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. A bimesogenic compound of formula I ##STR00139## wherein 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, 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 are each independently a mesogenic group and at least one of MG.sup.11 and MG.sup.12 comprises one, two or more 5-atomic rings, Sp.sup.1 is a spacer group of 1, 3 or 5 to 40 C atoms, wherein one or more non-adjacent groups may also be replaced by O, S, NH, N(CH.sub.3), CO, OCO, SCO, OCOO, COS, COO, CH(halogen)-, CH(CN), CHCH or CC, however in such a way that no two O-atoms are adjacent to one another, now two CHCH groups are adjacent to each other and no two groups selected from OCO, SCO, OCOO, COS, COO and CHCH are adjacent to each other, X.sup.11 is COS, SCO, CSS, SCS, CSO, OCS, SCOS, SCSS or S, X.sup.12 independently from X.sup.11 has one of the meanings given for X.sup.11 or is COO, OCO, CHCH, CC, O or a single bond, however under the condition that in X.sup.11-Sp.sup.1-X.sup.12 no two O atoms are adjacent to one another, no two CHCH groups are adjacent to each other and no two groups OCO, SCO, OCOO, COS, COO or CHCH are adjacent to each other.

2. A bimesogenic compound according to claim 1, wherein at least one of MG.sup.11 and MG.sup.12 is one, two or more 5-atomic rings, and one or more 6-atomic rings, and at least two of these are optionally linked by a 2 atom moiety.

3. A bimesogenic compound according to claim 1, wherein both MG.sup.11 and MG.sup.12 are one, two or more 5-atomic rings.

4. A bimesogenic compound according to claim 1, wherein R.sup.12 is OCF.sub.3, CF.sub.3, F, Cl or CN.

5. A bimesogenic compound according to claim 1, wherein Sp.sup.1 is (CH.sub.2).sub.o and o is 1, 3 or an integer from 5 to 15.

6. A liquid-crystalline medium, comprising one or more bimesogenic compounds according to claim 1.

7. A liquid-crystalline medium according to claim 6, additionally comprising one or more compounds of formulae III
R.sup.31-MG.sup.31-X.sup.31-Sp.sup.3-X.sup.32-MG.sup.32-R.sup.32III 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, COO, OCOO, SCO, COS, CHCH, CHCF, CFCF or CC 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 of 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, OCO, SCO, OCOO, COS, COO, CH(halogen)-, CH(CN), CHCH or CC, and X.sup.31 and X.sup.32 are each independently O, S, CO, COO, OCO, OCOO, CONH, NHCO, CH.sub.2CH.sub.2, OCH.sub.2, CH.sub.2O, SCH.sub.2, CH.sub.2S, CHCH, CHCHCOO, OCOCHCH, CC or a single bond, and with the condition that compounds of formula I are excluded.

8. A 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.

9. The liquid crystal device according to claim 8, that is a flexoelectric device.

10. The bimesogenic compound according to claim 1, wherein R.sup.11 and R.sup.12 are each independently F, Cl, CN, OCF.sub.3 or CF.sub.3.

Description

COMPOUND AND SYNTHESIS EXAMPLES

Synthesis Example 1: Preparation of

(1) ##STR00132##

(2) The compound of interest is prepared according to the following scheme.

(3) ##STR00133##

(4) Stage 1

(5) 1-bromo-3-fluoroiodobenzene (27.5 g, 0.092 mol) is added into a round bottom flask with tetrahydrofuran (30 ml) and the mixture is stirred under nitrogen atmosphere until comlegte dissolution. Then diisopropylamine (30 ml) is added and the reaction mixture is placed in an ultrasonic bath for 10 minutes. As 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 mixture is cooled in a water bath to a temperature of 20 C. 1,8-nonadiyne (5.0 g, 0.041 mol) is added slowly to the reaction mixture, which is stirred for a further 20 hours. The reaction mixture then is cooled and filtered under vacuum to remove the precipitates. The filtrate is acidified with dilute hydrochloric acid and extracted with diethyl ether. The organic material is separated and washed with water before concentrating it to yield the product as a black solid (19 g). The crude material is purified by column chromatography, eluting the product using a mixture of dichloromethane and petrol. This yields the desired product.

(6) Stage 2

(7) 21.5 g (0.040 mol) of the product of the previous stage (Example 1, Stage 1) are dissolved in tetrahydrofuran (600 ml) and passed through a Thalesnano hydrogenator. The conditions for the reactions are 70 bar pressure at a temperature of 60 C. The product is obtained as a pale coloured solid.

(8) Stage 3

(9) The product from the precious stage (Example 1, Stage 2, 10.0 g, 21.1 mmol), bis-pinacolatodiboron (11.8 g, 46.5 mmol) and dioxane (350 ml) are stirred together. Then potassium acetate (3.1 g, 31.4 mmol) and dichlorobis(tricyclohexylphosphine)palladium (0.77 g, 1.05 mmol) are added. Then the reaction mixture is heating to a temperature of 120 C. for 20 hours. The reaction mixture is then cooled and dilute hydrochloric acid (100 ml) is added. The resultant phases (layers) are separated. The organic material is washed with brine and water before it is dried over magnesium sulphate and concentrated in vacuo. The crude product is purified by column chromatography through silica gel, eluted with a mixture of dichloromethane and petroleum ether (1:1 ratio). The fractions comprising the product are combined and used in the next stage.

(10) Stage 4

(11) The product from the previous stage (Example 1, Stage 3, 4.2 g, 7.4 mmol) and 2-bromo-5-cyanothiophene (2.9 g, 15.5 mmol) are stirred together in tetrahydrofuran (35 ml). Then water (3.5 ml) is added and subsequently sodium metaborate octahydrate (6.1 g, 22 mmol) is added. The reaction vessel is evacuated and refilled with nitrogen before adding bis-triphenylphosphinepalladium dichloride (0.26 g, 0.37 mmol) and heating the reaction mixture to a temperature of to 90 C. for 125 hours. Then the reaction mixture is cooled and poured into water (50 ml). The resultant phases are separated and the organic phase is washed first with brine and then with water. The aqueous material is re-extracted with ethyl acetate (three times each time with 50 ml) before combining the organic material. After drying over magnesium sulphate, filtering and concentration in vacuo, the crude product is obtained as a brown solid. The crude product is purified by column chromatography through silica gel, eluting with a mixture of dichloromethane and petroleum ether (3:7 ratio). The fractions containing the product are combined and re-crystallised from isopropyl alcohol to yield the product as a white solid.

(12) ##STR00134##

(13) The product has the following phase range: K 65 N 110 I and an e/K of 2.1 Cm.sup.1N.sup.1 (=2.1 V.sup.1). The e/K has been determined for mixture M-1 as specified below. These properties make the material very useful for mixtures comprising bimesogenic compounds, in particular for use in the USH and in the ULH mode.

Compound Examples 2 and Following

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

(15) ##STR00135## ##STR00136## ##STR00137##

(16) 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

(17) ##STR00138##

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

Use Examples, Mixture Examples

(19) Typically a 5.6 m 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.

(20) 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.

(21) 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.

(22) 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.

(23) 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:

(24) $\tan =\frac{P_0}{2}\frac{e}{K}\underset{\_}{E}$

(25) wherein 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.

(26) 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 1.1

Host Mixture H-0

(27) The host mixture H-0 is prepared and investigated.

(28) 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 25.0 100.0

(29) 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.

(30) 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 24.5 100.0

(31) 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 1.1 to 1.4

(32) 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: Mixture M-1

(33) 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* 10.0 100.0 Remark: *Compound of Synthesis Example 1.

(34) This mixture (M-1) is prepared and investigated. It is well suitable for the ULH-mode. It shows an N to N2 transition [T(N,N2)] at 34 C. It has a transition from the nematic phase to the isotropic phase [T(N,I)] at 80.0 C. This mixture (M-1) is well suitable for the USH-mode. It has a cholesteric pitch of 299 nm at 47 C. The e/K of this mixture is 2.1 Cm.sup.1N.sup.1 at a temperature of 47 C.

(35) 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.

(36) TABLE-US-00009 T(N, I)/ T.sub.low/ P/ e/K/ Ex. Mixt. Compound C. C. nm V.sup.1 C1.1 H-1.0 None 82 33 291 1.80 C1.2 H-1.1 N-PGI-9-GP-N t.b.d. t.b.d. t.b.d. 2.25 C1.3 H-1.21 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 108 26.5 332 1.70 E1.1 M-1.1 Compound 1* 87 39 301 2.1 E1.2 M-1.2 Compound 2* 82 27 283 2.1 E1.3 M-1.3 Compound 3* t.b.d. 36 289 1.9 E1.4 M-1.4 Compound 4* t.b.d. t.b.d. t.b.d. t.b.d. E1.5 M-1.5 Compound 5* t.b.d. t.b.d. t.b.d. t.b.d. 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).

(37) The mixture, mixture M-2, shows an N to N2 transition [T(N,N2)] at 27 C. It has a transition from the nematic phase to the isotropic phase [T(N,I)] at 82.0 C. This mixture (M-2) is well suitable for the USH-mode.

(38) It has a cholesteric pitch of 283 nm at 47 C.

(39) The e/K of this mixture is 2.1 Cm.sup.1N.sup.1 at a temperature of 47 C.

(40) The mixture, mixture M-3, shows an N to N2 transition [T(N,N2)] at 36 C. It has a transition from the nematic phase to the isotropic phase [T(N,I)] at 76 C. This mixture (M-2) is well suitable for the USH-mode.

(41) It has a cholesteric pitch of 289 nm at 50 C.

(42) The e/K of this mixture is 2.09 Cm.sup.1N.sup.1 at a temperature of 50 C.