Dichroic azo dyestuffs and liquid crystal composition containing

Details Dichroic azo dyestuffs and liquid crystal composition containing Dichroic azo dyestuffs and liquid crystal composition containing

1986-07-18

1988-03-29

Higel, Floyd D.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

2522991, 25229962, 25229966, 534577, 534595, 534596, 534738, 534796, 534797, 534800, 534810, 534813, 534829, 534832, 534860, 534875, 350349, C09B 3102, C09B 3116, C09K 334, G02F 113

Patent

active

047342188

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
This invention relates to novel dichroic dyestuffs suitable for use in liquid crystals and liquid crystal compositions containing the above dyestuffs as well as display devices making use of these compositions.
2. Background Art
Liquid crystal display devices have found wide-spread commercial utility in recent years from the viewpoints of energy saving and size reduction. Most of liquid crystal display devices, which are currently in use, utilize electrooptical effects of twisted nematic liquid crystals and perform display operations with combined use of two polarizing films as essential conditions. Under the circumstances, numerous limitations are however imposed upon their applications. As a possible alternative liquid crystal display system, investigations have been made on so-called guest-host type liquid crystal displays each of which makes use of electrooptical effects of a colored liquid crystal composition obtained by dissolving a dichroic dyestuff in a nematic liquid crystal. Some of such liquid crystal displays have already been used as display devices in watches, clocks, electrical home appliances, inductrial meters, etc.
The principle of the guest-host type liquid crystal display system relies upon the phenomenon that molecules of a dichroic dyestuff as a guest tend to orient in accordance with the arrangement of molecules of a liquid crystal as a host. Namely, upon application of an external stimulus which is usually an electric field, the molecules of the liquid crystal change the direction of their orientation from the "off" state to the "on state" and at the same time, the molecules of the dichroic dyestuff vary the direction of their orientation. As a result, the degree of absorption of light by the molecules of the dyestuff in the former state becomes different from that in the latter state so that a display is performed. The guest-host type liquid crystal display system is based on this principle.
The dichroic dyestuff useful here is basically required to satisfy the following requirements: (1) to have sufficient color strength even at a low concentration; (2) to have a large dichroic ratio and to exhibit significant contrast by application and removal of a voltage; (3) to have sufficient solubility to the associated liquid crystal; (4) to have excellent durability and stability and to be free from deteriorating the performance of the device even when used over a long period of time; etc.
Various dichroic dyestuffs have been proposed as materials which fulfill the above-described requirements. Some of such dichroic dyestuffs have already been used in digital clocks, meters and so on. Under the circumstances, many of them are however still accompanied by drawbacks which should still be improved, that is, those having large dichroic ratios have poor durability or those excellent in durability are not equipped with such a dichroic ratio as enabling vivid display of practical utility.


DISCLOSURE OF THE INVENTION

With the foregoing in view, the present inventors have carried out an extensive investigation. As a result, novel dichroic dyestuffs having large dichroic ratios and excellent durability have now been found.
Namely, the present invention provides a novel dichroic azo dyestuff represented by the following general formula (I): ##STR2## wherein A means --CN, --COOR.sub.1, ##STR3## R.sub.1 is an alkyl group, alkoxyalkyl group, or a phenyl or cyclohexyl group which may be substituted with an alkyl or alkoxy group at the p-position thereof, R.sub.2 and R.sub.3 are individually a hydrogen atom, alkyl, cycloalkyl, alkoxy, alkoxyalkoxy, cycloalkyloxyalkoxy, aryloxyalkoxy or aryl group, halogen atom, or cyano or dialkylamino group; Y.sub.1 and Y.sub.2 denote individually a hydrogen or halogen atom or an alkyl, alkoxy, cyano or hydroxyl group, Ar.sub.1 and Ar.sub.2 stand individually for ##STR4## W.sub.1 and W.sub.2 are individually an --N.dbd.N-- or --N.dbd.CH-- group but W.sub.1 is an --N.dbd.N-- group when W.sub.2 is an --N.dbd.CH-- group, m stands for an i

REFERENCES:
patent: 1858928 (1932-05-01), Grether et al.
patent: 2397927 (1946-04-01), Dickey et al.
patent: 2620273 (1952-12-01), Jennen
patent: 4600527 (1986-07-01), Imazeki et al.
patent: 4610803 (1986-09-01), Claussen

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