GB2211843A

GB2211843A - Ferroelectric liquid crystals

Info

Publication number: GB2211843A
Application number: GB8825270A
Authority: GB
Inventors: Seiichi Arakawa; Hiroshi Tomimuro
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1987-10-30
Filing date: 1988-10-28
Publication date: 1989-07-12
Also published as: GB8825270D0; FR2622595A1; FR2622595B1; JPH01118593A; DE3836855A1; JP2636271B2

Description

221184-0 FERROELECTRIC LIQUID CRYSTALS This invention relates to

ferroelectric liquid crystals.

A ferroelectric liquid crystal is characterised by high speed response and bistable memory performance. Because of these characteristics, it can used as a raw material for high speed liquid crystal elements. The response time (C) of a ferroelectric liquid crystal is proportional to the value of spontaneous polarisation, as will be understood from the following approximation:

V:2; n/Ps:E where Ps is the spontaneous polarisation, n is the viscosity and E is the electric field.

For a ferroelectric liquid crystal to have a short response time, it should have a high value of Ps. In practice, however, a desired liquid crystal is prepared by blending different kinds of liquid crystals so that it meets the following requirements, which no single liquid crystal can meet.

(1) It should work over a broad temperature range in the vicinity of room temperature.

(2) It should have such a structure that the smectic phase has a sufficiently long helical pitch. (3) It should permit easy control of orientation. (4) It should have a low viscosity.

When a desired liquid crystal is prepared by blending different kinds of liquid crystals, it suffers from the defect that the value of spontaneous polarisation (Ps) decreases to a great extent.

According to the present invention there is provided a ferroelectric liquid crystal, in which a fluorine atom is attached to an asymmetric carbon atom, having the structural formula F H2..IC.0- 0 where n is an integer equal to 6 to 20, and m is an integer equal to 3 to 20.

Ferroelectric liquid crystals embodying the invention and described in the following examples each consist of a single liquid 2 crystal and still have a high value of spontaneous polarisation and a high chemical stability. Each such ferroelectric liquid crystal is based on or contains a biphenyl ester compound having a fluorine atom at an asymmetric carbon atom.

For a liquid crystal to have a high value of spontaneous polarisation (Ps), it should meet the following requirements.

(1) The dipole moment should be great in the direction perpendicular to the molecule.

(2) The permanent dipole should be close to the benzene ring core.

(3) The asymmetric carbon atom should be close to the permanent dipole.

In accordance with the present invention, these requirements are met by a fluorine atom, which is highly electronegative, being attached to an asymmetric carbon atom adjacent to the carbonyl group close to the benzene ring. The fluorine atom increases the dipole moment and hence increases the spontaneous polarisation (Ps). Moreover, the liquid crystal thus obtained is stable because the C-F bond is chemically stable.

Examples of ferroelectric liquid crystals embodying the invention and of processes for preparing them are set forth below. In the Examples, percentages are by weight.

EXAMPLES

The starting material for producing the ferroelectric liquid crystal has a fluorine atom at the asymmetric carbon atom and is an optically active carboxylic acid corresponding to the desired liquid crystal. It is synthesised from an optically active amino acid or chiral epoxide by any of the following three processes. The asymmetric carbon atom is marked with an asterisk and m is as defined above.

Process A NH2 F HF/pyridine 1 H 2m+i'm CHCOOH H2m+1cm CHCOOH amino acid NaNO 2 Process B NH2 NaN02 c 2 H 5 OH H 2m+1 c m CHCOOH amino acid aq. CH 3 COOH H 3 OH 1 (CF 3502)20 H2.+lc.CHCOW2H 5 0502CF 3 n-Bu4CF 1 d2m+lemcHCO0C2H 5 F F 1 NaOH 1 n2m+1L,mk,n0OC2H 5 > H2m+1cmCHCOOH Process C C02m+1 H HF/pyridine > H0H2C-C-CmH2m+1 0 F chiral epoxide KMn04 > HOOC-C-CmH2m+1 30 The configuration of the fluorinated carboxylic acid obtained by Process C has not yet been completely determined, because whether the ring opening of the epoxide leads to retention or inversion is not known, although the absolute configuration of the chiral epoxide is known. By contrast, the fluorinated carboxylic acids obtained by Process A and Process B differ from each other in configuration. In other words, the product obtained in Process A has the (S) configuration because the asymmetric part of an L-amino acid retains its (5) configuration. The product obtained by Process B has the (R) configuration because the reaction involved brings about inversion. The reaction products obtained by Process A and Process B are not enantiomers but are diastereoisomers. The product obtained by Process A from L-isoleucine, which has the (2S, 3S) configuration, has the (25, 3S) configuration, and the product obtained from L-isoleucine by Process B has the (2R, 35) configuration. The thus-obtained 4 fluorocarboxylic acid is converted into the ferroelectric liquid crystal according to the following process:

F F 1 SOC12 1 H CmCHCOOH H2m+1cmCHCOCI 2m+1 H2M.1c,O_ OH -O/H F 1 -OCCHCOH2.., H2..1C.0_ 0 More specific examples are set forth below.

E by Process A) F CH3 (2S, 3S) -n-H,1C.0_ -OCOCHCHCA 20 g of L-isoleucine was dissolved in 50 ml of 70% HF/pyridine.

16 g of dried sodium nitrite was added slowly to the solution with ice cooling and stirring. The solution was stirred further for 1 hour at room temperature. The solution was diluted with iced water and then extracted with diethyl ether. The extract was washed with a 5% aqueous solution of NaBC03. After drying with M9S04, the extract was freed of ether by distillation. Excess of thionyl chloride and dichloromethane were added to the residue (4 g) to form an acid chloride (2.5 g) in the usual way. The acid chloride was reacted in benzene with p,p' biphenyl-mono-n-octyl ether in the presence of triethylamine to provide a desired liquid crystal compound having the following characteristic properties.

Specific rotation [(X] D 20 +0.70 (C = 1, ethanol) 1 H-NMR (CDC1 3) 5 4.72 (d), 5.64 (d), (H-F, JHH = 3 Hz) Mass (M) 414 Incidentally, the 1H-NMR data gave peaks resulting from impurities in the vicinity of 53 and 5.95 ppm, and the Mass data gave a peak at m/e 394. This suggests that the product contains the following compound formed by the elimination of HF:

CH3 n-HIIC&0-C-C-OCOCH-C-C,H, The desired liquid crystal compound was found to exhibit spontaneous polarisation at 57.6 to 730C when measured by the triangular wave method. The spontaneous polarisation reached a maximum value of 112 nC/cm3 at 610C (measured at a frequency of 50 Hz).

Example 2 (Synthesis by Process B) F CH3 (2R, 3S) -n-H25C120- OCOCHCHC2H5 1 @- & g of L-isoleucine was dissolved in 200 mI of a 50% aqueous solution of acetic acid. 30 ml of an aqueous solution of NaN02 (21 g) was added dropwise to the solution with ice cooling. This solution was stirred further for 1 hour at room temperature. The solution was extracted with diethyl ether. The extract was freed of ether by distillation. 0.5 g of toluenesulphonic acid, 300 ml of ethanol and 100 ml of benzene were added to the residue. The solution was heated under refluxing. During refluxing, water was separated as an azeotrope with ethyl acetate, benzene, and ethanol. Twelve hours later, the solution was extracted with diethyl ether, and the extract was washed and dried. After distillation under reduced pressure, 15.9 g of ethyl 2- hydroxy-3-methylpentanoate (bp. 67-700C/267Pa(= 2 m Hg)) was obtained. This ethyl 2-hydroxy-3methylpentanoate (11 g) was dissolved, together with 8 ml of lutidine, in 20 ml of dichloromethane.

To the resulting solution there was added dropwise, with ice cooling, 15.4 ml of trifluoromethanesulphonic acid anhydride, followed by stirring for 0.5 hours. The solution was then passed through a short column of silica gel and then subjected to distillation under reduced pressure. 17.7 g of ethyl 2-(trifluoromethanesulphonyloxy)-3- methylpentanoate (bp. 71 to 750C/267Pa (= 2 mm Hg)) was obtained. This ester ( 17.7 g) was dissolved in 150 ml of acetonitrile, and 18 g of tetra(n-butyl)-amonium fluoride trihydrate was added to the solution, 6 which was then allowed to stand overnight at 50C. The resulting solution was passed through a short column of silica gel and subjected to distillation under reduced pressure. 6.1 g of ethyl 2-fluoro- 3methylpentanoate (bp. 70 to 740C/267Pa(= 2 m Hg)) was obtained. This compound was added to 150 mI of 1N NaOH, and the solution was stirred at room temperature for 12 hours. After neutralisation with dilute hydrochloric acid, the solution was extracted with diethyl ether and the extract was dried and freed of ether by distillation under reduced pressure. About 4 g of 2-fluoro-3-methyl-pentanoic acid was obtained.

The compound was converted into an acid chloride (about 3 g) in the usual way. The acid chloride was reacted with p,pl-biphenyl-mono-ndodecyl ether to give the desired liquid crystal compound, which had the following characteristic properties.

Specific rotation 1OCID 20 +1.10 (C = 1, CHCl 3) 1H-MR (CD1 3) 5 4.70 (d), 5.52 (d), (q.H-F) Mass (M') 470 Incidentally, the following compound was synthesised by Process B in the same manner as above.

F CH3 1 1 n-H,.C.0- -OCOCHCHC2H5 This compound was found to have the following characteristic properties.

Specific rotation 1OCID 20 _ 1.30 (C = 1, ethanol), +1.10 (C = 1, CHCl 3) 1H-MR (CDC1 3) 5 4.60 (d), 5.40 (d), (CH-F, JHH = 4.8 Hz) It is to be noted that this compound differs in chemical shift from that obtained in Example 1. In addition, the NMR data of this compound did not give the peaks resulting from impurities which were observed in Example 1. This suggests that the compounds obtained by Process A and Process B have the same structural formulae but are diastereoisomers having different chemical and physical properties.

The liquid crystal compound was found to exhibit spontaneous polarisation at 72 to 800C, which reached a maximum value of 200 nC/cm3 7 and 188 nC/cm3 at 76.60C (measured at frequencies of 3 Hz and 50 Hz, respectively).

Example 3 (Synthesis by Process C) F 1 OCCH (CH2) 5CH3 n-H17C80-@ -@- 1 0 ml of a solution in diethyl ether containing 9.15 9 of (R) 1,2-epoxyoctane was added dropwise to 80 mi of ice-cooled 70% HF/pyridine with stirring. The reaction was carried out with ice cooling for 1 hour and then at room temperature for 1 hour. The reaction liquid was neutralised with a 5% aqueous solution of NaHCO 3 The ethereal layer was separated and dried with MgSO4 and freed of solvent by distillation under reduced pressure (650C, 40 W= 0.3 m Hg)). 6.1 g of 2-fluorooctanol (a 58% yield) was obtained.

The 2-fluorooetanol was dissolved, together with 10 g of NaOH, in ml of water. Mn04 power, in an amount of about 17 g, was slowly added to the resulting solution with stirring. The solution was stirred at room temperature for 1 hour and then heated to 50 to 600C, and the reaction was continued for about 5 to 6 hours until the supernatant liquid became clear. The reaction liquid was filtered to remove Mn02, followed by washing 3 to 4 times with hot water. The filtrate was extracted with diethyl ether to remove the raw alcohol.

The aqueous layer was neutralised with dilute hydrocholoric acid and the diluted solution was extracted with diethyl ether. The extract was dried and freed of ether by distillation under reduced pressure.

2.15 g (32% yield) of 2-fluorooctanoic acid (bp. 70 to 1000C/40 to 53 Pa(= 0.3 to 0.4 m Hg)) was obtained.

This compound was converted into an acid chloride in the usual way, and the acid chloride was reacted with p,pl-biphenyl-mono-noctyl ether to give the desired liquid crystal compound having the following properties.

Specific rotation 1OCID 20 +0.30 (C = 17 CHCl 3) 1H-NMR (CDC1 3) S 4.72 (t), 5.56 (t), (CH-F) Mass W') 442 8 The liquid crystal compound exhibited spontaneous polarisation at 104.8 to 98.30C, which reached a maximum value of 192 nC/cm3 at 102.50C (measured at a frequency of 50 Hz).

The above mentioned processes can also be used to produce 5 compounds having a molecular skeleton other than biphenyl. The embodiments of the invention set forth above provide a stable ferroelectric liquid crystal having a high value of spontaneous polarisation (Ps). Because of this property, it can be blended with a variety of liquid crystal compounds to give compositions of practical use which have a desired value of spontaneous polarisation and a high speed response. In addition, the ferroelectric liquid crystal finds use as an electro-optical element because its smectic phase responds to electric fields. This element is superior in high-speed response to TN- type liquid crystal elements. In addition, it may be given a memory property if its orientation is properly controlled. Because of these characteristics, the ferroelectric liquid crystal embodying the invention can be applied to high speed optical shutters and display units that contain a large amount of information.

9

Claims

1. A ferroelectric liquid crystal, in which a fluorine atom is attached to an asymmetric carbon atom, having the structural formula F 0 where n is an integer equal to 6 to 20, and m is an integer equal to 3 10 to 20.

2. A ferroelectric liquid crystal according to claim 1, wherein is 8 and m is 4.

3. A ferroelectric liquid crystal according to claim 1, wherein is 8 and m is 6.

4. A ferroelectric liquid crystal substantially in accordance with any one of the foregoing examples.

Published 1989 atThe Patent Office, State House, 66.171 High Holborri, London WC1R 4TP. Further copies maybe obtainedfrom The Patent OfEice.

Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1187 baies ijrancn, bt mary cray, OrDington, Kent BR5 3RD. Printed b.v MultiDlex techniaues ltd. St Mary Crav. Kent. Con. 1187