GB2134535A - Liquid crystal compositions containing a bicyclo(2,2,2)octane derivative - Google Patents

Abstract

Liquid crystal compositions comprise a mixture of compounds and include at least one additive compound of Formula I: <IMAGE> wherein R1 represents an alkyl group, R2 represents in alkyl or alkoxy group or hydrogen and <IMAGE> represents a 1,4-disubstituted bicyclo(2,2,2)octane ring.

Description

SPECIFICATION Liquid crystal materials and additive compounds containing a bicyclo(2, 2, 2)octane structure suitable foruseinthem The present invention relates to liquid crystal materials and additives for use in them.

The use of liquid crystal materials to exhibit electro-optical effects in display devices such as digital calculators, watches, meters and simple word displays is now well known. However known liquid crystal materials are not ideal in all respects and a considerable amount of work is currently being carried out in the artto improve their properties.

Liquid crystal materials normally consist of mixtures of compounds and improved materials are obtained byforming new mixtures having an improved combination of properties.

Although liquid crystal materials normally consist mainly of compounds which exhibit a liquid cyrstal phase bythemselvesthe materials may contain components which do notexhibitsuch a phase.

Compounds forming such components exhibit a virtual or monotropic liquid crystal to isotropic liquid transition (clearing point) at a temperature below their melting point As is well known to those skilled in the art monotropic orvirtual transitions may be detected respectively by rapid cooling ofthe liquid phase or by dissolving the compound in a material exhibiting a liquid crystal phase, observing the change in the transition to the isotropic liquid phase ofthe material by the addition and calculating the virtual transition temperature by extrapolation of the data from a series of such mixtures of known composition.

Compounds which do notexhibita liquid crystal phase by themselves are useful as additives to liquid crystal materials, eg to improve the liquid crystal temperature range (iethe range overwhich the matrial exhibits a liquid crystal phase) and/orto improve the viscosity of the liquid crystal material: The liquid crystal temperature range of a material is important because it determines the operating temperature range ofthe display device. This range is desirably as great as possible.

The viscosity of a liquid crystal material isimpor- tant because it detemines the speed of response of the display device, ie the times required to switch the displayfromthe off state to the on state and vice versa. The viscosity is desirably as low as possible.

The viscosity of a mixture of compoundsforming a liquid crystal material is determined by the viscosity ofthe individual compounds.

Strictly speaking, the response times are dependent on a number of viscosity coefficients but the main coefficient to be considered is that known as the "flow aligned" viscosity coefficient (see for example the article entitled "Flow aligned viscosities of cyanobiphenyls" byJ. Constant and E. P. Raynes Mol. Cryst. Liq. Cryst. (1980) Vol 62 pages 115-124). The term "viscosity" as used in this specification is to be understood to mean the flow aligned coefficient in the nematic liquid crystal phase (mesophase) unless otherwise specified.

Compounds normally incorporated in liquid crystal materials for electro-optical applications may generally be represented intheirsimplestgeneralisedform byformula Aasfollows: X-Y-X' A where X and X' independently represent aromatic or alicyclic ring structures and Y represents a simple bridging group such as CO.O or a direct carboncarbon bond.

Formula A normally applies to such compounds whether or notthey exhibit a liquid crystal phase by themselves.

The groups Xand X' mayforexample include a 1,4 - disubstituted benzene ring, a trans -1,4 - disubstituted cyclohexane ring, or a 1,4 - disubstituted bicyclo(2, 2, 2)octane ring. Known compounds of the typewhch include a bicyclo(2, 2, 2)octane ring include known compounds of formulae B and C as follows:

where Rand R' are alkyl groups and Q is hydrogen or fluorine. Compounds offormulae B and C are described in published UK Patent Application Nos.

2027027A and 2063250A for example.

We have now discovered that a class of bicyclo(2, 2, 2)octane compounds which surprisingly are not of the generalised formuia A are useful as additives in liquid crystal materials.

According to the present invention in a first aspect there is provided a liquid crystal material which comprises a mixture of compounds and which includes at least one additive compound characterised in that the material includes one or more additive compounds of Formula I asfollows:

wherein R1 represents an alkyl group, R2 represents an alkvl oralkoxvarouD orhvdroaen and

represents a 1,4 - disu bstituted bicyclo(2, 2, 2)octane ring. Preferably R1 and R2 each contain not more than twelve carbon atoms.

According to the present invention in a second aspect there is provided a compound offormula I suitable for use in a liquid crystal material wherein R1 is an n-alkyl group having from 3to 8 carbon atoms inclusive and R2 is an n-alkyl or n-alkoxy group having from 1 to 8 carbon atoms inclusive.

Preferably, R2 is Formula I is n-alkyl having from 3 to 8 carbon atoms.

Compounds of Formula I can provide very attrac- tive low viscosity additives to liquid crystal material and may show aspects of superiority compared with known low viscosity additives.

For example, compounds of Formula I can show a similar reduction in viscosity but a smaller depression of clearing point (liquid crystal-to-isotropic liquid transition temperature) than the additives offormula D as follows:

where R is n-alkyl, when added to the same host liquid crystal material. Compounds offormula Dare described in copending UK PatentApplication No. GB 2106127A.

The compounds offormula I may be prepared by routes in which the individual procedures are known, the overall routes being new. For example the following routes may be used.

Routel (R2 = alkyl)

where CH2.R3 = R2 Route2 (R2= methyl) Route 2 (R2 = methyl)

Route 3 (R2 = alkoxy)

Route 4 (R2 = hydrogen)

The compounds of Formula (I) have a small dielectric anisotropy (when added to liquid crystal materials) and may be added to liquid crystal materials of positive or negative dielectric anisotropy, known and referred to herein respectively as "positive" or "negative" materials, without significantly affecting the dielectric anisotropy of such materials.As is well known to those skilled in the art the dielectric anisotropy ofthe liquid crystal material is necessary to give electro-optical operation and its sign (for a given frequency) is chosen according to the kind of electro-optical device in which the material is to be used.

Normally, the liquid crystal material in which the compound of Formula (I) is contained will comprise a host material which comprises one or more liquid crystal compounds having a low melting point ( < 80 C) which preferably together with the additive(s) show a liquid crystal phase (preferably nematic or chiral nematic) at room temperature (20"C) togetherwith one ormore additives, eg to reduce viscosity a nd/or enhance liquid crystal temperature range, the additive(s) including at least one compound of Formula I.

The upper limit of the percentage byweightwhich the compound(s) of Formula I consititute in the mixturewiththe host material will depend on the host materia I bottypical ly the compound(s) will form between 2 and 50% byweight in total, for example between 5 and 30% byweight inclusive in total.

The host material towhich the compound(s) of Formula I isadded maybeoneofthefollowing materials: (i) a positive nematic material for use in twisted nematic effect devices including multiplexed devices; an example of such a device is given below; (ii) a negative material preferably also with a pleochroic dye, for use in Fráederickszeffectdevices (negative nematic type) in which the molecufar arrangement may be changed from the homeotropic texture (OFF state) to the homogeneous texture (ON state) by an electricfield; an example of such a device is given below; (iii) a positive nematic material, preferably also with a pleochroic dye for use in Fréedericksz effect devices (positive nematictype) in which the molecular arrangement may be changed from the homogeneous texture (OFF state) to the homeotropic texture (ON state) by an electric field; (iv) a negative material which is a cholesteric (chiral nematic) of suitable resistivity (about 109 ohm-cm),foruse in cholesteric memory mode devices in which the molecular arrangement may be changed from a homogeneous texture (OFF state) to a turbulent scattering focal conictexture (ON state) by an electric field;; (v) a strongly negative material which is a cholesteric, preferably together also with a pleochroic dye, for use in cholesteric-to-nematic phase change effect devices (positive contrasttype) in which the molecular arrangement may be changed from a weakly scattering, ie clear, surface alignect homeotropic texture (OFF state) to a strongly-scattering twisted homogeneous texture (ON state) by an electricfield;; (vi) a positive material which is cholesteric, preferably together also with a pleochroic dye, in cholesteric-to-nematic phase change effect devices (negative contrast type) in which the molecular arrangement may be changed from a scattering-focal conictexture (OFF state) to clear homeotropictexturetON state) by an electric field; (vii) a negative nematiematerial of suitable resistivity (about 1.QCohm-cmh in dynamic scattering effect devices in which themoleculrarrangement may be changed from a clear homeotropic texture (OFF state) to a turbulent scattering texture (ON state) by an electric field; ; (viii) a positive nematic material in two frequency switching effect devices (which may betwisted nematic effect devices) in which the dielectric anisotropy ofthe material may be changed from (at low frequency) positive (OFF state) to negative (ON state) bythe application of a high frequency electric field.

The construction and operation ofthe above devices and the general kinds of material which are suitable for use in them are themselves known.

The host material to which one or more compounds of Formula I are added may itself be a mixture of two or more compounds selected for the particular device application.

Where a host material is for use in a twisted nematic effect, cholesteric to nematic phase change effect (negative contrast type) or Fréedericksz effect (positive nematic type) device the material preferably contains one or more compounds selected from the following families to give a liquid crystal phase at room temperature as well as a positive dielectric anisotropy.

Formula (IIIa) Formula (IIIb) Formula (IIIc) Formula (IIId) Formula (IIIe) Formula (IIIf) where the various groups Rare the same or different alkyl groups (preferably n - alkyl having up to 10 carbon atoms).

The material may also contain one or more high ( > 1 00 C) clearing point compounds (typically up to about 35% by weight) ofthefollowing classes to extend the liquid crystal temperature range ofthe material at its upper end:

Formula (IVa) Formula (IVD) Formula (IVc) Formula (IVd) Formula (IVe) Formula (IVf) Formula Formula (IVh) where R is as defined above.

The compounds of Formula I are particularly suitable for use in liquid crystal materials which may be used in multiplexed twisted nematic effect devices. As taught in published UK Patent Applications 2,031,01 OA and 2,063,287Athe multiplexibility of a strongly positive host material, eg consisting of biphenyl compounds of Formula (lila) and/or the PCH compounds of Formula (Illb),togetherwith one or more high clearing point compounds selected from the classes of Formulae (IVa to h), may be improved bytheaddition of a component of low dielectric anisotropy.This improvement is believed to be broughtabout bythe disruption of anti-parallel pairing ofthe molecules of the cyano compounds caused by introduction of the material of low dielectric anisotropy.

The component of low dielectric anisotropy may comprise one or more compounds of Formula I optionally together with one or more compounds selected from the following known families:

Formula (Va) Formula Cm) Formula (Vc) Formula (Vd) Formula (Ve) Formula (V ) Formula (Vg) Formula (Vh) Formula Cvi) Formula (V;) Formula (Vk) whereX = halo, preferablyfluoro, = bicyclo(2, 2, 2)octane and R is as defined above.

A multiplexed twisted nematic device may also contain a small amount, eg up to about 2% by weight, of a chiral additive, eg the BDH compound C 15.

Thus, a liquid crystal material suitable for a multiplexed twisted nematic effect device embodyins the present invention preferably comprises the components in Table 1 as follows: TABLE 1: Liquid crystal material composition for multiplexed twisted nematic operation Percentage by Component Constituents weight Component 1: One or more compounds 5-80%, low melting point positive selected from preferably compound(s) giving a room Formulae (Illa) to 40-70% temperature nematic phase. (Illf) above.

Component 2: One or more compounds 5-30%, high clearing point selected from preferably liquid crystal compounds Formulae (IVa) to 10-30% (IVh).

Component 3: One or more compounds 5-90% low dielectric anisotropy of Formula (I) optionally preferably compound(s). (1As1 < 3) together with one or more 20-50% compounds selected from Formulae (Va) to (Vk).

Component 4: One or more chiral 0-2% chiral compound(s) compounds.

The compound(s) of Formula (I) preferable constitutefrom 5 to 30% by weight of the overall material composition.

In the material whose composition is defined by Table 1 the compound(s) of Formula (I) not only help to reduce the viscosity and extend the temperature range ofthe nematic liquid crystal phase ofthe mixture at the lower end but also help to improve the multiplexibility ofthe mixture.

Liquid crystal mixtures including compounds of Formula (I) may be formed in a known way, eg simply by heating the constituent compounds to form an overall isotropic liquid, stirring the liquid for a short period, eg about 10 minutes, and allowing itto cool.

To provide more general examples of a mixture according to the second aspect at least one com pound according to Formula (I) above may be mixed togetherwith one ormore compounds in any one or more ofthe following known families for use in one or more ofthe applications given above (the actual application(s) depending on the mixture's properties)::

where

is a trans 1, 4 - disubstituted cyclohexane ring,

is a 1,4 - disubstituted bicyclo(2, 2, 2)octane ring, Xis a 1,4 phenylene group

a 4, 4' - biphenylyl group

a2,6-naphthyl group

ora trans -1, 4 - disubstituted cyclohexane ring, and Y1 is CN, or R or CO.O-X-Y whereY1 is CN, or R' or OR'; where Rand R' are alkyl groups; oraderivative of one ofthese wherein H is replaced by a halogen, eg F, in one ofthe benzene rings.

Preferably, the compound(s) of Formula (I) comprises between 5 and 30% byweight ofthe mixture.

According to the present invention in a second aspect a liquid crystal device includes two dielectric substrates at least one ofwhich is optically transpa- rent, a layer of liquid crystal material sandwiched between the substrates and electrodes on the inner surfaces ofthe substrates to enable an electric field to be applied acrossthe layer of liquid crystal material to provide an electro-optic effect therein, characterised in thatthe liquid crystal material consists of or includes a compound according to Formula (I) above.

The device according to the second aspect may be'a twisted nematic effect device, which may or may not be operated in a multiplexed fashion, a cholesteric-tonematic phase change effect device, a Fréedericksz effect device or a two-frequency switching effect device, all constructed in a known manner or any of the other devices mentioned above. The various ways in which compounds according to Formula I may be used in these devices are outlined above and will be further apparent to those skilled in the art.

Examples ofthe preparation and properties of compounds of Formula I will now be given.

The following abbreviations are used in the Exam ples.

Ms= massspectrum NMR = nuclear magnetic resonance spectrum IR = infrared absorption spectrum Vmax = infrared absorption peak oc = chemical shift (ppm) from denteriochloroform (CDCI3 solution) s = singlet t = triplet m = multiplet ppm = parts per million gic = gas-liquid chromatography THF = tetrahydrofuran Example 1: The preparation of 1,4- di - n pentylbicyclo(2, 2, 2)octane by route 1 given above.

StepA1: Preparation of 1 -pentanoyl -4- n pentylbicyclo(2, 2, 2)octane 1 - Bromobutane (10.45 g, 0.076 mol) in dry benzene (9 ml) was added dropwiseto magnesium (1,.68,0,069 mol) in dry benzene (3 ml) and dryTHF (9.98g) during 75 min. The reaction mixturewas stirred at room temperature for 1 h. Triethylamine (28.84 g, 0.285 mol) was added at 5-10 C and methyl 4 - n - pentylbicyclo(2, 2, 2)octane - 1- carboxylate (3.00 g, 0.013 mol) in dry benzene (27 ml) was added dropwise during 1 h at 5-15"C.The ice bath was removed and the reaction mixturewas left stirring at room temperature for4h, and the progress of the reaction was followed by glc until the ester peak had almost disappeared. The reaction mixture was di luted with water and the organic layer was washed with4N - hydrochloric acid (3 x 50 ml). The aqueous layerwaswashed with ether (3 x 50 ml) and the ether layers were combined with the organic layer and washed with water(3 x 50 ml) and dried (MgSO4).

The ether was removed and the residue dried in vacuo and used directly to make the required compound.

The crude yield was 3.01 g, 88% The product was confirmed by measuring the following infrared absorption peaks (Vmax)for a film specimen: Vmax(cm-1)2925,2860,1700 (C=0), 1455,1380 Step B1: Preparation of 1,4- di - n - pentylbicyclo(2, 2, 2)octane A mixture of 1 - pentanoyl - 4 - n - pentylbicyclo(2, 2, 2)octane (3.00 g, 0.01 mol), hydrazine hydrate (18 ml, 100%) and potassium hydroxide (5.00 g) in diethylene glycol (50 ml) was stirred and heated under refluxfor 5 h (170 C,oil bath temperature). The mixture was cooled and potassium hydroxide (2.00 g) and hydrazine hydrate (3 ml, 100%)were added and the apparatus was arranged for distillation.The oil bath temperature was raised slowly to 250 C during 2 hand maintained atthistemperaturefor2 h.The reaction mixture and the distillate were cooled separately, diluted with water and washed with ether (3 x 50 ml). The ether layers were combined, washed with water(2 x 50 ml) and then dried (MgSO4). The etherwas removed and the residuewaschromatographed on a neutral alumina column (Brockmann activity = 1; 30 cm x 1 cm) using light petroleum (bp 40-60 C). Fourfractions (15 ml each) were collected and analysed by gic. The solventwas removed and the residue was distilled to give the required di -alkyl compound.

The boiling point ofthe product was 120-140 C/0.5 mm Hg.

The yield was 1.83 g,65%.

The product showed the following 13CNMR spec troscopic results: oppm integration 14.08 1611 22.75 2971 23.40 3046 30.61 1706 31.48 7388 32.99 2837 42.88 2702 The product was confirmed by measuring the following IRVmax IRVmax (film): 2930,2860,1455,1380 cm-' and the following mass spectral (Ms) data: Ms: M+250 Example 2 1 - n - Pentyl - 4 - n - propylbicyclo(2, 2, 2)octane was prepared by a procedure analogous to that of Example 1.This product was obtained in a yield of 38% and had a boiling point of 158-162 C(15mmHg).

The product was confirmed by 'H NMR, IR and Ms mesurements.

Example 3 1-n - Heptyl - 4 - n - pentylbicyclo(2, 2, 2)octane was prepared by a precedure analogous to that of Example 1. This product had a boiling point of 120-124 C (0.15 mm Hg) and was obtained in a yield of 45 %.This productwas confirmed by 1H NMR, IR and Ms measurements.

Example 4 1 - Ethyl - 4-n - propyl - bicyclo(2, 2, 2)octane was prepared by 1. a procedure analogous to that of Example 1.This product had a boiling point of 84-98 C.

(15 mm Hg) and was obtained in a yield of This productwas confirmed by 1 H NMR, IR and Ms measurements.

Thefollowing compounds listed in Table 2 may also be prepared analogouslyto the procedure of Example 1: TABLE 2: Compounds offormula

C3E7 C3E7 c4ii9 C8E17 C4H9 c11 C5Et1 Cub13 C3E7 Cub15 C5E11 C8E17 C3E7 C7E15 C6E13 c6H13 c7 C8E17 Cosh13 C7E15 c4H9 c49 GsH13 C8E17 c4H9 C5E11 C7E15 c15 c4H9 Cub13 C7E15 C8E17 C4E9 C7E15 Cosh17 Cos17 Example 5: Preparation of 1 - methyl - 4 - n pentylbicyclo(2, 2, 2)octane by route 2 given above.

A mixture of 1 -chloromethyl -4-n- pentylbicyclo(2, 2, 2)octane (1.34 g, 0.006 mol) and t butanol (2.39 g, 0.032 mol) was added to finely cut lithium metal (0.55 g, 0.08 g atom) in dryTHF (34 ml).

The reaction mixture was left stirring at room temperature for 2 h. The temperature was raised to 65 C and the reaction mixture was left stirring at this temperature for 5 h, then it was cooled and diluted with water (100 ml) and washed with ether(3 x 70 ml). The ether solution was washed with water (4 x 30 ml) and dried (MgSO4). The solventwas removed and the residue was distilled in a short path distillation apparatus under reduced pressuretogivethe required compound.

The boiling point ofthe productwas 100-110 C (15 mm Hg).

The yield was 0.89 g,64%.

The product showed the following 1H NMR results: 1H NMR; 6 : 0.75(s, 3H), 0.90 (t, 3H), 1.15 (m, 8H), 1.33 (s, 12H) The product also showed thefollowing vmaxvmax (film) 2930, 2850, 1455, 1375 cm-1.

The product also showed the following Ms data: Ms;M+= 194.

Example 6:The preparation of 1 - n - butoxy-4- n propylbicyclo(2,2,2)octane prepared by Route 3 given above.

StepA3: Preparation of 4 - n - butoxy- 1 - n propylbicyclo(2, 2, 2)octane - 2 - one Amixtureof4-acetyl -4- n -propylcyclohexanone (3.65 g, 0.02 mol),tri -butylorthoformate (13.91 g, 0.06 mol) and toulene-p-sulphonic acid monophy drate (0.30 g) in AnalaR (Trade Mark) butan - 1 - ol (25 ml) was stirred at room temperature for 60 h. The progress of the reaction was followed by glc. The reaction mixture was diluted with ether (200 ml), washed with aqueous sodium carbonate (2 x 50 ml, 10%) and with water (2 x 50 ml) and the ether layer was dried (MgSO4). Etherwas removed and the residue was chromatographed on a neutral alumina column (1.5 x 30cm) using light petroleum (bp, 40-60 C) as eluent.Five fractions were collected (20 ml each) and combined. The solvent was removed and the residue was distilled in a short-path distillation apparatus to give the required compound.

The boiling point of the product of Step A3 was 105-115 C (0.5 mm Hg).

The yield was 3.72 g, 78%.

Thefollowing 1H NMR,IR,and Msdatawere measured fo the product: 1H NMR; #:0.90)zt,6H), 1.32(m,8H), 1.70(s,8H) 2.38 (s,2K), 3.34 (t, 2H) ppm.

IR(fil,):Vmax2960, 2870, 1725 (C=O), 1460, 1335, 1115(C-O)cm-1.

Ms;M+=238.

Step B3: The preparation of 1 - n - butoxy - 4 - n propylbicyclo(2, 2, 2)octane.

A mixture of 4 - n - butoxy - 1 n - propylbicyclo(2, 2, 2)octane -2 - one (2.08 g, 0.009 mol) hydrazine hydrate (8.4 ml, 98-100%) and potassium hydroxide (2.80 g, 0.050 mol) in diethylene glycol (40 mol) was stirred and heated under reflux for4 h (180 C, oil bath temperature). The reaction mixture was cooled and hydrazine hydrate (4ml) and potassium hydroxide (1.00 g) were added and the apparatus was arranged for distillation. Thetemperature was raised slowlyto 240 C in 2 h, and the reaction mixture was kept at this temperature for 2 h. The reaction mixture was cooled and the residue and the distillate wereseparately diluted with water, washed with ether (3 x 50 ml).All the etherwashings were combined and washed with water (2 x 50 ml) dilute hydrochloric acid (2 x 50 ml) and water (2 x 50 ml). The ether solution was dried (MgSO4) and ether was removed to give a residue which was chromatographed on a neutral alumina column (1.5 x 30 cm) using light petroleum (bp 40-60 C) as eluent. Four fractions were collected (20 ml each) the solvent was removed to leave a residue which was distilled in a short-path distillation apparatus under reduces pressure to give the required compound.

The boiling point ofthe productwas 1 42-146'C (15 mm Hg).

The yield was 1.02 g, 53%.

Thefollowing 1H NMR, IR and Ms data were measuredforthe product: H NMR:#:0.90 (t,6H), 1.08(m,8H), 1.54(s,12H), 3.28 (t, 2H), ppm.

IR(film):Vmax:2950, 2860, 1455, 1355, 1140, 1105 (C-O) cm-l.

Ms: M+ = 224.

Example 7 1 - n - Butoxy-4- n - pentylbicyclo(2, 2, 2)octane was prepared by a procedure analogous to that of Example 6.

This product, which had a boiling point of 178182 C (15 mm Hg) was obtained in a yield of 40%.

Thefollowing 'H NMR, IR and Ms data were measured forthe product: 1H NMR:#:0.90 (t,6H), 1.12(m,12H), 1.56(s,12H), 3.28 (t, 2H) ppm IR(film):Vmax:2950, 2860, 1455, 1355, 1140, 1105 (C-O) cm-1 Ms:M+=252.

Example 8 1 - n - Butoxy - 4- n - heptylbicyclo(2,2,2)octane was prepared buy a procedure analogous to that of Example 6.

This product, which had a boiling point of 125- 130 C (0.2 mm Hg) was obtained in a yield of 60%.

The following 1H NMR, IR and Ms data were measured for the product: 1H NMR:#:0.90(t,6H), 1.28(m,16H),1.56(s,12H), 3.32 (t, 2H) ppm IR (film): vmax: 2950, 2860, 1455, 1355, 1140, 1105 (C-O)cm-1.

Ms: M+ = 280.

Example 9 1-Ethoxy-4-n-propylbicyclo(2,2,2)octane was prepared buy a procedure analogous to that of Example 6.

This product, which was obtained in a yield of 47% had a boiling point of 118-124 C(15 mm Hg).

The following 1H NMR, IR and Ms data were measured for the product.

1H NMR:#:0.90(t,6H), 1.16(m,4H), 1.60(s,12H), 3.60 (q, 2H) ppm IR (film): vmax: 2955, 2870, 1455, 1335, 1140, 1110 (C-O)cm-1 Ms: M+ = 196.

The following additional compounds listed in Table 3 may also be prepared by a procedure analogous to that of Example 6.

Compounds of Formula

I R IRc'R0 C3F C3XF C11 C2XS C7H15 C2H5 3R 7! GÇ C5X11 C11 C7H15 C3E7 C3ET 6% C+11 c6H13 07K15 Cub13 3 7 95 1 C7X15 C7815 C7H15 C3E7 c8H17 Gt1 C8H17 C7515 Cosh17 C4E9 0285 C6g1,3 0285 Cosh17 C2I15 c489 0489 068Cb c387 C8X17 0387 4H9 C5E11 c6H13 C5E11 c8817 Cub11 0489 c6813 C6E13 C6X13 c8817 C6X13 c489 C7E15 C6E13 C7X15 Cub17 C7X15 0489 Cosh17 C6X13 C8X17 C^7 08817 08817 Example 10 The preparation of 1 - n - Pentylbicyclo(2, 2, 2)octanebyRoute4given above.

Lithium metal in small pieces(0.6865 g, 0.1 g.at.) was added two a mixture of 1-bromo-4- pentylbicyclo(2, 2, 2)octane (2.6043 g, 0.01 mol) in dry THF (75 ml). The reaction mixture was stirred and warmed at 60 C for 4 h and the progress of the reaction was followed by glo. The reaction mixture was then cooled, the lithium metal wasfiltered off and thefiltratewas diluted with water (180 ml) and washed with after(3 x 70 ml). The ether layerswere combined and washed with water (3 x 10 ml) dried (MgSO4) and the ether was removed to give a residue which was distilled in a short-path distillation apparatus under reduced pressure (water pump) to give the required compound.

The following measurements were made forthis product: Boiling Point: 100-100 C/15 mm Hg Yield:1.6805 g, 93%.

H NMR:#:0.90 (t,3H), 1.10(s,6H), 1.35 (s,6H)ppm IR:Vmax(film)2930, 2870, 1460 cm-1 Ms:M+=180.

The following properties listed in Table 4 have also been measured for compounds of Formula I: (i) Clearing point (denoted as ofthe or the compound which was obtained by extrapolation from the clearing point results obtained using 10% and 25% by weight mixtures ofthe compound in the known material ZLI 1132 obtained from E Merck Co.

(ii) "Nematic" viscosity (denoted as 9200 or 900) ofthe compound obtained by extrapolation of the viscosity results obtained using a 20% weight mixture of the compound in ZLI 1132 at:200C and 0 C respectively: TABLE 4: Properties of compounds of Formula::

Compound R1 R2 Tn-1( C) #20o(cps) #0o(cps) n-C3H7 C2H5 -147 to -142 5.0 3.5 n-C5H11 n-C5H11 -36 to -30 7.7 20.2 n-C5H11 n-C4HgO -92 to -88 14.4 21.7 n-C3H7 n-C4H9 -115 to -111 - n-C7H15 n-C4H90 -85 to -82 - n-C5H11 n-CH3 -136 to -125 9.7 12.0 n-C5H11 n-C3H7 -77 to -72 6.6 4.5 n-C5H11 n-C7H15 -30 to -24 8.4 22.2 n-C5H11 H -107 to -96 51.4 29.13 The compounds 1 - n - pentyl - 4 - n propylbicyclo(2,2,2)octane, compound X1, 1,4- di - n - pentylbicyclo(2,2,2)octane, compound X2, and 1-n - heptyl -4-n - pentylbicyclo(2, 2, 2)octane compound X3 were further investigated in comparison with the low viscosity compound offormu la

(trans-isomer), compound Y,as follows.Each additive compound ie compound X1,X2,X3 and Y was added in turn to Mixture A defined as follows, the additive compound forming in each case 27% by weight of the overall mixture. The clearing point TN-( C) and viscosity at various temperatures was measured for each overall mixture formed.

The Mixture A used was as defined in Table 5; (for each # the transisomer is used) TABLE5: MixtureA.

Compound Parts by weight bC3H7XcK 10 < çtiw 5 KC3H^l woGtt to ~CS HI\4+}C1MS 17 17 h Cçli +3H7 > 10 rt-3u7to In 8 hlSHII'QC- C0.0 -C) H7M 6 The results obtained for the overall mixtures are as shown in Table 6 as follows wherein Y, X1, X2 and X3 have the following formulae:

TABLE 6: Comparative properties of Mixture A together with various low viscosity additives Compound No. added V X, X2 X3 Viscosity at 20 C (cps) 22 21.0 22.1 24 Viscosity at 10 C (cps) 36 35.0 36.8 39.6 Viscosity at 0 C 64 63 68 71.5 Viscosity at -100C 135 136 145 152 Viscosity at -14 C - 192.4 226 Tn-I( C) 72 79 86 81.8 Table 6 demonstratesthat compounds X1, X2 and X3 show mixture viscosities similarto those shown by compound Y but, beneficially, compounds X1, X2, X3 show a mixture TN-I depression not as great as that shown by compound Y.

Examples offurther materials and devices embodying the invention will now be described by way of example only with reference to the accom panying drawings wherein: Figure lisa front view of a twisted nematic digital display; Figure 2 is a sectional view ofthe display shown in Figurel; Figure 3 shows a rear electrode configuration for Figure 1; Figure 4 shows a front electrode configuration for Figure 1; Figures 5,6,7 show schematic views ofthe device of Figures 1 to 4 with typical addressing voltages.

The display of Figures 1 to 4 comprises a cell 1, formed of two, front and back, glass slides 2,3 respectively, spaced about 7 calm apart by a spacer 4 all held together by an epoxy resin glue. A liquid crystal material 12 fills the gap between the slides 2,3 and the spacer4. In front ofthefrontglass slide 2 is a front polariser 5 arranged with its axis of polarisation axis horizontal. A reflector7 is arranged behind the slide 3. A rear polariser 6 or analyser is arranged between the slide 3 and reflector 7.

Electrodes 8,9 oftin oxide typically 100 A thick are deposited on the innerfaces of the slides 2,3 as a complete layer and etched to the shapes shown in Figures 3,4. The display has seven bars per digit 10 plus a decimal point 11 between each digit. As shown in Figure 3the rear electrode structure is formed into three electrodes X1 x2, X3 Similarlythe front electrode structure is formed into three electrodes per digit decimal point y1, y2, y3 ... Examination of the six electrodes per digit shows that each of the eight elements can independently have a voltage applied thereto by application of suitable voltage to appropriate x, y electrodes.

Priorto assembly the slides 2,3 bearing the electrodes are cleaned then dipped in a solution of 0.2% byweight of poly-vinyl alcohol (PVA) in water.

When dry,the slides are rubbed in a single direction with a soft tissue then assembled with the rubbing directions orthogonal to one another and parallel to the optical axis ofthe respective adjacent polarisers, ie so thatthe polarisers are crossed. When the nematic liquid crystal material 12 is introduced between the slides 2,3 the molecules at the slide surfaces lie along the respective rubbing directions with a progressive twist between the slides.

When zero voltage is applied to the cell 1 light passes through the front polariser 5, through the cell 1 (whilst having its plane of polarisation rotated 90 ) through its rear polariser 6to the reflector 7 where it is reflected back again to an observer (shown in Figure 1 atan angle of 45 tothe axis Z normal to axes Sandy in the plane of the slides 2,3). When a voltage above a threshold value is applied between two electrodes 8, 9 the liquid crystal layer 12 loses its optical activity, the molecules being re-arranged to lie perpendicular to the slides 2,3, ie along the axis Z. Thus light atthe position does not reach the reflector 7 and does not reflect back to the observer who sees a dark display of one or more bars of a digit 10.

Voltages are applied as follows as shown in Figures 5,6 and 7 forthree successive time intervals in a linescan fashion. An electrical potential of 3V/2 is applied to, ie scanned down, each x electrode in turn whilsttV/2 is applied to the remaining x electrodes.

Meanwhile-3V/2 or V/2 is applied to the y electrodes. A coincidence of 3V/2 and -3V/2 at an intersection results in a voltage 3Vacrossthe liquid crystal layer 12. Elsewhere the voltage is or-V.

Thus by applying -3V/2 to appropriatey electrndes as 3V/2 is scanned down the x electrodes selected intersections are turned ON as indicated bgsolid circles. The electric voltage V is an ac signal ofeg 100 Hzsquare wave, and the sign indicates the phase.

Twill be apparent to those skilled in the artthatthe device shown in Figures 1 to 7 is a multiplexed display because the electrodes are shared between ON and OFF intersections or display elements.

A material embodying the second aspect ofthe invention which issuitableforuseasthematerial 12 in the above device is Mixture A (73% by weight) together with 27% by weight of Compound X1 defined above.

Small amounts of a cholesteric material may be added to the nematic material to induce a preferred twist in the molecules in the liquid crystal layer. This and the use of appropriate slide surfacetreatment removes the problems of display patchiness as taught in UK Patent Serial Numbers 1,472,247 and 1,478,592.

Suitable cholesteric materials are: C15: about O.1 -0.5% byweightandCB15: about 0.01% to 0.05% by weight.

Small amounts of pleochroic dye may be added to enhance the display contrast, eg one ofthe anthroquinone dyes described in U K Patent Specification No 2011940A. One polariser is removed in this case.

In another embodiment mixtures embodying the second aspect ofthe invention may be used in a Fréedericksz effect cell. Such a cell may be constructed by sandwiching the liquid crystal material between glass slides having electrode films deposited on their inner surfaces as in the above device.

However, in this case the polarisers are not necessary; the glass slide inner surfaces are treated with a coating of lecithin and the liquid crystal material is a negative material whose molecules are aligned in the OFF state perpendicular to the slide substrates (homeotropictexture) by the lecithin coating. Application of an appropriate electricfield across the material in the ON state re-arranges the molecules parallel to the slide surfaces (homogeneoustexture).

A pleochroic dye may be incorporated in the liquid crystal material to enhance the contrast be > aNeen the ON and OFF states.

A Fréedericksz effect cell made in the above way may incorporate Mixture 3 below, the cell spacing being 10 cam.

TAX 7: Mixture 3

Compound Weight Percentage p -Q CS tJ II C3H- 30 -C4flCOOCti- TO 30 t- CSrHs ro C3 H7 E3CSHlr'n 20 Compound A

may optionally be added to Mixture 3 (up to 3% by weight of Mixture 3) as a negative additive.

The preparation of Compound A is described in published UK PatentApplication No 2061256A. About 1% byweightofa known pleochroic dye eg 1,5 - bis 4' - n - butylphenylaminoanthraquinone may be added to Mixture3to give a dyed mixture. (Mixture 3A).

When a voltage is applied across the cell, the colour changes from a weakly absorbing state to a strongly absorbing state.

In an alternative embodiment ofthe invention a (cholesteric-to-nematic) phase change effect device incorporates a material as defined above.

A cell is prepared containing a long helical pitch cholesteric material sandwiched between electrodebearing glass slides as in thetwisted nematic cell described above. Howeverthe polarisers and surface preparations for homogeneous alignment, eg treatment ofthe glass slide surfaces with SiO, are not used in this case.

lftheglass slides are untreated and the liquid crystal material has a positive dielectric anisotropy (Agl the liquid crystal material is in a twisted focal conic moleculartexture in the OFF state which scatters light. The effect of an electric field applied between a pair of electrodes on the respective inner surface ofthe glass slides is to convert the region of liquid crystal material between the electrodes into the ON state which is a homeotropic nematic texture which is less scattering than the OFF state. This is a 'negative contrast' type of phase change effect device.

If the inner glass slide surfaces are treated, eg with a coating of lecithin, to give alignment perpendicular to those surfaces, and the liquid crystal material has As negative the material in the OFF state is in a homeotropictextu re which has little scattering effect on incident light. If an electric field is applied between a pair of electrodes on the respective inner surfaces of the glass slides the region of liquid crystal material between the electrodes is converted to a twisted homogeneous texture which scatters light (the ON state). This is a 'positive contrast' type of phase change effect device.

The contrast between the two states in each case may be enhanced by the addition of a small amount of a suitable pleochroicdye (eg 1 % by weight of 1,5 - bis - 4'n - butylphenylaminoanthraquinone in the case where As is positive) to the liquid crystal material.

A suitable positive dielectric anisotropy material, Mixture 4, embodying the invention for use in a phase change effect (negative contrast type) device is: TABLE 8 : Mixture 4

Component Weight Percentage Mixture A defined above) 70 t-Ci eC7ls~~lt 23 g C 1 < 5 (Rc = (+)-2-methylbutyl) A suitable negative dielectric anisotropy material embodying the invention for use in a phase change effect (positive contrast type) device, Mixture 5, is as follows: : TABLE 9 Mixture 5

Material Weight Percentage Mixture 3 99 1 C8o-2?mathyl1atyl) Examples of high birefringence, low viscosity materials of positive dielectric anisotropy suitable for simple twisted nematic displays and which include a compound of Formula (I) are Mixtures 6 and 7 defined in Tables 12 and 13 asfollows:

Claims (8)

1. A liquid crystal composition which comprises a mixture of compounds and which includes at least one additive compound characterised in that the composition includes one or more additive compounds of Formula I asfollows:

wherein R1 represents an alkyl group, R2 represents an alkyl or alkoxy group or hydrogen and

represents a 1,4 - disubstituted bicyclo(2, 2, 2)octane ring.

2. A composition as claimed in claim land wherein in Formula I R1 is n - alkyl R2 is n - alkyl or n alkoxy and each of R1 and R2 independently has from 1 to 12 carbon atoms.

3. Acomposition as claimed in claim 2 and wherein each R1 and R2 independently has from 1 to 8 carbon atoms.

4. Acomposition as claimed in claim 1 and wherein the composition comprises a host material including one or more liquid crystal compounds which melt at less than 80 C,the composition exhibiting a nematicorchiral nematic liquid crystal phase at 20 C.

5. A composition as claimed in claim 1 and wherein the at least one compound of Formula I forms between 2% and 50% by weight of the composition.

6. Acomposition as claimed in claim 5 and wherein the at least one compound of Formula I forms between 5% and 30% by weight ofthe composition.

7. A composition as claimed in claim 1 and which comprises: Component 1: one or more compounds having a melting point less than 80 C and a positive dielectric anisotropy, the compound or compounds showing a nematic phase at 205C; Component2: one or more nematic compounds having a clearing point greater than 100 C.

Component 3: oneor more compounds showing a dielectricanisotropymagnitude less than 3 and including one or more compounds of Formula I; Component4: one or more chiral compounds; the components being in the following proportions by weight: Component 1:30% to 70% Component2: 10% to 30% Component3: 20% to 50% Component4: 0% to 2% the sum ofthe weight percentages of Components 1 to 4 adding to 100%.

8. A bicyclo - octane compound for use in the composition of claim 2, the compound having the formula;

wherein R1 is n - alkyl having from 1 to 8 carbon atoms inclusive and R2 is n - alkyl or n - alkoxy having from 1 to 8 carbon atoms inclusive.