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 ##STR00137## 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—, —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 group, wherein the total number of atoms connecting the groups MG.sup.11 and MG.sup.12 is an odd integer in the range from three to 17, the central atom of these atoms connecting the groups MG.sup.11 and MG.sup.12 is an O atom, preferably CG.sup.1 is X.sup.11-J-O—K—X.sup.12—, wherein J and K are each —(CH.sub.2—).sub.n-, wherein in n is an integer in the range from 1 to 8, and wherein one or more H atoms optionally may be replaced by an F atom, X.sup.11 and X.sup.12 are either both a single bond or both an O atom or are independently of one another selected from —CO—O— and —O—CO—.

2. Bimesogenic compounds according to claim 1, characterized in that CG.sup.1 is selected from -J-O—K—, —O-J-O—K—O-m, —O—CO-J-O—K—CO—O— and —CO—O-J-O—K—O—CO—, and J-O—K is selected from —CH.sub.2—O—CH.sub.2—, —(CH.sub.2—).sub.2—O—(CH.sub.2—).sub.2-, —(CH.sub.2—).sub.3—O—(CH.sub.2—).sub.3- and —(CH.sub.2—).sub.4—O—(CH.sub.2—).sub.4—(CH.sub.2—).sub.3-.

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).sub.3—, —CH.sub.2—CF.sub.2—O—, —O—CF.sub.2—CH.sub.2—, —CH.sub.2—C(O)—O— or —O—C(O)—CH.sub.2—.

5. Use of one or more bimesogenic compounds according to claim 1 in a liquid crystalline medium.

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. Use of a liquid crystal medium according to claim 6, in a liquid crystal device.

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 is mixed with one or more compounds of formula III, and/or one or more further compounds.

Description

EXAMPLE 1 AND COMPARATIVE EXAMPLES 1 AND 2

Compound Example 1

[0229] ##STR00132##

[0230] The compound of interest is prepared according to conventional synthetic means.

COMPARATIVE EXAMPLES 1.1 AND 1.2

[0231] Bimesogenic compounds having a more conventional structure, i.e. having a central group without a central O atom, are prepared for reference.

COMPARATIVE EXAMPLE 1.1

[0232] ##STR00133##

COMPARATIVE EXAMPLE 1.2

[0233] ##STR00134##

COMPOUND EXAMPLE 2

[0234] ##STR00135##

[0235] The compound of interest is prepared according to conventional synthetic means.

COMPARATIVE EXAMPLE 2

[0236] A bimesogenic compounds having a more conventional structure, i.e. having a central group without a central O atom, is prepared for reference.

##STR00136##

USE EXAMPLES, MIXTURE EXAMPLES

[0237] 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.

[0238] 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.

[0239] 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.

[0240] 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.

[0241] 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.

[0242] 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.

MIXTURE EXAMPLE 1 AND COMPARATIVE MIXTURE EXAMPLES 1.1 AND 1.2

Comparative Mixture Examples 1 and 2, Mixtures C-1 and C-2

Host Mixture H-0

[0243] The host mixture H-0 is prepared and investigated.

TABLE-US-00006 Composition Compound No. Abbreviation Conc./% 1 F-PGI-ZI-7-Z-PP-N 18.0 2 F-PGI-ZI-9-Z-PP-N 18.0 3 F-PGI-ZI-9-Z-PU-N 22.0 4 F-UIGI-ZI-9-Z-GP-N 12.0 5 N-GIGI-9-GG-N 16.0 6 N-UIUI-9-UU-N 14.0 Σ 100.0

[0244] 15% of the respective compound of Comparative Examples 1 and 2 are added to the mixture H-0 leading to the mixtures C-1 and C-2, respectively, which are investigated for their properties.

[0245] The properties of the mixtures are listed in the following table.

[0246] 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

[0247] Remark: *) Compound of Synthesis Example 1.

[0248] 15% of the compound of example 1 are added to the mixture H-0 leading to the mixture M-1, which is investigated for its properties.

TABLE-US-00007 Composition Compound No. Abbreviation Conc./% 1 F-PGI-ZI-7-Z-PP-N 15.3 2 F-PGI-ZI-9-Z-PP-N 15.3 3 F-PGI-ZI-9-Z-PU-N 18.7 4 F-UIGI-ZI-9-Z-GP-N 10.2 5 N-GIGI-9-GG-N 13.6 6 N-UIUI-9-UU-N 11.9 7 Compound 1* 15.0 Σ 100.0 Remark: *Compound of Example 1.

[0249] This mixture (M-1) has a transition from the nematic phase to the isotropic phase [T(N,I)] at 12.5° C. This mixture (M-1) is well suitable for the USH-mode.

[0250] The investigation described above is performed with 15% each of several compounds of formula I instead of that of synthesis example 1 used in host mixture H-0, each together with 2% R-5011. The results are shown in the following tables.

TABLE-US-00008 Ex. Mixt. Compound T(N.sub.TB, N)/° C. T.sub.low/° C. C-0 HH-0 None 30 67.6 C-1.1 C-1 C.E: 1.1.sup.§ 29.5 67 C-1.2 C-1 C.E. 1.2.sup.§ 23 62 E-1 M-1 Compound 1* 12.5 57.5 C-2 C-1 C.E. 2.sup.§ 22 57.8 E-1 M-1 Compound 2* 13.5 56.4 Remarks: .sup.§*C.E. n: Compound of comparative example No. n, and *Compound n: of compound example No. n.

TABLE-US-00009 ∈.sub.∥ Δ∈ Ex. Compound (20° C., 1 kHz) (20° C., 1 kHz) V.sub.relax/kHz C-0 None 14.2 2.0 15.8 C-1.1 C.E: 1.sup.§ 13.3 1.3 20.0 C-1.2 C.E. 2.sup.§ 14.0 1.2 25.1 E-1 Compound 1* 14.2 1.7 31.6 C-2 C.E. 2.sup.§ 14.3 1.4 25.1 E-2 Compound 2* 14.7 1.7 31.6 Remarks: .sup.§*C.E. n: Compound of comparative example No. n, and *Compound n: of compound example No. n.

[0251] As can be seen from the results in the tables above the compounds of example 1 significantly reduces the transition temperature to the 2.sup.nd nematic phase while it only slightly reduces the clearing point. Thus, it extends the width of the nematic phase range. It further significantly increases the frequency of the relaxation peak (V.sub.relax).

MIXTURE EXAMPLE 2 AND COMPARATIVE MIXTURE EXAMPLE 2

[0252] As described under mixture example 1, 15% of the compound of synthesis example 2 are used in host mixture H-0, each together with 2% R-5011. Alternatively, instead of the 15% of the compound of synthesis example 2, 15% of the compound of comparative example 2 are used. The results are also shown in the respective tables above.