Liquid crystalline alkenyl compounds incorporating an...

Details Liquid crystalline alkenyl compounds incorporating an... Liquid crystalline alkenyl compounds incorporating an...

2001-11-26

2004-02-24

Wu, Shean C (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299610, C548S136000, C548S143000, C548S146000, C548S215000, C549S029000, C549S049000, C349S136000

Reexamination Certificate

active

06696110

ABSTRACT:

The present invention describes new compounds. In particular it describes compounds for use in liquid crystal mixtures and in liquid crystal displays (LCDs) or in applications relating to inter alia thermography utilising nematic liquid crystal or chiral nematic liquid crystal mixtures.
LCDs, such as multiplexed Twisted Nematic TN-LCDs, Super Twisted Nematic STN-LCDs, Super Birefringent SBE-LCDs, Electrically Controlled Birefringence ECB-LCDs, or flexoelectric LCDs are currently used or being developed for computer monitors, laptop or notebook computers, portable telephones, video telephones, personal digital assistants, etc. The optical, electrical and temporal performance, e.g., contrast, threshold and driving voltages, and response times, of such displays depends crucially on the ratios of the elastic constants (k
33
, k
22
, k
11
) and the cell gap, d. In addition, flexoelectric LCDs also require nematic mixtures with advantageous ratios of the flexoelectric coefficients. Large banana shaped molecules have been found to increase the flexoelectric coefficients of nematic mixtures (1998, P57, Proceedings Freiburger Arbeitstagung Flüssigkristalle, Freiburg, Germany). However, due to their strongly non-linear shape and large number of aromatic rings and conjugated linking groups, they are highly viscous and relatively insoluble. They also exhibit high melting points and unusual smectic phases, which limits their miscibility with the nematic phase. Currently commercially available nematic mixtures for sophisticated high-information-content LCDs, such as STN-LCDs, incorporate trans-1,4-disubstituted-cyclohexyl derivatives with a terminal alkenyl chain (i.e., incorporating a carbon-carbon double bond) directly attached to the cyclohexane ring in order to produce the necessary elastic constant ratios for short response times, high multiplexing rates and low driving voltages. Such materials are costly and difficult to synthesise due to the requirement for a trans configuration of the 1,4-disubstituted cyclohexane ring and the necessity of synthesising the carbon-carbon double bond stepwise from this trans-1,4-disubstituted-cyclohexyl intermediate. If the carbon-carbon double bond is substituted at both carbon atoms, it must have a trans (E) configuration in order to exhibit an advantageous combination of elastic constants and to have an acceptably high nematic-isotropic transition temperature (N-I). The trans configuration is then generally produced by isomerisation of the cis (Z) form generated by the preceding Wittig reaction. These materials exhibit low or intermediate values of birefringence (&Dgr;n) due to the presence of the saturated cyclohexane rings. As the ratio d. &Dgr;n determines the optical properties of TN-LCDs and is fixed for driving the LCD in the first or second minimum, it is clear that higher values of &Dgr;n would allow smaller cell gaps. As the response time, t
on
of TN-LCDs is inversely proportional to d
2
, smaller cell gaps have a dramatic effect on t
on
. Low values of t
on
also allow the use of colour or more shades of colour due to the shorter frame times. Since the response times t
on
and especially t
off
also strongly depend on the magnitude of the viscosity of the nematic mixture, the combination of a low viscosity and a high birefringence would be highly advantageous. Furthermore TN-LCDs using thin film transistors (TFTs) as the backplate for active addressing require nematic liquid crystal mixtures with a positive dielectric anisotropy (&Dgr;&egr;) and a very high resistivity (holding ratio ≧98%) in order to avoid dielectric breakdown and inferior display performance. It has been shown that standard nematic liquid crystals with a terminal cyano group are unsuitable for TN-TFT-LCDs since they lead to low resistivity values due in part to their ability to solvate ions present in the alignment layers and electrodes. This has led to the wide-spread use of ‘super-fluorinated’ nematic liquid crystals with terminal trifluoromethoxy (DE 3732284 A1), difluoromethyl (WO 90/01056) or fluorine endgroups (JP2-233626, EPA 0 568 040 A1, EPA 0 563 981 A2) and/or several lateral fluoro substituents. However, this leads in general to low nematic-isotropic transition temperatures (N-I) for two-ring compounds. This requires a disproportionate use of three-ring compounds resulting in a high viscosity for the nematic mixture. There is therefore a requirement for synthetically readily-accessible nematic liquid crystals of high birefringence, low viscosity advantageous ratios of elastic constants and flexoelectric coefficients, as well as a relatively high value of N-I and a low melting point.
Liquid crystals with a five-membered heterocyclic ring are known (DE 3346175; EP 0 461 620) and are reviewed in for example Wiss. Z. Univ. HalleXXIX′80 M, H. 3, pp 35-55. They are generally characterised by a strong tendency for smectic phase formation (Mol. Cryst. Liq. Cryst., (1990), Vol.191, pp 223). Two-ring alkyl benzoates incorporating a five-membered heterocyclic ring, such as 2,5-disubstituted furan or 2,5-disubstituted 1,3,4-thiadiazole are known (EP 0 461 620; Mol. Cryst. Liq. Cryst., (1990), Vol. 191, pp 223). However, they are either non mesomorphic or exhibit smectic phases. Liquid crystals with a carbon-carbon double bond are also known (U.S. Pat. No. 4,676,604; U.S. Pat. No. 4,621,901; EPA 0195974; EPA 0315014; EPA 0355552) and are reviewed in for example Liq. Cryst., (1996) Vol. 20, pp 493. No alkenyl compounds incorporating a five-membered heterocyclic ring are described.
For all the above applications it is not usual for a single compound to exhibit all of the properties highlighted, normally mixtures of compounds are used which when mixed together induce the desired phases and required properties.
The present invention seeks to overcome or alleviate some of the above problems by incorporating a 5-membered heterocyclic ring in the core of a liquid crystal molecule in combination with a carbon-carbon double bond in the terminal end group of the molecule.
According to this invention compounds are provided of Formula I:
wherein
RJ is C
n
H
2n+1
CH═CHC
m
H
2m
Z
1
n may be 1-5;
m may be 0-5;
q may be 0, 1 or 2;
A
1
, A
2
, are independently chosen from 2,5-disubstituted furan, 2,5-disubstituted thiophene, 2,5-disubstituted oxazole, 2,5-disubstituted thiazole, 2,5-disubstituted 1,3,4-oxadiazole, 2,5-disubstituted 1,3,4-thiadiazole, 1,4-disubstituted benzene, 2,5-disubstituted pyrimidine, 2,5-disubstituted pyridine, 2,6-disubstituted naphthalene;
laterally substituted 1,4-disubstituted benzene, laterally substituted 2,5-disubstituted pyrimidine, laterally substituted 2,5-disubstituted pyridine, laterally substituted 2,6-disubstituted naphthalene wherein the lateral substituents are independently selected from F, Cl, Br or CN and may be present in any of the available substitution positions;
A
3
may be 2,5-disubstituted furan, 2,5-disubstituted thiophene, 2,5-disubstituted oxazole, 2,5-disubstituted thiazole, 2,5-disubstituted 1,3,4-oxadiazole, 2,5-disubstituted 1,3,4-thiadiazole, 1,4-disubstituted benzene, 2,5-disubstituted pyrimidine, 2,5-disubstituted pyridine, 2,6-disubstituted naphthalene; laterally substituted 1,4-disubstituted benzene, laterally substituted 2,5-disubstituted pyrimidine, laterally substituted 2,5-disubstituted pyridine, laterally substituted 2,6-disubstituted naphthalene wherein the lateral substituents are independently selected from F, Cl, Br or CN and may be present in any of the available substitution positions;
1,4-disubstituted bicyclo(2.2.2)octane, trans-1,4-disubstituted cyclohexane, trans-2,5-disubstituted dioxane, 1,4-disubstituted piperidine, Z
1
may be O, COO, OOC;
Z
2
, Z
3
are independently chosen from a direct bond, COO, OOC, C
2
H
4
, CH
2
O, OCH
2
, C
4
H
8
, C
3
H
6
O, (E)-CH═CHC
2
H
4
, (Z)-CH
2
CH═CHCH
2
, (E)-CH═CHCH
2
O, —C≡C— R may be alkyl, alkoxy, alkenyl, alkenyloxy, alkanoyloxy, alkenoyloxy or OC
p
F
2p+1
, R may contain 1 to 20 carbon atoms and may be branched or a str

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