Dioxane derivatives, and liquid-crystalline medium

Details Dioxane derivatives, and liquid-crystalline medium Dioxane derivatives, and liquid-crystalline medium

2001-08-06

2003-09-16

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299610, C252S299630, C549S369000, C549S370000

Reexamination Certificate

active

06620468

ABSTRACT:

The invention relates to tetrafluoroethylene-bridged dioxane derivatives, to their use as components of liquid-crystalline media, and to liquid-crystal and electro-optical display elements which contain the liquid-crystalline media according to the invention.
The dioxane derivatives according to the invention can be used as components of liquid-crystalline media, in particular for displays based on the principle of the twisted cell, the guest-host effect, the effect of deformation of aligned phases DAP or ECB (electrically controlled birefringence), the IPS (in-plane switching) effect or the effect of dynamic scattering.
The substances employed hitherto for this purpose all have certain disadvantages, for example inadequate stability to the action of heat, light or electric fields, or unfavorable elastic and/or dielectric properties.
The invention has an object of finding novel stable liquid-crystalline or mesogenic compounds which are suitable as components of liquid-crystalline media, in particular for TN, STN, IPS and TFT displays.
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 now been found that tetrafluoroethylene-bridged dioxane derivatives according to the invention are eminently suitable as components of liquid-crystalline media. With their aid, stable liquid-crystalline media, particularly suitable for TFT or STN displays, can be obtained. The novel compounds are distinguished, in particular, by high thermal stability, which is advantageous for a high holding ratio, and exhibit favorable clearing point values.
Through a suitable choice of the ring members and/or the terminal substituents, the physical properties of the dioxane derivatives according to the invention can vary within broad ranges. Thus, it is possible, for example, to obtain dioxane derivatives according to the invention which have very small optical anisotropy values or have low positive to highly positive dielectric anisotropy values.
In particular, the dioxane derivatives according to the invention are distinguished by high clearing points at the same time as unexpectedly low rotational viscosity. Preferably, the clearing points are ≧65° C.
Liquid-crystalline media having very low optical anisotropy values are particularly suitable for reflective and transflective applications, i.e. applications in which the respective LCD experiences no or only supporting background illumination. Further, it is preferred that the media exhibit a mesophase range of at least 80° C., more preferably at least 90° C. and most preferably at least 100° C. Furthermore, preferred values for the optical anisotropy of the medium are ≦0.08, more preferably ≦0.07 and particularly ≦0.06.
The provision of the dioxane derivatives according to the invention very generally considerably broadens the range of liquid-crystalline substances which are suitable, from various applicational points of view, for the preparation of liquid-crystalline mixtures.
The dioxane derivatives according to the invention have a broad range of applications. Depending on the choice of substituents, these compounds can serve as base materials of which liquid-crystalline media are predominantly composed; however, it is also possible to add liquid-crystalline base materials from other classes of compound to the dioxane derivatives according to the invention in order, for example, to modify the dielectric and/or optical anisotropy of a dielectric of this type and/or to optimize its threshold voltage and/or its viscosity.
In the pure state, the dioxane derivatives according to the invention are colourless and form liquid-crystalline mesophases in a temperature range which is favorably located for electro-optical use. They are stable chemically, thermally and to light.
The invention thus relates to tetrafluoroethylene-bridged dioxane derivatives of the formula I
R
1
—(A
1
—Z
1
)
m
—A
2
—C
2
F
4
—A
3
—(Z
2
—A
4
)
n
—R
2
  I
in which
R
1
and R
2
, independently of one another, are H, —CN, —F, Cl, —OCN, —NCS, —NO
2
, or an alkyl radical having 1-12 carbon atoms which is unsubstituted or monosubstituted or polysubstituted by halogen, CN or CF
3
, and in which one or more CH
2
groups may each, independently of one another, be replaced by —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O—, —CH═CH—, —CH═CF—, —CF═CF—, —C≡C— or
 in such a way that S and/or O atoms are not linked directly to one another,
A
1
, A
2
, A
3
and A
4
, independently of one another, are
a) trans-1,4-cyclohexylene, in which, in addition, one or more non-adjacent CH
2
groups may be replaced by —O— and/or —S—,
b) 1,4-phenylene, in which, in addition, one or two CH groups may be replaced by N,
c) a radical from the group consisting of 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl, or
d) 1,4-cyclohexenylene,
in which the radicals a), b) and d) may also be substituted by CN or halogen,
and where at least one of the radicals A
1
, A
2
, A
3
and A
4
is 1,3-dioxane-2,5-diyl,
Z
1
and Z
2
are each, independently of one another, —O—, —CH
2
O—, —OCH
2
—, —CO—O—, —O—CO—, —CF
2
O—, —OCF
2
—, —CF
2
CF
2
—, —CH
2
CH
2
—, —CH═CH—, —CH═CF—, —CF═CF—, —C≡C— or a single bond, and
m and n, independently of one another, are 0, 1 or 2, where m+n is 0, 1 or 2.
The invention furthermore relates to the use of compounds of the formula I as components of liquid-crystalline media.
The invention furthermore relates to a liquid-crystalline medium having at least two liquid-crystalline components which comprises at least one compound of the formula I.
The invention furthermore relates to a liquid-crystal display element, in particular an electro-optical display element, which contains, as dielectric, a liquid-crystalline medium according to the invention.
Particular preference is given to reflective and transflective liquid-crystal display elements and other liquid-crystal displays having low birefringence &Dgr;n, so-called “low &Dgr;n mode displays”, such as, for example, reflective TN displays. Preference is furthermore given to IPS (“in plane switching”) mode liquid-crystal displays.
The meaning of the formula I covers all isotopes of the chemical elements bound in the compounds of the formula I. In enantiomerically pure or enriched form, the compounds of the formula I are also suitable as chiral dopants and in general for achieving chiral mesophases.
Above and below, n, m, R
1
, R
2
, A
1
, A
2
, A
3
, A
4
, Z
1
and Z
2
are as defined, unless expressly stated otherwise. If the radical A
1
occurs more than once, it may adopt identical or different meanings. The same applies to all other groups which occur more than once.
Particular preference is given to compounds of the formula I having two, three or four six-membered rings, in particular those which contain one or two 1,3-dioxane-2,5-diyl radicals.
Preference is furthermore given to compounds of the formula I which, besides the dioxane radicals, contain at least one, preferably one or more, trans-1,4-cyclohexylene radicals.
Preference is furthermore given to compounds of the formula I in which R
1
and R
2
are alkyl and alkoxy having 1 to 12 carbon atoms or alkenyl or alkenyloxy having 2 to 10 carbon atoms.
A
1
, A
2
1
A
3
and A
4
are preferably 1,3-dioxane-2,5-diyl, trans-cyclohexane-1,4-diyl or unsubstituted or substituted 1,4-phenylene.
Preference is given to compounds of the formula I in which n is 1 or 2, and A
4
is 1,4-phenylene which is monosubstituted or disubstituted by F or CN, in particular
and R
2
is F, Cl, CN or halogenated alkyl or alkoxy having 1 to 5 carbon atoms or halogenated alkenyl having 2 to 6 carbon atoms.
Z
1
and Z
2
are preferably —CH
2
CH
2
—, —CH═CH—, —C≡C—, —CF
2
CF
2
—, —CF═CF—, —CF
2
O—, —OCF
2
— or a single bond, in particular a single bond, —CH
2
—CH
2
— or —CF
2
CF
2
—.
Compounds of the formula I in which R
1
is strai

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