Compositions – Liquid crystal compositions – Containing nonsteryl liquid crystalline compound of...
Patent
1989-06-19
1992-07-14
Stoll, Robert L.
Compositions
Liquid crystal compositions
Containing nonsteryl liquid crystalline compound of...
25229967, C09K 1930, C09K 1920
Patent
active
051300494
DESCRIPTION:
BRIEF SUMMARY
SUMMARY OF THE INVENTION
The invention relates to liquid crystalline compounds of the formula I ##STR3## wherein
R.sup.1 and R.sup.2 are each independently a normal or branched alkyl residue with up to 16 C atoms or a normal or branched alkenyl residue with 3 to 16 C atoms wherein one or two non-adjacent CH.sub.2 groups of these residues may be replaced by --O--, --CO--, --O--CO-- or --CO--O--,
X.sup.1 and X.sup.2 are each independently a methyl group or an halogen atom,
n and m are each independently 0, 1, 2, 3 or 4.
Liquid crystal phases are exhibited by certain organic compounds and constitute an intermediate state which exists between the crystalline solid and the fully disordered liquid phase and within which certain long range ordering of the molecules takes place.
There are two broad types of liquid crystal phase; the smectic mesophase in which the long range ordering is of a substantially lamellar type and the nematic mesophase in which the ordering is substantially linear, i.e., the molecules tend to line up with the long axes of the molecules parallel. Included sometimes as a subclass of the nematic mesophase and sometimes classified as a separate mesophase is the cholesteric mesophase. This last has a helical long range order imposed upon the linear order of the nematic mesophase. Compounds displaying a cholesteric mesophase are optically active (chiral) and the pitch of the helical twist is determined by the nature and extent of the optical activity. The pitch of the helical twist may be such that thin films of the cholesteric phase reflect visible light, resulting in the observation of bright colors, and the pitch may also be sharply temperature dependent resulting in the reflection of particular colors over particular temperature ranges so that the cholesteric mesophase in question can act as a "thermometer". This behavior is known as thermochromism.
The chiral compounds of the formula I exhibit a cholesteric mesophase (hereinafter designated Ch) because of their molecular shape and optical activity and also a chiral smectic C mesophase (hereinafter designated S.sub.c) underlying the cholesteric mesophase. They exhibit, either on their own or when mixed with one or more compounds capable of forming S.sub.c liquid crystal phases, a chiral S.sub.c liquid crystal phase in which the molecules lie tilted in the smectic layers which are themselves superimposed one upon the other to give a helical distribution of the tilt angles on passing through a stack of layers. A unique feature of the chiral S.sub.c phases of the compounds of the present invention is that, in their planar S.sub.c textures, these mesophases have a helical pitch which gives a selective reflection of colored light of specific wavelengths which are dependent on temperature, i.e., the compounds are thermochromic.
Also, above the S.sub.c -Ch transition, the compounds of the present invention exhibit, either on their own or when mixed with one of more other liquid crystal compounds, a cholesteric liquid crystal phase in which the molecules are arranged in the helical formulation of that phase such that a film of the phase in the Grandjean plane texture rotates the plane of polarization of incident polarized light and reflects elliptically polarized light of specific wavelengths when illuminated by ordinary light, so that the mesophases are thermochromic.
The compounds of the present invention have properties such that they may be used in a liquid crystal electrooptic device such as a "phase change" device in which the material is changed between a so-called "focalconic" cholesteric state, which scatters light, and a transparent nematic state by an applied electric field and in accordance with one aspect of the present invention an electro-optic device includes in its liquid crystalline material a compound as hereinbefore defined. It will of course be realized that there may be present, a mixture (solution) of compounds as hereinbefore defined and that other compounds exhibiting liquid crystalline behavior may be included. Preferably
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Grant & Hackh's Chemical Dictionary/5th Edition., Roger Grant and Claire Grant; 1987; p. 402.
S. M. Kelly et al., Ferroelectrics 1988, vol. 86, 300.
S. M. Kelly et al., Helv. Chim. Acta, vol. 71 (1988), 451-460.
Clemitson Robert W.
Sage Ian C.
Harris C.
Merck Patent Gesellschaft mit beschrankter Haftung
Stoll Robert L.
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