Compositions – Liquid crystal compositions – Containing nonsteryl liquid crystalline compound of...
Reexamination Certificate
1997-12-24
2001-10-30
Wu, Shean C. (Department: 1721)
Compositions
Liquid crystal compositions
Containing nonsteryl liquid crystalline compound of...
C252S299620, C252S299630, C544S303000, C546S346000, C548S215000, C549S324000, C549S380000, C568S634000, C568S649000, C568S669000, C570S128000, C570S130000, C570S131000, C570S132000, C570S144000, C570S183000, C570S188000
Reexamination Certificate
active
06309561
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to fluorinated chiral smectic liquid crystal compounds, to a process for the preparation of such compounds (and to intermediates for use therein), and to liquid crystal compound mixtures and electrooptical display devices containing such compounds.
BACKGROUND OF THE INVENTION
Devices employing liquid crystals have found use in a variety of electrooptical applications, in particular those which require compact, energy-efficient, voltage-controlled light valves, e.g., watch and calculator displays, as well as the flat-panel displays found in portable computers and compact televisions. Liquid crystal displays have a number of unique characteristics, including low voltage and low power of operation, which make them the most promising of the non-emissive electrooptical display candidates currently available.
One of the most important characteristics of a liquid crystal display device is its response time, i.e., the time required for the device to switch from the on (light) state to the off (dark) state. In a ferroelectric or anti-ferroelectric device, response time (&tgr;=&eegr;/P
s
E) is proportional to the rotational viscosity (&eegr;) of the liquid crystal compound(s) contained within the device and is inversely proportional to their polarization (P
s
) and to the applied electric field (E). Thus, response time can be reduced by using compound(s) having high polarizations or low viscosities, and such compounds are greatly desired in the art.
In the passive addressing of liquid crystal compounds exhibiting a spontaneous polarization, however, low polarization mixtures can be important for the practical operation of a liquid crystal device. Polarization reversal fields are larger for higher polarization mixtures, and polarization reversal fields cause switching or partial switching back to a material's original director alignment. This results in loss of the bistability that is crucial to the passive-matrix driving of ferroelectric liquid crystal devices.
Another potential disadvantage of using high polarization mixtures is the partial switching of their director alignment in response to non-switching (secondary) signals in a driving waveform. This continued response or fluctuation of the director causes a large decrease in the contrast ratio of a ferroelectric liquid crystal device.
In addition to fast response times, compounds should ideally possess broad smectic temperature ranges to enable operation of the device over a broad range of temperatures (or should be capable of combination with other liquid crystal compounds having different smectic temperature ranges without adversely affecting the smectic phase behavior of the base mixture).
SUMMARY OF THE INVENTION
Briefly, in one aspect, this invention provides fluorine-containing, chiral liquid crystal compounds having smectic mesophases or latent smectic mesophases. (Compounds having latent smectic mesophases are those which by themselves do not exhibit a smectic mesophase, but which, when in admixture with compounds having smectic mesophases or with other compounds having latent smectic mesophases, develop smectic mesophases under appropriate conditions.) The chiral liquid crystal compounds of the invention comprise (a) a chiral fluorochemical terminal portion that comprises (i) at least one chiral center (or chiral moiety), which can optionally be heteroatom-substituted; (ii) a terminal fluoroalkyl, fluoroether, perfluoroalkyl, or perfluoroether group (preferably, perfluoroalkyl or perfluoroether) wherein the fluoroalkyl and perfluoroalkyl groups are represented by the formula —C
q
F
2q
X′, wherein q is at least about 5 and X′ is hydrogen or fluorine; and (iii) an alkylene or fluoroalkylene group optionally containing at least one catenary, i.e., in-chain, ether oxygen atom; (b) a chiral or achiral terminal portion consisting of a hydrocarbon or hydrocarbon ether group and, when chiral, comprising at least one chiral center, which can optionally be heteroatom-substituted; and (c) a central core connecting the terminal portions; the alkylene or fluoroalkylene group of the chiral fluorochemical terminal portion having at least 3 in-chain atoms and being located between the chiral center of the chiral fluorochemical terminal portion and the central core (an “extended group”).
The chiral fluorochemical terminal portion of the compounds of the invention can be represented by the formula —D—R*—D—R
f
, where R* is a cyclic or acyclic chiral moiety containing at least one chiral center (asymmetric carbon atom); R
f
is fluoroalkyl, perfluoroalkyl, fluoroether, or perfluoroether; and each D is independently and non-directionally selected from the group consisting of a covalent bond,
and combinations thereof, where one or more hydrogen atoms can optionally be replaced with fluorine, and where r and r′ are independently integers of 0 to about 20, s is independently an integer of 1 to about 10 for each (C
s
H
2s
O), t is an integer of 1 to about 6, and p is an integer of 0 to about 4; with the proviso that at least one chiral center of R* is spaced from the central core by at least 3 in-chain atoms. Preferably, R
f
is perfluoroalkyl or perfluoroether; more preferably, R
f
is perfluoroether, as the perfluoroether-containing compounds of the invention exhibit, e.g., a broad smectic C mesophase, good compatibility with other smectic C compounds, and advantageous layer spacing behavior. When the R
f
group of the fluorochemical terminal portion is perfluoroalkyl or perfluoroether, it can contain small amounts of residual carbon-bonded hydrogen atoms but is preferably completely fluorinated.
In general, the compounds of this invention have a central core comprised of at least one or two rings independently selected from the group consisting of aromatic, heteroaromatic, alicyclic, substituted aromatic, substituted heteroaromatic, and substituted alicyclic rings, the rings being connected one with another by a covalent bond or by chemical groups selected from the group consisting of —COO—, —COS—, —HC═N—, —CH═CH—, —C≡C—, and —COSe—. The rings can be fused or non-fused. The heteroatoms within the heteroaromatic rings comprise at least one atom selected from the group consisting of nitrogen, oxygen, and sulfur. Non-adjacent ring carbon atoms in the alicyclic rings can be substituted by nitrogen, oxygen, or sulfur atoms. When the ring(s) are aromatic, heteroaromatic, substituted aromatic, or substituted heteroaromatic, the non-fused rings of the core are preferably no more than about two in number.
The chiral liquid crystal compounds of the invention exhibit exceptionally wide mesomorphic temperature ranges. When used in electrooptical devices, the compounds provide fast response times upon application of an electric field over broad temperature ranges. This makes them extremely useful in the preparation of mixtures that operate in their active mesomorphic phase in the range of from about −30° C. to about 70° C.
Surprisingly, in comparison with similar compounds having fewer than 3 in-chain atoms between at least one chiral center of the fluorochemical terminal portion and the central core, the compounds of the invention provide comparable electrooptic response speeds in spite of their lower measured polarization values. These lower polarization values in combination with broad mesogenic temperature ranges enable the utilization of liquid crystal mixtures that contain up to 100% of the chiral (optically active) compounds of the invention. In general, mixtures containing a high concentration of the compounds of this invention exhibit more temperature independent switching properties, which is important for the reliable and consistent operation of liquid crystal devices.
Furthermore, the use of high concentrations of liquid crystal compounds having low polarizations also provides a decrease (relative to the use of low concentrations of compounds having high polarizations) in the partial switching response of the resulting compositions to non-switchi
Hasegawa Masakazu
Keyes Michael P.
Radcliffe Marc D.
Savu Patricia M.
Snustad Daniel C.
3M Innovative Properties Company
Kokko Kent S.
Wu Shean C.
LandOfFree
Liquid crystal compounds having a chiral fluorinated... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid crystal compounds having a chiral fluorinated..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid crystal compounds having a chiral fluorinated... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2551982