GB2120674A

GB2120674A - Dichroic dyestuffs for liquid crystals and liquid crystal compositions comprising the same

Info

Publication number: GB2120674A
Application number: GB08306968A
Authority: GB
Inventors: Shigeo Yasui; Masashi Ono; Seiko Kobayashi; Shigeo Senzai; Tatsuo Uchida
Original assignee: Nippon Kanko Shikiso Kenkyusho KK
Current assignee: Nippon Kanko Shikiso Kenkyusho KK
Priority date: 1982-03-13
Filing date: 1983-03-14
Publication date: 1983-12-07
Also published as: GB8306968D0; FR2523147A1; FR2523147B1; DE3309045A1; DE3309045C2; GB2120674B

Abstract

Novel dichroic dyestuffs for use in liquid crystals are given increased dichroic ratio by inclusion at terminal positions of dichroic dyestuffs of lower dichroic ratio of groups selected from phenyl, cyclohexyl, phenylcarbonyloxy, phenyloxycarbonyl, cyclohexanecarbonyloxy and cyclohexanoxycarbonyl.

Description

SPECIFICATION Dichroic dyestuffs for liquid crystals and liquid crystal compositions comprising the same This invention relates to dichroic dyestuffs for use in guest-host type liquid crystals and to liquid crystal compositions containing these dyestuffs.

A dichroic dyestuff is an essential and indispensible material in colour displays using liquid crystals of guest-host type, and the superiority of a material for colour display of this kind completely depends upon characteristics of the dyestuff used. For this reason, extensive research and development have been carried out in respect of dichroic dyestuffs; as a result, dyestuffs which have appeared to be commercially acceptable have been proposed or developed. Typical examples of such dyestuffs include anthraquinone dyestuffs as disclosed in Japanese Patent Applications Laid-Open Nos. 1 55054/1 980, 32578/1981, 62873/1981 etc., and azo dyestuffs as disclosed in Japanese Patent Applications Laid Open Nos. 57850/1981, 104984/1981, etc.

Investigative and development work has been carried out on materials for colour display of guesthost type from a variety of viewpoints in attempting to put these dyestuffs into practical use. Of considerable concern is the need to ensure both the effectiveness of the display and its adherence to fashion trends in colours for such displays. In contrast to conventional colour display techniques and techniques similar thereto which have already been put into practical use, however, such materials are often inferior to conventional elements and require further improvements particularly in display characteristics.

Furthermore, display elements of this type may belong to various operating modes or systems. For example, with one operating mode one or two polarizing plates are employed. With another operating mode, of the so-called White-Taylor system, no polarizing plate is employed. The operating mode in which no polarizing plate is employed is generally inferior to the operating mode using a polarizing plate(s) when using the same dyestuff in each operating mode, particularly in contrast and appearance.

Thus, further improvements in display characteristics are required in this area.

If display characteristics are to be improved, it is generally necessary to improve the dichroism of existing dyestuffs, to adopt dyestuffs having improved dichroism or to use dyestuffs having a greater dichroic ratio. Accordingly, there is a general need to develop dyestuffs having more improved dichroism.

According to the present invention, there is provided a dichroic dyestuff of the general formula R-(A)1-Z-R1 (I) wherein: R denotes a cyclohexa necarbonyloxy, cyclohexaneoxycarbonyl, phenylcarbonyloxy or phenyloxycarbonyl group, or a group of formula:

wherein R' denotes hydrogen, alkyl, alkoxy, nitro, cyano, trihalomethyl, halogen; sulphonyl substituted by alkyl, dialkylamino, trihalomethyl or halogen; alkylcarbonyloxy, alkyloxycarbonyl or alkyloxycarbonyloxy; or carbonyloxy, oxycarbonyloxy or oxycarbonyl connected to a phenyl, biphenyl, cyclohhexyl- phenyl or cyclohexylcyclohexyl group; B denotes saturation or unsaturation of the ring with which it is associated; and m is O or an integer; and in which the moiety OCO- in a group

may alternatively be carbonyloxy or oxycarbonyl; A denotes

i is O or 1 ; R, denotes hydrogen, alkyl, alkoxy, cyano, nitro, trihalomethyl, sulphonyl substituted by alkyl, dialkylamino or halogen, or has a meaning attributable to R or R-A already defined; or denotes phenyl or cyclohexyl, mono- or dialkylamino, nitro, cyano, alkylsulphonyl, trihalomethyl, halogen, alkyloxycarbonyloxy, alkyloxycarbonyl, alkylcarbonyloxy, cycloalkyl, pyrrolidino, or julolidno; or a group of formula

wherein R', B and m are as already defined; and Z denotes a divalent group selected from

wherein Ar denotes

n is O or an integer of from 1 to 4; R2 and R3 which may be the same or different are hydroxy, free amino or monoalkylamino; R4 and R5 which may be the same or different are hydrogen, hydroxy, free amino or monoalkylamino; R6 is hydroxy, free amino or monoalkylamino; R7 to R9 which may be the same or different are hydrogen, hydroxy, nitro, free amino, or monoalkylamino; R10 is hydroxy, free amino or monoalkylamino; R" to R,3 which may be the same or different are hydrogen, hydroxy, free amino or monoalkylamino; and X is a heteroatom; in which diva lent group (i) any one of the benzene rings may be fused at any two adjacent positions thereof to a benzene ring to form a naphthalene ring.

This invention is based on the discovery that dyestuffs having excellent dichroism are obtained by introducing a specific group into a phenyl group or a cyclohexyl group, which is positioned at a terminal position in the molecule of a dyestuff which is itself dichroic. These groups are specifically a phenyl group, a cyclohexyl group, a phenylcarbonyloxy group, a phenyloxycarbonyl group, a cyclohexanecarbonyloxy group or a cyclohexanoxycarbonyl group which is introduced into a phenyl group or a cyclohexyl group at the 4-position thereof to produce terminal substitution in the dyestuff molecule, i.e. substitution in line with the major axis of the dyestuff molecule.

The term "phenyl group located at a terminal position of the dichroic dyestuff molecule" as used herein includes phenyl groups having a fused phenyl group (e.g. to produce a naphthyl group) at the 2and 3-positions or the 4- and 5-positions thereof.

The phenyl, cyclohexyl, phenylcarbonyloxy, phenyloxycarbonyl, cyclohexanecarbonyloxy or cyclohexaneoxycarbonyl group to be introduced at the 4-position of a terminal phenyl group or cyclohexyl group of a dichroic dyestuff is hereafter often referred to merely as either "the specific group", or as a "dichroism-improving specific group" and may also be substituted with substituents to be later described at the 4-position thereof.

More particularly, the group R is optionally substituted in the 4-position by alkyl, alkoxy or halogen or by phenyl or cyclohexyl in turn optionally substituted at the 4-position by alkyl, alkoxy, alkylca rbonyloxy, alkyloxyca rbonyl or a Ikyloxycarbonyloxy.

Moreover, a phenyl, biphenyl, cyclohexylphenyl or cyclohexylcyclohexyl group connected to a carbonyloxy, oxycarbonyloxy or oxycarbonyl group R' is preferably substituted by alkyl, alkoxy or halogen or by phenyl or cyclohexyl optionally substituted in the 4-position by alkyl, alkoxy, alkylcarbonyloxy, alkyloxycarbonyl or alkyloxycarbonyloxy.

R, preferably denotes phenyl or cyclohexyl substituted at its 4-position by alkyl, alkoxy, alkylcarbonyloxy, alkyloxycarbonyl, alkylcarbonyloxy or 4-alkyl or -alkoxy substituted phenyl or cyclohexyl.

It is possible for any benzene ring of a said divalent group (I) to be substituted by methyl, trifluoromethyl, chlorine, fluorine or hydroxy.

Any cyclohexyl group present in any one of the aforesaid groups is preferably in the trans form.

In the above general formula (I), "alkyl" or "alkoxy" denotes an alkyl or alkoxy group constituting a group R' or part of a group R, R, or R' or a substituent of a group R, R1 or R' is linear and contains from 1 to 12 carbon atoms. It is also preferred that an alkyl group forming part of a monoalkylamino group is linear and contains 1 to 5 carbon atoms more preferably 1 to 2 carbon atoms.

Thus, overall the preferred substituent R is cyclohexanecarbonyloxy or a phenylcarbonyloxy which may be substituted by linear C,~12 alkyl or alkoxy; halogen; linear C,~,2 alkylcarbonyloxy, alkyloxycarbonyloxy or alkyloxycarbonyl; or 4-linear C,~,2 alkyl or alkoxy substituted or unsubstituted phenyl or cyclohexyl; or

(wherein R' is hydrogen; a linear 1-12 alkyl or alkoxy a halogen; a linear C,~12 alkylcarbonyloxy, alkyloxycarbonyl or alkyloxycarbonyloxy; a carbonyloxy, oxycarbonyl or oxycarbonyloxy having a phenyl, a biohenyl, a cyclohexylphenyl or cyclohexylcyclohexyl which may be unsubstituted or substituted with a substituent mentioned above; or a said substituent of the carbonyloxy, the oxycarbonyl or the oxycarbonyloxy;B has the same meaning as defined above and m is O or an integer of 1 to 5.

The preferred substituent, R, is hydrogen; a linear C,~,2 alkyl or alkoxy; R or R-A having said preferred substituent; a phenyl or cyclohexyl unsubstituted or substituted, at its 4-position, by a linear C112 alkyl or alkoxy, a linear C1~12 alkylcarbonyloxy, alkyloxycarbonyl or alkyloxycarbonyloxy, or a 4linear C112 alkyl or alkoxy substituted phenyl or cyclohexyl; a halogen; a linear C;1-12 alkyloxycarbonyl, alkylcarbonyloxy or alkyloxycarbonyloxy; mono- or di-C112 alkylamino; pyrrolidino; julolidino; or, as a said preferred substituent,

defined above (wherein R', B and m has the same meaning as before).

The preferred dichroic dyestuffs of this invention are as follows:

wherein R" is a cyclohexanecarbonyloxy group optionally substituted at its 4-position, by linear C;1-12 alkyl or alkoxyi; a phenyl or cyclohexyl optionally substituted at the 4-position, linear C,~,2 alkyl or alkoxy, or a said substituent

wherein R' and m are defined as previously; R', is hydrogen; mono- or di-linear C,~12 alkylamino; has one of the meanings given for R" with m being 0 or an integer of 1 to 3; linear C,~,2 alkyl or alkoxy; phenyl or cyclohexyl unsubstituted or substituted at the 4-position by linear C,~,2 alkyl, alkoxy, alkyloxycarbonyl, alkylcarbonyloxy or alkyloxycarbonyloxy or 4-linear C,~,2 alkyl or alkoxy substituted phenyl or cyclohexyl; mono- or di-linear C1-12 alkylamino, pyrrolidino or julolidino;

wherein R2 to R5 have the same means as defined above and ~1 is 4-R"-phenyl, 4-R"-cyclohexyl, 4'-R"- biphenyl or 4'-R"-cyclohexylbiphenyl (R" is as defined above); or 4-linear C1~,2 alkyl- or alkoxysubstituted phenyl, cyclohexyl, biphenyl or cyclohexylphenyl;

wherein R" and R6 to R9 are as defined above and Y is hydrogen, a phenyl unsubstituted or substituted by linear C,~12 alkyl or alkoxy or mono- or di-linear C1-12 alkylamino;

wherein 1 and R10 to R13 are as defined above, and X is O or S; and

wherein gi1 is as already defined above and 2 is linear C;1-12 alkyl, has one of the meanings given for 1 or is a 4-substituted-phenyl or cyclohexyl in which the substituent is selected from a linear C1-12 alkyl or alkoxy, mono- or di-linear C1-12 alkylamino or 4-linear C1-12 alkyl or alkoxy substituted phenyl or cyclohexyl.

Dyestuffs of general formula (II) above include compounds in which any one of the benzene rings is fused at two positions thereof to a benzene ring to form a naphthalene structure and/or compounds in which one of the benzene rings is substituted at any one position with a methyl group, methoxy group a trifluoromethyl group, a chlorine atom, a fluorine atom or a hydroxy group.

In addition to the dyestuffs described above, azo dyes containing an azomethine group or a styryl group as a part of the molecule thereof, thioindigo dyestuffs as described in Japanese Patent Application Laid-Open No. 123678/1980 and quinophthalone dyestuffs as described in Japanese Patent Application Laid-Open No. 41288/1981, can form a basis for substitution to produce compounds of the present invention.

To introduce a 4-substituted cyclohexanecarbonyloxy group or cyclohexaneoxycarbonyl group at the 4-position of a phenyl group or a cyclohexyl group located at the terminal position of the backbone of a dichroic dyestuff to produce liquid crystals of the invention, the following processes are applicable.

For example, a dyestuff precursor containing a phenyl group or a cyclohexyl group having a hydroxy group at the 4-position thereof is reacted with a 4-substituted cyclohexanecarbonyl halide in an inert solvent; in the case of azo dyestuffs, their production will comprise firstly preparing an aniline having at the 4-position thereof a 4-substituted cyclohexanecarbonyloxy group (hereafter referred to as "aniline derivative") and then repeating diazotization and coupling using such an aniline derivative.

Furthermore the introduction of a phenyl group, a cyclohexyl group or a phenylcarbonyloxy or phenyloxycarbonyl group can be effected in accordance with known processes as described in Japaneses Patent Applications Laid-Open Nos. 57850/1981, 104984/1981, 2885/1977, etc. The introduction of a phenylcarbonyloxy or phenyloxycarbonyl group can also be effected by ester formation carried out using a precursor of the final product having a hydroxy group, a carboxy group or a carbonyl halide and a compound necessary for forming an ester bond.

To produce the dyestuffs of general formulae (III) to (VI), the dichroism-improving specific group can be introduced by reacting aniline derivatives with the corresponding acid anhydride in an inert solvent.

The dyestuffs into which the specific group is introduced at the 4-position of the terminal phenyl or cyclohexyl group of the backbone thereof may be purified to a high degree of purity by column chromatography, recrystallization, sublimation, or other methods to render them ready for practical use.

As indicated above, the terminal phenyl group may include a phenyl group in a fused structure such as a naphthyl group. Furthermore, the terminal phenyl or cyclohexyl group can also be part of a biphenyl group, a terphenyl group, a cyclohexylphenyl group, etc. As mentioned herein in discussing the problems of dichroism and guest-host type display systems, to enable dyestuffs to be put to practical use in guest-host type display elements, it is extremely important to develop dyestuffs having improved dichroism. Investigations carried out prior to this invention have shown that when transferring interest in azo dyes from mono-azo dyestuffs to higher azo dyestuffs, the number of azo groups researched for practical use increased to two and then three azo groups. However the synthesis of azo dyes becomes more complicated with increased azo groups.It also becomes more difficult to develop dyestuffs having good characteristics, coupled with other characteristics. There is a fear that dyestuffs having tetrakis or more azo groups might be impractical from viewpoints of complicated Steps and procedures in preparation, unsatisfactory properties, e.g., poor solubility, etc. With the dyes of the present invention, a dichroic ratio can easily be improved by about 1 or 2, as will be later shown in the examples, which is equal to the effect achieved by increasing one azo group, without the need for azo groups to be present or with their number kept at a low level.

Dyestuffs which have been thought to be most useful for practical use are those as described in Japanese Patent Applications Laid-Open Nos.1 55054/1980 (corresponding to Comparative Dyestuff 3 herein) and 32578/1981. Many dyestuffs are disclosed in the latter but the dichroic ratio is 10 at best (which corresponds to an order parameter of 0.75). Moreover, it is necessary for dyestuffs showing such a dichroic ratio to contain two phenyl groups introduced to the anthraquinone skeleton at both the 2and 6-position thereof. This gives rise to various problems from the viewpoints of synthesis, yield, characteristics of dyestuffs such as solubility, etc. and practical use. Most anthraquinone dyestuffs have a dichroic ratio of from 7 to 9 at best and an improvement in their dichroism is a desirable thing.

According to the present invention, the dichroic ratio can easily be improved by more than 1 or 2 without attendant problems as aforesaid. Similar effects can be exhibited also in dyestuffs of other types.

As described above, the present invention is characterised by introducing the dichroism-improving specific group to the 4-position of a terminal phenyl or cyclohexyl group in the main chain or skeleton of the dyestuff. This is a new departure in dyestuffs and is beneficial in relation to the colour display of liquid crystals containing them.

The use of such dyestuffs enables the display quality of guest-host type liquid crystals to be markedly improved and enhanced to enable such crystals to find ready practical use. Furthermore, the display properties can be much improved in some technical areas already in practical use by employing the novel dyes.

Thus the present invention also provides new liquid crystal compositions which comprise a dyestuff of this invention as guest and a liquid crystal as host. Such composition may simply be prepared by mixing a dyestuff of the invention and any convenient liquid crystal which may be used as the host. Such liquid crystals includes biphenyl liquid crystals such as biphenyl liquid crystal GR41 (manufactured and sold by Chisso Co., Ltd.), Shiff bases, biphenyls, azo, cyclohexylcyclohexanes, phenylcyclohexanes and ester liquid crystals.

Taking the structure of dyestuffs into consideration, the dyestuffs of the invention are particularly suited for use with cyclohexane ring containing liquid crystals and ester liquid crystals. The liquid crystal system may be nematic, cholestericnematic phase transition type or smectic.

The dichroic dyestuff is preferably used in an amount of 0.01 to 20% by weight of the host liquid crystal, more preferably 0.1 to 5% by weight. The choice of the dyestuff will depend on use requirements, the method for display and in particular, the kind of host liquid crystal to be used.

The dyestuffs of this invention may be used individually or as as mixture of two or more of them in the liquid crystal composition and they may be used in combination with other dyestuffs free of dichroism, optically active materials and/or other additives.

As to the display method, the dyestuffs of this invention may be used in any method which is based on the positive and negative facets of the dielectric anistropy of liquid crystals.

The following preparative examples illustrate the preparation of the dyestuffs of this invention.

EXAMPLE 1 Dyestuff 1:

2.2 g of 1 -amino-4-[4-(4-pentylcyclohexanecarbonyloxy)phenylazo] naphthalene were dissolved in 8 ml of dimethylformamide. After a 1 8% aqueous hydrochloric acid solution had been poured into the solution, the resulting mixture was thoroughly stirred. While the mixture had cooled to O to -50C, 0.34 g of sodium nitrate and 1.3 ml of water were dropwise added to the mixture to cause diazotization.

After completion of the diazotization, an alcohol solution of 0.73 g of N,N-dimethylaniline was added to the reaction mixture at the same temperature to effect a coupling reaction. After completion of this reaction, the reaction mixture was poured into a weakly alkaline solution. The precipitate which formed was removed by filtration and dried to obtain 1.3 g of a crude Dyestuff 1 in Table 1. The crude dyestuff was subjected to silica gel column chromatography several times to purify the same to a high purity.

The purified dyestuff to which a 4-pentylcyclohexanecarbonyhioxy group has been introduced, showed a maximum absorption wavelength at 516 nm in chloroform.

EXAMPLE 2 Dyestuff No. 2:

6 g of 1 ,4-diaminoanthraquinone-2,3-dicarboxylic anhydride and 8.5 g of 4-(trans-4cyclohexanecarbonyloxy)aniline were added to 50 ml of dichlorobenzene and the mixture was heated at an external temperature of 100 to 1 50 OC for several hours. After completion of the reaction, 150 ml of methanol were added to the system to form a precipitate. The precipitate was removed by filtration and dried to yield 5 g of the crude product, Dyestuff 2 in Table 1. The crude product contained a considerable amount of impurities and was thus subjected to silica gel column chromatography to purify it to a high degree of purity. The purified product to which a trans-4-cyclohexanecarbonyloxy group had been introduced showed a maximum absorption wavelength at 680 nm in chloroform.

EXAMPLE 3 Dyestuff No. 3:

4.6 g of 2-(4-hydroxyphenyl)-1 ,5-dihydroxy-4,8-diaminoanthraquinone were dissolved in 46 ml of pyridine. 3.2 g of trans-4-heptylcyclohexanecarbonylchloride were dropwise added at O to 50C to the resuiting solution. After the dropwise addition had been completed, the mixture was maintained at the same temperature of 3 hours. After completion of the reaction, 200 ml of methanol were added and the crystals which had formed were removed by filtration and dried to obtain 2.3 g of crude product Dyestuff 3 in Table 1. The crude product was subjected to silica gel chromatography several times to purify it to a high degree of purity.The purified product to which a trans-4-heptylcyclohexanecarbonyl had been introduced showed the maximum absorption wavelengths at 578 nm and 618 nm in chloroform.

Other dyestuffs can also be prepared in accordance with the procedures of any one of Examples 1 to 3. For example, dyestuffs falling within general formula (II) can be prepared by a procedure similar to that of Example 1, dyestuffs falling within general formulae (III) and (VI) by a procedure similar to that of Example 2, and dyestuffs falling within general formulae (IV) and (V) in accordance with a procedure similar to that of Example 3. These dyestuffs can also be prepared according to other processes referred to generally hereinabove.

EXAMPLE 4 The products of Examples 1 to 3 and other dichroic dyestuffs in accordance with the present invention are shown in Table 1 below, together with the colour, the maximum absorption wavelength (?max) in chloroform and dichroic ratio (D) of each of the dyestuffs formed when these dyestuffs were mixed with biphenyl liquid crystal GR-41 (tradename, manufactured by Chisso Co., Ltd.).

TABLE 1

D o0 -e 0 s No. Formula nm GR-41 D I N=Amo: o e, 10.92 o a Ct 8 8 0 Lrf U 2 $)0w E 680 blue 11.5 3 71115 :8201 blue 9.1 E 2; (; ss &commat; t i t oz TABLE 1 (Continued)

m cu T: T.

c] cX o cj h No. Formula nm GR-41 D O C2H5 5 Q m-N=NmNO 495 $ O I .s ,= ~ n o"C 6 E Two o O omCc2E 551 bluish purple 12.2 r rY) 8 y4w N5jj1 686 P 0 U) CO s co Z TABLE 1 (Continued)

> s Colour in No. Formula nm GR-41 9 o 0 ocO 9 I;5$MOOjO 71115 695 bluish green 6.1 Y 8 1 "$ cn n o 5 S XE c O fuzz CON 10 H9CN 0 H 5H11 492 pink 13.7 N (o 000 527 r PN t > t f W 4 t ms Ozo cn o - cq TABLE 1 (Continued)

o c a a; 85 8 8 No. Formula nm GR-41 0 E E uo lcNE2 606 t mb f t E ii a o Ch st In obtaining the dichroic ratios set out in Table 1 a dlchroic dyestuff was dissolved in GR-41 , the solution was sealed between two glass base plates equipped with transparent electrodes to effect homogenous orientation, extinction efficiencies were measured both in the main chain direction and in the side chain direction of the dyestuff at the maximum absorption wavelength thereof and the ratio of the extinction efficiency in the main chain direction to that in the side chain direction was calculated.

The dichroic ratio may vary to some extent depending upon property of host liquid crystals or concentration of a dichroic dyestuff.

For the purpose of comparison, known dyestuffs similar to the dyestuffs shown in Table 1 are given in Table 2 below, together with their optical characteristics.

TABLE 2

o V! '9 "9 D a) a; rs cn Dyestuff No. Formula nm GR-41 0 Ec C v &commat; 8- 8- D a, a, 8 2 NMC04} 683 mco q 3 05 587 blue 7.6 0 625 = ( E " f g t o 8 Z . . N C'7 t CoJE S TABLE 2 (Continued)

d (max) Colour in o No. Formula nm GR-41 D 5 il9C 492 red 9.4 CH3 ,~ .~ sl h: a, OCT e L 6 C CM O 0 (0 7 605 blue 9.1 2 v" 0o zo ut O s TABLE 2 (Continued)

D s o.

a, No. Formula nm GR-41 D 0 9 . c Y 3 t} u s s 0 '5 Cfii =5 63 10 o, C * pink 11.7 co 0 4 527 '0 m4H9 11 N 511 red 8.0 545 1I?o É t 0e=0 X o l 8X z t PWo e Z cu n aw o N QoE 03 , ~ ~ TABLE 2 (continued)

co a, ) (A max) Colour in oO No. Formula nm GR-41 D 0 EE $ W z C Li t 8 0 OH Lf , U 4 ' E St 3 < S oS , Z The dichroic ratios shown in Table 2 were determined as described above.

As is seen from a comparison between Table 1 and Table 2, the dichroism of dyestuffs can be markedly improved by introducing a 4-substituted cyclohexanecarbonyloxy group into the 4-position of a terminal phenyl group in the main chain of a dichroic dyestuff.

EXAMPLE 5 Specific examples of further dichroic dyestuffs in accordance with the present invention are given in Table 3, together with the maximum absorption wavelength max in chloroform, the colour of each of the dyestuffs when the dyestuffs were dissolved in biphenyl liquid crystal Go 41 (tradename, manufactured by Chisso Co. Ltd.) and the dichroic ratio D of each dyestuff.

In the table, the dichroic ratio was determined as described above.

TABLE 3

T; (may) o- o o O No. Formula nm GR-41 D N 00 a, c o o e p.

"o P ,II: P 16 H9(ThTh00N 520 reddish purple 10.7 17 11 t LO LD &commat; 18 if11C5Thff00=N =N NcC4H% 499 red 11.3 t e & Z LD TABLE 3 (Continued)

cu cu o cr, O - cq o (Amax) Colour ni No. Formula nm o n e c o X s s 20 H11C5Qmm a 8 8 LO > 21 R11C5coo 551 bluish purple 12.0 22 H9C-NN= 00YA, 570 bluish purple 11.8 CH3 TABLE 3 (Continued)

(o (A max) Colour in No. Formula nm c\i0 8 ~ B o ZF; P EE E9 8 f: H C 8 8 E X 25 H17C8Cm CV H Z '? Q W X m II z TABLE 3 (Continued)

a r No. Formula nm GR-41 D .c~ 3 o o o o AXE = 8 A > E t 3 3 3 tz mi R TABLE 3 (Continued)

t (Amax) Colour in No. Formula nm GR-41 D 31 B 8 7) 0 0 0 0 32 cu 8 33 H3COO cu8 f T t t LE t ) CrJ nrv > 3 Sz N X t TABLE 3 (Continued)

c\i (IjcM No. Formula nm GR-41 D c 'Z P He D7coo 424-7 yellow 11.0 37 MCuoo N rO Oco 5H11 424-7 yellow 12.4 38 5c7c6Q = N=N C2 HS 498 red 13.0 C2H5 (I3 sZ X TABLE 3 (Continued)

Dyestutf (Amax) Colour in No. Formula nm cu C2 H5 ö X n o E c w Xo ~ OO rl) eD ge a) Z 8 w t t TABLE 3 (Continued)

D a) o ai Colour in No. Formula nm GR-41 D o 43 1117c8H 8 e 568 bluish purple 9.4 n 44 K7C3COOmNN= 398 g o m A H11C4=N=N7H m yellow 11.6 t " 191 2 Z 1CN=N=N $ H 401 yellow 11.3 L 2 . 0 t TABLE 3 (Continued)

Dyestutf (Amax) Colour in No. Formula nm b o D 47 - - 8 9 o o 3 n 48 c W mo \/ -' CH3 $ t t? e > to3Js -a 3 O z W 0 TABLE 3 (Continued)

13 'S c L(d 8 o oOcr a, x > 1E OE o Ec a3 2;; 4 x 4 4 a H Z e For the purpose of comparison, the optical characteristics of known dyestuffs having structures similar to those described in Table 3 are given in Table 4 below. TABLE 4

D t o. * cd oi in ar No. Formula nm GR-41 D c 119C N==NTh2iIl3 435 orange o am I o n ,6a: s L c SC o =I v, s 8 E, m C t tn &commat; w Ipti: 3' LE t t zo 0 E o uz O s co Oog TABLE 4 (Continued)

o L t: ' =i CdE No. Formula nm GR-41 0 E, E3 E 4] tL 4 X v S 8 S O The dichroic ratio given in Table 4 was determined in a manner similar to that set out in Example 4.

As is clear from a comparison of Table 2 with Table 1 and Table 3 with Table 4, the dichroic property of the dyestuffs can be markedly improved by introducing a phenyl group, a cyclohexyl group, a phenylcarbonyloxy a phenyloxycarbonyl, a cyclohexanecarbonyloxy or cyclohexaneoxycarbonyl group, which may be substituted with an appropriate substituent, into the 4-position of the phenyl or naphthyl group located at a terminal position of the main chain of a dichroic dyestuff.

Differences in dichroism shown in Examples 4 and 5 above are significant; not only the representative examples described above but also other dyestuffs of the present invention show significant differences In dichroism over corresponding known dyestuffs free from the specific dichroism-improving group.

The phenyl groups present in molecules of dyes set out in the above examples can also be cyclohexyl groups; the phenyl or cyclohexyl group can also form a part of a a polycyclic ring system including a polycondensed ring, e.g., a biphenyl group, a terphenyl group, a cyclohexylphenyl group, a phenylcyclohexyl group, a cyclohexylcyclohexyl group or a naphthyl group. When these groups are directly bonded to the dyestuff skeleton, it means that the groups are bonded to a so called "hard skeleton" conventionally employed in the art: this is preferred in improving dichroism.

Claims

1. A dichroic dyestuff of the general formula RA)1-Z-R1 (I) wherein: R denotes a cyclohexanecarbonyloxy, cyclohexaneoxycarbonyl, phenylcarbonyloxy or phenyloxycarbonyl group, or a group of formula:

wherein R' denotes hydrogen, alkyl, alkoxy, nitro, cyano, trihalomethyl, halogen;sulphonyl substituted by alkyl, dialkylamino, trihalomethyi or halogen; alkylcarbonyloxy, alkyloxycarbonyl or alkyloxyca rbonyloxy; or carbonyloxy, oxycarbonyloxy or oxycarbonyl connected to a phenyl, biphenyl, cyclohhexyl- phenyl or cyclohexylcyclohexyl group; B denotes saturation or unsaturation of the ring with which it is associated: and m is O or an integer; and in which the moiety -OCO- in a group

may alternatively be carbonyloxy or oxycarbonyl: A denotes

iisOor 1; R, denotes hydrogen, alkyl, alkoxy, cyano, nitro, trihalomethyl, sulphonyl substituted by alkyl, dialkylamino or halogen, or has a meaning attributable to R or R-A already defined; or denotes phenyl or cyclohexyl, mono- or dialkylamino, nitro, cyano, alkylsulphonyl, trihalomethyl, halogen, alkyloxycarbonyloxy, al kyloxycarbonyl, alkylcarbonyloxy, cycloalkyl, pyrrolidino, or julolidino; or a gorup of formula

wherein R', B and m are as already defined; and Z denotes a divalent group selected from:

wherein Ar denotes

n is O or an integer of from 1 to 4; R2 and R3 which may be the same or different are hydroxy, free amino or monoalkylamino; R4 and R5 which may be the same or different are hydrogen, hydroxy, free amino or monoalkylamino; R6 is hydroxy, free amino or monoalkylamino; R, to A9 which may be the same or different are hydrogen, hydroxy, nitro, free amino, or monoalkylamino; A10 is hydroxy, free amino or monoalkylamino; R" to R13 which may be the same or different are hydrogen, hydroxy, free amino or monoalkylamino; and X is a heteroatom; in which divalent group (i) any one of the benzene rings may be fused at any two adjacen: positions thereof to a benzene ring to form a naphthalene ring.

2. A dyestuff as claimed in claim 1, wherein a said group R is substituted in the 4-position by alkyl; alkoxy or halogen or by phenyl or cyclohexyl in turn optionally substituted at the 4-position by alkyl, alkoxy, alkylcarbonyloxy, alkyloxycarbonyl or alkyloxycarbonyloxy.

3. A dyestuff as claimed in claim 1 or 2, wherein a phenyl, biphenyl, cyclohexylphenyl or cyclohexylcyclohexyl group connected to a carbonyloxy, oxycarbonyloxy or oxycarbonyl group R' is substituted by alkyl, alkoxy or halogen or by phenyl or cyclohexyl optionally substituted in the 4-position by alkyl, alkoxy, alkylcarbonyloxy, alkyloxycarbonyl or alkyloxycarbonyloxy.

4. A dyestuff as claimed in any one of the preceding claims, wherein R, denotes phenyl or cyclohexyl substituted at its 4-position by alkyl, alkoxy, alkylcarbonyloxy, alkyloxycarbonyl, alkyloxycarbonyloxy or 4-alkyl or -alkoxy substituted phenyl or cyclohexyl.

5. A dyestuff as claimed in any one of the preceding claims, wherein any benzene ring of a said divalent group (I) is substituted by methyl, trifluoromethyl, chlorine, fluoroine or hydroxy.

6. A dyestuff as claimed in any one of the preceding claims, wherein an alkyl or alkoxy group constituting a group R' or part of group R, R2 or R' or a substituent of a group, R, R, or R' is linear and contains from 1 to 12 carbon atoms.

7. A dyestuff as claimed in any one of the preceding claims, wherein an alkyl group forming part of a monoalkylamino group R2 to A13 is linear and contains 1 to 5 carbon atoms.

8. A dyestuff as claimed in claim 1, which is represented by the following general formula:

wherein R" is a cyclohexanecarbonyloxy group optionally substituted at the 4-position by linear C,~,2 alkyl or alkoxy; 4-linear C,~,2 alkyl or alkoxy substituted or unsubstituted phenyl or cyclohexyl; or a said substituent

wherein R' and m are as defined in any one of the preceding claims R, is hydrogen; mono- or di-linear C,-,2 alkylamino, has one of the meanings given for R", with m being 0 or an integer of 1 to 3; linear C,-,2 alkyl or alkoxy; phenyl or cyclohexyl optionally substituted at the 4-position by linear C,~,2 alkyl, alkoxy, alkylcarbonyloxy, alkyloxycarbonyl or alkyloxycarbonyloxy or 4-linear C1-12 alkyl or alkxoy substituted phenyl or cyclohexyl; mono- or di-linear C1-12 alkylamino; pyrrolidino; or julolidino; is 0 or an integer of 1 to 3 and Ar has the meaning given in claim 1.

9; A dyestuff as set forth in claim 1 wherein the dyestuff is represented by the following general formula:

wherein R2 to R5 have the same meanings set out in claim 1 and , is 4-R"-phenyl, 4-R"-cyclohexyl, 4'-R"-biphenyl or 4'-R"-cyclohexylphenyl in which R" is as defined in claim 8 or 4-linear C~12 alkyl- or alkoxy- substituted or unsubstituted phenyl, cyclohexyl, biphenyl or cyclohexylphenyl.

10. A dyestuff as claimed in claim 1 wherein the dyestuff is represented by the following general formula:

wherein R6 to R9 have the meanings set out in claim 1, R" has the meaning set out in claim 8 and Y is hydrogen, phenyl optionally substituted by linear C1-12 alkyl or alkoxy or mono- or di-linear C,~,2 alkylamino.

11. A dyestuff as claimed in claim 1, wherein the dyestuff is represented by the following general formula:

wherein R10 to R,3 are as defined in claim 1,, is as defined in claim 9 and x is O or S.

12. A dyestuff as claimed in claim 1, wherein the dyestuff is represented by the following general formula:

wherein QI, is as defined in claim 9 and 2 is linear C~12 alkyl, has one of the meanings given for 2' or is a 4-substituted-phenyl or cyclohexyl group in which the substituent is selected from linear C,~,2 alkyl and alkoxy, mono- and di-linear C,~,2 alkylamino, and 4-linear C,~,2 alkyl or alkoxy substituted phenyl and cyclohexyl.

13. A dyestuff as claimed in any one of the preceding claims, wherein a cyclohexane moiety which is present is in the trans form.

14. A dichroic dyestuff, substantially as set out in one of the foregoing Tables 1 and 3.

15. A liquid crystal composition for guest-host liquid crystal colour display which comprises at least one dichroic dyestuff as guest and liquid crystal as host, the dichroic dyestuff used being a dyestuff as claimed in any one of the preceding claims.

16. A liquid crystal composition as claimed in claim 1 5, wherein the liquid crystal as host is selected from biphenyl, cyclohexylcyclohexane, phenylcyclohexane and ester liquid crystals.

17, A liquid crystal composition as claimed in claim 15, substantially as described herein.