Chiral compounds

Details Chiral compounds Chiral compounds

2002-07-01

2004-04-20

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299610, C252S492000, C252S299200, C252S299700, C349S106000, C349S185000, C549S435000

Reexamination Certificate

active

06723395

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to chiral compounds with a high helical twisting power, to liquid crystal mixtures comprising them, and to chiral linear or crosslinked liquid crystal polymers obtained from a polymerizable mixture comprising one or more chiral compounds. The invention further relates to the use of the chiral compounds and the mixtures and polymers obtained thereof in liquid crystal displays, active and passive optical elements, adhesives, synthetic resins with anisotropic mechanical properties, cosmetic and pharmaceutical compositions, diagnostics, liquid crystal pigments, for decorative and security applications, nonlinear optics, optical information storage or as chiral dopants.
BACKGROUND AND PRIOR ART
For many applications it is desirable to have LC (Liquid Crystal) mixtures with a twisted phase. Among these are e.g. phase-change displays, guest-host displays, passive and active matrix TN and STN displays like AMD-TN, ferroelectric displays and cholesteric displays like SSCT (surface stabilized cholesteric texture) or PSCT (polymer stabilized cholesteric texture) displays, including displays with temperature compensated characteristics, e.g. by appropriate selection of the cholesteric compounds according to the invention either alone or in combination with further chiral dopants. For these applications it is advantageous to have available a chiral dopant with a high HTP (Helical Twisting Power) in order to reduce the amount of dopant needed to induce the desired pitch.
For some applications it is desired to have LC mixtures that exhibit a strong helical twist and thereby a short pitch length. For example in liquid crystal mixtures that are used in selectively reflecting cholesteric displays like SSCT or PSCT, the pitch has to be selected such that the maximum of the wavelength reflected by the cholesteric helix is in the range of visible light. Another possible application is in polymer films with a chiral liquid crystal phase for optical elements, such as cholesteric broadband polarizers or retardation films.
In a cholesteric LC material, the pitch p of the molecular helix in the first approximation, which is sufficient for most practical applications, is inversely proportional to the concentration c of the chiral dopant in the liquid crystal host mixture according to equation (1):
The proportionality factor is the helical twisting power (HTP) of the chiral dopant.
As can be seen from equation (1), a short pitch can be achieved by using high amounts of dopant or-by using a dopant with a high HTP. However, the chiral dopants of prior art often exhibit low values of the HTP, so that high amounts of dopant are needed. This is a disadvantage because chiral dopants can be used only as pure enantiomers and are therefore expensive and difficult to synthesize.
Furthermore, when using chiral dopants of prior art in high amounts, they often negatively affect the properties of the liquid crystal host mixture, e.g., the clearing point, the dielectric anisotropy AE, the viscosity, the driving voltage or the switching times.
The chiral dopants often show a high temperature dependence of the helical twisting power. When used in cholesteric mixtures this leads to a strong temperature dependence of the reflection wavelength of the mixture. This is especially disadvantageous for application in cholesteric displays, such as SSCT displays, where usually a low temperature dependence of the reflection wavelength is required.
Another disadvantage of prior art chiral compounds is that they often show low solubility in the liquid crystal host mixture, which leads to undesired crystallization at low temperatures. To overcome this disadvantage, typically two or more different chiral dopants have to be added to the host mixture. This implies higher costs and also requires additional effort for temperature compensation of the mixture because different dopants have to be selected such that their temperature coefficients of the twist compensate each other.
There is thus a considerable demand for chiral compounds with a high HTP which are easy to synthesize, can be used in low amounts, show low temperature dependence of the twisting power, e.g., for utilizing a constant reflection wavelength, do not affect the properties of the liquid crystal host mixture and show good solubility in the host mixture.
SUMMARY OF THE INVENTION
One of the first aims of the invention is providing chiral compounds having these properties, but which do not have the disadvantages of the chiral dopants of the state of the art as discussed above. Another aim of the invention is to extend the pool of chiral dopants available to the expert.
These aims and others can be achieved by providing chiral isosorbide derivatives as described below.
WO 95/16007 and WO 98/00428 disclose chiral mesogenic compounds with a high HTP based on 1,4:3,6-Dianhydro-D-sorbitol (isosorbide). However, many of these compounds do only have a limited solubility in liquid crystal host mixtures.
Chiral compounds derived from isosorbide
which are substituted unsymmetrically with two different mesogenic groups in the 2- and 5-position show a higher solubility in liquid crystal host mixtures compared to isosorbide derivatives that are substituted symmetrically with two identical mesogenic groups. Furthermore, the unsymmetrically substituted isosorbides show a remarkable difference in solubility depending on the respective position of the mesogenic groups. An isosorbide derivative with a larger mesogenic group, like a two-ring group, attached in 5-position and a smaller mesogenic group, like a one-ring group, attached in 2-position, for example, has a considerably higher solubility than its corresponding isomer where the two-ring group is attached in 2-position and the one-ring group in 5-position. This is a considerable unexpected improvement over the prior art.
One object of the present invention is chiral compounds of formula I
wherein
R
1
and R
2
are, independently of each other, P—Sp—X, F, Cl, Br, I, CN, SCN, SF
5
, or a straight chain or branched alkyl with up to 30 C atoms that is unsubstituted, mono- or poly-substituted by F, Cl, Br, I or CN, and wherein one or more non-adjacent CH
2
groups are optionally replaced, in each case independently from one another, by —O—, —S—, —NH—, —NR
0
—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —CH═CH— or —C≡C— in a manner that O and/or S atoms are not linked directly to one another,
R
0
is H or alkyl with 1 to 4 C atoms,
P is a polymerizable group,
Sp is a spacer group or a single bond,
X is —O—, —S—, —OCH
2
—, —CH
2
O—, —CO—, —COO—, —OCO—, —OCO—O—, —CO—NR
0
—, —NR
0
—CO—, —OCH
2
—, —CH
2
O—, —SCH
2
—, —CH
2
S—, —CH═CH—COO—, —OOC—CH═CH— or a single bond,
X
1
is—CO—, —OCO—, —NR
0
—CO—, —CH═CH—CO—, —CH
2
—, —C
2
H
4
—, —CF
2
— or a single bond,
X
2
is —CO—, —COO—, —CO—NR
0
—, —CO—CH═CH—, —CH
2
—, —C
2
H
4
—, —CF
2
— or a single bond,
Z
1
and Z
2
are independently of each other —O—, —S—, —CO—, —COO—, —OCO—, —O—COO—, —CO—NR
0
—, —NR
0
—CO—, —OCH
2
—, —CH
2
O—, —SCH
2
—, —CH
2
S—, —CF
2
O—, —OCF
2
—, —CF
2
S—, —SCF
2
—, —CH
2
CH
2
—, —CF
2
CH
2
—, —CH
2
CF
2
—, —CF
2
CF
2
—, —CH═N—, —N═CH—, —N═N—, —CH═CH—, —CF═CH—, —CH═CF—, —CF═CF—, —C≡C—, —CH═CH—COO—, —OCO—CH═CH— or a single bond,
A
1
and A
2
are, independently of each other, an aliphatic or aromatic carbocyclic or heterocyclic group with up to 16 C atoms that optionally contains one or more fused rings and is unsubstituted, mono- or polysubstituted with L,
L is halogen or a cyano, nitro, alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl group with 1 to 7 C atoms, wherein one or more H atoms are optionally substituted by F or Cl,
m
1
is 1, 2 or 3, and
m
2
is 0, 1, 2 or 3,
with the proviso that the total number of fused or unfused rings in the (Z
1
-A
1
)
m1
group is larger than in the (A
2
-Z
2
)
m2
group.
Another object of the invention is a liquid crystal mixture containing at least one compound of formula I.
Another object of the present inventi

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