Phenylcyclohexanes and a liquid-crystalline medium

Details Phenylcyclohexanes and a liquid-crystalline medium Phenylcyclohexanes and a liquid-crystalline medium

2001-02-08

2004-01-13

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299630, C252S299660, C568S656000, C570S129000

Reexamination Certificate

active

06677002

ABSTRACT:

The invention relates to novel phenylcyclohexanes of the formula I:
in which n is 0 to 7, Q
1
and Q
2
are H, or one of these radicals is alternatively CH
3
, r is 0, 1, 2, 3, 4 or 5, A is trans-1,4-cyclohexylene, 1,4-phenylene, 3-fluoro-1,4-phenylene or a single bond, X is F, Cl, —CF
3
, —CN, —OCF
3
or —OCHF
2
, and Y and Z are each, independently of one another, H or F, with the proviso that, in the case where A is a single bond, Q
1
═Q
2
═H and simultaneously X═CN, Y and/or Z are F.
EP-A 0 122 389 discloses similar compounds, for example of the formula A:
However, these compounds do not satisfy all the demands, in particular with respect to (long-term) stability, for example for use in displays having an active matrix.
German Offenlegungsschrift 29 07 332 discloses similar compounds of the formula:
These nematogenic compounds are preeminently suitable for improving the low-temperature behavior of nematic mixtures, but, on the other hand, have relatively high values for the vapor pressure at small values of n.
EP-A 0 280 902 discloses similar compounds of the formula:
in which A is F, Cl, Br, H or CN. Although these compounds have low values for the vapor pressure, they have, on the other hand, clearly smectogenic properties. There is thus a demand for highly nematogenic compounds having low values for the vapor pressure.
In particular in displays of the supertwist type (STN) having twist angles significantly greater than 220° or in displays having an active matrix, the materials employed hitherto have disadvantages.
Like similar compounds known, for example, from German Offenlegungsschriften 26 36 684 and 29 07 332, these compounds of the formula I can be used as components of liquid-crystalline media, in particular for displays based on the principle of the twisted cell.
All the substances employed hitherto for this purpose have certain disadvantages, for example excessively high melting points, excessively low clear points, excessively low stability to the action of heat, light or electrical fields, excessively low electrical resistance, excessively high temperature dependence of the threshold voltage, and unfavorable dielectric and/or elastic properties. The invention had the object of finding novel liquid-crystalline compounds which are suitable as components of liquid-crystalline media, in particular for nematic media having a positive dielectric anisotropy, and which do not have the disadvantages of the known compounds, or only do so to a lesser extent. This object has been achieved by the provision of the novel compounds of the formula I.
It has been found that the compounds of the formula I are preeminently suitable as components of liquid-crystalline media. In particular, they can be used to obtain liquid-crystalline media having broad nematic ranges, excellent nematogeneity down to low temperatures, excellent chemical stability, pronounced ∈⊥ with a positive dielectric anisotropy, low temperature dependence of the threshold voltage and/or low optical anisotropy. In addition, the novel compounds have good solubility for other components of media of this type and a high positive dielectric anisotropy with, at the same time, favorable viscosity and excellent elastic properties. The compounds of the formula I facilitate both STN displays having a very steep electrooptical characteristic line and displays having an active matrix with excellent long-term stability.
In the pure state, the compounds of the formula I are colorless and form a liquid-crystalline mesophase in a temperature range which is favorably located for electrooptical use.
The invention thus relates to the compounds of the formula I and to the use of the compounds of the formula I as components of liquid-crystalline media, to liquid-crystalline media containing at least one compound of the formula I, and to electrooptical displays which contain media of this type.
Above and below, n, Q
1
, Q
2
, r, A, X, Y and Z are as defined above, unless expressly stated otherwise.
In the compounds of the formula I, the alkyl groups C
n
H
2n+1
are preferably straight-chain. Accordingly, C
n
H
2n+1
is preferably methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl or likewise preferably H. n is preferably 0, 1, 2, 3, 4 or 5.
Compounds of the formula I having branched alkyl groups may occasionally be of importance due to better solubility in the customary liquid-crystalline base materials, but in particular as chiral dopes if they are optically active. Branched groups of this type generally contain not more than one chain branch. Preferred branched alkyl radicals are isopropyl, 2-butyl (=1-methylpropyl), isobutyl (=2-methylpropyl), 2-methylbutyl, isopentyl (=3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-heptyl (=1-methylhexyl), 2-octyl (=1-methylheptyl) and 2-ethylhexyl.
The radical
is preferably
X is preferably F, Cl, —CF
3
, OCHF
2
or —OCF
3
. X is furthermore preferably CN, in particular if simultaneously Z═F and Y═F or H, in particular Y═F. Very particular preference is given to compounds where X═CF
3
, —OCF
3
or —OCHF
2
.
r is preferably 1, 2 or 3 or furthermore preferably 0. A is preferably a single bond and furthermore preferably trans-1,4-cyclohexylene or 1,4-phenylene. In the case where Q
1
═Q
2
═H, r=2 or 3, Z═H, X═F or Cl and simultaneously Y═F or H, A is preferably a single bond, 1,4-phenylene or 3-fluoro-1,4-phenylene.
In addition, the compounds of the formula I are prepared by methods known per se, as 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), to be precise under reaction conditions which are known and suitable for the reactions mentioned. Use may also be made here of variants which are known per se, but are not described in greater detail.
If desired, the starting materials can also be formed in situ, by not isolating them from the reaction mixture but instead immediately reacting them further to form the compounds of the formula I.
Preferably, an aldehyde of the formula II:
in which X, Y and Z are as defined above, is converted into compounds of the formula I by the Wittig method using an appropriate phosphonium salt.
Some of the starting materials and the reactive derivatives thereof are known, and some can be prepared without difficulty from compounds known from the literature by standard methods of organic chemistry. For example, the precursors of the formula II which are suitable for the synthesis can be obtained by the following synthetic scheme:
The Grignard compound obtained from the corresponding bromobenzene derivative is reacted with chlorotrialkyl orthotitanate or -zirconate by the method of WO 87/05599 to give the tertiary cyclohexanol. Elimination of water, hydrogenation of the double bond and isomerization give the trans-cyclohexanecarboxylate by customary methods. From the latter, the suitable precursors of the formula II are obtained by customary standard methods.
A possible synthesis of compounds where A=trans-1,4-cyclohexylene or 1,4-phenylene is given in the following scheme:
Homologization of the cyclohexanecarboxylic acids or the corresponding aldehydes gives the compounds according to the invention completely analogously to the synthesis schemes given above.
The compounds of the formula I where A=3-fluoro-1,4-phenylene are increased [sic] entirely analogously to the first synthesis scheme (preparation of compounds where A=a single bond) by using
in place of the bromobenzene derivative. The bromobi-phenyl compound can be prepared in a manner known per se by coupling reactions catalyzed by transition metals (E. Poetsch, Kontakte (Darmstadt) 1988 (2), p. 15).
It is obvious to a person skilled in the art that the abovementioned synthetic methods can also be modified in that the syntheses described are carried out using precursors in which the radical X is repl

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