2,3-difluorophenyl derivative having negative dielectric...

Details 2,3-difluorophenyl derivative having negative dielectric... 2,3-difluorophenyl derivative having negative dielectric...

2000-08-11

2003-04-15

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299610, C252S299630, C570S127000, C570S129000

Reexamination Certificate

active

06548126

ABSTRACT:

TECHNICAL FIELD
This invention relates to new liquid crystalline compounds and liquid crystal compositions. More specifically, this invention relates to the liquid crystalline compounds having difluoromethyleneoxy moiety, liquid crystal compositions comprising the compounds, and liquid crystal display devices fabricated by using the liquid crystal composition.
BACKGROUND ART
Liquid crystal display devices fabricated by using liquid crystalline compounds (the term “liquid crystalline compounds” is used in this specification as a generic term for the compounds which have a liquid crystal phase and the compounds which do not have a crystal phase but are useful as a component of liquid crystal compositions) have widely been used for the display of computers, television sets, and the like.
For the purpose of reducing electric power consumption and decreasing the leakage of an electromagnetic wave, the liquid crystal compositions are required to lower their driving voltage. The driving voltage (threshold voltage) is known to be a function of a dielectric anisotropy value and an elastic constant as is shown in the following equation (M. F. Leslie, Mol. Cryst. Liq. Cryst., 12, 57 (1970)):
Vth
=&pgr;(
K/∈
0
&Dgr;∈)
½
wherein Vth is threshold voltage, ∈
0
is a dielectric constant in vacuum, K is an elastic constant, and &Dgr;∈ is dielectric anisotropy.
That is, in order to lower the driving voltage, it is required 1) to increase the dielectric anisotropy value, and 2) to decrease the elastic constant. It is generally difficult to adjust the elastic constant value of the liquid crystalline compounds, and a method of enlarging the dielectric anisotropy value is principally employed for lowering the driving voltage. Accordingly, new liquid crystalline compounds having a large value of dielectric anisotropy have been expected.
From some time ago, a most serious problem on the liquid crystal display devices is a narrow viewing angle, and various display modes have been proposed in recent years for the purpose of improving it. In-plane switching (IPS) display devices proposed in 1995 greatly widened the viewing angle compared with conventional display devices (Liquid Crystal Conference in Japan 2A07 (1995), ASIA DISPLAY '95, 557(1995), and ASIA DISPLAY '95, 707 (1995)). The characteristic of this mode is that various liquid crystal compositions can be utilized regardless of positive or negative in the dielectric anisotropy value.
In 1997, an attempt utilizing a vertical alignment (VA) cell was reported (SID 97 DIGEST, 845 (1997) and the display devices of this mode has also considerably wide viewing angle compared with conventional display devices. The characteristic of this mode is that the liquid crystal compositions having a negative dielectric anisotropy value can be utilized.
As a compound having a negative and large dielectric anisotropy value and a comparatively small optical anisotropy value, compound (13) in the following has been known (V. Reiffenrath et al., Liq. Cryst., 5 (1), 159 (1989)). It is reported that the dielectric anisotropy value (&Dgr;∈) of this compound is −4.1 and the optical anisotropy value (&Dgr;n) is 0.18.
Whereas compound (13) has a large dielectric anisotropy value, an optical anisotropy value is large. Then, it could not satisfy the values required for IPS mode or VA mode.
According to Maier and Meier, a dielectric anisotropy value and an optical anisotropy value are regarded as a function of the order parameters (W. Maier and G. Meier, Z. Naturf. (a), 16, 262 (1961)). Namely, it is possible to decrease the optical anisotropy value by the decrease of the order parameters. As the optical anisotropy value and the dielectric anisotropy value are generally proportional in a single liquid crystal molecule, decreasing the optical anisotropy value will cause a decrease of the dielectric anisotropy value. Therefore, a new compound having a unique property which decreases only the optical anisotropy value without a large decrease of the dielectric anisotropy value has been expected.
Compound (14) having cyano has also been known as a compound having a small optical anisotropy value (R. Eidenschink et al., Angew. Chem., 96, 151 (1984)). It has both a large dielectric anisotropy value and a small optical anisotropy value. However, the liquid crystal compositions containing the compound for IPS mode and VA mode have considerably low contrast, as specific resistance is small and temperature dependence of a voltage holding ratio is very large. Thus, such compound is unsuitable as liquid crystalline compound in the use of the liquid crystal composition for IPS mode or VA mode.
DISCLOSURE OF INVENTION
In view of the several characteristics required for the liquid crystal compositions described above, the object of this invention is to provide liquid crystalline compounds having a negative and extremely large dielectric anisotropy value and a small optical anisotropy value at the same time, to provide liquid crystal compositions comprising the compound, and to provide liquid crystal display devices fabricated by using the liquid crystal composition.
As a result in the diligent research and development of the present inventors to solve the subject described above, they found that the compounds with two rings, three rings or four rings, having both a moiety in which two rings are bridged by —CF
2
O— bonding group and a moiety of 2,3-difluoro-1,4-phenylene at the same time, have not only a negative and large dielectric anisotropy value but also are excellent in miscibility with other compounds, have high specific resistance and a high voltage holding ratio, and are stable physically and chemically, and then they completed this invention.
SUMMARY OF INVENTION
Namely, this invention contains items [1] to [22].
[1] A liquid crystalline compound expressed by formula (1)
wherein Ra and Rb each independently represents a linear or branched alkyl having 1 to 10 carbon, any methylene in the alkyl may be replaced by —O—, —S—, —CH═CH—, or —C≡C—, but —O— is not successive, and any hydrogen in the alkyl may be replaced by halogen; rings A
1
to A
4
each independently represents trans-1,4-cyclohexylene, cyclohexene-1,4-diyl, pyridine-1,4-diyl, pyrimidine-2,5-diyl, or 1,4-phenylene, wherein at least one hydrogen in these rings may be replaced by halogen, and any nonadjacent methylene in cyclohexane ring may be replaced by —O—; Y
1
and Y
2
each independently represents F or Cl; Z
1
, Z
2
and Z
3
each independently represents a single bond, —CH
2
CH
2
—, —(CH
2
)
4
—, —COO—, —OCO—, —CH
2
O—, —OCH
2
—, —CF
2
O—, or —OCF
2
—; and l, m and n each independently is 0, 1 or 2, and the sum of l+m+n is 3 and less.
[2] A liquid crystalline compound described in item [1], wherein in formula (1), Y
1
and Y
2
are fluorine.
[3] A liquid crystalline compound described in item [1], wherein in formula (1), Y
1
and Y
2
are fluorine and ring A
2
is trans-1,4-cyclohexylene.
[4] A liquid crystalline compound described in item [1], wherein in formula (1), Y
1
and Y
2
are fluorine and ring A
2
is cyclohexene-1,4-diyl.
[5] A liquid crystalline compound described in item [1], wherein in formula (1), Y
1
and Y
2
are fluorine and ring A
2
is 1,4-phenylene in which hydrogen in the ring may be replaced by fluorine.
[6] A liquid crystalline compound described in item [1], wherein, in formula (1), l=1, m=n=0, ring A
1
and ring A
2
are trans-1,4-cyclohexylene, Z
1
is a single bond, and Y
1
and Y
2
are fluorine.
[7] A liquid crystalline compound described in item [1], wherein in formula (1), l=1, m=n=0, ring A
1
is trans-1,4-cyclohexylene, and ring A
2
is cyclohexene-1,4-diyl, Z
1
is a single bond, and Y
1
and Y
2
are fluorine.
[8] A liquid crystalline compound described in item [1], wherein in formula (1), l&equals

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