Alkyl silane liquid crystal compounds

Details Alkyl silane liquid crystal compounds Alkyl silane liquid crystal compounds

2001-01-03

2004-08-31

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299610, C252S299620, C252S299630, C252S299640, C252S299660, C544S303000, C546S014000, C570S129000, C570S162000, C556S488000, C556S489000

Reexamination Certificate

active

06783812

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to compounds useful as components in liquid crystal (LC) compositions, particularly as components of LC compositions that exhibit smectic phases and more particularly as components of LC compositions that exhibit smectic A and/or smectic C phases. LC compositions of this invention may also exhibit nematic phases. LC compositions of this invention can be ferroelectric liquid crystals (FLCs). The invention also relates to optical devices employing LC compositions of the invention in optical switching and display elements.
Several types of smectic liquid crystal materials (LCs) have been investigated for rapid switching, view-angle enhancement and higher contrast, including surface-stabilized ferroelectric LCs (FLCs), deformed helix ferroelectric LCs (DHFLCs), and antiferroelectric LCs (AFLCs). Recently, smectic material exhibiting thresholdless or more properly V-shaped switching LCs (VSLCs) have been described (Inui, S. et al. (1996) J. Mater. Chem. 6(4):671-673; Seomun, S. S. et al. (1997) Jpn. J. Appl. Phys. 36:3580-3590). Ferroelectric LCs when aligned parallel to the substrate surfaces using the surface stabilized effect (in an surface-stabilized ferroelectric liquid crystal (SSFLC) device) exhibit two stable state switching on a microsecond time scale. Antiferroelectric LCs exhibit three stable-state switching, which by application of a bias field can be converted for use in a bistable switching mode LC devices. Two of the AFLC states have the same transmittance, so that alternate symmetrical switching can be used in AFLC devices. VSLCs, in contrast, exhibit very rapid, analog electro-optic response, allow symmetrical driving, and no dc balance is required. VSLCs are particularly attractive for applications requiring generation of multiple levels of gray scale.
Liquid crystal (LC) compositions exhibit one or more LC phases. LC compositions may be composed of one or more components. Components of LC compositions may exhibit liquid crystal phases, have latent liquid crystal phases or be compatible with (not suppress) liquid crystal phases in the LC composition. LC compounds and components of LC mixtures of this invention are rod-like molecules most typically having a generally linear mesogenic core with one or more directly or indirectly linked alicylic or aromatic rings (which may be fused aromatic rings) and linear or branched tail groups distributed on either side of the mesogenic core, e.g.:
LC components which do not themselves exhibit liquid crystal phases, but which exhibit LC phases on combination with one or more other components are described as having “latent” liquid crystal phases. Chiral nonracemic LCs useful in FLCS, DHFLCS, AFLC and VSLCS compositions have at least one component that has a chiral non-racemic tail group. FLCS, DHFLCS, AFLC and VSLCS compositions may be composed entirely of chiral non-racemic components, but are typically composed of a mixture of chiral nonracemic and achiral or racemic components.
SUMMARY OF THE INVENTION
The invention relates to liquid crystal compounds having silane tails which are useful as components in liquid crystal compositions, particularly those compositions exhibiting smectic liquid crystal compositions and more particularly those exhibiting chiral smectic phases, such as smectic C* phases. Silanes of this invention can be chiral nonracemic, chiral racemic or achiral molecules. Chiral racemic and achiral silanes of this invention are useful alone or in combination as liquid crystal host materials. The materials of this invention can also be combined with known liquid crystal host materials to impart improved properties. Chiral nonracemic silanes of this invention can function as additives or dopants in host materials to impart chirality into the material. When introduced into host materials the silanes of this invention tend to broaden a smectic C phase and/or lower melting and/or freezing points of the material and to improve alignment of the material in a liquid crystal cell. Of particular interest are compounds of this invention which are disilanes.
Compounds of this invention comprise a silane tail which has the general formula:
where:
R
1
is an alkyl or alkenyl group which may be straight-chain or branched having j (an integer greater than or equal to 1) carbon atoms and R
2
, R
2′
, R
3
and R
3′
, independently of one another, are alkyl groups, particularly lower alkyl groups having from 1-6 carbon atoms, and more particularly are methyl and ethyl groups;
n1 and m are integers from 1 to about 20, and are not equal to zero; n2 may be zero or an integer to indicate the presence (an integer) or absence (zero) of a double or triple bond between the silicons, the dashed line indicates a possible double or triple bond (when
either a double or triple bond is present the number of hydrogens on the adjacent carbons is decreased as needed); k is 0 or an integer from 1 to 10, preferably 0 or an integer from 1-4 and more preferably 0, 1 or 2;
k(n)+m+j preferably ranges from 6 to 20;
m, n and j are preferably 6-12; and
X is oxygen or a single bond.
Preferred liquid crystal silanes of this invention are those having a rod-like linear liquid crystal (mesogenic) core having 1, 2 or 3 rings and an alkyl, alkoxy or ether tail which can be fully or partially fluorinated.
Liquid crystal compounds of this invention include those having the structure:
where:
D is the silane tail as defined above;
a, b, x, y, z can be 0 or 1 to indicate the presence or absence of a given structural element; x+y+z is 1, 2 or 3, when x is 0, a is 0; when z is 0, b is 0;
A and B, independently, when present, can be —O—, —COO—, —OOC—, —CH
2
—CH
2
—, —CH═CH— (cis or trans), —C≡C—, —CH═CH—CH═CH— (cis or trans), —O—CH
2
— or —CH
2
—O; when a or b is 0 the rings are linked through a single bond;
the A, B and C rings, independently of one another, are aromatic rings or alicyclic rings, preferred aromatic rings are 5 or 6 member rings, but one ring can be replaced with an aromatic fused ring moiety, e.g., naphthalene, or partially aromatic fused ring system, i.e., dehydronaphthalene; alicylic rings can have from 3-10 carbon atoms, and may be unsaturated, but cyclohexane or cyclohexene rings are preferred; with one or two of the A, B or C rings being alicylic (preferably cyclohexyl or cyclohexenyl rings); one or two carbons in the A, B or C rings that are aromatic can be replaced with a heteroatom, e.g., O, S, or N; one or two of the carbons in the A, B or C rings that are alicylic can be replaced with a heteroatom (e.g., N, S or O) or a C═O group;
Y indicates substitution on the rings of the core and can represent up to four substituents on aromatic rings and up to 10 substituents on cyclohexyl or cyclohexenyl rings; Y can for example be a halogen, CN group, NO
2
, alkyl (lower having 1-6 carbons) or alkoxy (lower having 1-6 carbons), a preferred substituent is a halogen with fluorine more preferred;
Z is a single bond, an —O— or a —COO— or —OOC— group, preferred Z are single bonds and —O—; and
M is a tail group which can be:
a non-fluorinated alkyl, alkenyl or ether group or R
F
, where R
F
is an alkyl, or ether group which is fully or partially fluorinated, these alkyl and/or ether groups may be straight-chain or branched; preferred M contain from 3-20 carbon atoms.
Any one, two or three of the A or B rings can be aromatic and are preferably selected from phenyl rings, pyridine or pyrimidine rings including 1,4-phenylene, 2,5-pyridinyl and 2,5-pyrimidyl rings, fluorinated 1,4-phenylenes, fluorinated phenylpyrimidyl and terphenyl. Exemplary aromatic cores are illustrated in Scheme 2. The D group or the Z—M or Z—R
F
group can be positioned on either side of the cores as illustrated in Scheme 2.
Phenyl rings can carry up to 4 substituents, e.g., up to four fluorines. Pyridine rings can carry up to 3 substituents, e.g., up to 3 fluorines. Pyrimidine rings can carry up to 2 substituents, e.g., up to 2 fluorines. Preferred rings are nonsubstit

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