Mesogenic media and liquid crystal display

Abstract

The invention relates to mesogenic media comprising a first component, component A, consisting of bimesogenic compounds selected from the group of compounds of formulae A-I to A-III ##STR00001## a second component, component B, consisting of nematogenic compounds, preferably selected from the group of compounds of formulae B-I to B-III ##STR00002## and a third component, component C, consisting of one or more chiral molecules, wherein the parameters have the meaning given in claim 1, to the use of mesogenic media in flexoelectric liquid crystal devices and to those devices comprising a liquid crystal medium according to the present invention.

Claims

1. A mesogenic medium comprising a first component, component A, consisting of bimesogenic compounds selected from the group consisting of compounds of formulae A-I, A-II and A-III, wherein at least one compound of formula A-II and at least one compound of formula A-III are present in component A, ##STR00150## wherein R.sup.11 and R.sup.12, R.sup.21 and R.sup.22 and R.sup.31 and R.sup.32 are each independently H, F, Cl, CN, NCS or a straight-chain or branched alkyl group with 1 to 25 C atoms which is unsubstituted, or mono- or polysubstituted by halogen or CN, in which optionally one or more non-adjacent CH.sub.2 groups are replaced, in each occurrence independently from one another, by O, S, NH, N(CH.sub.3), CO, COO, OCO, OCOO, SCO, COS, CHCH, CHCF, CFCF or CC in such a manner that oxygen atoms are not linked directly to one another, MG.sup.11 and MG.sup.12, MG.sup.21 and MG.sup.22 and MG.sup.31 and MG.sup.32 are each independently a mesogenic group, Sp.sup.1, Sp.sup.2 and Sp.sup.3 are each independently a spacer group comprising 5 to 40 C atoms, wherein one or more non-adjacent CH.sub.2 groups, with the exception of the CH.sub.2 groups of Sp.sup.1 linked to O-MG.sup.11 and/or O-MG.sup.12, of Sp.sup.2 linked to MG.sup.21 and/or MG.sup.22 and of Sp.sup.3 linked to X.sup.31 and X.sup.32, are optionally replaced by O, S, NH, N(CH.sub.3) , CO, OCO, SCO, OCOO, COS, COO, CH(halogen)-, CH(CN) , CHCH or CC, in such a way that no two O-atoms are adjacent to one another, no two CHCH groups are adjacent to each other, and no two groups selected from the group consisting of OCO, SCO, OCOO, COS, COO and CHCH are adjacent to each other, and X.sup.31 and X.sup.32 are independently from one another a linking group selected from the group consisting of COO, OCO, CHCH, CC and S, and wherein alternatively one of X.sup.31 and X.sup.32 is O or a single bond, or one of X.sup.31 and X.sup.32 is O and the other one is a single bond, wherein the medium comprises component A in a concentration of 60 to 90% by weight of the medium, a second component, component B, consisting of one or more nematogenic compounds, which are of formulae B-I to B-III ##STR00151## wherein L.sup.B11, L.sup.B12, L.sup.B31 and L.sup.B32 are independently H or F, B.sup.B1, R.sup.B21, R.sup.B22, R.sup.B31 and R.sup.B32 are each independently H, F, Cl, CN, NCS or a straight-chain or branched alkyl group with 1 to 25 C atoms which is optionally unsubstituted, mono- or polysubstituted by halogen or CN, in which optionally one or more non-adjacent CH.sub.2 groups are replaced, in each occurrence independently from one another, by O, S, NH, N(CH.sub.3), CO, COO, OCO, OCOO, SCO, COS, CHCH, CHCF, CFCF or CC in such a manner that oxygen atoms are not linked directly to one another, X.sup.B1 is F, Cl, CN or NCS, Z.sup.B1,Z.sup.B2 and Z.sup.B3 are in each occurrence independently CH.sub.2CH.sub.2, COO, OCO, CF.sub.2O, OCF.sub.2, CHCH or a single bond, ##STR00152## and ##STR00153## are in each occurrence independently ##STR00154## or ##STR00155## or alternatively one or more of are ##STR00156## and n is 1, 2 or 3, and a third component, component C, consisting of one or more chiral molecules, which are of formulae C-I to C-III, ##STR00157## including the respective (S,S) enantiomers, wherein E and F are each independently 1,4-phenylene or trans- 1,4-cyclohexylene, v is 0 or 1, Z.sup.0 is COO, OCO, CH.sub.2CH.sub.2 or a single bond, and R is alkyl, alkoxy or alkanoyl with 1 to 12 C atoms.

2. The mesogenic medium according to claim 1, comprising one or more compounds of formulae A-I to A-III, wherein MG.sup.11 and MG.sup.12, MG.sup.21 and MG.sup.22 and MG.sup.31 and MG.sup.32 are independently of each other of formula II
-A.sup.1-(Z.sup.1-A.sup.2).sub.m-II wherein Z.sup.1 is COO, OCO,OCOO, OCH.sub.2, CH.sub.2O, CH.sub.2CH.sub.2, (CH.sub.2).sub.4, CF.sub.2CF.sub.2, CHCH, CFCF, CHCHCOO, OCOCHCH, CC or a single bond, A.sup.1 and A.sup.2 are each independently in each occurrence 1,4-phenylene, in which one or more CH groups are optionally replaced by N, trans- 1,4-cyclohexylene, in which one or two non-adjacent CH.sub.2 groups are optionally replaced by O and/or S, 1,4cyclohexenylene, 1,4-bicyclo-(2,2,2)-octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydro-naphthalene-2,6-diyl, 1,2,3,4-tetrahydro-naphthalene-2,6-diyl, cyclobutane-1,3-diyl, spiro[3.3]heptane-2,6-diyl or dispiro[3.1.3.1] decane-2,8-diyl, wherein the preceding groups are each unsubstituted, or mono-, di-, tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl groups with 1 to 7 C atoms, wherein one or more H atoms may be substituted by F or Cl, and m is 0, 1, 2or 3.

3. The mesogenic medium according to claim 1, comprising one or more compounds selected from formulae A-I to A-III, wherein MG.sup.11 and MG.sup.12, MG.sup.21 and MG.sup.22 and MG.sup.31 and MG.sup.32 are each independently one of the following formulae or their mirror images ##STR00158## ##STR00159## wherein L is in each occurrence independently of each other F, Cl, CN, OH, NO.sub.2 or an optionally fluorinated alkyl, alkoxy or alkanoyl group with 1 to 7 C atoms, and r is in each occurrence independently of each other 0, 1, 2, 3 or 4.

4. The mesogenic medium according to claim 1, which comprises one or more compounds of formula A-I.

5. The mesogenic medium according to claim 1, which comprises one or more compounds of formula A-II, which are of formulae A-II-1 to A-II-4 ##STR00160## wherein n is 1 to 15.

6. The mesogenic medium according to claim 1, which comprises one or more compounds of formula A-Ill, which are of formulae A-III-1 to A-III-11 ##STR00161## wherein n is 1 to 15.

7. The mesogenic medium according to claim 1, which comprises one or more compounds of formula B-I.

8. The mesogenic medium according to claim 1, which comprises one or more compounds of formula B-II.

9. The mesogenic medium according to claim 1, which comprises one or more compounds of formula B-III.

10. The mesogenic medium according to claim 1, which comprises component B, consisting of compounds selected from the group consisting of compound of formulae B-I, B-II and B-III, which are present in a concentration 40% or less by weight based on the medium as a whole.

11. The mesogenic medium according to claim 1, which exhibits first and second nematic phases.

12. A liquid crystal device comprising a mesogenic medium according to claim 1.

13. The liquid crystal device according to claim 12, which is a flexoelectric device.

14. A liquid crystal device according to claim 12, which comprises two plane parallel electrodes, the inner surfaces of which exhibit planar, anti-parallel alignment conditions.

15. The mesogenic medium according to claim 1, wherein X.sup.B1 is CN.

16. The mesogenic medium according to claim 1, wherein X.sup.31 and X.sup.32 are independently from one another a linking group selected from the group consisting of CHCH, CC and S.

17. The mesogenic medium according to claim 1, wherein the medium comprises component A in a concentration of 70 to 90% by weight of the medium.

18. The mesogenic medium according to claim 1, wherein X.sup.31 and X.sup.32 are independently from one another a linking group selected from the group consisting of COO, OCO, CHCH, CC and S.

19. The mesogenic medium according to claim 1, which contains the compound C-I in component C.

20. The mesogenic medium according to claim 1, which contains at least one of the following compounds of formulae A-II ##STR00162## ##STR00163## and at least one of the following compounds of formulae A-III ##STR00164## ##STR00165## ##STR00166##

Description

COMPOUND AND SYNTHESIS EXAMPLES

Synthesis Example 1

(1) Preparation of N-PGIZIGI-9-GZGP-N

(2) ##STR00040##
Step 1.1

(3) ##STR00041##

(4) 55.1 g (183 mmol) of the iodobromofluorobenzene and 60 ml tetrahydrofuran are added to a reaction flask, which is evacuated three times and subsequently filled with nitrogen, then treated in an ultrasonic bath to degas the reaction mixture, a procedure shortly referred to as ultasonication in this application, for 10 min. with additional evacuation/purging with nitrogen. Pd(PPh.sub.3).sub.2Cl.sub.2 (1.8 g, 2.6 mmol) and CuI (0.4 g, 2.1 mmol) as catalysts and diisopropylamine (60 ml) are added and the reaction vessel is purged again before being ultrasonicated for 10 minutes and then placed in a large water bath to control the reaction temperature.

(5) 1,8-nonadiyne (10 g, 83 mmol) are added slowly over a time span of 15 minutes a fine precipitate is formed. The reaction mixture is stirred overnight at ambient temperature.

(6) The reaction mixture is then filtered under vacuum and the filter pad washed with Dichloromethane. The filtrate is concentrated to a semi-solid, which is re-dissolved in dichloromethane before being passed through a silica column to purify. The target product is eluted with additional dichloromethane before final isolation by re-crystallisation from petroleum ether.

(7) Step 1.2

(8) ##STR00042##

(9) The hydrogenation reaction is performed in an H-Cube-hydrogenation apparatus. The parameters of the reaction are as follows: Flow rate: 7 ml/min, Mode: 100% H.sub.2, Catalysts: Pt/C, Temperature: 50 C. and Pressure: 30 bar.

(10) Step 1.3

(11) ##STR00043##

(12) Anhydrous tetrahydrofuran is charged into a three neck flask together with 9.4 g (19.8 mmol) of the dibromide with the saturated spacer. The flask is evacuated and filled with nitrogen. The reaction mixture is stirred and cooled to a temperature of 75 C. in a bath of acetone cooled by solid CO.sub.2.

(13) Then 31 ml 1.6 M, (49.5 mmol) n-butyl lithium are added drop wise over a time span of 30 minutes while keeping the temperature at 75 C. After 3 hours further stirring 8.7 g (200 mmol) of crushed, solid CO.sub.2 are cautiously added to the reaction mixture. A thick white sludge develops and this is stirred for a further 30 minutes before it is hydrolysed by the addition of dilute HCl. The mixture is extracted three times with diethyl ether, and the combined organic material washed with water until neutral. Then toluene is added and the whole solvent is solution is evaporated. The solid the product is isolated and used in the following without further purification.

(14) Step 1.4

(15) ##STR00044##

(16) 4.9 g (24 mmol) of the acid intermediate are added to flask filled with 50 ml dichloromethane. This mixture is thoroughly stirred before 6.5 g (31 mmol) of trifluoroacetic anhydride are added dropwise over a time span of 5 minutes. The reaction mixture is then stirred further for 5 minutes.

(17) Then 4.6 g (24.4 mmol) of solid 4-hydroxy-3-fluorobromobenzene are added and the reaction mixture is stirred at a temperature of 35 C. After complete reaction, water is added. The organic and aqueous layers are separated and the aqueous solution is extracted three times with dichloromethane. The combined organic solutions are washed with a solution of sodium carbonate before being dried over magnesium sulphate, filtered and concentrated. The crude product is purified by passing through a silica plug and eluting with a mixture of petrol and dichloromethane (1:2). The final purification is carried out by re-crystallisation from MeCN.

(18) Step 1.5

(19) ##STR00045##

(20) 1.0 g (1.33 mmol) of the bromide intermediate, 0.61 g (2.67 mmol) of 4-cyanophenyl boronate ester, 0.63 g (2.66 mmol) of sodium metaborate octahydrate, 9.0 ml (499 mmol) of water and 37.5 ml (463 mmol) of tetrahydrofuran are filled into a round bottom flask. This mixture is stirred, the flask is evacuated and filled with nitrogen before being untrasonicated for 30 minutes. Then 0.075 g (0.107 mmol) of palladium dichloride-(bistriphenylphosphine) are added and the vessel is evacuated then filled with nitrogen. The reaction mixture is heated to a temperature of 80 C. for 72 hours under reflux. Then the reaction mixture is cooled, water and diethyl ether are added subsequently. Then the resulting phases are separated. The aqueous phase is extracted twice with diethyl ether, and the combined organic phases are washed twice with water and once with an aqueous solution of NaCl. The organic solution is dried over sodium sulphate, filtered and the solvent evaporated. The crude product is purified over a short silica column, eluted with first petrol then with a mixture of petrol/dichloromethane (2:1). The product is isolated after repeated re-crystallisation from acetonitrile.

(21) ##STR00046##

(22) This compound has the phase sequence: K 130 Sm 255 N 271 I.

(23) Scheme for Synthesis Example 2Preparation of N-PO1GI-9-GO1P-N

(24) ##STR00047##

Synthesis Example 2

(25) Step 2.1

(26) 4-bromofluorophenol (33.9 g, 0.178 moles), benzylbromide (21.1 ml, 0.178 moles), potassium carbonate (34.4 g, 0.25 moles) and butan-2-one (300 ml) are heated together at a temperature of 85 C. under reflux overnight. The mixture is cooled, filtered, washed with butanone and diethyl ether and the solvent removed in vacuo. The material is re-crystallised from heptane at 20 C.

(27) Step 2.2

(28) The bromide (44.5 g, 115.8 mmol) from the previous step, triethylamine (89 ml), tetrahydrofuran (45 ml), Copper(I) Iodide (0.694 g, 3.6 mmol) and bis(triphenylphosphine)Palladium(II)dichloride (3.5 g, 4.91 mmol) are added to a flask and then 1,8-Nonadiyne (9.14 g (76.0 mmol) in tetrahydrofuran (45 ml) is slowly added over a time of 30 minutes. The reaction-mixture is warmed to 40 C. overnight. The mixture is then cooled, filtered and the filter pad washed with diethyl ether. The filtrate is acidified with dilute Hydrochloric acid and then neutralized with sodium hydroxide before drying over sodium sulphate. This was filtered and the solvent from the filtrate removed in vacuo to give a solid product. The solid was pre-adsorbed onto 50 g silica from a dichloromethane solution and columned through a short silica column using 10% DCM in petrol as eluent. The fractions containing the product were collected and re-crystallised first from petrol and then from acetonitrile to afford the clean product.

(29) Step 2.3

(30) The hydrogenation reaction is again performed in a an H-Cube Hydrogenator.

(31) Parameters: Flow: 10 ml/min., Mode: 100% H.sub.2 Catalysts: Pd/C

(32) Temp.: 50 C., Pressure: 30 bar Rising to 80 CC and 80 bar at the end of the reaction.

(33) Stage 2.4

(34) The phenol from stage 3 (2.80 g, 8.04 mmol), 4-bromomethylbenzonitrile (3.94 g, 20.09 mmol) and potassium carbonate (1.66 g, 12 mmol) are added to a flask with dimethylformamide (5.87 g) and ethyl methyl ketone (50 ml). The mixture is heated at 85 C. overnight. The mixture is cooled, filtered and the filter pad washed with diethyl ether and the solvent from the filtrate removed in vacuo to give a solid product. This solid crude product is purified over a short silica column using 33% DCM in petrol as eluent. The fractions containing the product are collected and re-crystallised from acetonitrile to afford the clean product.

(35) Scheme for Synthesis Example 3Preparation of N-PO1GI-9-GO1P-F

(36) ##STR00048##

Synthesis Example 3

(37) Steps 3.1 to 3.3 are identical to those of Synthesis example 2.

(38) Step 3.4

(39) The product of the synthesis example 2, step 2.3 (2.50 g, 7.18 mmol), 4-bromomethyl-benzonitrile (2.81 g, 14.4 mmol) and potassium carbonate (1.79 g, 19.9 mmol) are mixed together in ethylmethylketone (50 ml). The reaction mixture is heated under reflux at 80 C. for 12 hours. The reaction-mixture is then cooled and the solid precipitate formed is filtered off under vacuum, the filter pad is washed with ether then the solution is concentrated under reduced pressure. The crude product is purified by chromatography through silica, eluted with 30% DCM in petroleum ether (40-60). The material is then re-crystallised from acetonitrile to yield the desired non symmetrical intermediate alcohol.

(40) Step 3.5

(41) The product from the previous step, step 3.4 (2.15 g, 4.64 mmol), 1-bromomethyl-4-fluorobenzene (1.05 g, 5.56 mmol) and potassium carbonate (1.92 g, 14.0 mmol) are mixed together in ethylmethylketone (50 ml). The reaction mixture is heated under reflux at 80 C. for 18 hours. The reaction-mixture is then cooled and solids filtered off under vacuum, the filter pad is washed with diethyl ether then concentrated under reduced pressure. The crude product is purified by chromatography through silica, eluted with 30% DCM in petroleum ether (40-60). The material was then re-crystallised twice from acetonitrile to afford the product.

(42) Scheme for Synthesis Example 4-Preparation of N-PQIP-9-PQP-N

(43) ##STR00049##
Step 4.1

(44) 25.0 g (88.4 mmol) of iodobromobenzene and 80 ml tetrahydrofuran are added to a reaction flask, which is evacuated three times and subsequently filled with nitrogen each time, then ultasonicated for 10 min. with additional evacuation/purging with nitrogen. Pd(PPh.sub.3).sub.2Cl.sub.2 (0.9 g, 1.3 mmol) and CuI (0.2 g, 1.1 mmol) as catalysts and diisopropylamine (14 ml) are added and the reaction vessel is purged again before being placed back in an ultrasonic bath for 10 minutes and then placed in a large water bath to control the reaction temperature.

(45) 1,8-nonadiyne (5.0 g, 41.6 mmol) is mixed with tetrahydrofuran (20 ml) and added slowly over a time span of 15 minutes. A fine precipitate is formed. The reaction mixture is stirred overnight at ambient temperature. The reaction mixture is then filtered under vacuum and the filter pad washed with tetrahydrofuran. The filtrate is concentrated to a semi-solid, which is re-dissolved in dichloromethane before being passed through a silica column for purification. The target product is eluted with additional dichloromethane to afford a yellow crystalline solid.

(46) Step 4.2

(47) The hydrogenation reaction is performed in an H-Cube-hydrogenation apparatus. The parameters of the reaction are as follows: Flow rate: 7 ml/min., Mode: 100% H.sub.2, Catalysts: Pt/C, Temperature: 50 C., and Pressure: 30 bar.

(48) Step 4.3

(49) Anhydrous tetrahydrofuran is charged into a three neck flask together with 9.4 g (19.8 mmol) of the dibromide from the previous stage. The flask is evacuated and filled with nitrogen. The reaction mixture is stirred and cooled to a temperature of 75 C. in a bath of acetone cooled by solid CO.sub.2.

(50) Then n-butyl lithium (1.6 M, 31 ml, 49.5 mmol) are added drop wise over a time span of 30 minutes while keeping the temperature at 75 C. After 3 hours further stirring 8.7 g (200 mmol) of crushed, solid CO.sub.2 are cautiously added to the reaction mixture. A thick white sludge develops and this is stirred for a further 30 minutes before it is hydrolysed by the addition of dilute HCl. The mixture is extracted three times with diethyl ether, and the combined organic material washed with water until neutral. Then toluene is added and the whole solvent is solution is evaporated. The solid the product is isolated and used in the following without further purification.

(51) Step 4.4

(52) The intermediate product from the previous stage (5.5 g, 15 mmol) and propandithiol (3.6 g, 33 mmol) are added to flask before adding trifluoromethanesulphonic acid (6.8 g, 45 mmol) and starting to stir the mixture. The mixture is heated to 120 C. and the now clear orange mixture is then cooled to ambient before being treated with diethyl ether (300 ml). The resultant solution is added to a flask of vigorously stirred diethyl ether (700 ml) pre-cooled to 70 C. Within 30 minutes fine crystals appear in the stirred mixture. The solid is isolated by filtration under vacuum and washed with ether to give a pale yellow powder which is used immediately.

(53) Step 4.5

(54) The intermediate (10.1 g 12 mmol) from the previous stage is added to a flask with dichloromethane (50 ml) and then cooled to 70 C. A mixture of 4-cyanophenol (3.5 g, 30 mmol), dichloromethane (40 ml) and triethylamine (3.5 g, 34 mmol) is added dropwise. After 90 minutes further stirring triethylaminehydrogen fluoride (20 g, 125 mmol) is added dropwise. After a further hour of stirring bromine (19.9 g, 125 mmol) in dichloromethane (100 ml) is added dropwise. The reaction mixture is stirred for 30 minutes and allowed to warm to 30 C. before adding morpholine (10.9 g, 125 mmol) and finally warming to 0 C. where it is stirred for a further time span of 1 hour. The mixture is carefully poured onto a mixture of ice, water and potassium hydroxide, and the layers are separated. The organic material is washed with water, dried over sodium sulphate and concentrated in vacuo. The crude material is purified by flash chromatography, eluting with a solution of 30% DCM in petroleum ether. Final purification is carried out by repeated re-crystallisation from acetonitrile to afford the desired product.

(55) Scheme for Synthesis Example 5Preparation of N-PQIG-9-GQP-N

(56) ##STR00050##

(57) Steps 5.1 to 5.3 are identical to the respective steps of Synthesis Example 1.

(58) Step 5.4

(59) The intermediate product of Synthesis Example 1, step 1.3 (5.5 g, 15 mmol) and propandithiol (3.6 g, 33 mmol) are added to flask before adding trifluoromethanesulphonic acid (6.8 g, 45 mmol) and starting to stir the mixture. The mixture is heated to 120 C. and the then clear orange mixture is cooled to ambient before being treated with diethyl ether (300 ml). The resultant solution is added to a flask of vigorously stirred diethyl ether (700 ml) pre-cooled to 70 C. Within 30 minutes fine crystals appear in the stirred mixture. The solid is isolated by filtration under vacuum and washed with ether to give a pale yellow powder which is used immediately.

(60) Step 5.5

(61) The intermediate (10.1 g 12 mmol) from the previous step is added to a flask with dichloromethane (50 ml) and then cooled to 70 C. A mixture of 4-cyanophenol (3.5 g, 30 mmol), dichloromethane (40 ml) and triethylamine (3.5 g, 34 mmol) is added dropwise. After 90 minutes further stirring triethylaminehydrogen fluoride (20 g, 125 mmol) is added dropwise. After a further hour of stirring bromine (19.9 g, 125 mmol) in dichloromethane (100 ml) is added dropwise. The reaction mixture is stirred for 30 minutes and allowed to warm to 30 C. before adding morpholine (10.9 g, 125 mmol) and finally warming to 0 C. where it is stirred for a further time span of 1 hour. The mixture is carefully poured onto a mixture of ice, water and potassium hydroxide, and the layers are separated. The organic material is washed with water, dried over sodium sulphate and concentrated in vacuo. The crude material is purified by flash chromatography, eluting with a solution of 30% DCM in petroleum ether. Final purification is carried out by repeated re-crystallisation from acetonitrile to afford the desired product.

(62) Scheme for Synthesis Example 6Preparation of Chiral

(63) ##STR00051##
Step 6.1

(64) ##STR00052##

(65) Methylbutylbiphenyl (44.8 g, 0.2 mol), dichloromethane (250 ml), tetraethyl-ammonium bromide (2.1 g, 10 mmol) and hydrogen bromide (51.6 g, 0.3 mol) are introduced into a reaction flask and cooled to 0 C. Hydrogen peroxide (48.6 g, 0.5 mol) is added with a dosage of 0.1 ml/min.

(66) After the reaction is shown to have completed (by TLC analysis), the reaction is cooled to 0-10 C. and sodium sulfite (17.8 g, 014 mol) as an aqueous solution is added until de-coloration occurs. Thereby, the temperature is maintained at 10 C. The solution turns green. Then the reaction mixture is stirred for 2 hours. Subsequently a 10% sodium carbonate solution is prepared and added. The resultant two phases are separated. The aqueous phase is extracted with 100 ml of dichloromethane and added to the organic phase.

(67) The material is washed with sodium carbonate solution and then water before being concentrated in vacuo.

(68) The residue is then dissolved in 150 ml ethanol and heated for 3 hours under reflux.

(69) The solution is drained and cooled in an ice bath. The resulting crystals are filtered off and dried under ambient atmosphere.

(70) Step 6.2

(71) ##STR00053##

(72) To a stirred solution of the cyano biphenol (25.0 g, 128 mmol) in acetone (625 ml), potassium carbonate (37.5 g, 271 mmol) is added, heated under reflux for 1 hour under a nitrogen atmosphere, and then cooled to ambient temperature. Dibromononane (200 ml, 961 mmol) is then added in a single portion. The reaction mixture is heated again to reflux. After heating under reflux overnight the reaction was cooled and filtered under vacuum, the filter pad washed with dcm, and the filtrate evaporated under reduced pressure to afford the crude material. This was vacuum distilled on Kugelrohr apparatus to remove excess dibromononane affording a solid pale yellow product.

(73) Step 6.3

(74) ##STR00054##

(75) 4-methoxybenzoic acid (10 g, 65.7 mmol), intermediate from step 6.1 (15.7 g, 65.3 mmol), Dicyclohexylcarbodiimide (13.5 g, 65.4 mmol), Dimethylamino pyridine (0.5 g) and Dichloromethane (250 ml) are added to a flask under nitrogen atmosphere stirred at 30 C. overnight. The progress of the reaction procedure is monitored by TLC. When the reaction appears complete, Oxalic acid (5.9 g, 65.7 mmol) is added, then the reaction mixture is filtered using vacuum and the filtrate evaporated to dryness in vacuo. The product is isolated as a white solid.

(76) Step 6.4

(77) ##STR00055##

(78) The ester from step 6.3 (20 g, 53.4 mmol) is dissolved in Dichloromethane (80 ml) and added to a suspension of aluminium chloride (35 g, 262 mmol) in Dichloromethane (80 ml) at a temperature in the range from 0 C. to 5 C. Dimethyl sulphide (21 ml, 284 mmol)) is then added dropwise, while the temperature is maintained below 0 C. and the resulting mixture (brown solution) is stirred overnight.

(79) The reaction is quenched by the addition (which is exothermic) of (saturated) ammonium chloride solution until the resultant mixture is acidic leading to a white solid precipitate, diluted with Dichloromethane and filtered off under vacuum collecting the precipitate.

(80) Step 6.5

(81) ##STR00056##

(82) The intermediate from Step 6.4 (3.5 g, 9.71 mmol), the intermediate from step 5.2 (4.0 g, 9.9 mmol), potassium iodide (1.8 g, 10.9 mmol), potassium carbonate (0.9 g, 6.5 mmol) and dimethylformamide (100 ml) are added to a flask and heated at 100 C. under reflux for 48 hours.

(83) The reaction is cooled, the reaction mixture poured into a mixture of dichloromethane and water, the layers are separated and the organic solution is washed with water, the organics are dried over sodium sulphate, filtered and concentrated in vacuo to yield a yellow solid.

(84) The material is purified by column chromatography, eluting with DCM with increasing amounts of Industrial methylated spirits. The product is re-crystallized from acetone to give the final material.

(85) ##STR00057##

(86) Phase sequence: to be determined.

Compound Examples 7 to 24

(87) The following compounds of formula I are prepared analogously.

(88) ##STR00058##

(89) Phase sequence: K 108.7 (N.sub.2 60 N 86) I.

(90) ##STR00059##

(91) Phase sequence: K 118.6 N 135.8 I.

(92) ##STR00060##

(93) Phase sequence: K 85.1.

(94) ##STR00061##

(95) Phase sequence: K 69.9 I.

(96) ##STR00062##

(97) Phase sequence: K 109.81 I.

(98) ##STR00063##

(99) Phase sequence: K 77.5 I.

(100) The materials in the above table generally showed increased performance in the screening mixtures, as compared to known, rather conventional bimesogenic compounds.

Example 25

General Synthesis Scheme for Compounds of Formula A-II Wherein R21-MG21- and R22-MG22- in Formula A-II are Identical to Each Other

(101) ##STR00064##
Step 25.1: Synthesis of (1)

(102) 1-bromo-3-fluoroiodobenzene (53.3 g, 0.177 mol) is added to a round bottom flask with 3,5-difluorobenzenboronic acid (29.0 g, 0.184 mol). Tetrahydrofuran (500 ml) is added and the mixture is stirred under nitrogen until dissolved. A solution of potassium carbonate (36.7 g, 0.265 mol) in water (100 ml) is added to the reaction. A catalyst, bis(triphenylphosphine)-palladium(II) dichloride (1.98 g, 2.83 mmol) is added and the reaction is heated to reflux for 18 hours. The reaction is cooled and diluted with water before being acidified with dilute Hydrochloric acid. The layers are separated and the organics are washed with water before being concentrated to obtain the product as a brown solid.

(103) The crude solid is dissolved in Dichloromethane and adsorbed onto silica gel (100 g) by concentration. The material is purified by column chromatography, eluting with a mixture of petroleum spirit (40-60 C.) and dichloromethane to obtain a purified product as a yellow solid.

(104) Step 25.2: Synthesis of (2)

(105) 2,-3-5-trifluoro-4-bromobiphenyl (26.1 g, 0.091 mol) is added to a round bottomed flask. Triethylamine (25.0 ml) and tetrahydrofuran (50.0 ml) is added and the whole evacuated and replaced with nitrogen. Copper(I)iodide (0.404 g, 2.12 mmol) and bis(triphenylphosphine)-palladium(II) dichloride (0.71 g, 1.01 mmol) are added, the reaction is evacuated and replaced with nitrogen. The reaction mixture is heated to 40 C. and 1,8-nonadiyne (5.25 g, 0.044 mol) is slowly added over 30 minutes. The mixture is heated for a further 24 hours at 40 C. followed by 48 hours at 80 C.

(106) The reaction mixture is cooled and filtered under vacuum to remove precipitates. The filtrate is acidified with dilute Hydrochloric acid and extracted with diethyl ether. The organic material is washed with water before concentrating to afford the product as a black solid (26.0 g). The crude solid is dissolved in dichloromethane and adsorbed onto 50.0 g silica gel. The material is purified by column chromatography, eluting the product using a mixture of dichloromethane in petrol.

(107) Step 25.3: Synthesis of (3)

(108) The material (2) (21.5 g, 0.040 mol) is dissolved in Tetrahydrofuran (600 ml) and passed through a Thales nano hydrogenator. The material required conditions of 70 bar pressure and 60 C. to produce the product as pale colored solid.

(109) Step 25.4: Synthesis of (4)

(110) Material (3) (21.5 g, 0.04 mol) is added to a round bottom flask with Tetrahydrofuran (150 ml). The reaction is stirred under nitrogen and cooled to 70 C. n-Butyl Lithium solution (1.6 M in hexanes, 55.0 ml, 0.087 mol) is slowly added over 45 minutes, and the reaction stirred for a further hour at 70 C. A solution of Iodine (45.8 g, 00.179 mol) in tetrahydrofuran (125 ml) is slowly added keeping the temperature between 60 and 70 C. The reaction is stirred overnight and allowed to warm to room temperature. The reaction is quenched by slowly adding wet THF before water and then ethyl acetate is added. The layers are separated and the aqueous extracted three times with ethyl acetate. The organics are washed twice with sodium thiosulphate solution (100 ml, 2 M in water) then washed with water. Concentration afforded a brown solid. The material is purified by sequential recrystallisations from Industrial methylated spirits, acetone and acetonitrile/acetone.

(111) Step 25.5: Synthesis of (5)

(112) 4-bromo-2-fluorobenzonitrile (42.4 g, 212 mmol) is added to a round bottom flask along with bis(pinacolato)diborane (59.8 g, 235 mmol). Potassium acetate (31.1 g, 317 mmol), tricyclohexylphosphine (3.57 g, 12.7 mmol), Tris(dibenzylideneacetone)dipalladium(0) (3.66 g, 6.36 mmol) and 1,4-dioxane (600 ml) are all added to the reaction flask and the mixture stirred under nitrogen at 80 C. for 72 hours. After cooling the reaction mixture, water and diethyl ether are added and the layers separated. The organic material is washed with brine and water before concentrating to a brown solid. The product is purified by recrystallisation from petrol/dichloromethane to obtain a brown crystalline solid.

(113) Step 25.6: Synthesis of (6)

(114) Material (4) (10.17 g, 12.8 mmol) and material (5) (7.70 g, 31.2 mmol) are added to a round bottom flask and dissolved in Tetrahydrofuran (250 ml). Bis(triphenylphosphine)-palladium(II) dichloride (450.6 mg, 0.642 mmol) is added along with a solution of sodium carbonate (1 M in water, 77.0 ml, 77.0 mmol). The reaction is heated to 85 C. for 24 hours, after which it is cooled and diluted with water before being acidified with dilute Hydrochloric acid. The layers are separated and the organic layer is washed with water before being concentrated to yield the product as a brown solid. The material is purified by column chromatography, eluting the product with 40% ethyl acetate in petrol. The product is further purified by recrystallisation from, first, acetone/methanol, then acetone and finally IPA/petrol.

Example 26 to 42

(115) The following compounds of formula A-II are prepared analogously:

(116) ##STR00065##

(117) Phase sequence: K 84.1 SmC 105.7 N 122 I.

(118) ##STR00066##

(119) Phase sequence: to be determined.

(120) ##STR00067## ##STR00068## ##STR00069##

Example 43

General Synthesis for Compounds of Formula A-II Wherein R21-MG21- and R22-MG22- in Formula A-II are Different from One Another

(121) ##STR00070##
Step 43.1: Synthesis of (1)

(122) 1-bromo-3-fluoroiodobenzene (27.5 g, 92 mmol) is added to a round bottom flask with tetrahydrofuran (30 ml) and the mixture is stirred under nitrogen until dissolved. Diisopropylamine (30 ml) is added and the reaction placed in an ultrasonic bath for 10 minutes. Catalysts, bis(triphenyl-phosphine)palladium(II) dichloride (0.9 g, 1.28 mmol) and copper(I)iodide (0.2 g, 1.05 mmol) are added and the reaction is cooled in a water bath to 20 C. 1,8-nonadiyne (5.0 g, 41 mmol) is slowly added to the reaction and stirred for a further 20 hours. The reaction is cooled and filtered under vacuum to remove precipitates. The filtrate is acidified with diluted hydrochloric acid and extracted with diethyl ether. The organic material is washed with water before concentrating to afford the product as a black solid (19 g). The material is purified by column chromatography, eluting the product using a mixture of dichloromethane in petrol. This produces the desired product.

(123) Step 43.2: Synthesis of (2)

(124) Material (1) (21.5 g, 40 mmol) is dissolved in tetrahydrofuran (600 ml) and passed through a Thales nano hydrogenator. The material required conditions of 70 bar pressure and 60 C. to produce the product as pale coloured solid.

(125) Step 43.3: Synthesis of (3)

(126) Material (2) (14.35 g, 30.3 mmol), 4-cyanophenylboronic acid (4.45 g, 30.3 mmol), potassium phosphate (25.4 g, 120 mmol), dioxane (57.4 ml) and water (28.7 ml) are sonicated in an ultrasound bath for 30 minutes under a nitrogen atmosphere. The mixture is stirred at room temperature and Pd(DPPF)Cl.sub.2-DCM complex (215 mg) are added. The mixture is heated to 90 C. for 2 hours. The mixture is cooled. The two layers are separated and the solvent from the organic layer removed in vacuo to giv a black oil. This is dissolved in a minimum of DCM and applied to a column of silica eluting with petrol: DCM, 1:1 to give the desired product.

(127) Step 43.4: Synthesis of (4)

(128) Material (3) (3.5 g, 7.05 mmol), 3,4-difluorobenzeneboronic acid (1.7 g, 8 mmol) potassium phosphate (1.7 g, 8 mmol), dioxane (10.6 ml) and water (5.3 ml) are sonicated in an ultrasound bath for 30 minutes under a nitrogen atmosphere. The mixture is stirred at room temperature and Pd(DPPF)Cl.sub.2-DCM complex (59 mg) are added. The mixture is heated to 90 C. for 5 hours. The two layers are separated and the solvent from the organic layer removed in vacuo. This is dissolved in a minimum of DCM and applied to a column of silica, eluting with petrol: DCM, 2:1. The crude product is crystallized twice from DCM/acetonitrile (cooled with dry ice/acetone bath) and the product is dissolved in a minimum of DCM and applied to a column of silica eluting with petrol: DCM, 2:1. The crude product is crystallized from acetonitrile (cooled with dry ice/acetone bath) to give the desired product.

(129) Another object of the invention is the use of bimesogenic compounds of formulae A-I and/or A-II and/or A-III in liquid crystalline media.

(130) Compounds of formula A-II, when added to a nematic liquid crystalline mixture, producing a phase below the nematic. In this context, a first indication of the influence of bimesogenic compounds on nematic liquid crystal mixtures was reported by Barnes, P. J., Douglas, A. G., Heeks, S. K., Luckhurst, G. R., Liquid Crystals, 1993, Vol. 13, No. 4, 603-613. This reference exemplifies highly polar alkyl spacered dimers and perceives a phase below the nematic, concluding it is a type of smectic.

(131) A photo evidence of an existing mesophase below the nematic phase was published by Henderson, P. A., Niemeyer, O., Imrie, C. T. in Liquid Crystals, 2001, Vol. 28, No. 3, 463-472, which was not further investigated.

(132) In Liquid Crystals, 2005, Vol. 32, No. 11-12, 1499-1513 Henderson, P. A., Seddon, J. M. and Imrie, C. T. reported, that the new phase below the nematic belonged in some special examples to a smectic C phase. A additional nematic phase below the first nematic was reported by Panov, V. P., Ngaraj, M., Vij, J. K., Panarin, Y. P., Kohlmeier, A., Tamba, M. G., Lewis, R. A. and Mehl, G. H. in Phys. Rev. Lett. 2010, 105, 1678011-1678014.

(133) In this context, liquid crystal mixtures comprising the new and inventive bimesogenic compounds of formulae A-I and/or A-II and/or A-III show also a novel mesophase that is being assigned as a second nematic phase. This mesophase exists at a lower temperature than the original nematic liquid crystalline phase and has been observed in the unique mixture concepts presented by this application.

(134) Accordingly, the bimesogenic compounds of formula A-II according to the present invention allow the second nematic phase to be induced in nematic mixtures that do not have this phase normally. Furthermore, varying the amounts of compounds of formula A-II allow the phase behaviour of the second nematic to be tailored to the required temperature.

(135) Some preferred embodiments of the mixtures according to the invention are indicated below.

(136) Preferred are compounds of formulae A-I and/or A-II and/or A-III wherein the mesogenic groups MG.sup.11 and MG.sup.12, MG.sup.21 and MG.sup.22 and MG.sup.31 and MG.sup.32 at each occurrence independently from each other comprise one, two or three six-atomic rings, preferably two or three six-atomic rings.

(137) Particularly preferred are the subformulae II-1, II-4, II-6, II-7, II-13, II-14, II-15, II-16, II-17 and II-18.

(138) Especially preferred are the subformulae IIa, IId, IIg, IIh, IIi, IIk and IIo, in particular the subformulae IIa and IIg, wherein L is in each occurrence independently of each other preferably F, Cl, CN, OH, NO.sub.2 or an optionally fluorinated alkyl, alkoxy or alkanoyl group with 1 to 7 C atoms, very preferably F, Cl, CN, OH, NO.sub.2, CH.sub.3, C.sub.2H.sub.5, OCH.sub.3, OC.sub.2H.sub.5, COCH.sub.3, COC.sub.2H.sub.5, COOCH.sub.3, COOC.sub.2H.sub.5, CF.sub.3, OCF.sub.3, OCHF.sub.2, 0C.sub.2F.sub.5, in particular F, Cl, CN, CH.sub.3, C.sub.2H.sub.5, OCH.sub.3, COCH.sub.3 and OCF.sub.3, most preferably F, Cl, CH.sub.3, OCH.sub.3 and COCH.sub.3.

(139) Preferably R.sup.11 and R.sup.12, R.sup.21 and R.sup.22 and R.sup.31 and R.sup.32 in formula I are selected of H, F, Cl, CN, NO.sub.2, OCH.sub.3, COCH.sub.3, COC.sub.2H.sub.5, COOCH.sub.3, COOC.sub.2H.sub.5, CF.sub.3, C.sub.2F.sub.5, OCF.sub.3, OCHF.sub.2, and OC.sub.2F.sub.5, in particular of H, F, Cl, CN, OCH.sub.3 and OCF.sub.3, especially of H, F, CN and OCF.sub.3.

(140) Typical spacer groups (Sp) are for example (CH.sub.2).sub.o, (CH.sub.2CH.sub.2O).sub.pCH.sub.2CH.sub.2, with o being an integer from 5 to 40, in particular from 5 to 25, very preferably from 5 to 15, and p being an integer from 1 to 8, in particular 1, 2, 3 or 4.

(141) Especially media comprise one or more compounds of formula A-I wherein R.sup.11-MG.sup.11- and R.sup.12-MG.sup.12- are identical to each other.

(142) In another preferred embodiment of the present invention the media media comprise one or more to compounds of formula A-I wherein R.sup.11-MG.sup.11- and R.sup.12-MG.sup.12- are different from one another.

(143) Especially media comprise one or more compounds of formula A-II wherein R.sup.21-MG.sup.21- and R.sup.22-MG.sup.22- are identical to each other.

(144) In another preferred embodiment of the present invention the media media comprise one or more to compounds of formula A-II wherein R.sup.21-MG.sup.21- and R.sup.22-MG.sup.22- are different from one another.

(145) Especially media comprise one or more compounds of formula A-III wherein R.sup.31-MG.sup.31-X.sup.31 and R.sup.32-MG.sup.32-X.sup.32 are identical to each other.

(146) In another preferred embodiment of the present invention the media comprise one or more to compounds of formula A-III wherein R.sup.31-MG.sup.31-X.sup.31 and R.sup.32-MG.sup.32-X.sup.32 are different from one another.

(147) Especially preferred are compounds of formula A-III wherein the mesogenic groups MG.sup.31 and MG.sup.32 comprise one, two or three six-atomic rings very preferably are the mesogenic groups selected from formula II as listed below.

(148) For MG.sup.31 and MG.sup.32 in formula A-III are particularly preferred are the subformulae II-1, II-4, II-6, II-7, II-13, II-14, II-15, II-16, II-17 and II-18. In these preferred groups Z in each case independently has one of the meanings of Z.sup.1 as given in formula II. Preferably Z is COO, OCO, CH.sub.2CH.sub.2, CC or a single bond.

(149) Very preferably the mesogenic groups MG.sup.31 and MG.sup.32 are selected from the formulae IIa to IIo and their mirror images.

(150) Particularly preferred for MG.sup.31 and MG.sup.23 are the subformulae IId, IIg, IIh, IIi, IIk and IIo, in particular the subformulae IId and IIk.

(151) In case of compounds with a non-polar group, R.sup.11, R.sup.12, R.sup.21, R.sup.22, R.sup.31 and R.sup.32 are preferably alkyl with up to 15 C atoms or alkoxy with 2 to 15 C atoms.

(152) If In case of compounds with an non-polar group, R.sup.11, R.sup.12, R.sup.21, R.sup.22, R.sup.31 or R.sup.32 is an alkyl or alkoxy radical, i.e. where the terminal CH.sub.2 group is replaced by O, this may be straight-chain or branched. It is preferably straight-chain, has 2, 3, 4, 5, 6, 7 or 8 carbon atoms and accordingly is preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy, or octoxy, furthermore methyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetradecoxy, for example.

(153) Oxaalkyl, i.e. where one CH.sub.2 group is replaced by O, is preferably straight-chain 2-oxapropyl (=methoxymethyl), 2- (=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3-, or 4-oxapentyl, 2-, 3-, 4-, or 5-oxahexyl, 2-, 3-, 4-, 5-, or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl, for example.

(154) Preferred spacer groups are pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, octadecylene, diethyleneoxyethylene, dimethyleneoxybutylene, pentenylene, heptenylene, nonenylene and undecenylene, for example.

(155) Especially preferred are inventive compounds of formula A-I and A-II and A-III wherein Sp.sup.1 respectively Sp.sup.2, respectively Sp.sup.3 is denoting alkylene with 5 to 15 C atoms. Straight-chain alkylene groups are especially preferred.

(156) Particularly preferred media according to the invention comprise at least one or more chiral dopants which themselves do not necessarily have to show a liquid crystalline phase and give good uniform alignment themselves.

(157) The compounds of formula C-II and their synthesis are described in WO 98/00428. Especially preferred is the compound CD-1, as shown in table D below. The compounds of formula C-III and their synthesis are described in GB 2 328 207.

(158) Especially preferred are chiral dopants with a high helical twisting power (HTP), in particular those disclosed in WO 98/00428.

(159) Further typically used chiral dopants are e.g. the commercially available R/S-5011, CD-1, R/S-811 and CB-15 (from Merck KGaA, Darmstadt, Germany).

(160) The above mentioned chiral compounds R/S-5011 and CD-1 and the (other) compounds of formulae C-I, C-II and C-III exhibit a very high helical twisting power (HTP), and are therefore particularly useful for the purpose of the present invention.

(161) The liquid crystalline medium preferably comprises preferably 1 to 5, in particular 1 to 3, very preferably 1 or 2 chiral dopants, preferably selected from the above formula C-II, in particular CD-1, and/or formula C-III and/or R-5011 or S-5011, very preferably the chiral compound is R-5011, S-5011 or CD-1.

(162) The amount of chiral compounds in the liquid crystalline medium is preferably from 1 to 20%, in particular from 1 to 15%, very preferably 1 to 10% by weight of the total mixture.

(163) Further preferred are liquid crystalline media comprising in component B one or more nematogens of formula B-I selected from the from the group of formulae B-I-1 to B-I-, preferably of formula B-I-2 and/or B-I-4, most preferably B-I-4

(164) ##STR00071##
wherein the parameters have the meanings given above and preferably R.sup.B1 is alkyl, alkoxy, alkenyl or alkenyloxy with up to 12 C atoms, and L.sup.B1 and L.sup.B1 are independently H or F, preferably one is H and the other H or F and most preferably both are H.

(165) Further preferred are liquid crystalline media comprising in component B one or more nematogens of formula B-II selected from the from the group of formulae B-II-1 and B-II-2, preferably of formula B-II-2 and/or B-II-4, most preferably of formula B-II-1

(166) ##STR00072##
wherein the parameters have the meanings given above and preferably R.sup.B21 and R.sup.B22 are independently alkyl, alkoxy, alkenyl or alkenyloxy with up to 12 C atoms, more preferably R.sup.B21 is alkyl and R.sup.B22 is alkyl, alkoxy or alkenyl and in formula B-II-1 most preferably alkenyl, in particular vinyl or 1-propenyl, and in formula B-II-2, most preferably alkyl.

(167) Further preferred are liquid crystalline media comprising in component B one or more nematogens of formula B-III, preferably of formula B-III-1

(168) ##STR00073##
wherein the parameters have the meanings given above and preferably R.sup.B31 and R.sup.B32 are independently alkyl, alkoxy, alkenyl or alkenyloxy with up to 12 C atoms, more preferably R.sup.B31 is alkyl and R.sup.B32 is alkyl or alkoxy and most preferably alkoxy, and L.sup.B31 and L.sup.B32 are independently H or F, preferably one is F and the other H or F and most preferably both are F.

(169) The liquid crystal media according to the present invention may contain further additives in usual concentrations. The total concentration of these further constituents is in the range of 0.1% to 10%, preferably 0.1% to 6%, based on the total mixture. The concentrations of the individual compounds used each are preferably in the range of 0.1% to 3%. The concentration of these and of similar additives is not taken into consideration for the values and ranges of the concentrations of the liquid crystal components and compounds of the liquid crystal media in this application. This also holds for the concentration of the dichroic dyes used in the mixtures, which are not counted when the concentrations of the compounds respectively the components of the host medium are specified. The concentration of the respective additives is always given relative to the final doped mixture.

(170) The liquid crystal media according to the present invention consists of several compounds, preferably of 3 to 30, more preferably of 4 to 20 and most preferably of 4 to 16 compounds. These compounds are mixed in conventional way. As a rule, the required amount of the compound used in the smaller amount is dissolved in the compound used in the greater amount. In case the temperature is above the clearing point of the compound used in the higher concentration, it is particularly easy to observe completion of the process of dissolution. It is, however, also possible to prepare the media by other conventional ways, e.g. using so called pre-mixtures, which can be e.g. homologous or eutectic mixtures of compounds or using so called multi-bottle-systems, the constituents of which are ready to use mixtures themselves.

(171) Particularly preferred mixture concepts are indicated below: (the acronyms used are explained in Table A).

(172) The mixtures according to the invention preferably comprise as component A one or more compounds selected from the group of formulae A-I to A-III, preferably one or more compounds of formula A-I and one or more compounds of formula A-II, or one or more compounds of formula A-I and one or more compounds of formula A-III, or one or more compounds of formula A-II and one or more compounds of formula A-III, or, most preferred, one or more compounds of formula A-I and one or more compounds of formula A-II and one or more compounds of formula A-III, preferably in a total concentration of 90% or less, more preferably in the range from 60 to 90%, more preferably from 70 to 90%, and most preferably from 70 to 85% by weight of the total mixture, preferably these compounds are selected from one or more compounds of formula A-I (i.e. ether-linked dimers), preferably in a concentration of 40% or less, more preferably of 30% or less, based on component A, particularly preferred one or more compounds of formula A-I-1 to A-I-3, and especially preferred selected from the group of formulae N-GIGIGI-O-n-O-GGG-N, in particular N-GIGIGI-9-GGG-N, if present, preferably in concentration >5%, in particular from 10 to 30%, based on component A, and/or one or more compounds of formula A-II (i.e. methylene-linked dimers), preferably in a concentration of 60% or less, more preferably of 40% or less, in exceptional cases also 80 to 100% and in these cases preferably 90 to 100%, based on component A, particularly preferred one or more compounds of formula A-II-1 to A-II-4, and especially preferred selected from the group of formulae F-UIZIP-n-PZU-F, preferably FUIZIP-7-PZU-F and/or F-UIZP-9-PZU-F, preferably in concentrations of 5% more, in particular of 10 to 20%, based on component A, and/or one or more compounds of formula A-III (e.g. ester-linked dimers), preferably in a concentration of 80% or less, more preferably of 70% or less, based on component A, particularly preferred one or more compounds of formula A-III-1 to A-III-11, and especially preferred selected from the group of formulae F-PGI-ZI-n-Z-GP-F and F-PGI-ZI-n-Z-GP-F, preferably F-PGI-7-GP-F and/or F-PGI-9-GP-F and/or N-PGI-7-GP-N and/or N-PGI-9-GP-N, preferably in concentrations of 5% or more, in particular of 15 to 30% per compound, based on component A,
and/or as component B one or more compounds selected from the group of formulae B-I to B-III, preferably one or more compounds of formula B-I and one or more compounds of formula B-II, or one or more compounds of formula B-I and one or more compounds of formula B-III, or one or more compounds of formula B-II and one or more compounds of formula B-III, or one or more compounds of formula B-I and one or more compounds of formula B-II and one or more compounds of formula B-III, preferably in a total concentration of 40% or less, preferably in the range from 5 to 40%, more preferably from 10 to 30%, and most preferably from 10 to 20% by weight of the total mixture, preferably these compounds are selected from formulae B-I and/or B-II and/or B-III, and especially preferred selected from the group of formulae PP-n-N, PPP-n-N, CC-n-V, CC-n-V1, CEPGI-n-m, PY-n-Om, CCY-n-Om, CPY-n-Om and PYP-n-(O)m, preferably PP-5-N and/or PPP-3-N and/or CC-3-V and/or CC-4-V and/or CC-5-V and/or CC-3-V1 and/or CC-4-V1 and/or CEPGI-3-2 and/or CEPGI-5-2 and/or PY-3-04, preferably in concentrations of 1% or more, in particular in the range from 2 to 10% per compound, based on the mixture as a whole,
and/or as component C one or more chiral compounds preferably in a total concentration in the range from 1 to 20%, in particular from 1 to 15%, very preferably 1 to 10% by weight of the total mixture, preferably these compounds are selected from formulae C-I, C-I I, and C-III, in particular R-5011 or S-5011 or CD-1, especially preferred they comprise R-5011, S-5011 or CD-1, preferably in a concentration of 1% or more, in particular 1-20%, based on the mixture as a whole particularly preferred between 1 and 3%, in particular 2%, of R-5011 or S-5011 for displays in the ULH mode and 3.5 to 5.5%, in particular 4.5%, of R-5011 or S-5011 for displays in the USH mode, or a another chiral material in a concentration leading to the same cholesteric pitch as R-5011 or S-5011 in the preferred concentrations mentioned.

(173) Further preferred conditions for the mesogenic media are the following. They are fulfilled independently from one another and from the conditions mentioned above. Preferably, however, two, three four or more of these conditions and of the conditions mentioned above are fulfilled simultaneously.

(174) The media preferably comprise 40% or more, preferably 60% or more, based on component B, of bimesogens comprising exactly two rings in each of their mesogenic groups.

(175) The media preferably comprise one or more bimesogens comprising exactly three rings in each of their mesogenic groups and/or one or more bimesogens comprising exactly two rings in one of their mesogenic groups and comprising exactly three rings in their other mesogenic group.

(176) The media preferably comprise one or more non-symmetrical bimesogens, preferably in a total concentration of 50% or more, based on component A, preferably based on the mixture as a whole.

(177) A further, especially preferred condition is that the mixture has a low absolute value of , but preferably is dielectrically positive, especially at the temperatures between T(N,I) and 0.8 T(N,I). Preferably preferably is dielectrically positive at the temperatures from T(N,I) to the temperatures at which the ULH texture is still stable, preferably at least down to 40 C. Preferably the value of at these temperatures is 3 or less, more preferably in the range from 0 or more to 2 or less. In this respect it is not very important, if the value of becomes negative at lower temperatures, then it preferably is the in the range from between 1 or more to 0 or less.

(178) The bimesogenic compounds of formulae A-I, A-II and A-III and the liquid crystalline media comprising them can be used in liquid crystal displays, such as STN, TN, AMD-TN, temperature compensation, guest-host, phase change or surface stabilized or polymer stabilized cholesteric texture (SSCT, PSCT) displays, in particular in flexoelectric devices, in active and passive optical elements like polarizers, compensators, reflectors, alignment layers, color filters or holographic elements, in adhesives, synthetic resins with anisotropic mechanical properties, cosmetics, diagnostics, liquid crystal pigments, for decorative and security applications, in nonlinear optics, optical information storage or as chiral dopants.

(179) The compounds of formulae A-I and/or A-II and/or A-III and the mixtures obtainable thereof are particularly useful for flexoelectric liquid crystal display. Thus, another object of the present invention is a flexoelectric display comprising one or more compounds of formulae A-I and/or A-II and/or A-III, or comprising a liquid crystal medium comprising one or more compounds of formulae A-I and/or A-II and/or A-III.

(180) The inventive mesogenic mixtures comprising compounds of formulae A-I and/or A-II and/or A-III can be aligned in their cholesteric phase into different states of orientation by methods that are known to the expert, such as surface treatment or electric fields. For example, they can be aligned into the planar (Grandjean) state, into the focal conic state or into the homeotropic state. Inventive compounds of formula I comprising polar groups with a strong dipole moment can further be subjected to flexoelectric switching, and can thus be used in electrooptical switches or liquid crystal displays.

(181) The switching between different states of orientation according to a preferred embodiment of the present invention is exemplarily described below in detail for a sample of an inventive mixture comprising compounds of formulae A-I and/or A-II and/or A-III.

(182) The total concentration of all compounds in the media according to this application is 100%.

(183) According to this preferred embodiment, the sample is placed into a cell comprising two plane-parallel glass plates coated with electrode layers, e.g. ITO layers, and aligned in its cholesteric phase into a planar state wherein the axis of the cholesteric helix is oriented normal to the cell walls. This state is also known as Grandjean state, and the texture of the sample, which is observable e.g. in a polarization microscope, as Grandjean texture. Planar alignment can be achieved e.g. by surface treatment of the cell walls, for example by rubbing and/or coating with an alignment layer such as polyimide.

(184) A Grandjean state with a high quality of alignment and only few defects can further be achieved by heating the sample to the isotropic phase, subsequently cooling to the chiral nematic phase at a temperature close to the chiral nematic-isotropic phase transition, and rubbing the cell.

(185) In the planar state, the sample shows selective reflection of incident light, with the central wavelength of reflection depending on the helical pitch and the mean refractive index of the material.

(186) When an electric field is applied to the electrodes, for example with a frequency from 10 Hz to 1 kHz, and an amplitude of up to 12 V.sub.rms/m, the sample is being switched into a homeotropic state where the helix is unwound and the molecules are oriented parallel to the field, i.e. normal to the plane of the electrodes. In the homeotropic state, the sample is transmissive when viewed in normal daylight, and appears black when being put between crossed polarizers.

(187) Upon reduction or removal of the electric field in the homeotropic state, the sample adopts a focal conic texture, where the molecules exhibit a helically twisted structure with the helical axis being oriented perpendicular to the field, i.e. parallel to the plane of the electrodes. A focal conic state can also be achieved by applying only a weak electric field to a sample in its planar state. In the focal conic state the sample is scattering when viewed in normal daylight and appears bright between crossed polarizers.

(188) A sample of an inventive compound in the different states of orientation exhibits different transmission of light. Therefore, the respective state of orientation, as well as its quality of alignment, can be controlled by measuring the light transmission of the sample depending on the strength of the applied electric field. Thereby it is also possible to determine the electric field strength required to achieve specific states of orientation and transitions between these different states.

(189) In a sample of an inventive compound of formula I, the above described focal conic state consists of many disordered birefringent small domains. By applying an electric field greater than the field for nucleation of the focal conic texture, preferably with additional shearing of the cell, a uniformly aligned texture is achieved where the helical axis is parallel to the plane of the electrodes in large, well-aligned areas. In accordance with the literature on state of the art chiral nematic materials, such as P. Rudquist et al., Liq. Cryst. 23 (4), 503 (1997), this texture is also called uniformly-lying helix (ULH) texture. This texture is required to characterize the flexoelectric properties of the inventive compound.

(190) The sequence of textures typically observed in a sample of an inventive compound of formula I on a rubbed polyimide substrate upon increasing or decreasing electric field is given below:

(191) ##STR00074##

(192) Starting from the ULH texture, the inventive flexoelectric compounds and mixtures can be subjected to flexoelectric switching by application of an electric field. This causes rotation of the optic axis of the material in the plane of the cell substrates, which leads to a change in transmission when placing the material between crossed polarizers. The flexoelectric switching of inventive materials is further described in detail in the introduction above and in the examples.

(193) It is also possible to obtain the ULH texture, starting from the focal conic texture, by applying an electric field with a high frequency, of for example 10 kHz, to the sample whilst cooling slowly from the isotropic phase into the cholesteric phase and shearing the cell. The field frequency may differ for different compounds.

(194) The bimesogenic compounds of formula I are particularly useful in flexoelectric liquid crystal displays as they can easily be aligned into macroscopically uniform orientation, and lead to high values of the elastic constant k.sub.11 and a high flexoelectric coefficient e in the liquid crystal medium.

(195) The liquid crystal medium preferably exhibits a k.sub.11<110.sup.10 N, preferably <210.sup.11 N and a flexoelectric coefficient e>110.sup.11 C/m, preferably >110.sup.10 C/m.

(196) Apart from the use in flexoelectric devices, the inventive bimesogenic compounds as well as mixtures thereof are also suitable for other types of displays and other optical and electrooptical applications, such as optical compensation or polarizing films, color filters, reflective cholesterics, optical rotatory power and optical information storage.

(197) A further aspect of the present invention relates to a display cell wherein the cell walls exhibit hybrid alignment conditions. The term hybrid alignment or orientation of a liquid crystal or mesogenic material in a display cell or between two substrates means that the mesogenic groups adjacent to the first cell wall or on the first substrate exhibit homeotropic orientation and the mesogenic groups adjacent to the second cell wall or on the second substrate exhibit planar orientation.

(198) The term homeotropic alignment or orientation of a liquid crystal or mesogenic material in a display cell or on a substrate means that the mesogenic groups in the liquid crystal or mesogenic material are oriented substantially perpendicular to the plane of the cell or substrate, respectively.

(199) The term planar alignment or orientation of a liquid crystal or mesogenic material in a display cell or on a substrate means that the mesogenic groups in the liquid crystal or mesogenic material are oriented substantially parallel to the plane of the cell or substrate, respectively.

(200) A flexoelectric display according to a preferred embodiment of the present invention comprises two plane parallel substrates, preferably glass plates covered with a transparent conductive layer such as indium tin oxide (ITO) on their inner surfaces, and a flexoelectric liquid crystalline medium provided between the substrates, characterized in that one of the inner substrate surfaces exhibits homeotropic alignment conditions and the opposite inner substrate surface exhibits planar alignment conditions for the liquid crystalline medium.

(201) Planar alignment can be achieved e.g. by means of an alignment layer, for example a layer of rubbed polyimide or sputtered SiO.sub.x, that is applied on top of the substrate.

(202) Alternatively it is possible to directly rub the substrate, i.e. without applying an additional alignment layer. For example, rubbing can be achieved by means of a rubbing cloth, such as a velvet cloth, or with a flat bar coated with a rubbing cloth. In a preferred embodiment of the present invention rubbing is achieved by means of a at least one rubbing roller, like e.g. a fast spinning roller that is brushing across the substrate, or by putting the substrate between at least two rollers, wherein in each case at least one of the rollers is optionally covered with a rubbing cloth. In another preferred embodiment of the present invention rubbing is achieved by wrapping the substrate at least partially at a defined angle around a roller that is preferably coated with a rubbing cloth.

(203) Homeotropic alignment can be achieved e.g. by means of an alignment layer coated on top of the substrate. Suitable aligning agents used on glass substrates are for example alkyltrichlorosilane or lecithine, whereas for plastic substrate thin layers of lecithine, silica or high tilt polyimide orientation films as aligning agents may be used. In a preferred embodiment of the invention silica coated plastic film is used as a substrate.

(204) Further suitable methods to achieve planar or homeotropic alignment are described for example in J. Cognard, Mol. Cryst. Liq. Cryst. 78, Supplement 1, 1-77 (1981).

(205) By using a display cell with hybrid alignment conditions, a very high switching angle of flexoelectric switching, fast response times and a good contrast can be achieved.

(206) The flexoelectric display according to present invention may also comprise plastic substrates instead of glass substrates. Plastic film substrates are particularly suitable for rubbing treatment by rubbing rollers as described above.

(207) Another object of the present invention is that compounds of formula I, when added to a nematic liquid crystalline mixture, produce a phase below the nematic.

(208) Accordingly, the bimesogenic compounds of formula I according to the present invention allow the second nematic phase to be induced in nematic mixtures that do not show evidence of this phase normally. Furthermore, varying the amounts of compounds of formula I allow the phase behaviour of the second nematic to be tailored to the required temperature.

(209) Examples for this are given and the mixtures obtainable thereof are particularly useful for flexoelectric liquid crystal display. Thus, another object of the present invention is liquid crystal media comprising one or more compounds of formula I exhibiting a second nematic phase.

(210) Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following examples are, therefore, to be construed as merely illustrative and not limitative of the remainder of the disclosure in any way whatsoever.

(211) Unless the context clearly indicates otherwise, as used herein plural forms of the terms herein are to be construed as including the singular form and vice versa.

(212) Throughout the description and claims of this specification, the words comprise and contain and variations of the words, for example comprising and comprises, mean including but not limited to, and are not intended to (and do not) exclude other components.

(213) Throughout the present application it is to be understood that the angles of the bonds at a C atom being bound to three adjacent atoms, e.g. in a CC or CO double bond or e.g. in a benzene ring, are 120 and that the angles of the bonds at a C atom being bound to two adjacent atoms, e.g. in a CC or in a CN triple bond or in an allylic position CCC are 180, unless these angles are otherwise restricted, e.g. like being part of small rings, like 3-, 5- or 5-atomic rings, notwithstanding that in some instances in some structural formulae these angles are not represented exactly.

(214) It will be appreciated that variations to the foregoing embodiments of the invention can be made while still falling within the scope of the invention. Each feature disclosed in this specification, unless stated otherwise, may be replaced by alternative features serving the same, equivalent or similar purpose. Thus, unless stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

(215) All of the features disclosed in this specification may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. In particular, the preferred features of the invention are applicable to all aspects of the invention and may be used in any combination. Likewise, features described in non-essential combinations may be used separately (not in combination).

(216) In the foregoing and in the following examples, unless otherwise indicated, all temperatures are set forth uncorrected in degrees Celsius and all parts and percentages are by weight.

(217) The following abbreviations are used to illustrate the liquid crystalline phase behavior of the compounds: K=crystalline; N=nematic; N2=second nematic; S=smectic; Ch=cholesteric; I=isotropic; Tg=glass transition. The numbers between the symbols indicate the phase transition temperatures in C.

(218) In the present application and especially in the following examples, the structures of the liquid crystal compounds are represented by abbreviations, which are also called acronyms. The transformation of the abbreviations into the corresponding structures is straight forward according to the following three tables A to C.

(219) All groups C.sub.nH.sub.2n+1, C.sub.mH.sub.2m+1, and C.sub.lH2.sub.l+1 are preferably straight chain alkyl groups with n, m and l C-atoms, respectively, all groups C.sub.nH.sub.2n, C.sub.mH.sub.2m and C.sub.lH.sub.2l are preferably (CH.sub.2).sub.n, (CH.sub.2).sub.m and (CH.sub.2).sub.l, respectively and CHCH preferably is trans-respectively E vinylene.

(220) Table A lists the symbols used for the ring elements, table B those for the linking groups and table C those for the symbols for the left hand and the right hand end groups of the molecules.

(221) Table D lists exemplary molecular structures together with their respective codes.

(222) TABLE-US-00002 TABLE A Ring Elements C P D DI A AI 0 G GI G(Cl) GI(Cl) G(1) GI(1) U UI Y M 0 MI N NI np n3f n3fl th thl th2f th2fl 00 o2f 01 o2fl 02 dh 03 K 04 KI 05 L 06 LI 07 F 08 FI 09

(223) TABLE-US-00003 TABLE B Linking Groups n (CH.sub.2).sub.n n is an integer except 0 and 2 E CH.sub.2CH.sub.2 V CHCH T CC W CF.sub.2CF.sub.2 B CFCF Z COO ZI OCO X CFCH XI CHCF O CH.sub.2O OI OCH.sub.2 Q CF.sub.2O QI OCF.sub.2

(224) TABLE-US-00004 TABLE C End Groups Left hand side, used alone or Right hand side, used alone or in combination with others in combination with others -n- C.sub.nH.sub.2n+1 -n C.sub.nH.sub.2n+1 -nO- C.sub.nH.sub.2n+1O -On OC.sub.nH.sub.2n+1 -V- CH.sub.2CH -V CHCH.sub.2 -nV- C.sub.nH.sub.2n+1CHCH -nV C.sub.nH.sub.2nCHCH.sub.2 -Vn- CH.sub.2CHC.sub.nH.sub.2n -Vn CHCHC.sub.nH.sub.2n+1 -nVm- C.sub.nH.sub.2n+1CHCHC.sub.mH.sub.2m -nVm C.sub.nH.sub.2nCHCHC.sub.mH.sub.2m+1 -N- NC -N CN -S- SCN -S NCS -F- F -F F -CL- Cl -CL Cl -M- CFH.sub.2 -M CFH.sub.2 -D- CF.sub.2H -D CF.sub.2H -T- CF.sub.3 -T CF.sub.3 -MO- CFH.sub.2O -OM OCFH.sub.2 -DO- CF.sub.2HO -OD OCF.sub.2H -TO- CF.sub.3O -OT OCF.sub.3 -A- HCC -A CCH -nA- C.sub.nH.sub.2n+1CC -An CCC.sub.nH.sub.2n+1 -NA- NCCC -AN CCCN Left hand side, used in Right hand side, used in combination with others only combination with others only -...n...- C.sub.nH.sub.2n -...n... C.sub.nH.sub.2n -...M...- CFH -...M... CFH -...D...- CF.sub.2 -...D... CF.sub.2 -...V...- CHCH -...V... CHCH -...Z...- COO -...Z... COO -...ZI...- OCO -...ZI... OCO -...K...- CO -...K... CO -...W...- CFCF -...W... CFCF
wherein n and m each are integers and three points . . . indicate a space for other symbols of this table.

(225) Preferably the liquid crystalline media according to the present invention comprise, besides the compound(s) of formula I one or more compounds selected from the group of compounds of the formulae of the following table.

(226) TABLE-US-00005 TABLE D 0 F-PGI-O-n-O-GP-F F-PG-O-n-O-GIP-F N-PP-O-n-O-GU-F F-PGI-O-n-O-PP-N R-5011 respectively S-5011 CD-1 PP-n-N PPP-n-N CC-n-V CPP-n-m 0 CEPGI-n-m CPPC-n-m PY-n-Om CCY-n-Om CPY-n-Om PPY-n-Om F-UIGI-ZI-n-Z-GU-F N-PGI-ZI-n-Z-GP-N F-PGI-ZI-n-Z-GP-F N-GIGIGI-n-GGG-N 0 N-PGIUI-n-UGP-N N-GIUIGI-n-GUG-N N-GIUIP-n-PUG-N N-PGI-n-GP-N N-PUI-n-UP-N N-UIUI-n-UU-N N-GIGI-n-GG-N F-UIGI-n-GU-F UIP-n-PU N-PGI-n-GP-N 0 N-PGI-ZI-n-Z-GP-N F-PGI-ZI-n-Z-GP-F F-UIGI-ZI-n-Z-GU-F F-PGI-ZI-n-Z-PP-N F-PGI-ZI-n-Z-PUU-N F-PGI-ZI-n-Z-GUU-N N-GIGI-n-GG-N N-PUI-n-UP-N N-PUI-n-UP-N F-UIP-ZI-n-Z-PZU-F

MIXTURE EXAMPLES

Mixture Example 1

Mixture M1

(227) TABLE-US-00006 Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2 F-PGI-ZI-7-Z-PP-N 29.0 3 F-PGI-ZI-9-Z-PUU-N 29.0 4 N-PGI-ZI-7-Z-GP-N 15.0 5 F-UIZIP-7-PZU-F 15.0 6 CC-3-V 5.0 7 PPP-3-N 5.0 100.0

(228) This mixture is particularly well suitable for the ULH-mode. It is investigated in antiparallel rubbed cells with polyimide orientation layers (e.g. AL3046) of appropriate cell gap, typically of 5.4 m.

(229) It has a range of the (chiral) nematic phase from 20 C. to 90 C. The cholesteric pitch (P) is 300 nm and the flexoelectric ratio (e/K) is 3.6 V.sup.1, both determined at a temperature of 35 C. The electric field has been varied from 0 V/m) to about 3.0 V/m), leading to a tilt angle () increasing from 0 to about 27.5 over that range of electric fields.

(230) It has a double response time for switching on (T.sub.on) of about 1 ms at an electric field of 3.0 V/m and of about 0.5 ms at an electric field of 3.5 V/m. I.e. the sum of the response times (.sub.on,driven+.sub.off,driven) is below 1 ms at electrical fields of 3.0 V/m and more. The sum of the response times for switching off by relaxation only (.sub.on,driven+.sub.off,driven) is below 5 ms at electrical fields of 3.0 V/m and more. Here the double of the response time for switching on (.sub.on) is the decisive feature for several applications, as the mixture can be actively switched on as well as off.

(231) The transmission under crossed polarizers of this mixture relative to an empty cell (for reference of 100%) has a maximum value switched at an electric field of 3.0 V/m with 60%. At an electric field of 3.5 V/m the relative transmission of this mixture is about 58%. Probably the maximum the transmission is limited by the insufficient alignment of the helix: some of the ULH is at an undesired angle to the direction required.

Mixture Example 2 and Comparative Mixture Example 2

Comparative Mixture Example 2

Mixture C2

(232) TABLE-US-00007 Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2 F-PGI-ZI-7-Z-PP-N 29.6 3 F-PGI-ZI-9-Z-PP-N 19.4 4 F-UIGI-ZI-9-Z-GP-N 31.6 5 F-PGI-ZI-9-Z-PUU-N 17.4 100.0

(233) This comparative mixture is investigated as described under mixture example 1.

(234) It has a range of the (chiral) nematic phase from below 20 C. to 97 C. The cholesteric pitch (P) is 310 nm and the flexoelectric ratio (e/K) is 4.41 V.sup.1, both determined at a temperature of 35 C. The total response time for switching driven both on and off (.sub.on,driven+.sub.off,driven) is 3.9 ms at an electric field of 3.33 V/m.

Mixture Example 2

Mixture M2

(235) 10% of the following mixture (mixture N1),

(236) TABLE-US-00008 Composition Compound No. Abbreviation Conc./% 1 PY-3-O2 14.5 2 CCY-3-O2 3.5 3 CCY-4-O2 13.5 4 CPY-2-O2 11.0 5 CPY-3-O2 11.0 6 CC-3-V 29.0 7 CPP-3-2 13.5 5 CPPC-3-3 4.0 100.0
which has the following physical properties: T.sub.N,I=103.6 C; n=0.124 @25 C; =2.8 @25 C; and .sub.1=114 mPa.Math.s,

(237) are added to 90% of the mixture C2 of the respective comparative example.

(238) The resultant mixture (M2) is investigated as described under mixture example 1. It has a range of the (chiral) nematic phase from 2 C. to 102 C. The cholesteric pitch (P) is 363 nm and the flexoelectric ratio (e/K) is 3.21 V.sup.1, both determined at a temperature of 35 C. The total response time (.sub.on,driven+.sub.off,driven) is 2 ms and the total response time (.sub.on,driven+.sub.off,driven) is 6 ms (.sub.on,driven=1 ms and .sub.off,driven=5.2 ms), all at an electric field of 3.33 V/m.

Mixture Example 3 and Comparative Mixture Example 3

Comparative Mixture Example 3

Mixture C3

(239) TABLE-US-00009 Composition Compound No. Abbreviation Conc./% 1 R-5011 1.8 2 N-GIGI-ZI-9-Z-GG-N 8.5 3 N-PGI-ZI-9-Z-GP-N 8.5 4 F-PGI-ZI-9-Z-GP-F 16.8 5 F-UIGI-ZI-9-Z-GP-N 22.6 6 F-PGI-ZI-9-Z-PUU-N 8.4 7 N-GIGI-9-GG-N 25.1 8 N-UIUI-9-UU-N 8.4 100.0

(240) This comparative mixture is investigated as described under mixture examples 1 and 2.

(241) It has a clearing point from the (chiral) nematic phase of 64 C. The cholesteric pitch (P) is 348 nm and the flexoelectric ratio (e/K) is 5.2 V.sup.1, both determined at a temperature of 35 C. The total response time (.sub.on,driven+.sub.off,driven) is 8.4 ms at an electric field of 3.33 V/m.

Mixture Example 3

Mixture M3

(242) 10% of the following binary mixture (mixture N2),

(243) TABLE-US-00010 Composition Compound No. Abbreviation Conc./% 1 PP-5-N 50.0 2 PPP-5-N 50.0 100.0
are added to 90% of the mixture C3 of the respective comparative example.

(244) The resultant mixture (M3) is investigated as described under mixture examples 1 and 2. It has a clearing point from the (chiral) nematic phase of 70 C. The cholesteric pitch (P) is 283 nm and the flexoelectric ratio (e/K) is 3.7 V.sup.1, both determined at a temperature of 35 C. The total response time (.sub.on,driven+.sub.off,driven) is 5.5 m sat an electric field of 3.33 V/m.

Mixture Example 4

Mixture M4

(245) TABLE-US-00011 Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2 N-PGI-ZI-9-Z-PUU-N 25.0 3 N-PGI-ZI-7-Z-GP-N 9.0 4 N-PGI-ZI-9-Z-GP-N 15.0 5 F-GIP-ZI-9-Z-PG-F 10.0 6 F-UIGI-ZI-9-Z-GP-N 15.0 7 TO-GIGI-ZI-9-Z-GP-N 9.0 8 CC-3-V 7.5 9 PYP-2-3 7.5 100.0

(246) This mixture is investigated as described under mixture example 1.

Mixture Example 5

Mixture M5

(247) TABLE-US-00012 Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2 F-PGI-O-9-O-GP-F 16.0 3 F-PG-O-9-O-PP-N 21.4 4 F-PI-ZI-7-Z-PP-N 12.7 5 F-PI-ZI-9-Z-PP-N 10.4 6 N-GIGI-ZI-9-Z-GG-N 8.0 7 F-UIGI-ZI-9-Z-GP-N 9.5 8 CP-3-N 1.4 9 CY-3-O2 1.3 10 PGIGI3-F 2.0 11 CP-3-O1 2.2 12 PTP-1-O2 0.7 13 CCG-V-F 1.0 14 PPTUI-3-2 4.0 15 PPTUI-3-4 7.4 100.0

(248) This mixture is investigated as described under mixture example 1.

Mixture Example 6

Mixture M6

(249) TABLE-US-00013 Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2 N-PGI-ZI-9-Z-PUU-N 25.0 3 N-PGI-ZI-9-Z-GP-N 15.0 4 N-PGI-ZI-7-Z-GP-N 9.0 5 F-GIP-ZI-9-Z-PG-F 10.0 6 F-UIGI-ZI-9-Z-GP-N 15.0 7 TO-GIGI-ZI-9-Z-GP-N 9.0 8 CC-3-V 5.0 9 PYP-2-3 5.0 100.0

(250) This mixture is investigated as described under mixture example 1.

BRIEF DESCRIPTION OF DRAWINGS

(251) FIG. 1: Schematic illustration of the 2mode

(252) FIG. 2: Schematic illustration of the mode