Substituted anthracene-type isotropic dyes for liquid crystal display devices

DETAILED DESCRIPTION The isotropic dyes of this invention have the general formula: ##STR1## wherein W is selected from the group consisting of ##STR2## wherein: R is independently selected from the group consisting of H and C.
sub.
n H.
sub.
2n+1 ; Q is independently selected from the group consisting of H, OH, NH.
sub.
2, CN, OC.
sub.
n H.
sub.
2n+1, NO.
sub.
2, C.
sub.
n H.
sub.
2n+1, ##STR3## F, Cl, Br, SH, CHO and CF.
sub.
3 ; x is 1 to 8; and n is 0 to about 20.
Exemplary of the preferred anthracene-type isotropic dyestuffs are the following:
______________________________________
S in ROTN .
sup.
.
lambda.
max in ROTN
Dye Structure 404' 404' (nm)
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##STR4## 0 .
+-.
0.
1
420
##STR5## 0 .
+-.
0.
1
440
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'"ROTN 404" is a eutectic mixture of biphenylpyrimidine liquid crystals
commercially available from Hoffman LaRoche Co.

The isotropic dyes of this invention may be synthesized by the condensation of the appropriately substituted anthrone with the appropriate para-substituted benzaldehyde in inert solvents.
The isotropic dyes of the present invention have absorption maxima at wavelengths between about 400 and 700 nanometers.
The absorption maxima for several of the preferred isotropic dyes have been shown hereinabove.
The isotropic dyes of the invention have optical order parameters S which are very close to zero.
The optical order parameter is a measure of the efficiency with which the dye is oriented by the liquid crystal material.
The determination of the optical order parameter, S, is discussed in Journal of Applied Physics, Vol.
45, No.
11, 4718-23 (1974).
##EQU1## wherein: Ao is the absorbance in the absence of an electric field; and A.
sub.
1 is the absorbance in the presence of an electric field.
Since the isotropic dyes of this invention are not aligned along any particular axis by the liquid crystal materials, their absorptivity is not dependent upon the presence or absence of an electric field and their optical order parameters are very close to zero, i