Chiral compounds, and their use as chiral dopants for the...

Details Chiral compounds, and their use as chiral dopants for the... Chiral compounds, and their use as chiral dopants for the...

2000-10-03

2003-05-27

Huff, Mark F. (Department: 1756)

Compositions

Liquid crystal compositions

C424S059000, C252S582000

Reexamination Certificate

active

06569355

ABSTRACT:

The present invention relates to chiral compounds and to their use as chiral dopants for nematic or cholesteric liquid crystals for the generation of layers which reflect in color in the UV or IR region or for the preparation of pigments having a liquid-crystalline, cholesteric order.
Cholesteric liquid crystals (CLCs) reflect circular-polarized electromagnetic radiation in a wavelength region which is dependent on the helical structure of the CLC. The central wavelength of the reflection band is determined by the pitch p of the helical structure, and the width of the band is determined by the optical anisotropy of the mesogens. The central wavelength of the reflection band, which is referred to below as the reflection wavelength, is dependent on the viewing angle. The direction of rotation of the reflected light corresponds to the direction of rotation of the cholesteric helix.
Cholesteric liquid-crystal mixtures generally comprise one or more optically active components for inducing a chiral structure. For example, cholesteric liquid-crystal mixtures can consist of a nematic base material and one or more optically active dopants, which generate either a right- or left-handed twist in the nematic phase which determines the direction of rotation of the reflected circular-polarized light.
Numerous compounds have been disclosed as chiral dopants for liquid-crystalline phases (for example in DE-A 43 42 280, DE-A 195 41 820 and DE-A 196 11 101, and in GB-A-2 314 839 and WO 98/00428).
For left-handed helical materials, cholesterol compounds are frequently suitable; apart from chirality, these introduce sufficiently mesogenic properties in order to generate a stable mesophase. Such compounds are described, for example, by H. Finkelmann, H. Ringsdorf et al., in Makromol. Chem. 179, 829-832 (1978). However, these compounds have the disadvantage of complex synthesis and a high preparation price.
It is an object of the present invention to provide novel chiral compounds which are suitable for the preparation of cholesteric liquid-crystalline compositions and which do not have the abovementioned disadvantages.
We have found that this object is achieved in accordance with the invention by the use of compounds of the general formula I
in which the substituents, independently of one another, have the following meanings:
R
1
is Z
1
—Y
1
—(A
1
)
m
—Y
2
—M
1
—Y
3
—(A
2
)
n
—Y
4
—;
R
2
is hydrogen, C
1
-C
12
-alkyl, C
1
-C
12
-alkylcarbonyl, aryl, arylcarbonyl or Z
2
—Y
5
—(A
3
)
o
—Y
6
—M
2
—Y
7
—(A
4
)
p
—Y
11
—;
R
3
is hydrogen, C
1
-C
12
-alkyl, aryl or OR
5
;
R
4
is hydrogen, C
1
-C
12
-alkyl, aryl or OR
6
;
R
5
and R
6
are hydrogen, C
1
-C
12
-alkyl, C
1
-C
12
-alkylcarbonyl, aryl, arylcarbonyl or Z
3
—Y
8
—(A
5
)
q
—Y
9
—M
3
—Y
10
—(A
6
)
r
—Y
12
—;
A
1
to A
6
are spacers having a chain length of from 1 to 30 carbon atoms;
M
1
to M
3
are mesogenic groups;
Y
1
to Y
10
are chemical bonds, —O—, —S—, —C(═O)—, —C(═O)—O—, —O—C(═O)—, —CH═CH—C(═O)—O—, —O—C(═O)—O—, —C(═O)—N(R)— or —(R)N—C(═O)—, —CH
2
—O—, —O—CH
2
—, —CH═N—, —N═CH— or —N═N—;
Y
11
and Y
12
are chemical bonds, —C(═O)—, —O—C(═O)—, —CH═CH—C(═O)—, —(R)N—C(═O)—, —CH
2
— or —O—CH
2
—;
R is hydrogen or C
1
-C
4
-alkyl;
Z
1
to Z
3
are hydrogen, C
1
-C
12
-alkyl, polymerizable groups or radicals carrying polymerizable groups;
m to r is are 0 or 1,
where the radicals A
1
to A
6
, Y
1
to Y
10
, Y
11
and Y
12
and Z
1
to Z
3
may be identical or different, and where, in the case where one or more of the indices m to r are zero, at least one of the radicals Y in each case adjacent to A is a chemical bond,
as chiral dopants for nematic or cholesteric liquid crystals for the generation of layers which reflect in color in the UV or IR region or for the preparation of pigments having a liquid-crystalline, cholesteric order.
Examples of alkyl radicals which may be mentioned for R
2
to R
6
and for Z
1
to Z
3
are branched or unbranched C
1
-C
12
-alkyl chains, for example methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl, 1-ethyl-2-methylpropyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl and n-dodecyl.
Preferred alkyl radicals which may be mentioned for R
2
to R
6
from the abovementioned list are the branched or unbranched C
1
-C
6
-alkyl chains, for example methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 2-ethylpropyl and n-hexyl.
Preferred alkyl radicals which may be mentioned for Z
1
to Z
3
from the abovementioned list are the branched or unbranched C
4
-C
10
-alkyl chains, for example n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl and n-decyl.
The term “aryl” for R
2
to R
6
is taken to mean aromatic rings or ring systems having 6 to 18 carbon atoms in the ring system, for example phenyl or naphthyl, which can be unsubstituted or substituted by one or more radicals, such as halogen, for example fluorine, chlorine or bromine, cyano, nitro, amino, C
1
-C
4
-alkylamino, C
1
-C
4
-dialkylamino, hydroxyl, C
1
-C
4
-alkyl, C
1
-C
4
-alkoxy or other radicals.
Alkyl and arylcarbonyl radicals which may be mentioned for R
2
, R
5
and R
6
are carbonyl groups with the abovementioned C
1
-C
12
-alkyl chains or the abovementioned aromatic rings or ring systems having 6 to 18 carbon atoms.
Suitable spacers A
1
to A
6
are all groups known for this purpose. The spacers generally contain from 1 to 30, preferably from 1 to 12, particularly preferably from 1 to 6, carbon atoms and consist of predominantly linear aliphatic groups. They may be interrupted in the chain, for example by non-adjacent oxygen or sulfur atoms or imino or alkylimino groups, for example methylimino groups. Suitable substituents for the spacer chain are fluorine, chlorine, bromine, cyano, methyl and ethyl.
Examples of representative spacers are the following:
—(CH
2
)
u
—, —(CH
2
CH
2
O)
v
CH
2
CH
2
—, —CH
2
CH
2
SCH
2
CH
2
—, —CH
2
CH
2
NHCH
2
CH
2
—,
 where u is from 1 to 12, and v is from 1 to 3.
Preferred spacers are ethylene, propylene, n-butylene, n-pentylene and n-hexylene.
It is furthermore also possible to link one or more of the mesogenic radicals M
1
to M
3
directly to the associated radicals Z
1
to Z
3
without spacers. In these cases, the indices m, o and q are 0, and Y
1
/Y
2
, Y
5
/Y
6
and Y
8
/Y
9
together are a chemical bond, in particular a single chemical bond.
The radicals M
1
to M
3
can be all known mesogenic groups.
Particularly suitable mesogenic groups are those of the formula
(—T—Y
17
)
w
—T—
in which the variables have the following meanings:
T are identical or different divalent, saturated or unsaturated, isocyclic or heterocyclic radicals,
Y
17
are groups as defined for Y
1
to Y
10
, and
w is 0, 1, 2 or 3,
where, in the case where w>0, both the radicals T and the groups Y
17
may in each case be identical to or different from one another.
w is preferably 1 or 2.
The radicals T may also be ring systems which are substituted by fluorine, chlorine, bromine, cyano, hydroxyl or nitro. Preferred radicals T are the following:
Examples of preferred mesogenic groups M are the following:
Particular preference is given to mesogenic groups M of the following formulae
where each aromatic ring may carry up to three identical or different substituents from the following group:
hydrogen, C
1
-C
20
-alky

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