FLUORINATED OLIGOPHENYLS AND THEIR USE IN LIQUID CRYSTAL MATERIALS

Abstract: This invention relates to fluorinated oligophenyls of formula (I), in which a is 0 or 1 and in which the terminal substituents R<1>, R<2> and R<3> are each independently an alkyl or alkenyl residue each with up to 15 C atoms, optionally substituted by CN or by at least one halogen atom, and wherein one or more non adjacent CH2 groups of these residues may be replaced by -O-, -S-, -CO-, -O-CO-, -CO-O-, -O-CO-O- or -C=C-, one of the residues R<1> and R<2> may also denote a group of formula (II), any one of the following pairs of lateral substituents are both fluorine: (A, B), (C, D), (D, E), (C, E), (B, C), (D, J), (D, K), (A, C), (C, J), (C', D'), (D', E), (D', A), (C', E), (C', A), (D', J'), (D', K'), (C', J'), (B, G), (A, G), all of the other lateral substituents being hydrogen or fluorine, and to their use as components of liquid crystalline compositions.

Description: Fluorinated oligophenyls and their use in liquid crystal materials This invention relates to laterally fluorinated oligo¬ phenyls and their use in liquid crystal materials. Liquid crystal materials are well known, and generally exploit the electro-optical switching properties of the nematic (N) or smectic, especially chiral smectic C (S*) or smectic I (S*), phases, the asterisk denoting a chiral phase. They are used widely in electrooptical display devices. Such materials are generally mixtures of compounds selec¬ ted so that the mixture shows desirable properties. In particular such properties include: (i) a broad temperature range over which a suitable liquid crystal phase, e.g. S., S c , S*, S- S or N persists, this range preferably including room temperature (ca. 20 °C). (ii) low viscosity (iii) ease of manufacture (iv) good electro-optical response (v) In the case of compounds or mixtures which show an S c phase, miscibility with one or more optical¬ ly active compounds, i.e. which contain an asym¬ metrically substituted carbon atom, to form a helical chiral phase having a long pitch and a high spontaneous polarisation coefficient P g . It is also useful if the compound or mixture shows an S. phase at a higher temperature than its S c phase to assist in aligning the S-, phase with the electrodes of a liquid crystal electro- optical device. Fluorinated terphenyls are known for use in liquid crystal materials. For example: EP-A-8430494.3 describes the preparation and use of mono- fluorinated terphenyls of general formula: where R 1 and R~ are independently alkyl or alkoxy, in nema¬ tic liquid crystal materials. GB-A-8725928 and WO/0.7890 disclose the use of these monofluorinated terphenyls in S* mixtures. EP-A-0084194 contains a wholly speculative references to laterally difluorinated terphenyls, including a theoreti¬ cal reference to the compound: for use in nematic mixture. PCT/EP87/00515, which at the date of this patent application was unpublished, contains a speculative general formula which would include difluoro¬ phenyl, and also refers specifically to the two compounds: F F used exclusively in nematic liquid crystal mixtures. This invention seeks to identify other useful difluori- nated terphenyls, and in particular to investigate their use in smectic liquid crystal materials. According to the invention fluorinated derivatives of bi-, p-ter- or p-quaterphenyl are provided of the formula I in which a is 0 or 1, and in which the terminal substituents R 1 , R 2 3 and R are each independently an alkyl or alkenyl residue each with up to 15 C atoms, option¬ ally substituted by CN or by at least one halogen atom, and wherein one or more non- adjacent CH 2 groups of these residues may be replaced by -0-, -S-, -CO-, -0-CO-, -CO-0-, -O-CO-O- or -C≡C-, one of the rreessiidduueess RR 1 1 aanndd RR22 maay; also denote a group of the formula, any one of the following pairs of lateral substituents are both fluorine: (A, B), (C, D), (D, E), (C, E), (B, C), (D, J), (D, K), (A, C), (C, J), (C « , D'), (D « , E), (D « , A), (C, E), (C « , A), (D « , J'), (D » f K'), (C » , J'), (B, G), (A, G), all of the other lateral substituents being hydrogen or fluorine. The structural preferences discussed below are inter alia on the basis of usefulness in liquid crystal mixtures, and/or ease of preparation. Preferred overall structures for difluorinated terphenyls of formula I are those of the part formulae I, 1 to I, 6 Preferred overall structures for trifluorinated terphe¬ nyls of formula I are those of part formulae 1,7 to I,12 F F Rl -®-<°><≥>-* 1 , 7 F F Compositions exhibiting smectic C phases which contain compounds of the formula I wherein a is 0 are particu- larly preferred. Preferred overall structures of difluori¬ nated biphenyls of formula I (a = 0) are those of part formulae 1,13 to 1,19: F F ■ -<S>-<£>- R: 1,13 F F F F For the sake of simplicity in the following Phe denotes a 1,4-phenylen group, PheF a group of the formula -<£ - and PheF, a group of the formula ~(θ_ - - F F 2 The compounds of the formula I can be used as components of liquid crystal mixtures, preferably for displays based on the principle of the twisted cell, the guest-host-effect, the effect of the deformation of alligned phases or the effect of dynamic scattering. Compounds of the formula I with a negative anisotropy of the dielectric constants (Δε = β jj -ε, < wherein ε„ denotes the dielectric constant parallel to the axis of the molecule and ε perpendicular to this axis) are aligned perpendicular to an applied electric field. This effect is previously known and is used to control the optical transparency in various liquid crystal display elements, for example, in display elements using the effect of dynamic scattering or the effect of the deforma- tion of aligned phases or of the guest-host interaction. The ECB effect (electrically controlled birefringence) or DAP effect (deformation of aligned phases) was described first by M.F. Schieckel and K. Fahrenschon, Appl. Phys. Lett. (1971), 3912. The work of J. Robert and F. Clerc (SID 80, Digest. Techn. Papers (1980) 80) showed that liquid crystalline phases have to exhibit large values of the relation of the elas¬ tic constants K^/I ,, large values of the optical aniso¬ tropy Δn and values between -0.5 and -5.0 for the dielec- trie anisotropy, in order to used in high informative display elements based on the ECB effect. Electrooptical display elements based on the ECB effect exhibit a homeotropic alignment which means the liquid crystalline phase has a negative dielectric anisotropy. The lc-phase used in electro-optical display elements based on this effect have to suffice many requirements. They have to be chemical stable against humidity and air, physi¬ cal stable against heat, radiation of infra-red, visible and ultra-violet liquid and against A.C.- and D.C.-fields. In addition, technical applicable lc-phases are required to have a liquid crystalline mesophase in a suitable temperature range and a low viscosity. There is, however, a great need for liquid crystalline phases with suitable mesophase ranges, high values of K 3^ K 1' - ~ ~i < 3* 1 optical anisotropy Δn, negative dielectric anisotropy and high stability. According to another important aspect of the invention the compounds of the formula I are highly suitable as components of chirally tilted smectic phases. Chiral tilted smectic liquid crystalline phases with ferro-electric properties can be prepared by adding a suitable chiral dopant to a base-mixture which exhibits one or more tilted smectic phases (L.A. Veresnev et al., Mol. Cryst. Liq. Cryst. 89, 327 (1982); H.R. Brand et al., J. Physique 44 (lett.), L-771 (1983). Such phases can be used as dielectrics for displays based on the SSFLC-technology described by Clark and Lagerwall (N.A. Clark and S.T. Lagerwall, Appl. Phys. Lett. 35_, 889 (1980); U.S. Patent 4,367,924). The invention was based on the object of discovering fluorinated oligophenyls of the formula I which are suitable as components of liquid crystalline mixtures. Particularly liquid crystalline mixtures with a broad mesophase range and a comparable low viscosity are preparable with their aid. In addition, the compounds of the formula I are suitable as components for chiral tilted smectic liquid crystal¬ line phases. The compounds of the formula I have a wide range of appli- cation. Depending on the choice of the substituents, these compounds can be used as the base materials from which liquid crystalline mixtures are composed up to 50 %; how¬ ever, it is also possible for compounds of the formula I to be added to liquid crystalline base materials of other classes of-compounds in order to influence the dielectric and/or optical anisotropy and/or for the viscosity and/or the spontaneous polarization and/or the mesophase range and/or the tilt angle and/or the pitch of such a dielec¬ tric. The compounds of the formula I are furthermore suit- able as intermediates for the preparation of other sub¬ stances, which are useful ' as components of liquid crystal¬ line dielectrics. The compounds of the formula I are colourless in the pure state. They are very stable towards chemicals, heat and light. The invention thus relates to compounds of the formula I, wherein a is I, in particular to compounds of the formu¬ lae I, 1 to I, 6. Furthermore the invention relates to compounds of the formula I 1 ^- ■ (^A 1 ).m—-^o\—-(CA A22 ) ) ^-R 2 ι « F F wherein 1 and 9 are each independently a 1,4-phenylene group optionally substituted by one to four fluorines, R1 and R2 are each independently an alkyl or alkenyl residue each with up to 15 C atoms, option¬ ally substituted by CN or by at least one halogen atom, and wherein one or more non- adjacent CH 2 groups of these residues may be replaced by -0-, -S-, -CO-, -0-CO-, -CO-0-, -O-CO-O- or -C≡C-, m is 0 or 1, n is 1, 2 or 3, and the sum of m and n is 2 or 3. In addition, the invention relates to a liquid crystalline composition with at least two liquid crystalline components wherein at least one component is a compound of the formu¬ la I, wherein a is 1 and to liquid crystalline composition, exhibiting a smectic C phase wherein at least one component is a compound of the formula I wherein a denotes 0 or 1. Furthermore, the invention relates to liquid crystalline display elements which contain such compositions. Above and below R 1, R2 , R3, A1, A2, m and n have the meaning given, unless expressly indicated otherwise. The compounds of the formula I accordingly include pre¬ ferred compounds with three rings of the part formulae la to Id: R 1 -Phe-Phe-PheF 2 -R 2 la R 1 -Phe-PheF 2 -Phe-R 2 lb R 1 -PheF-Phe-PheF-R 2 Ic R 1 -PheF-PheF-Phe-R 2 Id compounds with four rings of the part formulae Ie to Ij R 1 -Phe-Phe-Phe-PheF 2 -R 2 Ie R 1 -Phe-Phe-PheF 2 -Phe-R 2 If R 1 -PheF-Phe-Phe-PheF-R 2 Ig R 1 -PheF-Phe-PheF-Phe-R 2 Ih R 1 -PheF-PheF-Phe-Phe-R 2 Ii R 1 -PhePheF-PheF-Phe-R 2 Ij and compounds with two rings of the part formula Ik R 1 -PheF 2 -Phe-R 2 Ik. Above and below R 1 and R2 denote preferably alkyl or alkoxy. ■ In the compounds of the formula I 1 A 1 and A2 are Phe, PheF and PheF 2 , preferably the compounds of the formula I 1 do not exhibit more than one group PheF 2 . n preferably is 1, 2 or 3, particularly 1. m preferably is 0. Above and below R 1 and R2 each preferably denote alkyl with preferably 1 to 13 C atoms, particularly 3 to 12 C atoms. The compounds of the formula I wherein R 1, R2 and R3 have 1 to 7 C atoms, preferably 1 to 5 C atoms, are particu- larly suitable for liquid crystalline phase used in dis¬ plays based on the ECB effect. The compounds of the formula I, wherein R 1, R2 and R3 have 2 to 15 C atoms, preferably 2 to 12 C atoms, parti¬ cularly 3 to 9 C atoms, are suitable for liquid crystal- line phases exhibiting ferroelectric properties. In the residues R 1, R2 and R3 one or two CH 2 -groups may be replaced by -0-, -S-, -CO-, -0-CO-, -CO-0-, -O-CO-O- or ' -C≡C-. Preferably only one CH 2 group is replaced, particularly preferred by -0-, -0-CO-, -CO-O- or -C=C-. If R 1, R2 and R3 each are an alkyl radical wherein one ("alkoxy" or "oxaalkyl") or two ("alkoxyalkoxy" or "dioxaalkyl") nonadjacent CH 2 groups may be replaced by -0-, these radicals can be straight-chain or branched. Preferably, it is straight-chain and has 2, 3, 4, 5, 6, 7, 8, 9 or 10 C atoms and is accordingly preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl . , ethoxy, propoxy, butoxy, pentoxy, hex- oxy, heptoxy, nonoxy, decyloxy, also methyl, undecyl, dodecyl, tridecyl, tetradecyl, methoxy, undecyloxy, dodecyloxy, tridecyloxy or tetradecyloxy. Oxaalkyl is preferably straight chain 2-oxapropyl (= methoxymethyl), 2- (= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3- oder 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl, 1,3-dioxabutyl (= methoxymethoxy), 1,3-, 1,4-, 2,4-dioxa- pentyl, 1,3-, 1,4-, 1,5-, 2,4-, 2,5- or 3,5-dioxahexyl, 1,3-, 1,4-, 1,5-, 1,6-, 2,4-, 2,5-, 2,6-, 3,5-, 3,6- or 4,6-dioxaheptyl. ' If R 1, R_? and R3 are each an alkyl radi.cal wherei•n one CH~ group is replaced by -S-, this thiaalkyl radical can be straight-chain or branched. Preferably, it is straight chain and denotes 2-thiapropyl, 2- or 3-thiabutyl, 2-, 3- or 4-thiapentyl, 2-, 3-, 4- or 5-thiahexyl, 2-, 3-, 4-, 5- or 6-thiaheptyl, 2-, 3-, 4-, 5-, 6- or 7-thiaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-thianonyl or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-thiadecyl. Thiaalkyl radicals are particularly preferred wherein the CH 2 group adjacent to a ring Phe, PheF or PheF 2 is replaced by -S-. Accordingly, it denotes methylthio, ethylthio, propylthio, butylthio, pentylthio, hexylthio, heptylthio, octylthio, nonylthio or decylthio. If R 1, R2 and R3 each are an alkenyl radical, it can be straight-chain or branched. Preferably, it is straight- chain and.has 2 to 10 C atoms. Accordingly, it is vinyl, prop-1-, or prop-2-enyl, but-1-, 2- or but-3-enyl, pent-1-, 2-, 3- or pent-4-enyl, hex-1-, 2-, 3-, 4- or hex-5-enyl, hept-1-, 2-, 3-, 4-, 5- or hept-6-enyl, oct-1-, 2-, 3-, 4-, 5-, 6- or oct-7-enyl, non-1-, 2-, 3-, 4-, 5-, 6-, 7- or non-8-enyl, dec-1-, 2-, 3-, 4-, 5-, 6-, 7-, 8- or dec-9-enyl. If R 1, R2 and R3 are each an alkyl radical wherein one CH 2 group is replaced by -O-CO- or -CO-O-, it can be straight-chain or branched. Preferably, it is straight- chain and has 2 to 6 C atoms. It is accordingly preferably acetyloxy, propionyloxy, butyryloxy, pentanoyloxy, hexa- noyloxy, acetyloxymethyl, propionyloxymethyl, butyryloxy- methyl, pentanoyloxy ethyl, 2-acetyloxyethyl, 2-propionyl- oxyethyl, 2-butyryloxyethyl, 3-acetyloxypropyl, 3-propionyl oxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxy- carbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxy¬ carbonyl)ethyl, 2-(propoxycarbonyl)ethyl, 3-(methoxycarbo¬ nyl)propyl, 3-(ethoxycarbonyl)propyl or 4-(methoxycarbonyl) butyl. Compounds of the formula I with branched terminal groups R 1, R2 and R3 can occasionally be of importance because of the improved solubility in the costumary liquid crystal base materials, but in particular as chiral doping sub- stances if they are optically active. Smectic compounds of this type are suitable as components for ferro-electric materials. Branched groups of this type as a rule do not contain more than one chain branching. Preferred branched chain radicals R 1, R2 or R3 are isopropyl, 2-butyl (= 1-methyl- propyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, iso- pentyl (= 3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, .3-methylbutoxy, 2-methylpentoxy, 3-methyl- pentoxy, 2-ethylhexoxy, 1-methylhexoxy, 1-methylheptoxy, 2-oxa-3-methylbutyl, 3-oxa-4-methylpentyl, 4-methylhexyl, 2-nonyl, 2-decyl, 2-dodecyl, 6-methyloctoxy, 6- ' methyloc-. tanoyloxy, 5-methylheptyloxycarbonyl, 2-methylbutyryloxy, 3-methylvaleryloxy, 4-methylhexanoyloxy, 2-chlorpropionyl- oxy, 2-chlor-3-methylbutyryloxy, 2-chlor-4-methylvaleryl- oxy, 2-chlor-3-methylvaleryloxy, 2-methyl-3-oxapentyl, 2-methyl-3-oxahexyl, 2-fluoro-3-methylvaleryloxy, 2-fluoro- 3-methylbutoxy. If R 1, R2 and R3 are each an alkyl radical wherei.n two or more CH 2 groups are replaced by -O- and/or -CO-0-, it can be straight-chain or branched. Preferably, it is branched and has 3 to 12 C atoms. It is accordingly pre¬ ferably bis-carboxy- ethyl, 2,2-bis-carboxy-ethyl, 3,3- bis-carboxy-propyl, 4,4-bis-carboxy-butyl, 5,5-bis-carb- oxy-pentyl, 6,6-bis-carboxy-hexyl, 7,7-bis-carboxy-heptyl, 8,8-bis-carboxy-octyl, 9,9-bis-carboxy-nonyl, 10,10-bis- carboxy-decyl, bis-(methoxycarbonyl)-methyl, 2,2-bis- (methoxycarbonyl)-ethyl, 3,3-bis-(methoxycarbonyl)-propyl, ,4-bis-(methoxycarbonyl)-butyl, 5,5-bis-(methoxycarbonyl)- pentyl, 6,6-bis-(methoxycarbonyl)-hexyl, 7,7-bis-( ethoxy¬ carbonyl)-heptyl, 8,8-bis-(methoxycarbonyl)-octyl, bis- (ethoxycarbonyl)-methyl, 2,2-bis-(ethoxycarbonyl)-ethyl, 3,3-bis-(ethoxycarbonyl)-propyl, ,4-bis-(ethoxycarbonyl)- butyl, 5,5-bis-(ethoxycarbonyl)-pentyl. Compounds of the formula I wherein the terminal groups R , R 2 and/or R3 are s " ui.table for poly-condensation reactions are useful for the preparation of liquid crystalline poly- condensates. Formula I includes both the racemates of these compounds and the optical antipodes, as well as mixtures thereof. The compounds of the formula I are prepared by methods which are known per se, such as are described in the literature (for example in the standard works, such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg Thieme Verlag, Stuttgart), and in particular under reaction conditions which are known and suitable for the reactions mentioned. Variants which are known per se and are not mentioned in more detail here can also be used in this connection. If desired, the starting materials can also be formed in situ, such that they are not isolated from the reac¬ tion mixture but are immediately reacted further to give the compounds of the formula I. The compounds of the formula I 1 can be prepared from 1,2-difluorobenzene as startig material. This is deprotonated using a procedure known from M.A. Roe et al. (J. Chem. Soc. Chem. Comm. 22_, 582 (1965)) and reacted with the corresponding electrophilic reagent. This reaction sequence can be carried out a second time with the so obtained l-substituted-2,3-difluorobenzene. Accordingly, l,4-disubstituted-2,3-difluorobenzene deri¬ vatives of the formula I can be obtained. 1,2-Difluorobenzene or l-substituted-2,3-difluorbenzene, respectively, is reacted in an inert solvent as, for example, in an ether as diethylether, tetrahydrofuran, dimethoxyethane, tert.-butylmethylether or dioxane or in a hydrocarbon as hexane, heptane, cyclohexane, benzene, tolene or a mixture of these solvents, optionally with a complexing agent as, for example, tetramethylethylen- diamin (TMEDA), hexamethylphosphoric acid triamide (HMPTA), or N,N-dimethylpropylene-urea (DMPU) with an organometallic reagent as, for example, phenyllithium, n-, sec-, or tert.-butyllithium, lithium tetramethyl- piperidinidi at temperatures of -120 °C to +50 °C, preferably -78 °C to 0 °C. The 2,3-difluorphenyllithium compounds are reacted with the corresponding electrophilic reagents at -120 °C to 0 °C, preferably at 0 °C. Suitable electrophilic reagents are aldehydes, ketones, nitriles, epoxides, carboxylic acid derivatives as, for example esters, anhydrides or carboxylic halides, halogenformic acid esters or carbon- dioxide. Particularly suitable electrophilic reagents are derivatives of cyclohexanone. For the reaction with aliphatic halides the lithium derivatives have to be transmetallized to the potassium derivatives using potassium tert. butylate at tempera¬ tures of -80 °C to -120 °C. For the reaction with aromatic halides the lithium deri¬ vatives are, for example, trans etallized to the zinc-, boron- or titanium-derivatives which are suitable for cross-coppling reactions under transition-metall catalysis. Terphenyls of formula I may for example be prepared using general routes 1 to 10 shown schematically in Figs. 1 to 8 of the accompanying drawings. Although illustrated therein for cases in which R, and R 2 are alkyl or alkoxy, it will be understood that perfluoroalkyl or perfluoro- alkoxy analogues may be made by analogous routes. Other methods of making these compounds will be apparent to those skilled in the art. Terphenyls of formula I in which one of the pairs (D, K) or (C, J) are both fluorine may for example be made using the starting difluorophenol of route 9, or the known l,3-difluoro-2-amino phenol, and adding appropriately 4-substituted phenyl rings to such precursors, using for example routes which couple these rings via known phenylboronic acids. Difluorobiphenyls of formula I may be prepared by modifi- cations of routes 1 to 9 in which the various intermedia¬ tes formed in these routes are coupled with phenyls, e.g. - 2 (5B) (5A) ( 5A) ( 5B) -I .2 ( 8C ) ( 9D) Trifluoroterphenyls may also be prepared by modification of routes 1 to 9, e.g. by coupling the intermediates formed, e.g. (6C) Compounds of formula I often show nematic or smectic C phases which persist over a broad temperature range and are useful constituents of liquid crystal mixtures. Therefore according to a second aspect of the invention there is provided a liquid crystal material, being a mixture of compounds, at least one of which is a p-bi-, p_ter- or p-quaterphenyl of formula I,. preferably one selected of the part formulae 1,1 to 1,19. The liquid crystalline phases according to the invention consist of 2 to 25, preferably 3 to 15, components, at least one of which is a compound of the formula I. The other constituents are preferably chosen from nematic, smectic, nematogenic of smectogenic substances, in parti¬ cular the known substances, from the classes of azoxyben- zenes, benzylideneani1ines, biphenyls, p-terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl cyclohexane carboxylates, phenylcyclohexanes, cyclohexylbiphenyles, cyclohexylcyclohexanes, cyclohexylnaphthalenes, 1,4-bis- cyclohexylbenzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexyldithianes, phenyl- or cyclohexyldioxanes, 1,2-bis-phenylethanes, 1,2-bis-cyclohexylethane, l-phenyl-2-cyclohexylethanes, optionally halogenated stilbenes, benzylphenyl ethers, tolanes and substituted cinnamic acids. Important compounds which are possible constituents of liquid crystalline mixtures according to the invention can be characterized by the formula III R'-L-G-E-R" wherein L and E are each an unsubstituted or laterally fluoro or cyano substituted carbo- or heterocyclic ring system chosen from the group comprising 1,4-di- substituted benzene or cyclohexane rings, 1,4-di- substituted 1-cyanocyclohexane rings, 4,4*-di- substituted biphenyl, phenylcyclohexyl or bicyclo- hexyl systems, 2,5-disubstituted pyrimidine, pyri- dine and 1,3-dioxane rings, 2,6-disubstituted naphthalene, di- and tetrahydronaphthalene, quinoline and tetrahydroquinazoline, is -CH=CH-, -CH=CY-, -C≡C-, -CO-0-, -CO-S-, -CH=N-, -N(0)=N-, -CH=N(0)-, -CH 2 CH 2 -, -CH^ -CH 2 -S-, -COO-Phe-COO- or a single bond, is halogen, preferably chlorine or -CN, :' and R" are each alkyl, alkoxy, alkanoyloxy, alkoxy- carbonyl or alkoxycarbonyloxy with up to 18, pre¬ ferably up to 10 C atoms, it also being possible for one CH 2 group nonadjacent to an oxygen to be replaced by -0-, -CH=CH- or -C=C-, or one of these radicals R 1 and R" may also be -CN, -N0 2 , -CF_, -NCS, -F, -Cl, or -Br. In the most of these compounds R 1 and R" are different for one another, one of these radicals usually being an alkyl or alkoxy group. However, other variants of the substituents envisaged can also be used. Many such substances or mixtures thereof are commercially avail¬ able. All of these substances can be prepared by methods which are known from the literature. The liquid crystalline mixtures according to the inven- tion are prepared in a manner which is customary per se. As a rule, the components are dissolved in one another, preferably at elevated temperature. The liquid crystalline mixtures according to the inven¬ tion can be modified by suitable additives such that they can be used in all the types of liquid crystal display elements disclosed to date. Such additives are known to the expert and are described in detail in the literature. For example, it is possible to add conductive salts, preferably ethyl-di ethyl-do- decyl-ammonium 4-hexyloxybenzoate, tetrabutylammonium tetraphenylboranate or complex salts or crown ethers (compare., for example, I. Haller et al., Mol.Cryst.Liq. Cryst.. Volume 24, pages 249-258 (1973) for improving the÷conductivity, dichroic dyestuffs for the production of: coloured guest-host systems or substances for changing theedielectric anisotropy, the viscosity and/or the orientation of the nematic phases. Such substances are described, for example, in German Offenlegungsschrift 2,209,127, 2,240,863, 2,321,632, 2,338,281, 2,450,088, 2,637,430, 2,853,728 and 2,902,177. When the liquid crystal material is a nematic liquid crystal material, the other constituents of the material may be selected from a wide variety of compounds which are known to be useful constituents of nematic liquid crystal materials, for example those structural types of the part formulae 2.1 to 2.6 where R a and R^ are independently alkyl or alkoxy: 2.4 R a -< ) ' o} 'coo -(o} 'R b 2 ' 6 Generally a nematic liquid crystal material of this as- pect of the invention contains up to about 25 % by weight of a terphenyl of formula I. For twisted nematic (TN), Freedericksz effect, cholesteric to nematic phase change effect devices, the bulk of the material may usefully comprise compounds selected from formulae 2.1 to 2.6. If a cholesteric phase is required, one or more of the alkyl groups R or R. may contain an asymmetric carbon atom, e.g. in a 2-methylbutyl group. Certain terphenyls of formula I have been found to be particularly useful in liquid crystal materials which employ the electrically controlled birefringence (ECB) effect. In such materials one or more terphenyls of formula I may constitute up to about 50 % by weight, typically up to about 25 %. The bulk of such a mixture may usefully comprise compounds of the part formulae 3.1 to 3.6, in which R a and R^ may be alkyl or alkoxy: R a-<S>0 R b 3 .2 R a-®-<£>-(> R b 3 - 3 O®^ 0 -®-^ 3 - 5 Certain bi- and terphenyls of formula I have been found to be useful components of liquid crystal materials which ex¬ ploit the ferroelectric properties of the S* phase. Cer¬ tain terphenyls of formula I show smectic C phases which persist over a broad temperature range. Therefore this invention provides a liquid crystal material which shows an S c phase which is a mixture containing one or more bi- or terphenyls of formula I, and which may consist wholly of two or more bi- and/or terphenyls of formula I. To pro¬ vide an Si phase, one of the constituents of this mixture must contain an asymmetric carbon atom, and this constituen may itself be a bi- or terphenyl of formula I, but it is preferably a compound not of formula I. Mixtures with a S phase which contain in addition to one or more terphenyls of the formula I one ore more biphenyls of the formula I are particularly preferred. Such a mixture may usefully contain compounds of the part formulae 4.1 to 4.8, in which R and R, may be alkyl or alkoxy and X denotes O or S, preferably O: R a -@-C0X-(0>-R b 4.1 R a-<£>-<£> C0X -<E R b 4.2 In the compounds of the formulae 4.1 to 4.8 one 1,4- phenylene group may be substituted by halogen, preferab¬ ly by fluorine. Preferred fluorinated forms of formulae 4.1 to 4.8 are those of the formulae 4.9 and 4.10: R a r -<®0 )--C C O O O O --<0 O -< O°) >--R R tb 4. 9 R a " <≤>-<2$-<2>- R t 4.10 The smectic phases according to the invention may also contain in addition to the compounds of the formula I and of the formulae 4 a component exhibiting a negative value of the dielectric anisotropy (Δε -2), e.g. compounds of the formulae 5.1 to 5.3: In S c and S* mixtures of this aspect of the invention, terphenyls of formulae 1,1 to 1,6, especially 1,1, 1,2 and 1,4 are preferred constituents as they show useful S_ phases. When the S Q or S* material of this aspect of the invention does not consist wholly of bi- or terphenyls of formula I, other constituents are compounds which are known to be use¬ ful constituents of S„ and/or S* liquid crystal materials. A useful S* liquid crystal material may comprise a mixture of oneτ or more terphenyls of formula I, " plus one or more other compounds which contain an asymmetrically substituted carbon: atom. I tι_air. Sfi, mixture of this aspect of the invention, R., and — are preferably of a longer carbon chain length than would be used for nematic materials, for example each preferably contains 5 or more carbon atoms. R, and R 2 are preferably n-alkyl or n-alkoxy in such mixtures. The discovery that S* mixtures may be prepared using ter- phenyls of formula I, and their advantages, i.e. good S_ phases and fast switching speeds, are wholly unexpec¬ ted over the prior art which refers exclusively to nema¬ tic or ECB mixtures. Indeed nematic or ECB mixtures are generally designed to exclude compounds which show smec- tic character. P-referred compounds containing asymmetric carbon in an S_*smaterial of this aspect of the invention include the lirmethylheptyl (20ct*) esters disclosed in EP-A-0110299, orrone or more of the compounds containing a -COO.CH(CN) group disclosed in WO 87/07890 or UK Patent Applications 872.9502, 8729503, 8729865 or 8729982. Derivatives of the optical active lactic acid are disclosed in WO 86/02938 or PCT/GB 87/00132. Optical active deriva¬ tives of terpinoids are described in WO 86/04328, naphthoic esters in WO 87/06577, mandelic acid esters in WO 88/02390 and derivatives of optical active amino acids are disclosed in WO 86/02937 or UK Patent Application 86 20 111. The chiral dopants of the part formulae 6.1 to 6.6, wherein X denotes an alkoxy- or alkylamino-residue, Y denotes H, CF 3 or CH 3 , m is 0 or 1 , n is 1 or 2 and p is 0 or 1 are particularly preferred: R-a--(Phe)n-Phe-COO-20ct* 6*1 CN I R-a-( he)„-Phe-COO-C ~~ H-R, D 6.2 R a -(Phe) n -Phe-(CO) -O-CH-CO-X 6.3 I CH 3 R a.-(Phe)n-Phe-CH___.CH_,<,__-C00-20ct* 6.4 Ra-(Phe)n-(COO)m-Phe-(CO)p-0-CH2_-C | F-alky - 1 l 6.5 Y R a -(Phe) n -(COO) m -Phe-(CO) -0C(CN)R 1 R 2 6.6 In the compounds of the formulae 6.1 to 6.6 one or more group Phe may be substituted by fluorine, R and R, are as defined above, R, being preferably C..-C. n- lkyl, cycloalkyl or branched alkyl. R in the last-above formulae is preferably C 5 -C 12 n-alkyl or n-alkoxy, particularly n-octyloxy. R, is preferably methyl or a group of general formula: where a is 0 or an integer 1-6, and each of b and c are independently integers 1-6, preferably at least one of b or c being 1. R χ and R 2 are each alkyl having a different number of carbon atoms or taken together preferably denote an alicyclic group, for example, of the formula: CN ■ . When the S* mixture of this aspect of the invention con¬ tains two or ' more compounds which contain an asymmetric carbon atom, then two or more of these compounds may use¬ fully be of opposite optical handedness, i.e. having (+) and (-) optical rotation or D and L stereoisomerism. In this way the length of the helical S* pitch may be controlled, and/or a useful S. phase may be induced, assisting alignment of the liquid crystal material with the electrodes of an electro-optic device. Generally an S* mixture of this aspect of the invention contains 1 to 30 weight % of chiral dopant(s). The rest of the mixture may comprise one or more compounds of the formula I, especially of the formulae 1,1 to 1,6 or of 1,13 and 1,17 to 1,19. The total being 100 weight %. Alternatively the S* mixture may consist of 1 to 30 weight % of chiral dopant(s), the rest being a mixture of compounds of formula I plus one or more of formulae 4,1 to 4,10 or 5,1 to 5,3 and/or other known smectic C components or other suitable additives. Generally the weight % of the compounds of the formulae 4,1 to 4,10 or 5,1 to 5,3 will not exceed 80 % of the mixture. The liqud crystal materials of this invention may be used in liquid crystal electro-optical display devices of known construction. The invention will now be illustrated by way of example only with reference to accompanying figs. 1-8 which show preparative routes 1-10 referred to above. The following abbreviations are used: K = solid crystal N = nematic liquid crystal S. = smectic A liquid crystal S_ = smectic C liquid crystal I = isotropic liquid Example 1 Preparation of 4-n-hexyloxy-4"-n-pentyl-2 l ,5'-difluoro- p-terphenyl 1A 4-n-Hexyloxybromobenzene A solution of 1-bromohexane (60 g) in acetone (150 ml) is added dropwise to a stirred mixture of 4-bromphenol (71 g) and K 2 C0 3 (120 g) in acetone (600 ml) at room temperature. The stirred mixture is heated under reflux for 43 hrs (i.e. until glc revealed complete reaction) . The product is ex¬ tracted into ether twice, and the combined ethereal extracts are washed with water, 5 % NaOH water and dried (MgS0 4 ). The solvent is removed in vacuo and the residue was distilled (bp = 100-110 °C at 0.1 mm Hg) to yield a colour¬ less liquid. IB 4-n-Hexyloxyphenylboronic acid A solution of the Grignard Reagent prepared from 1A (72 g) and Mg (7.75 g) in dry THF (250 ml) is added dropwise to a stirred, cooled (-78 °C) solution of tri-isopropyl , borate (109.1 g) in dry THF (40 ml) under dry N... The stirred mixture is allowed to warm to room temperature overnight and stirred with 10 % HC1 (320 ml) at room temperature for 1 hr. The product is extracted into ether twice, and the combined etheral extracts are washed with water and dried (MgSO.). Solvent is removed in vacuo to yield a colourless solid, mp = 80-85 °C. 1C 4-Amino-2,5-difluorobromobenzene N-Bromosuccinimide (42 g) is added in small amounts over 1 1/2 h to a .stirred, coold (-10 °-0 °C) solution of 2-5-difluoroaniline (30-96 g) in dry CH 2 Cl 2 (180 ml). The mixture is stirred at 0 °C for 2 h. The red solution is washed with a large amount of water twice, and dried (MgS0 4 ). The solvent is removed in vacuo to yield a red solid, mp = 74-75 °C. ID 2,5-Difluoro-4-bromobiphenyle A solution of 1C in dry benzene (200 ml) is added drop¬ wise with stirring, over 1 1/2 h to a stirred, cooled (0 °C) solution of isopentylnitrile (33.6 g) in dry ben¬ zene. The mixture is heated under reflux for 1 1/2 hrs and cooled. The product is extracted with ether twice and the combined organic layer is washed successively with water, aqueous sodium hydrogen carbonate, 2M hydro¬ chloric acid, and water, and dried (MgS0 4 ). The solvent is removed in vacuo and the crude product is steam distilled to give a brown-black solid. This is further purified by column chromatography (silica gel/dichloro- methane) to give a dark brown low melting solid. IE 4'-Pentanoyl-2,5-difluoro-4-bromobiphenyl A1C1 3 .(25.4 g) is ground and added to a stirred, cooled (0 °C) solution valeroyl chloride (34.9 g) in dry di- chloromethane (120 ml). A solution of ID (13.2 g) in dry dichloromethane (120 ml) is added dropwise over 2 h at 0 °C. The mixture is stirred at room temperature for 48 h and poured onto crushed ice/conc. HCl. The sepa¬ rated aqueous layer is washed with CH 2 C1 2 twice, the combined organic layers are washed with water, NaHC0 3 , and water, and dried (MgS0 4 ). The solvent is removed in vacuo to ' yield a dark red oil which was distilled under reduced pressure (0.1 mm Hg, temperature not re¬ corded) to give a low melting red-brown solid which is further purified by column chromatography (silica gel/ CH-C1 2 ) to yield a low melting red-brown solid. IF 4 , -n-Pentyl-2,5-difluoro-4-bromobiphenyl Triethylsilane (7.0 g) is added dropwise over 2 h to a cooled, stirred (0 °C) solution of IE (8.0 g) in tri- fluoroacetic acid (40 ml). The reaction mixture is stirred at room temperature overnight and poured into NaHC0 3 solution. The product is extracted into ether twice and the combined ether layers are washed with water and dried (MgSO.) . The solvent was removed in vacuo to yield an orange-brown oil. The crude product is dis¬ tilled under reduced pressure (short path, 110-120 °C at 0.01 mm Hg) to give a red oil. IG 4'-n-Hexyloxy-4"-n-pentyl-2' ,5'-difluoro-p-terphenyl A solution of IB (0.9806 g) in ethanol (15 ml) is added dropwise to a stirred mixture of IF (1.25 g) and tetrakis (triphenylphosphine) palladium (0) (0.1392 g) in benzene (20 ml) and 2M-Na 2 C0 3 (20 ml) at room temperature under dry N 2 .. The stirred mixture is heated under reflux (90- 95 " _ °c). for 23 h (i.e. until glc analysis confirmed ab¬ sencesf starting materials). The mixture is cooled, optionally stirred with 30 % H 2 0 2 (2 ml) for 1 h at room temperature. The product is extracted with ether twice and the combined organic extracts are washed with brine and dried (MgSO.). The solvent is removed in vacuo and the residue is purified by column chromato¬ graphy (silica gel/petroleum ether (bp 40-60 °C) - dichlo- romethane, 3-1) to give a colourless solid which is re- crystallised from ethanol to give colourless plates, K 53.0 N 118.0 I. Example 2 Preparation of 4,4"-Di-n-pentyl-2' ,5'-difluoro-p- terphenyl 2A" 4-Pentanoyl-bromobenzene Pentanoyl chloride (50 g) is added dropwise to a stirred, cooled (0 °C) mixture of bromobenzene (150 ml) and alu¬ minium chloride (0.2 g). The mixture is stirred at 0 °C for 1 h, heated at 80 °C for 2 h, cooled and poured into 18 % hydrochloric acid. The product is extracted into CHCl twice, the combined organic extracts are washed with water and steam distilled to remove chloroform and the excess of bromobenzene. The product is extracted into chloroform twice, the combined organic phases are washed with water and dried (MgS0 4 ). The solvent is re¬ moved in vacuo and the residue is distilled (bp 180-184 °C at 20 mm Hg) to yield a colourless solid. 2B 4-n-Pentylbromobenzene A mixture of 2A (77.1 g), hydrazine hydrate (46.4 g) and KOH (590 g) in diethylene glycol (250 ml) is heated at 130 °C for 2 h, the excess of hydrazine hydrate is dis- tilled off and the temperature is raised to 200 °C for 2 h. The cooled mixture is poured into 18 % HCl, the product is extracted into ether twice and the combined ethereal extracts are washed with water and dried (MgS0 4 ). The solvent is removed in vacuo and the resi- due is distilled (bp 145-148 °C at 20 mm Hg) to yield a colourless liquid (58.1 g, 80 %] 2C 4-n-Pentylphenylboronic acid The Grignard Reagent prepared from 2B is convated into the boron compound with tri-isopropylborate in an ana- logous manner as for IB described. The product from 2C is coupled with the product from IF in an analogous manner as for IG described to yield 4,4"- di-n-pentyl^^δ'-difluoro-p-terphenyl, K 65.0 N 86.0 I. Example 3 Preparation of 4-n-Hexyloxy-4"-n-pentyl-2,2"-difluoro-p- terphenyl 3A 4-n-Hexyloxy-2-fluorobromobenzene A solution of 1-bromohexane (9.33 g) in acetone (20 ml) is added dropwise to a stirred mixture of 4-bromo-3- fluorophenol (9.00 g) and potassium carbonate (13.5 g) in acetone (75 ml) at room temperature. The stirred mixture is heated under reflux for 21 h (i.e. until glc analysis revealed a complete reaction). The product is extracted into ether twice, and the combined ether ex¬ tracts are washed with water, 10 % sodium hydroxide, water and dried (MgS0 4 ). The solvent is removed under vacuo and the residue is distilled (bp 100-105 °C at 0.1 mm Hg) to yield a colourless liquid. 3B 4-Hexyloxy-2-fluorophenylboronic acid A solution of n-butyllithium (10.0 M in hexane, 3.30 ml) is added dropwise to a stirred cooled (-78 °C) solution of 3A (9.0 g) in dry THF (70 ml) under dry N 2 - The stirred mixture is maintained under these conditions for 2.5 h and then a cooled solution of tri-isopropylborate (11.28 g) in dry THF (50 ml) is added dropwise at -78 °C. The stir¬ red mixture is allowed to warm to room temperature over- night and then stirred for 1 h at room temperature with 10 % HCl (50 ml). The product is extracted into ether twice and the combined ethereal extracts are washed with water and dried (MgS0 4 ). The solvent is removed in vacuo to afford an off-white solid. 3C 4-n-Hexyloxy-4"-n-pentyl-2,2"-difluoro-p-terphenyl The product from 3B is coupled with 4'-bromo-2-fluoro-4- pentylbiphenyl in an analogous manner as described for IG. The crude product is purified by column chromatography (silica gel/petroleum fraction (bp 40-60 °C) - dichloro- methane 3:1) to yield a colourless solid which is recrys- tallised from ethanol to give colourless waxy plates, K 45.0 N 131.0 I. Example 4 Preparation of 4-n-Octyloxy-4"-pentyl-2,2"-difluoro-p- terphenyl 4A 4-n-Octyloxy-2-fluoro-bromobenzene The method used is as for 3A Quantities 4-bromo-4-fluorophenol 6.00 g 1-bromooctane 7.40 g K 2 C0 3 10.00 g Product is distilled under reduced pressure (bp = 140- 142 °C at 0.5 mm Hg) to yield a colourless liquid. 4B 4'-n-Pentyl-2'-fluorobiphenyl-4-ylboronic acid The method is used as for 3B Quantities 3'-bromo-2-fluoro-4-n-pentylbiphenyl 9.90 g Magnesium 0.871 g tri-isopropylborate 11.66 g crude yield 8.85 g 4C 4-n-Octyloxy-4"-pentyl-2,2"-difluoro-p-terphenyl The method is as for IG Quantities 4A 6.00 g 4B 1.75 g Tetrakis(triphenylphosphine)pal1adium(0) 0.2979 g Product is purified by column chromatography to give a colourless solid, K 42.5 N 121.5 I. Example 5 Preparation of 4-n-hexyloxy-4"-n-pentyl-3,2"-difluoro- p-terphenyl 4-n-Hexyloxy-3-fluorophenylboronic acid is coupled with 4'-bromo-2-fluoro-4-n-pentylbiphenyl in an ana¬ logous manner as described for IG. The crude product is purified by column chromatography (silica gel/petroleum fraction (bp 40-60 °C) - CH 2 C1 2 6:1) to give a colourless solid which was recrystallised from ethanol - ethyl acetate (10:1) to yield colourless plates, K 96.0 S c 105.5 N 139.0 I. Example 6 Preparation of 4-n-Hexyloxy-4"-n-pentyl-2'3'-difluoro- p-terphenyl 6A 2,3-Difluorophenylboronic acid 1,2-Difluorobenzene is converted to 6A with tri-iso¬ propylborate in an analogous manner as described for 3B. 6B 4-n-Pentyl-2' ,3*-difluorobiphenyl The method used is as for IG. Quantities: l-bromo-4-pentylbenzene 3.80 g 6A 3.50 g Tetrakis (triphenylphosphine)palladium (0) 0.651 g Coupling to give biphenyls was found to be faster than for terphenyls so this reaction was complete within 5 h. The crude product was purified by column chromato¬ graphy (silica gel/petroleum fraction (bp 40-60 °C): CH 2 C1 2 3:1) to yield a colourless liquid. 6C 4*-n-Pentyl-2,3-difluorobiphenyl-4-ylboronic acid The method used is as for 3B. Quantities: 6B 4.00 g n-butyllithium 1.50 ml, 10.0 M in hexane tri-isopropylborate 5.70 g 6D 4-n-Hexyloxy-4"-pentyl-2' ,3 f -difluoro-p-terphenyl The method used was as for IG. Quantities: IB 1.30 g 6C 2.0 g Tetrakis (triphenylphosphine) palladium (0) 0.312 g The crude product was purified by column chromatography (silica gel/petroleum Pro-ition (bp 40-60 °C): dichloro- methane 6:1) to yield a colourless solid which was re¬ crystallised from ethanol to give colourless plates. K53° S c 65.5° N 149° I The analogous compound 6E: 4-n-octyloxy-4"-n-pentyl-2 ' '3'-p-terphenyl is prepared using an analogous route in which 1-bromo- 4-octyloxybenzene is used instead of IB. This compound is prepared by the same method as for IB: Quantities: 4-bromophenol 64.54 g 1-bromooctane 60.00 g K 2 C0 3 103.5 g as a colourless liquid bp = 145 °C at 0.1 mm Hg. In the preparation of 6E the method used is as for 6D. Quantities: l-bromo-4-octoxybenzene 1.40 g 6C 1.90 g Tetrakis (triphenylphosphine) palladium (0) 0.3102 g The crude product is purified by column chromatography (silica gel/petroleum fraction (bp 40-60 °C) - CH 2 C1 2 , 5:1) to give a colourless solid which is recrystallised from ethanol - ethyl acetate (4:1) to yield colourless plates, K 48.5 S__ * 95.1 N 141.5 I. Example 7 Preparation of 4,4"-di-n-pentyl-2 l ,3'-difluoro-p- terphenyl The method used is as for IG. Quantities: 2B 1.30 g 6C 2.10 g Tetrakis (triphenylphosphine) palladium (0) 0.28 g The crude product was purified by column chromatography (silica gel/petroleum fraction (bp 40-60 °C) - CH 2 C1 2 , 5:1) to yield a colourless solid which was recrystallised from ethanol to give colourless plates, K 60 N 120 I. Example 8 Preparation of 4-n-hexyloxy-4"-n-pentyl-2,3-difluoro- terphenyl 8A 2,3-Difluorophenol The method used is a modification of M.F. Hawthorne, J. Org. Chem. (1957), 22_, 1001. Quantities: 6A 4.40 g 10 % hydrogen peroxide 30 ml Yield: off-white solid, mp 34-36 °C. 8B 2,3-Difluoro-n-hexyloxybenzene The method used is as for 3A. The crude product is distilled (bp 122 °C at 15 mm Hg) to give a colourless liquid. 8C 4-n-Hexyloxy-2,3-difluorophenylboronic acid The method used is as for 3B. Quantities: 8B 10.0 g n-butyllithium 4.70 ml, 10.0 M in hexane Tri-isopropylborate 17.70 g 8D 4-n-Hexyloxy-4"-n-pentyl-2,3-difluoro-p-terphenyl The method used is as for IG. Quantities: 4-bromo-4'-pentylbiphenyl 1.40 g 8C 1.50 g Tetrakis (triphenylphosphine) palladium (0) 0.2868 g The crude product is purified by column chromatography (silica gel/petroleum fraction (bp 40-60 °C) - CH 2 C1 2 , 3:1) to give a colourless solid which is recrystallised from ethanol - ethyl acetate (10:1) as colourless crystals, K 97.5° Sc 145.5° N 166° I. Example 8b Preparation of 4-n-octyloxy-4"-n-pentyl-2,3-difluoro-p- terphenyl This compound is prepared by an analogous route using l,2-difluoro-3-octoxybenzene instead of 8B. This is prepared using the method as for 3A. The crude product is distilled (bp 150 °C at 15 mm Hg) to give a colourless liquid. 8 " E 4-n-Octyloxy-2,3-difluorophenylboronic acid To prepare 8E using the method as for 8C. Quantities: l,2-difluoro-3-octoxybenzene 7.50 g n-butyllithium 3.10 ml 10.0 M in hexane triisopropylborate 11.66 g To yield a colourless solid. 8F 4-n-Octyloxy-4"-n-pentyl-2,3-difluoro-p-terphenyl method as for 8D Quantities: 4-bromo-4 1 -pentylbiphenyl 1.54 g 2,3-difluoro-4-octoxyphenylboronic acid 1.75 g • Tetrakis (triphenylphosphine) palladium (0) 0.309 g The crude product is purified by column chromatography (silica gel/petroleum fraction (bp 40-60 °C) - CH 2 C1 2 , 3:1) to give a colourless solid which is recrystallised from ethanol - ethyl acetate 4:1 to give colourless crystals K 93.5 SC 144 SA Λ 148 N 159 I. Example 9 • Preparation of 4,4"-di-n-pentyl-2,6-difluoro-p-terphenyl 9A 1,3-Difluoro-5-(1-hydroxypentyl)-benzene A solution of pentanal (19.0 g, 0.22 mol) in dry ether (75 ml) is added dropwise to a stirred solution of the Grignard reagent at room temperature, under dry nitrogen, prepared from l-bromo-3,5-difluoro-benzene (50.2 g, 0.26 mol) and magnesium (7.25 g, 0.30 mol) in dry THF (100 ml). The stirred mixture is heated under reflux for 2 h, cooled and a saturated solution of ammonium chloride (300 ml) is added. The product is extracted into ether (twice), and the combined ethereal extracts are washed with water and dried (MgS0 4 ). The solvent is removed in vacuo to give a pale-orange liquid (51.1 g) which is distilled to yield a colourless liquid. Smaller quantities of crude product are purified by column chromatography (silica gel/dichloromethane) to yield a colourless liquid, bp 90 °C at 0.5 mm Hg. 9B 1,3-Difluoro-5-pent-l-enylbenzene Phosphorus(v) oxide (64.5 g, 0.45 mol) is added to a stirred solution of compound 9A (35.0 g, 0.175 mol) in dry pentane (150 ml) at room temperature. The mix- ture is stirred at room temperature overnight (glc analysis revealed absence of starting material) and filtered. 9C 1,3-Difluoro-5-pentylbenzene 5 % Palladium-!-on-charcoal (4.0 g) is added to the above filtrate [i.e. compound 9B in pentane (150 ml)] at room temperature. The stirred mixture is hydrogenated at atmospheric pressure for 4 h (i.e., until glc analysis revealed absence of starting material) and the mixture is filtered. The majority of the pentane is removed in vacuo, and the final amount of pentane is distilled off (760 mm Hg) at 38 °C and the residue was then dis¬ tilled to yield a colourless liquid, bp: 200 °C at 760 mm Hg 9D 2 ,6-Difluor-5- -pentylphenylboronic acid A solution of n-butyllithium (10.4 M in hexane; 2.70 ml, 0.028 mol) is added dropwise to a stirred, cooled (-78 °C) under dry nitrogen. The stirred mixture is maintained under these conditions for 2.5 h and a pre¬ viously cooled solution of tri-isopropyl borate (10.22 g, 0.054 mol) in dry THF (50 ml) is added dropwise at -78 °C. The stirred mixture was allowed to warm to room tempera¬ ture overnight and stirred for 1 h with 10 % hydrochloride acid (30 ml). The product is extracted into ether (twice), and the combined ethereal extracts are washed with water and dried (MgS0 4 ). The solvent is removed in vacuo to give a colourless solid, mp: 95-100 °C 9E 3-pentyl-4"-hexyloxy-2,6-difluoro-p-terphenyl The method used is as for IG. Quantities: 4-bromohexoxybiphenyl 1.30 g 9D 1.10 g Tetrakis (triphenylphosphine) palladium (0) 0.157 g The crude product is purified by column chromatography (basic aluminia/petroleum fraction (bp 40-60 °C) with the gradual introduction of dichloromethane) to give a colourless solid which is recrystallised from ethanol to give colourless plates, K 62° N 123° I. 9F 4,4"-dipentyl-2,6-difluoro-p-terphenyl The method used is as for IG. Quantities: 4-bromo-4'-pentylbiphenyl 1.40 g 9D 1.37 g Tetrakis (triphenylphosphine) palladium (0) 0.157 g The crude product is purified by column chromatography (silica gel/petroleum fraction (bp 40-60 °C) - CH 2 C1 2 , 1:1) to give a colourless liquid which contained a solid. The solid is filtered off and washed with petroleum fraction (bp 40-60 °C). The solvent is removed in vacuo to give a colourless liquid, two impurities are removed by using a Kugelrohr distillation apparatus to give a colourless solid which is recrystallised from ethanol to yield colourless crystals. K 50° N 82° I. Example 10 Preparation of 4,4"-Di-n-alkyl-2 l , 3 ' -dif luoro-p-terphenyls 10A 4-n-Alkyl-l-(2 , 3-difluorophenyl )-cyclohex-l-enes A mixture of 0.3 mol n-butyllithium and n-hexane (188 ml) is added to a cooled (-60 ° to -70 °C) mixture of 1,2-di- fluorobenzene (0.3 mol), tetrahydrofuran (THF) (600 ml) and tetramethylethylendiamin (TMEDA, 0.3 mol). The stirred - mixture is maintained for 3 h and then a mixture of 4-n- pentylcyclohexanone (0.32 mol) and tetrahydrofuran (100 ml) is added. After usual work-up the residue is solved in toluene (1000 ml) and boiled with p-toluene sulfonic (PTSA) acid in a Dean Starck trapp for 3 hrs. The solvent is remove under vacuo and the residue is distilled to yield 4-n- pentyl-l-(2,3-fluorophenyl)-cyclohex-l-en as a colourless liquid (bp 123 ° at 0.5 mm Hg). Analogously are obtained 4-ethyl-l-(2,3-difluorphenyl)-cyclohex-1-ene 4-propyl-l-(2,3-difluorphenyl)-cyclohex-1-ene 4-butyl-l-(2,3-difluorphenyl)-cyclohex-1-ene 4-hexyl-l-(2,3-difluorphenyl)-cyclohex-1-ene 4-heptyl-l-(2,3-difluorphenyl)-cyclohex-1-ene 4-octyl-l-(2,3-difluorphenyl)-cyclohex-1-ene 4-nonyl-l-(2,3-difluorphenyl)-cyclohex-l-ene 4-decyl-l-(2,3-difluorphenyl)-cyclohex-1-ene 4-dodecyl-l-(2,3-difluorphenyl)-cyclohex-l-ene 4-ethoxy-l-(2,3-difluorphenyl)-cyclohex-l-ene 4-propoxy-l-(2,3-difluorphenyl)-cyclohex-l-ene 4-butoxy-l-(2,3-difluorphenyl)-cyclohex-1-ene 4-pentoxy-l-(2,3-difluorphenyl)-cyclohex-l-ene 4-hexoxy-l-(2,3-difluorphenyl)-cyclohex-1-ene 4-heptoxy-l-(2,3-difluorphenyl)-cyclohex-l-ene 4-octoxy-l-(2,3-difluorphenyl)-cyclohex-l-ene 4-nonoxy-l-(2,3-difluorphenyl)-cyclohex-l-ene 4-decoxy-l-(2,3-difluorphenyl)-cyclohex-l-ene 4-undecoxy-l-(2,3-difluorphenyl)-cyclohex-l-ene 10B 4-Alkyl-2' ,3 ■ -difluorbiphenyles To a mixture of 0.1 mol 4-pentyl-l-(2,3-difluor¬ phenyl)-cyclohex-l-en and 500 ml toluene is added 0.22 mol 2,3-dichlor-5,6-dicyano-p-benzoquinone (DDQ) and refluxed for 2 h. After usual work-up 2' ,3'- difluorbiphenyl, bp: 125 °C at 0.5 mm Hg is obtained. Analogously are obtained: 4-ethyl-2' ,3'-difluorbiphenyl 4-propyl-2' ,3'-difluorbiphenyl 4-butyl-2' ,3'-difluorbiphenyl 4-hexyl-2' ,3'-difluorbiphenyl 4-heptyl-2' ,3'-difluorbiphenyl 4-octyl-2' ,3'-difluorbiphenyl 4-nonyl-2' ,3'-difluorbiphenyl 4-decyl-2' ,3'-difluorbiphenyl 4-ethoxy-2' ,3'-difluorbiphenyl 4-propoxy-2' ,3'-difluorbiphenyl 4-butoxy-2 r ,3'-difluorbiphenyl 4-pentoxy-2' ,3 l -difluorbiphenyl 4-hexoxy-2* ,3'-difluorbiphenyl 4-heptoxy-2' ,3'-difluorbiphenyl 4-octoxy-2' ,3 l -difluorbiphenyl 4-nonoxy-2' ,3'-difluorbiphenyl 4-decoxy-2' ,3'-difluorbiphenyl 4-dodecoxy-2 f ,3'-difluorbiphenyl The 4,4'-dialkyl-(or alkoxy)-2,3-difluorobiphenyls are obtained analogously by using alkyl-(or alkoxy)- 2,3-difluorobenzene as starting material: 4-octyloxy-4*-pentyl-2,3-difluorobiphenyl K 14 (N 13.5) I 4-octyloxy-4'-heptyl-2,3-difluorobiphenyl K 24 (S c 6 S A 13 N 23) I 4-nonyloxy-4'-decyl-2,3-difluorobiphenyl K 47 I 4-ethoxy-4'-pentyl-2,3-difluorobiphenyl K -10 I 4-pentyloxy-4*-octyloxy-2,3-difluorobiphenyl K 8.0 S, 12.0 N 18.0 I 4-heptyloxy-4'-pentyl-2,3-difluorobiphenyl K 0.5 I 4-nonyloxy-4'-octyloxy-2,3-difluorobiphenyl K 25.0 (S c 11.5) S A 33.0 N 34.0 I IOC 4,4"-Dialkyl-2 • -3*-difluoro-p-terphenyle 0.1 mol 4-pentyl-2' ,3'-difluorobiphenyl are depro- taned with n-butyllithium in THF/TMEDA according to example 10A and reacted with 0.1 mol 4-propylcyclo- hexanon. After oxidation with 0.2 mol of DDQ accord¬ ing to example 10B 4-pentyl-4"-propyl-2' ,3'-difluoro- p-terphenyl are obtained. Analogously are obtained 4-ethyl-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-propyl-4"-propyl-2' ,3'-difluoro-p-rterphenyl K 94 N 133 I 4-butyl-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-pentyl-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-hexyl-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-heptyl-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-octyl-4"-propyl-2' ,3•-difluoro-p-terphenyl 4-nonyl-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-decyl-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-dodecyl-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-ethoxy-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-propoxy-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-butoxy-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-pentoxy-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-hexoxy-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-heptoxy-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-octoxy-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-nonoxy-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-decoxy-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-dodecoxy-4"-propyl-2' ,3'-difluoro-p-terphenyl 4-ethyl-4"-pentyl-2' ,3'-difluoro-p-terphenyl 4-propyl-4"-pentyl-2' ,3 • -difluoro-p-terphenyl 4-butyl-4"-pentyl-2' ,3'-difluoro-p-terphenyl 4-pentyl-4"-pentyl-2' ,3'-difluoro-p-terphenyl K 60,0° N 120,0° I 4-hexyl-4"-pentyl-2' ,3'-difluoro-p-terphenyl 4-heptyl-4"-pentyl-2' ,3'-difluoro-p-terphenyl K 36.5 (S c 24.0) N 110.5 I 4-octyl-4"-pentyl-2' ,3'-difluoro-p-terphenyl 4-nonyl-4"-pentyl-2' ,3'-difluoro-p-terphenyl 4-decyl-4"-pentyl-2' ,3'-difluoro-p-terphenyl 4-dodecyl-4"-pentyl-2' ,3'-difluoro-p-terphenyl 4-ethoxy-4"-pentyl-2' ,3'-difluoro-p-terphenyl 4-propoxy-4"-pentyl-2' ,3'-difluoro-p-terphenyl 4-butoxy-4"-pentyl-2' ,3'-difluoro-p-terphenyl 4-pentoxy-4"-pentyl-2 • ,3 r -difluoro-p-terphenyl 4-hexoxy-4"-pentyl-2' ,3'-difluoro-p-terphenyl K 53,0° S„ 65,5° N 149,0 °I 4-heptoxy-4"-pentyl-2' ,3'-difluoro-p-terphenyl 4-octoxy-4"-pentyl-2 » ,3'-difluoro-p-terphenyl K 48,5° S c 95,1° N 141,5° I 4-nonoxy-4"-pentyl-2' ,3'-difluoro-p-terphenyl 4-decoxy-4"-pentyl-2' ,3'-difluoro-p-terphenyl 4-dodecoxy-4"-pentyl-2' ,3*-difluoro-p-terphenyl . 4-nonyl-4"-heptyl-2 r ,3'-difluoro-p-terphenyl K 49.0 S c 77.0 S A 93.0 N 108.5 I 4-ethyl-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-propyl-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-butyl-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-pentyl-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-hexyl-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-heptyl-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-octyl-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-nonyl-4"-octyl-2' ,3*-difluoro-p-terphenyl 4-decyl-4"-octyl-2' ,3*-difluoro-p-terphenyl 4-dodecyl-4"-octyl-2* ,3'-difluoro-p-terphenyl 4-ethoxy-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-propoxy-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-butoxy-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-pentoxy-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-hexoxy-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-heptoxy-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-octoxy-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-nonoxy-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-decoxy-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-dodecoxy-4"-octyl-2' ,3'-difluoro-p-terphenyl 4-nonoxy-4"-ethoxy-2' ,3'-difluoro-p-terphenyl 4-decoxy-4"-ethoxy-2' ,3'-difluoro-p-terphenyl 4-dodecoxy-4"-ethoxy-2' ,3'-difluoro-p-terphenyl 4-ethyl-4"-heptoxy-2• ,3'-difluoro-p-terphenyl 4-butyl-4"-heptoxy-2' ,3'-difluoro-p-terphenyl 4-hexyl-4"-heptoxy-2' ,3'-difluoro-p-terphenyl 4-heptyl-4"-heptoxy-2' ,3'-difluoro-p-terphenyl 4-nonyl-4"-heptoxy-2 • ,3'-difluoro-p-terphenyl 4-dodecyl-4"-he toxy-2 ,3'-difluoro-p-terphenyl 4-ethoxy-4"-heptoxy-2' 3'-difluoro-p-terphenyl 4-propoxy-4"-heptoxy-2 ,3'-difluoro-p-terphenyl 4-butoxy-4"-heptoxy-2' 3'-difluoro-p-terphenyl 4-pentoxy-4"-heptoxy-2 ,3'-difluoro-p-terphenyl 4-hexoxy-4"-heptoxy-2' 3'-difluoro-p-terphenyl 4-heptoxy-4"-heptoxy-2 ,3'-difluoro-p-terphenyl 4-octoxy-4"-heptoxy-2' 3'-difluoro-p-terphenyl 4-nonoxy-4"-heptoxy-2' 3'-difluoro-p-terphenyl 4-decoxy-4"-heptoxy-2' 3'-difluoro-p-terphenyl 4-dodecoxy-4"-heptoxy-2' ,3'-difluoro-p-terphenyl Example 11 4,4' ' *-Di-n-alkyl-2' ,3'-difluoro-p-quaterphenyles 4-Pentyl-2',3'-difluorbiphenyl (0.1 mol, prepared accord¬ ing to example 10B) is deprotonated according example 10A and reacted with 0.1 mol of 4-(p-propylphenyl)-cyclo- hexanone. After oxidation with 0.2 mol of DDQ according to example 10B 4-pentyl-4' ' '-propyl-2' ,3'-difluoro-p-qua- terphenyl is obtained. Analogously are obtained 4-ethyl-4' ' -propyl-2' ,3'-difluoro-p-quaterphenyl 4-propyl-4' 1 -propyl-2' ,3'-difluoro-p-quaterphenyl 4-butyl-4' » -propyl-2* ,3'-difluoro-p-quaterphenyl 4-hexyl-4' ' -propyl-2' ,3'-difluoro-p-quaterphenyl 4-heptyl-4' 1 -propyl-2' ,3'-difluoro-p-quaterphenyl 4-octyl-4' ' -propyl-2' ,3 l -difluoro-p-quaterphenyl 4-nonyl-4' ' -propyl-2' ,3'-difluoro-p-quaterphenyl 4-decyl-4* ' -propyl-2' ,3'-difluoro-p-quaterphenyl 4-dodecyl-4 1 -propyl-2' ,3'-difluoro-p-quaterphenyl 4-ethoxy-4' -propyl-2' ,3' " -difluoro-p-quaterphenyl 4-propoxy-4 '-propyl-2* ,3'-difluoro-p-quaterphenyl 4-butoxy-4* -propyl-2' ,3*-difluoro-p-quaterphenyl 4-pentoxy-4 1 -propyl-2* ,3'-difluoro-p-quaterphenyl 4-hexoxy-4* -propyl-2' ,3'-difluoro-p-quaterphenyl 4-heptoxy-4 1 -propyl-2 l ,3'-difluoro-p-quaterphenyl 4-octoxy-4' -propyl-2' ,3'-difluoro-p-quaterphenyl 4-nonoxy-4' -propyl-2' ,3*-difluoro-p-quaterphenyl 4-decoxy-4' -propyl-2' ,3'-difluoro-p-quaterphenyl 4-ethyl-4' ' -octyl-2' ,3'-difluoro-p-quaterphenyl 4-propyl-4' '-octyl-2' ,3'-difluoro-p-quaterphenyl 4-butyl-4' ' -octyl-2' ,3*-difluoro-p-quaterphenyl 4-pentyl-4' 1 -octyl-2* ,3'-difluoro-p-quaterphenyl 4-hexyl-4' ' -octyl-2' ,3'-difluoro-p-quaterphenyl 4-heptyl-4' 1 -octyl-2' ,3*-difluoro-p-quaterphenyl 4-octyl-4' ' -octyl-2' ,3'-difluoro-p-quaterphenyl 4-nonyl-4* ' -octyl-2' ,3'-difluoro-p-quaterphenyl 4-decyl-4' ' -octyl-2* ,3'-difluoro-p-quaterphenyl 4-dodecyl-4 ' '-octyl-2' ,3*-difluoro-p-quaterphenyl 4-ethoxy-4' '-octyl-2' ,3'-difluoro-p-quaterphenyl 4-propoxy-4 ' '-octyl-2' ,3'-difluoro-p-quaterphenyl 4-butoxy-4' f -octyl-2' ,3'-difluoro-p-quaterphenyl 4-pentoxy-4 ' '-octyl-2' ,3'-difluoro-p-quaterphenyl 4-hexoxy-4' '-octyl-2' ,3'-difluoro-p-quaterphenyl 4-heptoxy-4 ' '-octyl-2 ,3'-difluoro-p-quaterphenyl 4-octoxy-4 •-octyl-2' 3'-difluoro-p-quaterphenyl 4-nonoxy-4 '-octyl-2' 3'-difluoro-p-quaterphenyl 4-decoxy-4 '-octyl-2 • 3'-difluoro-p-quaterphenyl 4-ethyl-4' -ethoxy-2' 3'-difluoro-p-quaterphenyl 4-propyl-4 1 -ethoxy-2 ,3'-difluoro-p-quaterphenyl 4-butyl-4' -ethoxy-2* 33'-difluoro-p-quaterphenyl 4-pentyl-4 1 -ethoxy-2 ,3'-difluoro-p-quaterphenyl 4-hexyl-4' -ethoxy-2' 33'-difluoro-p-quaterphenyl 4-heptyl-4 '-ethoxy-2 ,3*-difluoro-p-quaterphenyl 4-octyl-4' -ethoxy-2' 3'-difluoro-p-quaterphenyl 4-nonyl-4' -ethoxy-2* 3'-difluoro-p-quaterphenyl 4-decyl-4' -ethoxy-2' 3'-difluoro-p-quaterphenyl 4-dodecyl-4 '-ethoxy-2 1 ,3'-difluoro-p-quaterphenyl 4-ethoxy-4 -ethoxy-2 ,3'-difluoro-p-quaterphenyl 4-propoxy-4 '-ethoxy-2 ,3'-difluoro-p-quaterphenyl 4-butoxy-4 -ethoxy-2* 3'-difluoro-p-quaterphenyl 4-pentoxy-4 '-ethoxy-2 ,3'-difluoro-p-quaterphenyl 4-hexoxy-4 -ethoxy-2' 3'-difluoro-p-quaterphenyl 4-heptoxy-4 1 -ethoxy-2 ,3'-difluoro-p-quaterphenyl 4-octoxy-4 -ethoxy-2' 3'-difluoro-p-quaterphenyl 4-nonoxy-4 -ethoxy-2' 3'-difluoro-p-quaterphenyl 4-decoxy-4 -ethoxy-2' 3'-difluoro-p-quaterphenyl 4-ethyl-4' -heptoxy-2' 3'-difluoro-p-quaterphenyl 4-propyl-4 '-heptoxy-2 ,3'-difluoro-p-quaterphenyl 4-butyl-4' -heptoxy-2' 3'-difluoro-p-quaterphenyl 4-pentyl-4 '-heptoxy-2 ,3'-difluoro-p-quaterphenyl 4-hexyl-4' -heptoxy-2' 3'-difluoro-p-quaterphenyl 4-heptyl-4 1 -heptoxy-2 ,3'-difluoro-p-quaterphenyl 4-octyl-4' -heptoxy-2' ,3'-difluoro-p-quaterphenyl 4-nonyl-4' ' -heptoxy-2' ,3'-difluoro-p-quaterphenyl 4-decyl-4' ' -heptoxy-2' ,3'-difluoro-p-quaterphenyl 4-dodecyl-4 1 -heptoxy-2' ,3'-difluoro-p-quaterphenyl 4-ethoxy-4' -heptoxy-2' ,3'-difluoro-p-quaterphenyl 4-propoxy-4 1 -heptoxy-2 1 ' ,3'-difluoro-p-quaterphenyl 4-butoxy-4' -heptoxy-2' ,3'-difluoro-p-quaterphenyl 4-pentoxy-4 '-heptoxy-2 1 ,3'-difluoro-p-quaterphenyl 4-hexoxy-4' -heptoxy-2' ,3'-difluoro-p-quaterphenyl 4-heptoxy-4 1 -heptoxy-2 1 , ' 3'-difluoro-p-quaterphenyl 4-octoxy-4* -heptoxy-2' ,3'-difluoro-p-quaterphenyl 4-nonoxy-4' -heptoxy-2 ! ,3'-difluoro-p-quaterphenyl 4-decoxy-4' -heptoxy-2' ,3'-difluoro-p-quaterphenyl Example 12 Preparation of 4,4"-dialkyl-2,3-difluoro-p-terphenyles 12A l-(2,3-difluorophenyl)-4-(p-alkylphenyl)-cyclohex- * 1-enes To a mixture of 1,2-difluorobenzene (0.1 mol) and 100 ml THF a mixture of n-butyllithium (0.105 ml) and 60 ml hexane is added at -70 °C. After stirring for 6 h a mixture of 4-(p-propylphenyl)-cyclohexanone (0.1 mol) and 50 ml THF is added. After stirring for 2 h, warming to room temperatures, boiling with PTSA as described for 10A and usual work-up l-(difluoro-phenyl)-4-(p-propyl- phenyl)-cyclohex-l-ene is obtained. Analogously are obtained 1-(2,3-difluorophenyl)-4-(p-ethylphenyl)-cyclohex- 1-ene 1-(2,3-difluorophenyl)-4-(p-butylphenyl)-cyclohex- 1-ene 1-(2,3-difluorophenyl -4- p-pentylphenyl)-cyclohex- 1-ene 1-(2,3-difluorophenyl -4- p-hexylphenyl)-cyclohex- 1-ene l-(2,3-difluorophenyl -4- p-heptylphenyl)-cyclohex- 1-ene 1-(2,3-difluorophen l -4- p-octylphenyl)-cyclohex- 1-ene 1-(2,3-difluorophenyl _4_ p-nonylphenyl)-cyclohex- 1-ene 1-(2,3-difluorophenyl _4- p-decylphenyl)-cyclohex- 1-ene 1-(2,3-difluorophenyl _4- p-dodecylpheny1)-cyclohex- 1-ene l-(2,3-difluorophenyl _4- p-ethoxyphenyl)-cyclohex- 1-ene 1-(2,3-difluorophenyl _4_ p-pentoxyphenyl)-cyclohex- 1-ene 1-(2,3-difluorophenyl _-4__ p-octoxyphenyl)-cyclohex- 1-ene 1-(2,3-difluorophenyl _4- p-dodecyloxyphenyl)-cyclo- hex-1-ene 1-(2,3-Difluorphenyl)-4-.(4-ethylbiphenyl-4'-yl)- cyclohex-1-ene 1-(2,3-Difluorphenyl)-4-(4-pentylbiphenyl-4'-yl)- cyclohex-1-ene 1-(2,3-Difluorphenyl)-4-(4-octylbiphenyl-4'-yl)- cyclohex-1-ene 1-(2,3-Difluorphenyl)-4-(4-dodecylbiphenyl-4'-yl) ■ cyclohex-1-ene 1-(2,3-Difluorphenyl)-4-(4-pentoxybiphenyl-4"-yl) • cyclohex-1-ene 12B 4"-Alkyl-2,3-difluoro-p-terphenyles 1-(2,3-difluorophenyl)-4-(p-propylphenyl)-cyclohex-1-ene (0.1 mol) are oxidized according to example 9B with DDQ (0.2 mol). After usual work-up 4"-propyl-2,3-difluo- 5. ro-p-terphenyl, K 121 I., is obtained. Analogously are obtained: 4"-ethyl-2,3-difluoro-p-terphenyl 4"-butyl-2 , 3-dif luoro-p-terphenyl 4"-pentyl-2,3-difluoro-p-terphenyl 0 4"-hexyl-2,3-difluoro-p-terphenyl 4"-heptyl-2,3-difluoro-p-terphenyl 4"-octyl-2,3-difluoro-p-terphenyl 4"-nonyl-2,3-difluoro-p-terphenyl 4"-decyl-2,3-difluoro-p-terphenyl 5 4"-dodecyl-2,3-difluoro-p-terphenyl 4"-ethoxy-2,3-difluoro-p-terphenyl 4"-pentoxy-2,3-difluoro-p-terphenyl 4"-octoxy-2,3-difluoro-p-terphenyl 4"-dodecyloxy-2,3-difluoro-p-terphenyl 0 4 '-ethyl-2,3-difluoro-p-quaterphenyl 4 '-pentyl-2,3-difluoro-p-quaterphenyl 4 '-octyl-2,3-difluoro-p-quaterphenyl 4 1 -dodecyl-2,3-difluoro-p-quaterphenyl 4 '-pentoxy-2,3-difluoro-p-quaterphenyl 12C 4, 4"-Dialkyl-2 , 3-difluoro-p-terphenyles A solution of n-butyllithium (0.1 mol) in 65 ml of hexane is added to a mixture of 4"-propyl-2,3-difluoro- p-terphenyl (0.1 mol), potassium t-butylate (0.1 mol) and 200 ml of THF at -100 °C. After stirring 5 minutes at -100 °C a mixture of brompentane (0.1 mol) and N,N- dimethyIpropylene urea (0.1 mol, DMPU) is added. After warming-up to -30 °C and usual work-up 4"-propyl-4- pentyl-2,3-difluoro-p-terphenyl is obtained. Analogously are obtained 4"-ethyl-4-pentyl-2,3-difluoro-p-terphenyl 4"-propyl-4-pentyl-2,3-difluoro-p-terphenyl 4"-butyl-4-pentyl-2,3-difluoro-p-terphenyl 4"-pentyl-4-pentyl-2,3-difluoro-p-terphenyl K 80.0 S c 115.5 S A 131.5 N 142.0 I 4"-hexyl-4-pentyl-2,3-difluoro-p-terphenyl 4"-heptyl-4-pentyl-2,3-difluoro-p-terphenyl K 65.5 S c 117.0 S A 135.0 N 136.0 I 4"-octyl-4-pentyl-2,3-difluoro-p-terphenyl 4"-nonyl-4-pentyl-2,3-difluoro-p-terphenyl 4"-decyl-4-pentyl-2,3-difluoro-p-terphenyl 4"-dodecyl-4-pentyl-2,3-difluoro-p-terphenyl 4"-ethoxy-4-pentyl-2,3-difluoro-p-terphenyl 4"-pentoxy-4-pentyl-2,3-difluoro-p-terphenyl 4"-hexoxy-4-pentyl-2,3-difluoro-p-terphenyl K 100.5 S c 156.5 S A 166.5 N 171.5 I 4"-octoxy-4-pentyl-2,3-difluoro-p-terphenyl K 87.5 S c 155.5 S A 165.0 N 165.7 I 4"-(4-methylhexyl)-4-pentyl-2,3-difluoro-p- terphenyl K 71.0 S c 120.0 N 128.0 I 4"-dodecyloxy-4-pentyl-2,3-difluoro-p-terphenyl 4"-ethyl-4-propyl-2,3-difluoro-p-terphenyl 4"-propyl-4-propyl-2,3-difluoro-p-terphenyl K 133 N 150 I 4"-butyl-4-propyl-2,3-difluoro-p-terphenyl 4"-pentyl-4-propyl-2,3-difluoro-p-terphenyl 4"-hexyl-4-propyl-2,3-difluoro-p-terphenyl 4"-heptyl-4-propyl-2,3-difluoro-p-terphenyl 4"-octyl-4-propyl-2,3-difluoro-p-terphenyl 4"-nonyl-4-propyl-2,3-difluoro-p-terphenyl 4"-decyl-4-propyl-2,3-difluoro-p-terphenyl 4"-dodecyl-4-propyl-2,3-difluoro-p-terphenyl 4"-ethoxy-4-propyl-2,3-difluoro-p-terphenyl 4"-pentoxy-4-propyl-2,3-difluoro-p-terphenyl 4"-octoxy-4-propyl-2,3-difluoro-p-terphenyl 4"-dodecyloxy-4-propyl-2,3-difluoro-p-terphenyl 4"-ethyl-4-octyl-2,3-difluoro-p-terphenyl 4"-propyl-4-octyl-2,3-difluoro-p-terphenyl 4"-butyl-4-octyl-2,3-difluoro-p-terphenyl 4"-pentyl-4-octyl-2,3-difluoro-p-terphenyl 4"-hexyl-4-octyl-2,3-difluoro-p-terphenyl 4"-heptyl-4-octyl-2,3-difluoro-p-terphenyl 4"-octyl-4-octyl-2,3-difluoro-p-terphenyl 4"-nonyl-4-octyl-2,3-difluoro-p-terphenyl 4"-decyl-4-octyl-2,3-difluoro-p-terphenyl 4"-dodecyl-4-octyl-2,3-difluoro-p-terphenyl 4"-ethoxy-4-octyl-2,3-difluoro-p-terphenyl 4"-pentoxy-4-octyl-2,3-difluoro-p-terphenyl 4"-octoxy-4-octyl-2,3-difluoro-p-terphenyl 4"-dodecyloxy-4-octyl-2,3-difluoro-p-terphenyl 4"-pentyl-4-heptyl-2,3-difluoro-p-terphenyl K 55.0 S c 105.5 S A 130.5 N 135.0 I 4"-propyl-4-nonyl-2,3-difluoro-p-terphenyl K 63.0 S c 84.5 S A 116.5 N 129.0 I 4 '-ethyl-4-dodecyl-2,3-difluoro-p-terphenyl 4 '-propyl-4-dodecyl-2,3-difluoro-p-terphenyl 4 1 -butyl-4-dodecyl-2,3-difluoro-p-terphenyl 4 •-pentyl-4-dodecyl-2,3-difluoro-p-terphenyl 4 '-hexyl-4-dodecyl-2,3-difluoro-p-terphenyl 4 '-heptyl-4-dodecyl-2,3-difluoro-p-terphenyl 4 '-octyl-4-dodecyl-2,3-difluoro-p-terphenyl 4 '-nonyl-4-dodecyl-2,3-difluoro-p-terphenyl 4 '-decyl-4-dodecyl-2,3-difluoro-p-terphenyl 4 '-dodecyl-4-dodecyl-2,3-difluoro-p-terphenyl 4 '-ethoxy-4-dodecyl-2,3-difluoro-p-terphenyl 4 '-pentoxy-4-dodecyl-2,3-difluoro-p-terphenyl 4 '-octoxy-4-dodecyl-2,3-difluoro-p-terphenyl 4 -dodecyloxy-4-dodecyl-2,3-difluoro-p-terphenyl 4 -ethyl-4-propyl-2,3-difluoro-p-terphenyl 4 -pentyl-4-propyl-2,3-difluoro-p-terphenyl 4 -octyl-4-propyl-2,3-difluoro-p-terphenyl 4 -dodecyl-4-propyl-2,3-difluoro-p-terphenyl 4 -pentoxy-4-propyl-2,3-difluoro-p-terphenyl 4 -ethyl-4-pentyl-2,3-difluoro-p-terphenyl 4 -pentyl-4-pentyl-2,-3-difluoro-p-terphenyl 4 -octyl-4-pentyl-2,3-difluoro-p-terphenyl 4 -dodecyl-4-pentyl-2,3-difluoro-p-terphenyl 4 -pentoxy-4-pentyl-2,3-difluoro-p-terphenyl 4 -ethyl-4-octyl-2,3-difluoro-p-terphenyl 4 -pentyl-4-octyl-2,3-difluoro-p-terphenyl 4 -octyl-4-octyl-2,3-difluoro-p-terphenyl 4 -dodecyl-4-octyl-2,3-difluoro-p-terphenyl 4 -pentoxy-4-octyl-2,3-difluoro-p-terphenyl 4' '-ethyl-4-dodecyl-2,3-difluoro-p-terphenyl 4 ! '-pentyl-4-dodecyl-2,3-difluoro-p-terphenyl 4' '-octyl-4-dodecyl-2,3-difluoro-p-terphenyl 4' '-dodecyl-4-dodecyl-2,3-difluoro-p-terphenyl 4' 1 -pentoxy-4-dodecyl-2,3-difluoro-p-terphenyl Example 13 Preparation of 4-alkoxy-4"-alkyl-2,3-difluoro-p- terphenyles l,2-Difluoro-3-ethoxybenzene (0.2 mol) is deprotonated with n-butyllithium in THF/TMEDA according example 10A and reacted with 4-(p-propylphenyl)-cyclohexanone (0.2 mol) according example IOC. After elimination with PTSA according example 10A and oxidation with DDQ 4-ethoxy-4"-propyl-2,3-di luorό-p-terphenyl is obtained. Analogously are obtained 4-propoxy-4"-propyl-2,3-difluoro-p-terphenyl 4-butoxy-4"-propyl-2,3-difluoro-p-terphenyl 4-pentoxy-4"-propyl-2,3-difluoro-p-terphenyl 4-hexoxy-4"-propyl-2,3-difluoro-p-terphenyl 4-heptoxy-4"-propyl-2,3-difluoro-p-terphenyl 4-octoxy-4"-propyl-2,3-difluoro-p-terphenyl 4-nonoxy-4 ιr -propyl-2,3-difluoro-p-terphenyl 4-decyloxy-4"-propyl-2,3-difluoro-p-terphenyl 4-dodecyloxy-4"-propyl-2,3-difluoro-p-terphenyl 4-ethoxy-4"-pentyl-2,3-difluoro-p-terphenyl 4-propoxy-4"-pentyl-2,3-difluoro-p-terphenyl 4-butoxy-4"-pentyl-2,3-difluoro-p-terphenyl 4-pentoxy-4"-pentyl-2,3-difluoro-p-terphenyl 4-hexoxy-4"-pentyl-2,3-difluoro-p-terphenyl K 97,5° S_ 145,5° N 166,0° I 4-heptoxy-4"-pentyl-2,3-difluoro-p-terphenyl 4-octoxy-4"-pentyl-2,3-difluoro-p-terphenyl K 93,5° S„ 144,0° S. 148,0° N 159,0° I 4-nonoxy-4"-pentyl-2,3-difluoro-p-terphenyl 4-decyloxy-4"-pentyl-2,3-difluoro-p-terphenyl 4-dodecyloxy-4"-pentyl-2,3-difluoro-p-terphenyl 4-ethoxy-4"-octyl-2,3-difluoro-p-terphenyl 4-propoxy-4"-octyl-2,3-difluoro-p-terphenyl 4-butoxy-4"-octyl-2,3-difluoro-p-terphenyl 4-pentoxy-4"-octyl-2,3-difluoro-p-terphenyl 4-hexoxy-4"-octyl-2,3-difluoro-p-terphenyl 4-heptoxy-4"-octyl-2,3-difluoro-p-terphenyl 4-octoxy-4"-octyl-2,3-difluoro-p-terphenyl 4-nonoxy-4"-octyl-2,3-difluoro-p-terphenyl 4-decyloxy-4"-octyl-2,3-difluoro-p-terphenyl 4-dodecyloxy-4"-octyl-2,3-difluoro-p-terphenyl 4-ethoxy-4"-dodecyl-2,3-difluoro-p-terphenyl 4-propoxy-4"-dodecyl-2,3-difluoro-p-terphenyl 4-butoxy-4"-dodecyl-2,3-difluoro-p-terphenyl 4-pentoxy-4"-dodecyl-2,3-difluoro-p-terphenyl 4-hexoxy-4"-dodecyl-2,3-difluoro-p-terphenyl 4-heptoxy-4"-dodecyl-2,3-difluoro-p-terphenyl 4-octoxy-4"-dodecyl-2,3-difluoro-p-terphenyl 4-nonoxy-4"-dodecyl-2,3-difluoro-p-terphenyl 4-decyloxy-4"-dodecyl-2,3-difluoro-p-terphenyl 4-dodecyloxy-4"-dodecyl-2,3-difluoro-p-terphenyl 4-octoxy-4"-(4-methylhexyl)-2,3-difluoro-p-terphenyl K 71.0 S c 120.0 N 128.0 I 4-ethoxy-4"-ethoxy-2,3-difluoro-p-terphenyl 4-propoxy-4"-ethoxy-2,3-difluoro-p-terphenyl 4-butoxy-4"-ethoxy-2,3-difluoro-p-terphenyl 4-pentoxy-4"-ethoxy-2,3-difluoro-p-terphenyl 4-hexoxy-4"-ethoxy-2,3-difluoro-p-terphenyl 4-heptoxy-4"-.ethoxy-2,3-difluoro-p-terphenyl 4-octoxy~4 ιr -ethoxy-2,3-difluoro-p-terphenyl 4-r_r>nOxy<-4 ι '-et_hoxy-2,3-difluoro-p-terphenyl 4-deeyloxy-4"-ethoxy-2,3-difluoro-p-terphenyl 4-dodecyloxy-4"-ethoxy-2,3-difluoro-p-terphenyl 4-ethoxy-4"-pentoxy-2,3-difluoro-p-terphenyl 4-propoxy-4"-pentoxy-2,3-difluoro-p-terphenyl 4-butoxy-4"-pentoxy-2,3-difluoro-p-terphenyl 4-pentoxy-4"-pentoxy-2,3-difluoro-p-terphenyl 4-hexoxy-4"-pentoxy-2,3-difluoro-p-terphenyl 4-heptoxy-4"-pentoxy-2,3-difluoro-p-terphenyl 4-octoxy-4"-pentoxy-2,3-difluoro-p-terphenyl 4-nonoxy-4"-pentoxy-2,3-difluoro-p-terphenyl 4-decyloxy-4"-pentoxy-2,3-difluoro-p-terphenyl 4-dodecyloxy-4"-pentoxy-2,3-difluoro-p-terphenyl 4-ethoxy-4"-dodecyloxy-2,3-difluoro-p-terphenyl 4-proραxy-4"-dodecyloxy-2,3-difluoro-p-terphenyl 4-fe_trtoxy-4"-dodecyloxy-2,3-difluoro-p-terphenyl 4 i pentQxy-4 ll -dodecyloxy-2,3-difluoro-p-terphenyl 4--hexoxy-4"-dodecyloxy-2,3-difluoro-p-terphenyl 4-heptoxy-4"-dodecyloxy-2,3-difluoro-p-terphenyl 4-octoxy-4"-dodecyloxy-2,3-difluoro-p-terphenyl 4-nonoxy-4"-dodecyloxy-2,3-difluoro-p-terphenyl 4-decyloxy-4"-dodecyloxy-2,3-difluoro-p-terphenyl 4-dodecyloxy-4"-dodecyloxy-2,3-difluoro-p-terphenyl 4-octoxy-4"-pentyl-2,3,2"-trifluoro-p-terphenyl K 58.0 S c 61.5 N 119.5 I 4-ethoxy-4' ' '-propyl-2,3-difluoro-p-quaterphenyl 4-propoxy-4' ' '-propyl-2,3-difluoro-p-quaterphenyl 4-butoxy-4' ' '-propyl-2,3-difluoro-p-quaterphenyl 4-pentoxy-4' ' '-propyl-2,3-difluoro-p-quaterphenyl 4-hexoxy-4' ' 1 -propyl-2,3-difluoro-p-quaterphenyl 4-heptoxy-4' ' '-propyl-2,3-difluoro-p-quaterphenyl 4-octoxy-4' ' '-propyl-2,3-difluoro-p-quaterphenyl 4-nonoxy-4' ' 1 -propyl-2,3-difluoro-p-quaterphenyl 4-decyloxy-4• ' '-propyl-2,3-difluoro-p-quaterphenyl 4-dodecyloxy-4' ' '-propyl-2,3-difluoro-p-quaterphenyl 4-ethoxy-4' '-pentyl-2,3-difluoro-p-quaterphenyl 4-propoxy-4 ' '-pentyl-2,3-difluoro-p-quaterphenyl 4-butoxy-4' 1 -pentyl-2,3-difluoro-p-quaterphenyl 4-pentoxy-4 ' '-pentyl-2,3-difluoro-p-quaterphenyl 4-hexoxy-4' '-pentyl-2,3-difluoro-p-quaterphenyl 4-heptoxy-4 ' '-pentyl-2,3-difluoro-p-quaterphenyl 4-octoxy-4' 1 -pentyl-2,3-difluoro-p-quaterphenyl 4-nonoxy-4* 1 -pentyl-2,3-difluoro-p-quaterphenyl 4-decyloxy-4 1 ' '-pentyl-2,3-difluoro-p-quaterphenyl 4-dodecyloxy-4' ' '-pentyl-2,3-difluoro-p-quaterphenyl 4-ethoxy-4' -octyl-2,3-difluoro-p-quaterphenyl 4-propoxy-4 1 -octyl-2,3-difluoro-p-quaterphenyl 4-butoxy-4' -octyl-2,3-difluoro-p-quaterphenyl 4-pentoxy-4 '-octyl-2,3-difluoro-p-quaterphenyl 4-hexoxy-4' -octyl-2,3-difluoro-p-quaterphenyl 4-heptoxy-4 '-octyl-2,3-difluoro-p-quaterphenyl 4-octoxy-4' -octyl-2,3-difluoro-p-quaterphenyl 4-nonoxy-4' -octyl-2,3-difluoro-p-quaterphenyl 4-decyloxy-4 1 '-octyl-2,3-difluoro-p-quaterphenyl 4-dodecyloxy 4' ' '-octyl-2,3-difluoro-p-quaterphenyl 4-ethoxy-4' -dodecyl-2,3-difluoro-p-quaterphenyl 4-propoxy-4 1 -dodecyl-2,3-difluoro-p-quaterphenyl 4-butoxy-4' -dodecyl-2,3-difluoro-p-quaterphenyl 4-pentoxy-4 1 -dodecyl-2,3-difluoro-p-quaterphenyl 4-hexoxy- ' -dodecyl-2,3-difluoro-p-quaterphenyl 4-heptoxy-4 1 -dodecyl-2,3-difluoro-p-quaterphenyl 4-octoxy-4' -dodecyl-2,3-difluoro-p-quaterphenyl 4-nonoxy-4' -dodecyl-2,3-difluoro-p-quaterphenyl 4-decyloxy-4' 1 '-dodecyl-2,3-difluoro-p-quaterphenyl 4-dodecyloxy-4 1 ' *-dodecyl-2,3-difluoro-p-quaterphenyl 4-ethoxy-4' -ethoxy-2,3-difluoro-p-quaterphenyl 4-propoxy-4 '-ethoxy-2,3-difluoro-p-quaterphenyl 4-butoxy-4' -ethoxy-2,3-difluoro-p-quaterphenyl 4-pentoxy-4 1 -ethoxy-2,3-difluoro-p-quaterphenyl 4-hexoxy-4' -ethoxy-2,3-difluoro-p-quaterphenyl 4-heptoxy-4 '-ethoxy-2,3-difluoro-p-quaterphenyl 4-octoxy-4' -ethoxy-2,3-difluoro-p-quaterphenyl 4-nonoxy-4' -ethoxy-2,3-difluoro-p-quaterphenyl 4-decyloxy-4 1 '-ethoxy-2,3-difluoro-p-quaterphenyl 4-dodecyloxy ■4 ! ' '-ethoxy-2,3-difluoro-p-quaterphenyl 4-ethoxy- ' -pentoxy-2,3-difluoro-p-quaterphenyl 4-propoxy-4 '-pentoxy-2,3-difluoro-p-quaterphenyl 4-butoxy-4' -pentoxy-2,3-difluoro-p-quaterphenyl 4-pentoxy-4 1 -pentoxy-2,3-difluoro-p-quaterphenyl 4-hexoxy-4' -pentoxy-2,3-difluoro-p-quaterphenyl 4-heptoxy-4 1 -pentoxy-2,3-difluoro-p-quaterphenyl 4-octoxy-4' -pentoxy-2,3-difluoro-p-quaterphenyl 4-nonoxy-4' -pentoxy-2,3-difluoro-p-quaterphenyl 4-decyloxy-4 * '-pentoxy-2,3-difluoro-p-quaterphenyl 4-dodecyloxy .41 1 '-pentoxy-2,3-difluoro-p-quaterphenyl 4-ethoxy-4' ι -dodecyloxy-2,3-difluoro-p-quaterphenyl 4-propoxy-4' '-dodecyloxy-2,3-difluoro-p-quaterphenyl 4-butoxy-4' ' -dodecyloxy-2,3-difluoro-p-quaterphenyl 4-pentoxy-4' '-dodecyloxy-2,3-difluoro-p-quaterphenyl 4-hexoxy-4' ' -dodecyloxy-2,3-difluoro-p-quaterphenyl 4-heptoxy-4* •-dodecyloxy-2,3-difluoro-p-quaterphenyl 4-octoxy-4' ' -dodecyloxy-2,3-difluoro-p-quaterphenyl 4-nonoxy-4' ' -dodecyloxy-2,3-difluoro-p-quaterphenyl 4-decyloxy-4 • « -dodecyloxy-2,3-difluoro-p-quaterphenyl 4-dodecyloxy-4' ' *-dodecyloxy-2,3-difluoro-p-quaterphenyl Example 14 Ferroelectric smectic C liquid crystal mixtures contain¬ ing difluoroterphenyls. Mixture 14A 4-n-octyloxy-2,3-difluoro-4"-n-pentyl-p-terphenyl 95 wt % (+)-(l-cyano-2-methylpropyl)-4'-octyloxybiphenyl- 4-ylcarboxylate 5 wt % The optically active compound in this mixture is of L configuration. The mixture showed the liquid crystal transitions (°C) K 85.9 S c 125.4 S A 143.2 N 150.6 I The S c phase supercooled to 76 °C. 4-n-hexyloxy-4"-pentyl-2'3'-difluoro-p-terphenyl 45 wt % 4-n-octyloxy-4"-pentyl-2* ,3'-difluoro-p-terphenyl 45 wt % (+)-(l-cyano-2-methylpropyl)-4'-octyloxybiphenyl- 4-ylcarboxylate 6.25 wt % (-)-(l-cyano-2-methylpropyl)-4'-octyloxybiphenyl- 4-ylcarboxylate 3.75 wt % The mixture showed the following liquid crystal transi¬ tions (°C): > 20 S c 84 .7 S A 98.6 N 128 I i.e. the mixture showed a room temperature S c phase. Using a liquid crystal electro-optic cell of well known construction, mixture 14B showed a switching time of about 100 μsec with a 20 V applied voltage, and a 2 μm spaced cell with polyimide alignment films. Example 15 A 1:1 by weight mixture of: 4-n-hexyloxy-4"-n-pentyl-2' ,3'-difluoro-p-terphenyl and 4-n-octyloxy-4"-n-pentyl-2' ,3'-difluoro-p-terphenyl showed an S c phase which supercooled to 28 °C, S c 79.1 N 142.4 I. The birefringence of the mixture was 0.19. Example 16 A mixture is formulated containing the following liquid crystalline components: 4-octyl-4' '-propyl-2'-fluoro-p-terphenyl 29.45 % 4-heptyl-4 r '-propyl-2'-fluoro-p-terphenyl 19.80 %- L-(-)4-hexoxy-4' '-(2-methylbutyl)-2'-fluoro- p-terphenyl 29.40 % S-(+)-2-octyl 4'-octoxybiphenyl-4-ylcarboxylate 6.45 % 4-octoxy-4' '-pentyl-2* ,3'-difluoro-p-terphenyl 5.00 % Example 17 A mixture is formulated containing the following liquid crystalline components: 4-octyl-4' '-propyl-2'-fluoro-p-terphenyl 41.55 % L-(-)-4-hexoxy-4' '-(2-methylbutyl)-2'-fluoro-p- terphenyl 41.75 % S-(+)-2-octyl 4'-octoxybiphenyl-4-ylcarboxylate 11.70 % 4-octoxy-4' '-pentyl-2,3-difluoro-p-terphenyl 5.00 % Example 18 A mixture is formulated containing the following liquid crystalline components: 4-octyl-4' '-pentyl-2'-fluoro-p-terphenyl " 72.00 % S-(+)-2-octyl 4'-octoxybiphenyl-4-ylcarboxylate 4.50 % 2-fluor-4-pentylphenyl 4-octoxybenzoate 13.50 % 4-octoxy-4' '-pentyl-2,3-difluoro-p-terphenyl 5.00 % 4-octoxy-4' '-pentyl-2' ,3'-difluoro-p-terphenyl 5.00 % Example 19 A mixture for ECB-application formulated containing the following liquid crystalline components: 4,4'-dipropyl-2,3-difluorobiphenyl 4,4*-dipentyl-2,3-difluorobiphenyl 4,4''-dipropyl-2,3-difluoro-p-terphenyl 4-(trans-4-propylcyclohexyl)-methoxybenzene 4-(trans-4-propylcyclohexyl)-ethoxybenzen 4,4'-bis-(trans-4-propylcyclohexyl)-2- fluorobiphenyl 4-ethyl-4'-methoxytolane 4-methoxy-4'-methyltolane exhibits clearing point 86 °C, Δε -1.5, Δn +0.185. Example 20 A mixture for ECB-application formulated containing the following liquid crystalline components: 4-propyloxy-4'-propyl-2,3-difluorobiphenyl 15 % 4-pentyloxy-4'-pentyl-2,3-difluorobiphenyl 15 % 4-pentyl-4' '-hexyloxy-2' ,3'-difluoro-p-ter- phenyl 15 % 4-pentyl-4' '-octyloxy-2' ,3'-difluoro-p-ter¬ phenyl 15 % 4-(trans-4-propylcyclohexyl)-methoxybenzene 15 % 4-(trans-4-propylcyclohexyl)-ethoxybenzene 15 % 4,4'-bis-(trans-4-propylcyclohexyl)-2- fluorobiphenyl 4 % 4,4'-bis-(trans-4-pentylcyclohexyl)-2- fluorobiphenyl 3 % 4-(trans-4-propylcyclohexyl)- '-(trans- pentylcyclohexyl)-2-fluorobiphenyl 3 % exhibits clearing point 82 °C, Δε -1.7, Δn +0.17. Example 21 A mixture formulated for ECB-application containing the following liquid crystalline components: 4-propyloxy-4*-propyl-2,3-difluorobiphenyl 15 % 4-pentyloxy-4'-pentyl-2,3-difluorobiphenyl 15 % 4-pentyl-4' '-hexyloxy-2,3'-difluoro-p-ter¬ phenyl 15 % 4-pentyl-4' '-octyloxy-2,3'-difluoro-p-ter¬ phenyl 15 % 4-(trans-4-propylcyclohexyl)-methoxybenzene 17 % 4-ethyl-4'-methoxytolane 4 % 4-ethoxy-4'-methyltolane 4 % 4-(trans-4-propylcyclohexyl)-4'-methoxytolane 5 % 4-(trans-4-propylcyclohexyl)-4-ethoxytolane 5 % 4-(trans-4-propylcyclohexyl)-4'-propoxytolane 5 % exhibits clearing point 91 °C, Δε -1.5, Δn +0.23. Example- 22 Ferroelectric mixtures are formulated containing di- fluoroterphenyls based on a eutectic host (Host I) which contains 4-hexyloxy-4"-pentyl-2' ,3'-difluor-p-terphenyl 37.25 wt% 4-hexyloxy-4"-pentyl-2,3-difluor-p-terphenyl 13.60 wt% 4-octyloxy-4"-pentyl-2' ,3'-difluor-p-terphenyl 40.8 wt% 4-octyloxy-4"-pentyl-2,3-difluor-p-terphenyl 8.35 wt% Mixture 22A Host I 4-octyloxy-4'-pentyl-2,3-difluorobiphenyl (+)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate (-)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate S c 60 S A 79.7 N 109.4 I and P g 6.6 nC/cm 2 (at 30 °C), S Q tilt angle 21.5°• The mixture exhibits a switching time of about 40 μsec using an electrooptic cell of Example 14. Mixture 22B Host I 90 wt% (+)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 6.75 wt% (-)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 3.75 wt% K < 20 S_ 90.4 S, 109.6 N 133 I, P ς 8.9 nC/cm 2 (at 30 °C), S c tilt ingle 23.5, switching time about 90 μsec. Mixture 22C Host I 90 wt% (+)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 5.63 wt% (-)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 4.37 wt% S c 93 S A 109.6 N 133 I, P g 4.24 nC/cπT2 (at 30 °C), S c tilt angle 23.5°, switching time about 260 μsec. Mixture 22D 4-octyloxy-4'-pentyl-2,3-difluorobiphenyl 20 wt% (+)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 5.63 wt% (-)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 4.37 wt% S c 60 S A 79.7 N 109.4 I, P g 2.7 nC/cm 2 (at 30 °C), S c twist angle 19.5, switching time about 75 μsec. Mixture 22E Host I 45 wt% 4,4"-dipentyl-2' ,3'-difluoro-p-terphenyl 45 wt% (+)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 6.25 wt% (-)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 3.75 wt% S c 60.5 S A 87.1 N 114.7 I, P g 5.6 nC/cm 2 , S Q twist angle 22°, switching time 54 μsec. Example 23 Ferroelectric mixtures are formulated containing di- fluoroterphenyls based on a host (Host II) which contains 4-heptyl-5"-pentyl-2,3-difluor-p-terphenyl 33.33 wt% 4' ,4"-dipentyl-2,3-difluor-p-terphenyl 33 " .33 wt% 4 « ,4"-dipentyl-2' ,3'-difluor-p-terphenyl 33.33 wt% Mixture 23 A Host II 90.00 wt% (+)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 6.25 wt% (-)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 3.75 wt% S c 60 S A 105 N 115 I, P g 7.2 nC/cm 2 (at 30 °C), S c twist angle 21.5°, switching time 17 μsec. Mixture 23B Host II 90.00 Wt% (+)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 10.00 wt% S c 59 S A 105.4 N 116 I P g 30 nC/cm 2 (at 30 °C), S c twist angle 21.5°, switching time 4 μsec. Mixture 23C Host II 97.5 wt% (+)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 2.5 wt% S c 86.7 S A 107.1 N 124.7, P g 7.0 nC/cm 2 (at 30 °C) S c twist ablge 23°, switching time about 70 μsec. Example 24 Ferroelectric mixtures are formulated containing differ¬ ent amounts of difluorterphenyls and chiral dopants. Mixture 24A 4-heptyl-4"-nonyl-2,3-difluor-p-terphenyl 97.5 (+)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 2.5 K 48 S c 62.6 S A 92.5 N 103.8 I, P g 2.9 (at 50 °C), switch¬ ing time 15 μsec. Mixture 24B 4-pentyl-4"-(4-methylhexyl)-2,3-difluoro-p- terphenyl 90 (+)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 6.2 (-)-(l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 3.8 K 56.1 S * r 80,3 SA 82.7 N 89.4 I, SC_ * twist angle 26* Mixture 24C 4-pentyl-4"-heptyl-2' ,3'-difluor-p-terphenyl 29.25 4-heptyl-4"-nonyl-2' ,3'-difluor-p-terphenyl 34.125 4-heptyl-4"-pentyl-2,3-difluor-p-terphenyl 19.50 4-pentyl-4"-heptyl-2,3-difluor-p-terphenyl 14.625 (+)-1—cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 2.50 wt% S c 68 S A 94.2 N 111 I, P g 5.9 nC/cπt (at 30 °C), S c twist angle 22.5°, switching time about 40 μsec. Mixture 24D 4,4"-dipentyl-2' ,3'-difluoro-p-terphenyl 45 % 4,4"-dipentyl-2,3-difluoro-p-terphenyl 22.5 4-heptyl-4"-pentyl-2,3-difluoro-p-terphenyl 22.5 wt% (+)-l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 6.2 wt% (-)-l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 3.8 wt% S c 43.6 S A 95.5 N 109.5 I, P g 5.1 nC/cm 2 (at 25 °C). Mixture 24E 4-heptyl-4"-pentyl-2' ,3 • -difluoro-p-terphenyl 48.5 wt% 4-heptyl-4"-pentyl-2,3-difluoro-p-terphenyl 24.25 wt% 4,4"-dipentyl-2,3-difluoro-p-terphenyl ,24.25 wt% (+)-l-cyano-2-methylpropyl)-4'-octyloxy- biphenyl-4-yl-carboxylate 3.0 wt% S c 75 S A 91 N 116 I, P s 7.9 nC/cm 2 (at 30 °C), S c twist angle 23°.

Claims: Claims Fluorinated oligophenyls of the formula I in which a is 1 and in which the terminal substituents R 1 , R 2 and R 3 are each independently an alkyl or alkenyl residue each with up to 15 C atoms, option¬ ally substituted by CN or by at least one halogen atom, and wherein one or more non- adjacent CH 2 groups of these residues may be replaced by -0-, -S-, -CO-, -0-CO-, -CO-O-, -O-CO-O- or -C≡C-, one of the residues R 1 and R2 may also denote a group of the formula, any one of the following pairs of lateral substituents are both fluorine: (A, B), (C, D), (D, E), (C, E), (B, C), (D, J), (D, K), (A, C), (C, J), (C « , D'), (D', E), D', A), (C, E), (C, A), (D', J'), (D', K'), (C, J'), (B, G), (A, G), all of the other lateral substituents being hydrogen or fluorine. Derivatives of Claim 1 in which the terminal substi- tuents R 1 and R2 or R3 and one of the residues of R 1 and R2 are independently alkoxy, alkyl, perfluoro- alkyl or perfluoroalkoxy each with up to 15 C atoms. 3. Derivatives of Claim 2 excluding the p-terphenyl in which (C, D) are both fluorine, R is ethdxy and 2 is n-pentyl or (B , C) are both fluorine, R 1 is 2 ethoxy and R is n-propyl 4. Derivatives of at least one of Claims 1 to 3, characterized in that only one pair of lateral substituents is fluorine and all of the other lateral substituents are occupied by hydrogen. 5. Derivatives of Claim 4 characterized in that they are difluoroterphenyls. 6. Derivatives of Claim 5 which are' selected from the following group of terphenyls I, 4 7. Derivatives of at least one of Claims 1, 2 or 3 characterized in that only one pair of lateral substituents is fluorine, and one other lateral substituent is fluorine. 8. Derivatives of Claim 7 characterized in that they are trifluoroterphenyls. 9. Derivatives of Claim 8 characterized by a formula: 10. Derivatives of at least one of Claims 1 to 9, charac¬ terized in that the terminal substituents are each independently n-alkyl or n-alkoxy with 5 to 12 carbon atoms. 11. Derivatives of at least one of Claims 1 to 10 characterized in that at least one terminal sub¬ stituent is a chiral alkyl or alkoxy group with 5 to 12 carbon atoms. 12. Derivatives of Claim 1, characterized by the formu¬ la I' wherein A 1 and A2 are each independently a 1,4-phenylene group optionally substituted by one to four fluorines, R 1 and R2 are each independently an alkyl or alkenyl residue each with up to 15 C atoms, option¬ ally substituted by CN or by at least one halogen atom, and wherein one or more non- adjacent CH 2 groups of these residues may be replaced by -0-, -S-, -CO-, -0-CO-, -CO-0-, -O-CO-O- or -C≡C-, m is 0 or 1, n is 1, 2 or 3, and the sum of m and h is 2 or 3. 13. Derivatives of p-terphenyl of Claim 12, charac¬ terized in that the sum of m and n is 2. 14. Derivatives of at least one of Claims 1 to 11 or of at least one of Claims 12 and 13, characterized in that the terminal substituents are each independent¬ ly normal alkyl or alkoxy with 1 to 7 carbon atoms. 15. Use of the compounds of at least one of Claims 1 to 14 as components of liquid crystalline phases. 16. Liquid crystalline composition with at least two liquid crystalline components, characterized in that at least one component is a compound of at least one of Claims 1 to 14. 17. Liquid crystalline composition according to Claim 16 which is a nematic composition. 18. Liquid crystalline composition according to Claim 16 which is a chiral tilted smectic composition. 19. Chiral tilted smectic composition with at least two liquid crystalline components characterized in that at least one component is a compound of the formula I in which a is 0 or 1 and R 1, R2, A, B, C, D, E, G, J and K have the meaning given in Claim 1. 20. Chiral tilted smectic composition according to Claim 19 characterized that in the compound of the formula I a denotes 0. 21. Chiral tilted smectic composition according to Claim 19 characterized in that the compound of the formula I is selected from the following group of biphenyls I, 18 I, 19 22. Chiral tilted smectic composition according to Claim 19 characterized in that in addition to at least one compound of the formula I, wherein a denotes 0, it contains at least one component of the formula I, wherein a denotes 1. 23. Liquid crystalline composition according to at least one of Claims 18 to 22 characterized in that in addition to at least one compound of formula I it contains at least one compound of formula: wherein R A is alkyl or alkoxy, R β is alkyl and (F) indicates that the ring may carry a lateral fluoro- substituent, n is 1 or 2, m is 0 or 1. 24. Liquid crystalline composition according to Claim 23 characterized in that R^ is C-,-C 4 n-alkyl, cyclo¬ hexyl or a branched or chiral alkyl of structure: where a is 0 or 1-6, and each of b and c are in¬ dependently 1-6. 25. Liquid crystalline display element, characterized in that it contains a liquid crystalline phase according to at least one of the Claims 16 to 24. 26. Electro-optical display element, characterized in that it contains a liquid crystalline phase accord¬ ing to at least one of the Claims 16 to 24.

Inventors: FINKENZELLER ULRICH, GEELHAAR THOMAS, GRAY GEORGE WILLIAM, HIRD MICHAEL, KRAUSE JOACHIM, LACEY DAVID, REIFFENRATH VOLKER, TOYNE KENNETH JOHNSON, WAECHTLER ANDREAS, FINKENZELLER, ULRICH, GEELHAAR, THOMAS, GRAY, GEORGE, WILLIAM, HIRD, MICHAEL, KRAUSE, JOACHIM, LACEY, DAVID, REIFFENRATH, VOLKER, TOYNE, KENNETH, JOHNSON, WAECHTLER, ANDREAS
Applicants: MERCK PATENT GMBH, MERCK PATENT GESELLSCHAFT MIT BESCHRAENKTER HAFTUNG
Application year: 1988
Main classification: C07C25
IPC codes: C09K19