DE19538404B4 - Difluoroquinoline derivatives and liquid crystal mixtures containing them, and switching and / or display device - Google Patents

Abstract

in der die Symbole folgende Bedeutung haben:
R¹, R² gleich oder verschieden, -H, -F, -Cl, -CN, -NCS, -CF₃, -OCF₃, -OCHF₂ oder geradkettiges oder verzweigtes (mit oder ohne asymmetrische C-Atom) Alkyl mit 1 bis 16 C-Atomen, wobei auch eine oder zwei nicht benachbarte -CH₂-Gruppen durch -O-, -S-, -CO-, -CO-O-, -O-CO-, -CO-S-, -S-CO-, -O-CO-O-, -CH=CH-, -C≡C-,

oder -Si(CH₃)₂- ersetzt sein können, und wobei auch ein oder mehrere H-Atome des Alkylrestes durch -F, -Cl, -Br oder -CN substituiert sein können, oder eine der nachfolgenden chiralen Gruppen bedeuten.

. . .Difluoroquinoline derivatives of the general formula (I)

in which the symbols have the following meaning:
R ¹ , R ^{2 are} identical or different, -H, -F, -Cl, -CN, -NCS, -CF ₃ , -OCF ₃ , -OCHF ₂ or straight-chain or branched (with or without asymmetric carbon atom) alkyl with 1 to 16 carbon atoms, where also one or two non-adjacent -CH ₂ groups by -O-, -S-, -CO-, -CO-O-, -O-CO-, -CO-S-, -S-CO-, -O-CO-O-, -CH = CH-, -C≡C-,

or -Si (CH ₃ ) ₂ - can be replaced, and where one or more H atoms of the alkyl radical can be substituted by -F, -Cl, -Br or -CN, or one of the following chiral groups.

, , ,

Description

The invention relates to difluoroquinoline derivatives and their use in liquid crystal mixtures.

The unusual combination of anisotropic and fluid behavior of the liquid crystals has for their use in electro-optical switching and display devices guided. You can their electrical, magnetic, elastic and / or thermal Orientation change properties be used. You can use optical effects, for example With the help of birefringence, the incorporation of dichroic absorbent dye molecules ("guest-host mode") or the light scatter

To meet the ever increasing There are practical requirements in the different areas of application there is a constant need for new improved liquid crystal mixtures and thus also on a large number of mesogenic compounds of different types Structure. This applies to both the areas where nematic LC phases are used as also for those with smectic LC phases

In recent years, ferroelectric liquid crystalline mixtures (FLC mixtures) have been of particular interest (see, for example, JJW Goodby, Ferroelectric Liquid Crystals, Gordon and Breach, Philadelphia 1991). For the practical use of ferroelectric liquid crystals in electro-optical displays, chiral, inclined-smectic phases, such as S _C * phases, are required [see e.g. BRB Meyer, L. Liebert, L. Strzelecki and P. Keller, J. Physique 36, L-69 (1975)], which are stable over a wide temperature range. This goal can be achieved with compounds that themselves have such phases, e.g. B. S _C * phases, or by doping non-chiral inclined smectic phases forming compounds with optically active compounds [see, for. BM Brunet, Cl. Williams, Ann. Phys. 3, 237 (1978)].

When using ferroelectric liquid crystal mixtures There is a uniform planar orientation in electro-optical components of liquid crystals necessary to achieve a high contrast ratio It has shown that achieve a uniform planar orientation in the Sc * phase leaves if the phase sequence of the liquid crystal mixture with decreasing temperature reads: Isotropic → nematic → smectic A → smectic C (see, e.g., K. Flatischler et al., Mol. Cryst. Liq.-Cryst. 131, 21 (1985); T. Matsumoto et al., P. 468-470, Proc. of the 6th Int. Display Research Conf., Japan Display, September 30-2. october 1986, Tokyo, Japan; M. Murakami et al., Ibid, p. 344-347).

For ferroelectric (chiral smectic) liquid-crystal mixtures in addition, the condition must be satisfied that the pitch (pitch) * phase is large, ie, greater than 5 microns of the helix in the S _C, and * phase is very large in the N, ie, greater than 10 μm, or is infinite

The optical switching time τ [μs] of ferroelectric liquid crystal systems, which should be as short as possible, depends on the rotational viscosity of the system γ [mPa], the spontaneous polarization P _s [nC / cm ² ] and the electric field strength E [V / m] according to relationship

Since the field strength E is due to the distance between the electrodes in the electro-optical component and determined by the applied voltage is, it must ferroelectric display medium be low viscosity and high Show spontaneous polarization so that a short switching time is reached will eventually in addition to thermal, chemical and photochemical stability, a small optical anisotropy Δn, preferably ≈ 0.13, and a low positive or preferably negative dielectric Anisotropy Δε caught (See, e.g., S. T. Lagerwall et al. "Ferroelectric Liquid Crystals for Displays "SID Symposium, Oct. Meeting 1985, San Diego, Ca, USA).

All of these requirements can generally only be met with mixtures of several components. The basis (or matrix) used here are preferably compounds which themselves already have the desired phase sequence I → N → S _A → S _C. Other components of the mixture are often added to lower the melting point and broaden the S _C - and usually also the N phase, to induce optical activity, to compensate for pitch and to adapt the optical and dielectric anisotropy, but, for example, do not increase the rotational viscosity if possible shall be.

Individual of these components and also certain mixtures are already known from the prior art. However, since the development, especially of ferroelectric liquid crystal mixtures, are still in no way considered complete the manufacturers of displays are interested in different mixtures. This is u. a. also because the interaction of the liquid crystalline mixtures with the individual components of the display devices or the cells (e.g. the orientation layer) conclusions on the quality of the liquid crystalline Allows mixtures.

Furthermore, it is known that mono- and difluorophenyl compounds can be used as components of liquid-crystal mixtures (see, for example, JP-A 2169-537; V. Reiffenrath, The Twelfth International Liquid Crystal Conference, Freiburg, August 15-19, 1988) , However, some of these compounds have no S _C phase. Furthermore, miscibility problems often occur due to fluorophobic interactions structurally different mixture components, e.g. B. phenylpyrimidines.

Pyridine derivatives also show liquid-crystalline behavior with the formation of an S _C phase (T. Geelhaar, 1st International Symposium on Ferroelectric Liquid Crystals, Arcachon, September 2-23, 1987; US 4,952,335 ).

However, an S _I phase that frequently occurs in these compounds impairs their use in ferroelectric liquid crystal mixtures.

Object of the present extension are difluoroquinoline derivatives of the formula (I) and their use as components for ferroelectric liquid crystal mixtures, where at least one difluoroquinoline of the general formula (I) as a component in a liquid crystal mixture is used.

oder -Si(CH₃)₂- ersetzt sein können, und wobei auch ein oder mehrere H-Atome des Alkylrestes durch -F, -Cl, -Br oder -CN substituiert sein können, oder eine der nachfolgenden chiralen Gruppen:

The symbols have the following meanings: R ¹ , R ² identical or different, -H, -F, -Cl, -CN, -NCS, -CF ₃ , -OCF ₃ , -OCHF ₂ or straight-chain or branched (with or without asymmetric carbon atom) alkyl with 1 to 16 carbon atoms, where also one or two non-adjacent -CH ₂ groups by -O-, -S-, -CO-, -CO-O-, -O-CO- , -CO-S-, -S-CO-, -O-CO-O-, -CH = CH-, -C≡C-,

or -Si (CH ₃ ) ₂ - can be replaced, and wherein one or more H atoms of the alkyl radical can be substituted by -F, -Cl, -Br or -CN, or one of the following chiral groups:

• A ¹ , A ² , A ³ , A ^{4 the} same or different, 1,4-phenylene, pyrazine-2,5-diyl, pyradizine-3,6-diyl, pyridine-2,5-diyl, pyrimidine-2,5 -diyl, where one or two H atoms can each be replaced by -F, trans-1,4-cyclohexylene, in which one or two H atoms can be replaced by -CN, (1,3,4) thiadiazole -25-diyl, 1,3-dioxane-2,5-diyl, naphthalene-2,6-diyl, bicyclo [2.2.2] otane-1,4-diyl or 1,3-dioxaborinane-2,5-diyl ;
• M ¹ , M ² , M ³ , M ^{4 the} same or different, -O-, -S-, -CO-, -CO-O-, -O-CO-, -CO-S-, -S-CO- , -O-CO-O-, -CH ₂ O-, -CH ₂ -CH ₂ -, CH = CH- or -C≡C-;
• R ³ , R ⁴ , R ⁶ , R ^7, identically or differently, H or straight-chain or branched alkyl having 1 to 16 carbon atoms or R ³ and R ⁴ together also - (CH ₂ ) ₄ - or - (CH ₂ ) ₃ - when bound to a dioxolane system as a substituent;
• M ⁵ -CH ₂ -O-, -CO-O-, -O-CH ₂ -, -O-CO- or a single bond;
• k, l, m, n, o, p, g, r, 0 or 1, provided that the sum k + m + p + r is less than 4 and greater than 0.

oder -Si(CH₃)₂ ersetzt sein kann, oder eine der nachfolgenden chiralen Gruppen:

In a preferred embodiment of the invention, the symbols in the formula (I) have the following meaning:
R ¹ , R ^{2 are the} same or different, -H, -F, -CN or straight-chain or branched (with or without asymmetrical carbon atom) alkyl having 1 to 16 carbon atoms, where also a -CH ₂ group by -O -, S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, -CH = CH-, -C≡C-,

or -Si (CH ₃ ) ₂ can be replaced, or one of the following chiral groups:

• A ¹ , A ² , A ³ , A ^{4 the} same or different, 1,4-phenylene, pyrazine-2,5-diyl, pyridazine-3,6-diyl, pyridine-2,5-diyl, pyrimidine-2,5 -diyl, where one or two H atoms can be replaced by F, trans-1,4-cyclohexylene, (1,3,4) thiadiazole-2,5-diyl, 1,3-dioxane-2,5-diyl , Naphthalene-2,6-diyl, biocyclo- [2.2.2] octane-1,4-diyl or 1,3-dioxaborinane-2,5-diyl,
• M ¹ , M ² , M ³ , M ⁴ identical or different -O-, -CO-, -CO-O-, -O-CO-, -CH ₂ -O-, -O-CH ₂ -, -CH ₂ -CH ₂ -, -CH = CH or -C≡C-;
• R ³ , R ⁴ , R ⁶ , R ^7, identical or different, H or straight-chain or branched alkyl having 1 to 10 C atoms or R ³ and R ⁴ together also - (CH ₂ ) ₄ - or - (CH ₂ ) ₅ - when bound to a dioxolane system as a substituent;
• M ⁵ -CH ₂ -O-, -CO-O-, -O-CH ₂ -, O-CO- or a single bond.

worin R¹, R², A¹, A², M¹, M², k, l, m und n die angegebene Bedeutung besitzen.Difluoroquinoline derivatives of the formula (Ia) are particularly preferred

wherein R ¹ , R ² , A ¹ , A ² , M ¹ , M ² , k, l, m and n have the meaning given.

Difluoroquinoline derivatives of the formula (I) in which the symbols have the following meanings are also preferred:
R ¹ , R ^{2 are the} same or different, -H, -F, -CN or straight-chain or branched (with or without asymmetrical carbon atom) alkyl having 1 to 16 carbon atoms, where also a -CH ₂ group by -O -, -CO-, -CO-O-, -O-CO-, -CH = CH- or -Si (CH ₃ ) ₂ - can be replaced, or one of the following chiral groups:

• A ¹ , A ² , A ³ , A ^{4 the} same or different, 1,4-phenylene, pyrazine-2,5-diyl, pyridazine-3,6-diyl, pyridine-2,5-diyl, pyrimidine-2,5 -diyl, in which one or two H atoms can be replaced by F, trans-1,4-cyclohexylene, 1,3-dioxane-2,5-diyl, naphthalene-2,6-diyl or 1,3-dioxaborinane -2,5-diyl;
• M ¹ , M ² , M ³ , M ^{4 the} same or different -O-, -CO-O-, -O-CO-, -O-CH ₂ -, -CH ₂ -O-, -CH ₂ -CH ₂ - or -CH = CH-;
• R ³ , R ⁴ , R ⁶ , R ^7, identical or different, H or straight-chain or branched alkyl having 1 to 10 C atoms or R ³ and R ⁴ together also - (CH ₂ ) ₄ - or - (CH ₂ ) ₅ - when bound to a dioxolane system as a substituent;
• M ⁵ -CH ₂ -O-, -CO-O-, -O-CH ₂ -, -O-CO- or a single bond.

A¹, A², A³, A⁴ gleich oder verschieden, 1,4-Phenylen, Pyrazin-2,5-diyl, Pyridazin-3,6-diyl, Pyridin-2,5-diyl, Pyrimidin-2,5-diyl, bei dem ein oder zwei H-Atome jeweils durch F ersetzt sein können, trans-1,4-Cyclohexylen, 1,3-Dioxan-2,5-diyl, Naphthalin-2,6-diyl oder 1,3-Dioxaborinan-2,5-diyl;
M¹, M², M³, M⁴ sind gleich oder verschieden, -O-, -CO-O-, -O-CO-, -OCH₂-, -CH₂-O- oder -CH₂CH₂-; R³, R⁴, R⁶ gleich oder verschieden H oder ein geradkettiges Alkyl mit 1 bis 10 C-Atomen;
M⁵ -CH₂-O- oder -CO-O- ist. Die erfindungsgemäßen Verbindungen sind chemisch und photochemisch stabil. Sie verfügen über niedrige Schmelzpunkte und im allgemeinen breite flüssigkristalline Phasen, insbesondere breite nematische, smektische A und smektische C-Phasen.Particularly preferred is a difluoroquinoline of the formula (I) in which R ¹ R ^{2 is the} same or different H or alkyl having 1 to 16 carbon atoms, a -CH ₂ group also being represented by -O-, -CO-O- or -O-C can be replaced, or the chiral group

A ¹ , A ² , A ³ , A ^{4 the} same or different, 1,4-phenylene, pyrazine-2,5-diyl, pyridazine-3,6-diyl, pyridine-2,5-diyl, pyrimidine-2,5 -diyl, in which one or two H atoms can each be replaced by F, trans-1,4-cyclohexylene, 1,3-dioxane-2,5-diyl, naphthalene-2,6-diyl or 1,3- dioxaborinane-2,5-diyl;
M ¹ , M ² , M ³ , M ⁴ are the same or different, -O-, -CO-O-, -O-CO-, -OCH ₂ -, -CH ₂ -O- or -CH ₂ CH ₂ - ; R ³ , R ⁴ , R ^{6 are} identical or different H or a straight-chain alkyl having 1 to 10 C atoms;
M ^{5 is} -CH ₂ -O- or -CO-O-. The compounds according to the invention are chemically and photochemically stable. They have low melting points and generally broad liquid-crystalline phases, in particular broad nematic, smectic A and smectic C phases.

The compounds according to the invention are also distinguished by an increased Miscibility, low viscosity and Δε values lie close to zero.

From liquid crystalline compounds With this structural element, both ferroelectric mixtures can be made as well as producing nematic or chiral nematic mixtures, the for the application in electro-optical or completely optical elements, e.g. B. display elements, switching elements, light modulator elements for image processing, signal processing or in general in the field the nonlinear optics are suitable.

The liquid crystal mixtures according to the invention generally consist of 2 to 20, preferably 2 to 15 components, including at least one compound of the formula (I). The other constituents are preferably selected from the known compounds with nematic, cholesteric and / or inclined smectic phases, these include, for example, Schiff bases, biphenyls, pyridines, thiadiazoles, difluorophenyls, terphenyls, phenylcyclohexanes, cyclohexylbiphenyls, pyrimidines, cinnamic acid esters, choles terine esters and polynuclear esters of p-alkylbenzoic acids. In general, the commercially available liquid crystal mixtures are present as mixtures of various components, at least one of which is mesogenic, before the addition of the compound (s) according to the invention.

Of the difluoroquinoline derivatives according to the invention contain the liquid crystal mixtures generally 0.1 to 70 mol%, preferably 0.5 to 50 mol%, in particular 1 to 25 mol%.

The values for the spontaneous polarization P _s [nC / cm ² ), the contrast K and the optical switching time τ [μs] were determined for the ready-to-use ferroelectric liquid crystal mixtures, all measurements being carried out at a temperature of 25 ° C.

The P _s values are determined according to the method of H. Diamant et al. (Rev. Sci. Instr., 28, 30, 1957) measured using measuring cells with 2 μm electrode spacing and rubbed polyimide as an orientation layer. To determine T and K, the measuring cell is attached to a rotary table of a polarizing microscope between crossed analyzer and polarizer the determination of the contrast (K), the measuring cell is positioned by turning so that a photodiode shows minimal light passage (dark state) The microscope illumination is regulated so that the photodiode shows the same light intensity for all cells After a switching process, the light intensity changes ( Bright state) and the contrast is calculated from the ratio of the light intensities of these states

To determine τ and the switching _angle ⌀ _eef , the position of the table with minimal light passage for the two switching states in the cell is determined by rotating the table. The difference between the two positions on the turntable is twice the effective tilt angle. With the help of a photodiode, the switching time τ is determined by measuring the rise time of the light signal from 10 to 90% signal level. The switching voltage consists of rectangular pulses and is ± 10 V / μm.

The phase transition temperatures are determined on heating with the aid of a polarizing microscope based on the texture changes. The determination of the melting point, however, was carried out with a DSC device. The indication of the phase transition temperatures between the phases
Nematic (N or N ')
Smectic-C (S _C or S _C *)
Smectic-A (Sn or Sn ')
Crystalline (X)
takes place in ° C and the values are between the phase names in the phase sequence.

Liquid crystalline mixtures, the compounds of general formula (I) contain are especially for use in electro-optical switching and display devices (displays) suitable. Switch and display devices (LC displays) have u. a. the following components: a liquid crystalline medium, carrier plates (e.g. made of glass or plastic, coated with transparent electrodes, at least one orientation layer, spacers, adhesive frame, Polarizers as well as for Color displays thin Color filter layers Other possible Components are anti-reflective, passivation, compensation and barrier layers as well as non-linear elements such as thin film transistors (TFT) and metal-insulator-metal (MIM) elements. The structure is in detail of liquid crystal displays already in relevant Monographs described (e.g. E. Kaneko, "Liquid Crystal TV Displays: Principles and Applications of Liquid Crystal Displays ", KTK Scientific Publishers, 1987, pages 12-30 and 63-172 The compounds according to the invention can be prepared, for example by the procedure outlined in Scheme 1.

Starting compound of the manufacturing process according to the invention is the commercially available formyl compound, which are converted into the corresponding acrolein derivatives using Mannich reagents.

The difluoroquinolines according to the invention can, for. B. can be produced according to the following scheme.

Scheme 1

The cross coupling of connection II with aryl halides using transition metal catalysts, z. B. [1,3-bis (diphenylphosphino) propane] nickel (II) chloride and tetrakis (triphenylphosphine) palladium (O) at temperatures between –40 and 200 ° C, especially between –10 and 100 ° C in reaction media, such as benzene / ethanol / water also provides Type I compounds

The ending is through the following Examples closer explains:

example 1

7,8-Difluoro-2- (4-propylphenyl) -6-ethoxychinolin

1A 2,3-difluoro-4-ethoxyaniline

To a mixture of 2,3-difluorophenethol (48.7 g, 0.31 mol) and 300 ml of THF become 194 ml of a 1.6 molar at -75 ° C solution dropped from n-butyllithium in n-hexane (0.31 mol). After stirring for two hours, drips a mixture of 40 g of trimethylsilyl azide (0.31 mol) and 200 ml THF added. After warming up to room temperature as usual worked up. You get 12.8 g of the product as an oil.

1B 4-propylcinnamaldehyde

To a mixture of 4-propylbenzaldehyde (31.1 g, 0.21 mol), 4.7 g zinc bromide (0.21 mol) and 200 ml THF at room temperature a mixture of 50 g of N-tert-butyl-N- (2,2-di- (trimethylsilyl) thylidenamine and 100 ml of THF.

After stirring for one hour at room temperature and usual Refurbishment receives 37.7 g of a dark liquid, which is used without further purification.

1C 2- (4-propylphenyl) 6-ethoxy 7,8-difluoroquinoline

A mixture of 12 g IA (63 mmol) 29.7 g iron (II) chloride hexahydrate (110 mmol) 1.1 g zinc chloride (8 mmol), 6.7 ml concentrated hydrochloric acid and 60 ml ethanol is brought to 65 ° C heated. 10 ml IB (57 mmol) are added within 90 minutes. After heating to 80 ° C. for 20 hours, the mixture is worked up in the customary manner. Repeated recrystallization from ethanol gives 0.9 g of the pure product with a melting point of 130 ° C.
MS: m / e = 327 (M +, 67%), 298 (29%), 270 (100%), 241 (19%)
¹ H NMR: δ = 1.00 (t, 3H), 1.55 (t, 3H), 1.70 (mc, 2H), 2.65 (mc, 2H), 4.25 (mc, 2H) ), 6.90 (mc, 1H), 7.15-8.15 (mc, 6H)

hergestellt.The following compounds of the formula become analogous

manufactured.

Application example 1

a) A ferroelectric Mixture made up of the components

• 5-nonyl-2- (4-heptyloxyphenyl) pyrimidine 18%
• 5-nonyl-2- (4-otyloxyphenyl) pyrimidine 18%
• 5-nonyl-2- (4-nonyloxyphenylpyrimidine 18%
• 5-nonyl (-2- (2,3-difluoro-4-heptyloxyphenyl) pyrimidine 6.0%
• 5-nonyl (-2- (2,3-difluoro-4-nonyloxyphenyl) pyrimidine 6.0%
• 2- (4-octyloxy) 6-nonyloxy-7,8-difluoroquinoline 6.0%
• 5-hexyloxy-2 (4-hexyloxyphenyl) pyrimidine 18%
• 4 (2-fluoroctyloxy) -4 '- (4-cyano-4-heptylcyclohexyl) biphenyl 10%, shows the following phase transitions: K <- 20 S _C * 66 S _A Ch 75 I

Claims (6)

Difluoroquinoline derivatives of the general formula (I)

in which the symbols have the following meaning: R ¹ , R ² identical or different, -H, -F, -Cl, -CN, -NCS, -CF ₃ , -OCF ₃ , -OCHF ₂ or straight-chain or branched (with or without asymmetric carbon atom) alkyl with 1 to 16 carbon atoms, where also one or two non-adjacent -CH ₂ groups by -O-, -S-, -CO-, -CO-O-, -O-CO -, -CO-S-, -S-CO-, -O-CO-O-, -CH = CH-, -C≡C-,

or -Si (CH ₃ ) ₂ - can be replaced, and where one or more H atoms of the alkyl radical can be substituted by -F, -Cl, -Br or -CN, or one of the following chiral groups.

A ¹ , A ² , A ³ , A ^{4 the} same or different, 1,4-phenylene, pyrazine-2,5-diyl, pyradizine-3,6-diyl, pyridine-2,5-diyl, pyrimidine-2,5 -diyl, where one or two H atoms can each be replaced by -F, trans-1,4-cyclohexylene, in which one or two H atoms can be replaced by -CN, (1,3,4) thiadiazole -2,5-diyl, 1,3-dioxane-2,5-diyl, naphthalene-2,6-diyl, bicyclo [2.2.2] octane-1,4-diyl or 1,3-dioxaborinane-2.5 diyl; M ¹ , M ² , M ³ , M ^{4 the} same or different, -O-, -S-, -CO-, -CO-O-, -O-CO-, -CO-S-, -S-CO- , -O-CO-O-, -CH ₂ O-, -CH ₂ -CH ₂ -, CH = CH- or -C≡C-; R ³ , R ⁴ , R ⁶ , R ^7, identical or different, H or straight-chain or branched alkyl having 1 to 16 carbon atoms or R ³ and R ⁴ together also - (CH ₂ ) ₄ - or - (CH ₂ ) ₅ - when bound to a dioxolane system as a substituent; M ⁵ -CH ₂ -O-, -CO-O-, -O-CH ₂ -, -O-CO- or a single bond; k, l, m, n, o, p, q, r, 0 or 1, provided that the sum k + m + p + r is less than 4 and greater than 0. Difluoroquinoline derivative according to claim 1, characterized in that the symbols of the general formula (I) have the following meaning: R ¹ , R ² identical or different, -H, -F, -CN or straight-chain or branched (with or without asymmetrical C -Atom) alkyl with 1 to 16 carbon atoms, where also a -CH ₂ group by -O-, S-, -CO-, -CO-O-, -O-CO-, -O-CO-O -, -CH = CH-, -C≡C-,

or -Si (CH ₃ ) ₂ can be replaced, or one of the following chiral groups:

A ¹ , A ² , A ³ , A ^{4 the} same or different, 1,4-phenylene, pyrazine-2,5-diyl, pyridazine-3,6-diyl, pyridine-2,5-diyl, pyrimidine-2,5 -diyl, where one or two H atoms can be replaced by F, trans-1,4-cyclohexylene, (1,3,4) -Thiadiazol-2,5-diyl, 1,3-dioxane-2,5- diyl, naphthalene-2,6-diyl, biocyclo [2.2.2] octane-1,4-diyl or 1,3-dioxabonnan-2,5-diyl; M ¹ , M ² , M ³ , M ⁴ identical or different -O-, -CO-, -CO-O-, -O-CO-, -CH ₂ -O-, -O-CHr, -CH ₂ - CH ₂ -, -CH = CH or -C≡C-; R ³ , R ⁴ , R ⁶ , R ^7, identical or different, H or straight-chain or branched alkyl having 1 to 10 C atoms or R ³ and R ⁴ together also - (CH ₂ ) ₄ - or - (CH ₂ ) ₅ - when bound to a dioxolane system as a substituent; M ⁵ -CH ₂ -O-, -CO-O-, -O-CH ₂ -, O-CO- or a single bond. Difluoroquinoline derivative of the formula (Ia)

wherein R ¹ , R ² , A ¹ , A ² , M ¹ , M ² , k, l, m and n have the meaning given Liquid crystal mixture, containing at least one compound of formula I according to one or several of the claims 1 to 3. liquid crystal mixture according to claim 4, characterized in that the liquid crystal mixture is ferroelectric is. Switching and / or display device containing carrier plates, Electrodes, at least one polarizer, at least one orientation layer as well as a liquid crystalline Medium, characterized in that the liquid-crystalline medium is a liquid crystal mixture according to one of the claims 4 to 5.