BIMESOGENIC COMPOUNDS AND MESOGENIC MEDIA

Abstract

The invention relates to bimesogenic compounds of formula I

##STR00001##

wherein R.sup.11, R.sup.12, MG.sup.11, MG.sup.12, X.sup.11, X.sup.12 and Sp.sup.1 have the meaning given in claim 1, to the use of bimesogenic compounds of formula I in liquid crystal media and particular to flexoelectric liquid crystal devices comprising a liquid crystal medium according to the present invention.

Claims

1. Bimesogenic compounds of formula I ##STR00167## R.sup.11 and R.sup.12 are each independently H, F, Cl, CN, NCS or a straight-chain or branched alkyl group with 1 to 25 C atoms, which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH.sub.2 groups to be replaced, in each occurrence independently from one another, by —O—, —S—, —NH—, —N(CH.sub.3)—, —CO—, —COO—, —OCO—, —O—CO—O—, —S—CO—, —CO—S—, —CH═CH—, —CH═CF—, —CF═CF— or —C≡C— in such a manner that oxygen atoms are not linked directly to one another, preferably F, Cl, CN, a straight-chain or branched alkyl group with 1 to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN more preferably a polar group, most preferably F, Cl, CN, OCF.sub.3, CF.sub.3, and at least one of R.sup.11 and R.sup.12 is an alkenyl group or an alkinyl group either straight-chain or branched, with 2 to 25 C atoms, preferably with 2 to 7 C atoms, which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH.sub.2 groups to be replaced, in each occurrence independently from one another, by —O—, —S—, —NH—, —N(CH.sub.3)—, —CO—, —COO—, —OCO—, —O—CO—O—, —S—, CO—, —CO—S—, —CH═CH—, —CH═CF—, —CF═CF— or —C≡C— in such a manner that oxygen atoms are not linked directly to one another, MG.sup.11 and MG.sup.12 are each independently a mesogenic group, at least one of MG.sup.11 and MG.sup.12 comprises one, two or more 5-atomic and/or 6-atomic rings, in case of comprising two or more 5- and/or 6-atomic rings at least two of these may be linked by a 2-atomic linking group, preferably selected from the group of linking groups —CO—O—, —O—CO—, —CH.sub.2—O—, —O—CH.sub.2—, —CF.sub.2—O— and —O—CF.sub.2—, Sp.sup.1 is a spacer group comprising 1, 3 or 5 to 40 C atoms, wherein one or more non-adjacent and non-terminal CH.sub.2 groups may also be replaced by —O—, —S—, —NH—, —N(CH.sub.3)—, —CO—, —O—CO—, —S—CO—, —O—COO—, —CO—S—, —CO—O—, —CH(halogen)-, —CH(CN)—, —CH═CH— or —C≡C—, however in such a way that no two O-atoms are adjacent to one another, now two —CH═CH— groups are adjacent to each other and no two groups selected from —O—CO—, —S—CO—, —O—COO—, —CO—S—, —CO—O— and —CH═CH— are adjacent to each other, preferably —CH.sub.2).sub.n— (i.e. 1,n-alkylene with n C atoms), with n an integer, preferably from 3 to 19, more preferably from 3 to 11, most preferably an odd integer (i.e. 3, 5, 7, 9 or 11), X.sup.11 and X.sup.12 are independently from one another a linking group selected from —CO—O—, —O—CO—, —O—, —CH═CH—, —C═C—, —CF.sub.2—O—, —O—CF.sub.2—, —CF.sub.2—CF.sub.2, —CH.sub.2—O—, —O—CH.sub.2—, —CO—S—, —S—CO—, —CS—S—, —S—, and a single bond, preferably —CO—O—, —O—CO— or a single bond, most preferably a single bond, however under the condition that in —X.sup.l—Sp-X.sup.12— no two O atoms are adjacent to one another, no two —CH═CH— groups are adjacent to each other and no two groups selected from —O—CO—, —S—CO—, —O—COO—, —CO—S—, —CO—O— and —CH═CH— are adjacent to each other.

2. Bimesogenic compounds according to claim 1, characterized in that R.sup.11 is an alkenyl group.

3. Bimesogenic compounds according to claim 1, characterized in that R.sup.11 is an alkinyl group.

4. Bimesogenic compounds according to claim 1, characterized in that R.sup.12 is an alkenyl group.

5. Bimesogenic compounds according to claim 1, characterized in that R.sup.12 is an alkinyl group.

6. Bimesogenic compounds according to claim 1, characterized in that R.sup.12 is selected from OCF.sub.3, CF.sub.3, F, Cl and CN.

7. Bimesogenic compounds according to claim 1, characterized in that Sp.sup.1 is —(CH.sub.2).sub.o— and o is 1, 3 or an integer from 5 to 15.

8. (canceled)

9. Liquid-crystalline medium, characterised in that it comprises one or more bimesogenic compounds according to claim 1.

10. Liquid-crystalline medium according to claim 9, characterised in that it additionally comprises one or more compounds selected from the group of the compounds of the formulae III
R.sup.31-MG.sup.31-X.sup.31—Sp.sup.3—X.sup.32-MG-R.sup.32  III wherein 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 may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH.sub.2 groups to be replaced, in each case independently from one another, by —O—, —S—, —NH—, —N(CH.sub.3)—, —CO—, —COO—, —OCO—, —O—CO—O—, —S—CO—, —CO—S—, —CH═CH—, —CH═CF—, —CF═CF— or —C≡C— in such a manner that oxygen atoms are not linked directly to one another, MG.sup.31 and MG.sup.32 are each independently a mesogenic group, Sp.sup.3 is a spacer group comprising 5 to 40 C atoms, wherein one or more non-adjacent CH.sub.2 groups may also be replaced by —O—, —S—, —NH—, —N(CH.sub.3)—, —CO—, —O—CO—, —S—CO—, —O—COO—, —CO—S—, —CO—O—, —CH(halogen)-, —CH(CN)—, —CH═CH— or —C≡C—, and X.sup.31 and X.sup.32 are each independently —O—, —S—, —CO—, —COO—, —OCO—, —O—CO—O—, —CO—NH—, —NH—CO—, —CH.sub.2CH.sub.2—, —OCH.sub.2—, —CH.sub.2O—, —SCH.sub.2—, —CH.sub.2S—, —CH═CH—, —CH═CH—COO—, —OCO—CH═CH—, —C≡C— or a single bond, and with the condition that compounds of formula I are excluded.

11. (canceled)

12. Liquid crystal device comprising a liquid crystalline medium comprising two or more components, one or more of which is a bimesogenic compound of formula I according to claim 1.

13. Liquid crystal device according to claim 12, characterized in that it is a flexoelectric device.

14. Preparation of a liquid crystal medium according to claim 9, by blending one or more compounds of formula I, one or more chiral dopants and one or more bimesogenic compounds.

Description

COMPOUND AND SYNTHESIS EXAMPLES

Synthesis Example 1: Preparation of 6-(2,3′,4′-Trifluoro-biphenyl-4-yl)-hexanoic acid 4′-prop-1-ynyl-biphenyl-4-yl ester

[0237] ##STR00137##

[0238] The compound of interest is prepared according to the following scheme.

##STR00138##

[0239] Stage 1.1

##STR00139##

[0240] 1-Bromo-4-iodo-benzene (30.00 g; 106.04 mmol) is dissolved in diisopropylamine (14.86 mL; 106.04 mmol), then the catalysts bis(triphenylphosphine-palladium(II) chloride (Pd(dppf)Cl.sub.2, 1.41 g; 2.01 mmol) and copper(I) iodide (0.19 g; 1.01 mmol) are added. The reaction mixture is cooled to −10° C. At this temperature the propyne, (ca. 3% in heptane) (200.00 g; 149.74 mmol) is slowly added. The mixture is stirred for 16 hours at ambient temperature (also called room temperature, short RT), which is 20° C. in this application, unless explicitly specified otherwise. The insoluble solid is filtered off. The mixture is extracted with ethyl acetate. The organic phase is washed with water and dried over magnesium sulphate. The crude product is purified by column chromatography over silica gel using petroleum ether as an eluent. The product is obtained as a white solid.

[0241] Stage 1.2

##STR00140##

[0242] 1-Bromo-4-prop-1-ynyl-benzene (4.00 g; 20.51 mmol), (4-hydroxy-phenyl)boronic acid (2.83 g; 20.51 mmol), water (20.00 mL), potassium carbonate (4.25 g; 30.76 mmol) and tetrahydrofuran (200.00 mL) are added into a flask. The reaction mixture is purged with nitrogen before the addition of bis(diphenylphosphine)palladium(II) chloride (0.23 g; 0.33 mmol). The reaction mixture is then stirred at 60° C. for 16 hours. Subsequently the mixture is cooled and acidified with dilute hydrochloric acid. The reaction mixture is extracted with ethyl acetate (3×100 mL). The combined organic phases are dried over magnesium sulphate and the solvent is evaporated. The crude product is purified by column chromatography over silica gel using petroleum ether:ethyl acetate (10:1). This yields the product as a beige coloured solid.

[0243] Stage 1.3

##STR00141##

[0244] Methyl 5-hexynoate (15.5 g, 122.86 mmol), 4-bromo-3-fluoroiodobenzene (36.97 g, 122.86 mmol), diisopropylamine (45 mL) and tetrahydrofuran (225 mL) are placed in a round bottom flask under nitrogen. The flask is flushed with nitrogen before bis(triphenylphosphine)palladium(II) dichloride (0.33 g) and copper(I) iodide (0.165 g) are added to the mixture, which is then warmed to 30° C. for 20 minutes and then to 40° C. for 1 hour. The mixture is cooled and the solids are filtered off and washed thoroughly with ethyl acetate. The solvent of the organic phase is evaporated under reduced pressure. The pure product is obtained after column chromatography over silica eluted with petroleum ether:dichloromethane (ratio 2:1).

[0245] Stage 1.4

##STR00142##

[0246] Platinum on carbon (2.7 g, 10% on carbon) is placed under a nitrogen atmosphere in a 1 litre 3 necked round bottom flask. To this tetrahydrofuran (270 mL) and methyl 6-(4-bromo-3-fluorophenyl)hex-5-ynoate (26.9 g, 89.9 mmol) are added. The flask is flushed with hydrogen gas from a balloon twice. The mixture then stirred vigorously for 5 hours under a hydrogen atmosphere. Then the mixture is filtered through celite to give a clear solution. This is concentrated under reduced pressure to give the product.

[0247] Stage 1.5

##STR00143##

[0248] Under a nitrogen atmosphere, a mixture of methyl 6-(4-bromo-3-fluorophenyl)-hexanoate (26 g, 86.9 mmol), 3,4-difluorobenzeneboronic acid (13.74 g, 87 mmol), potassium phosphate (72.7 g, 316 mmol), dioxan (160 mL), water (80 mL) and Pd(dppf)Cl.sub.2 (615 mg) are degassed for 30 minutes. The reaction mixture is then stirred at 90° C. for 16 hours. The mixture is subsequently cooled to ambient temperature. The organic phase is separated, dried over magnesium sulphate and concentrated under reduced pressure. The crude product is purified on a column of silica and eluted with petroleum ether:dichloromethane (ratio 1:1), which yields the product as clear oil.

[0249] Stage 1.6

##STR00144##

[0250] Methyl 6-[4-(3,4-difluorophenyl)-3-fluorophenyl]hexanoate (22 g, 65.4 mmol), sodium hydroxide (5.23 g, 131 mmol), ethanol (100 ml) and water (100 mL) are heated to 100° C. for 2 hours. The volume of the reaction mixture is reduced by half under reduced pressure, and then the reaction mixture is acidified with concentrated hydrochloric acid. The crude mixture is cooled in an ice bath and the resulting solid is filtered off and washed with water. Re-crystallisation from ethanol:water (1:1 ratio) gives the desired product.

[0251] Stage 1.7

##STR00145##

[0252] 6-(2,3′,4′-Trifluoro-biphenyl-4-yl)-hexanoic acid (2.48 g; 7.68 mmol) is added into a flask containing 50 mL dichloromethane. Trifluoroacetic anhydride (2.42 g; 11.52 mmol) is added and the mixture is stirred for 30 minutes. 4′-Prop-1-ynyl-biphenyl-4-ol (1.60 g; 7.68 mmol) is added and the mixture is stirred at room temperature for 16 hours. Water (20 mL) is added and the organic phase is separated, dried over magnesium sulphate and the solvent is evaporated. Column chromatography on silica gel using petroleum ether:ethyl acetate (ratio 1:1) gives the product as pale yellow solid.

Synthesis Example 2: Preparation of

[0253] ##STR00146##

[0254] The compound of interest is prepared according to the following scheme.

##STR00147##

[0255] Stage 2.1

##STR00148##

[0256] Allyl magnesium chloride (2M in tetrahydrofuran) (300.00 mL; 0.60 mol), is added into a flask at −5° C. under nitrogen. The solution of 1-bromo-4-bromomethyl-benzene (100.00 g; 0.40 mol) in tetrahydrofuran (400.00 mL) is added to a grignard solution at this temperature over a time span of 90 minutes. The reaction mixture is then stirred at room temperature for 16 hours. The reaction is then quenched by saturated aqueous tetrahydrofuran. Then brine (200 mL) is added and the organic phase is separated and washed with brine (200 mL), dried over magnesium sulphate and concentrated under reduced pressure. Filtration through silica with petroleum ether as the eluent and subsequent evaporation of the solvent afforded product as a colorless oil.

[0257] Stage 2.2

##STR00149##

[0258] 1-Bromo-4-but-3-enyl-benzene (7.00 g; 33.16 mmol) is added into a flask containing 140 mL tetrahydrofuran. Then 4-methoxyphenylboronic acid (5.543 g; 36.48 mmol), water (35.00 mL) and sodium carbonate (4.22 g; 39.79 mmol) are added. The reaction mixture is degassed and tetrakis(triphenylphosphine) palladium(0) (1.15 g; 0.99 mmol) is added. Then the reaction mixture is stirred at 70° C. for 16 hours. The organic phase is separated and dried over magnesium sulphate and evaporated under reduced pressure. Column chromatography over silica using petroleum ether gives the product as a white solid.

[0259] Stage 2.3

##STR00150##

[0260] 4-But-3-enyl-4′-methoxy-biphenyl (4.70 g; 19.72 mmol) is added under nitrogen into a flask containing dry dichlormethane (125 mL). The solution is cooled to −78° C. Boron tribromide (1 M in dichloromethane) (39.44 mL; 39.44 mmol) is added dropwise at this temperature. The mixture is stirred for a further 30 minutes at −78° C., then allowed to warm up to room temperature and stirred for further 30 min. Then the reaction mixture is quenched by addition of 50 mL methanol at −78° C. The mixture is allowed to warm up to room temperature and the solvent is evaporated under reduced pressure. Column chromatography on silica gel using petroleum ether:ethyl acetate (ratio 8:2) gives the pure product as a white solid.

[0261] Stage 2.4

##STR00151##

[0262] 3-fluoro-4-bromo phenol (10.00 g; 52.36 mmol), (4-cyanophenyl)boronic acid (7.69 g; 52.36 mmol), [1,1′-bis(diphenylphosphino)ferrocene]dichloro-palladium(II) (0.37 g; 0.50 mmol), sodium carbonate (10.60 g; 0.10 mol) and water (50.00 mL) are added into a flask containing 200 mL 1,4-dioxane. The system is degassed and stirred for 16 hours at 80° C. The reaction mixture is then cooled to room temperature and neutralised with dilute hydrochloric acid. The mixture is extracted with ethyl acetate. The organic phases are combined and dried over magnesium sulphate and the solvent is evaporated under reduced pressure. Column chromatography over silica gel eluted with petroleum ether:ethyl acetate (ratio 3:1) gives the product, which is re-crystallised from ethyl acetate/dichloromethane.

[0263] Stage 2.5

##STR00152##

[0264] Heptanedioic acid (5.00 g; 31.22 mmol), Dicyclohexylcarbodiimide (6.44 g; 31.22 mmol) and dimethylaminopyridine (381.16 mg; 3.12 dmmol) are charged into a flask containing 50 mL dichloromethane. The reaction mixture is stirred for 30 min then 2′-fluoro-4′-hydroxy-biphenyl-4-carbonitrile (6.66 g; 31.22 mmol) is added and the reaction mixture is stirred at room temperature overnight. Then water (50 mL) is added and the organic phase is separated, dried over magnesium sulphate and evaporated under reduced pressure. Column chromatography over silica gel eluted with dichloromethane:ethyl acetate (ratio 7:3) gives the product as white solid.

[0265] Stage 2.6

##STR00153##

[0266] Heptanedioic acid mono-(4′-cyano-2-fluoro-biphenyl-4-yl) ester (2.00 g; 5.63 mmol), dicyclohexylcarbodiimide (1.16 g; 5.63 mmol) and dimethylaminopyridine (68.72 mg; 0.56 mmol) are charged to a flask containing 50 mL dichloromethane. The reaction mixture is stirred for 30 minutes then 4′-but-3-enyl-biphenyl-4-ol (1.26 g; 5.63 mmol) is added and the reaction mixture is stirred at room temperature for 16 hours. Then water (50 mL) is added and the organic phase is separated, dried over magnesium sulphate and evaporated under reduced pressure. Column chromatography over silica gel eluted with dichloromethane:ethyl acetate (1:1 ratio) gives the product as white solid.

[0267] The compound shows an e/K=1.99 V.sup.−1 at 0.9 T.sub.NI).

Synthesis Example 3: Preparation of

[0268] ##STR00154##

[0269] The compound of interest is prepared according to the following scheme.

##STR00155##

[0270] Stage 3.5

##STR00156##

[0271] 6-(2,3′,4′-Trifluoro-biphenyl-4-yl)-hexanoic acid (2.00 g; 6.20 mmol), dicyclohexylcarbodiimide (1.28 g; 6.20 mmol) and dimethylaminopyridine (75.76 mg; 0.62 mmol) are charged into a flask containing 50 mL dichloromethane. The reaction mixture is stirred for 30 min then 4′-but-3-enyl-biphenyl-4-ol (1.53 g; 6.83 mmol) is added and stirred at room temperature for 16 hours. Then water (50 mL) is added and the organic phase is separated, dried over magnesium sulphate and evaporated under reduced pressure. Column chromatography over silica gel eluted with dichloromethane:ethyl acetate (2:1) gives the product as a white solid.

[0272] The compound shows an e/K=2.13 V.sup.−1 at 0.9 T.sub.NI).

Synthesis Example 4: Preparation of

[0273] ##STR00157##

[0274] The compound of interest is prepared according to the following scheme.

##STR00158##

[0275] Stage 4.1

##STR00159##

[0276] Lithium acetylide ethylenediamine complex (27.3 g, 296 mmol) is added into a flask containing anhydrous dimethylsulfoxid (DMSO, 70 mL) keeping the temperature below 13° C. 6-bromohexanoic acid (19.22 g, 99 mmol) in DMSO (70 mL) is added dropwise over 1 hour at 5-15° C. The mixture is warmed to 30° C. and stirred for 1.5 hours at 30° C. Then the mixture is cooled to 15° C. Water (50 mL) is very cautiously added. There is a rapid evolution of acetylene. Then, first, water:conc. HCl (25:75 mL/mL) and finally water:conc. HCl (75:75 mL/mL) are added. The mixture is extracted with dichloromethane (DCM, CH.sub.2Cl.sub.2, 3×150 mL). The organic layer is separated and dried over anhydrous sodium sulphate, filtered and the solvent removed in vacuo. The crude oil is purified by flash chromatography on silica eluting with dichloromethane (100 mL). Two fractions containing the product are collected. The solvent is removed in vacuo. Fraction 1 contains the product and 14% DMSO, whereas fraction 2 contains the product and 54% DMSO (as concluded by .sup.1H NMR).

[0277] Stage 4.2

##STR00160##

[0278] 7-Octynoic acid (7.4 g, 45.5 mmol, fraction 1 of stage 4.1), 4-bromo-3-fluoroiodobenzene (15 g, 49.8 mmol), diisopropylamine (20 mL, 140 mmol) and tetrahydrofuran (50 mL) are placed in an ultrasonic bath under nitrogen (a procedure, which is called short “ultrasonicated” or “sonicated” in this application) for 15 minutes. Copper (I) iodide (100 mg) and Pd(Ph.sub.3).sub.2Cl.sub.2 (200 mg) are added and the mixture is heated to 40-45° C. and stirred at that temperature for 2 hours. Water:conc. HCl (85 mL:15 mL) is added and the mixture extracted with dichloromethane (2×100 mL). The solvent from the organic layer is removed in vacuo. The crude product is purified by flash chromatography on silica (60 g) eluting with the following mixtures of dichloromethane:isopropyl alcohol (mixing ratios [mL/mL] 100:0, 100:0, 100:0, 99:1, 98:2, 97:3, 96:4, 95:5, 94:6 and 93:7, respectively). The fractions containing the product, are the fractions 2 to 8. These are collected and the solvent is removed in vacuo. The residue is crystallized from acetonitrile to give the desired product.

[0279] Stage 4.3

##STR00161##

[0280] 8-(4-Bromo-3-fluoro-phenyl)-oct-7-ynoic acid (10.47 g, 33.5 mmol) is dissolved in 220 mL tetrahydrofuran, platinum on carbon (2.2 g, 10% loading) is added and the mixture is hydrogenated for 5 hours. The catalyst is removed by filteration through celite. Then the crude product is washed with tetrahydrofuran and the solvent is removed in vacuo. The residue is crystallized from acetonitrile (30 mL). The mixture is cooled in the freezer for 1 hour, filtered off, washed with cold acetonitrile directly from the freezer to give the desired product.

[0281] Stage 4.4

##STR00162##

[0282] 8-(4-Bromo-3-fluoro-phenyl)-octanoic acid (1.59 g, 5 mmol), ), 4-cyanobenzeneboronic acid (0.74 g, 5 mmol), dioxane (8 mL), water (4 mL) and potassium phosphate hydrate (2.3 g, 10 mmol) are sonicated for 15 minutes. [1,1-Bis(diphenylphosphino)ferrocene]dichloropalladium(II) (60 mg, 1.7 mmol) is added and the mixture heated to 90° C. for 5 hours. The mixture is then cooled and extracted with dichloromethane (3×100 mL). The organic phase is separated and the solvent evaporated under reduced pressure. The residue is purified by flash chromatography on silica (60 g) eluting with dichloromethane/isopropyl alcohol (mixing ratios [mL/mL] 100:0, 99:1, 98:2, 97:3, 96:4, 95:5, 94:6, 93:7, 92:8, 91:9 and 90:10, respectively). The fractions 5 to 7, containing the product are collected and the solvent is removed in vacuo. The residue is crystallized from acetonitrile (5 mL), the mixture is cooled in the freezer, filtered off, washed with cold acetonitrile fresh from the freezer to give the desired product.

[0283] Stage 4.5

##STR00163##

[0284] 8-(4′-Cyano-2-fluoro-biphenyl-4-yl)-octanoic acid (1.50 g; 4.42 mmol), dicyclohexylcarbodiimide (0.91 g; 4.42 mmol) and dimethylaminopyridine (269.81 mg; 2.21 mmol) are charged into a flask containing 50 mL dichloromethane. The mixture is stirred for 30 minutes, then 4′-but-3-enyl-biphenyl-4-ol (1.09 g; 4.86 mmol) is added and the mixture is again stirred at room temperature for 16 hours. The solid is filtered off and the solvent evaporated under reduced pressure. The crude product is purified by column chromatography over silica gel eluting with petroleum ether:ethyl acetate (ratio 7:3). The pure product is obtained as white solid.

[0285] The compound shows an e/K=2.09 V.sup.−1 at 0.9 T(N,I).

Compound Examples 5 and Following

[0286] The following compounds of formula I are prepared analogously.

Compound Example 5

[0287] ##STR00164##

Compound Example 6

[0288] ##STR00165##

[0289] The materials in the above table generally show increased performance in the screening mixtures, as compared to known, more conventional bimesogenic compounds as e.g. those shown in the table below.

Comparative Compound Example 1

[0290] ##STR00166##

[0291] Phase sequence: K 98 (N 83) I, e/K=2.25 V.sup.1.

USE EXAMPLES, MIXTURE EXAMPLES

[0292] Typically a 5.6 μm thick cell, having an anti-parallel rubbed PI alignment layer, is filled on a hotplate at a temperature at which the flexoelectric mixture in the isotropic phase.

[0293] After the cell has been filled phase transitions, including clearing point, are measured using Differential Scanning Calorimetry (DSC) and verified by optical inspection. For optical phase transition measurements, a Mettler FP90 hot-stage controller connected to a FP82 hot-stage is used to control the temperature of the cell. The temperature is increased from ambient temperature at a rate of 5 degrees C. per minute, until the onset of the isotropic phase is observed. The texture change is observed through crossed polarizers using an Olympus BX51 microscope and the respective temperature noted.

[0294] Wires are then attached to the ITO electrodes of the cell using indium metal. The cell is secured in a Linkam THMS600 hot-stage connected to a Linkam TMS93 hot-stage controller. The hot-stage is secured to a rotation stage in an Olympus BX51 microscope.

[0295] The cell is heated until the liquid crystal is completely isotropic. The cell is then cooled under an applied electric field until the sample is completely nematic. The driving waveform is supplied by a Tektronix AFG3021B arbitrary function generator, which is sent through a Newtons4th LPA400 power amplifier before being applied to the cell. The cell response is monitored with a Thorlabs PDA55 photodiode. Both input waveforms and optical response are measured using a Tektronix TDS 2024B digital oscilloscope.

[0296] In order to measure the flexoelastic response of the material, the change in the size of the tilt of the optic axis is measured as a function of increasing voltage. This is achieved by using the equation:

[00001]$\tan .Math..Math.\varphi =\frac{P_0}{2.Math.\pi }.Math.\frac{e}{K}.Math.\underset{\_}{E}$

wherein φ is the tilt in the optic axis from the original position (i.e. when E=0), E is the applied field, K is the elastic constant (average of K.sub.1 and K.sub.3) and e is the flexoelectric coefficient (where e=e.sub.1+e.sub.3). The applied field is monitored using a HP 34401A multimeter. The tilt angle is measured using the aforementioned microscope and oscilloscope. The undisturbed cholesteric pitch, P.sub.0, is measured using an Ocean Optics USB4000 spectrometer attached to a computer. The selective reflection band is obtained and the pitch determined from the spectral data.

[0297] The mixtures shown in the following examples are well suitable for use in USH-displays. To that end an appropriate concentration of the chiral dopant or dopants used has to be applied in order to achieve a cholesteric pitch of 200 nm or less.

Comparative Mixture Example 1.0

[0298] Host Mixture H-0

[0299] The host mixture H-0 is prepared and investigated in particular studying it's properties for being aligned.

TABLE-US-00006 Composition Compound No. Abbreviation Conc./% 1 F-PGI-O-9-O-GP-F 25.0 2 F-PGI-O-9-O-PP-N 25.0 3 F-PGI-ZI-9-Z-GP-F 25.0 4 F-PGI-ZI-9-Z-PP-N 25.0 Σ 100.0

[0300] The alignment of the mixtures, like mixture H-0, is determined in a test cell with anti-parallel rubbed PI orientation layers, for planar alignment, having a cell gap of 10 μm at a wavelength of 550 nm. The optical retardation of the samples is determined using an elipsometer instrument for various angles of incidence ranging from −60° to +40°. The results are compiled in the following table.

[0301] The sample of H-0 shows an optical retardation of 25 nm under perpendicular observation (i.e. at an angle of incidence of 0°). This already indicates the presence of a homogeneous alignment. For various angles of incidence the values of the retardation range from 2 nm to 55 nm. Though they scatter quite significantly as a function of the angle of incidence, there seems to be a trend of the retardation increasing with increasing angle of incidence. However, the significant scatter of the retardation values indicate a rather poor quality of the homeotropic alignment.

TABLE-US-00007 Angle/° −60 −40 −20 0 20 40 Example Mixt. d .Math. Δn/nm C H-0 2 33 42 25 55 44

[0302] 2% of the chiral dopant R-5011 are added to the mixture H-0 leading to the mixture H-1, which is investigated for its properties.

TABLE-US-00008 Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2 F-PGI-O-9-O-GP-F 24.5 3 F-PGI-O-9-O-PP-N 24.5 4 F-PGI-ZI-9-Z-GP-F 24.5 5 F-PGI-ZI-9-Z-PP-N 24.5 Σ 100.0

[0303] The mixture H-1 may be used for the USH-mode. It has a clearing point of 82° C. and a lower transition temperature [T(N2,N)] of 33° C. It has a cholesteric pitch of 301 nm at 35° C. The e/K of this mixture is 1.9 Cm.sup.−1N.sup.−1 at a temperature of 34.8° C.

Mixture Examples 1.0 and 1.1

[0304] 25% of the compound of synthesis example 1 are added to the mixture H-0 leading to Mixture M-1.0, which is also investigated for its alignment.

Mixture Example 1.0: Mixture M-1.0

[0305]

TABLE-US-00009 Composition Compound No. Abbreviation Conc./% 1 F-PGI-O-9-O-GP-F 18.75 2 F-PGI-O-9-O-PP-N 18.75 3 F-PGI-ZI-9-Z-GP-F 18.75 4 F-PGI-ZI-9-Z-PP-N 18.75 5 Compound 1* 25.0 Σ 100.0

[0306] Remark: *) Compound of Synthesis Example 1.

[0307] This mixture (M-1.0) is prepared and investigated. Its orientation behaviour is very good. It shows almost perfect homeotropic alignment, as observable by the retardation at normal incidence, which is very close to zero and the retardation increases symmetrically with increasing absolute value of the angle of incidence.

[0308] Compare to this, the mixture H-0 shows completely homogeneous alignment, indicated by the respective different dependence of retardation on the angle of incidence.

[0309] 2% of the chiral dopant R-5011 and 10% of the compound of synthesis example 1 are added to the mixture H-0 leading to the mixture M-1.1, which is investigated for its properties.

Mixture Example 1.1: Mixture M-1.1

[0310]

TABLE-US-00010 Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2 F-PGI-O-9-O-GP-F 22.0 3 F-PGI-O-9-O-PP-N 22.0 4 F-PGI-ZI-9-Z-GP-F 22.0 5 F-PGI-ZI-9-Z-PP-N 22.0 6 Compound 1* 10.0 Σ 100.0

[0311] Remark: *) Compound of Synthesis Example 1.

[0312] This mixture (M-1.1) is prepared and investigated. It is well suitable for the ULH-mode. It has a good response time, especially at lower temperatures.

Mixture Examples 2.0 to 2.2

Mixture Example 2.0: Mixture M-2.0

[0313] 25% of the compound of synthesis example 2 are added to the mixture H-0 leading to Mixture M-2.0, which is also investigated for its alignment.

TABLE-US-00011 Composition Compound No. Abbreviation Conc./% 1 F-PGI-O-9-O-GP-F 18.75 2 F-PGI-O-9-O-PP-N 18.75 3 F-PGI-ZI-9-Z-GP-F 18.75 4 F-PGI-ZI-9-Z-PP-N 18.75 5 Compound 2* 25.0 Σ 100.0

[0314] Remark: *) Compound of Synthesis Example 2.

[0315] This mixture (M-2.0) is prepared and investigated. Its orientation behaviour is very good. It shows almost perfect homeotropic alignment, as observable by the retardation at normal incidence, which is very close to zero and the retardation increases symmetrically with increasing absolute value of the angle of incidence.

Mixture Example 2.1: Mixture M-2.1

[0316] 10% of the compound of synthesis example 2 are added to the mixture H-0 leading to Mixture M-2.1, which is also investigated for its alignment.

Mixture Example 2.1: Mixture M-2.1

[0317]

TABLE-US-00012 Composition Compound No. Abbreviation Conc./% 1 F-PGI-O-9-O-GP-F 22.5 2 F-PGI-O-9-O-PP-N 22.5 3 F-PGI-ZI-9-Z-GP-F 22.5 4 F-PGI-ZI-9-Z-PP-N 22.5 5 Compound 2* 10.0 Σ 100.0

[0318] Remark: *) Compound of Synthesis Example 2.

[0319] This mixture (M-2.1) is prepared and investigated. The data for its orientation behaviour are similarly good, like those of the previous example. Is shows only slightly inferior homeotropic alignment, compared to mixture M-2-0 as described above.

Mixture Example 2.2: Mixture M-2.2

[0320] 2% of the chiral dopant R-5011 and 10% of the compound of synthesis example 2 are added to the mixture H-0 leading to the mixture M-2.1, which is investigated for its properties.

TABLE-US-00013 Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2 F-PGI-O-9-O-GP-F 22.0 3 F-PGI-O-9-O-PP-N 22.0 4 F-PGI-ZI-9-Z-GP-F 22.0 5 F-PGI-ZI-9-Z-PP-N 22.0 6 Compound 2* 10.0 Σ 100.0

[0321] Remark: *) Compound of Synthesis Example 2.

[0322] This mixture (M-2.1) is prepared and investigated. It is well suitable for the ULH-mode. It has a transition from the nematic phase to the isotropic phase [T(N,I)] at 77.0° C. This mixture (M-1.1) is well suitable for the ULH-mode and for the USH-mode. It has an e/K of 2.32 Cm.sup.−1N.sup.−1 (i.e. 2.32 V.sup.−1) at a temperature of 35.0° C. The response times of this mixture at this temperature are τ.sub.on=2.1 ms and τ.sub.off=1.3 ms, respectively.

Mixture Examples 3.0 and 3.1

[0323] 25% of the compound of synthesis example 1 are added to the mixture H-0 leading to Mixture M-3.0, which is also investigated for its alignment.

Mixture Example 3.0: Mixture M-3.0

[0324]

TABLE-US-00014 Composition Compound No. Abbreviation Conc./% 1 F-PGI-O-9-O-GP-F 18.75 2 F-PGI-O-9-O-PP-N 18.75 3 F-PGI-ZI-9-Z-GP-F 18.75 4 F-PGI-ZI-9-Z-PP-N 18.75 5 Compound 3* 25.0 Σ 100.0

[0325] Remark: *) Compound of Synthesis Example 3.

[0326] This mixture (M-3.0) is prepared and investigated. The data for its orientation behaviour are compiled in the table above. The mixture shows good homeotropic alignment.

Mixture Example 3.1: Mixture M-3.1

[0327] 2% of the chiral dopant R-5011 and 10% of the compound of synthesis example 1 are added to the mixture H-0 leading to the mixture M-3.1, which is investigated for its properties.

[0328] Mixture M-3.1

TABLE-US-00015 Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2 F-PGI-O-9-O-GP-F 22.0 3 F-PGI-O-9-O-PP-N 22.0 4 F-PGI-ZI-9-Z-GP-F 22.0 5 F-PGI-ZI-9-Z-PP-N 22.0 6 Compound 3* 10.0 Σ 100.0

[0329] Remark: *) Compound of Synthesis Example 3.

[0330] This mixture (M-3.1) is prepared and investigated. It is well suitable for the ULH-mode. It has a transition from the nematic phase to the isotropic phase [T(N,I)] at 77.0° C. This mixture (M-1.1) is well suitable for the ULH-mode and for the USH-mode. It has an e/K of 2.33 V.sup.−1 at a temperature of 35.0° C. The response times of this mixture at this temperature are τ.sub.on=3.0 ms and τ.sub.off=1.9 ms, respectively.

Mixture Examples 3.0 and 3.1

[0331] 25% of the compound of synthesis example 1 are added to the mixture H-0 leading to Mixture M-3.0, which is also investigated for its alignment.

Mixture Example 4.0: Mixture M-4.0

[0332]

TABLE-US-00016 Composition Compound No. Abbreviation Conc./% 1 F-PGI-O-9-O-GP-F 18.75 2 F-PGI-O-9-O-PP-N 18.75 3 F-PGI-ZI-9-Z-GP-F 18.75 4 F-PGI-ZI-9-Z-PP-N 18.75 5 Compound 4* 25.0 Σ 100.0

[0333] Remark: *) Compound of Synthesis Example 4.

[0334] This mixture (M-4.0) is prepared and investigated. The data for its orientation behaviour are compiled in the table above. The mixture shows good homeotropic alignment.

Mixture Example 4.1: Mixture M-4.1

[0335] 2% of the chiral dopant R-5011 and 10% of the compound of synthesis example 1 are added to the mixture H-0 leading to the mixture M-4.1, which is investigated for its properties.

[0336] Mixture M-4.1

TABLE-US-00017 Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2 F-PGI-O-9-O-GP-F 22.0 3 F-PGI-O-9-O-PP-N 22.0 4 F-PGI-ZI-9-Z-GP-F 22.0 5 F-PGI-ZI-9-Z-PP-N 22.0 6 Compound 4* 10.0 Σ 100.0

[0337] Remark: *) Compound of Synthesis Example 4.

[0338] This mixture (M-4.1) is prepared and investigated. It is well suitable for the ULH-mode. It has a transition from the nematic phase to the isotropic phase [T(N,I)] at 77.0° C. This mixture (M-4.1) is well suitable for the ULH-mode and for the USH-mode. It has an e/K of 2.27 V.sup.−1 at a temperature of 40.0° C. The response times of this mixture at this temperature are τ.sub.on=3.0 ms and τ.sub.off=1.9 ms, respectively.

[0339] The investigation described above is performed with 10% each of several compounds of formula I instead of that of synthesis example 1 used in host mixture H-0, together with 2% R-5011. The results are shown in the following table.

TABLE-US-00018 T(N, I)/ T.sub.low/ P/ Ex. Mixt. Compound ° C. ° C. nm e/K/V.sup.−1 C1.1 H-1.0 None 82 33 301 1.9  C1.2 H-1.1 N-PGI-9-GP-N t.b.d. t.b.d. 298 2.22 C1.3 H-1.2 N-PP-9-PP-N t.b.d. 42 t.b.d. t.b.d. C1.4 H-1.3 F-PGI-O-7-O-GP-F t.b.d. t.b.d. t.b.d. t.b.d. E1.1 M-1.1 Compound 1* t.b.d. t.b.d. 314 2.03 E1.2 M-1.2 Compound 2* t.b.d. t.b.d. 299 2.32 E1.3 M-1.3 Compound 3* t.b.d. t.b.d. 310 2.27 E1.34 M-1.4 Compound 4* t.b.d. t.b.d. 310 2.27 Remarks: *compound n: of Synthesis Example No. n, t.b.d.: to be determined the cholesteric pitch (P) is given at 0.9T(N, I) and e/K is given in V.sup.−1 (i.e. Cm.sup.−1N.sup.−1) at 0.9T(N, I).