WO2006053628A1

WO2006053628A1 - Liquid crystal compounds, liquid crystal medium and liquid crystal display

Info

Publication number: WO2006053628A1
Application number: PCT/EP2005/011431
Authority: WO
Inventors: Diane Louise Farrand; Kevin Adlem; John Patrick; Peter Best
Original assignee: Merck Patent Gmbh
Priority date: 2004-11-20
Filing date: 2005-10-25
Publication date: 2006-05-26
Also published as: GB2435583A; GB0710267D0; GB2435583B

Abstract

The instant invention relates to mesogenic compounds of formula (I) wherein the parameters are as specified in the text. The instant invention further relates to mesogenic media, preferably liquid crystal media showing a blue phase and their use in electro-optical light modulation elements and their respective use in displays, as well as to such devices.

Description

Liquid Crystal Compounds, Liquid Crystal Medium and Liquid Crystal Display

Field of the invention

The present invention relates to mesogenic compounds, mesogenic media and to electro-optical displays comprising these mesogenic media as light modulation media, in particular to displays, which are operated at a temperature at which the mesogenic modulation media are in an optically isotropic phase, preferably in a blue phase.

Problem to be solved and state of the art

Electro-optical displays and mesogenic light modulation media, which are in the isotropic phase when being operated in the display are described in DE 102 17 273 A. Electro-optical displays, and mesogenic light modulation media, which are in the so-called blue phase, when being operated in the display are described in DE 103 13 979.6, which is not yet laid open.

The mesogenic media and displays described in these references provide several significant advantages compared to well-known and widely used displays using liquid crystals in the nematic phase, like for example liquid crystal displays (LCDs) operating in the twisted nematic (TN)-, the super twisted nematic (STN)-, the electrically controlled birefringence (ECB)- mode with its various modifications and the in-pjane switching (IPS)-mode. Amongst these advantages most pronounced are their much faster switching times, and significantly wider optical viewing angle.

Whereas, compared to displays using mesogenic media in another liquid crystalline phase, as e.g. in the smectic phase in surface stabilized ferroelectric Nquid crystal displays (SSF LCDs), the displays of DE 102 17 273.0 and DE 103 13 979.6 are much easier to produce For example, they do not require a very thin cell gap and the electro-optical effect is not very sensitive to small variations of the cell gap. However, the liquid crystal media described in these mentioned patent applications still require operating voltages, which are not low enough for some applications. Further the operating voltages of these media vary with temperature, and it is generally observed, that at a certain temperature the voltage dramatically increases with increasing temperature. This limits the applicability of liquid crystal media in the blue phase for display applications. A further disadvantage of the liquid crystal media described in these patent applications is their moderate reliability which is insufficient for very demanding applications. This moderate reliability may be for example expressed in terms of the voltage holding ratio parameter (VHR), which in liquid crystal media as described above may be below 90%.

Some compounds and compositions have been reported which possess a blue phase between the cholesteric phase and the isotropic phase and can usually be observed by optical microscopy. These compounds or compositions for which the blue phases are observed are typically single mesogenic compounds or mixtures showing a high chirality. However, generally the blue phases observed only extend over a very small temperature range, which is typically less than 1 degree centigrade (Kelvin) wide. In order to operate the novel fast switching display mode of DE 103 13 979.6 the light modulation medium to be used has to be in the blue phase. Thus a light modulation medium possessing a blue phase, which is as wide as possible, is required.

Therefore there is a strong need for a modulation medium with a blue phase with a wide phase range, which may be achieved either by an appropriate mixture of mesogenic compounds themselves or, preferably by mixing a host mixture with appropriate mesogenic properties with a single dopant or a mixture of dopants that stabilises the blue phase over a wide temperature range.

Summarizing, there is a need for liquid crystal media, which can be operated in liquid crystal displays, which are operated at temperatures where the media is in the blue phase, which provide the following technical improvements: a reduced operating voltage, a reduced temperature dependency of the operating voltage and an improved reliability, e.g. VHR.

Present invention

Surprisingly, it has now been found that compounds of formula I,

wherein

and

are, independently of each other, 1 ,4-phenylen or trans-1 ,4-cyclohexylen, which optionally may be substituted with 1 or 2 substituents selected from the group of substituents F, Cl, OCF₃, OCH₃ and/or CH₃.

and

are, independently of each other,

1 ,4-phenylen which optionally may be substituted with 1 or 2 substituents selected from the group of substituents F, Cl₁ OCH₃ and/or CH₃.

R¹¹ and R¹² are, independently of each other, H or alkyl, which is straight chain or branched, preferably has 1 to 20 C- atoms, most preferably 1 to 12 C-atoms, is unsubstituted, mono- or poly-substituted by F, Cl, Br, I or CN, and in which one or more non-adjacent CH₂ groups are optionally replaced, in each case independently from one another, by -O-, -S-, -NH-, -

NR⁰¹-, -SiR⁰¹R⁰²-, -CO-, -COO-, -OCO-, -OCO-O-, -S- CO-, -CO-S-, -CY⁰¹=CY⁰²- or -C≡C- in such a manner that O and/or S atoms are not linked directly to one another, preferably H, n-alkyl, n-alkoxy with 1 to 7 C- atoms preferably 2 to 5 C-atoms, alkenyl, alkenyloxy or alkoxyalkyl with 2 to 7 C-atoms, preferably with 2 to 5 C- atoms or CN, NCS, halogen, preferably F, Cl, halogenated alkyl, alkenyl or alkoxy, preferably mono-, di- or oligo-fluorinated alkyl, alkenyl or alkoxy, especially preferred CF₃, OCF₂H or OCF₃, or one of R¹¹ and

R¹²denotes or both denote independently of each other PG-SG, most preferably R¹² is H or alkyl with 1 to 12 C- atoms,

R⁰¹ and R⁰² are, independently of each other, H or alkyl with 1 to 12

C-atoms,

PG is a polymerisable or reactive group,

SG is a spacer group or a single bond,

Y⁰¹ and Y⁰² are, independently of each other, F, Cl or CN, and alternatively one of them may be H,

X has one of the meanings given for R and preferably is a polar endgroup and most preferably is CN, OCF₃, CF₃, F or Cl, and

m and n are, independently of each other, O or 1 , are suitable to considerably enhance the range of temperatures over which the blue phase is stable or even induce a blue phase in respective mesogenic hosts, which do not show such a phase on their own.

Preferably the mesogenic hosts are liquid crystalline hosts.

Particularly preferred are compounds of formula Ia, wherein

wherein the parameters have the respective meanings given under formula I above and

Y /11 i to~ \ Y/14 are, independently of each other, H or F.

Particularly preferred are compounds of formula I, preferably of formula Ia, wherein

m and n are 0 and/or

ring A is phenylene that is optionally substituted by one or more F- atoms or a cycloheylene and/or

R¹¹ and/or R¹², is alkyl or alkoxy with 1 to 12, preferably 1 to 8 C- atoms, or alkenyl, alkenyloxy or alkynyl with 2 to 12, preferably 2 to 7 C-atoms and/or

R¹¹ and/or R¹², preferably R¹¹, is PG-SG- and/or

SG is alkylene with 1 to 12 C atoms which is optionally mono- or polysubstituted by F and wherein one or more non-adjacent CH₂ may be replaced, in each case independently from one another, by -O-, -CH=CH- or -C≡C-, and that is linked to a ring, preferably to ring A¹ via a group selected from -O-, -CO-O-, -O-CO-, -O-CO-O- and a single bond and/or

SG is a single bond and/or m + n is 0 or 1 and/or R¹² is H or alkyl.

Preferably

and

are, independently of each other,

or their mirror images.

Preferably

and

are, independently of each other,

In a preferred embodiment of the present invention the group

in formula Ia is

Further preferred are compounds of formula I, respectively Ia, wherein the group

is selected from the group of patial formulae (1) to (5)

(1)

wherein R¹² has the meaning given above.

An alkyl or an alkoxy radical, i.e. an alkyl where the terminal CH₂ group is replaced by -O-, in this application may be straight-chain or branched. It is preferably straight-chain, has 1 , 2, 3, 4, 5, 6, 7 or 8 carbon atoms and accordingly is preferably methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy, or octoxy, furthermore methyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetradecoxy, for example.

Oxaalkyl, i.e. an alkyl group in which one non-terminal CH₂ group is replaced by -O-, is preferably straight-chain 2-oxapropyl (= methoxy- methyl), 2- (= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3-, or 4- oxapentyl, 2-, 3-, 4-, or 5-oxahexyl, 2-, 3-, 4-, 5-, or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl or 2-, 3-, 4-, 5-, 6-,7-, 8- or 9-oxadecyl, for example. An alkenyl group, i.e. an alkyl group wherein one or more CH₂ groups are replaced by -CH=CH-, may be straight-chain or branched. It is preferably straight-chain, has 2 to 10 C atoms and accordingly is preferably vinyl, prop-1-, or prop-2-enyl, but-1-, 2- or but-3-enyl, pent-1-, 2-, 3- or pent-

4-enyl, hex-1 -, 2-, 3-, 4- or hex-5-enyl, hept-1-, 2-, 3-, 4-, 5- or hept-6-enyl, oct-1 -, 2-, 3-, 4-, 5-, 6- or oct-7-enyl, non-1-, 2-, 3-, A-, 5-, 6-, 7- or non- 8-enyl, dec-1-, 2-, 3-, A-, 5-, 6-, 7-, 8- or dec-9-enyl.

Especially preferred alkenyl groups are C₂-C₇-I E-alkenyl, C₄-C₇-3E- alkenyl, C₅-C₇-4-alkenyl, C₆-C₇-5-alkenyl and C₇-6-alkenyl, in particular C₂-C₇-I E-alkenyl, C₄-C₇-3E-alkenyl and C₅-C₇-4-alkenyl. Examples for particularly preferred alkenyl groups are vinyl, 1 E-propenyl, 1 E-butenyl, 1 E-pentenyl, 1 E-hexenyl, 1 E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having up to 5 C atoms are generally preferred.

In an alkyl group, wherein one CH2 group is replaced by -O- and one by -CO-, these radicals are preferably neighboured. Accordingly these radicals together form a carbonyloxy group -CO-O- or an oxycarbonyl group -O-CO-. Preferably such an alkyl group is straight-chain and has 2 to 6 C atoms.

It is accordingly preferably acetyloxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl, 2-propionyloxy- ethyl, 2-butyryloxyethyl, 3-acetyloxypropyl, 3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxy- carbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(propoxy- carbonyl)ethyl, 3-(methoxycarbonyl)propyl, 3-(ethoxycarbonyl)propyl, 4-(methoxycarbonyl)-butyl. An alkyl group wherein two or more CH₂ groups are replaced by -O- and/or -COO-, it can be straight-chain or branched. It is preferably straight-chain and has 3 to 12 C atoms. Accordingly it is preferably bis-carboxy-methyl, 2,2-bis-carboxy-ethyl, 3,3-bis-carboxy-propyl, 4,4-bis-carboxy-butyl, 5,5-bis-carboxy-pentyl, 6,6-bis-carboxy-hexyl, 7,7-bis-carboxy-heptyl,

8,8-bis-carboxy-octyl, 9,9-bis-carboxy-nonyl, 10,10-bis-carboxy-decyl, bis- (methoxycarbonyl)-methyl, 2,2-bis-(methoxycarbonyl)-ethyl, 3,3-bis- (methoxycarbonyl)-propyl, 4,4-bis-(methoxycarbonyl)-butyl, 5,5-bis- (methoxycarbonyl)-pentyl, 6,6-bis-(methoxycarbonyl)-hexyl, 7,7-bis- (methoxycarbonyl)-heptyl, 8,8-bis-(methoxycarbonyl)-octyl, bis- (ethoxycarbonyl)-methyl, 2,2-bis-(ethoxycarbonyl)-ethyl, 3,3-bis- (ethoxycarbonyl)-propyl, 4,4-bis-(ethoxycarbonyl)-butyl, 5,5-bis- (ethoxycarbonyl)-hexyl.

A alkyl or alkenyl group that is monosubstituted by CN or CF₃ is preferably straight-chain. The substitution by CN or CF₃ can be in any desired position.

An alkyl or alkenyl group that is at least monosubstituted by halogen, it is preferably straight-chain. Halogen is preferably F or Cl, in case of multiple substitution preferably F. The resulting groups include also perfluorinated groups. In case of monosubstitution the F or Cl substituent can be in any desired position, but is preferably in ω-position. Examples for especially preferred straight-chain groups with a terminal F substituent are fluormethyl, 2-fluorethyl, 3-fluorpropyl, 4-fluorbutyl, 5-fluorpentyl, 6-fluorhexyl and 7-fluorheptyl. Other positions of F are, however, not excluded.

Halogen means F, Cl, Br and I and is preferably F or Cl, most preferably F.

Each of R¹¹ and R¹² may be a polar or a non-polar group. In case of a polar group, it is preferably selected from CN, SF₅, halogen, OCH₃, SCN, COR⁵, COOR⁵ or a mono- oligo- or polyfluorinated alkyl or alkoxy group with 1 to 4 C atoms. R⁵ is optionally fluorinated alkyl with 1 to 4, preferably 1 to 3 C atoms. Especially preferred polar groups are selected of F, Cl, CN, OCH₃, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, CHF₂, CH₂F, OCF₃, OCHF₂, OCH₂F, C₂F₅ and OC₂F₅, in particular F, Cl, CN, CF₃, OCHF₂ and OCF₃. In case of a non-polar group, it is preferably alkyl with up to 15 C atoms or alkoxy with 2 to 15 C atoms.

Each of R¹¹ and R¹² may be an achiral or a chiral group. In case of a chiral group it is preferably of formula I^*:

wherein

Q¹ is an alkylene or alkylene-oxy group with 1 to 9 C atoms or a single bond,

Q² is an alkyl or alkoxy group with 1 to 10 C atoms which may be unsubstituted, mono- or polysubstituted by F, Cl, Br or CN, it being also possible for one or more non-adjacent CH₂ groups to be replaced, in each case independently from one another, by -C≡C-, -O-, -S-, -NH-, -N(CH₃)-, -CO-, -COO-, -OCO-, -OCO-O-, -S-CO- or

-CO-S- in such a manner that oxygen atoms are not linked directly to one another,

Q³ is F, Cl, Br, CN or an alkyl or alkoxy group as defined for Q² but being different from Q².

In case Q¹ in formula I* is an alkylene-oxy group, the O atom is preferably adjacent to the chiral C atom.

Preferred chiral groups of formula I* are 2-alkyl, 2-alkoxy, 2-methylalkyl, 2- methylalkoxy, 2-fluoroalkyl, 2-fluoroalkoxy, 2-(2-ethin)-alkyl, 2-(2-ethin)-alkoxy, 1 ,1 ,1-trifluoro-2-alkyl and 1 ,1 ,1 -trifluoro-2-alkoxy.

Particularly preferred chiral groups I^* are 2-butyl (=1-methylpropyl), 2- methylbutyl, 2-methylpentyl, 3-methylpentyl, 2-ethyihexyl, 2-propylpentyl, in particular 2-methylbutyl, 2-methylbutoxy, 2-methylpentoxy, 3- methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy, 2-octyloxy, 2-oxa-3- methylbutyl, 3-oxa-4-methylpentyl, 4-methylhexyI, 2-hexyl, 2-octyl, 2-nonyl, 2-decyl, 2-dodecyl, 6-methoxyoctoxy, 6-methyloctoxy, 6- methyloctanoyloxy, 5-methylheptyloxycarbonyl, 2-methylbutyryloxy, 3- methylvaleroyloxy, 4-methylhexanoyloxy, 2-chlorpropionyloxy, 2-chloro-3- methylbutyryloxy, 2-chloro-4-methylvaleryloxy, 2-chloro-3-methylvaleryloxy, 2-methyl-3-oxapentyl, 2-methyl-3-oxahexyl, 1 -methoxypropyl-2-oxy, 1 - ethoxypropyl-2-oxy, 1-propoxypropyl-2-oxy, 1 -butoxypropyl-2-oxy, 2- fluorooctyloxy, 2-fluorodecyloxy, 1 ,1 ,1 -trifIuoro-2-octyloxy, 1 ,1 ,1 -trifluoro-2- octyl, 2-fluoromethyloctyloxy for example. Very preferred are 2-hexyl, 2- octyl, 2-octyloxy, 1 ,1 ,1 -trifluoro-2-hexyl, 1 ,1 ,1 -trifluoro-2-octyl and 1 ,1 ,1- trifluoro-2-octyloxy.

In addition, compounds containing an achiral branched alkyl group may occasionally be of importance, for example, due to a reduction in the tendency towards crystallization. Branched groups of this type generally do not contain more than one chain branch. Preferred achiral branched groups are isopropyl, isobutyl (= methylpropyl), isopentyl (= 3-methylbutyl), isopropoxy, 2-methyl-propoxy and 3-methylbutoxy.

The polymerisable or reactive group PG is preferably selected from

CH₂=CW¹-COO-,

,

CH₂=CW²-(O)_ki-, CH₃-CH=CH-O-, (

(CH₂=CH-CH₂)₂CH-OCO-, (CH₂=CH)₂CH-O-, (CH₂=CH-CH₂)₂N-, HO-CW²W³-, HS-CW²W³-, HW²N-, HO-CW²W³-NH-, CH₂=CW¹-CO-NH-, CH₂=CH-(COO)_ki-Phe-(0)_k2-, Phe-CH=CH-, HOOC-, OCN-, and W⁴W⁵W⁶Si-, with W¹ being H, Cl, CN, phenyl or alkyl with 1 to 5 C-atoms, in particular H, Cl or CH₃, W² and W³ being independently of each other H or alkyl with 1 to 5 C-atoms, in particular methyl, ethyl or n- propyl, W⁴, W⁵ and W⁶ being independently of each other Cl, oxaalkyl or oxacarbonylalkyl with 1 to 5 C-atoms, Phe being 1 ,4-phenylene and ki and k₂ being independently of each other O or 1. Especially preferably PG is a vinyl group, an acrylate group, a methacrylate group, an oxetane group or an epoxy group, especially preferably an acrylate or methacrylate group.

As for the spacer group SG all groups can be used that are known for this purpose to those skilled in the art. The spacer group SG is preferably of formula SG'-X, such that PG-SG- is PG-SG'-X-, wherein

SG¹ is alkylene with up to 20 C atoms which may be unsubstituted, mono- or poly-substituted by F, Cl, Br, I or CN, it being also possible for one or more non-adjacent CH₂ groups to be replaced, in each case independently from one another, by -O-, -S-, -NH-, -NR⁰¹-, -SiR⁰¹R⁰²-, -CO-, -COO-, -OCO-, -OCO-O-, -S-, -CO-, -CO-S-, -CH=CH- or -OC- in such a manner that O and/or S atoms are not linked directly to one another,

X is -O-, -S-, -CO-, -COO-, -OCO-, -O-COO-, -CO-NR⁰¹-, -NR⁰¹-CO-, - OCH₂-, -CH₂O-, -SCH₂-, -CH₂S-, -CF₂O-, -OCF₂-, -CF₂S-, -SCF₂-, -CF₂CH₂-, -CH₂CF₂-, -CF₂CF₂-, -CH=N-, -N=CH-, -N=N-, -CH=CR⁰¹-, -CY⁰¹=CY⁰²-, -C≡C-, -CH=CH-COO-, -OCO-, -CH=CH- or a single bond, and

R⁰¹, R⁰², Y⁰¹ and Y⁰² have one of the respective meanings given above.

X is preferably -O-, -S-, -OCH₂-, -CH₂O-, -SCH₂-, -CH₂S-, -CF₂O-,

-OCF₂-, -CF₂S-, -SCF₂-, -CH₂CH₂-, -CF₂CH₂-, -CH₂CF₂-, -CF₂CF₂-, -CH=N-, -N=CH-, -N=N-, -CH=CR⁰-, -CY⁰²=CY⁰²-, -C≡C- or a single bond, in particular -O-, -S-, -C≡C-, -CY⁰¹=CY⁰²- or a single bond, very preferably a group that is able to from a conjugated system, such as -C≡C- or -CY⁰¹=CY⁰²-, or a single bond.

Typical groups SG' are, for example, -(CH₂)_P-, -(CH₂CH₂O)_q -CH₂CH₂-, -CH₂CH₂-S-CH₂CH₂- or -CH₂CH₂-NH-CH₂CH₂- or -(SiR°R⁰⁰-O)p-, with p being an integer from 2 to 12, q being an integer from 1 to 3 and R⁰, R⁰⁰ and the other parameters having the meanings given above. Preferred groups SG' are ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, octadecylene, ethyleneoxyethylene, methyleneoxybutylene, ethylene-thioethylene, ethylene-N-methyl-iminoethylene, 1 -methylalkylene, ethenylene, propenylene and butenylene for example.

In another preferred embodiment SG¹ is a chiral group of formula I*':

wherein

Q¹ and Q³ have the meanings given in formula I*, and

Q⁴ is an alkylene or alkylene-oxy group with 1 to 10 C atoms or a single bond, being different from Q¹,

with Q¹ being linked to the polymerisable group PG.

Further preferred are compounds with one or two groups PG-SG- wherein SG is a single bond.

In case of compounds with two groups PG-SG₁ each of the two polymerisable groups PG and the two spacer groups SG can be identical or different.

Preferably the liquid crystalline media according to the instant invention contain a compound A comprising, preferably predominantly consisting of and most preferably entirely consisting of compounds of formula I.

The compounds of formula I preferably are prepared according to the following scheme.

Scheme I

wherein

R¹¹, R¹², Y¹¹, Y¹², Y¹³, Y¹⁴ and X have the respective meanings given above.

R¹¹, R¹² have the respective parameters given above.

Comprising in this application means in the context of compositions that the entity referred to, e.g. the medium or the component, contains the compound or compounds in question, preferably in a total concentration of 10 % or more and most preferably of 20 % or more.

Predominantly consisting, in this context, means that the entity referred to contains 80 % or more, preferably 90 % or more and most preferably 95 % or more of the compound or compounds in question.

Entirely consisting, in this context, means that the entity referred to contains 98 % or more, preferably 99 % or more and most preferably 100.0 % of the compound or compounds in question.

The concentration of the compounds according to the present application are contained in the media according to the present application preferably is in the range from 0.5% or more to 30% or less, more preferably in the range from 1% or more to 20% or less and most preferably in the range from 5% or more to 12% or less.

The compounds of formula I are preferably selected from the group of sub- formulae 1-1 to I-6

wherein the parameters have the respective meanings given under formula I above and preferably

R 11 is alkyl, alkoxy, alkenyl, alkynyl, F or CN, preferably alkyl, and

R 12 is alkyl, alkoxy, alkenyl or alkynyl, preferably alkyl

and chiral compounds of these compounds are encompassed too.

Examples of compounds of formula I according to the present invention with a terminal alkyl group are

Examples of compounds of formula I according to the present invention with a terminal alkenyl group are

Examples of compounds of formula I according to the present invention with a reactive terminal group are

In a preferred embodiment the mesogenic modulation media according to the instant invention comprise

- a component A, preferably in a concentration of 1 % to 25 % by weight, comprising, preferably predominantly consisting of and most preferably entirely consisting of, one compound or more compounds of the formula I given above and

- optionally a dielectrically positive component B comprising, preferably predominantly consisting of and most preferably entirely consisting of one compound or of more compounds of formula Il

wherein

R² has the meaning given under formula I for R¹¹,

21 22 23

A , A and A are, each independently of each other,

whereby each of A²¹ and A²² may have the same or a different meaning if present twice,

Z²¹ and Z²² are, each independently of each other, a single bond,

-(CH₂)₄)-, -CH₂CH₂-, -CF₂-CF₂-, -CF₂-CH₂-, -CH₂-CF₂-, -CH=CH-, -CF=CF-, -CF=CH-, -(CH₂)₃O-, -O(CH₂)₃-, -CH=CF-, -C≡C-, -CH₂O-, -OCH₂-, -CF₂O-, -OCF₂-, -CO-O- or -O-CO-, whereby each of Z²¹ and Z²² may have the same or a different meaning if present twice,

X² is halogen, -CN, -NCS, -SF₅, -SO₂CF₃, alkyi, alkenyl, alkenyloxy or alkylalkoxy or alkoxy radical each mono- or polysubstituted by CN and/or halogen,

L²¹ and L²² are, each independently of each other, H or F, and

m is O, 1 or 2,

n is 0, 1 , 2 or 3,

o is 0, 1 or 2, preferably 0 or 1 and

m + n + o is 3 or less, preferably 2 or less,

- optionally a component C, preferably in a concentration of 1 % to 25 % by weight, comprising, preferably predominantly consisting of and most preferably entirely consisting of one compound or of more compounds of formula III

wherein

a, b, c and d are each independently of each other 0, 1 or 2, whereby

a + b + c + d is 4 or less,

A³¹, A³², A³³ and A³⁴ are, each independently of each other;

whereby each of A³¹, A³², A³³ and A³⁴ may have the same or a different meaning if present twice,

Z³¹, Z³², Z³³ and Z³⁴ are, each independently of each other, a single bond,

-(CHa)₄)-, -CH2CH2-, -CF2-CF2-, -CF2-CH2-, -CH2-CF2-, -CH=CH-, -CF=CF-, -CF=CH-, -(CH₂)₃O-, -O(CH₂)₃-, -CH=CF-, -C≡D-, -CH₂O-, -OCH₂-, -CF₂O-, -OCF₂-, -CO-O- or -O-CO-, whereby each of Z³¹ , Z³², Z³³ and Z³⁴ may have the same or a different meaning if present twice,

R³ is an alkyl or alkoxy radical having from 1 to 15 carbon atoms, wherein one or more methylene groups of said alkyl or alkoxy radical may be replaced independently of each other by -O-, -S-, -SiR^xR^y-, -CH=CH-, -C≡D-, -CO-O- and/or -O-CO- such that oxygen and/or sulfur atoms are not linked directly to each other, said alkyl or alkoxy radical being unsubstituted or mono-substituted with a -CN group or mono- or poly-substituted with halogen, preferably R¹¹ is a straight-chain alkyl, alkoxy, alkenyl, alkenyloxy or -O-alkylene-O-alkyl radical with up to 10 carbon atoms, said radicals being unsubstituted or mono- or poly-substituted with halogen,

L³¹, L³², L³³ and L³⁴ are each independently of each other hydrogen, halogen, a CN group, an alkyl or alkoxy radical having from 1 to 15 carbon atoms wherein one or more methylene groups of said alkyl or alkoxy radical may be replaced independently of each other by -O-, -S-, -SiR^xR^y-, -CH=CH-, -C≡D-, -CO-O- and/or -O-CO- such that oxygen and/or sulfur atoms are not linked directly to each other, said alkyl or alkoxy radical being unsubsti- tuted or mono-substituted with a -CN group or mono- or poly-substituted with halogen, with the proviso that at least one of L³¹, L³², L³³ and L³⁴ is not hydrogen,

X³ is F, Cl, CF₃, OCF₃, CN, NCS₁ -SF₅ or -SO₂-R²,

R^x and R^y are independently of each other hydrogen or an alkyl radical having from 1 to 7 carbon atoms; preferably R^x and R^y are both methyl, ethyl, propyl or butyl, and

R^z is an alkyl radical having from 1 to 7 carbon atoms, said alkyl radical being unsubstituted or mono- or poly- substituted with halogen; preferably R^z is CF₃, C₂F₅ or n-C₄Fg and

- 1 -20 % by weight of component D comprising one chiral compound or more chiral compounds with a HTP of ≥ 20 μm.

The inventive mixtures contain 1 -25 wt.%, preferably 2-20 wt.% and most preferably 3-15 wt.% of component A.

Suitable chiral compounds of component D are those which have an absolute value of the helical twisting power of 20 μm or more, preferably of 40 μm or more and most preferably of 60 μm or more. The HTP is measured in MLD-6260 at a temperature of 2O°C.

The chiral component D comprises preferably one or more chiral compounds which have a mesogenic structure and exhibit preferably one or more mesophases themselves, particularly at least one cholesteric phase. Preferred chiral compounds being comprised in the chiral component D are, inter alia, well known chiral dopants like cholesteryl- nonanoate (CN), R/S-811 , R/S-101 1 , R/S-201 1 , R/S-3011 , R/S-401 1 , R/S-5011 , CB-15 (Merck KGaA, Darmstadt, Germany). Preferred are chiral dopants having one or more chiral moieties and one or more mesogenic groups or having one or more aromatic or alicyclic moieties forming, together with the chiral moiety, a mesogenic group. More preferred are chiral moieties and mesogenic chiral compounds disclosed in DE 34 25 503, DE 35 34 777, DE 35 34 778, DE 35 34 779, DE 35 34 780, DE 43 42 280, EP 01 038 941 and DE 195 41 820 that disclosure is incorporated within this application by way of reference. Particular preference is given to chiral binaphthyl derivatives as disclosed in EP 01 111 954.2, chiral binaphthol derivatives as disclosed in WO 02/34739, chiral TADDOL derivatives as disclosed in WO 02/06265 as well as chiral dopants having at least one fluorinated linker and one end chiral moiety or one central chiral moiety as disclosed in WO 02/06196 and WO 02/06195.

The controlling medium of the present invention has a characteristic temperature, preferably a clearing point, in the range from about -30 °C to about 80 °C, especially up to about 55 °C.

The inventive mixtures contain one or more (two, three, four or more) chiral compounds in the range of 1-25 wt.%, preferably 2-20 wt.%. Especially preferred are mixtures containing 3-15 wt.% of a chiral compound.

Preferred embodiments are indicated below:

The medium comprises one, two or more compounds of formula I;

Component B preferably contains besides one compound ore more compounds of formula Il one ester compound or more ester compounds of the formula Z

wherein R^z has the meaning given under formula I for R¹¹,

X' is F₁ Cl, CN₁ NCS, OCF₃, CF₃ or SF₅.

wherein R^z has the meaning given under formula Il for R².

Especially preferred are mixtures containing 5 % to 35 %, preferably 10 % to 30 % and especially preferred 10 % to 20 % of compounds of formula Z.

The component B preferably contains additionally one or more compounds of formula N

wherein

R has the meaning given under formula I for R¹¹ and preferably is alkyl or Alkyl-C≡C,

"Alkyl" is alkyl with 1 to 7 C-atoms, preferably n-alkyl, and

n is O or i .

The component B preferably additionally comprises one or more compounds selected from the group of ester compounds of formulae

E

in which R⁰ has the meaning given for R¹¹ under formula I and preferably is alkyl and

The proportion of the compounds of the formulae E is preferably 10- 30% by weight, in particular 15 % to 25 %.

The medium preferably comprises one compound or more compounds selected from the group of formulae Q-1 and Q-2

Q-1

wherein R⁰ has the meaning given for R¹¹ under formula I and n and m are, independently of each other 0 or 1.

The medium preferably comprises one compound or more compounds selected from the group of compounds of formulae Il in which R⁰ is methyl.

The medium preferably comprises one dioxane compound, two or more dioxane compounds, preferably one dioxane compound or two dioxane compounds, selected from the group of formulae Dx-1 and Dx-2

wherein R⁰ has the meaning given for R¹¹ under formula It has been found that even a relatively small proportion of compounds of the formulae I mixed with conventional liquid-crystal materials, but in par¬ ticular with one or more compounds of the formulaell and III, results in a lower operating voltage and a broader operating temperature range. Preference is given, in particular, to mixtures which, besides one or more compounds of the formula I₁ comprise one or more compounds of the formula II, in particular compounds of the formula Il in which X² is F, Cl, CN, NCS, CF₃ or OCF₃. The compounds of the formulae I to III are colourless, stable and readily miscible with one another and with other liquid-crystalline materials.

The optimum mixing ratio of the compounds of the formulae I and Il and III depends substantially on the desired properties, on the choice of the components of the formulae I, Il and/or III, and on the choice of any other components that may be present. Suitable mixing ratios within the range given above can easily be determined from case to case.

The total amount of compounds of the formulae I to III in the mixtures according to the invention is not crucial. The mixtures can therefore com¬ prise one or more further components for the purposes of optimisation of various properties. However, the observed effect on the operating voltage and the operating temperature range is generally greater, the higher the total concentration of compounds of the formulae I to III.

In a particularly preferred embodiment, the media according to the inven¬ tion comprise compounds of the formula III which X³ is F, OCF₃, OCHF₂, OCH=CF₂, OCF=CF₂ or OCF₂-CF₂H. A favourable synergistic effect with the compounds of the formulae I results in particularly advantageous prop¬ erties. In particular, mixtures comprising compounds of formula I and of formula Il and of formula IN are distinguished by their low operating voltages.

The individual compounds of the formulae Il to III and their respective sub- formulae which can be used in the media according to the invention are either known or can be prepared analogously to the known compounds. The construction of the MLC display according to the invention from polarisers, electrode base plates and surface-treated electrodes corre¬ sponds to the conventional construction for displays of this type. The term conventional construction is broadly drawn here and also covers all derivatives and modifications of the MLC display, in particular including matrix display elements based on poly-Si TFT or MIM, however, particularly preferred are displays, which have electrodes on just one of the substrates, i.e. so called interdigital electrodes, as those used in IPS displays, preferably in one of the established structures.

A significant difference between the displays according to the invention and the conventional displays based on the twisted nematic cell consists, however, in the choice of the liquid-crystal parameters of the liquid-crystal layer.

The media according to the invention are prepared in a manner conven¬ tional per se. In general, the components are dissolved in one another, advantageously at elevated temperature. By means of suitable additives, the liquid-crystalline phases in accordance with the invention can be modified in such a way that they can be used in all types of liquid crystal display elements that have been disclosed hitherto. Additives of this type are known to the person skilled in the art and are described in detail in the literature (H. Kelker and R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). For example, pleochroic dyes can be added for the preparation of coloured guest-host systems or substances can be added in order to modify the dielectric anisotropy, the viscosity and/or the alignment of the nematic phases. Furthermore, stabilisers and antioxidants can be added.

The mixtures according to the invention are suitable for TN, STN, ECB and IPS applications and isotropic switching mode (ISM) applications. Hence, there use in an electro-optical device and an electro-optical device containing liquid crystal media comprising at least one compound according to the invention are subject matters of the present invention. The inventive mixtures are highly suitable for devices which operate in an optically isotropic state. The mixtures of the invention are surprisingly found to be highly suitable for the respective use.

Electro-optical devices that are operated or operable in an optically isotropic state recently have become of interest with respect to video, TV, and multi-media applications. This is because conventional liquid crystal displays utilizing electro-optical effects based on the physical properties of liquid crystals exhibit a rather high switching time which is undesired for said applications. Furthermore most of the conventional displays show a significant viewing angle dependence of contrast that in turn makes necessary measures to compensate this undesired property.

With regard to devices utilizing electro-optical effects in an isotropic state the German Patent Application DE 102 17 273 A1 for example discloses light controlling (light modulation) elements in which the mesogenic controlling medium for modulation is in the isotropic phase at the operating temperature. These light controlling elements have a very short switching time and a good viewing angle dependence of contrast. However, the driving or operating voltages of said elements are very often unsuitably high for some applications.

German Patent Application DE 10241 301 yet unpublished describes specific structures of electrodes allowing a significant reduction of the driving voltages. However, these electrodes make the process of manufacturing the light controlling elements more complicated.

Furthermore, the light controlling elements, for example, disclosed in both DE 102 17 273 A1 and DE 102 41 301 show a significant temperature dependence. The electro-optical effect that can be induced by the electrical field in the controlling medium being in an optical isotropic state is most pronounced at temperatures close to the clearing point of the controlling medium. In this range the light controlling elements have the lowest values of their characteristic voltages and, thus, require the lowest operating voltages. As temperature increases the characteristic voltages and hence the operating voltages increase remarkably. Typical values of the temperature dependence are in the range from about a few volts per centigrade up to about ten or more volts per centigrade. While DE 102 41 301 describes various structures of electrodes for devices operable or operated in the isotropic state, DE 102 17 273 A1 discloses isotropic media of varying composition that are useful in light controlling elements operable or operated in the isotropic state. The relative temperature dependence of the threshold voltage in these light controlling elements is at a temperature of 1 centigrade above the clearing point in the range of about 50%/centigrade. That temperature dependence decreases with increasing temperature so that it is at a temperature of 5 centigrade above the clearing point of about 10%/centigrade. However, for many practical applications of displays utilizing said light controlling elements the temperature dependence of the electro-optical effect is too high. To the contrary, for practical uses it is desired that the operating voltages are independent from the operating temperature over a temperature range of at least some centigrades, preferably of about 5 centigrades or more, even more preferably of about 10 centigrades or more and especially of about 20 centigrades or more.

Now it has been found that the use of the inventive mixtures are highly suitable as controlling media in the light controlling elements as described above and in DE 102 17 273 A1 , DE 102 41 301 and DE 102 536 06 and broaden the temperature range in which the operating voltages of said electro-optical operates. In this case the optical isotropic state or the blue phase is almost completely or completely independent from the operating temperature.

This effect is even more distinct if the mesogenic controlling media exhibit at least one so-called "blue phase" as described in yet unpublished DE 103 13 979. Liquid crystals having an extremely high chiral twist may have one or more optically isotropic phases. If they have a respective cholesteric pitch, these phases might appear bluish in a cell having a sufficiently large cell gap. Those phases are therefore also called "blue phases" (Gray and Goodby, "Smectic Liquid Crystals, Textures and Structures", Leonhard Hill, USA, Canada (1984)). Effects of electrical fields on liquid crystals existing in a blue phase are described for instance in H.S. Kitzerow, "The Effect of Electric Fields on Blue Phases", MoI. Cryst. Liq. Cryst. (1991), Vol. 202, p. 51-83, as well as the three types of blue phases identified so far, namely BP I, BP II, and BP III, that may be observed in field-free liquid crystals. It is noteworthy, that if the liquid crystal exhibiting a blue phase or blue phases is subjected to an electrical field, further blue phases or other phases different from the blue phases I, Il and III might appear.

The inventive mixtures can be used in an electro-optical light controlling element which comprises

one or more, especially two substrates; an assembly of electrodes; one or more elements for polarizing the light; and said controlling medium;

whereby said light controlling element is operated (or operable) at a temperature at which the controlling medium is in an optically isotropic phase when it is in a non-driven state.

The operating temperature of the light controlling elements is preferably above the characteristic temperature of the controlling medium said temperature being usually the transition temperature of the controlling medium to the blue phase; generally the operating temperature is in the range of about 0.1 ° to about 50 °, preferably in the range of about 0.1 ° to about 10 ° above said characteristic temperature. It is highly preferred that the operating temperature is in the range from the transition temperature of the controlling medium to the blue phase up to the transition temperature of the controlling medium to the isotropic phase which is the clearing point. The light controlling elements, however, may also be operated at temperatures at which the controlling medium is in the isotropic phase. (For the purposes of the present invention the term "characteristic temperature" is defined as follows:

If the characteristic voltage as a function of temperature has a minimum, the temperature at this minimum is denoted as characteristic temperature.

If the characteristic voltage as a function of temperature has no minimum and if the controlling medium has one or more blue phases, the transition temperature to the blue phase is denoted as characteristic temperature; in case there are more than one blue phase, the lowest transition temperature to a blue phase is denoted as characteristic temperature.

If the characteristic voltage as a function of temperature has no minimum and if the controlling medium has no blue phase, the transition temperature to the isotropic phase is denoted as characteristic temperature.)

In the context of the present invention the term "alky!" means, as long as it is not defined in a different manner elsewhere in this description or in the claims, straight-chain and branched hydrocarbon (aliphatic) radicals with 1 to 15 carbon atoms. The hydrocarbon radicals may be unsubstituted or substituted with one or more substituents being independently selected from the group consisting of F, Cl, Br₁ 1 or CN.

The dielectrics may also comprise further additives known to the person skilled in the art and described in the literature. For example, 0 to 5% of pleochroic dyes, antioxidants or stabilizers can be added.

C denotes a crystalline phase, S a smectic phase, Sc a smectic C phase, N a nematic phase, I the isotropic phase and BP the blue phase.

V_x denotes the voltage for X% transmission. Thus e.g. V₁₀ denotes the voltage for 10% transmission and V₁₀₀ denotes the voltage for 100% transmission (viewing angle perpendicular to the plate surface). t_on (respectively τ_on) denotes the switch-on time and τ_off (respectively τ_off) the switch-off time at an operating voltage corresponding the value of V₁₀₀, respectively of V_max.

denotes the optical anisotropy.

denotes the dielectric anisotropy

where

denotes the dielectric constant parallel to the longitudinal molecular axes and

denotes the dielectric constant perpendicular thereto). The electro-optical data are measured in a TN cell at the 1^st minimum of transmission (i.e. at a

value of 0.5 μm) at 20°C, unless expressly stated otherwise. The optical data are measured at 20°C, unless expressly stated otherwise.

Optionally, the light modulation media according to the present invention can comprise further liquid crystal compounds in order to adjust the physical properties. Such compounds are known to the expert. Their concentration in the media according to the instant invention is preferably 0 % to 30 %, more preferably 0 % to 20 % and most preferably 5 % to15 %.

Preferably inventive media have a range of the blue phase or, in case of the occurrence of more than one blue phase, a combined range of the blue phases, with a width of 9° or more, preferably of 10° or more, more preferably of 15° or more and most preferably of 20° or more.

In a preferred embodiment this phase range at least from 1O°C to 30°C, most preferably at least from 10°C to 4O°C and most preferably at least from 0°C to 5O°C, wherein at least means, that preferably the phase extends to temperatures below the lower limit and at the same time, that it extends to temperatures above the upper limit.

In another preferred embodiment this phase range at least from 20°C to 40°C, most preferably at least from 3O°C to 8O°C and most preferably at least from 30°C to 9O°C. This embodiment is particularly suited for displays with a strong back light, dissipating energy and thus heating the display. In the present application the term dielectrically positive compounds describes compounds with Δε > 1.5, dielectrically neutral compounds are compounds with -1.5 < Δε < 1.5 and dielectrically negative compounds are compounds with Δε < -1.5. The same holds for components. Δε is determined at 1 kHz and 20 °C. The dielectrical anisotropies of the compounds is determined from the results of a solution of 10 % of the individual compounds in a nematic host mixture. The capacities of these test mixtures are determined both in a cell with homeotropic and with homogeneous alignment. The cell gap of both types of cells is approximately 20 μm. The voltage applied is a rectangular wave with a frequency of 1 kHz and a root mean square value typically of 0.5 V to 1.0 V, however, it is always selected to be below the capacitive threshold of the respective test mixture.

For dielectrically positive compounds the mixture ZLI-4792 and for dielectrically neutral, as well as for dielectrically negative compounds, the mixture ZLI-3086, both of Merck KGaA, Germany are used as host mixture, respectively. The dielectric permittivities of the compounds are determined from the change of the respective values of the host mixture upon addition of the compounds of interest and are extrapolated to a concentration of the compounds of interest of 100 %.

Components having a nematic phase at the measurement temperature of 20 °C are measured as such, all others are treated like compounds.

The term threshold voltage refers in the instant application to the optical threshold and is given for 10 % relative contrast (V₁₀) and the term saturation voltage refers to the optical saturation and is given for 90 % relative contrast (V₉₀) both, if not explicitly stated otherwise. The capacitive threshold voltage (V₀, also called Freedericksz-threshold VF_Γ) is only used if explicitly mentioned.

The ranges of parameters given in this application are all including the limiting values, unless explicitly stated otherwise. Throughout this application, unless explicitly stated otherwise, all concentrations are given in mass percent and relate to the respective complete mixture, all temperatures are given in degrees centigrade (Celsius) and all differences of temperatures in degrees centigrade. All physical properties have been and are determined according to "Merck Liquid Crystals, Physical Properties of Liquid Crystals", Status Nov. 1997, Merck KGaA, Germany and are given for a temperature of 20 °C, unless explicitly stated otherwise. The optical anisotropy (Δn) is determined at a wavelength of 589.3 nm. The dielectric anisotropy (Δε) is determined at a frequency of 1 kHz. The threshold voltages, as well as all other electro- optical properties have been determined with test cells prepared at Merck KGaA, Germany. The test cells for the determination of Δε had a cell gap of 22 μm. The electrode was a circular ITO electrode with an area of 1.13 cm² and a guard ring. The orientation layers were lecithin for homeotropic orientation (ε| |) and polyimide AL-1054 from Japan Synthetic Rubber for homogenous orientation (ε±). The capacities were determined with a frequency response analyser Solatron 1260 using a sine wave with a voltage of 0.3 or 0.1 V_rms. The light used in the electro-optical measurements was white light. The set up used was a commercially available equipment of Otsuka, Japan. The characteristic voltages have been determined under perpendicular observation. The threshold voltage (Vio), mid-grey voltage (V₅₀) and saturation voltage (V₉₀) have been determined for 10 %, 50 % and 90 % relative contrast, respectively.

The mesogenic modulation material has been filled into an electro optical test cell prepared at the respective facility of Merck KGaA. The test cells had inter-digital electrodes on one substrate side. The electrode width was 10 μm, the distance between adjacent electrodes was 10 μm and the cell gap was also 10 μm. This test cell has been evaluated electro-optically between crossed polarisers.

At low temperatures, the filled cells showed the typical texture of a chiral nematic mixture, with an optical transmission between crossed polarisers without applied voltage. Upon heating, at a first temperature (T-O the mixtures turned optically isotropic, being dark between the crossed polarisers. This indicated the transition from the chiral nematic phase to the blue phase at that temperature. Up to a second temperature (T₂) the cell showed an electro-optical effect under applied voltage, typically of some tens of volts, a certain voltage in that range leading to a maximum of the optical transmission. Typically at a higher temperature the voltage needed for a visible electro-optical effect increased strongly, indicating the transition from the blue phase to the isotropic phase at this second temperature (T₂).

The temperature range (ΔT(BP)), where the mixture can be used electro- optically in the blue phase most beneficially has been identified as ranging from Ti to T₂. This temperature range (ΔT(BP)) is the temperature range given in the examples of this application. The electro-optical displays can also be operated at temperatures beyond this range, i.e. at temperatures above T₂, albeit only at significantly increased operation voltages.

The liquid crystal media according to the present invention can contain further additives and chiral dopants in usual concentrations. The total concentration of these further constituents is in the range of 0 % to 10 %, preferably 0.1 % to 6 %, based in the total mixture. The concentrations of the individual compounds used each are preferably in the range of 0.1 to 3 %. The concentration of these and of similar additives is not taken into consideration for the values and ranges of the concentrations of the liquid crystal components and compounds of the liquid crystal media in this application.

The inventive liquid crystal media according to the present invention consist of several compounds, preferably of 3 to 30, more preferably of 5 to 20 and most preferably of 6 to 14 compounds. These compounds are mixed in conventional way. As a rule, the required amount of the compound used in the smaller amount is dissolved in the compound used in the greater amount. In case the temperature is above the clearing point of the compound used in the higher concentration, it is particularly easy to observe completion of the process of dissolution. It is, however, also possible to prepare the media by other conventional ways, e. g. using so called pre-mixtures, which can be e. g. homologous or eutectic mixtures of compounds or using so called multi-bottle-systems, the constituents of which are ready to use mixtures themselves.

By addition of suitable additives, the liquid crystal media according to the instant invention can be modified in such a way, that they are usable in all known types of liquid crystal displays, either using the liquid crystal media as such, like TN-, TN-AMD, ECB-, VAN-AMD and in particular in compo- site systems, like PDLD-, NCAP- and PN-LCDs and especially in HPDLCs.

The melting point T(C, N)₁ the transition from the smectic (S) to the nematic (N) phase T(S,N) and the clearing point T (N,I) of the liquid crystals are given in degrees centigrade.

In the present application and especially in the following examples, the structures of the liquid crystal compounds are represented by abbreviations also called acronyms. The transformation of the abbreviations into the corresponding structures is straight forward according to the following two tables A and B. All groups C_nH_2n+1 and C_mH_2m+1 are straight chain alkyl groups with n respectively m D-atoms. The interpretation of table B is self evident. Table A does only list the abbreviations for the cores of the structures. The individual compounds are denoted by the abbreviation of the core followed by a hyphen and a code specifying the substituents R1, R2, L1 and L2 follows:

Particular preference is given to liquid-crystalline mixtures which, besides the compounds of the formula I, comprise at least one, two, three or four compounds from Table B.

Table C:

Table C shows possible dopants according to component D which are generally added to the mixtures alone or in combination two, three or more) according to the invention.

The liquid crystal media according to the instant invention do contain preferably

- four or more compounds selected from the group of compounds of tables A and B and/or

- five or more compounds selected from the group of compounds of table B and/or

- two or more compounds selected from the group of compounds of table A. Examples

The examples given in the following are intended to illustrate the present invention without limiting it in any way.

However, the physical data especially of the compounds and mixtures illustrate which properties can be achieved in which ranges, as well as the combination of the various properties, which can be preferably achieved.

Example 1

Preparation of 2-{4-[1 ,1-Difluoro-1-(3,4,5-trifluoro-phenoxy)-methyl]-3,5- difluoro-phenyl}-5-propyl-[1 ,3,2]dioxaborinane

2-{4-[1 ,1-Difluoro-1-(3,4,5-trifluoro-phenoxy)-methyl]-3,5-difluoro- phenyljboronic acid (5.0 g, 14.12 mmol), 2-propyl propane-1 ,3-diol (1.7 g, 14.13 mmol), 4-toluenesulphonic acid(0.29 g, 1.50 mmol) and toluene (75ml) are heated together and subsequently the water is removed using a Dean-Stark apparatus. After cooling the mixture is passed through a filter pad of silica gel (75 g), and eluted well with toluene (500 ml). The eluate is concentrated under vacuum to afford the crude material. This is purified by flash column chromatography using 25% dichloromethane in petroleum ether (40-60) as eluant to give a white solid (68% of the theoretical yield) on evaporation of the appropriate fractions. The structure is confirmed by ¹H NMR. The purity is 99.9% by HPLC and the phase transition K 34°C I is observed by optical microscopy. Example 2

Preparation of 5-Butyl-2-{4-[1 ,1-difluoro-1-(3,4,5-trifluoro-phenoxy)-methyl]- 3,5-difluoro-phenyl}-5-ethyl-[1 ,3,2]dioxaborinane

2-{4-[1 ,1-Difluoro-1 -(3,4,5-trifluoro-phenoxy)-methyl]-3,5-difluoro- phenyl}boronic acid (5.0 g, 14.12 mmol), 2-butyl,2-ethyl propane-1 ,3-diol (2.26 g, 14.13 mmol), 4-toluenesulphonic acid(0.29 g, 1.50 mmol) and toluene (75 ml) are heated together and subsequently the is water removed using a Dean-Stark apparatus. After cooling the mixture is passed through a filter pad of silica gel (75g) and well eluted with toluene(500 ml). The eluate is concentrated under vacuum to afford the crude material. This is purified by flash column chromatography using 40% dichloromethane in petroleum ether (40-60) as eluant to give a solid on evaporation of the appropriate fractions. Final purification by recrystallisation from petroleum ether (40-60) /dichloromethane at O°C gives the final product as a white solid (30% of the theoretical yield). The structure is confirmed by ¹H NMR. The purity is 99.5% by HPLC and the phase transition K 44°C I is observed by optical microscopy.

Example 3

Preparation of 2-{4-[1 ,1-Difluoro-1-(3,4,5-trifluoro-phenoxy)-methyl]-3,5- difluoro-phenyl}-5-p-tolyl-[1 ,3,2]dioxaborinane

2-{4-[1 ,1 -Difluoro-1 -(3,4,5-trifluoro-phenoxy)-methyl]-3,5-difluoro- phenyljboronic acid (4.0 g, 11.30 mmol), 2-p-Tolyl-propane-1 ,3-diol (1.88 g, 11.30 mmol), 4-toluenesulphonic acid (0.29 g, 1.50 mmol) and toluene (75 ml) are heated together and subsequently the water is removed using a Dean-Stark apparatus. After cooling the mixture is passed through a filter pad of silica gel (75 g), well eluted with toluene(500 ml). The eluate is concentrated under vacuum to afford the crude material. Recrystallisation of the material from petroleum ether (40-60)/dichloromethane at 0°C is o followed by flash column chromatography using dichloromethane as eluant to give a white solid (33% of the theoretical yield) on evaporation of the appropriate fractions. The structure is confirmed by ¹H NMR. The purity is 99.9% by HPLC and the phase transition K 125°C I is observed by optical microscopy. 5

Example 4

Preparation of 2-{4-[1 ,1 -Difluoro-1 -(3,4,5-trif luoro-phenoxy)-methyl]-3,5- difluoro-phenyl}-5-(4-propyl-cyclohexyl)-[1 ,3,2]dioxaborinane

5

2-{4-[1 , 1 -Difluoro-1 -(3,4,5-trif luoro-phenoxy)-methyl]-3,5-dif luoro- phenyl}boronic acid (3.75 g, 10.59 mmol), 2-(4-Propyl-cyclohexyl)- propane-1 ,3-diol (2.12 g, 10.60 mmol), 4-toluenesulphonic acid (0.29 g, 1.50 mmol) and toluene (100 ml) are heated together and the water is 0 removed using a Dean-Stark apparatus. After cooling the mixture is passed through a filter pad of silica gel (75 g), well eluting with toluene(500 ml). The eluate is concentrated under vacuum to afford the crude material. This is purified by repeated flash column chromatography using 40% dichloromethane in petroleum ether (40-60) as eluant to give a solid on 5 evaporation of the appropriate fractions. Final purification by recrystallisation from petroleum ether (40-60) /ethanol at 0°C gives the final product as a white solid (24%% of the theoretical yield). The structure is confirmed by ¹H NMR. The purity is 99.9% by HPLC and the phase transitions K 78°C N 125°C I are observed by optical microscopy.

Comparative Example

Preparation of 2-(2,4'-Difluoro-biphenyl-4-yl)-5-propyl-[1 ,3,2]dioxaborinane

(2,4'-Difluoro-biphenyl-4-yl)-boronic acid (1.80 g, 7.69 mmol), 2-propyl propane-1 ,3-diol (1.09 g, 9.24 mmol), 4-toluenesulphonic acid(0.29 g, 1.50 mmol) and toluene (50 ml) are heated together and the water is removed using a Dean-Stark apparatus. After cooling the mixture is passed through a filter pad of silica gel (5Og) and well eluted with toluene(300 ml). The eluate is concentrated under vacuum to afford the crude material. This is purified by flash column chromatography using 40% dichloromethane in petroleum ether (40-60) as eluant to give a solid on evaporation of the appropriate fractions. Final purification by recrystallisation from petrol ether (40-60) /dichloromethane at 0°C gives the final product as a white solid (33% of the theoretical yield). The structure is confirmed by ¹H NMR. The purity is 99.9% by HPLC and the phase transitions K 89°C (N 55°C) I are observed by optical microscopy.

Examples 5 to 37

Analogously to Example 1 the following compounds are prepared:

Examples 38 to 71

Analogously to Example 2 the following compounds are prepared:

Examples 72 to 105

Analogously to Example 4 the following compounds are prepared:

Comparative Use-example

5% of the chiral agent R-5011 has been solved in the achiral liquid crystal mixture M-O with the composition and properties given in table 1 below.

The resulting mixture CM is filled into an electro optical test cell with interdigital electrodes on one substrate side. The electrode width is 10 μm, the distance between adjacent electrodes is 10 μm and the cell gap is also 10 μm. This test cell has been evaluated electro-optically between crossed polarisers.

At low temperatures, the filled cell showed the typical texture of a chiral nematic mixture, with an optical transmission between crossed polarisers without applied voltage. On heating, at a temperature of 36°C the mixture was optically isotropic, being dark between the crossed polarisers. This indicated the transition from the chiral nematic phase to the blue phase at 36°C. This temperature is called Ti or T_trans .

Up to a temperature of 43°C the cell showed a clear electro optical effect under applied voltage, for example at 38°C, applying a voltage of 46 V lead to a maximum of the optical transition. This temperature is called T₂ and threspective voltage is called V_max or Vi₀₀. At a temperature of 43°C the voltage needed for a visible electro-optical effect started to increase strongly, indicating the transition from the blue phase to the isotropic phase at this temperature. The temperature range (ΔT(BP)), where the mixture can be used electro- optically in the blue phase was identified as ranging from 36°C to 43 °c, i.e. as being 7° wide (= T₂ - Ti = 43°C - 36°C). The results are listed in table 2 below.

Further the response times for switching on (τ_on) and for switching off (τ_off) have been determined. The response times decrease with increasing temperature above Ti and the temperature at which both response times have fallen below 5 ms each is called T₃. This is the case in this comparative use example at a temperature of 43°C or slightly above. Thus, the range of usable flat behaviour i.e. the usable flat range (ΔT(FR)), defined as ΔT(FR) = T₂ - T₃, in case T₂ > T₃ and ΔT(FR) = 0, in case T₂ < T₃, is 0° in this comparative use example.

Table 2:

Remark: n.d. not determined.

Use-example 1

In this use-example 10% of the compound of example 1 and 5% of the chiral agent R-5011 are solved in the achiral liquid crystal mixture M-O with the composition and properties given above. The resulting mixture M-1 is filled into an electro optical test cell like that used in the comparative example and investigated as described there.

At low temperatures, the filled cell shows the typical texture of a chiral nematic mixture, with an optical transmission between crossed polarisers without applied voltage. On heating, at a temperature of 21.8°C the mixture is optically isotropic, being dark between the crossed polarisers. This indicates the transition from the chiral nematic phase to the blue phase at this temperature. Up to a temperature of 29°C, the cell shows a clear electro optical effect under applied voltage, for example at 23.8°C, applying 43 volt leads to a maximum of the optical transition. At a temperature of 29°C the voltage needed for a visible electro- optical effect decreases strongly, indicating the transition from the blue phase to the isotropic phase at 29°C.

The range, where the mixture can be used electro-optically in the blue phase is identified as 29.0°C - 21.8°C = 7.2° and the usable flat range as 29.0°C - 24.4°C = 4.6°. The results are shown in table 2.

Use-example 2

In this use-example 10 % of the compound of example 2 and 5% of the chiral agent R-5011 are solved in the achiral liquid crystal mixture M-O.

The resulting mixture M-2 is filled into an electro optical test cell like that used in the comparative example and investigated as described there. The results are also shown in table 2.

Use-example 3

Like in use-example 1 , alternatively 10 % of the compound of example 3 are solved together with 5% of the chiral agent R-5011 in the achiral liquid crystal mixture M-O of use-example 1. The respective mixture (M-3) has been investigated as described under comparative-use-example and under use-example 1.

Use-example 4

Like in use-example 1 , alternatively 10 % of the compound of example 4 are solved together with 5% of the chiral agent R-5011 in the achiral liquid crystal mixture M-O of use-example 1.

The respective mixture (M-3) has been investigated as described under comparative-use-example and under use-example 1. The results are also shown in table 2.

Use-example 5

In this use-example a nematic liquid crystal mixture (called A-1) has been prepared, which contains 9.49 % of the compound of example 1 and evaluated for its physical properties, as given in the following table, table 3.

The properties of the compound of example 1 are extrapolated from the change of the properties from the host mixture (A-O, not containing the compound in question) upon its inclusion. The results are included in the following table, table 4.

Comparative Use-example 2

Like in use-example 5 about 10% of a compound of interest are dissolved in mixture A-O. This time the compound is the compound of the comparative example. The results of the extrapolated properties are included in table 4 for comparison.

Use-examples 6 to 8

As in use-example 5 about 10% each of various compounds of interest are dissolved alternatively in mixture A-O. Now the compounds are those of examples 6 to 8. The results of the extrapolated properties are compiled in table 4.

Table 3: Composition and properties of mixture A-1

Claims

1. compound, of formula I,

wherein

and

are, independently of each other,

1 ,4-phenylen or trans-1 ,4-cyclohexylen, which optionally may be substituted with 1 or 2 substituents selected from the group of substituents F, Cl, OCF₃, OCH₃ and/or CH₃

and

are, independently of each other,

1 ,4-phenylen, which optionally may be substituted with 1 or 2 substituents selected from the group of substituents F, Cl, OCH₃ and/or CH₃

NR⁰¹-, -SiR⁰¹R⁰²-, -CO-, -COO-, -OCO-, -OCO-O-, -S- CO-, -CO-S-, -CY⁰¹=CY⁰²- or -C≡C- in such a manner that O and/or S atoms are not linked directly to one another, preferably H, n-alkyl, n-alkoxy with 1 to 7 C- atoms preferably 2 to 5 C-atoms, alkenyl, alkenyloxy or alkoxyalkyl with 2 to 7 C-atoms, preferably with 2 to 5 C- atoms or CN, NCS, halogen, preferably F, Cl, halogenated alkyl, alkenyl or alkoxy, preferably mono-, di- or oligo-fluorinated alkyl, alkenyl or alkoxy, especially preferred CF₃, OCF₂H or OCF₃, or one of R¹¹ and R¹² denotes or both independently of each other denote PG-SG, most preferably H or alkyl with 1 to 12 C-atoms,

R⁰¹ and R⁰² are, independently of each other, H or alkyl with 1 to 12 C-atoms,

PG is a polymerisable or reactive group,

SG is a spacer group or a single bond,

X has one of the meanings given for R and preferably is a polar endgroup and most preferably is CN, OCF₃, CF₃,

F or Cl, and

m and n are, independently of each other, O or 1.

Compound according to claim 1 , characterized in that they are of formula Ia

wherein the parameters have the respective meanings given in claim 1 and

Y¹¹ to Y¹⁴ are, independently of each other, H or F.

3. Compound according to claim 2, characterised in that

Y¹¹ to Y¹⁴ all are F.

4. Compound according to at least one of claims 1 to 3, characterized in that it group

is selected from the group of patial formulae (1) to (5)

wherein R¹² has the meaning given in claim 1 ,

5. Medium, characterized in that it comprises a compound of formula I according to at least one of claims 1 to 4.

6. Medium according to claim 5, characterized in that it is a mesogenic medium.

7. Medium according to at least one of claims 5 and 6, characterized in that it is a light modulation medium.

8. Medium according to at least one of claims 5 to 7, characterized in that it has a blue phase.

9. Light modulation element, characterized in that it comprises a medium according to at least one of claims 5 to 8.

10. Use of a compound according to at least one of claims 1 to 4 in a mesogenic medium.

11. Use of a medium according to at least one of claims 5 to 8 in a light modulation element. 12. Electro-optical display, characterized in that it comprises a medium according to at least one of claims 5 to 8.