Benzothiophenes, and their use in liquid-crystalline mixtures

Details Benzothiophenes, and their use in liquid-crystalline mixtures Benzothiophenes, and their use in liquid-crystalline mixtures

2000-03-22

2002-06-11

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299610, C252S299620, C549S049000, C549S050000, C549S051000, C549S052000

Reexamination Certificate

active

06403172

ABSTRACT:

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention provides for benzothiophenes and their use in liquid-crystalline mixtures and the use of these mixtures in display devices.
2. Description of Related Art
Besides nematic and cholesteric liquid crystals, optically active, tilted, smectic (ferroelectric) liquid crystals have also recently been used in commercial display devices.
Clark and Lagerwall have been able to show that the use of ferroelectric liquid crystals (FLCs) in very thin cells results in opto-electrical switching or display elements which have response times which are faster by a factor of up to 1000 compared with conventional TN (“twisted nematic”) cells (see, for example, EP-A 0 032 362). Owing to this and other favorable properties, for example the possibility of bistable switching and the fact that the contrast is virtually independent of the viewing angle, FLCs are basically highly suitable for areas of application such as computer displays.
For a more in-depth explanation of the technical requirements of FLCs, see European Patent Application 97118671.3 and DE-A 197 48 432.
Thiophene derivatives have already been described for use in liquid-crystal mixtures:
thiophene derivatives, for example, in DE-A 33 46 175, EP-A-0 458 347, EP-A-0 364 923, EP-A-0 392 510, EP-A-0 459 406,
derivatives of benzothiophene-2-carboxylic acid in DE-A 196 30 068.
Since the development, in particular of ferroelectric liquid-crystal mixtures, can in no way be regarded as complete, the manufacturers of displays are interested in a very wide variety of components for mixtures, partly because only the interaction of the liquid-crystalline mixtures with the individual components of the display device or of the cells (for example the alignment layer) allow conclusions to be drawn on the quality of the liquid crystalline mixtures too.
SUMMARY OF THE INVENTION
It has now been found that benzothiophenes of the formula (I), even when admixed in small amounts, have a favorable effect on the properties of liquid-crystal mixtures, in particular chiral smectic mixtures, for example regarding the dielectric anisotropy and/or the melting point, but also regarding the switching behavior.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
Not applicable.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to the use of benzothiophenes of the formula (I) as components of liquid-crystal mixtures
where the symbols and indices have the following meanings:
X
1
and X
2
, independently of one another, are —CH—, —CF—, the —(R
1
)C— group or the —(R
1
—A
1
M
1
)C— group, with the provisos that
x1) X
1
and X
2
are not simultaneously the —(R
1
)C— or —(R
1
—A
1
—M
1
)C— group, and
x2) X
1
and X
2
are only simultaneously —CH— or —CF— if Z is fluorine
Y
1
and Y
2
, independently of one another, are hydrogen or fluorine, but both are not simultaneously fluorine
Z is hydrogen or fluorine
R
1
and R
2
, independently of one another, are a straight-chain or branched alkyl radical (with or without asymmetrical carbon atoms) having 1 to 20 carbon atoms, where
a) one or two non-terminal —CH
2
— groups may be replaced by —O—and/or —C(═O)— and/or —Si(CH
3
)
2
—, with the proviso that two adjacent —CH
2
— groups cannot be replaced by heteroatoms, and/or
b) one or more —CH
2
— groups may be replaced by —CH═CH— and/or —C≡C—, and/or
c) one —CH
2
— group may be replaced by cyclopropane-1,2-diyl, cyclobutane-1,3-diyl, cyclopentane-1,3-diyl, bicyclo-[1.1.1] pentane-1,3-diyl or cyclohexane-1,4-diyl, and/or
d) one or more H atoms may be replaced by F, and/or in the case of a branched alkyl radical containing asymmetrical carbon atoms, the asymmetrical carbon atoms either have —CH
3
, —OCH
3
, —CF
3
, F, CN and/or Cl as substituents, or are incorporated into a 3-to 7-membered ring, in which, in addition, one or two non-adjacent —CH
2
— groups may be replaced by —O— and one —CH
2
— group may be replaced by —OC(═O)—
A
1
and A
2
, independently of one another, are phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by CN or F, phenylene-1,3-diyl, unsubstituted, monosubstituted or disubstituted by CN or F, cyclohexane-1,4-diyl, in which one or two H atoms may be replaced by CN and/or CH
3
and/or F, 1-cyclohexene-1,4-diyl, in which one H atom may be replaced by F, 1-alkyl-1-silacyclohexane-1,4-diyl, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F, 1,1′-biphenyl-4,4′-diyl, unsubstituted, monosubstituted or disubstituted by F, or 1,1′-phenylcyclohexyl-4,4′-diyl, in which the phenyl moiety is unsubstituted, monosubstituted or disubstituted by F
M
1
is undirected and is —OC(═O)—, —OC(═O)O—, —OCH
2
—, —(CH
2
)
n
—, —OC(═O)CH
2
CH
2
—, —OCH
2
CH
2
CH
2
—, —C≡C— or a single bond
m is 0 or 1
n is from 1 to 6, i.e. 1, 2, 3, 4, 5or 6.
Undirected is intended to mean that, in the case of asymmetrical groups, mirror and mirror image of the group can be employed.
The symbols and indices in the formula (I) preferably have the following meanings:
R
1
and R
2
, independently of one another, are preferably a straight-chain or branched alkyl radical (with or without asymmetrical carbon atoms) having 2 to 18 carbon atoms, where
a) one —CH
2
— group may be replaced by —O—, and/or
b) one or more H atoms may be replaced by F.
R
1
and R
2
, independently of one another, are particularly preferably a straight-chain or branched alkyl radical (with or without asymmetrical carbon atoms) having 3 to 16 carbon atoms, where
c) one —CH
2
— group may be replaced by —O—.
A
1
and A
2
, independently of one another, are preferably phenylene-1,4-diyl, phenylene-1,3-diyl, 1,1′-biphenyl-4,4′-diyl or 1,1′-phenyl-cyclohexyl-4,4′-diyl.
A
1
and A
2
are particularly preferably phenylene-1,4-diyl.
Z is preferably F, or
Z=H and Y
1
=F or Y
2
=F or X
1
=—CF— or X
2
=—CF—.
The following compounds of the formula (I-1) to (I-10) are particularly preferably employed:
where R
1
and R
2
have the above-mentioned meanings and preferences.
The invention also relates to the benzothiophenes of the formula (I), as defined above.
The compounds according to the invention and employed according to the invention are prepared by methods known per se from the literature, as described in standard works on organic synthesis, for example Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart.
However, it may prove necessary to vary or modify the literature methods for the requirements of mesogenic units, since, for example, functional derivatives having long (>C6) alkyl chains frequently have lower reactivity than, for example, the methyl and ethyl analogs.
Particular reference is made in this connection to the following references, which describe in general terms the synthesis of benzothiophene derivatives which are to be used, inter alia, as pharmaceuticals, but which do not reveal to the person skilled in the art the benzothiophenes according to the invention and their suitability as components of liquid-crystalline mixtures:
Reference 1:
Sauter et al., Monatshefte für Chemie 101, 1806-1816 (1970), for the preparation of 5-alkoxy-2-arylbenzothiophenes, which can also contain an additional carboxyl group in position 3.
Reference 2:
WO 97/34888 for the synthesis of 6-alkoxy-2-arylbenzothiophenes, which can also contain a bromine or carbonyl substituent in position 3.
Reference 3:
WO 96/02537 for the synthesis of 6-alkyl- or -alkoxybenzothiophenes, which can also contain a carbonyl substituent in position 3.
Reference 4:
U.S. Pat. No. 4,133,814 for the synthesis of 6-alkoxy-2-arylbenzothiophenes and a review of further routes to benzothiophenes.
Reference 5:
WO 97/01549 for the synthesis of 6-alkoxy-2-arylbenzothiophenes, which can also have a bromine or carbonyl substituent in position 3.
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