Organic compounds -- part of the class 532-570 series – Organic compounds – Azo
Patent
1997-04-18
1998-08-04
Powers, Fiona T.
Organic compounds -- part of the class 532-570 series
Organic compounds
Azo
25229961, 25229962, 25229963, 25229966, 349182, C09B 3556, C09K 1912, C09K 1932, C09K 1934
Patent
active
057895562
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/JP96/02316 filed Aug. 20, 1996.
TECHNICAL FIELD
The present invention relates to a novel yellow dichroic azo dye, a liquid-crystal composition containing the same, and a liquid-crystal display element using the same.
BACKGROUND ART
Various display modes for liquid-crystal display elements have been proposed so far, besides the twisted nematic (TN) display mode, the super-twisted nematic (STN) mode, and the like. Among those, the guest-host (GH) display mode which employs a dye dissolved in a liquid crystal is currently widely used in automotive and other display panels because of characteristics thereof such as a wide viewing angle and brightness, and is receiving attention because of its suitability for, e.g., reflection type displays for use in portable information apparatus.
Dyes for use in the GH mode are required to be excellent in
Since dye dichroism or order parameter, among those properties, directly correlates with the display qualities, such as contrast, of guest-host liquid-crystal display elements, there has hitherto been required a guest-host type liquid-crystal composition having a high order parameter. In particular, a guest-host liquid-crystal composition having a high order parameter which comprises a new host liquid-crystal composition such as a fluorinated one and which can be used in active-matrix operation type LCDs and the like is recently required.
Azo dyes having a biphenyl framework are advantageous in that they have a high extinction coefficient (coloring power), and that since azo structures can be simultaneously incorporated respectively on both sides of the biphenyl framework, the cost of the production thereof is low and a dye having a large molecular length so as to be suitable for use with liquid crystals can be easily produced. In U.S. Pat. No. 4,610,803 there are shown various dichroic trisazo dyes including the dyes of the structures shown below, which are given therein in Examples 2 and 3, as specific examples of yellow dichroic dyes having an azo group on each side of a biphenyl framework. ##STR2## Example 3 ##STR3##
However, such azo dyes having a biphenyl framework have had considerable limitations on the production and use thereof because of the high toxicity (carcinogenicity and mutagenicity) of the benzidine compounds used as starting materials therefor.
On the other hand, guest-host liquid-crystal compositions each comprising a mixture of a host liquid crystal and a single dichroic dye have had a problem that because of the structure, etc., of the dichroic dye used, the order parameter thereof is not constant throughout the whole light absorption region and often decreases in a light absorption wavelength range apart from the main absorption wavelength (.lambda..sub.max) This problem has led to the phenomenon in which a guest-host liquid-crystal composition containing various dichroic dyes in combination so as to have hues such as black, brown and dark blue has a reduced order parameter in the wavelength spectral range where light absorption by the individual dichroic dyes overlaps, and the reduced order parameter renders the whole liquid-crystal composition to have insufficient contrast. Such a phenomenon is noticeable when dichroic azo dyes having a wide light absorption wavelength range are used. Because of this, a guest-host liquid-crystal composition having a high order parameter has been difficult to realize.
DISCLOSURE OF THE INVENTION
An object of the present invention is (1) to provide a dichroic dye which is reduced in the drawbacks described above and is excellent in structural safety and dichroism. Another object of the present invention is (2) to provide, using the dye, a guest-host liquid-crystal composition and a liquid-crystal display element, which have hues such as black, brown, dark blue, etc., and having a high order parameter throughout the whole light absorption wavelength range.
As a result of extensive studies made by the present inventors in view of subject (1) described above, they have found that
REFERENCES:
patent: 4519935 (1985-05-01), Claussen
patent: 4610803 (1986-09-01), Claussen
patent: 4770809 (1988-09-01), Heidenreich et al.
patent: 5536818 (1996-07-01), Kaneko et al.
Kadowaki Masami
Kaneko Masaharu
Yoneyama Tomio
Mitsubishi Chemical Corporation
Powers Fiona T.
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