WO2010022891A1 - Liquid crystalline medium and liquid crystal display - Google Patents

Abstract

The instant invention relates to dielectrically positive nematic media comprising one, two or more compounds of formula I and one or more compounds selected from the group of formulae Il and III and optionally one or more compounds selected from the group of formulae IV and V wherein the parameters are as defined in claim 1 and the media optionally comprise one or more chiral dopants, as well as to liquid crystal displays comprising these media, especially to TN-displays and in particular to active matrix displays.

Description

Liquid Crystalline Medium and Liquid Crystal Display

Field of the invention

The present invention relates to liquid crystalline media, preferably to dielecthcally positive, nematic media, comprising one or more dielectrically positive compounds and one or more dielectrically neutral compounds, preferably are comprising on or more chiral dopants and preferably are encapsulated in a polymer matrix and to liquid crystal displays comprising these media, especially to displays operating in reflective mode and preferably addressed by an active matrix.

State of the art and problem to be solved

Liquid Crystal Displays (LCDs) are widely used to display information. LCDs are used for direct view displays, as well as for projection type displays. The electro-optical mode which is employed for most displays still is the twisted nematic (TN)-mode with its various modifications. Besides this mode, the super twisted nematic (STN)-mode and more recently the optically compensated bend (OCB)-mode and the electrically controlled birefringence (ECB)-mode with their various modifications, as e. g. the vertically aligned nematic (VAN), the patterned ITO vertically aligned nematic (PVA)-, the p_olymer stabilized vertically aligned nematic (PSVA)- mode and the multi domain vertically aligned nematic (MVA)-mode, as well as others, have been increasingly used. All these modes use an electrical field, which is substantially perpendicular to the substrates, respectively to the liquid crystal layer. Besides these modes there are also electro-optical modes employing an electrical field substantially parallel to the substrates, respectively the liquid crystal layer, like e.g. the |n Plane Switching (short IPS) mode (as disclosed e.g. in DE 40 00 451 and EP 0 588 568) and the Fringe Field Switching (FFS) mode. Especially the latter mentioned electro-optical modes, which have good viewing angle properties and improved response times, are increasingly used for LCDs for modern desktop monitors and even for displays for TV and for multi media applications and thus are competing with the TN-LCDs. The liquid crystals (LCs) according to the present invention are preferably used in improved LCDs using cholesteric liquid crystals, which are also known as chiral nematic liquid crystals, with short helical pitch and with high dielectric anisotropy especially for advanced applications. They are particularly useful for operation in reflected mode, as cholesteric liquid crystals having an appropriate cholesteric pitch selectively reflect light they may be coloured and allow to avoid the use of colour filters in LCDs.

It is also possible to encapsulate the cholesteric liquid crystals in a polymer matrix e.g. as a PDLC or a NCAP.

For these applications new liquid crystalline media with improved properties are required. Thus liquid crystalline media with improved behaviour are required. Their rotational viscosity should be as low as possible. Besides this parameter, the media have to exhibit a suitably wide range of the nematic phase, an appropriate birefringence (Δn), preferably in the range from 0.100 to 0.300 and a suitably high dielectric anisotropy (Δε). Δε has to be sufficiently high to allow a reasonably low operation voltage. Preferably Δε should be 10 or more, in order to allow use easy accessible drivers with reasonably low operation voltages. However, Δε should preferably 40 or less and in particular not higher than 35, as this would be detrimental for an at least reasonably high specific resistivity, which in turn is another requirement, especially for active matrix addressing. Most preferably Δε should be in the range of 20 to 30.

The displays according to the present invention are preferably active matrix LCDs, short AMDs, addressed by an active matrix, preferably by a matrix of thin film transistors (TFTs). However, the inventive liquid crystals can also beneficially be used in displays with other known addressing means.

Liquid crystal compositions suitable for LCDs and in particular for TN- displays are already widely known. These compositions, however, do have significant drawbacks. Most of them, besides having other deficiencies, lead to unfavourably high response times and/or to contrast ratios, which are too low for many applications. They also most generally have - -

insufficient reliability and stability, in particular against exposure to heat, moisture or irradiation by light and in particular UV, especially when one or more these stressors are combined with each other.

Thus, there is a significant need for liquid crystalline media with improved suitable properties for practical applications such as a wide nematic phase range, appropriate optical anisotropy Δn, according to the display mode used, a high value of Δε, low viscosities, in particular low rotational viscosities (γi), high contrast ratios in displays and especially fast response times and a good reliability.

Present invention

Surprisingly, it now has been found that liquid crystalline media with a suitable phase range, suitably high values of Δε and Δn and suitably low viscosities can be realized, which do not exhibit the drawbacks of the materials of the prior art or at least do exhibit them to a significantly lesser degree.

These improved liquid crystalline media according to the instant application comprise at least

- one, two or more compounds of formula I

wherein

R¹ is alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy, alkenyl, alkenyloxy, alkoxyalkyl, fluorinated alkenyl or fluorinated alkenyloxy, preferably alkyl or alkoxyalkyl and most preferably n-alkyl, - -

L¹¹ and 12 are independently of each other H or F, preferably L 11 is

F and L 12

X¹ is CN or NCS, preferably CN, and

is 0 or 1 , preferably 0, and

one, two or more dielectrically positive compounds, preferably having a dielectric anisotropy of more than 3, selected from the group of compounds of formulae Il and III, preferably one or more compounds of each of them,

wherein

R² and R³ are independently of each other alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1 to 7 C- atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C-atoms and R² and R³ preferably are alkyl or alkenyl,

are independently of each other

L²¹, L²², L³¹ and L³², are independently of each other H or F, preferably L²¹ and/or L³¹ is F₁

X² and X³ are independently of each other halogen, halogenated alkyl or alkoxy with 1 to 3 C-atoms or halogenated alkenyl or alkenyloxy with 2 or 3 C-atoms, preferably F, Cl, -OCF₃ or -CF₃, most preferably F, Cl or -OCF₃,

is -CH₂CH₂-, -CF₂CF₂-, -COO-, trans- -CH=CH-, trans- -CF=CF-, -CH₂O- or a single bond, preferably -CH₂CH₂-, -COO-, trans- -CH=CH- or a single bond and most preferably -COO-, trans- -CH=CH- or a single bond and

I, m, n and o are independently of each other O or 1 and optionally

one, two or more dielectrically neutral compounds selected from the group of formulae IV and V, preferably one or more compounds of each of them,

wherein

R⁴¹ to R⁵² independently of each other have the meaning given for R² under formula Il above, preferably R⁴¹ is alkyl and R⁴² is alkyl or alkoxy or R⁴¹ is alkenyl and R⁴² is alkyl, preferably R⁵¹ is alkyl and R⁵² is alkyl or alkenyl, or R⁵¹ is alkenyl and R⁵² is alkyl or alkenyl, preferably alkyl,

independently of each other and in case

is present twice, also these independently of each other are

preferably at least one of

independently of each other and in case

is present twice, also these independently of each other are

Z⁴¹ to Z 52 independently of each other, and in case Z⁴¹ and/or Z⁵¹ is/are present twice, also these independently of each other, are -CH₂CH₂-, -COO-, trans- -CH=CH-, trans- -CF=CF-, -CH₂O-, -CF₂O-, -C≡C- or a single bond, preferably at least one of Z⁴¹ and Z⁴² and at least one of Z⁵¹ and Z⁵² each is a single bond,

p and q are independently of each other 0, 1 or 2,

preferably is 0 or 1 and

the media comprise one or more compounds selected from the group of compounds of formula III, wherein n and o both are 1 , Z³ preferably is a single bond, and all rings are 1 ,4-phenylene, which independently of each other optionally are fluorinated once or twice, and of compounds of formula V, wherein q is 2 and Z⁵¹ and Z⁵¹ preferably are both a single bond. Alternatively or additionally to compounds of formulae Il and/or III the media according to the present invention may comprise one or more dielectrically positive compounds of formula Vl

wherein

R^b is alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1 to 7 C-atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C-atoms and preferably is alkyl or alkenyl,

are independently of each other

L⁶¹ and L 62 are independently of each other H or F, preferably L 61 : i,s F,

X^b is halogen, halogenated alkyl or alkoxy with 1 to 3 C- atoms or halogenated alkenyl or alkenyloxy with 2 or 3 C-atoms, preferably F, Cl, -OCF₃ or -CF₃, most preferably F, Cl or -OCF₃,

Z⁶ is -CH₂CH₂-, -CF₂CF₂-, -COO-, trans- -CH=CH-, trans- -CF=CF- or -CH₂O-, preferably -CH₂CH₂-, -COO- or trans- -CH=CH- and most preferably -COO- or -CH₂CH₂- and

r is O or 1.

In a preferred embodiment of the present invention the liquid crystalline media according to the instant application comprise one or more polymerisable compounds. These polymerisable compounds may be non- mesogenic compounds, like e.g. the well known EHA, resp. 2EHA, or mesogenic compounds. These polymerisable mesogenic compounds are called here "reactive mesogens " (short RMs). These polymerisable compounds, whether mesogenic or non-mesogenic, may be mono-reactive or multi-reactive, preferably di-reactive. Preferably the media comprise both one or more mono-reactive compounds and one or more multi- reactive, preferably di-reactive compounds. Most preferably the media comprise one or more RMs, while non-mesogenic compounds may be present additionally.

The RMs can be chiral or achiral, and can comprise an acrylate/methacrylate group or another polymerisable group. In an especially preferred embodiment the RM are chiral compounds, as this allows the simple adjustment of the wavelength of the selective reflection by polymerising a certain amount of the chiral RM, which thus is no longer available to twist the liquid crystal material, leading to an increased cholesteric pitch and consequently to selective reflection at longer wavelengths. The resultant cholesteric pitch may be beneficially stabilized against further change e.g. by use of an appropriate filter (e.g. UV filter) protecting the liquid crystal from ambient radiation.

In case chiral reactive mesogens are used in the liquid crystalline media according to the present invention, in many cases it is desirable to use a photo initiator in the media, too, when an exposure to UV radiation is applied. The use of a photo initiator leads to a significant reduction of the dose of UV radiation required.

Chiral reactive mesogens may be used in the liquid crystalline media according to the present invention as the only chiral compounds present in the media. However, in a preferred embodiment of the present invention, the chiral reactive mesogens are used together with conventional (non reactive) chiral dopant(s). In that preferred embodiment the desired starting value of the cholesteric pitch, or alternatively a value already rather close to that desirable value, may be fixed by one or more conventional chiral dopant(s). The additional use of one or more chiral reactive mesogen(s) then allows to further adjust the cholesteric pitch by exposure of the medium to UV radiation and the subsequent depletion of the chiral reactive mesogen(s).

In this last embodiment it is in many cases desirable to use conventional chiral dopant(s) and chiral reactive mesogen(s) having the same sign of the HTP relative to each other. In this embodiment only a small total concentration is required to achieve the short cholesteric pitch and the overall physical properties of the mesogenic host material are altered to a relatively small degree only. This preferred embodiment leads to comparatively low requirements for protection of the media against further change of the wavelength of selective reflection after the desired value has been achieved by irradiation with UV.

In some cases, however, it is beneficial to use one or more conventional chiral dopant(s) and one or more chiral reactive mesogen(s), the conventional chiral dopant(s) having signs of the HTP mutually opposite to those of the chiral reactive mesogen(s). In this case a central wavelength of the selective reflection may be fixed by the conventional chiral dopant(s). This central wavelength may then be shifted towards longer wavelengths by the chiral reactive mesogen(s) used. This effect may then be reversed by exposure of the media to UV radiation. Especially this last preferred embodiment leads to the lowest requirements for protection of the media against further change of the wavelength of selective reflection after the desired value has been achieved by irradiation with UV.

It has to be noted here that, as a first approximation, the HTP of a mixture of chiral compounds, i.e. of conventional chiral dopants as well as of chiral reactive mesogens, may be approximated by the addition of their individual HTP values weighted by their respective concentrations in the medium.

The RMs can be mono-reactive or di- or multi-reactive. Especially preferred is a material comprising at least one di-reactive compound

(cross-linking agent), which is also preferably liquid crystalline or at least mesogenic with a functional group at each end; for instance it can be based on diacrylate type RMs.

In case the media comprise one or more polymerisable compounds they preferably additionally comprise one or more polymerisation initiators, e.g. photo initiators and/or thermal initiators.

The liquid crystalline media according to the present invention may be and in a preferred embodiment are stabilized by polymerisation of respective polymer precursors are consisting of said one or more polymerisable compounds and optionally one or more of said initiators. Preferably the stabilising polymer has the morphology of a polymer network, i.e. the liquid crystalline material having a low molecular weight, i.e. the non- polymerisable liquid crystalline material / mesogenic material is present in a more or less continuous form interspersed with more or less smoth strands of polymeric material. Polymer network stabilised liquid crystals are disclosed e.g. in Dierking, I., Adv. Mater. 12, No. 3, pp. 167-181 (2000). In a preferred embodiment of the present invention the liquid crystalline media according to the instant application comprise one or more polymerisable compounds and preferably RMs.

The host mixture contains liquid crystalline compounds having a low molar mass and preferably an amount of one or more chiral dopants sufficient to lead to selective reflection in the visible range of the electromagnetic spectrum. These cholesteric phases with a relatively short cholesteric pitch preferably are stabilised by a polymer. The stabilisation of the (cholesteric) phase is carried out by adding to the chiral liquid crystalline host mixture one or more polymerisable compounds, preferably RMs, preferably a mixture comprising mono-reactive and di-reactive RMs, plus a suitable photo-initiator, and polymerising the polymerisable compounds, for example by exposure to UV irradiation, for a short time. Preferably the polymerisation is carried out in electro-optical cells maintained at a temperature in the cholesteric phase of the chiral liquid crystalline host mixture.

The mesogenic mono-reactive compounds used according to the present invention preferably comprise one or more ring elements, linked together by a direct bond or via a linking group and, where two of these ring elements optionally may be linked to each other, either directly or via a linking group, which may be identical to or different from the linking group mentioned. The ring elements are preferably selected from the group of four-, five-, six- or seven-, preferably of five- or six-, membered rings.

The RMs used according to the present invention are preferably selected from the group of formulae VIIA and VIIB

wherein

R⁷¹ is H, F, Cl, Br, I, CN, NO₂, NCS₁ SF₅, SO₂CF₃ or alkyl which is straight chain or branched, preferably has 1 to 20 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, Halogen, 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,

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

is a mesogenic moiety, preferably comprising one or more rings and most preferably is a divalent radical of the formula

are, independently of each other, an aromatic and/or alicyclic ring, or a group comprising two or more fused aromatic or alicyclic rings, wherein these rings optionally contain one or more hetero atoms selected from N, O and/or S, and are optionally mono- or poly-substituted by R⁷², 771 74

Z" to Z are, independently of each other, -O-, -S-, -CO-, -CO-O-, -O-CO-, -S-CO-, -CO-S-, -

O-CO-O-, -CO-NR⁰¹-, -NR⁰¹-CO-, -OCH₂-, -CH₂O-, -SCH₂

-, -CH₂S-, -CF₂O-, -OCF₂-, -CF₂S-, -SCF-, -CH₂CH₂-, -CF₂

CH₂-, -CH₂CF₂-, -CF₂CF₂-, -CH=N-, -N=CH-, -N=N-, -CH=

CR⁰¹-, -CY⁰¹=CY⁰²-, -C≡C-, -(CH₂)

₄-, -CH=CH-CO-O-, -0-CO-CH=CH- or a single bond,

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

R 72 is H or alkyl, preferably H or alkyl with 1 to 10 C-atoms,

PG 71 is a polymerisable or reactive group,

SP 71 is a spacer group or a single bond, and

X 71 has one of the meanings given for Z⁷¹ and preferably is -O-, -CO-O-, -O-CO-, -CF₂O-, -OCF₂-, -CH₂O-, -OCH₂- or a single bond. wherein

PG x 72 and PG »73 independently of each other have one of the meanings given for PG 71 above,

SP i72 and SP ,73 independently of each other have one of the meanings given for SP 11 above, and

X⁷² and X⁷³ independently of each other have one of the meanings given for X 71 above. In a preferred embodiment of the present invention the precursor of the polymer comprises, besides the compound(s) of formula VIIA one or more di-reactive mesogenic monomers, preferably of formula VIIB.

The compounds of formulae VIIA and VIIB according to the present invention may be chiral compounds.

Particularly preferred are polymer precursors comprising one or more compounds of formula VIIA and/or of formula VIIB, wherein

Z⁷¹ and/or Z⁷⁴ is -O-, -CO-O-, -OCO-, -O-CO-O-, -CH₂-O-, -O-CH₂-, - CF₂-O-, -0-CF₂-, -C≡C-, -CH=CH- or a single bond, most preferably -CO-O- or -O-CO- or -O- and/or

Z⁷¹ is different from a single bond and/or ring A⁷¹ is phenylene that is optionally substituted by one or more groups R and/or

R⁷¹ 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

SP⁷¹ 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 71

"A via a group selected from -O-, -CO-O-, -O-CO-, -O-CO-O- and a single bond and/or SP⁷¹ is a single bond.

Preferences for MG⁷² to X⁷³ are the same as for MG⁷¹ to X⁷¹.

In a preferred embodiment rings A⁷¹ to A⁷³ are, independently of each other, an aromatic or alicyclic ring, preferably a 5-, 6- or 7-membered ring, or a group comprising two or more, preferably two or three, fused aromatic or alicyclic rings, wherein these rings optionally contain one or more hetero atoms selected from N, O and/or S, and are optionally mono- or poly- substituted with L⁷, wherein L⁷ is F, Cl, Br, CN, OH, NO₂, and/or an alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl group with 1 to 12 C atoms, wherein one or more H atoms are optionally replaced by F or Cl.

L⁷ is preferably F, Cl, CN, OH, NO₂, CH₃, C₂H₅, OCH₃, OC₂H₅, COCH₃,

COC₂H₅, COOCH₃, COOC₂H₅, CF₃, OCF₃, OCHF₂ or OC₂F₅, in particular F, Cl, CN, CH₃, C₂H₅, OCH₃, COCH₃ or OCF₃, most preferably F, Cl, CH₃, OCH₃ or COCH₃.

Preferred rings A⁷¹ to A⁷³ are, for example, furan, pyrrol, thiophene, oxazole, thiazole, thiadiazole, imidazole, phenylene, cyclohexylene, cyclohexenylene, pyridine, pyrimidine, pyrazine, azulene, indane, naphthalene, tetrahydronaphthalene, decahydronaphthalene, tetrahydropyrane, anthracene, phenanthrene and fluorene.

Particularly preferably one or more of these rings A⁷¹ to A⁷³ is selected from furane-2,5-diyl, thiophene-2,5-diyl, thienothiophene-2,5-diyl, dithienothiophene-2,6-diyl, pyrrol-2,5-diyl, 1 ,4-phenylene, azulene-2,6-diyl, pyridine-2,5-diyl, pyrimidine-2,5-diyl, naphthalene-2,6-diyl, 1 ,2,3,4- tetrahydro-naphthalene-2,6-diyl, indane-2,5-diyl, or 1 ,4-cyclohexylene wherein one or two non-adjacent CH₂ groups are optionally replaced by O and/or S, wherein these groups are unsubstituted, mono- or polysubstituted by L as defined above.

independently of each other are,

or their mirror images

wherein

R is alkyl with 1 to 12 C-atoms, preferably with 1 to 7 C- atoms, or alkenyl or alkynyl with 2 to 12 C-atoms, preferably with 2 to 7 C-atoms, in both of which one or more non-adjacent -CH₂- groups, not adjacent to the phenyl ring, may be replaced by -O- and/or -CH=CH- and/or one or more H-atoms may be replaced by halogen, preferably by F,

and/or preferably

In a preferred embodiment of the present invention the group

71 7*\ contains only monocyclic rings A to A . Very preferably this is a group with one or two 5- and/or 6-membered rings.

Preferred sub formulae for this group are listed below. For reasons of simplicity, Phe in these groups is 1 ,4-phenylene, PheL is a 1 ,4-phenylene group which is substituted by 1 to 4 groups L as defined above, Cyc is 1 ,4- cyclohexylene, Pyd is pyridine-2,5-diyl and Pyr is pyrimidine-2,5-diyl. The following list of preferred groups comprises the sub formulae VII-1 to VII- 20 as well as their mirror images,

-Phe- VII-1

-Pyd- VII-2

-Pyr- VII-3

-PheL- VII-4

-Cyc- VII-5

-Phe-Z-Cyc- VII-6

-Cyc-Z-Cyc- VII-7

-PheL-Cyc- VII-8

-Phe-Z-Phe- VII-9

-Phe-Z-Pyd- VII-10

-Pyd-Z-Phe- VII-11

-Phe-Z-Pyr- VII-12

-Pyr-Z-Phe- VII-13

-PheL-Z-Phe- VII-14

-PheL-Z-Pyd- VII-15

-PheL-Z-Pyr- VII-16

-Pyr-Z-Pyd- VII-17

-Pyd-Z-Pyd- VII-18

-Pyr-Z-Pyr- VII-19

-PheL-Z-PheL- VII-20

In these preferred groups Z has the meaning of Z⁷¹ as given in formula VIIA. Preferably Z is -COO-, -OCO-, -CH₂CH₂-, -C≡C- or a single bond. Very preferably the group

is selected from the following formulae Vila to VIIj and their mirror images

wherein L is F, Cl₁ Br, CN₁ OH, NO₂, and/or an alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl group with 1 to 12 C atoms, wherein one or more H atoms are optionally replaced by F or Cl and r is 0, 1 , 2, 3 or 4, preferably 0, 1 or 2.

in these preferred formulae is very preferably

with L having each independently one of the meanings given above.

Especially preferred compounds of formula I comprise at least

one group wherein r is 1 or 2

Further preferred compounds of formula I comprise at least two groups wherein r is 1 and/or at least one group

wherein r is 2.

wherein the 1 ,4-phenylene rings may optionally be substituted by R, preferably by alkyl, preferably by methyl, and/or by alkoxy and/or by halogen, preferably F.

More preferably



or their mirror images

wherein R has the meaning given above and preferably is alkyl, preferably with 1 to 6 C-atoms, preferably n-alkyl, wherein one or more non-adjacent - CH₂- groups optionally may be replaced by -O- and/or by -CH=CH- and/ or one or more H-atoms may be replaced by halogen, preferably by F. In a preferred embodiment of the present invention the liquid crystalline media according to the instant application comprise one or more compounds of formula I selected from the compounds of its sub-formulae 1-1 to I-5, preferably selected from formulae I-2, I-4 and I-5, most preferably of formula I-2

wherein R¹ has the respective meanings given under formula I above and preferably is alkyl, most preferably n-alkyl, and X¹ preferably is CN.

In a preferred embodiment of the present invention the liquid crystalline media according to the instant application comprise one or more compounds selected from the group of compounds of formulae 11-1 and 11-2, preferably of formula 11-2

wherein the parameters have the respective meanings given under formula Il above and X /2 : is preferably F or -OCF₃.

Preferably the media comprise one or more compounds selected from the ggrrcoup of compounds of formulae 11-1 and II-2, wherein L²¹ and L²² both are

F.

Preferably the media comprise one or more compounds of formula 11-1 , which preferably are selected from the group of compounds of formulae 11-1 a to 11-1 c, preferably of formula 11-1 c

wherein the parameters have the respective meanings given above and preferably

L²¹ and L²² are both F and L³²and L²⁴ are both H or

L²¹, L²², L²³ and L²⁴ are all F.

In a preferred embodiment the media comprise one or more compounds of formula IMc, wherein L²¹, L²², L²³ and L²⁴ all are F.

Preferably the media comprise one or more compounds selected from the group of compounds of formulae ll-2a to ll-2c, preferably of formula ll-2c,

wherein the parameters have the respective meanings given above and

L²³ to L²⁷ are independently of each other and of the other parameters H or F and preferably L²¹ and L²² are both F and two or three of L²³ to L²⁷, most preferably L²³ to L²⁵, are F and the others of L²¹ to L²⁷ are H or F, preferably H and X ,2 is preferably F or -OCF₃ and most preferably F.

Especially preferred compounds of formula II-2 are the compounds of formula ll-2c-1

wherein R has the meaning given above.

In a further preferred embodiment of the present invention the media comprise one or more compounds selected from the group of compounds of formulae III-1 and III-2

wherein the parameters have the respective meanings given under formula III above.

Preferably the media comprise one or more compounds of formula 111-1 , preferably selected from the group of compounds of formulae Hl-I a to lll-1f, preferably selected from the group of compounds of formulae Ml-I a, 111-1 c and ill-Id, and most preferably one or more compounds each of formulae 11-1 a and/or Hl-Ic and/or Ill-Id

wherein the parameters have the respective meanings given above and L³³ to L³⁷ are independently of each other and of the other parameters H or F and preferably L³¹ and L³² are both F and two or three of L³³ to L³⁷ most preferably L³³ to L³⁵, are F and the others of L³¹ to L³⁷ are H or F, preferably H and X³ is preferably F or -OCF₃.

Most preferable compounds of formula 111-1 are selected from the group of compounds of formulae lll-1a, IIMc-1 , and IIMd-1

wherein R has the meaning given above.

Preferably the compounds of formula IV are selected from the group of compounds of formulae IV-1 to IV-7, more preferably of formulae IV-6 and/or IV-7

wherein R⁴¹ and R⁴² have the respective meanings given under formula IV above and generally and in particular in formulae IV-1 and IV-5, R⁴¹ preferably is alkyl or alkenyl, preferably alkenyl and R⁴² preferably is alkyl or alkenyl, preferably alkyl and alternatively in formula IV-2 R⁴¹ and R 42 preferably both are alkyl and in formula IV-4 R ,41 preferably is alkyl or aallkkeennyyll,, preferably alkyl and R⁴² preferably is alkyl or alkoxy, preferably alkoxy.

Preferably the media comprise one or more compounds selected from the group of compounds of formulae IV-6 and IV-7 and, most preferably, one or more compounds each of formulae IV-6 and IV-7.

Preferred compounds of formula IV-6 are compounds of formulae CPTP-n-m and CPTP-n-Om, more preferably compounds of formula CPTP-n-Om, whereas preferred compounds of formula IV-7 are compounds of formula CPGP-n-m. The definitions of these abbreviations (acronyms) are explained in tables A to C and illustrated in table D below.

In a preferred embodiment the liquid crystalline media according to the present invention comprise one or more compounds of formula V selected from the group of compounds of formulae V-1 to V-6

wherein R⁵¹ and R⁵² have the respective meanings given under formula V above and R⁵¹ preferably is alkyl, more preferably n-alkyl and in formula V-1 R⁵² preferably is alkenyl, preferably 3-alkenyl and most preferably -(CH₂)₂-CH=CH-CH₃ and in formula V-3 R⁵² preferably is alkyl or alkenyl, preferably n-alkyl or 3-alkenyl and most preferably -(CH₂)₂-CH=CH₂, in formulae V-3 to V-6 R⁵² preferably is alkyl and in V-4 "F_0/i" preferably is F.

Preferred compounds of formula V-1 are compounds of formulae PP-n-2V and PP-n-2Vm, more preferably compounds of formula PP-1-2V1. Preferred compounds of formula V-2 are compounds of formulae PTP-n-Om, especially preferred PTP-1-02, PTP-2-O1 and PTP-3-O1. Preferred compounds of formula V-3 are compounds of formulae PGP-n-m, PGP-n-2V and PGP-n-2Vm, more preferably of formulae PGP-2-m, PGP-3-m and PGP-n-2V. Preferred compounds of formula V-4 are compounds of formulae PPTUI-n-m, especially preferred PPTUI-3-2, PPTUI-3-3, PPTUI-3-4 and PPTUI-4-4. Preferred compounds of formula V-5 are compounds of formulae PGGIP-n-m. Preferred compounds of formula V-6 are compounds of formulae PGIGP-n-m. The definitions of these abbreviations (acronyms) are explained in tables A to C and illustrated in table D below. The compounds of formula Vl are preferably selected from the group of compounds of formulae VI-1 and VI-2, preferably of formula VI-1

wherein the parameters have the respective meanings given above and the parameters L⁶³ and L⁶⁴ are, independently of each other and of the other parameters H or F and preferably Z is -CH₂-CH₂- and preferably X is F. Preferably the liquid crystalline media according to the instant invention comprise, more preferably predominantly consist of, more preferably essentially consist of and most preferably entirely consist of compounds selected from the group of compounds of formulae I to Vl and Vila and VIIb, more preferably of formulae I to V and Vila and/or VIIb.

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

In this context the term "predominantly consisting of means that the entity referred to contains 55 % or more, preferably 60 % or more and most preferably 70 % or more of the component or components or of the compound or compounds in question unless explicitly defined otherwise. In this context the term "essentially consisting of means that the entity referred to contains 80 % or more, preferably 90 % or more and most preferably 95 % or more of the component or components or of the compound or compounds in question unless explicitly defined otherwise.

In this context the term "entirely consisting of means that the entity referred to contains 98 % or more, preferably 99 % or more and most preferably 100.0 % of the component or components or of the compound or compounds in question unless explicitly defined otherwise.

Also other mesogenic compounds, which are not explicitly mentioned above, can optionally and beneficially be used in the media according to the instant invention. Such compounds are known to the expert in the field.

The liquid crystal media according to the instant invention are characterised by a clearing point of 85 ⁰C or more, preferably of 90 ⁰C or more.

The Δn, at 589 nm (Na^D) and 20 °C, of the liquid crystal media according to the instant invention preferably is in the range of 0.150 or more to 0.350 or less, more preferably in the range of 0.170 or more to 0.250 or less and most preferably in the range of 0.180 or more to 0.220 or less.

The Δε, at 1 kHz and 20 ⁰C, of the liquid crystal medium according to the invention preferably is 10 or more, preferably 15 or more, more preferably 20 or more and most preferably 25 or more, whereas it preferably is 40 or less, more preferably 35 or less and more preferably it is in the range of 10 or more, to 40 or less and most in the range of 20 to 30 (how about 10 to 40.

Preferably the nematic phase of the inventive media without the chiral dopants extends at least from 0 ⁰C or less to 80 ⁰C or more, more preferably at least from -20 ⁰C or less to 85 ⁰C or more, most preferably at least from -20 ⁰C or less to 90 ⁰C or more and in particular at least from -30 ⁰C or less to 95 ⁰C or more. The liquid crystalline media are preferably characterized for comparison purposes in TN displays operating in the second transmission minimum according to Gooch and Tarry having an optical retardation (d • Δn) in the range of 1.0 μm or more to 1.1 μm or less. They are, however, preferably used as cholesteric liquid crystals, also called chiral nematic liquid crystals, having a rather short cholesteric pitch, preferably their cholesteric pitch is selected such, that their wavelength of selective reflection is in the in the range in the visible range of the electromagnetic spectrum i.e. in the range from of 400 nm to 800 nm.

Preferably the liquid crystal media contain one or more chiral dopants preferably having an absolute value of the helical twisting power (HTP) of 20 μm^"1 or more, preferably of 40 μm^"1 or more, more preferably in the range of 60 μm^"1 or more, most preferably in the range of 80 μm^"1 or more to 260 μm^"1 or less.

Preferably the liquid crystal media contain 50 % to 100 %, more preferably 70 % to 100 % more preferably 80 % to 100 % and in particular 90 % to 100 % totally of compounds of formulae I, II, III, IV, V and Vl, preferably of formulae I, II, III, IV and V.

More preferably the liquid crystal media comprise, more preferably predominantly consist of, more preferably essentially consist of and most preferably entirely consist of compounds of formulae I, II, III, IV, V and Vl, preferably of formulae I, II, III, IV and V.

Compounds of formula I preferably are used in the media in a total concentration from 1 % to 35 %, more preferably from 2 % to 30 %, more preferably from 3 % to 20 % and most preferably from 5 % to 15 % of the total mixture.

Compounds of formulae Il and III preferably are used together in the media in a total concentration from 40% to 80 %, more preferably from 45 % to 75 %, more preferably from 50 % to 70 % and most preferably from 55 % to 65 % of the total mixture. Compounds of formula Il preferably are used in the media in a total concentration from 15 % to 35 %, more preferably from 20 % to 30 % and most preferably from 22 % to 28 % of the total mixture.

Compounds of formula III preferably are used in the media in a total concentration from 20 % to 45 %, more preferably from 25 % to 40 % and most preferably from 30 % to 35 % of the total mixture.

Compounds of formula IV preferably are used in the media in a total concentration from 10 % to 35 %, more preferably from 15 % to 30 % and most preferably from 20 % to 25 % of the total mixture.

Compounds of formula V preferably are used in the media in a total concentration from 10 % to 30 %, preferably from 12 % to 28 % and most preferably from 16 % to 23 % of the total mixture.

Compounds of formula Vl preferably are used in the media in a total concentration from 0 % to 30 %, preferably from 0 % to 15 % and most preferably from 1 % to 10 % of the total mixture.

Compounds of the polymerisable compounds, preferably of formulae VIIA and/or VIJB, preferably are used in the media in a total concentration from 0 % to 10 %, more preferably from 0 % to 7 % and most preferably from 0.5 % to 5 % of the total mixture.

Preferably one or more polymerisation initiators, preferably one or more photo initiators are used. The concentration of the initiators is from 0.1 % to 10 %, more preferably from 0.2 % to 5 % and most preferably from 0.5 % to 2 % of the total concentration of the polymerisable compounds.

Preferably the media according to the present invention further comprise one or more chiral compounds as chiral dopants in order to adjust their cholesteric pitch. Their total concentration in the media according to the instant invention is preferably in the range 0.1 % to 15 %, more preferably from 1 % to 10 % and most preferably from 2 % to 6 %. Optionally the media according to the present invention may 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 0.1 % to 20 % and most preferably 1 % to 15 %.

Preferably the media according to the present invention comprise one or more compounds of

- formula I-2 and/or

- formula 11-1 c preferably of formula PUQU-n-F, and/or

- formula ll-2c, preferably of formulae ll-2c-1 , and/or

- formula Hl-Ia, preferably of formulae lll-i a-1 , and/or

- formula lll-1c, preferably of formulae Ill-1 c12, and/or

- formula Ill-Id, preferably of formulae lll-1d-1 , and/or

- formula IV-6, preferably of formulae CPTP-n-Om and/or CPTP-n-m, and/or

- formula IV-7, preferably of formulae CPGP-n-Om and/or CPGP-n-m, and/or

- formula V- 1 , preferably of formula PP-n-mV, and/or PP-n-mVI, and/or

- formula V-2, preferably of formula PTP-n-Om and/or

- formula V-3, preferably of formulae PGP-n-m and/or PGP-n-mV and/or

- formula V-4, preferably of formula PPTUI-n-m and/or

- formula R-5011 or S-5011 and/or one or more reactive polymerisable compounds and/or

- one or more polymerisation initiators.

In the present application the term dielectrically positive is used for compounds or components with Δε > 3.0, dielectrically neutral with -1.5 < Δε < 3.0 and dielectrically negative with Δε < -1.5. Δε is determined at a frequency of 1 kHz and at 20 °C. The dielectric anisotropy of the respective compound is determined from the results of a solution of 10 % of the respective individual compound in a nematic host mixture. In case the solubility of the respective compound in the host mixture is less than 10 % its concentration is reduced by a factor of 2 until the resultant mixture is stable enough at least to allow the determination of its properties. Preferably the concentration is kept at least at 5 %, however, in order to keep the significance of the results a high as possible. The capacities of the 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.

Δε is defined as (εn - ε_i_), whereas ε_av. is (εn + 2 ε_x) / 3. 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. The values are extrapolated to a concentration of the compounds of interest of 100 %.

Components having a nematic phase at the measurement temperature of 20 ⁰C 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 (\Λo) and the term saturation voltage refers to the optical saturation and is given for 90 % relative contrast (Vg₀) both, if not explicitly stated otherwise. The capacitive threshold voltage (V₀), also called Freedericks-threshold (V_Fr) 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 approximately 20 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 (εn) and polyimide AL-1054 from Japan Synthetic Rubber for planar homogeneous orientation (ε_ι_). The capacities were determined with a frequency response analyser Solatron 1260 using a sine wave with a voltage of 0.3 V_rms. The test cells used have cell gap selected to have an optical retardation matching the first transmission minimum according to Gooch and Tarry or below, typically of about 0.45 μm^"1. The light used in the electro-optical measurements was white light. The set up used was commercially available equipment of Autronic Melchers, Karlsruhe, Germany. The characteristic voltages have been determined under perpendicular observation. The threshold (V₁₀) - mid grey (V₅₀) - and saturation (Vg₀) voltages have been determined for 10 %, 50 % and 90 % relative contrast, respectively.

The response times are given as rise time (τ_on) for the time for the change of the relative contrast from 0 % to 90 % (t_go - 1₀), i.e. including the delay time (tio - to), as decay time (τ_Off) for the time for the change of the relative contrast from 100 % back to 10 % (t_1Oo - 1₁₀) and as the total response time (τtotai) = τ_on + τ_Off), respectively.

The liquid crystal media according to the present invention may contain further additives in usual concentrations. The total concentration of these further constituents is in the range of 0 % to 10 %, preferably 0.1 % to 6 %, based on 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. This also holds for the concentration of the dichroic dyes used in the mixtures, which are not counted when the concentrations of the compounds respectively the components of the host mixture are specified. The concentration of the respective additives is always given relative to the final doped mixture.

The liquid crystal media according to the present invention consist of several compounds, preferably of 3 to 30, more preferably of 4 to 20 and most preferably of 4 to 16 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.

Preferably the liquid crystal media according to the present invention comprising one or more chiral dopants selectively reflect radiation in the visible range of the electromagnetic spectrum, i.e. in the range from 400 nm to 800 nm. Preferably their band of selective reflection extends into this range of wavelengths more preferably the centre wavelength of their reflection band lies within this range and most preferably their complete reflection band lies within this range. Preferably they have a selective reflection with a half bandwidth (1/2 FWHM) in the range from 15 nm to 60 nm, preferably in the range from 20 nm to 55 nm and most preferably from 25 nm to 50 nm. In particular, the relative half bandwidth, i.e. ratio of the half bandwidth (1/2 FWHM) and the centre wavelength of the reflection band, preferably is in the range from 1 % to 20 %, more preferably in the range from 2 % to 16 %, more preferably in the range from 4 % to 10 %, and most preferably in the range from 6 % to 8 %.

The wavelength of the centre of the resultant selective reflection at a given temperature may be calculated from the actual concentration of the chiral dopant in the host used via the approximation of the polynomial series (I):

λ_cen,_.[c(dop.)] = α • [c(dop.)r¹ + β • [c(dop.)r² + γ ^■ [c(dop.)r³ + ... (I) wherein

α, β and γ are material constants specific for the combination of a given chiral dopant in a given host mixture and

c(dop.) is the concentration of the chiral dopant in the host mixture.

In many practical cases, even consideration only of the first term, the linear term ("α • [c(dop.)]^"1"), yields results with sufficient accuracy. The parameter "α" is analogous to the inverse of the HTP (i.e. HTP^"1). Here, in the determination of the wavelength of the selective reflection of a cholesteric LC, which is similar to a "Bagg" reflection, however, the effective refractive index of the mixture has to be taken into account additionally for a more exact numerical description.

Typically the parameters α, β and γ do depend more strongly on the type of the chiral dopant, than on the specific liquid crystal mixture used.

Obviously, they depend on the enantiomeric excess of the respective chiral dopant. They have their respective largest absolute values are for the pure enantiomers and are zero for racemates. In this application the values given are those for the pure enantiomers, having an enantiomeric excess of 98 % or more.

Preferably the absolute value of the parameter α of the chiral dopant, respectively the chiral dopants, in the respective liquid crystal medium according to the present application is in the range from 5 nm to 25 nm, more preferably in the range from 10 nm to 20 nm and most preferably in the range from 12 nm to 16 nm.

These media may comprise more than one chiral dopant. In case they comprise two or more chiral dopants, these may beneficially selected in one of the known ways to compensate e.g. against the temperature dependence of the cholesteric pitch and, hence, of the wavelength of selective reflection. Here in one host mixture chiral dopants having the same sign of the parameter α may be used as well as chiral dopants having the opposite sign of this parameter, depending on the nature of the parameters for the terms of higher order of equation (I), in particular of the parameter β, the parameter of the quadratic term.

More preferred is an embodiment of the present invention using a single chiral dopant, which shows a small temperature dependence of the chiral pitch induced in the respective host mixture, i.e. has a small parameter β. 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-AMD, VAN-AMD, IPS and OCB LCDs and in particular in composite systems, like PDLC, NCAP, PN LCDs and especially in ASM-PA LCDs.

The melting point T(C₁N), the transition from the smectic (S) to the nematic (N) phase T(S₁N) and the clearing point T(N₁I) 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, which are also called "acronyms". The transformation of the abbreviations into the corresponding structures is straight forward according to the following three tables A to C.

All groups C_nH_2n+I- C_mH_2m+i and C|H₂ι₊i are preferably straight chain alkyl groups with n, m and I C-atoms, respectively, all groups C_nH_2n, C_mH_2m and

C|H₂| are preferably (CH₂)_n, (CH₂)_m and (CH₂),, respectively and -CH=CH- preferably is trans- respectively E vinylene.

Table A lists the symbols used for the ring elements, table B those for the linking groups and table C those for the symbols for the left hand and the right hand end groups of the molecules.

Table D lists exemplary molecular structures together with their respective codes.

wherein n und m each are integers and three points "..." indicate a space for other symbols of this table.

Preferably the liquid crystalline media according to the present invention comprise, besides the compound(s) of formula I one or more compounds selected from the group of compounds of the formulae of the following table.



Table E lists chiral dopants, which are preferably used in the liquid crystalline media according to the present invention.

Table E

In a preferred embodiment of the present invention the media according to the present invention comprise one or more compounds selected from the group of compounds of table E.

Table F lists stabilizers, which are preferably used in the liquid crystalline media according to the present invention.

Remark: In this table "n" means an integer in the range from 1 to 12.

In a preferred embodiment of the present invention the media according to the present invention comprise one or more compounds selected from the group of compounds of table F.

The liquid crystalline media according to the present invention comprise preferably four or more, preferably six or more, compounds selected from the group of compounds of table D, preferably

seven or more, preferably eight or more compounds, preferably compounds of three or more different formulae, selected from the group of formulae of table D.

Examples

The examples given in the following are illustrating the present invention without limiting it in any way.

However, the physical properties and compositions illustrate for the expert, which properties can be achieved and in which ranges they can be modified. Especially the combination of the various properties, which can be preferably achieved, is thus well defined for the expert.

Liquid crystal mixtures are realized with the compositions and properties given in the following tables. Their optical performance is investigated. Especially their reflection spectra are recorded.

Example 1

Table 1 : Composition and Properties of Liquid Crystal Mixture A-O

Examples 1.1 and 1.2

Either 3.2 % or 2.3 % of the chiral dopant R-5011 available from Merck KGaA, Darmstadt, Germany are added to 96.8 %, respectively to 97.7 %, of the mixture A-O from example 1 to prepare respective cholesteric mixtures called A-1 and A-2, respectively, both having a relatively short cholesteric pitch. The transition temperatures from the cholesteric liquid crystalline phase to the isotropic phase (i.e. the clearing points) are 83.5 ⁰C for mixture A-1 with 3.2 % R-5011 and 86.5 ⁰C for mixture A-2 with 2.3 % R-5011 , respectively.

Mixture A-1 shows a reflection in the blue range of the spectrum ranging from 377 nm to 435 nm (FWHM), as shown in figure 1 , whereas mixture A- 2 has a selective reflection in the green spectral region, ranging from 506 nm to 576 nm (FWHM), see also figure 1. The commas in the figures on the "R"-axis of the figure are representing decimal points.

Example 1.3

Analogously to example 1.1 1.6 % of the chiral dopant R-5011 are added to 98.4 % of the mixture A-O from example 1 to prepare the cholesteric mixture A-3. This mixture has a selective reflection in the red region of the visible spectrum.

In the same manner, using a respective concentration of the chiral dopant, a mixture reflecting in any desired spectral region can be easily realized.

The results of all examples are compiled in table 2 below. There also the parameter "α" is calculated for each individual example. And, as predicted, it is almost a constant for the combination of the chiral dopant R-5011 with the host mixture A-O, being (12.7 ± 0.3) nm for the concentrations used here.

- -

Example 2

Table 3: Composition and Properties of Liquid Crystal Mixture B-O

Examples 2.1 to 2.4

Example 2.1

3.2 % of the chiral dopant R-5011 is added to 96.8 % of the mixture B-O from example 2 to prepare a respective cholesteric mixture called B-1 having a relatively short cholesteric pitch. The transition temperature of the mixture B-1 for the transition from the cholesteric liquid crystalline phase to the isotropic phase (i.e. the clearing point) is 74.5 ⁰C. Mixture B-1 shows a reflection in the blue range of the spectrum, ranging from 418 nm to 488 nm (FWHM). Example 2.2

2.6 % of the chiral dopant R-5011 are added to 97.4 % of the mixture B-O from example 2 to prepare a respective cholesteric mixture called B-2 having a short cholesteric pitch somewhat longer than that of mixture B-1 of example 2.1. The clearing point of the mixture B-2 is 76.5 ⁰C. Mixture B- 2 shows a reflection in the green range of the spectrum, ranging from 512 nm to 590 nm (FWHM). The central wavelength of the selective reflection is 551 nm.

Example 2.3

2.2 % of the chiral dopant R-5011 are added to 97.8 % of the mixture B-O from example 2 to prepare a respective cholesteric mixture called B-3 having an even longer cholesteric pitch than mixture B-2 of example 2.2. The clearing point of the mixture B-3 is 77.5 ⁰C. Mixture B-3 shows a reflection in the red range of the spectrum, ranging from 600 nm to 693 nm (FWHM).

The resultant spectra of selective reflection for mixtures B-1 and B-3 of examples 2.1 and 2.3 are both shown in figure 2. The commas in the figures on the "R"-axis of the figure are representing decimal points. In this figure the results for mixture B-2 of example 2.2 have not been included, in order to avoid any confusion by the overlapping spectra. The band of selective reflection of mixture B-2 is filling the gap in the visible spectrum between those of the two mixtures B-1 and B-2 almost completely.

Example 2.4

2.7 % of the chiral dopant R-5011 are added to 97.3 % of the mixture B-O from example 2 to prepare a respective cholesteric mixture called B-4 having a short cholesteric pitch slightly shorter than that of mixture B-2 of example 2.2. The clearing point of the mixture B-4 is 76.0 ⁰C. Mixture B-4 shows a reflection in the green range of the spectrum. The central wavelength of the selective reflection is about 530 nm. The results for the mixtures B-2 and B-4 are well comparable to those for the mixture A-2 from example 1.2, which has a band of selective reflection with a slightly smaller bandwidth compared to that of mixture B-2 and a central wavelength almost exactly in the centre between those of the two mixtures B-2 and B-4.

Example 2.5

2.43 % of the chiral dopant R-5011 are added to 97.57 % of the mixture B-O from example 2 to prepare a respective cholesteric mixture called B-5 having a short cholesteric pitch slightly longer than that of mixture B-2 of example 2.2. The clearing point of the mixture B-5 is 77.0 ⁰C. Mixture B-6 shows a reflection in the yellow range of the spectrum. The central wavelength of the selective reflection is at about 584 nm, ranging from 541 nm to 626 nm (FWHM).

Example 2.6

2.13 % of the chiral dopant R-5011 are added to 97.87 % of the mixture B-O from example 2 to prepare a respective cholesteric mixture called B-6 having a short cholesteric pitch slightly longer than that of mixture B-3 of example 2.3. The clearing point of the mixture B-6 is 78 ⁰C. Mixture B-6 shows a reflection in the red range of the spectrum. The central wavelength of the selective reflection is about 670 nm, ranging from 619 nm to 720 nm (FWHM).

Table 4: Results of Example 2

Remarks: See table 2.

The parameter "α" for the combination of the chiral dopant R-5011 with the host mixture B-O is (14.3 ± 0.2) nm) for all concentrations used here. Example 3

Here the mixture B-2 of example 2.2, consisting of 2.6 % of R-5011 and of 97.4 % of the mixture B-O and having a reflection in the green range of the spectrum, is used as a starting mixture, which is then stabilized by a polymer formed in the material. To this end the di-reactive mesogen, RM1 (a bis-methacrylate) of the following formula

is added to the mixture B-2 together with the photo initiator Irgacure® 651 (IRG-651®), available from Ciba, Switzerland

The concentration of the RM used is 1 %, whereas the concentration of the photo initiator is set to 1 % of the concentration of the RM.

This mixture is heated once to a temperature of 60 ⁰C on a hot plate for 20 minutes in order to facilitate it's homogenization (Series A) and investigated for its properties. Then it is heated a second time the same temperature on a hot plate for 20 minutes (Series B) and investigated again. The mixture (B2M1-1) is investigated as such, as described above. It is also additionally filled into test cells and the reactive mesogen is subsequently polymerised by exposure to UV radiation. Table 5: Results of Example 3

Remarks: See table 2.

Example 4

Examples 4.1 to 4.3

Like in example 3, the mixture B-2 of example 2.2 is stabilized by a polymer formed in the material. The concentration of the RM is again changed from 1 % over 3 % to 5 % of the mixture, whereas the concentration of the photo initiator is set to 1 % of the RM in each case. Here, however, a different RM, the di-reactive mesogen, RM2 (a bis- acrylate) of the following formula

is used.

These mixtures (B2M2-1 to B2M2-3) are heated to a temperature of 60 ⁰C on a hot plate for 20 minutes in order to facilitate their homogenization and are investigated as such as described above. They are additionally filled into test cells and the reactive mesogen subsequently is polymerised by exposure to UV radiation.

Table 6: Results of Example 4

Remarks: See table 2. Example 5

Examples 5.1 to 5.3

Like in examples 3 and 4, a basic mixture is stabilized by a polymer formed in the material. The concentration of the RM is again changed from 1 % over 3 % to 5 % of the mixture, whereas the concentration of the photo initiator is set to 1 % of the RM in each case. Here, like in example 4, the di-reactive mesogen, RM2 is used.

Here, however, the mixture B-6 of example 2.6 is used.

These respective mixtures (B6M2-1 to B6M2-3) are heated to a temperature of 60 ⁰C on a hot plate for 20 minutes in order to facilitate their homogenization and are investigated as such as described above. They are additionally filled into test cells and the reactive mesogen subsequently is polymerised by exposure to UV radiation.

Table 7: Results of Example 5

Remarks: See table 2. Example 6

Table 8: Composition and Properties of Liquid Crystal Mixture C-O

2.8 % of the chiral dopant R-5011 are added to 97.2 % of the mixture C-O to prepare the cholesteric mixture called C-1 having a short cholesteric pitch. The clearing point of the mixture C-1 is 84.0 ⁰C. Mixture C-1 shows a reflection in the green range of the spectrum. The central wavelength of the selective reflection is about 526 nm. The band of the selective reflection ranges from 484 nm to 567 nm (FWHM), thus Δλ/2 is 42 nm. Example 7

Examples 7.1 to 7.4

Alternatively 2.7, 3.1 , 3.2 and 3.3 %, respectively, of the chiral dopant R-5011 are added to the respective amount of the mixture D-O leading to a total of 100 % to prepare the cholesteric mixtures called D-4 to D-1 , all having a relatively short cholesteric pitch. The clearing point of the mixtures are 78.5, 77.0, 77.0 and 76.5 °C, respectively. Mixture D-4 shows a reflection in the green range of the spectrum, whereas the three four mixtures D-1 to D-3 all show a reflection in the blue range of the spectrum. The variation of the concentration of the chiral dopant in these three mixtures allows the selection of the proper blue colour. The central wavelength of the selective reflection of mixture D-4 is at about 536 nm, whereas those of the following mixtures are successively shifted towards shorter wavelengths with increasing concentration of the chiral dopant. Table 10: Comparison of Results of Example 7

Remarks: See table 2.

Table 11 : Comparison of Results of Examples 6 and 7

Remarks: See table 2. Example 8

Examples 8.1 to 8.3

Either 3.28 % or 2.82% or 2.27 % of the chiral dopant R-5011 available from Merck KGaA, Darmstadt, Germany are added to 96,72 %, respectively to 97.18 %, respectively to 97.73 %, of the mixture E-O from example 8 to prepare respective cholesteric mixtures called E-1 to E-3, respectively, all having a relatively short cholesteric pitch. The transition temperatures from the cholesteric liquid crystalline phase to the isotropic phase (i.e. the clearing points) are 73.5 °C for mixture E-1 with 3.28 % R- 5011 , 75.0 ⁰C for mixture E-2 with 2.82 % R-5011 and 76.0 ⁰C for mixture E-3 with 2.27 % R-5011 , respectively. Mixture E-1 shows a reflection in the blue range of the spectrum, ranging from 438 nm to 510 nm (FWHM), mixture E-2 has a selective reflection in the green spectral region, ranging from 490 nm to 567 nm (FWHM) and mixture E-3 has a selective reflection in the red spectral region, ranging from 595 nm to 681 nm (FWHM).

The results of all examples are compiled in table 13 below. There also the parameter "α" is calculated for each individual example. And, as expected, it is almost a constant for the combination of the chiral dopant R-5011 with the host mixture E-O, being (15.0 ± 0.5) nm for the concentrations used here.

Table 13: Comparison of Results of Example 8

Remarks: See table 2. Example 9

Table 14: Composition and Properties of Liquid Crystal Mixture F-O

To 97.61 % of the mixture F-O 2.39 % of the chiral dopant R-5011 are added. The resultant mixture F- 1 has a clearing point of 86.0 ⁰C and a central wavelength of the selective reflection of 558 nm. The band of selective reflection ranges from 524 nm to 592 nm (FWHM) and Δλ/2 is thus 34 nm.

To each one of these mixtures (G-O to J-O) a given amount of the chiral dopant R-5011 is given. The respective concentrations are 2.73 %, 2.22 %. 3.02 % and 2.93 % for the respective mixtures G-1. H-1. 1-1 and J-1.

Table 16: Comparison of the results for Liguid Crystal Mixtures G-1 to J-1

Remarks: See table 2.

Example 14

To the liquid crystalline host mixture B-O of example 2 a chiral reactive mesogen (RM3^*) with the following formula

is added to the mixture B-2. This reactive mesogen RM3^* has a chiral structure and the compound used has an enatiomeric excess. To the host mixture B-O 4.75 % of RM3^* are added. Then three cells are filled with the resultant mixture. The cells for the LC are made from AF glass and have orientation layers of AL3046 (from JSR, Japan). The first one of these cells is investigated as such. The parameter α is 21.2 nm here. The 2^nd and 3^rd one of these cells are exposed to UV-irradiation with a different dose each. A high pressure mercury lamp EXECURE-w 3000 from HOYA Schott, Japan is used. The intensity of the UV radiation is 100 mW/cm. A cut-off filter with a cut-off wave length of 320 nm is placed between the lamp and the LC cell. The 2^nd cell is exposed to UV radiation with an energy of 22 J, whereas the 3^rd cell is exposed to 71 J.

Table 17: Results of Example 14

Remarks: See table 2.

Obviously, the wavelength of the selective reflection can be altered to any desired colour simply by varying the intensity/energy of the UV irradiation. Example 15

In this example 1.19 % of the chiral dopant R-5011 and 3.00 % of the chiral reactive mesogen RM3^* are added to the liquid crystalline host mixture B-O of example 2. R-5011 RM3^*both have a positive value of the HTP. Like in example 14, several cells are filled with the resultant mixture and processed and investigated as described under example 14. Here four cells are prepared. The 1^st cell is investigated as such. The 2^nd cell is exposed to UV radiation having an energy of 60 J, the 3^rd cell is exposed to 120 J and the 4^th cell is exposed to 300 J, respectively.

Table 18: Results of Example 15

Remarks: See table 2.

Obviously, here again, the wavelength of the selective reflection can be altered to any desired colour by variation of the intensity/energy of the UV irradiation. Example 16

Now, 1.19 % of the chiral dopant R-5011 , 3.00 % of the chiral reactive mesogen RM3^* together with 0.030 % the photo initiator Irgacure® 651 (short IRG-651®, available from Ciba, Switzerland) are added to the liquid crystalline host mixture B-O of example 2. Like in example 15, again four cells are prepared, processed and investigated. The 1^st cell again is investigated as such. The 2^nd cell is exposed to UV radiation with an eenneerrggyy ooff 3300 JJ,, tthhee : 3^rd cell is exposed to 60 J and the 4^th cell is exposed to 120 J, respectively.

Table 19: Results of Example 16

Remarks: See table 2.

Obviously, also here the wavelength of the selective reflection can be adjusted to any desired colour by variation of the intensity/energy of the UV irradiation. The energy of the Uv radiation needed to achieve a given shift of the wavelength of selective reflection is significantly lower when a photo initiator is used, as in the present example, compared to the situation with out presence of a photo initiator, like in the previous example, example 15. Starting with one and the same wavelength of selective reflection (i.e. (452 ± 1 ) nm) in both cases, a given, longer value of the wavelength of selective reflection (e.g. (598 ± 3) nm) is reached at a significantly lower energy dose of 120 J, compared to 300 J. This leads to a reduction of the exposure of the medium to UV radiation and to an increase of reliability.

These results are summarized and compared in the following table.

Table 20: Comparison of the results of Examples 15 and 16

Remarks: See table 2.

Claims

Claims

Liquid crystal medium, characterised in that it comprises

- one or more compounds of formula I

wherein

R¹ is alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy, alkenyl, alkenyloxy, alkoxyalkyl, fluorinated alkenyl or fluorinated alkenyloxy,

L¹¹ and L¹² are independently of each other H or F,

X¹ is CN or NCS and

is 0 or 1 and

one or more compounds selected from the group of compounds of formulae Il and

wherein

R² and R³, independently of each other, are alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1 to 7 C- atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C-atoms,

are independently of each other

L²¹, L²², L³¹ and L³², are independently of each other H or F,

X² and X³ are independently of each other halogen, halogenated alkyl or alkoxy with 1 to 3 C-atoms or halogenated alkenyl or alkenyloxy with 2 or 3 C-atoms,

is -CH₂CH₂-, -CF₂CF₂-, -COO-, trans- -CH=CH-, trans- -CF=CF-, -CH₂O- or a single bond, and I, m, n and o are independently of each other 0 or 1 and optionally

one or more compounds selected from the group of formulae IV and V

wherein

R⁴¹ to R⁵² independently of each other have the meaning given for R² under formula Il above,

independently of each other and in case

is present twice, also these independently of each other are

independently of each other and in case

is present twice, also these independently of each other are

Z⁴¹ to Z⁵² independently of each other, and in case Z⁴¹ and/or Z⁵¹ is/are present twice, also these independently of each other, are -CH₂CH₂-, -COO-, trans- -CH=CH-, trans- -CF=CF-, -CH₂O-, -CF₂O-, -C≡C- or a single bond, and

p and q are independently of each other 0, 1 or 2 and

the media optionally comprise one or more chiral compounds.

2. Liquid crystal medium according to claim 1 , characterised in that the total concentration of the compounds of formula I in the medium is in the range from 1 % or more to 35 % or less.

3. Liquid crystal medium according to at least one of claims 1 and 2, characterised in that it comprises one or more compounds of formula I-2

wherein R¹ and X¹ have the respective meanings given in claim 1 under formula I.

4. Liquid crystal medium according to one or more of claims 1 to 3, characterised in that it comprises one or more compounds of formula II-2C-1

wherein R has the meaning given in claim 1.

Liquid crystal medium according to one or more of claims 1 to 4, characterised in that it comprises one or more compounds of formula lll-1d-1

wherein R³ has the meaning given in claim 1.

6. Liquid crystal medium according to one or more of claims 1 to 5, characterised in that it comprises one or more compounds of formula

R-5011 or S-5011

Liquid crystal medium according to one or more of claims 1 to 6, characterised in that it comprises one or more polymerisable compounds.

8. Liquid crystal medium according to one or more of claims 1 to 7, characterised in that it comprises one or more compounds of formulae V- 1 and/or V-2

wherein R⁵¹ and R⁵² have the respective meanings given in claim 1.

9. Liquid crystal display, characterised in that it comprises a liquid crystal medium according to at least one of claims 1 to 8.

10. Use of a liquid crystal medium according to at least one of claims 1 to 8 in a liquid crystal display.

11. Method of preparation of a liquid crystal medium according to at least one of claims 1 to 8, characterised in that one or more compounds of formula I, one or more compounds of formulae Il and/or III and one or more compounds of formulae IV and/or V and/or VIIA and/or VIIB, all as given in claim 1 , are mixed.

12. Composite material comprising a low molecular a liquid crystalline medium and a polymer obtainable from a medium according to at least one of claims 7 and 8.

13. Use of a composite material according to claim 12 in a liquid crystal display.

14. Method of preparation of a composite material according to claim 12 by polymerisation of a polymer precursor in a liquid crystalline medium.

15. Liquid crystalline medium comprising one or more compounds having a nematic phase and one or more chiral reactive mesogens.

16. Medium according to claim 15, comprising one or more non-reactive chiral compounds (i.e. chiral dopants).

17. Medium according to at least one of claims 15 and 16, characterised in that it additionally comprises a photo initiator.

18. Medium according to at least one of claims 15 to 17, characterised in that it has a wavelength of selective reflection in the near UV (above e.g. 250 nm) or in the visible range of the electromagnetic spectrum.

19. Medium according to at least one of claims 15 to 19, characterised in that it is medium according to at least one of claims 1 to 8.

20. Liquid crystal display, characterised in that it comprises a liquid crystal medium according to at least one of claims 15 to 19.

21. Use of a liquid crystal medium according to at least one of claims 15 to 19 in a liquid crystal display.

22. Method of preparation of a liquid crystal medium according to at least one of claims 15 to 19, characterised in that one or more compounds having a nematic phase and one or more chiral reactive mesogens are mixed.

23. Composite material comprising a low molecular a liquid crystalline medium and a polymer obtainable from a medium according to at least one of claims 15 to 19.

24. Use of a composite material according to claim 23 in a liquid crystal display.

25. Method of preparation of a composite material according to claim 23 by polymerisation of a polymer precursor in a liquid crystalline medium.

26. Method of adjusting the colour and/or the bandwidth of selective reflection of a composite material according to claim 23 by exposure of the medium to UV radiation.