DE4333838A1 - 3,4-difluorobenzenes and their use in liquid crystal mixtures - Google Patents

Description

The unusual combination of anisotropic and fluid behavior of the Liquid crystals have their use in electro-optical switching and Display devices led. Your electrical, magnetic, elastic and / or their thermal properties too Orientation changes can be used. Optical effects can be for example with the help of birefringence, the incorporation of dichroic Achieve dye molecules (guest host mode) or light scattering.

The practical requirements are constantly increasing, not least because of the always increasing number of light valve types (TN, STN, DSTN, TFT, ECB, DECB, DS, GH, PDLC, NCAP, SSFLC, DHF, SBF etc.). Next thermodynamic and electro-optical variables, such as phase sequence and Phase temperature range, refractive index, birefringence and dielectric Anisotropy, switching time, threshold voltage, steepness of the electro-optical Characteristic curve, elastic constants, electrical resistance, multiplexability or pitch and / or polarization in chiral phases, is the stability of the Liquid crystals against moisture, gases, temperature and electromagnetic radiation, as well as the materials with which they are connected during and after the manufacturing process (e.g. Orientation layers), of great importance. The toxicological and ecological harmlessness as well as the price are coming more and more Meaning too.

The following references and the references contained therein provide a broad overview of the field of liquid crystals: H. Kelker, H. Hatz: Handbook of Liquid Crystals, Verlag Chemie, Weinheim 1980 WE De Jeu: Physical Properties of Liquid Crystal Materials, Gordon and Breach, 1980; H. Kresse: Dielectric Behavior of Liquid Crystals, Physics Progress, Berlin 30 (1982) 10, 507-582.
B. Bahadur: Liquid Crystals: Applications and Uses, World Scientific, 1990. Landolt-Börnstein, New Series, Group IV, Volume 7 Liquid Crystals, 1992-1993.
JW Goodby et al., Ferroelectric Liquid Crystals: Principals, Properties and Applications, Gordon Breach, 1991.

As individual connections so far have not met the requirements mentioned simultaneously can meet, there is a constant need for new improved Liquid crystal mixtures and therefore on a variety of mesogenic and not mesogenic compounds of different structure, which adapt the Allow mixtures for a wide variety of applications. this applies both for the areas where nematic LC phases are used in Find light valves, as well as for those with smectic phases.

The use of special derivatives of 3,4-difluorobenzene in nematic Liquid crystal mixtures have been known for a long time (see: DE-A 41 08 448, EP-A 0 507094, EP 502407, DE 41 12 025, DE 41 11 766, WO 9009419).

The present invention relates to new 3,4-difluorobenzene derivatives Formula (I),

where the symbols have the following meaning:
R¹ is H, a straight-chain or branched (with or without an asymmetric carbon atom) alkyl having 1 to 15 carbon atoms, with one or two non-adjacent -CH₂ groups by

may be replaced, and one or more H atoms of the alkyl radical may also be substituted by F;
A¹, A², A³ is the same or different 1,4-phenylene, 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 or naphthalene-2,6-diyl;
M¹, M², are the same or different -CH₂CH₂-, CH = CH-, -C≡C-, -CH₂CH₂CH₂CH₂-, -CH₂CH₂CH₂-O-, -O-CH₂CH₂CH₂-, -CH₂CH₂CO-O-, -OCO-CH₂CH₂- , -CH₂O-, -OCH₂-, -CO-O- or -O-CO-;
k, l, m, n, o, p are zero or one, provided that the sum k + m + o is greater than zero;
X is equal to -CH₂O- or -OCH₂-.

In a preferred embodiment of the invention, the symbols in the formula (I) have the following meaning:
R¹ is a straight-chain alkyl with 1 to 15 C atoms;
A¹, A², A³ is the same or different 1,4-phenylene, in which one or two H atoms can be replaced by F or trans-1,4-cyclohexylene;
M¹, M² are identical or different -CH₂CH₂-, -C≡C-, -CH₂O-, -OCH₂-, -CO-O- or -O-CO-;
k, l, m, n, o, p are zero or one, provided that the sum k + m + o is greater than zero.
X is -CH₂-O- or -O-CH₂-.

In particular, the 3,4-difluorobenzenes (I1) to (I4) listed below are prefers:

R¹ means methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, Decyl.

The substances according to the invention are particularly low Melting points. In mixtures they have an advantageous effect, i. H. lowering on the Glass transition temperature. This is for a low viscosity and its low Favorable temperature dependence.

The compounds according to the invention can be prepared according to methods known from the literature and familiar to the skilled worker as a rule done easily.  

Species are obtained from commercially available 3,4-difluorophenol of formula (I) by etherification with hydroxymethyl or halomethyl derivatives of Z¹ (see scheme 1).

The etherification of also commercially available 3,4-difluorobenzyl alcohol or 3,4-difluorobenzyl bromide with alcohols from Z¹ also provides Compounds of formula (I) (see Scheme 2).

For the synthesis, see u. a .:

• - Journal of the American Chemical Society 69 (1947) 2451
• - Synthesis 1981, 1st

Scheme 1

Y = OH, Cl, Br; Z¹ = R¹ (-A¹) _k (-M¹) _l (-A²) _m (-M²) _n (-A³) _o

Scheme 2

Y; Z¹ see scheme 1

The compounds of general formula (I) according to the invention are chemical and photochemically stable. They have low melting points and general broad liquid-crystalline phases, in particular broad nematic.

Liquid crystalline compounds of the formula (I) can be used, for example Production of nematic or chiral nematic Use liquid crystal mixtures for use in electro-optical or completely optical elements, e.g. B. display elements, switching elements, Light modulators, elements for image processing, signal processing or are generally suitable in the field of nonlinear optics. Generally they are for introducing or widening a nematic phase in LC mixtures suitable.

The invention also relates to liquid crystal mixtures, the one or contain several compounds of formula (I).

The liquid crystal mixtures according to the invention generally consist of 2 to 20, preferably 2 to 15 components, including at least one, preferably 1 to 5, particularly preferably 1 to 3, compounds of the formula (I). The LC mixtures according to the invention can for example be nematic, be chiral nematic, smectic and / or ferroelectric. Other components of the mixtures according to the invention are preferably selected from the known compounds with nematic or cholesteric phases include, for example, biphenyls, terphenyls, phenylcyclohexanes, Bicyclohexanes, cyclohexylbiphenyls, mono-, di- and trifluorophenyls. in the in general, the commercially available liquid crystal mixtures are already there before adding the compound (s) according to the invention as mixtures various components, at least one of which is mesogenic.

Suitable further components of nematic or chiral according to the invention Nematic liquid crystal mixtures are for example

• 4-fluorobenzenes, such as, for example, in EP-A 494 368, WO 92/06 148, EP-A 460 436, DE-A 41 11 766, DE-A 41 12 024, DE-A 41 12 001, DE-A 41 00 288, DE-A 41 01 468, EP-A 423 520, DE-A 39 23 064, EP-A 406 468, EP-A 393 577, EP-A 393 490,
• 3,4-difluorobenzenes, such as, for example, in DE-A 41 08 448, EP-A 507 094 and EP-A 502 407,
• 3,4,5-trifluorobenzenes, as for example in DE-A 41 08 448, EP-A 387 032,
• 4-benzotrifluorides, as described for example in DE-A 41 08 448,
• - Phenylcyclohexanes, as described for example in DE-A 41 08 448.

Contain of the compound or compounds of formula (I) according to the invention the liquid crystal mixtures generally 0.1 to 70 mol%, preferably 0.5 up to 50 mol%, in particular 1 to 25 mol%.

Liquid-crystalline mixtures, the compounds of the general formula (I) included, are especially for use in electro-optical switching and Suitable display devices. Switching and display devices (LC displays) generally 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 frames, polarizers and thin ones for color displays Color filter layers. Other possible components are anti-reflective, Passivation, compensation and barrier layers as well as non-linear electrical Elements such as thin film transistors (TFT) and metal insulator metal (MIM) - Elements. The structure of liquid crystal displays is already in detail  relevant monographs (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).

Examples

For the physical characterization of the compounds according to the invention different measuring methods are used.

The phase transition temperatures are determined using a Polarization microscope determined based on the texture changes. The The melting point, however, is determined with a DSC device carried out. The indication of the phase transition temperatures between the Phases

Isotropic (I)
Nematic (N or N *)
Smectic-C (S _C or S _C *)
Smectic-A (S _A or S _A *)
Crystalline (X)
Glass transition (Tg)

takes place in ° C and the values are between the phase names in the Phase sequence.

With different values for heating and cooling, the latter are in Brackets or it is the phase sequence ascending and descending in the Temperature specified.

Electro-optical investigations are carried out using methods known from the literature (e.g. Baladur: Liquid Crystals Application and Uses, World Scientific, 1990, Vol. I).  

For nematic liquid crystals (pure or in a mixture) the values for the optical and dielectric anisotropy and the electro-optical characteristic a temperature of 20 ° C added.

Liquid crystals that have no nematic phase at 20 ° C become too 10% by weight in ZLI-1565 (commercial nematic liquid crystal mixture of E. Merck, Darmstadt) mixed and the values from the results of the Mix extrapolated.

Electro-optical characteristics are based on the transmission of a measuring cell determined. To do this, the cell is placed between crossed polarizers in front of one Positioned light source. There is a light detector behind the cell Sensitivity is optimized by filters on the visible range of light. Analogous to the gradual increase in the voltage applied to the cell the change in transmission is recorded. Sizes like threshold voltage and steepness are determined from it.

The optical anisotropy is measured with an Abb refractometer (Zeiss company) certainly. To orient the liquid crystal, a Orientation layer, obtained from a 1% by weight lecithin-methanol Solution, applied.

A measuring cell is used to determine the dielectric anisotropy made with homeotropic and planar orientation and their capacities and dielectric losses with a multi-frequency LCR meter (Hewlett Packard 4274 A). The dielectric constants are calculated as described in the literature (W. Maier, G. Meier: Z. Naturforsch., 16a, 1961, 262 and W.H. de Jeu, F. Leenhonts: J. Physique 39, 1978, 869).

The electrical variable HR (holding ratio) is in accordance with the References determined (M. Schadt, Linear and nonlinear liquid crystal materials, Liquid Crystals, 1993, Vol. 14, No. I, 73-104).  

To determine T and K, the measuring cell on the turntable is one Polarizing microscope between crossed analyzer and polarizer attached. The measuring cell is used to determine the contrast (K) Rotate positioned so that a photodiode indicates minimal light transmission (Dark state). The microscope lighting is controlled so that the Photodiode shows the same light intensity for all cells. After one Switching process changes the light intensity (bright state) and the contrast calculated from the ratio of the light intensity of these states.

example 1 3,4-difluorophenyl (trans-4-pentylcyclohexyl) methyl ether

1.97 g (7.50 mmol) triphenylphosphine are at 0 ° C in 30 ml Tetrahydrofuran with 1.31 g (7.5 mmol) of diethyl azodicarboxylic acid and stirred for 0.5 h at room temperature. Then 0.98 g (7.50 mmol) 3,4-difluorophenol and 0.92 g (5.00 mmol) of trans-4-pentylcyclohexylmethanol added and stirred at room temperature for 18 h. After evaporating the Solvent and chromatography on silica gel with hexane are 0.79 g Received product.

Phase sequence: Tg -80 X 21 I-32 S _x -42 X -87 Tg

The following are prepared as in Example 1:  

Example 2

3,4-difluorophenyl (trans-4-ethylcyclohexyl) methyl ether

Example 3

3,4-difluorophenyl (trans-4-propylcyclohexyl) methyl ether

Example 4

3,4-difluorophenyl (trans-4-butylcyclohexyl) methyl ether

Example 5

3,4-difluorophenyl- [trans-4- (trans-4-ethylcyclohexyl) cyclohexyl] methyl ether

Example 6

3,4-difluorophenyl- [trans-4- (trans-4-propylcyclohexyl) cyclohexyl] methyl ether

Example 7

3,4-difluorophenyl- [trans-4- (trans-4-butylcyclohexyl) cyclohexyl] methyl ether

Example 8

3,4-difluorophenyl- [trans-4- (trans-4-pentylcyclohexyl) cyclohexyl] methyl ether

Phase sequence: X 60 N 109 I 109 N 37 S _x 11 X

Example 9

3,4-difluorophenyl- [4- (trans-4-ethylcyclohexyl) phenyl] methyl ether

Example 10

3,4-difluorophenyl- [4- (trans-4-propylcyclohexyl) phenyl] methyl ether

Example 11

3,4-difluorophenyl- [4- (trans-4-butylcyclohexyl) phenyl] methyl ether

Example 12

3,4-difluorophenyl- [4- (trans-4-pentylcyclohexyl) phenyl] methyl ether

Example 13

3,4-difluorophenylmethyl [4- (trans-4-ethylcyclohexyl) phenyl] ether

Example 14

3,4-difluorophenylmethyl [4- (trans-4-propylcyclohexyl) phenyl] ether

Example 15

3,4-difluorophenylmethyl [4- (trans-4-butylcyclohexyl) phenyl] ether

Example 16

3,4-difluorophenylmethyl [4- (trans-4-pentylcyclohexyl) phenyl] ether

Examples of use

Table 1 shows application examples. The substances from Examples 1 and 8 were as pure substance and in a mixture (10% by weight) with ZLI 1565 (commercial nematic liquid crystal mixture from E. Merck, Darmstadt) examined and compared with known reference substances.

It now shows how low the melting points of the invention Substances are compared and how they are even lower when mixed Can induce glass transitions.  

Claims (7)

1. 3,4-difluorobenzene derivatives of the formula (I), where the symbols have the following meaning:
R¹ is H, a straight-chain or branched (with or without an asymmetric carbon atom) alkyl having 1 to 15 carbon atoms, with one or two non-adjacent -CH₂ groups by may be replaced, and one or more H atoms of the alkyl radical may also be substituted by F;
A¹, A², A³ is the same or different 1,4-phenylene, 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 or naphthalene-2,6-diyl;
M¹, M², are the same or different -CH₂CH₂-, CH = CH-, -C≡C-, -CH₂CH₂CH₂CH₂-, -CH₂CH₂CH₂-O-, -O-CH₂CH₂CH₂-, -CH₂CH₂CO-O-, -OCO-CH₂CH₂- , -CH₂O-, -OCH₂-, -CO-O- or -O-CO-;
k, l, m, n, o, p are zero or one, provided that the sum k + m + o is greater than zero;
X is equal to -CH₂O- or -OCH₂-. 2. 3,4-difluorobenzenes according to claim 1, characterized in that the Symbols have the following meaning: R¹ is a straight-chain alkyl with 1 to 15 C atoms;
A¹, A², A³ is the same or different 1,4-phenylene, in which one or two H atoms can be replaced by F or trans-1,4-cyclohexylene;
M¹, M² are identical or different -CH₂CH₂-, -C≡C-, -CH₂O-, -OCH₂-, -CO-O- or -O-CO-;
k, l, m, n, o, p are zero or one, provided that the sum k + m + o is greater than zero;
X is -CH₂-O- or -O-CH₂-. 3. 3,4-difluorobenzenes of the formula (I1) to (I4): R1 represents methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl. 4. Liquid crystal mixture containing at least one compound of Formula (I) according to one or more of claims 1 to 3. 5. Liquid crystal mixture according to claim 5, characterized in that the liquid crystal mixture is nematic. 6. switching and / or display device, comprising carrier plates, Electrodes, at least one polarizer, at least one orientation layer and a liquid-crystalline medium, characterized in that the liquid crystalline medium a liquid crystal mixture according to one or more of claims 4 and 5.