Tetrahydrothiophene derivatives, and their use in...

Details Tetrahydrothiophene derivatives, and their use in... Tetrahydrothiophene derivatives, and their use in...

2000-11-07

2002-10-15

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299610, C549S062000, C549S065000, C549S066000, C549S067000, C549S072000

Reexamination Certificate

active

06465060

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
Besides nematic and cholesteric liquid crystals, optically active, tilted, smectic (ferroelectric) liquid crystals have also recently been used in commercial display devices.
2. Description of Related Art
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 virtually viewing angle-independent contrast, FLCs are basically highly suitable for areas of application such as computer displays.
For a more detailed explanation of the technical requirements of FLCs, reference is made to European Patent Application 0 916 714 and DE-A 197 48 432.
Thiophene derivatives have already been described for use in liquid-crystal mixtures, for example in EP-B-0 364 923 or 0 500 072.
However, since the development, in particular of ferroelectric liquid-crystal mixtures, can in no way be regarded as complete, display manufacturers are interested in a 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) allows conclusions to be drawn on the quality of the liquid-crystalline mixtures too.
BRIEF SUMMARY OF THE INVENTION
It has now been found that tetrahydrothiophene derivatives 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, the tilt angle values and the temperature dependence of the tilt angle.
DETAILED DESCRIPTION OF THE INVENTION
The invention therefore provides tetrahydrothiophene derivatives of the formula (I)
R
1
—X—(A
1
—M
1
)
a
—(A
2
—M
2
)
b
—A
3
—Y—T—Z—R
2
  (I)
where the symbols and indices have the following meanings:
T is undirected and is tetrahydrothiophene-2,5-diyl or tetrahydrothiophene-2,4-diyl
R
1
is hydrogen or a straight-chain or branched C
1-20
-alkyl or C
2-20
-alkenyl radical (with or without asymmetric carbon atoms), where
a) one or two nonterminal CH
2
groups may be replaced, independently of one another, by —O— or —C(═O)—, with the proviso that two adjacent CH
2
groups cannot be replaced in the same way, and/or
b) one CH
2
group may be replaced by —C≡C—, and/or
c) one CH
2
group may be replaced by —Si(CH
3
)
2
—, cyclopropane-1,2-diyl, cyclobutane-1,3-diyl, cyclopentane-1,4-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 CN,
e) in the case of an alkyl or alkenyl radical containing asymmetric carbon atoms, the asymmetric carbon atoms 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 non-adjacent to these groups may be replaced by —OC(═O)—;
R
2
is hydrogen or a straight-chain or branched alkyl radical (with or without asymmetric carbon atoms) having 1 to 20 carbon atoms, where one nonterminal CH
2
group may be replaced by —O— or —OC(═O)— or —C(═O)O— and/or one or more H atoms may be replaced by F, with the provisos that
a) the CH
2
group attached to Z cannot be replaced by —O— when Z is —O—
b) R
2
can only be hydrogen when Z is a single bond and R
1
is not hydrogen
X is a single bond, —O—, OC(═O)—, —C(═O)O— or
Y is —OC(═O)—, —SC(═O)—, —OCH
2
— or —CH
2
CH
2
—
Z is a single bond or —O—
A
1
, A
2
and A
3
are undirected and are each, independently of one another phenylene-1,4-diyl, unsubstituted or monosubstituted or disubstituted by CN or F, phenylene-1,3-diyl, unsubstituted or monosubstituted or disubstituted by CN or F, cyclohexane-1,4-diyl, in which one or two H atoms may be replaced, independently of one another, by CN, CH
3
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, thiophene-2,5-diyl or (1,3,4)-thiadiazol-2,5-diyl
M
1
and M
2
are undirected and are each, independently of one another —OC(═O)—, —OCH
2
—, —CH
2
CH
2
—, —OC(═O)CH
2
CH
2
—, —OCH
2
CH
2
CH
2
—, —C≡C—, —CH
2
CH
2
CH
2
CH
2
— or a single bond;
a and b are each, independently of one another, 0 or 1.
“Terminal” means, for example in R
1
, the CH
2
groups connected to X or to H. “Undirected” means that incorporation of the group in the form of its mirror image is possible.
Preference is given to the following compounds of the formulae (I-1) to (I-1 5):
in which:
R
3
is hydrogen or a straight-chain or branched alkyl radical (with or without asymmetric carbon atoms) having 1 to 16 carbon atoms, in which, in addition, one nonterminal CH
2
group may be replaced by —O— or, undirected, by —OC(═O)— and in which one or more H atoms may be replaced by F;
R
4
is hydrogen or a straight-chain or branched alkyl radical (with or without asymmetric carbon atoms) having 1 to 16 carbon atoms,
F
x
denotes a substitution of the biphenyl by one or two (adjacent) F atoms.
Particular preference is given to compounds of the formulae (I), in particular (I-1) to (I-15), in which R
3
and R
4
are each, independently of one another, a straight-chain alkyl radical having 2 to 16 carbon atoms.
Particular preference is likewise given to compounds of the formula (I), in particular (I-1) to (I-15), in which R
3
is a straight-chain alkoxy radical having 2 to 12 carbon atoms and R
4
is hydrogen or a straight-chain alkyl radical having 2 to 12 carbon atoms.
Of the compounds of the formula (I) which are to be used as optically active components (dopants) in liquid-crystal mixtures, preference is given to those in which the alkyl group contains the asymmetric carbon atoms in the form of at least one of the following groups:
a) —C*H(CH
3
)C
m
H
2m+1
, where m has a value of from 2 to 8
b) —OC*H(CH
3
)C
m
H
2m+1
, where m has a value of from 2 to 8
c) —OC*H(CH
3
)CO
2
C
m
H
2m+1
, where m has a value of from 1 to 10
d) —OC(═O)C*H(CH
3
)OC
m
H
2m+1
, where m has a value of from 1 to 10
e) —OC(═O)C*H(F)C
m
H
2m+1
, where m has a value of from 1 to 10
f) —OCH
2
C*H(F)C
m
H
2m+1
, where m has a value of from 1 to 10
g) —OCH
2
C*H(F)C*H(F)C
m
H
2m+1
, where m has a value of from 1 to 10
h) oxirane-2,3-diyl
in which C* denotes the asymmetric carbon atom.
The compounds 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 (>C
6
) alkyl chains tend to be less reactive than, for example, the methyl or ethyl analogues.
Particular reference is made in this connection to the following synthesis schemes, in which the synthesis of the tetrahydrothiophene derivatives of the invention is illustrated in more detail by way of example.
Scheme1
i: 1. Na(Hg), H
2
O 2. HCl, C
2
H
5
OH as described in
D. J. Gram, J.Am.Chem.Soc.
89, 4651 (1967).
ii: 1. NAOH 2. HCl
iii: R
1
—X—(A
1
—M
1
)
a
—(A
2
—M
2
)
b
—A
3
—OH, DCC/CH
2
Cl
2
The 5-alkylthiophene-2-carboxylic acids 1 required for the synthesis of Scheme 1 are prepared according to the method described in EP-B-0 364 923.
As far as the linking of functional deri

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