in 50.0 ml of dry dichloromethane and cooled to 3° C. 5.47 ml (27.03 mmol) of valeric anhydride are added at this temperature, and the mixture is stirred at room temperature for 14 h. When the reaction is complete, the mixture is carefully poured into ice-water, adjusted to pH 6 using 2N HCl, and the organic phase is separated off. The aqueous phase is extracted with dichloromethane, and the combined organic phases are washed with saturated NaCl solution, a mixture of water and triethylamine (300:50 ml) and dried over MgSO.sub.4, filtered and evaporated. Purification on silica gel with heptane/methyl tert-butyl ether (9:1) gives the product as a colourless oil.

Synthesis Example 6

Synthesis of 1,4-bis(1-hydroxy-2,2,6,6-tetramethyl-4-piperidinyl) butanedioate (Substance Example 49

(18) ##STR00311##

(19) 40 ml of water and 80 ml of dioxane are mixed and carefully degassed by means of a stream of argon. 2.0 g (4.7 mmol) of the free radical from Substance Example 1 (Synthesis Example 1) are dissolved in the solvent mixture, and 4.95 g (28.1 mmol) of ascorbic acid are added in portions. The reaction mixture becomes colourless during this addition and is stirred at 40° C. for 18 h under a protective-gas atmosphere. The mixture is cooled to room temperature, and 100 ml of water are added, the mixture is stirred briefly, and the crystals formed are filtered off with suction. The crystals are dissolved in 50 ml of hot degassed THF, and the insoluble constituents are filtered off, and the filtrate is crystallised at −25° C. The pale-pink crystals are then washed by stirring in acetonitrile at room temperature for 18 h, giving the product as pale-pink crystals having an HPLC purity of 100%.

Synthesis Example 8

Synthesis of 1,10-bis(1-hydroxy-2,2,6,6-tetramethyl-4-piperidinyl) decanedioate (Substance Example 50

(20) ##STR00312##

(21) All solvents used are thoroughly degassed in advance by means of a stream of argon. During work-up, brown glass equipment must be used. 1.70 g (3.32 mmol) of the free radical from Substance Example 4 (Synthesis Example 2) are dissolved in 60 ml of dioxane. 3.6 g (20 mmol) of ascorbic acid dissolved in 30 ml of water are subsequently added dropwise to the solution at room temperature. The reaction solution starts to become colourless during this dropwise addition, and the reaction is complete after stirring at room temperature for 1 h. The mixture is extracted with 100 ml of dichloromethane, and the organic phase is washed with water, dried over Na.sub.2SO.sub.4, filtered and evaporated. The yellow crystals formed are dried at 160° C. and 10.sup.−2 mbar for 5 min, giving a viscous, slowly crystallising oil.

(22) Liquid-crystal mixtures having the compositions and properties as indicated in the following tables are prepared and investigated.

USE EXAMPLES

Use Example 1

Comparative Example 1 and Use Example 1.1

(23) TABLE-US-00007 Mixture M-1: Composition Compound No. Abbreviation c/% 1 APUQU-3-F 4.5 2 PGUQU-3-F 5.0 3 PGUQU-4-F 9.0 4 PGUQU-5-F 1.5 5 CCQU-3-F 4.0 6 CCQU-5-F 9.0 7 CCU-3-F 9.0 8 CCU-5-F 9.0 9 CC-3-V 38.5 10 CC-3-V1 4.0 11 PGP-2-3 6.5 Σ 100.0 Physical properties T(N, I) = 80.5° C. n.sub.e (20° C., 589.3 nm) = 1.5780 Δn (20° C., 589.3 nm) = 0.0990 ε|| (20° C., 1 kHz) = 12.3 Δε (20° C., 1 kHz) = 9.1 k.sub.1(20° C.) = 12.6 pN k.sub.3(20° C.) = 14.0 pN γ.sub.1 (20° C.) = 76 mPa .Math. s V.sub.0 (20° C.) = 1.24 V

(24) This mixture (mixture M-1) is prepared and divided into two parts. The first part is investigated without addition of a further compound. 100 ppm of the compound to be investigated, here the compound of the formula I-1a-1, are added to the second part of the mixture. The two parts of the mixture are investigated as follows.

(25) In each case, six test cells having the alignment layer AL-16301 (Japan Synthetic Rubber (JSR), Japan) and a layer thickness of 3.2 μm and transversal electrodes as for TN cells are filled and investigated with respect to their voltage holding ratio. The initial value and the value after UV exposure with an Execure 3000 high-pressure mercury vapour lamp from Hoya with an edge filter (T=50% at 340 nm), at a certain exposure intensity in J/cm.sup.2, are determined at a temperature of 25° C. The respective exposure intensity is measured at a wavelength of 365 nm using an Ushio UIT-101+UVD-365PD sensor. In each case, the HR is measured at a temperature of 100° C. after 5 minutes in the oven. The voltage is 1 V at 60 Hz. The results are summarised in the following table.

(26) TABLE-US-00008 I.sub.UV/J/cm.sup.2 0 3 6 12 Example X: formula c(X)/ppm HR.sub.0/% HR.sub.UV/% V1.0 None  0 98.6 94.2 90.8 85.2 1.1 I-1a-1 100 98.0 95.7 94.8 93.9 Notes: X: compound of the formula I-1a-1 I.sub.UV at 365 nm.

(27) The mixtures of Use Example 1.1, which comprise a compound of the formula I (I-1a-2), are distinguished, in particular, by excellent stability to UV irradiation.

(28) Corresponding investigations of the two different mixtures were then carried out in sealed test cells with exposure to commercial LCD TV backlighting (CCFL). The temperature of the test cells here was about 40° C. due to the heat evolution by the backlighting. The results are summarised in the following table.

(29) TABLE-US-00009 t/h 0 24 168 1000 Example X: formula c(X)/ppm HR.sub.0/% HR.sub.BL/% V1.0 None  0 98.1 89.8 69.3 36 1.1 I-1a-1 100 97.9 98.3 95.8 68.5 Note: X: compound of the formula I-1a-1.

(30) Corresponding investigations were subsequently carried out on the two different mixtures in sealed test cells with heating. The temperature stability is checked by a heat test. To this end, the HR is determined before and after heating. To this end, the cells are stored in an oven at a temperature of 100° C. for certain times. The HR is then determined as described above. The results are summarised in the following table.

(31) TABLE-US-00010 t/h 0 24 72 336 Example X: formula c(X)/ppm HR.sub.0/% HR.sub.T (t)/% V1.0 None  0 98.5 97.1 95.8 93.9 1.1 I-1a-1 100 98.0 97.8 97.5 95.8 Notes: X: compound of the formula I-1a-1 Temperature: 100° C.

Use Example 2

Comparative Example 2.0 and Use Examples 2.1 to 2.4

(32) TABLE-US-00011 Mixture M-2: Composition Compound No. Abbreviation c/% 1 DGUQU-4-F 8.0 2 APUQU-2-F 8.0 3 APUQU-3-F 6.5 4 PGUQU-3-F 3.5 5 PGUQU-4-F 9.0 6 DPGU-4-F 6.0 7 CCP-3-OT 8.0 8 CC-3-V 33.5 9 CC-3-V1 11.5 10 CCP-V2-1 6.0 Σ 100.0 Physical properties T(N, I) = 93.0° C. n.sub.e (20° C., 589.3 nm) = 1.5876 Δn (20° C., 589.3 nm) = 0.1086 ε|| (20° C., 1 kHz) = 19.0 Δε (20° C., 1 kHz) = 15.4 k.sub.1(20° C.) = 14.7 pN k.sub.3(20° C.) = 15.6 pN γ.sub.1 (20° C.) = 97 mPa .Math. s V.sub.0 (20° C.) = 1.03 V

(33) Mixture M-2 is prepared here as in Use Example 1, but is divided into five parts here. The first part is investigated without addition of a further compound. 100 ppm or 200 ppm of the compound of the formula TINUVIN 770® or 100 ppm or 200 ppm of the compound of the formula I-1a-1 are added to the four further parts of the mixture.

(34) In each case, six test cells having the alignment layer AL-16301 (Japan Synthetic Rubber (JSR), Japan) and a layer thickness of 3.2 μm are filled (electrodes: TN layout) and investigated with respect to their voltage holding ratio. The initial value and the value after UV exposure with a high-pressure mercury vapour lamp from Hoya (Execure 3000) with an edge filter (T=50% at 340 nm), at a certain exposure intensity in J/cm.sup.2, are determined at a temperature of 25° C. The exposure intensity is measured using an Ushio UIT-101+UVD-365PD sensor at a wavelength of 365 nm. In each case, the HR is measured at a temperature of 100° C. after 5 minutes in the oven. The voltage is 1 V at 60 Hz. The results are summarised in the following table.

(35) TABLE-US-00012 I.sub.UV/J/cm.sup.2 0 3 Example X: formula c(X)/ppm HR.sub.0/% HR.sub.UV/% V2.0 None 0 95.8 90.0 2.1 TINUVIN 770 ® 100 97.0 94.5 2.2 TINUVIN 770 ® 200 97.7 96.8 2.3 I-1a-1 100 95.1 93.4 2.4 I-1a-1 200 95.2 94.1 Notes: X: TINUVIN 770 ® in the case of Examples 2.1 and 2.2 and the compound of the formula I-1a-1 in the case of Examples 2.3 and 2.4, I.sub.UV at 365 nm.

(36) The mixtures of Use Examples 2.1 to 2.4, each of which comprise a compound of the formula TINUVIN 770® or a compound of the formula I (I-1a-2), are distinguished, in particular, by excellent stability to UV irradiation. In the case of the corresponding two mixture pairs, the stability here increases with increasing concentration of the compound of the formula TINUVIN 770® or of the formula I-1a-2.

(37) Corresponding investigations of the five different mixtures were then carried out in test cells with exposure to LCD backlighting as described above. The results are summarised in the following table.

(38) TABLE-US-00013 t/h 0 24 168 Example X: formula c(X)/ppm HR.sub.0/% HR.sub.BL/(t)/% V2.0 None 0 96.2 82.9 56.8 2.1 TINUVIN 770 ® 100 97.6 95.1 93.0 2.2 TINUVIN 770 ® 200 98.7 98.5 95.8 2.3 I-1a-1 100 96.1 97.2 92.4 2.4 I-1a-1 200 95.7 97.3 95.5 Note: X: TINUVIN 770 ® in the case of Examples 2.1 and 2.2 and the compound of the formula I-1a-1 in the case of Examples 2.3 and 2.4.

(39) The difference in the HR of the host in the case of Comparative Example 2.0 in this table from those in the preceding table of this comparative example is attributable to the reproducibility of the measurement values. Within a measurement series in an example and the associated comparative measurements, the reproducibility is significantly better (about ½ to ⅓ times as great) and the variation latitude is thus correspondingly significantly lower.

(40) Corresponding investigations of the five different mixtures were subsequently carried out in test cells with heating, as described above. The results are summarised in the following table.

(41) TABLE-US-00014 t/h 0 24 48 96 Example X: formula c(X)/ppm HR.sub.0/% HR.sub.T (t)/% V2.0 None  0 95.8 95.0 93.7 92.8 2.1 TINUVIN 770 ® 100 97.0 98.3 98.8 98.8 2.2 TINUVIN 770 ® 200 97.7 98.8 98.9 98.9 2.3 I-1a-1 100 95.1 96.1 96.8 96.6 2.4 I-1a-1 200 95.2 96.6 96.8 96.7 Notes: X: TINUVIN 770 ® in the case of Examples 2.1 and 2.2 and the compound of the formula I-1a-1 in the case of Examples 2.3 and 2.4 Temperature: 100° C.

Use Example 3

Comparative Example 3.0 and Use Example 3.1

(42) TABLE-US-00015 Mixture M-3: Composition Compound No. Abbreviation c/% 1 CDUQU-3-F 8.0 2 APUQU-2-F 8.0 3 APUQU-3-F 8.5 4 PGUQU-3-F 1.5 5 PGUQU-4-F 9.0 6 PGUQU-5-F 4.0 7 DPGU-4-F 6.0 8 CCP-3-OT 8.0 9 CC-3-V 32.5 10 CC-3-V1 12.5 11 CCP-V2-1 2.0 Σ 100.0 Physical properties T(N, I) = 93.0° C. n.sub.e (20° C., 589.3 nm) = 1.5870 Δn (20° C., 589.3 nm) = 0.1089 ε|| (20° C., 1 kHz) = 19.2 Δε (20° C., 1 kHz) = 15.4 k.sub.1(20° C.) = 14.9 pN k.sub.3(20° C.) = 15.2 pN γ.sub.1 (20° C.) = 99 mPa .Math. s V.sub.0 (20° C.) = 1.03 V

(43) Mixture M-3 is prepared here as in Use Example 1 and divided into two parts. The first part is investigated without addition of a further compound. 200 ppm of the compound to be investigated, here the compound of the formula I-1a-1, are added to the second part of the mixture. In each case, six test cells having the alignment layer AL-16301 (Japan Synthetic Rubber (JSR), Japan) and a layer thickness of 3.2 μm are filled (electrodes: TN layout) and investigated with respect to their voltage holding ratio. The initial value and the value after UV exposure to a high-pressure mercury vapour lamp from Hoya (Execure 3000) with an edge filter (T=50% at 340 nm), at a certain exposure intensity in J/cm.sup.2, are determined at a temperature of 25° C. The exposure intensity is measured using an Ushio UIT-101+UVD-365PD sensor at a wavelength of 365 nm. In each case, the HR is measured at a temperature of 100° C. after 5 minutes in the oven. The voltage is 1 V at 60 Hz. The results are summarised in the following table.

(44) TABLE-US-00016 I.sub.UV/J/cm.sup.2 0 3 6 12 Example c(X)/ppm HR.sub.0/% HR.sub.UV/% V3.0 0 97.0 91.6 t.b.d. t.b.d. 3.1 200 96.0 93.4 t.b.d. t.b.d. Notes: X: compound of the formula I-1a-1, t.b.d.: to be determined, I.sub.UV at 365 nm.

(45) The mixtures of Use Example 3.1, which comprise a compound of the formula I (formula I-1a-1), are distinguished, in particular, by excellent stability to UV irradiation.