Dichroic dye and liquid crystalline composition for color display

An anthraquinonic dye of the formula ##STR1## is provided. When used as dichloric dyes in liquid crystalline color display elements, these dyes (1) have sufficient coloring ability in small amounts, (2) have a high dichloric ratio, (3) are fully soluble in liquid crystals, and (4) have excellent durability, are stable and do not degrade the performance of a display device upon long-term use.

This invention relates to novel dichroic dyes and a liquid crystalline 
composition for color display comprising such a dichroic dye. 
More specifically, this invention relates to novel anthraquinonic compounds 
having dichroic property represented by the formula 
##STR2## 
wherein each of X.sub.1, X.sub.2, X.sub.3 and X.sub.4 represents a 
hydrogen atom, a halogen atom, an amino group or a hydroxyl group, in 
which the amino or hydroxyl group may be substituted by an alkyl group 
having 1 to 4 carbon atoms; 
each of X.sub.5 and X.sub.6 represents a hydrogen atom, a halogen atom, an 
amino group, a hydroxyl group or an alkyl group having 1 to 15 carbon 
atoms, in which at least one methylene moiety in the alkyl group may be 
replaced by an oxygen atom, a carboxyl group, an oxycarbonyl group and/or 
a phenylene group, and the amino group or the hydroxyl group may be 
substituted by an alkyl group having 1 to 4 carbon atoms; 
Y represents an oxygen or sulfur atom; and 
Z represents an alkyl group having 3 to 15 carbon atoms, in which at least 
one methylene moiety in the alkyl group may be replaced by an oxygen atom, 
a carboxyl group, an oxycarbonyl group and/or a phenylene group. 
The invention also relates to a liquid crystalline composition for use in 
display devices utilizing the electro-optical effects of liquid crystals, 
said composition comprising liquid crystals and dissolved therein at least 
one anthraquinonic dichroic dye represented by formula (I) above. 
In recent years, liquid crystal display elements have gained widespread 
acceptance in the field of display elements to save energy and reduce the 
size of display devices. Most of the liquid crystal display elements now 
in use utilize the electro-optical effect of twisted nematic liquid 
crystals. They are required to be used in combination with two polarized 
films, and many restrictions are imposed on their use. As an alternative 
crystal display method, liquid crystal display by the guest-host mode 
which utilizes the electro-optical effect of a colored liquid crystal 
composition obtained by dissolving a dichroic dye in nematic liquid 
crystals has been studied, and to some extent come into practical use in 
watches, household electrical appliances, and industrial measuring 
instruments. 
The guest-host mode liquid crystal display method operates on the principle 
that dichroic dye molecules as a guest are oriented according to the 
alignment of liquid crystal molecules as a host. Application of an 
external stimulus which is usually an electric field changes the aligning 
direction of liquid crystal molecules from the "off" state to the "on" 
state, and at the same time, the aligning direction of the dichroic dye 
molecules also changes. Consequently, the degree of light absorption by 
the dye molecules differs between the two states, and display is thus 
effected. The dichroic dye used in this method should at least meet the 
following requirements. (1) It has sufficient coloring ability in small 
amounts. (2) It has a high dichroic ratio, and shows a high contrast 
between the application of a voltage and the absence of a voltage. (3) It 
has sufficient solubility in liquid crystals. (4) It has excellent 
durability, is stable, and does not degrade the performance of a display 
device even when it is used for a long period of time. Various dichroic 
dyes meeting the above requirements have already been proposed and to some 
extent gained acceptance in digital clocks, meters, etc. But they have one 
or more defects which are desired to be remedied. For example, those 
having a high dichroic ratio have poor durability, and those having 
excellent durability do not have a dichroic ratio which permits clear 
display in practical applications. In particular, with regard to dichroic 
dyes having a reddish color, some azoic dyes of a reddish color are known 
to have a relatively high dichroic ratio, but they have too low durability 
to be practical. The anthraquinonic dyes generally having good durability 
have been proposed, but none of them can be said to have a dichroic ratio 
on a practically feasible level. This situation markedly restricts the 
usage of guesthost mode crystal display elements. Accordingly, it has been 
strongly desired in the art to develop dyes having excellent durability 
and a high dichroic ratio, particularly those of a reddish color tone. 
The present inventors, in an attempt to meet this requirement, have alrady 
proposed many dichroic dyes, but these dyes have not proved to be entirely 
satisfactory. Particularly, the compound of the following formula 
##STR3## 
which the present inventors proposed in Japanese Laid-Open Patent 
Publication No. 123673/1980 is similar in structure to the compounds of 
general formula (I) in accordance with this invention cannot fully meet 
the demand of the market in regard to its solubility in liquid crystals, 
and its improvement has been desired. 
It is an object of this invention therefore to provide a novel dichroic dye 
which can completely meet the aforesaid requirement. 
According to this invention, novel anthraquinonic compounds of general 
formula (I) are provided as dichroic dyes meeting the above object. Most 
of the compounds of formula (I) have a characteristically higher dichroic 
ratio than the anthraquinonic dichroic dyes proposed heretofore. They also 
have excellent durability, are stable, and have good solubility in various 
liquid crystals. Thus, the compounds of formula (I) fully meet the 
requirements of dichroic dyes to be applied to liquid crystal color 
display devices. 
The dichroic dyes of formula (I) in accordance with this invention can be 
synthesized by subjecting a compound of the formula 
##STR4## 
wherein X'.sub.1, X'.sub.2, X'.sub.3, X'.sub.4, X'.sub.5, X'.sub.6 and Y' 
are the same atoms or groups as X.sub.1, X.sub.2, X.sub.3, X.sub.4, 
X.sub.5, X.sub.6 and Y in formula (I), or precursor groups capable of 
being converted to the same groups, and a compound represented by the 
formula 
##STR5## 
wherein Z' represents the same atom or group as Z in formula (I), or a 
precursor group capable of being converted to the same group, to 
dehydrochlorinating condensation and dehydrocyclization in a high-boiling 
inert organic solvent such as o-dichlorobenzene and nitrobenzene, and 
optionally subjecting the product to a required additional reaction. 
Specific examples of the compound of formula (Ia) include 
3-amino-1,2-dihydroxyanthraquinone, 
3-amino-1,2,4-trihydroxyanthraquinone, 
3-amino-1,2,5,8-tetrahydroxyanthraquinone, 
2-amino-3-hydroxy-5,8-dibromoanthraquinone, 
2-amino-3-hydroxy-5,8-di(methylamino)-anthraquinone, 
2-amino-3-hydroxy-5,8-dibromo-7- methylanthraquinone, 
3-amino-1,2,5,7,8-pentahydroxyanthraquinone, 
3-amino-1,2-dihydroxy-anthraquinone-7- carboxylic acid, 
2-amino-3-hydroxy-4,8-dibromo-7-methoxycarbonylanthraquinone, 
3-amino-1,2,4-trihydroxy-7-(4'-butylphenyl)- anthraquinone, 
3-amino-1-hydroxy-2-mercaptoanthraquinone, 
2-amino-3-mercapto-5,8-dibromoanthraquinone, 
3-amino-1,2-dihydroxy-6-isopropylanthraquinone, 
3-amino-1,2,5-trihydroxy-6-butylanthraquinone, 
3-amino-1,2-dihydroxy-4-bromoanthraquinone, 
3-amino-2-hydroxy-1,4-dibromoanthraquinone, and 
3-amino-2-hydroxy-1-methylaminoanthraquinone. 
Specific examples of the group Z' in formula (Ib) include alkyl groups such 
as propyl, isopropyl, butyl, isobutyl, s-butyl, t-butyl, pentyl, hexyl, 
heptyl, octyl, nonyl, dodecyl and pentadecyl; a hydroxyl group; alkoxy 
groups such as ethoxy, pentoxy, octoxy and dodecyloxy; a carboxyl group; 
alkoxycarbonyl groups such as methoxycarbonyl and ethoxycarbonyl; 
hydroxyalkyl groups such as hydroxymethyl and hydroxyethyl; alkoxyalkyl 
groups such as methoxyethyl and methoxypropyl; aralkyl groups such as 
4'-methyl-phenethyl; and alkyl-, alkoxy- or acyloxy-substituted phenyl 
groups such as 4'-ethylphenyl, 4'-butylphenyl, 4'-octylphenyl, 
4'-methoxyphenyl, 4'-octoxyphenyl, 4'-nonaxyphenyl, and 4'-acetoxyphenyl. 
When a compound of the formula 
##STR6## 
wherein X'.sub.1, X'.sub.2, X'.sub.3, X'.sub.4, X'.sub.5, X'.sub.6, Y', 
and Z' are the same as defined with regard to formulae (Ia) and (Ib), is 
not a compound corresponding to formula (I), it may be converted to a 
compound corresponding to formula (I) by subjecting it to a required 
additional reaction. Such an additional reaction may, for example, be the 
introduction of an amino group by nitration and subsequent reduction, the 
substitution of a halogen atom by an amino, alkylamino or hydroxyl group, 
hydrolysis with an acid or alkali, esterification, alkylation, etc. 
The crude dye of formula (I) obtained as above can be purified to a high 
degree by recrystallization, column chromatography, sublimation, and other 
means. 
Examples of preferred dichroic dyes of the invention so obtained are 
summarized in Table 1. 
The dichroic ratios shown in Table 1 are characteristic values which most 
characterize the utility of the novel dichroic dyes of the invention. 
The dichroic ratio is determined as follows: 
1.0% by weight of a dye sample was dissolved in liquid crystals E-8 (a 
product of Merck & Co.), typical biphenyl-type nematic liquid crystals, 
and the solution was sealed in a glass liquid crystal cell having a gap of 
10 microns which had been treated in advance so as to induce homogeneous 
aligning. The cell was placed in the light path of a spectro-photometer. 
Straight polarized light parallel to the alignment of the liquid crystals 
was applied to the cell, and the absorbance (A.sub.81 ) was measured. 
Furthermore, straight polarized light at right angles to the alignment of 
the liquid crystals was applied, and the absorbance (A .sub.195 ) was 
measured. The dichroic ratio was calculated from the following equation. 
##EQU1## 
TABLE 1 
__________________________________________________________________________ 
Sample 
No. X.sub.1 
X.sub.2 
X.sub.3 
X.sub.4 
X.sub.5 
X.sub.6 Y 
__________________________________________________________________________ 
1 OH NH.sub.2 
H H H H O 
2 OH NH.sub.2 
H NH.sub.2 
H H O 
3 OH H OH OH H H O 
4 OH H H H H H O 
5 OH NH.sub.2 
H H H H O 
6 OH Br H H H H O 
7 OH OH H H H H O 
8 OH NH.sub.2 
H H H H O 
9 OH NH.sub.2 
H H H H O 
10 NH.sub.2 
NH.sub.2 
H H H H O 
11 OH H H H H H S 
12 OH NH.sub.2 
H H H H S 
13 OH H H H H H S 
14 OH NH.sub.2 
OH NH.sub.2 
H H O 
15 OH NH.sub.2 
H H CH.sub.3 
H O 
16 NH.sub.2 
OH H H H H O 
17 NHCH.sub.3 
H H H H H O 
18 OH H OH OH H H O 
19 OH NH.sub.2 
OH NH.sub. 2 
H H O 
20 OH H NHCH.sub.3 
NHCH.sub.3 
H H O 
21 OH H OH H H CH.sub.2 CH(CH.sub.3).sub.2 
O 
22 OH NH.sub.2 
H OH H H O 
23 NH.sub.2 
H OH H H O 
24 OH NH.sub.2 
H H H COOC.sub.4 H.sub.9 (n) 
O 
25 NH.sub.2 
NH.sub.2 
H H H COOC.sub.4 H.sub.9 (n) 
O 
26 OH Cl OH Cl H H O 
27 OH NH.sub.2 
OH NH.sub.2 
H H O 
__________________________________________________________________________ 
Dichroic ratio 
Sample Color in 
in liquid 
No. Z toluene crystals E-8 
__________________________________________________________________________ 
1 C.sub.4 H.sub.9 (n) 
Red 9.5 
2 C.sub.9 H.sub.19 (n) 
Violet 8.2 
3 COOC.sub.5 H.sub.11 (n) 
Orange 9.3 
4 C.sub.5 H.sub.11 (n) 
Yellow 7.2 
Red 10.1 
6 C.sub.2 H.sub.4 OC.sub.4 H.sub.9 (n) 
Orange 6.8 
7 C.sub.2 H.sub.4 CHCH.sub.3 CH.sub.2 C(CH.sub.3).sub.3 
Orange 8.1 
8 C.sub. 5 H.sub.11 (n) 
Red 9.5 
9 C.sub.12 H.sub.25 (n) 
Red 9.3 
10 C.sub.5 H.sub.11 (n) 
Reddish violet 
8.1 
11 C.sub.5 H.sub.11 (n) 
Yellow 8.5 
12 OCOC.sub.9 H.sub.13 (n) 
Red 8.7 
13 C(CH.sub.3).sub.3 
Yellow 7.8 
14 C.sub.8 H.sub.17 (n) 
Blue 10.5 
15 C.sub.9 H.sub.19 (n) 
Red 10.2 
16 C.sub.7 H.sub.15 (n) 
Red 8.0 
17 C.sub.5 H.sub.11 (n) 
Orange 6.9 
18 C.sub.5 H.sub.11 (n) 
Orange 9.8 
19 CH.sub.2 CH.sub.2 CH(CH.sub.3)CH.sub.2 C(CH.sub.3).sub.3 
Blue 10.3 
20 C.sub.7 H.sub.15 (n) 
Blue 9.2 
21 C.sub.5 H.sub.11 (n) 
Orange 8.1 
22 C(CH.sub.3).sub.2 CH.sub.2 C(CH.sub.3).sub.3 
Reddish violet 
11.6 
23 COOC.sub.4 H.sub.9 (n) 
Reddish violet 
8.2 
24 C.sub.7 H.sub.15 (n) 
Reddish violet 
8.6 
25 C.sub.7 H.sub.15 (n) 
Reddish violet 
9.3 
26 
##STR7## Orange 8.0 
27 
##STR8## Blue 9.2 
__________________________________________________________________________ 
The dichroic dyes of the invention not only have a high dichroic ratio, but 
also exhibit other desirable properties required of dyes for liquid 
crystals, for example excellent solubility in liquid crystals and the 
excellent durability, particularly excellent light fastness, of liquid 
crystalline composition containing such dyes. Specifically, when a 
solution of the anthraquinonic dye of the invention in liquid crystals is 
sealed in a display element, and left to stand under irradiation of solar 
light for a long period of time, the electric current increases only to a 
degree corresponding to an increase in power consumption depending upon 
the liquid crystals used, and no change in color tone is observed. This 
light fastness is much superior to that of conventional azoic dichroic 
dyes. For example, dye No. 8 given in Table 1 which is a typical dichroic 
dye of the invention has higher solubility and light fastness than known 
dyes A, B and C for liquid crystals as shown in Table 2. 
Known dyes for liquid crystals 
##STR9## 
Solubility 
This is the solubility (% by weight) of each dye in liquid crystals E-8 
(made by Merck & Co.) at 25.degree. C. 
Light fastness 
0.5% by weight of each dye was dissolved in the liquid crystals E-8, and 
the solution was sealed into a liquid crystal wall having a gap of 10 
microns and including a pair of facing transparent electrodes with an area 
of 1.0 cm.sup.2. The cell was exposed to solar light for 200 hours. Then, 
a voltage of a rectangular wave form (6V.sub.p-p, 32 Hz) was applied, and 
the total current was measured (.mu.A/cm.sup.2). 
TABLE 2 
______________________________________ 
Light fastness 
Dye Solubility (%) 
(.mu.A/cm.sup.2) 
______________________________________ 
A (known) 1.1 4.2 
B (known) 0.7 3.6 
C (known) 0.4 -- 
No. 8 (invention) 
4.7 2.0 
Liquid crystals E-8 alone 
-- 1.6 
______________________________________ 
Thus, the novel dichroic dyes of this invention markedly remedy the defects 
of the conventional dichroic dyes for liquid crystals. 
The dichroic dyes of the invention, either singly or as a mixture of two or 
more, can give compositions of various color tones for liquid crystal 
display elements. In such a composition, the amount of the dye may be such 
that the dye can dissolve in the liquid crystals. Usually, it is not more 
than 10% by weight, preferably 0.01 to 5% by weight, based on the liquid 
crystals. To obtain the desired color, the dichroic dye of the invention 
may be used in admixture with another dichroic dye or a dye having no 
dichroic property. 
The liquid crystals used in the composition of this invention may, for 
example, be nematic liquid crystals which show positive or negative 
dielectric anisotropy, such as biphenyl-type liquid crystal mixtures, 
phenylcyclohexane-type liquid crystal mixtures, Schiff base-type liquid 
crystal mixtures, ester-type liquid crystal mixtures and pyrimidine-type 
liquid crystal mixtures. A mixture of two or more such liquid crystal 
mixtures may also be used. Liquid crystal mixtures containing at least 80% 
by weight of the biphenyl-type liquid crystal mixtures, the 
phenylcyclohexane-type liquid crystal mixtures and/or the ester-type 
liquid crystal mixtures are especially preferred for use in combination 
with the dichroic dyes of the invention. Specific examples include E-7 and 
E-8 (tradenames for products of Merck & Co.) which are the biphenyl-type 
liquid crystal mixtures, ZLI-1132 and ZLI-1840 (tradenames for products of 
Merck & Co.) which are the phenylcyclohexane-type liquid crystal mixtures, 
ZLI-1275 (a tradename for a product of Merck & Co.) which is the 
ester-type liquid crystal mixtures, and EN-17 (a tradename for a product 
of Chisso Co., Ltd.). 
So-called phase-transition type chiral nematic liquid crystals can also be 
used which are obtained by adding optically active substances, such as 
cholesteryl nonanoate or rotatory 4-cyano-4'-isopentyl biphenyl, to these 
nematic liquid crystals. 
The liquid crystal compositions of this invention for color display can be 
prepared by dissolving the dichroic dye in liquid crystals in accordance 
with known methods. Usually, the desired liquid crystal composition for 
color display is prepared by mixing required amounts of the dichroic dye 
of the invention or a dye composition containing it with the liquid 
crystal mixtures, stirring the mixture for a long period of time, or 
stirring it after heating it to above a temperature at which the liquid 
crystal mixture becomes an isotropic liquid, thereby to dissolve the dye 
in the liquid crystal mixture. 
As required, other additives may be added to the liquid crystalline 
composition of the invention during, before or after the mixing of the 
dichroic dye with the liquid crystals.

The following Examples illustrate the present invention more specifically. 
It should be understood, however, that the invention is in no way limited 
by the description of these Examples. 
EXAMPLE 1 
10.2 Parts by weight of 1,2-dihydroxy-3-aminoanthraquinone and 0.6 part by 
weight of zinc chloride were dispersed in 30 parts by weight of 
o-dichlorobenzene at 70.degree. C., and 10.8 parts by weight of 
trans-4-n-pentyl-cyclohexanecarbonyl chloride was added dropwise. The 
mixture was stirred at 170.degree. to 180.degree. C. for 5 hours, and 
cooled. Then, 30 parts of methanol was added. The precipitate was 
filtered, washed with methanol, and dried to give 13.6 parts by weight of 
a crude dye. 
The crude dye was purified by chromatographing it on a column filled with 
silica gel powder using toluene as an eluent. A yellow dye having a 
melting point of 165.degree. to 168.degree. C. was obtained (Dye No. 4 in 
Table 1). 
EXAMPLE 2 
12.5 Parts by weight of compound No. 4 in Table 1 was dissolved in 75 parts 
by weight of 98% sulfuric acid, and 2.4 parts by weight of 94% nitric acid 
was added dropwise at 0.degree. to 5.degree. C. The mixture was stirred at 
this temperature for 7 hours, and poured into 400 parts by weight of 
water. The precipitate was filtered and washed with water. The filtration 
cake was dissolved in 250 parts by weight of monochlorobenzene, and 70 
parts by weight of an aqueous solution containing 10.4 parts by weight of 
60% sodium sulfide was added. The mixture was stirred under reflux for 10 
hours. The resulting product was neutralized with 65.5 parts by weight of 
23.6% sodium hydrogen sulfite and 6.3 parts by weight of 50% sulfuric 
acid, and then steam distilled. Monochlorobenzene was thus distilled out, 
and the precipitate was filtered, washed with water and dried to give 11.2 
parts by weight of a crude dye. 
The crude dye was purified by the same column chromatographic technique as 
in Example 1 to give a red dye having a melting point of 215.degree. to 
216.degree. C. (Dye No. 8 in Table 1). 
EXAMPLE 3 
6.0 Parts by weight of 1,2,5,8-tetrahydroxy-3-aminoanthraquinone and 0.5 
part of zinc chloride were dispersed in 25 parts by weight of 
o-dichlorobenzene, and 6.8 parts by weight of 
trans-4-n-pentylcyclohxanecarbonyl chloride was added dropwise at 
80.degree. C. over the course of 30 minutes. The mixture was stirred at 
170.degree. C. for 4 hours. By steam distillation, o-dichlorobenze was 
distilled out. The residue was filtered, washed with water and dried to 
give 7.2 parts by weight of a crude dye. 
The crude dye was purified by the same column chromatographic technique as 
in Example 1 to give an orange dye having a melting point of 217.3.degree. 
to 218.6.degree. C. (Dye No. 18 in Table 1). 
EXAMPLE 4 
0.1 Part by weight of the dye No. 8 in Table 1 was dissolved in 10 parts by 
weight of a liquid crystal mixture composed of 43% of 
4-n-pentyl-4'-cyano-biphenyl, 17% of 4-n-propoxy-4'-cyanobiphenyl, 13% of 
4-n-pentoxy-4'-cyanobiphenyl, 17% of 4-n-octoxy-4'-cyanobiphenyl and 10% 
of 4-n-pentyl-4'-cyanoterphenyl. The resulting color liquid crystal 
mixture was sealed into a glass cell having a gap of 10 microns which had 
been subjected to homogeneous aligning treatment. The maximum absorption 
wavelength was 512 nm and the dichroic ratio was 10.2. A display device 
obtained by sealing this color liquid crystal mixture into a glass liquid 
crystal display element of the same structure as above including 
transparent electrodes assumed a red color entirely in the absence of a 
voltage applied, and when a voltage was applied, only the part of the 
electrodes became nearly colorless, thus showing a good contrast. 
EXAMPLE 5 
6.0 Parts by weight of 3-amino-1,2,5-trihydroxyanthraquinone and 0.5 part 
by weight of zinc chloride were dispersed in 55 parts by weight of 
o-dichlorobenzene, and 8.3 parts by weight of 
trans-4-(3',5',5'-trimethylhexyl)-cyclohexanecarbonyl chloride was added 
dropwise at 80.degree. C. over the course of 30 minutes. The mixture was 
stirred at 175.degree. C. for 7 hours, and cooled. Methanol (150 parts by 
weight) was added, and the precipitate was collected by filtration, washed 
with methanol and water, and dried to give 9.1 parts by weight of an 
oxazole compound. The product was dissolved in 100 parts by weight of 
nitrobenzene, and 45 parts by weight of sulfuryl chloride was added. The 
mixture was stirred at 70.degree. to 85.degree. C. for 5 hours. An aqueous 
solution of sodium carbonate was added to adjust the mixture to pH 7. By 
steam distillation, nitrobenzene was evaporated, and the precipitate was 
collected by filtration, washed with water and dried to give 10 parts by 
weight of a dichloro compound. The product was stirred at 120.degree. to 
130.degree. C. for 4 hours together with 120 parts by weight of 
nitrobenzene, 8.4 parts by weight of potassium carbonate, 0.8 part by 
weight of copper acetate, 0.8 part by weight of copper powder and 15.3 
parts of p-toluenesulfonamide, and then cooled. The mixture was 
neutralized to pH 7 with 50% sulfuric acid. By steam distillation, 
nitrobenzene was evaporated, and the precipitate was collected by 
filtration and dried. The resulting compound was added to 200 parts by 
weight of 95% sulfuric acid, and the mixture was stirred at 40.degree. C. 
for 3 hours. It was then poured into 2,000 parts by weight of ice water. 
The precipitate was collected by filtration, washed with water and dried 
to give 9.8 parts by weight of a crude dye. 
The crude dye was purified by the same column chromatographic technique as 
in Example 1 to give a blue dye having a melting point of 155.degree. to 
157.degree. C. (Dye No.19 in Table 1). The dichroic ratio of the dye was 
measured in the liquid crystals E-8 in the same way as described above 
with regard to Table 1, and found to be 10.3 (.lambda..sub.max 616 nm). 
The dye had a solubility in E-8 of 7.2% by weight. When liquid crystals 
ZLI-1840 were used instead of the liquid crystals E-8, the dichroic ratio 
of the dye was 10.8 (.lambda..sub.max 612 nm). When liquid crystals 
ZLI-1275 were used, the dichroic ratio was 10.1 (.lambda..sub.max 616 nm). 
EXAMPLE 6 
A crude compound was prepared in the same way as in Example 1 except that 
18.8 parts by weight of 1,2,8-trihydroxy-3-aminoanthraquinone and 20 parts 
by weight of 4-methoxycarbonylcyclohexanecarbonyl chloride were used 
instead of 1,2-dihydroxy-3-aminoanthraquinone and 
trans-4-n-pentyl-cyclohexanecarbonyl chloride. 
Six parts by weight of the crude compound was dissolved in 75 parts by 
weight of 98% sulfuric acid together with 2 parts by weight of boric acid, 
and 2 parts by weight of 94% nitric acid was added dropwise at 0.degree. 
to 5.degree. C. The mixture was stirred at this temperature for 4 hours. 
The reaction mixture was poured into 400 parts by weight of ice water, and 
the precipitate was filtered and washed with water. The filtration cake 
was dispersed in 250 parts by weight of a 50% aqueous solution of ethanol, 
and 70 parts by weight of an aqueous solution containing 5 parts by weight 
of 60% sodium sulfide was added. The mixture was stirred under reflux for 
8 hours. Then, it was neutralized by adding 21 parts by weight of 38% 
sodium hydrogen sulfite and 4 parts by weight of conc. hydrochloric acid. 
Ethanol was distilled off, and the precipitate was filtered, washed with 
water and dried. The dried product was stirred under reflux for 3 hours 
together with 50 parts by weight of n-butanol, 50 parts by weight of 
toluene and 1 part by weight of p-toluenesulfonic acid, and the mixture 
was then concentrated until its total amount reached 50 parts by weight. 
After cooling, the precipitate was filtered, washed with methanol and 
water, and dried to give 3.2 parts by weight of a crude dye. 
The crude dye was purified by the same column chromatographic technique as 
in Example 1 to give a reddish violet dye having a melting point of 
183.degree. to 185.degree. C. (Dye No. 23 in Table 1). It had a dichroic 
ratio in the liquid crystals E-8 of 8.2. 
EXAMPLE 7 
A crude compound was prepared in the same way as in Example 1 except that 
18.5 parts by weight of 1,2,8-trihydroxy-3-aminoanthraquinone and 26 parts 
by weight of trans-4-(1',1',3',3'-tetramethylbutyl)cyclo-hexanecarbonyl 
chloride were used instead of 1,2-dihydroxy-3-aminoanthraquinone and 
trans-4-n-pentyl-cyclohexanecarbonyl chloride. 
34 Parts by weight of the crude compound was dissolved in 375 parts by 
weight of 98% sulfuric acid containing 10.9 parts by weight of boric acid, 
and 11 parts by weight of 94% nitric acid was added dropwise at 0.degree. 
to 5.degree. C. The mixture was stirred at this temperature for 4 hours. 
The reaction mixture was poured into 2400 parts by weight of water, and 
the precipitate was filtered and washed with water. The filtration cake 
was dissolved in 1,500 parts by weight of monochlorobenzene, and 470 parts 
by weight of an aqueous solution containing 30 parts by weight of 60% 
sodium sulfide was added. The mixture was stirred under reflux for 4 
hours, and then neutralized with 54 parts by weight of 38% sodium hydrogen 
sulfite and 50% sulfuric acid. By steam distillation, monochlorobenzene 
was distilled off, and the precipitate was filtered, washed with water and 
dried to give 31 parts by weight of a crude dye. 
The crude dye was purified by the same column chromatographic technique as 
in Example 1 to give a reddish violet dye having a melting point of 
240.degree. to 243.degree. C. (Dye No. 22 in Table 1). The dye had a 
dichroic ratio of 12.3 in liquid crystals ZLI-1840. It had a dichroic 
ratio of 11.6 and a solubility of 4.0% in liquid crystals E-8.