WO2005019156A2

WO2005019156A2 - Biphenyl-4-carboxylic acid alkyloxycarbonyl phenyl esters and uses thereof

Info

Publication number: WO2005019156A2
Application number: PCT/GB2004/003573
Authority: WO
Inventors: Steven J. Cowlings; Alan W. Hall; John W. Goodby
Original assignee: The University Of Hull
Priority date: 2003-08-19
Filing date: 2004-08-19
Publication date: 2005-03-03
Also published as: WO2005019156A3; GB0319401D0

Abstract

The present invention relates to a compound of the general structure of formula (I): X-Alkylene1-A-1-Alkylene2-A2-(Z1)x-B-(Z2)y-C-(Z3)z-A3-Alkyl3 in which A1, A2 and A3, which may be the same or different, are each -O-, -COO-, -OCO- or -S-; Z1, Z2 and Z3, which may be the same or different, may each be selected from the group : Formula (a) : in which the cyclic rings may be laterally substituted by hydrogen, -CH3, -CF3, -CN, -NO2, halogen, e.g., F, Cl, Br, B and C, which may be the same or different, are each selected from the group: single bond, -COO-, -OCO-, -CH2O-, -CF=CF- or -C=C-; X is selected from the group: cycloalkyl, bicycloalkyl and polycycloalkyl; and x, y and z, which may be the same or different, are each an integer, being 1 or 2, as the racemate, the S or the R enantiomers or mixtures thereof.

Description

Materials

This invention relates to novel compounds, novel uses thereof and to novel devices which may, optionally, comprise such materials.

In particular the present invention comprises a novel group of biphenyl-4-carboxylic acid alkyloxycarbonyl phenyl esters, intermediates thereto and to processes for their preparation.

Telecommunication devices and the like generally employ chiral liquid crystals and are therefore subject to problems of optical purity and helical pitch. However, we have now found a novel group of compounds which overcome or mitigate these disadvantages.

The novel compounds of the invention exhibit synclinic and/or anticlinic mesophases with preferably nematic (N) and Smectic A (SmA) phases at higher temperatures for the purposes of alignment.

Thus, according to a first aspect of the invention we provide a compound of the general structure of formula I,

-Alkylene'-A-'-Alkylene^A^CZ x-B-CZ yC-CZ _z-A -Alkyl³ I

in which A¹, A² and A³, which may be the same or different, are each -O-, -COO-,

-OCO- or-S-;

Z¹, Z²and Z³, which may be the same or different, may each be selected from the group:

in which the cyclic rings may be laterally substituted by hydrogen, -CH₃, -CF₃, -CN, - NO₂, halogen, e.g., F, Cl, Br, B and C, which may be the same or different, are each selected from the group: single bond, -COO-, -OCO-, -CH₂0-, -CF=CF- or -G≡C-; X is selected from the group: cycloalkyl, bicycloalkyl and polycycloalkyl; and x, y and z, which may be the same or different, are each an integer, being 1 or 2 as the racemate, the S or the R enantiomers or mixtures thereof. In a preferred aspect of the invention Alkylene¹ may be -(CH₂)_n-, wherein n is an integer, 0 or 1.

In addition, Alkylene² may be -(CH₂)_m- wherein m is an integer from 5 to 16. Most preferably m is 11.

B is preferably a single bond.

C is preferred to be -COO-.

A¹ is preferably to be -COO-

A is preferably to be -0-.

A³ is preferably to be -COO-

Alkyl³ is preferably a branched alkyl group, e.g. a secondary alkyl. Most preferably, Alkyl³ is -CH(CH₃)C6H₁₃. The group Alkyl³ may be optically active and it is within the scope of the present invention to included isomers of the group Alkyl³ and/or the racemate.

X is preferably selected from the group:

Most preferably X is cyclohexyl.

Z¹, Z²and Z³, are preferably each the same. However, it is especially preferred that each of Z¹, Z²and Z³, comprises the group:

In a preferred aspect of the invention the compounds comprise a compound of formula π,

in which X is as hereinbefore described as the racemate, the S or the R enantiomers or mixtures thereof.

Specific compounds which may be mentioned include;

4'-[l l-(2-cyclopropylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (5);

4'-[l l-(2-cyclobutylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (20);

4 ' - [ 11 -(2-cyclopentylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-( 1 - methylheptyloxycarbonyl)-phenyl ester (6);

4 ' - [ 11 -(2-cyclohexylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-( 1 - methylheptyloxycarbonyl)-phenyl ester (7);

4'-[l l-(2-cycloheptylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (8); 4'-[l l-(2-adamantylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (9); and 4 ' - [ 11 -(2-norboranylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-( 1 - methylheptyloxycarbonyl)-phenyl ester (10); as the racemate, the S or the R enantiomers or mixtures thereof.

The above compounds may comprise the racemate, the S or the R enantiomers.

An especially preferred compound which may be mentioned is 4'-[ll-(2- cyclohexylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (7).

Specific enantiomers which may be mentioned include;

R-4'-[l l-(2-cyclopropylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (5R);

R-4'-[l l-(2-cyclobutylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyPj-phenyl ester (20R);

R-4'-[l l-(2-cyclopentylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyi phenyl ester (6R); R-4'-[ll-(2-cyclohexylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (7R);

R-4'-[l l-(2-cycloheptylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (8R);

S-4'-[l l-(2-cyclopropylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (5S);

S-4'-[l l-(2-cyclobutylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (20S);

S-4'-[l l-(2-cyclopentylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (6S); S-4'-[l l-(2-cyclohexylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (7S); S-4'-[l l-(2-cycloheptylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (8S); S-4'-[l l-(2-adamantylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (9S); and S-4'-[ll-(2-norboranylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (10S).

According to a further aspect of the invention we provide a process for the manufacture of a compound of formula I which comprises esterifying a compound of formula in,

HO-Alkylene²-A²-(Z¹)_x-B-(Z²)_y-C-(Z³)_z-A³-Alkyl³ in

in which Alkylene², Alkyl³, A², A³, B, C, Z¹, Z², Z³, x, y and z are each as hereinbefore described, with a compound of formula IV,

X-Alkylene¹ CO₂ H IV

in which X and Alkylene¹ are each as hereinbefore described.

According to a further aspect of the invention we provide a process for the manufacture of a compound of formula II which comprises esterifying a compound of formula V,

with a compound of formula VI,

XCH₂CO₂ H VI

in which X is as hereinbefore described.

Compounds of formulae in and especially compounds of formula V are novel per se. Such compounds may be manufactured according to the following reaction sequence, or by analogous methods which would be understood by one skilled in the art;

Thus according to a further aspect of the invention we provide a compound of formula IE as hereinbefore described. We especially provide a compound of formula HI which is a compound of formula V. A specific intermediate compound of formula V which may be mentioned is 4'-(ll-hydroxyundecyloxy)-biphenyl-4-carboxylic acid 4-(l-methylheptyloxycarbonyl)-phenyl ester) as the racemate, the S or the R enantiomers or mixtures thereof.

The compounds of the invention are advantageous in that, inter alia, they exhibit synclinic and/or anticlinic mesophases.

Thus, they may be useful in the manufacture of display units, telecommunication devices, 3-D imaging devices, projection displays and spatial light modulators.

The invention of a new light shutter device that may be used to modulate or gate light. The invention may be used in displays, telecommunication devices, 3-D imaging devices, projection displays and spatial light modulators. The device is based upon the Surface Stabilised Ferroelectric Liquid Crystal Display of Clark and Lagerwall (N. A. Clark and S. T. Lagerwall, Appl. Phys. Lett., 36, 899, 1980) which is incorporated herein by reference, but significantly it does not employ chiral liquid crystals and is therefore not subject to problems of optical purity and helical pitch. Furthermore, it is possible to create grey-scale images from the device, thereby allowing for application to television.

Therefore, according to a further aspect of the invention we provide the use of a compound of formula I or π in the manufacture of a unit as hereinbefore described, e.g. display units, telecommunication devices, 3-D imaging devices, projection displays arid/or spatial light modulators. Such devices utilising achiral molecules are therefore also novel per se.

Thus according to a yet further aspect of the invention we provide a light shutter device comprising an achiral compound, e.g. an achiral liquid crystal.

Thus the device of this aspect of the invention may be, for example, a display unit, a telecommunication device, a 3-D imaging devices, a projection display and/or a spatial light modulator.

Such devices of the invention preferably comprise a compound of formula I or more preferably a compound of formula H It is especially preferred that the device of the invention comprises one of the specific compounds hereinbefore described.

Thus, we especially provide a light shutter device as hereinbefore described characterised in that the compound of formula II is selected from the group: 4'-[ll-(2-cyclopropylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester;

4'-[l l-(2-cyclobutylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester;

4'-[l l-(2-cyclopentylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester;

4'-[l l-(2-cyclohexylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester;

4'-[l l-(2-cycloheptylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; 4'-[ll-(2-adamantylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; and

4'-[l l-(2-norboranylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-ρhenyl ester; as the racemate, the S or the R enantiomers or mixtures thereof. The invention will now be described by way of example only with reference to the following figures wherein:

Figures 1 to 4 are graphs showing tilt angle measurements for compounds according to the invention;

Figure 5 shows reaction sequences for the manufacture of compounds according to the invention;

Figure 6 is a graph showing transition temperatures as a function of increasing size of the terminal group (i.e. Compound Number);

Figure 7: The textures exhibited by materials based on structure 11; the schlieren textures of the smectic C phase of racemate 11(R/S), (a) between glass plates and (b) for a free standing film; the mosaic texture of the TGBA phase (c) and Grandjean plane texture (d) of enantiomer 11(R); and, the mosaic texture of the TGB phase (e), the filamentary texture of the TGBA phase (f), and the Grandjean plane textures of the smectic C* phase (g) and the antiferroelectric smectic CA* phase (h) of enantiomer 12(S), (x 100);

Figure 8: The textures exhibited by materials based on structure 12; the schlieren (a) and the focal-conic (b) textures of the smectic C phase of racemate 12 (R/S); the spherulitic (c) and filamentary (d) textures of the TGBA phase of enantiometer \2(R); and, the mosaic texture of the TGB phase (e), the Grandjean texture of the smectic C* phase (f), and the transition (g) to the artiferroelectric smectic CA* phase (h) of enantiomer 2(S), (xlOO);

Figure 9: The schlieren texture obtained for a free standing film of the S'-enantiomer of compound 14 at 45°C (x 100); Figure 10: Differential scanning thermograms as a function of temperature (°C), at a cooling scan rate of 10 °Cmin^"1 for the racemic modification, i?-enantiomer and S- enantiomer of material 11. The arrows of a thermal event occurring in the isotropic liquid for both enantiomers;

Figure 11: X-ray diffraction results of materials (R/S), 1 (R) and 11 (S). The left- hand figures show the small angle scattering region, the center figures show the small and wide angle scattering as a function of temperature (°C), and the right-hand figures show the layer spacing (A) as a function of temperature;

Figure 12: X-ray diffraction results materials 12(R/S), 12(R) and 12(S). The left- hand figures show the small angle scattering region, the center figures show the small and wide angle scattering as a function of temperature (°C), and the right-hand figures show the layer spacing (A) as a function of temperature (°C);

Figure 13: X-ray diffraction results for materials 13 (R/S), 13(7?) and \ >(S). The left- hand figures show the small angle scattering region, the center figures show the small and wide angle scattering as a function of temperature (°C), and the right-hand figures show the layer spacing (A) as a function of temperature (°C);

Figure 14: The optical tilt angle determined from electrical field studies as a function of reduced temperature for the S-enantiomers of materials 9 to 15;

Figure 15: The value of the spontaneous polarization (nCcm-²) as a function of the reduced temperature for the ^-enantiomers of compounds 9-15;

Figure 16: The transmission as a function of applied electric field, and the microscopic textures at various points shown on the optical response curve for racemic modification 11 (R/S) while in its smectic C phase (photomicrographs x Figure 17: Photomicrographs of two extreme switched states for compound 17 contained within a cell with a 5 μm spacing and an electric field of 10 volts peak to peak applied (xlOO). Materials and Methods Electrooptical Measurements The type of cells used in the measurement of the physical properties of the smectic liquid crystals have glass separations of either 1.5±0.1 μm or 5 μm cells. The alignment layer is a rubbed polyimide. h the case of the 1.5 μm spacing cells the polyimide is rubbed in the same direction on each surface (parallel) and in the 5 μm spacing cells the alignment layer is rubbed in opposing direction (antiparallel).

The cells are filled by capillary action. The liquid crystal is placed on one side of the cell and then heated into the isotropic state which allows the material to flow into the device. For the 1.5 μm cells this process is aided by being carried out in a vacuum oven.

Alignment is achieved by a different process depending on the cell thickness. For the thin cells the alignment is achieved by cooling the sample down from the isotropic state into the smectic A mesophase at a rate of 0.1 °C min^"1 and then down into the smectic mesophase. For comparison results, measurements are reported as a function of reduced temperature, Tc-T. Tc is the Curie point, i.e. the transition point between aN-SmC or SmA-SmC.

Direction of the Induced Polarisation (Using the 1.5 μm cells)

The direction of the induced polarisation can be determined by cooling the sample into the smectic C phase from the Smectic A phase in the absence of an applied electric field. At this point the aligned sample produces a mixture of light and dark domains. A DC voltage of known polarity is applied to the cell (assuming the top plate is positive and the bottom negative) and the liquid crystal is poled in one direction. By rotating the sample through the minimum angle clockwise (Ps-) or anticlockwise (Ps+) in order to achieve a dark state indicates positive or negative polarisation.

Measurement of Spontaneous Polarisation (Using the 5 μm cells) Upon alignment the spontaneous polarisation of a chiral smectic liquid crystal can be determined, on cooling, using a triangular waveform current reversal technique. An AC field triangular waveform current reversal technique. An AC field triangular waveform (typically 10 V μm^"1 at 30 Hz) is applied to the cell. As the induced polarisation reorients and aligns with the field across the cell, a current pulse is observed using an oscilloscope. The signal is downloaded via an RS232 cable to a PC (using HP Benchlink) and the magnitude of polarisation is determined using a computer programme "Ps and optical response" (Marcus Watson, University of Hull, 1994). The polarisation is determined as a function of temperature but reported as a function of reduced temperature (Tc-T).

Measurement of Tilt Angles (using 1.5 μm cells)

The tilt angle is determined by applying an AC field square waveform (typically 10V μm^"l at 30 Hz) to a chiral smectic liquid crystal. The liquid crystal cell is mounted in a hostage oven on a microscope between crossed polarisers. The tilt angle is determined by measuring the transmittance of light through the cell using a photodiode in conjunction with the oscilloscope. The microscope stage is rotated to an angle at which there is a minimum in transmittance (optical extinction) and then the stage is rotated around until the transmittance reaches minimum again. The angle through which the stage has been rotated is the cone angle, 2Θ, and half this value is the tilt angle, θ. This measurement is carried out as a function of temperature and reported as a function of the reduced temperature.

For some samples the tilt angle has been measured as a function of voltage at Tc-T = 10 °C. The tilt angle was determined in the same manner as described for the temperature dependant tilt angle measurements but the voltage is varied from 1 V up to 20V. Measurement of Transmission Through a Cell (1.5 μm cells) The transmission through a cell is determined using a photodiode in conjunction with a voltmeter. Initially an empty cell is placed into the hotstage oven and the transmittance value between crossed polarisers (extinction) and with parallel polarisers (maximum transmittance) is taken. The filled cell is then placed into the hotstage oven and at a set reduced temperature (typically Tc-T = 10°C) the cell is poled with a DC voltage and aligned so that the poled state is set to extinction and the transmittance value is recorded. The cell is switched, by applying a DC field of opposite polarity, while the cell remains in position and the value of transmittance for the bright state is recorded, the switched dark state can be found and the measurement carried out in reverse to see that the sample is switching evenly. Comparing the values for the filled cell with those for the empty cell gives the percentage of transmission through the cell.

Direction of Polarisation

Although racemic compounds did not exhibit a measurable polarisation, it was possible to determine the preferred direction of orientation when poled in one direction. The result for all of the racemic compounds showed that they behave as induced Ps+ compounds, i.e., with a +ve voltage applied, top surface +ve, bottom - ve, the sample is rotated anticlockwise to the point of extinction.

EXAMPLE 1

This synthesis is representative for compounds of this general structure. Other end groups (X) using this synthetic route are: cyclopropyl, cyclopentyl, cycloheptyl, adamantyl and norboranyl (see Table 1).

4-cyano-4'-(l l-hydroxyundecyloxy)biphenyI (1) 4-cyano-4'-hydroxybiphenyl (8.22 g; 0.042 mol), 11-bromo-l-undecanol (10.00 g; 0.040 mol) and potassium carbonate (23.00 g; 0.170 mol) were heated under reflux in dry butanone (125 ml) for 15 h. The solids were removed by filtration and washed with acetone (2 x 50 ml). The combined solvents were removed in vacuo to give a white solid which was recrystallised from acetonitrile. Yield 14.31 g (93%) 1H nmr (CDC1₃) δl.30 (12H, m), 1.50 (5H, m), 1.80 (2H, quint), 3.64 (2H, t), 4.00 (2H, t), 6.90 (2H, d), 7.52 (2H, d), 7.66 (4H, q) ppm.

4'Hydroxyundecyloxy)biphenyl-4-carboxylic acid (2)

Compound 1 (5.00 g; 0.0137 mol) was heated under reflux in a mixture of sodium hydroxide 2.00 g; 0.0500 mol) in ethanol (100 ml) and water (50 ml) for 18h. Upon completion, to the cooled reaction mixture (ice bath) c. hydrochloric acid was added

(until pH 1) and the reaction mixture was stirred for a further lh and then filtered.

The retained solid was washed with ethanol (60 ml) and then air dried to give a white powdery solid. Yield 5.14g (98%)

1H nmr (DMSO) δl.24 (18H, m), 1.70 (2H, quint), 3.99 (2H, t), 4.36 (IH, broad s), 7.02 (2H, d), 7.66 (2H, d), 7.73 (2H, d), 7.98 (2H, d), 12.90 (IH, broad s) ppm, IR

(KBr) v_max 1202, 1256, 1293, 1604, 1686, 2500-3500 cm^"l. MS (m/z) 384 (M⁺), 214,

197.

3a) 4-MethoxycarbonyIoxybenzoic acid (12) 4-Hydroxybenzoic acid (143.2 g, 1.04 mol) was added with vigorous stirring to a solution of sodium hydroxide (120 g, 3.00 mol) in water (3.2 1) maintained at -10 °C; methyl chloroformate (160.0 g, 1.69 mol) was then added slowly keeping the temperature below 0 °C. The resulting slurry was left stirring overnight and then acidified to pH 5 by the addition of a mixture of cone, hydrochloric acid and water (1:1); the voluminous, colourless precipitate produced was filtered off and recrystallised (ethanol). Yield 168.4 g (83%), mp 181-182 °C. ¹Hnmr (CDC1₃) δ 3.92 (3H, s), 7.25 (2H, d), 8.10 (2H, d), 11.35 (IH, br s) ppm; IR (KBr) v_max 840, 940, 1460, 1500, 1580, 1600, 1750, 1680, 2830, 3000 cm^"1; Ms m/z 196 (M⁺), 152, 135 (100%), 108, 92, 77.

3b) l-Methylheptyl 4-methoxycarbonyloxybenzoate (13) Compound 12 (15.0 g, 77 mmol), octan-2-ol (10.0 g, 77 mmol) and diethyl azodicarboxylate (3.4 g, 77 mmol) were dissolved in THF (250 ml) and triphenylphosphine (22.3 g, 85 mmol) in THF (50 ml) was added dropwise with stirring. The reaction mixture was left stirring under nitrogen until no further reaction was detected by TLC. The solvent was then removed in vacuo and the resulting slurry was purified by column chromatography [petrol : dichloromethane (12:1) on silica] to yield a colourless oil. Yield 11.6 g (50%). ¹Hnmr (CDC1₃) δ 0.90 (3H, t), 1.30 (3H, d), 1.22-1.43 (8H, m), 1.52-1.80 (2H, m), 3.90 (3H, s), 5.15 (IH, sext), 7.25 (2H, d), 8.15 (2H, d) ppm; IR (neat) v_max 830, 1260, 1270, 1440, 1500, 1600, 1710, 1760 cm^"1; Ms m/z 308 (M ), 197, 179, 135, 92, 77, 59 (100%).

3c) 1-Methylhepryl 4-hydroxybenzoate (3)

Compound 13 (11.6 g, 38 mmol) was stirred overnight in ethanol (200 ml) and aqueous ammonia (50 ml). The solvents were removed in vacuo and the resulting colourless oil was purified by column chromatography (ethyl acetate on silica). Yield

9.15 g (96%).

¹Hnmr (CDC1₃) δ 0.85 (3H, t), 1.23-1.42 (11H, m), 1.52-1.78 (2H, m), 5.13 (IH, sext), 6.91 (2H, d), 7.70 (IH, br s), 7.96 (2H, d) ppm; IR (neat) v_max 850, 1170, 1320, 1670, 3350 cm^"1; Ms m/z 250 (M÷), 138, 121 (100%), 112, 93, 65.

4'-(ll-UndecyIoxy)-biphenyl-4-carboxylic acid 4-(l-methyIheptyIoxycarbonyl)- phenyl ester (4)

Compound 2 ( 1.00 g; 2.6 mmol), compound 3 (0.65 g; 2.6 mmol), l-(3- dimethylaminopropyl)-3 -ethyl carbodiimide. HCl (0.50 g; 2.6 mol) and 4- (dimethylamino)pyridine (0.20g) were stirred together at room temperature in a mixture of dimethylformamide and dichloromethane (30 ml; 3:") for 4h. Upon completion, the solvent was removed in vacuo and the product purified by column chromatography on silica (dichloromethane as eluent) and recrystallised from acetonitrile to give a white powder. Yield 1.17 g (73% tø nmr (CDC1₃) δ0.88(3H, t), 1.20-1.40 (22H, m), 1.47-1.70 (7H, m), 1.75-1.90 (3H, m), 3.64 (2H, t), 4.02 (2H, t), 5.16 (IH, sext), 7.01 (2H, d), 7.31 (2H, d), 7.60 (2H, d), 7.70 (2H, d), 8.13 (2H, d), 8.23 (2H, d) ppm. IR (KBr) v_max 1290, 1603, 1714, 1732, 2851, 2919, 3200-3600^"1. MS (m/z) 616 (M*), 540. OR [ ] ^ = 0.00°; 0.00710 gmr n CHCLs.

4'-[ll-(2-cyclohexylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyIoxycarbonyl)-phenyl ester (7)

Compound 4 (0.25 g; 0.41 mmol), 2-cyclohexylacetic acid (0.06 g; 0.41 mmol), 1- (3-dimethylaminopropyι)-3-ethyl carbodiimide. HCl (0.08 g; 0.41 mmol) and 4- (dimethylamino)pyridine (0.01 g) were stirred together at room temperature in dichloromethane (25 ml) for 15h. Upon completion, the solvent was removed in vacuo and the product purified by column chromatography on silica (dichloromethane as eluent) and recrystallised from acetonitrile to give a white powder. Yield 0.23 g (77%).

^!H nmr (CDC1₃) δ0.86-1.01(5H, m), 1.20-1.40 (24H, m), 1.47 (2H, quint), 1.53-1.87 (14H), m), 2.17 (2H, d), 4.02 (2H, t), 4.05 (2H, t), 5.16 (IH, sext), 7.00 (2H, d), 7.31 (2H, d) 7.60 (2H, d), 8.13 (2H, d), 8.23 (2H, d) ppm. IR (KBr) v_max 1262, 1601, 1720, 1738, 2848, 2922 cm^"l. CHN (expected C 76.18; H 8.70%; found C76.ll; H 8.92%). OR [a] = 0.00°; 0.00258 g mil in CHCI3

The following compounds were prepared using methods analogous to that described in 5:

4'-[ll-(2-cyclopropylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (5)

4'-[l l-(2-cyclopentylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (6) 4'-[l l-(2-cycloheptylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (8)

4'-[l l-(2-adamantylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (9)

4'-[l l-(2-norboranylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (10)

4'-[ll-(2-cyclobutylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (20)

The synthesis was carried out using optically active alcohols to produce compound 3 as an optically active intermediate. The optically active analogues (R- and S-) of compounds 5 to 10 (see Table 2) can be mixed together to produce a racemic mixture which give similar results to the racemic compounds prepared from racemic alcohols. To produce the racemic mixture the optically active materials are dissolved into dichloromethane and mixed together by weight, according to their optical purity, to produce a racemic mixture which gives an optical rotation of 0.00°.

R-4'-[ll-(2-cyclopentyIacetoxy)-undecyloxyI-biphenyl-4-carboxyIic acid 4-(l- methylheptyloxycarbonyI)-phenyI ester (6R)

R-4'-[ll-(2-cycIohexylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyI ester (7R)

R-4'-[ll-(2-cycloheptylacetoxy)-undecyloxyl-biphenyl-4-carboxyIic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (8R)

R-4'-[ll-(2-cyclobutyIacetoxy)-undecyloxyI-biphenyl-4-carboxylic acid 4-(l- methylhepryloxycarbonyI)-phenyl ester (20R); S-4'-[ll-(2-cyclopropylacetoxy)-undecyloxyI-biphenyl-4-carboxylic acid 4-(l- methylheptyIoxycarbonyl)-phenyI ester (5S)

S-4'-[ll-(2-cyclopentyIacetoxy)-undecyϊoxyI-biphenyl-4-carboxyIic acid 4-(l- methy!heptyIoxycarbonyl)-phenyl ester (6S)

S-4'-[ll-(2-cyclohexylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyI ester (7S)

S-4'-[ll-(2-cycIoheptyIacetoxy)-undecyIoxyl-biphenyl-4-carboxylic acid 4-(l- methyIhepryloxycarbonyI)-phenyl ester (8S)

S-4'-[ll-(2-adamantylacetoxy)-undecyloxyl-biphenyl-4-carboxyIic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (9S)

S-4'-[ll-(2-norboranylacetoxy)-undecyloxyl-biphenyI-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (10S)

S-4'-[ll-(2-cyclobutyIacetoxy)-undecyloxyl-biphenyl-4-carboxyIic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (20S)

Results

Tilt Angle Measurements

Are shown in Figures 1 to 4.

Transmission Results Compound (6): Empty cell: x-polars = 0.0032 V; parallel-polars = 1.0168V Filled cell: +DC dark state = 0.0725 V; bright state = 1.0003 V - DC dark state = 0.0673 V; bright state = 1.0001 V

Compound (7): Empty cell: x-polars = 0.0668 V; parallel-polars = 1.0367 V Filled cell: +DC dark state = 0.0112 V; bright state = 0.9743 V - DC dark state = 0.0148 V; bright state = 0.9982 V

Compound (8): Empty cell: x-polars = 0.0008 V; parallel-polars = 0.8760 V Filled cell: +DC dark state = 0.0327 V; bright state = 0.6940V - DC dark state = 0.0326 V; bright state = 0.7020 V

The transmission results show that the aligned samples exhibit a transmission of >75% when compared to the empty cell. This shows that there is an inequivalence in the domains exhibited within the cell. If there were a 50:50 mix of domains as would be expected for this system the transmission would be 50% due to the equal proportion of light and dark domains.

EXAMPLE 2

Synthesis of Materials

General Synthetic Pathways: The following synthetic pathway, see the Scheme, for the preparation of racemic modification 12(R/S) is representative of all of the target materials shown in Table 3. The synthetic 6 route is relatively standard for the synthesis of such materials, however, we report it here in detail simply because the results obtained concerning the physical characterization of the racemic materials are unusual and raise issues of optical purity. Indeed for compounds such as 12(R/S), the synthesis was repeated a number of times using different sources of racemic 2- octanol (Aldrich, Avocado etc) in order to examine the reproducibility of the physical test results. For the synthesis of the enantiomers the racemic 2-octanol was replaced by optically active (R or S) 2-octanol (Aldrich). Compound 3, 4'-(ll-hydroxyundecyloxy)biphenyl-4-carboxylic acid, was prepared starting from 4- cyano-4'-hydroxybiphenyl, 1, which was first alkylated with 11- bromoundecan-1-ol in the presence of potassium carbonate in butanone, followed by acid hydrolysis of the nitrile. Compound 7 was prepared by standard methods starting from 4-hydroxy-benzoic acid, 4. The hydroxy group was first protected as the carbonate to give 5, this intermediate was esterified with 2-octanol in the presence of diisopropyl azodicarboxylate (DIAD) in the presence of triphenylphosphine and THF to give 6. Ester 6 was deprotected using a mixture of ammonia and ethanol to generate the phenol 7.

Compound 3 and compound 7 were esterified in the presence of l-(3- dimethylaminopropyl)-3 -ethyl carbodiimide.HCl (ED AC) and 4-

(dimethylamino)pyridine to give 8. Under these conditions 8 is formed without any self-esterification of 3. The last step in the pathway was the esterification, under the same condition, of 8 with one of the selected acids (XCH2COOH) to give products 9 to 15.

^H°-^"C_}-Q^~' CN 1 . i) 1 NaOH, CH₃OCCCI iι) HCI HO(CH₂)ιιBr κ₂co₃ CH.OCOO Butanone ^■.o- COOH 5

is 6

HO(CH₂)₁₁0- ^"Λ— ^"Y-COOH 3 EtOH, NH, HO— , jb— COO-CH-C₆H₁₃

EDAC, DMAP XCH,COOH CH,CI,, DMF

In addition to the target materials, the following two compounds were prepared so that direct comparisons could be made with materials not possessing bulky end groups as in the case of 16, and with non-chiral materials that were found to reorient in applied electric fields as in the case of 17. Compound 16 was prepared using the same procedure except compound 8 was esterified with hexanoic acid. Compound 17 was prepared by the scheme reported above except that 2-octanol was replaced by heptan-lol.

CH₃ CsHnCCrøCCHaJnO-Q-^-CXXJ-Q-OOO-CH-CβHw 16

Q-CHa-COOlCH^n-O-Q-Q-COO-Q-COO-C_T-H^ 17

-Cyano-4'-(l 1-hydroxyundecyloxy) biphenyl (2) 4-Cyano-4'-hydroxybiphenyl (8.22 g; 0.042mol), 1, 11-bromo-l-undecanol (10.0 g; 0.040 mol) and potassium carbonate (23.0 g; 0.170 mol) were heated under reflux in dry butanone (125 ml) for 15 h. The solids were removed by filtration and washed with acetone (2 x 50 ml). The combined solvents were removed in vacuo to give a white solid which was recrystallised from acetonitrile. Yield 14.31 g (93%) IH nmr (CDC13): d 1.30 (12H, m), 1.50 (5H, m), 1.80 (2H, quint), 3.64 (2H, t), 4.00 (2H, t), 6.90 (2H, d), 7.52 (2H, d), 7.66 (4H, q) ppm.

4'-(ll-Hydroxyundecyloxy)biphenyl-4-carboxylic acid (3)

Compound 2 (5.00 g; 0.0137 mol) was heated under reflux in a mixture of sodium hydroxide (2.0 g; 0.05 mol) in ethanol (100 ml) and water (50 ml) for 18 h. Upon completion, to the cooled reaction mixture (ice bath) c. hydrochloric acid was added (until pH 1) and the reaction mixture was stirred for a further lh and then filtered. The retained solid was washed with ethanol (60 ml) and then air dried to give a white powdery solid. Yield 5.14 g (98%) IH nmr (DMSO): d 1.24 (18H, m), 1.70 (2H, quint), 3.99 (2H, t), 4.36 (IH, broad s), 7.02 (2H, d), 7.66 (2H, d), 7.73 (2H, d), 7.98 (2H, d), 12.90 (IH, broad s) ppm. IR (KBr) nmax 1202, 1256, 1293, 1604, 1686, 2500-3500 cm-1. MS (m/z) 384 (M+), 214, 197.

4-(l-Methylheptyloxycarbonyl)phenyl4'-(ll-hydroxyundecyloxy)biphenyl-4- carboxylate (8) Compound 3 (1.0 g; 2.6 mmol), compound 7 (0.65 g; 2.6 mmol), l-(3- dimethylaminopropyl)-3 -ethyl carbodiimide.HCl (0.50 g; 2.6 mol) and 4- (dimethylamino)pyridine (0.20 g) were stirred together at room temperature in a mixture of dimethylformamide and dichloromethane (30 ml; 3:1) for 4h. Upon completion, the solvent was removed in vacuo and the product purified by column chromatography over silica (dichloromethane as eluent) and recrystallised from acetonitrile to give a white powder. Yield 1.17 g (73%) IH nmr (CDC13): d 0.88(3H, t), 1.20-1.40 (22H, m), 1.47-1.70 (7H, m), 1.75-1.90 (3H, m), 3.64 (2H, t), 4.02 (2H, t), 5.16 (IH, sext), 7.01 (2H, d), 7.31 (2H, d), 7.60 (2H, d), 7.70 (2H, d), 8.13 (2H, d), 8.23 (2H, d) ppm. IR (KBr) nmax 1290, 1603, 1714, 1732, 2851, 2919, 3200-3600 cm-1. MS (m/z) 616 (M+), 540.

Racemate OR: [a]27 D = 0.00°; 0.00710 g ml-1 in CHC13 R-enantiomer OR: [a]20 D = -15.94°; 0.004352 g ml-1 in CHC13 9

S-enantiomer OR: [a]23

D = +18.43°; 0.02207 g ml-1 in CHC13

4-(l-Methylheptyloxycarbonyl)phenyl 4'-[ll-(2- cyclohexylacetoxy)undecyloxy]biphenyl-4-carboxylate (12 R/S)

Compound 8 (0.25 g; 0.41 mmol), 2-cyclohexylacetic acid (0.06 g; 0.41 mmol), l-(3- dimethylaminopropyl)-3 -ethyl carbodiimide.HCl (0.08 g; 0.41 mmol) and 4- (dimethylamino)pyridine (0.01 g) were stirred together at room temperature in dichloromethane (25 ml) for 15h. Upon completion, the solvent was removed in vacuo and the product purified by column chromatography over silica (dichloromethane as eluent) and recrystallised from acetonitrile to give a white powder. Yield 0.23 g (77%). IH nmr (CDC13) d 0.86-1.01(5H, m), 1.20-1.40 (24H, m), 1.47 (2H, quint), 1.53-1.87 (14H, m), 2.17 (2H, d), 4.02 (2H, t), 4.05 (2H, t), 5.16 (IH, sext), 7.00 (2H, d), 7.31 (2H, d), 7.60 (2H, d), 7.70 (2H, d), 8.13 (2H, d), 8.23 (2H, d) ppm. IR (KBr) nmax 1262, 1601, 1720, 1738, 2848, 2922 cm-1. CHN (expected C 76.18; H 8.70%; found C 76.11; H 8.92%). OR [ ]D 23 = 0.00°; 0.00258 g ml-1 in CHC13 R-enantiomer OR: [a]24 D = -18.28°; 0.01634 g ml-1 in CHC13 S- enantiomer OR: [a]23 D = +12.91°; 0.0101 g ml-1 in CHC13 Results

Transition Temperatures

The transition temperatures, enthalpies of transition, tilt angles and values of the maximum spontaneous polarization for materials 9 to 15 (R/S, R and S) are given in Table 3. Similarly, in Table 4 analogous results are given for the parent terminally hydroxylated material 8 (R S, R and S).

In addition, Table 5 lists the transition temperatures of a similar set of known and new materials based on the MHPOBC motif. These materials do not have bulky terminal end groups, and therefore provided reasonable comparisons with the new materials reported. Compound 16 was synthesized for this study to provide a direct comparison of the materials with bulky terminal groups. Compound 17 was prepared for comparative switching studies in applied electric fields to materials based on structure 12.

The first simple observation which can be made from the tables is that the materials with bulky end units do not exhibit any SmCg (ferri-) and, except for 11(R), any SmCa phases. Unlike the parent analogous materials (see Table 3, and in particular compound 16), the compounds with bulky end groups exhibit twist grain boundary phases. Remarkably many of the racemic materials exhibit smectic A phases whereas the enantiomers do not exhibit smectic A* modifications.

Similarly, the intermediates with terminal hydroxylated end groups, shown in Table 2, were found to exhibit smectic A/A* and smectic C/C* phases, again unlike the final products which have bulky end groups. For the hydroxy-terminated materials the temperature range of the smectic A phase of the racemate 8(R/S) is much larger (approximately 23°) in comparison to the values obtained for the racemic modifications of compounds 9-15 (between 4 and 10°). The enthalpies of the isotropization points for materials of structure 8, were in most cases more than twice the values determined for materials 9-15. This indicates that the layer structuring for the hydroxy-compounds is stronger than in the materials with bulky end groups. This may be related to the strengthening of the structure caused by inter-molecular hydrogen bonding occurring across the layer interfaces.

A more detailed analysis of the trends in transition temperatures is given graphically in figure 6 for the Senantiomers of compounds 9 to 15. The clearing temperatures are shown to fall linearly with increasing size of the terminal group. The smaller the terminal group the greater the tendency for a material to exhibit orthogonal phases and complex polymorphism. The antiferroelectric phase shows higher thermal stabilities when the terminal group is relatively rigid, ie where the terminal group is either small in size, or has a rigid cage structure. The melting points vary most greatly when the terminal group is a flexible ring, but generally the melting points oscillate up and down (+/- 10 °C) across the series of compounds about a median of 50 °C. Compound 14 which has a structure based on the norbornyl ring system exhibits anomalous mesophase behavior when compared to the other materials. The other materials may be considered to have spherical terminal groups because the

- adamantane unit has a fixed spherical shape and the flexibility of the alicyclic ring systems means that on average they will also be spherical. The norbornyl moiety has a more anisotropic shape which may lead to different packing arrangements of the molecules at the interfaces between the layers.

Thermal Polarized Light Microscopy

Initial mesophase classification was achieved by polarized-light optical microscopy (POM). Thermal microscopy yielded some novel textures which are compared in the following section in relation to the differences observed between the racemic modification and the enantiomeric forms of each material.

Figure 7 shows eight different defect textures for the cyclopentyl terminated material 11. Figures 7 (a) and (b) show the defect textures of the racemic modification in a supported sample under a glass cover-slip (a), and for a free-standing film (b). The schlieren texture (a) is typical of an achiral smectic C phase. Upon rotation of the analyzer no color change was observed which would indicate that the material is not at all helical, thereby confirming that the material is racemic. The free standing film (b) shows that the material exhibits loops/defect walls. When the R-enantiomer is examined a twist grain boundary phase formed first from the isotropic liquid, an example of the texture that this phase exhibits is shown in (c) for the material contained within a 5 mm cell. When the enantiomer is obtained in its smectic C* phase an iridescent petal texture is obtained, at approximately 35°, as shown in (d). The color shows that the pitch of the phase is comparable to the wavelength of visible light, ie 0.4 - 0.7 mm. Comparison of (a) and (d) gives an indication to the relationship between optical purity and helical pitch length. Textures (e) to (h) are typical examples of defect patterns exhibited for the S-enantiomer. Plates (e) and (f) show the textures of the twist grain boundary phase, where (e) is the texture obtained in a 5 mm cell and (f) is the typical filamentary texture obtained for a specimen sandwiched between a slide and cover-slip. The filamentary texture confirms that the twist grain boundary phase that is exhibited is a TGBA phase. Plate (g) shows the petal texture for a free standing film of the helical smectic C* phase, and (h) shows the subsequent schlieren texture of the antiferroelectric SmCA* phase formed on cooling. This phase sequence observed for the S-enantiomer differs from that of the R-enantiomer in that the S-isomer possesses an anticlinic phase in addition to a synclinic modification. The introduction of the anticlinic phase is indicative of the higher optical purity of the S-enantiomer.

Figure 8 shows eight plates for the racemic, R- and S-enantiomeric forms of the cyclohexyl terminated material 12. Plates (a) and (b) show the schlieren and focal- conic foπns of the smectic C phase of the racemate. The schlieren texture is typical of an achiral smectic C phase, which shows no color change upon rotation of the analyzer indicating that the phase has no helical structure. The focal-conic texture (b) was obtained when the material was placed in a 1.5 mm cell. This texture is interesting in that grain boundaries between different tilt domains are relatively long and straight indicating that the tilt has relatively long range ordering on moving from one layer to the next. Plates (c) and (d) are textures exhibited by the TGB phase of the R-enantiomer. From (c), where the enantiomer is contained a 5 mm cell, it might be concluded that the phase is actually a columnar liquid crystal. However, Galerne et al[14] have explained that this type of texture may be formed by twist grain boundary phases. The filamentary texture shown in Plate (d) confirms this classification as a TGBA phase. Plates (e) to (h) show textures exhibited between a glass slide and cover-slip by the S-enantiomer. Plate (e) shows a very unusual texture for the TGB phase. Plate (f) shows the iridescent texture of the smectic C* phase, (g) shows the transition to the antiferroelectric phase, and (h) shows the texture of the fully formed antiferroelectric phase; the lack of iridescence indicating that the pitch length of the helical structure in this phase was considerably longer than in the chiral smectic C phase.

The helical twist direction for all of the materials tested followed the Goodby-Chin rules for ferroelectric liquid crystals, the S-enantiomers gave left-handed helices (Sol), whereas the R-enantiomers gave righthand helices (Rod).

The norbornyl terminated material 14 exhibited some unusual defects in its antiferroelectric phase. Multiple brushed defects, eg S = 2, were observed. These defects were either derived from complex singularities, screw dislocations or dispirations[15] or else they were formed by two singularities coming close together. A free-standing film of the S-enantiomer is shown in figure 9.

Differential Scanning Calorimetry

The enthalpies of transition for all of the compounds 9-15 are shown together in

Table 3. Apart from confirming the transition temperatures differential scanning calorimetry also served to demonstrate the differences between the enantiomers and their racemic modifications. The isotropization points were shown to be sensitive to optical purity, with the racemic modifications clearing at as much as 8° higher than the enantiomer of greater optical purity. These results are similar to those obtained for many other systems where twist grain boundary (TGB) phases are exhibited by the enantiomers. The extensive lowering of the isotropization points for enantiomers 11(R) and 11(S) in comparison to the racemic modification 11(R/S); and enantiomers 12(R) and 12(S) relative to racemate 12(R/S), are strong indicators to the fact that the optical purities of the racemic modifications are close to, or are, zero. Furthermore, for all of the enantiomers a thermal event was found to take place in the isotropic liquid just before the isotropization points. This effect is associated with the transition to structurally frustrated TGB phases via the formation of proposed entangled or disentangled flux phases, in analogy with such phases formed by type II superconductors. Similar thermal effects were also observed before the 18 transitions from the liquid state for materials that exhibited either isotropic liquid to smectic C* or isotropic liquid to smectic CA* phase transitions.

In addition, the phase transition from the smectic A to the smectic C phase in the racemic modifications, and the TGB phase¹ to the chiral smectic C* phase in the enantiomers, appeared to be first order rather than typically second order, see for example Figure 10 for the R-, S- and racemic forms of compound 11.

X-Ray Diffraction

X-ray diffraction studies on aligned and unaligned specimens of the racemic and enantiomeric forms of materials 11, 12 and 13 were performed as a function of temperature, as shown in figures 11, 12 and 13 respectively, hi each figure the narrow and wide angle scattering and the layer spacing as a function of temperature are shown for comparison. In all cases the X-ray patterns obtained were for layered phases with disorganized arrangements of their constituent molecules. For example, the results obtained for the racemic modification of compound 11 are shown in the top part of figure 11. i the wide angle region (center figure) the broad diffuse peaks are related to lateral positional order between the molecules, which can be seen to be uncorrelated and diffuse. In the narrower angle region (left-hand figure), strong reflections can be seen related to the correlations 19 between layer of each mesophase. At low temperatures the layer spacings are at a higher q value in the tilted smectic C phase, than they are in the smectic A phase.

The layer spacing as a function of temperature is shown in the right-hand part of the figure. For the racemate, the smectic A layer spacing was found to be approximately 41.25 A. As the temperature is lowered further the transition to the smectic C phase is marked by a rapid decrease in the layer spacing over a temperature range of approximately 5 °C, upon which the layer spacing becomes temperature independent. This behavior is not typical of a smectic C phase formed from an A phase via a second order phase transition, in this case the layer spacing would be expected to fall and eventually level off with falling temperature.

For the R- and S-enantiomers, a similar pattern of behavior was found to the racemic modification except for the changes which occur near to the clearing points. For the enantiomers, TGB phases are exhibited rather than the smectic A phase found for the racemate. The layer spacings shown in the right-hand figures show that the they are commensurate with the TGB phases being of the A type, ie TGBA. In the liquid phase near to the clearing points for both enantiomers there are strong reflections observed which would suggest an increase in ordering near the transition to the TGB phase in the isotropic liquid. Moreover, the TGBA phase does not stay stable for long with the layer spacing falling rapidly as the temperature is lowered. The layer spacings in the smectic C* phases of both enantiomers remain relatively constant over a wide temperature range. The layer spacing is slightly higher for the R- enantiomer than for the S-enantiomer. This means that the tilt angle for the S- enantiomer is larger than for the R-enantiomer and reflects the fact that the S- enantiomer has the higher optical purity.

For materials 12 and 13 similar results are reported in figures 12 and 13 respectively, except for the fact that compound 13 does not exhibit a TGB phase. Nevertheless for both of these materials the low angle scattering data show even stronger reflections occurring near to the clearing points, which indicates that there is considerable ordering occurring in the liquid state. Furthermore, the temperature range over which the layer spacing is commensurate with the presence of a TGBA phase for compound 12 is so short that in actual fact the TGB phases are mostly tilted phases, ie they are TGBC phases.

Tilt Angle Measurements

The optical tilt angles were determined as a function of temperature as described in the experimental section. Figure 14 shows the tilt angles as a function of reduced temperature for the S-enantiomers of compounds 9 to 15.

Figure 14 shows that the tilt angle for materials 9 to 14 typically rises and then levels off as the temperature falls. The temperature over which the rise occurs is approximately 20 °C, which is about 10 °C than more than range over which it rises when determined by X-ray diffraction. For the S-enantiomer of compound 15, as the material exhibits a direct transition from the liquid to the smectic C* phase, the tilt angle is independent of temperature, and has a relatively high value of approximately 45°. The comparative tilt angle for the whole set of materials shows that as the terminal group is increased in size, so too does the tilt angle.

Spontaneous Polarization Measurements

The spontaneous polarization was determined as a function of the reduced temperature as described in the experimental section. Figure 15 groups all of the materials together in graphical form. For all of the materials, including compound 15 which has a temperature independent tilt angle of 45°, the spontaneous polarization jumps near to the Curie point, then rises and nearly levels off as each material approaches recrystallisation. The results for compound 14, which exhibits an antiferroelectric phase on cooling from the isotropic liquid, also follows the same pattern in switching between its ferroelectric states.

Interestingly the materials with the higher tilt angles, i.e. 15, 14, 13 etc have the lower spontaneous polarization values. This is probably due to a volume factor because the spontaneous polarization is dependent on the dipoles per unit volume, and as the terminal group size increases in volume so the spontaneous polarization falls. Yet at the same time the tilt angle increases with increasing size of the terminal groups, which means that the spontaneous polarization also should increase with the tilt angle. As a consequence, the curves for all of the materials are grouped tightly together in figure 15.

Electrical Field Studies Electrical field studies were performed using a variety of wave forms and ITO coated cells of different alignment agents (parallel- and anti-parallel rubbed) and cell spacings (1.5 and 5 mm). Normal switching behavior was observed for all of the optically active materials, however, switching was also surprisingly observed for the achiral synclinic smectic C phases of racemic modifications 11 (R/S), 12(R/S) and 13(R/S). Thus rather than discuss the typical behavior of the enantiomers, in the following sections the behavior of the racemates will be described.

The three racemates, 11 (R/S), 12(R S) and 13 (R/S), were found to be relatively sensitive to the nature and quality of the aligning agent and the origins of the cells, with the best results being obtained in cells obtained from the University of Chalmers (Sweden). Figure 16 shows the optical transmission curve for the racemic modification 11 (R/S) as function of the applied electric field, where the microscope textures illustrate the nature of the switching at various points on the curve. For the bright extreme switched state, 95% transmission was obtained relative to the transmission through an empty cell (ie to act as a baseline for the contrast ratio). For the fully switched dark state transmission was close to that for an empty cell observed between crossed polars. Similar results were obtained in thin cells (1.5 mm) and thick cells (5 mm) alike. The switching was also found to be present for racemate 12, and to a lesser extent for racemate 13, and for all of the racemates. If the switching is related to ferroelectric behavior then the sign of the polarization was determined to be positive, h thicker cells the switching profiles gave V-shaped optical/transmission and electrical responses. As a result, this gives the possibility of creating devices with gray-scale operation.

As the results from the electrical field studies suggested that the switching could be of a ferroelectric nature, the racemic modifications were double checked to ensure they were truly racemic with optical purities of zero. Thus, the racemates were re- synthesized from different sources of racemic 2-octanol (Aldrich, Avocado etc), and the optical rotation of the final products and the intermediates at each stage of the synthesis were determined and in each case the measured specific rotation was found to be zero. Furthermore, to ensure that there was no operator error with respect to the determination of the optical rotation measurements were carried out under blind conditions. Within experimental resolution the materials reproducibly gave zero optical rotations. Therefore we conclude from these studies that the racemic modifications 11 (R/S), 12(R/S) and 13 (R/S) had zero optical purities or the optical purities were at such a low level that we were unable to measure them by standard methods. Even though the syntheses of the racemates were achieved by different methods, the results obtained for the switching studies were essentially the same across all of the materials prepared. We conclude that the effects observed were independent of the source of the 2-octanol, and that the optical purities were zero within experimental error. While we cannot rule out extremely small differences in the concentration of enantiomers in the racemic mixtures, it is still remarkable that the modifications 11(R/S), 12(R S) and 13(R/S) switched.

High frequency electric field studies however gave further insights into the switching process. As the frequency was increased for the 12(R/S) racemate the switching appeared to stop at value of approximately 250-300 Hz and partially switched domains appeared, as the frequency was raised further towards values of 300-500 KHz one of the switched states dominated. These results suggest that dielectric properties may also be involved in the switching process. In order to further elucidate the switching mechanism in achiral systems compound 17 was prepared. This material was designed to be almost exactly the same length and shape as the racemate 12(R/S). Compound 17, like racemate 12(R/S), was found to exhibit smectic A and C phases, but with an additional hexatic I phase appearing monotropically. The SmA to Iso Liq phase transition temperature was found to be 47 °C higher than the racemate demonstrating the effect that the lateral methyl group has on the isotropization point and other liquid crystal transitions.

For compound 17 (see Table 5), contained within a 5 mm cell with a field of 10 volts peak to peak applied, switching was effected as shown by the two extreme switched states in figure 17. The contrast ratio between the switched states was found to be considerably lower in comparison to that observed for the racemate 12(R/S). This may have been due to the alignment not being of a high enough quality in the thicker cell, or alternatively it may have been related to domain formation. As this material is non-chiral, any possibility that the switching was associated with conventional ferroelectricity was removed.

Conclusion

In conclusion we have shown that it is possible to switch, in a ferroelectric fashion, racemic modifications of materials possessing bulky terminal units and negative dielectric anisotropy. We propose a model where such materials have weakened interlayer interactions so that the torque involved in the switching procedure is reduced to a low enough level that small enantiomeric excesses coupled to the dielectric properties are sufficient enough to effect switching. This phenomenon is of interest in device applications because the materials do not need the pitch compensation required of chiral materials. We also suggest that the inclusion of bulky terminal groups into the molecular structures of the liquid crystals can have the effect of inducing in-plane modulations or undulations, which could, if strong enough, lead to novel mesophase formation where the modulations are in-phase or out-of-phase.

Claims

1. A compound of the general structure of formula I,

X-Alky -A- -Alkylene²-A²-(Z¹)_x-B-(Z²)_y C-(Z³)_Z-A³- Alkyl

in which A¹, A² and A³, which may be the same or different, are each -O-, -COO-, -OCO- or -S-;

in which the cyclic rings may be laterally substituted by hydrogen, -CH₃, -CF₃, -CN, - N0₂, halogen, e.g., F, Cl, Br,

B and C, which may be the same or different, are each selected from the group: single bond, -COO-, -OCO-, -CH₂0-, -CF=CF- or -C≡C-;

X is selected from the group: cycloalkyl, bicycloalkyl and polycycloalkyl; and x, y and z, which may be the same or different, are each an integer, being 1 or 2, as the racemate, the S or the R enantiomers or mixtures thereof.

2. A compound according to claim 1 characterised in that Alkylene¹ is -(CH )_n-, wherein n is an integer, 0 or 1.

3. A compound according to claim 1 characterised in that Alkylene² is -(CH₂)_m- wherein m is an integer from 5 to 16.

4. A compound according to claim 3 characterised in that ^"m is 11.

5. A compound according to claim 1 characterised in that B is a single bond.

6. A compound according to claim 1 characterised in that C is -COO-.

7. A compound according to claim 1 characterised in that A¹ is -COO-

8. A compound according to claim 1 characterised in that A² is -O-.

9. A compound according to claim 1 characterised in that A³ is preferably to be - COO-.

10. A compound according to claim 1 characterised in that Alkyl³ is a branched alkyl group

11. A compound according to claim 10 characterised in that Alkyl³ a secondary alkyl.

12. A compound according to claim 11 characterised in that Alkyl³ is - CH(CH₃)C₆H₁₃.

13. A compound according to claim 1 characterised in that X is selected from the group:

14. A compound according to claim 13 characterised in that X is cyclohexyl.

15. A compound according to claim 1 characterised in that Z¹, Z²and Z³, are each the same.

16. A compound according to claim 15 characterised in that each of Z , Z and Z , is selected from the group:

17. A compound according to claim 1 characterised in that the compound of formula I is a compound of formula IT,

in which X is as defined in claim 1 as the racemate, the S or the R enantiomers or mixtures thereof.

18. A compound according to claim 17 characterised in that the compound is selected from the group including;

4'-[l l-(2-cycloproρylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester;

4'-[l l-(2-cyclobutylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester (20); 4'-[ll-(2-cyclopentylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-ρhenyl ester;

4'-[l l-(2-cycloheptylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; 4'-[l l-(2-adamantylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; and 4'-[l l-(2-norboranylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; as the racemate, the S or the R enantiomers or mixtures thereof.

19. A compound according to claim 18 characterised in that the compound is 4'- [1 l-(2-cyclohexylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester as the racemate, the S or the R enantiomers or mixtures thereof.

20. A compound according to claim 17 characterised in that the compound is selected from the group including;

R-4'-[l l-(2-cyclopropylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester;

R-4'-[l l-(2-cyclobutylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester;

R-4 '-[11 -(2-cyclohexylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-( 1 - methylheptyloxycarbonyl)-phenyl ester; R-4'-[l l-(2-cycloheptylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester;

S-4'-[l l-(2-cyclopropylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester;

S-4'-[l l-(2-cyclobutylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester;

S-4 ' - [ 11 -(2-cyclopentylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-( 1 - methylheptyloxycarbonyl)-phenyl ester;

S-4'-[l l-(2-cyclohexylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; S-4'-[ll-(2-cycloheptylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; S-4'-[l l-(2-adamantylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; and S-4'-[l l-(2-norboranylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester.

21. A process for the manufacture of a compound of formula I which comprises esterifying a compound of formula HI,

HO-Alkylene²-A²-(Z¹)_x-B-(Z²)_y-C-(Z³)_z-A³-Alkyl³ HI

in which Alkylene², Alkyl³, A², A³, B, C, Z¹, Z², Z³, x, y and z are each as defined in claim 1 with a compound of formula IV, X-Alkylene¹ C0₂ H IV

in which X and Alkylene¹ are each as defined in claim 1.

22. A process according to claim 21 characterised in tat the compound of formula I is a compound of formula II, the process comprising esterifying a compound of formula V,

with a compound of formula VI,

XCH₂CO₂ H VI

in which X is as defined in claim 1.

23. A compound of formula HI.

HO-Alkylene²-A²-(Z¹)_x-B-(Z²)_y-C-(Z³)_z-A³-Alkyl³ HI in which Alkylene², Alkyl³, A², A³, B, C, Z¹, Z², Z³, x, y and z are each as defined in claim 1.

24. A compound according to claim 23 characterised in that the compound of formula HI is a compound of formula V,

25. A compound according to claim 24 characterised in that the compound is 4'- (1 l-hydroxyundecyloxy)-biphenyl-4-carboxylic acid 4-(l-methylheptyloxycarbonyl)- phenyl ester) as the racemate, the S or the R enantiomers or mixtures thereof.

26. The use of a compound of formula I in the manufacture of a tight shutter device consist of a display unit, a telecommunication device, a 3-D imaging device, a projection display and/or a spatial light modulator.

27. The use according to claim 26 characterised in that the compound of formula I is a compound of formula H as defined in claim 17.

28. The use according to claim 27 characterised in that the compound of formula H is selected from the group:

4'-[l l-(2-cyclopentylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; 4'-[ll-(2-cyclopentylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; 4'-[l l-(2-cyclohexylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; 4'-[l l-(2-cycloheptylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; 4'-[l l-(2-adamantylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; 4'-[l l-(2-norboranylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; as the racemate, the S or the R enantiomers or mixtures thereof.

29. A light shutter device comprising an achiral compound.

30. A light shutter device according to claim 29 characterised in that the achiral compound is an achiral liquid crystal.

31. A light shutter device according to claim 29 characterised in that the device is selected from the group comprising display units, telecommunication devices, 3-D imaging devices, projection displays and/or spatial light modulators.

32. A light shutter device according to claim 29 characterised in that the device comprises a compound of formula I.

33. A light shutter device according to claim 32 characterised in that the compound of formula I is a compound of formula II as defined in claim 17.

34. A light shutter device according to claim 33 characterised in that the compound of formula II is selected from the group:

4'-[l l-(2-cyclopropylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; 4'-[ll-(2-cyclobutylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; 4 ' - [ 11 -(2-cyclopentylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-( 1 - methylheptyloxycarbonyl)-ρhenyl ester;

4 ' - [ 11 -(2-cyclohexylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-( 1 - methylheptyloxycarbonyl)-phenyl ester; 4'-[l l-(2-cycloheptylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester;

4'-[l l-(2-adamantylacetoxy)-undecyloxyl-biρhenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; and

4'-[l l-(2-norboranylacetoxy)-undecyloxyl-biphenyl-4-carboxylic acid 4-(l- methylheptyloxycarbonyl)-phenyl ester; as the racemate, the S or the R enantiomers or mixtures thereof.

35. A compound or a device substantially as described with reference to the accompanying description and examples.