Chiral compounds

Details Chiral compounds Chiral compounds

1999-10-04

2002-12-17

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C428S001200, C428S001300, C428S001500, C252S299610, C252S299650, C252S299640, C252S299660, C252S299670, C549S450000, C560S060000, C560S126000

Reexamination Certificate

active

06495217

ABSTRACT:

The invention relates to chiral compounds of formula I
wherein
Y
1
is —Y—R
3
and Y
2
is —Y—R
4
, or alternatively Y
1
and Y
2
form together the bivalent radical —CO— or —C(XR
3
)(XR
4
)—;
R
1
, R
2
, R
3
and R
4
are independently of each other H, CN, halogen, or an aromatic, aliphatic or araliphatic group with 1 to 50 C atoms;
X is in each case independently —O—, —S—, —CO—, —COO—, —OCO—, —OCO—O—, —CO—NH—, —NH—CO—, —OCH
2
—, —CH
2
O—, —CH═CH—, —C≡C, —SCH
2
—, —CH
2
S—, —CH═CH—COO—, —OOC—CH═CH— or a single bond; and
Y is in each case independently —CO—, —COO—, —CO— NH—, —CO— CH═CH— or a single bond.
The invention also relates to a liquid crystalline mixture containing at least one chiral compound of formula I.
The invention also relates to a polymerizable liquid crystalline mixture comprising at least one chiral compound of formula I and at least one polymerizable mesogenic compound.
The invention furthermore relates to the use of chiral compounds of formula I and liquid crystalline mixtures and polymers obtained thereof in liquid crystal displays, such as STN, TN, AMD-TN, temperature compensation, guest-host, phase change or surface stabilized or polymer stabilized cholesteric texture (SSCT, PSCT) displays, in active and passive optical elements like polarizers, compensators, alignment layers, color filters or holographic elements, in adhesive, synthetic resins with anisotropic mechanical properties, cosmetics, diagnostics, liquid crystal pigments, for decorative and security applications, in nonlinear optics, optical information storage or as chiral dopants,
The invention also relates to a liquid crystal display comprising a mixture comprising at least one chiral compound of formula I.
Chiral compounds can be used as dopants to induce or enhance a helical twist of the molecules of a liquid crystalline mixture that can be used for example in liquid crystal displays. 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):
p
=
1
HTP
·
1
C
(
1
)
The proportionality factor is the helical twisting power (HTP) of the chiral dopant.
For many applications it is desirable to have LC mixtures that exhibit a twist. Among these are, e.g., phase-change displays, guest-host displays, passive and active matrix TN and STN displays like AMD-TN, including such 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 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 crystalline mixtures that are used in selectively reflecting cholesteric displays, 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 are polymer films with a chiral liquid crystalline phase for optical elements, such as cholesteric broadband polarizers or chiral liquid crystalline retardation films.
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 crystalline host mixture, such as, e.g., the dielectric anisotrophy &Dgr;&egr;, the viscosity, the driving voltage or the switching times.
Thus, there is a considerable demand for chiral compounds with a high HTP which are easy to synthesize, which can be used in low amounts, show improved temperature stability of the cholesteric pitch, e.g., for utilizing a constant reflection wavelength and do not affect the properties of the liquid crystalline host mixture.
The invention has the aim of 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 poor of chiral compounds that can be used as dopants available to the expert.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
It has been found that these aims can be achieved by providing chiral compounds according to formula I.
The inventive chiral compounds bear several advantages. Thus, they contain a chiral structure element exhibiting two centers of chirality and thus exhibit a high twisting power. Also, enantiomerically pure compounds of formula I are easy to prepare from cheap, readily available starting materials. The preparation methods are also suitable for large scale production. Furthermore, it is possible to prepare the R,S and S,R enantiomers which can be used to produce a cholesteric phase with either a right or a left-handed helix. The availability of both helices can be a considerable advantage, e.g., for the use in security film applications.
The EP 0 441 213-B1 describes chiral compounds comprising a 1,3-dioxolane group attached in 2-position to a mesogenic group, but does not specifically disclose compounds of formula I of the present invention.
Thus, an object of this invention are chiral compounds of formula I
wherein
Y
1
is —Y—R
3
and Y
2
is —Y—R
4
, or alternatively Y
1
and Y
2
form together the bivalent radical —CO— or —C(XR
3
)(XR
4
)—,
R
1
, R
2
, R
3
and R
4
are independently of each other H, CN, halogen or an aromatic, aliphatic group with up to 50 C atoms;
X is in each case independently —O—, —S—, —CO—, —COO—, —OCO—, —OCO—O, —CO—NH—, —NH—CO—, —OCH
2
—, —CH
2
O—, —CH═CH—, —C═—C, —SCH
2
—, —CH
2
S—, —CH═CH—COO—, —OOC—CH═CH— or a single bond; and
Y is in each case independently —CO—, —COO—, —CO—NH—, —CO—CH═CH— or a single bond.
Another object of the invention is a liquid crystalline mixture containing at least one chiral compound of formula I.
Another object of the invention is a polymerizable liquid crystalline mixture comprising at least one chiral compound of formula I and at least one polymerizable mesogenic compound having at least one polymerizable functional group. Another object of the invention is a chiral linear or crosslinked crystalline polymer obtainable by polymerizing such a polymerizable mixture.
A further object of the invention is the use of a chiral compound, mixture or polymer as described above in liquid crystal displays, such as STN, TN, AMD-TN, temperature compensation, guest-host, phase change or surface stabilized or polymer stabilized cholesteric texture (SSCT, PSCT) displays, in active and passive optical elements like polarizers, compensators, alignment layers, color filters or holographic elements, in adhesives, synthetic resins with anisotropic mechanical properties, cosmetics, diagnostics, liquid crystal pigments, for decorative and security applications, in nonlinear optics, optical information storage or as chiral dopants.
Yet another object of the invention is a liquid crystal display comprising a liquid crystalline mixture or a polymerizable liquid crystalline mixture comprising at least one chiral compound of formula I.
The inventive chiral compounds can additionally be mesogenic or even liquid crystalline, i.e., they can induce or enhance mesophase behavior for example in admixture with other compounds, or even exhibit one or more mesophases themselves. It is also possible that the inv

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