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 and CG.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 ##STR00149## wherein R.sup.1 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, a straight-chain or branched alkyl group with 1 to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, 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, and CG.sup.1 is a central atom or a central group, having a total length of one atom,

2. Bimesogenic compounds according to claim 1, characterized in that CG.sup.1 is selected from —CH.sub.2—, —CHF—, —CF.sub.2—, —O—, —S—, —(C═O)—, —CH(OR)—, —CH(R)—, —C(R)(R′)—, —SO.sub.2—, —CF.sub.2—, —CH(CF.sub.3)—, —C(═CH.sub.2)—, —NH—, —N(R)— and —S(R)(R′)—.

3. Bimesogenic compounds according to claim 1, characterized in that at least one of R.sup.11 and R.sup.12 is selected from OCF.sub.3, CF.sub.3, F, Cl and CN.

4. Bimesogenic compounds according to claim 1, characterized in that CG.sup.1 is —CH.sub.2—, —CF.sub.2—, —O—, —CO—, or —SO.sub.2—.

5. (canceled)

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

7. Liquid-crystalline medium according to claim 6, 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.sup.32-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.

8. (canceled)

9. 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.

10. Liquid crystal device according to claim 9, characterized in that it is a flexoelectric device.

11. Preparation of a compound of formula I according to claim 1, characterized in that an aromatic aldehyde is reacted with another organic intermediate by a condensation reaction.

12. Preparation of a compound of formula I according to claim 1, characterized in that an aromatic boronic acid is reacted with an organic triflate or organic halide, known generally as a Suzuki cross coupling reaction.

13. Preparation of a liquid crystal medium according to claim 7, characterized in that one or more compounds of formula I are mixed with one or more compounds of formula III, and/or one or more further compounds.

Description

COMPOUND AND SYNTHESIS EXAMPLES

Synthesis Example 1: Preparation of

[0214] ##STR00141##

[0215] The compound of interest is prepared according to the following scheme.

##STR00142##

Stage 1.1

[0216] ##STR00143##

[0217] Magnesium turnings (1.3 g, 54 mmol) and tetrahydrofuran (THF, 2 mL) are placed in an ultrasonic bath under nitrogen (a procedure, which is called short “ultrasonicated” or “sonicated” in this application) for 30 minutes. Iodine (0.15 g, 0.6 mmol) is added and the mixture is heated until the colour of the iodine disappears. 4-Bromo-2,4′difluorobiphenyl (13.1 g, 50 mmol) dissolved in THF (20 mL) is charged into a pressure equalizing funnel. Approximately five percent thereof are added and the mixture is heated under reflux until the Grignard reaction has started. The remainder of the 4-bromo-2,4′-difluorobiphenyl is added over a time span of 10 minutes under reflux and then the mixture is heated under reflux for a further 2 hours. Then the mixture is cooled to 20° C. Ethyl formate (2 mL, 25 mmol) is added dropwise over a time span of five minutes at a temperature in the range from 20° C. to 30° C. Then the mixture is stirred for a further 1.5 hours. Subsequently the mixture is acidified with concentrated sulphuric acid (5 mL) and water (75 mL). The mixture is extracted with dichloromethane (DCM, CH.sub.2Cl.sub.2, 1×200 mL and 2×50 mL). The organic layer is dried over anhydrous sodium sulphate, filtered, washed with DCM and the solvent from the filtrate is removed in vacuo. The residue is purified by vacuum flash chromatography on silica (50 g) eluting with the following mixtures DCM:Petrol (B.p. 40:60), 50:50, 60:40, 70:30, 80:20, 90:10, then 100:0 mL:mL. The fractions containing the product are collected and the solvent is removed in vacuo. The solid is triturated with petrol (B.p. 40:60) to give the desired product.

Stage 1.2

[0218] ##STR00144##

[0219] The product from stage 1 of Example 1 (5 g, 12.2 mmol) is dissolved in THF (100 mL) and 10% palladium on carbon (1 g) are added. The material is hydrogenated at ambient temperature (also called room temperature, short RT), which is 20° C. in this application, unless explicitly specified otherwise, for 16 hours. TLC shows no reaction. The catalyst is filtered off and the solvent from the filtrate removed in vacuo. The residue is dissolved in THF (100 mL) and 20% palladium hydroxide (1 g) added. The mixture is hydrogenated at 30° C. for 5 hours and then kept for 16 hours at room temperature. Glacial acetic acid (20 mL) is added and the mixture is hydrogenated for a further 5 hours at 40° C. The catalyst is filtered off and the solvent from the filtrate removed in vacuo. The residue is purified by vacuum flash chromatography on silica (50 g) eluting with the following mixtures toluene: Petrol (B.p. 40:60) 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20 mL/mL. The fractions containing the product are collected and the solvent removed in vacuo. The solid is re-crystallized from acetonitrile (15 mL) to give the desired product.

[0220] The product has the following properties. Phase sequence: K 70.9 l, e/K=1.97 V.sup.−1.

Synthesis Example 2: Preparation of

[0221] ##STR00145##

[0222] The compound of interest is prepared according to the following scheme.

##STR00146##

[0223] Bis-(4-chlorophenyl) sulphone (2.87 g, 10 mmol, 3,4,5-trifluorobenzene boronic acid (4.22 g, 24 mmol), palladium acetate (PdOAc, 448 mg, 2 mmol), 1,3-Bis(diphenylphosphino)propane (dppp, 840 mg, 1 mmol), caesium fluoride (CsF, 6.07 g, 40 mmol) and N 1-methyl-2-pyrollidinone (35 mL) are ultasonicated for 30 minutes. Then the mixture is heated for 16 hours at 100° C. and then cooled. Subsequently water (200 mL) is added and the mixture is extracted with ethyl acetate (2×100 mL) in a separating funnel. The organic layers are combined and concentrated under reduced pressure to give a dark coloured solid. This is dissolved in DCM (10 mL) and applied to a column of silica eluted with the following mixtures of petrol 2: DCM 2:1, 1:1, 1:2 and finally pure DCM until all product is eluted. The appropriate fractions are combined and concentrated to give a solid which is re-crystallised from acetonitrile.

[0224] The product has the following properties. Phase sequence: K 204 l, e/K=1.79 V.sup.−1.

[0225] The following compound(s) of formula I are prepared analogously.

Compound Example 3

[0226] ##STR00147##

[0227] Phase sequence: K 147.8 l, e/K to be determined.

[0228] 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

[0229] ##STR00148##

[0230] Phase sequence: K 98 (N 83) l, e/K=2.25 V.sup.−1.

Use Examples, Mixture Examples

[0231] 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.

[0232] 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 polarisers using an Olympus BX51 microscope and the respective temperature noted.

[0233] 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.

[0234] 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.

[0235] 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]$\tan .Math..Math.\varphi =\frac{P_0}{2.Math..Math.\pi }.Math.\frac{e}{K}.Math.\underset{\_}{E}$

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.

[0236] 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

Host Mixture H-0

[0237] The host mixture H-0 is prepared and investigated.

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

[0238] 2% of the chiral dopant R-5011 are added to the mixture H-0 leading to the mixture C-1, which is investigated for its properties.

TABLE-US-00007 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

[0239] The mixture C-1 may be used for the ULH-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.−1.Math.N.sup.−1 at a temperature of 34.8° C.

Mixture Example 1: Mixture M-1

[0240] Remark:*) Compound of Synthesis Example 1.

[0241] 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, 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 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 Remark: *Compound of Synthesis Example 1.

[0242] This mixture (M-1) is well suitable for the USH-mode and for the ULH-mode. It has a cholesteric pitch of 322 nm at 30.8° C. The e/K of this mixture is 1.97 Cm.sup.−.Math.N.sup.−1, i.e. 1.97 V.sup.−1.Math., at a temperature of 49.8° C.

Mixture Example 2

[0243] 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, which is prepared and investigated for its properties.

TABLE-US-00009 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 Remark: *Compound of Synthesis Example 2.

[0244] This mixture (M-2) is well suitable for the USH-mode and for the ULH-mode. The e/K of this mixture is 1.79 Cm.sup.−1.Math.N.sup.−.

Mixture Example 3: Mixture M-3

[0245] 2% of the chiral dopant R-5011 and 10% of the compound of synthesis example 3 are added to the mixture H-0 leading to the mixture M-3, which is prepared and investigated for its properties.

Mixture M-3

[0246]

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 3* 10.0 Σ 100.0 Remark: *Compound of Synthesis Example 3.

[0247] This mixture (M-3) is well suitable for the USH-mode and for the ULH-mode.