Chiral dopants

Details Chiral dopants Chiral dopants

1998-12-30

2001-04-17

Kelly, C. H. (Department: 1743)

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

C428S001100

Reexamination Certificate

active

06217792

ABSTRACT:

The invention relates to chiral dopants of formula I
R
1
—X
1
—MG
1
—G—MG
2
—X
2
—R
2
  I
wherein
R
1
and R
2
are independently of each other a straight-chain or branched alkyl radical with up to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH
2
groups to be replaced, in each case independently from one another, by —O—, —S—, —NH—, —N(CH
3
)—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S— or —C≡C— in such a manner that oxygen atoms are not linked directly to one another,
X
1
and X
2
are independently of each other —O—, —S—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S— or a single bond,
G is the following chiral bivalent structure element
and
MG
1
and MG
2
are each independently a mesogenic or mesogenity supporting group of formula II
—(A
1
—A)
m
—A
2
—  II
with
Z denoting —COO—, —OCO—, —CH
2
CH
2
—, —OCH
2
—, —CH
2
O—, —CH═CH—, —CH═CH—COO—, —OCO—CH═CH—, —C≡C— or a single bond,
A
1
and A
2
being each independently 1,4-phenylene in which, in addition, one or more CH groups may be replaced by N, 1,4-cyclohexylene in which, in addition, one or two non-adjacent CH
2
groups may be replaced by O and/or S, 1,4-cyclohexenylene, 1,4-bicyclo(2,2,2)octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, or 1,2,3,4-tetrahydronaphthalene-2,6-diyl, it being possible for all these groups to be unsubstituted, mono- or polysubstituted with halogen, cyano or nitro groups or alkyl, alkoxy or alkanoyl groups having 1 to 7 C atoms wherein one or more H atoms may be substituted by F or Cl, and
m being 0, 1, 2 or 3.
The invention also relates to a liquid crystalline material comprising at least one chiral dopant of formula I and optionally at least one polymerizable mesogenic compound.
The invention furthermore relates to the use of such a liquid crystalline material for the preparation of polymer films with a chiral liquid crystalline phase, for active and passive optical elements or colour filters and for liquid crystal displays, for example STN, TN, AMD-TN, temperature compensation, guest-host or phase change displays, or polymer free or polymer stabilized cholesteric texture (PFCT, PSCT) displays.
The invention also relates to liquid crystal displays comprising a liquid crystalline material comprising at least one chiral dopant of formula I and to polymer films with a chiral liquid crystalline phase obtainable by (co)polymerizing a liquid crystalline material comprising at least one chiral dopant of formula I and at least one polymerizable mesogenic compound.
Chiral dopants are used to induce or enhance a helical twist of the molecules of a liquid crystalline medium 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 inverse 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 dopants 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, as chiral dopants can be used only as pure enantiomers, they are expensive and difficult to synthesize.
Further and in many cases even more important, 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 anisotropy &Dgr;&egr;, the viscosity, the driving voltage or the switching times.
There is thus a considerable demand for chiral dopants 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 object of providing chiral dopants having these properties, but which do not have the disadvantages of the dopants of the state of the art as discussed above.
It has been found that this object can be achieved by the provision of chiral dopants according to formula I.
The inventive chiral dopants contain a chiral structure element based on 1,4:3,6-Dianhydro-D-sorbitol, which is economically and easily available from sugars as natural source.
Chiral polymerizable mesogenic compounds comprising 1,4:3,6-Dianhydro-D-sorbitol as structure element are disclosed in WO 95/16007.
G. Wulff et al. in Makromolekulare Chemie, 188 (4), 731-40 (1987) describe non-mesogenic 1,4:3,6-Dianhydro-D-sorbitol-2,5-dimethacrylate used as chiral crosslinking agent for template-imprinted vinyl and acrylic polymers.
However the compounds described in WO 95/16007 and by G. Wulff et al. are reactive and consequently not sufficiently stable for most applications.
Thus the object of this invention are chiral dopants of formula I
R
1
—X
1
—MG
1
—G—MG
2
—X
2
—R
2
  I
wherein
R
1
and R
2
are each independently a straight-chain or branched alkyl radical with up to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH
2
groups to be replaced, in each case independently from one another, by —O—, —S—, —NH—, —N(CH
3
)—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S— or —C≡C— in such a manner that oxygen atoms are not linked directly to one another,
X
1
and X
2
are independently of each other —O—, —S—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S— or a single bond,
G is the following chiral bivalent structure element
MG
1
and MG
2
are each independently a mesogenic or mesogenity supporting group of the formula II
—(A
1
—Z)
m
—Z
2
—  II
with
Z denoting —COO—, —OCO—, —CH
2
CH
2
—, —OCH
2
—, —CH
2
O—, —CH═CH—, —CH═CH—COO—, —OCO—CH═CH—, —C≡C— or a single bond,
A
1
and A
2
being each independently 1,4-phenylene in which, in addition, one or more CH groups may be replaced by N, 1,4-cyclohexylene in which, in addition, one or two non-adjacent CH
2
groups may be replaced by O and/or S, 1,4-cyclohexenylene, 1,4-bicyclo(2,2,2)octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, or 1,2,3,4-tetrahydronaphthalene-2,6-diyl, it being possible for all these groups to be unsubstituted, mono- or polysubstituted with halogen, cyano or nitro groups or alkyl, alkoxy or alkanoyl groups having 1 to 7 C atoms wherein one or more H atoms may be substituted by F or Cl, and
m being 0, 1, 2 or 3.
Another object of the invention is a liquid crystalline material comprising at least one chiral dopant of formula I

Affiliated with

Also associated with

Rating

Chiral dopants does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Chiral dopants, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Chiral dopants will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2479026