Fluorinated naphthalene derivatives and their use in liquid...

Details Fluorinated naphthalene derivatives and their use in liquid... Fluorinated naphthalene derivatives and their use in liquid...

2000-07-10

2002-12-10

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299610, C252S299620, C544S303000, C544S334000, C544S335000, C546S339000, C546S346000, C570S183000, C570S187000, C570S188000

Reexamination Certificate

active

06491989

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application was filed pursuant to 35 U.S.C. 371 from international application no. PCT/EP98/06938, filed Mar. 11, 1998, which in turn claims priority to German Application Nos. 197 48 432.8, 197 48 440.9, 197 48 438.7 and 19748 435.2, all filed Nov. 3, 1997.
BACKGROUND OF THE INVENTION
Field of the Invention
In addition to nematic and cholesteric liquid crystals, chiral tilted smectic (ferroelectric) liquid crystals have also been used recently in commercial display devices.
BACKGROUND OF THE INVENTION
Clark and Lagerwall have been able to show that the use of ferroelectric liquid crystals (FLCs) in very thin cells results in opto-electrical switching or display elements which have response times which are faster by a factor of up to 1000 compared with conventional TN (“twisted nematic”) cells (see, for example, EP-A 0 032 362). On the basis of this and other favorable properties, for example the possibility of bistable switching and the fact that the viewing angle is virtually independent of the contrast, FLCs are fundamentally highly suitable for areas of application such as computer displays.
The use of FLCs in electro-optical or fully optical components requires either compounds which form tilted or orthogonal smectic phases and are themselves optically active, or the induction of ferroelectric smectic phases by doping compounds which, although forming such smectic phases, are not themselves optically active, with optically active compounds. The desired phase should be stable over the broadest possible temperature range.
In order to achieve good contrast in electro-optical components, a uniform planar alignment of the liquid crystals is necessary. Good alignment in the S
A
and S
C
phase can be achieved, for example, if the phase sequence of the liquid-crystal mixture is, with decreasing temperature:
isotropic→N*→S
A
→S*
C
The prerequisite is that the pitch of the helix in the N* phase is very large (greater than 10 &mgr;m) or, even better, is fully compensated (see, for example, T. Matsumoto et al, Proc. of the 6th Int. Display Research Conf., Japan Display, Sep. 30-Oct. 2, 1986, Tokyo, Japan, pp. 468-470; M. Murakami et al., ibid. pp. 344-347). This is achieved by mixing the chiral liquid-crystal mixture having, for example, a left-handed helix in the N* phase with one or more optically active dopants which induce a right-handed helix, in such amounts that the helix is compensated.
Use of Clark and Lagerwall's SSFLCD (surface-stabilized ferroelectric liquid-crystal display) effect for uniform, planar alignment furthermore requires that the pitch in the smectic C* phase is significantly greater than the thickness of the display element (Mol. Cryst. Liq. Cryst. 1983, 94, 213 and 1984, 114, 151).
The optical response time &tgr; [&mgr;s] of ferroelectric liquid-crystal systems, which should be as short as possible, depends on the rotational viscosity of the system &ggr; [mPas], the spontaneous polarization P
s
[nC/cm
2
] and the electric field strength E [V/m], in accordance with the equation
τ
∼
γ
P
s
·
E
Since the field strength E is determined by the electrode separation in the electro-optical component and by the applied voltage, the ferroelectric display medium must have low viscosity and high spontaneous polarization in order to achieve a short response time.
Finally, in addition to thermal, chemical and photochemical stability, a low optical anisotropy &Dgr;n and a low positive or preferably negative dielectric anisotropy &Dgr;&egr; are required (see, for example, S. T. Lagerwall et al., “Ferroelectric Liquid Crystals for Displays”, SID Symposium, October Meeting 1985, San Diego, Calif., USA).
The totality of these requirements can only be achieved by means of mixtures of a plurality of components. The base (or matrix) used preferably comprises compounds which if possible themselves already have the desired phase sequence I→N→S
A
→S
C
. Further components of the mixture are frequently added in order to lower the melting point and to broaden the S
C
and usually also the N phase, to induce optical activity, for pitch compensation and to match the optical and dielectric anisotropies; however, the rotational viscosity, for example, should if possible not be increased.
Ferroelectric liquid-crystal displays can also be operated by utilizing the DHF (distorted helix formation) effect or the PSFLCD effect (pitch-stabilized ferroelectric liquid-crystal display, also known as SBF=short pitch bistable ferroelectric effect). The DHF effect has been described by B. I. Ostrovski in Advances in Liquid Crystal Research and Applications, Oxford/Budapest, 1980, 469 ff., and the PSFLCD effect is described in DE-A 39 20 625 and EP-A 0 405 346. In contrast to the SSFLCD effect, utilization of these effects requires a liquid-crystalline material having a short S
C
pitch.
3,4-Difluorotetralin derivatives for use in liquid-crystal mixtures are disclosed, for example, in DE-A 19522145. Tetrafluorotetralin derivatives for use in liquid-crystal mixtures are disclosed, for example, in DE-A 19522152. Trifluoronaphthalene derivatives for use in liquid-crystal mixtures are disclosed, for example, in DE-A 19522195. Difluoronaphthalene derivatives for use in liquid-crystal mixtures are disclosed, for example, in DE-A 19522167.
However, since the development, in particular of ferroelectric liquid-crystal mixtures, can in no way be regarded as complete, the manufacturers of displays are interested in a very wide variety of components for mixtures. Another reason for this is that only the interaction of the liquid-crystalline mixtures with the individual components of the display device or of the cells (for example the alignment layer) allows conclusions to be drawn on the quality of the liquid-crystalline mixtures too.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention was therefore to provide novel compounds which, in liquid-crystalline mixtures, are suitable for improving the property profile of these mixtures.
Surprisingly, it has been found that fluorinated naphthalene derivatives of the formula (I) are particularly suitable for use in liquid-crystal mixtures. These are, in particular, 6,7difluoro-1,2,3,4-tetrahydronaphthalene derivatives, 1,1,6,7-tetrafluoro-1,2,3,4-tetrahydronaphthalene derivatives, 1,6,7-trifluoronaphthalene derivatives and 2,3-difluoronaphthalene derivatives of the formula (I).
DETAILED DESCRIPTION OF THE INVENTION
6,7-Difluoro-3,4-dihydro-2H-naphthalen-1-one is disclosed, for example, in Synth. Commun. 1991, 21, 981-7, but there is no mention therein of this molecule or its derivatives being suitable as part of a component of liquid-crystal mixtures.
The invention therefore relates to fluorinated naphthalene derivatives of the formula (I)
R
1
(—A
1
—M
1
)
a
(—A
2
—M
2
)
b
—B—(—M
3
—A
3
)
c
—(M
4
—A
4
)
d
—R
2
  (I)
where the symbols and indices are defined as follows:
group B is
 having the meaning
R
1
and R
2
are identical or different and are
a) hydrogen, —OCF
3
, —CF
3
, —CN, —F, —Cl, —OCHF
2
, —OCH
2
F, —CHF
2
or —CH
2
F
b) a straight-chain or branched alkyl radical (with or without an asymmetrical carbon atom) having 1 to 20 carbon atoms, where
b1) one or more non-adjacent and non-terminal —CH
2
— groups may be replaced by —O—, —S—, —CO—O—, —O—CO—, —O—CO—O— or —Si(CH
3
)
2
—, and/or
b2) one or more —CH
2
— groups may be replaced by —CH═CH—, —C≡C—, cyclopropane-1,2-diyl, 1,4-phenylene, 1,4-cyclohexylene or 1,3-cyclopentylene, and/or
b3) one or more H atoms may be replaced by F and/or Cl, and/or
b4) the terminal —CH
3
group may be replaced by one of the following chiral groups (optically active or racemic):
with the proviso that at most one of the radicals R
1
and R
2
is hydrogen, —OCF
3
, —CF
3
, —CN, —F, —Cl, —OCHF
2
, —OCH
2
F, —CHF
2
or —CH
2
F;
R
3
, R
4
, R
5
, R
6
and R
7
are identical or different and are
a) hydrogen
b) a straight-chain or branched alkyl rad

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