WO2004087835A1

WO2004087835A1 - Chiral polymerizable compounds

Info

Publication number: WO2004087835A1
Application number: PCT/EP2004/002157
Authority: WO
Inventors: Ian Victor Edward Hassall; Alison Linda May
Original assignee: Merck Patent Gmbh
Priority date: 2003-04-01
Filing date: 2004-03-04
Publication date: 2004-10-14
Also published as: JP2006526669A

Abstract

The invention relates to chiral polymerizable and photoisomerizable compounds and their use in liquid crystal media, liquid crystal devices, anisotropic polymers, optical, electrooptical, decorative, security, cosmetic, diagnostic, electric, electronic, charge transport, semiconductor, optical recording, electroluminescent, photoconductor, electrophotographic and lasing applications, and to liquid crystal media, polymers, optical components, displays and decorative or security markings comprising the chiral polymerizable compounds.

Description

Chiral Polymerizable Compounds

Field of the Invention

The invention relates to chiral polymerizable and photoisomerizable compounds, methods of their preparation, and to their use in liquid crystal media, liquid crystal devices, anisotropic polymers, optical, electrooptical, decorative, security, cosmetic, diagnostic, electric, electronic, charge transport, semiconductor, optical recording, electroluminescent, photoconductor, electrophotographic and lasing applications. The invention further relates to liquid crystal media, polymers, optical components, displays and decorative or security markings comprising the chiral polymerizable compounds.

Background and Prior Art

Chiral materials which change their chirality upon photoirradiation are known in prior art. For example, photoisomerizable chiral materials were reported which show E-Z or cis-trans isomerization upon photoirradiation and are thereby converted from one chiral form into another chiral form. Further known are photodegradable or (photo)tunable chiral materials (TCM) that change from chiral to achiral or to a racemic mixture upon photoirradiation, due to destruction of their chirality by photoelimination or photocleavage of the chiral center.

Photoisomerizable chiral materials have been suggested inter alia for the preparation of cholesteric polymer films with patterned optical properties, which can be used as optical components like colour filters or broadband reflective polarizers in liquid crystal displays. The preparation of patterned cholesteric films is described for example in WO 00/34808.

Furthermore, photoisomerizable and phototunable chiral materials have been suggested for use in cholesteric or multi-domain liquid crystal displays. For example, WO 98/57223 discloses a multi-domain liquid crystal display with a nematic liquid crystal material comprising a polymerizable menthone derivative as photoisomerizable chiral dopant. The display comprises different sub-pixels in which the twist sense of the liquid crystal material is mutually opposite. It is manufactured by photoirradiation of a layer of liquid crystal material containing a photoisomerizable chiral dopant with a given twist sense and a non-isomerizable chiral dopant with opposite twist sense through a photomask. This causes the isomerizable dopant in the exposed parts of the layer to change its chirality, leading to a change of the helical pitch in the exposed parts.

US 5,668,614 discloses a multicolour cholesteric display made from a cholesteric liquid crystal mixture comprising a tunable chiral material (TCM). The display is prepared by partially exposing the liquid crystal mixture with the TCM to photoirradiation through a photomask. This leads to a change of the chirality of the TCM by photocleavage or photoracemisation and thus to a change of the helical pitch in the exposed parts of the cholesteric liquid crystal material. Thereby regions with different pitch and thus different colours of the reflected wavelength are obtained and a multicolour display is realized.

Photoisomerizable chiral materials comprising menthone, camphor or nopinone derivatives or chiral stilbenes have been reported by P. van de Witte et al., Liq. Cryst. 24 (1998), 819-27, J. Mat. Chem. 9 (1999), 2087-94 and Liq. Cryst. 27 (2000), 929-33 and A. Bobrovski et al., Liq. Cryst. 25 (1998), 679-687.

Tunable chiral materials (TCMs) comprising a photocleavable carboxylic acid group or aromatic keto group attached to the chiral center are disclosed in US 5,668,614. Furthermore, F. Vicentini, J. Cho and L. Chien, Liq. Cryst. 24 (1998), 483-488 describe binaphthol derivatives as TCMs and their use in multicolour cholesteric displays. However, the isomerizable and tunable chiral materials of prior art have several drawbacks. The TCMs reported in US 5,668,614 and by F. Vicentini et al. have the general disadvantage that photocleavage is an irreversible process and leads to destruction of the chiral compound. The photoisomerizable menthone and stilbene derivatives disclosed in in WO 98/57223 and the articles of P. van de Witte et al. and A. Bobrovsky et al. have the disadvantage that they are not easily structurally modified due to a lack of functionality.

Another drawback of many photoisomerizable compounds known from prior art is that they do often exhibit only a low helical twisting power (HTP). The HTP describes the effectiveness of a chiral compound to induce a helically twisted molecular structure in a liquid crystal host material, and is given in first approximation, which is sufficient for most practical applications, by equation (1 ) :

wherein c is the concentration of the chiral compound and p is the helical pitch. As can be seen from equation (1), a short pitch can be achieved by using a high amount of the chiral compound or by using a chiral compound with a high absolute value of the HTP. Thus, in case chiral compounds with low HTP are used, high amounts are needed to induce a short pitch. This is disadvantageous, because chiral compounds often negatively affect the properties of the liquid crystal host mixture, like for example the clearing point, dielectric anisotropy, viscosity, driving voltage or switching times, and because chiral compounds can be used only as pure enantiomers and are therefore expensive and difficult to synthesize.

Another disadvantage of chiral compounds of prior art is that they often show low solubility in the liquid crystal host mixture, which leads to undesired crystallization at low temperatures. To overcome this disadvantage, typically two or more different chiral compounds have to be added to the host mixture. This implies higher costs and also requires additional effort for temperature compensation of the mixture, as the different chiral compounds usually have to be selected such that their temperature coefficients of the twist compensate each other.

Therefore, there is a considerable demand for chiral photoisomerizable compounds with a high HTP which are easy to synthesize in a large range of derivatives, can be used in low amounts, show improved temperature stability of the cholesteric pitch e.g. for utilizing a constant reflection wavelength, do not affect the properties of the liquid crystal host mixture and show good solubility in the host mixture.

The invention has the aim of providing chiral photoisomerizable compounds having these properties, but not having the disadvantages of the chiral compounds of prior art as discussed above. Another aim of the invention is to extend the pool of chiral photoisomerizable compounds available to the expert.

The inventors of the present invention have found that these aims can be achieved by providing chiral polymerizable compounds as described below, comprising a chiral sugar group selected from isosorbide (1), isomannite (2) or isoidite (3)

(1 ) (2) (3)

that is linked in 2- and 5-position to a mesogenic group based on a cinnamic acid derivative and comprises one or more terminal polymerizable groups attached thereto, optionally via flexible spacers, wherein the mesogenic group is laterally substituted. The sugar group imparts chirality to the molecule, while the cinnamic acid groups are photoisomerizable. GB 2 314 839 discloses chiral polymerizable mesogenic compounds with a high HTP based on 1 ,4:3,6-Dianhydro-D-sorbitol (isosorbide) cinnamates. However, these compounds do only have a limited solubility in liquid crystal host mixtures.

In contrast, the chiral polymerizable compounds according to the present invention with laterally substituted mesogenic groups show increased solubility in liquid crystal host mixtures. Also, the method disclosed in the present invention allows simpler synthetis of these compounds.

Summary of the Invention

The invention relates to compounds of formula I

P-Sp-(A¹-Z¹)_m1-A³-CH=CH-CO-G-CO-CH=CH-A⁴-(Z²-A²)_m2-R I

wherein

P is a polymerizable or reactive group,

Sp is a spacer group or a single bond,

G is selected from the following groups

A¹ and A² are independently of each other an aromatic or alicyclic a group, which optionally contain one or more hetero atoms selected from N, O and S, and are optionally mono- or polysubstituted by L,

A³ and A⁴ are independently of each other 1 ,4-phenylene in which one or more CH groups are optionally replaced by N, and which is optionally mono- or polysubstituted by L,

L is F, CI, Br, I, CN, N0₂₎ OH, NCS, SF₅ or alkyl which is straight chain or branched, has 1 to 8 C-atoms, is unsubstituted, mono- or polysubstituted by F, CI, 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 -0-, -S-, -NH-, -NR⁰-, -SiR°R⁰⁰-, -CO-, -

COO-, -OCO-, -OCO-0-, -S-CO-, -CO-S-, -CY¹=CY²- or -C≡C- in such a manner that O and/or S atoms are not linked directly to one another,

Z¹ and Z² are independently of each other -0-, -S-, -CO-, -COO-, -

OCO-, -S-CO-, -CO-S-, -0-COO-, -CO-NR⁰-, -NR°-CO-, - NR°-CO-NR°, -NR°-CO-0-, -O-CO-NR⁰-, -OCH₂-, -CH₂0-, -SCH₂-, -CH₂S-, -CF₂0-, -OCF₂-, -CF₂S-, -SCF₂-_, - CH₂CH₂-, -CF₂CH₂-, -CH₂CF₂-, -CF₂CF₂-, -CH=N-, - N=CH-, -N=N-, -CH=CR⁰-, -CY¹=CY²-, -C≡C-, -CH=CH- COO-, -OCO-CH=CH- or a single bond,

Y¹ and Y² are independently of each other H, F, CI or CN,

R is H, F, CI, Br, I, CN, NO₂, NCS, SF₅ or alkyl which is straight chain or branched, has 1 to 20 C-atoms, is unsubstituted, mono- or polysubstituted by F, CI, 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 -0-, -S-, -NH-, -NR⁰-, -SiR°R⁰⁰-, -CO-, - COO-, -OCO-, -OCO-0-, -S-CO-, -CO-S-, -CY¹=CY²- or

-C≡C- in such a manner that O and/or S atoms are not linked directly to one another, or has one of the meanings of P-Sp,

R° and R⁰⁰ are independently of each other H or alkyl with 1 to 12

C-atoms, and

ml and m2 are independently of each other 0, 1 or 2,

with the proviso that the compounds comprise at least one group A¹, A², A³ or A⁴ that is at least monosubstituted by L.

The invention further relates to an LC medium comprising at least one compound of formula I.

The invention further relates to a polymerizable LC medium comprising at least one compound of formula I.

The invention further relates to a chiral anisotropic polymer obtained by polymerizing a compound of formula I or a polymerizable LC medium as described above and below.

The invention further relates to a chiral anisotropic polymer obtained by polymerizing a compound of formula I or a polymerizable LC medium as described above and below in its oriented state, preferably in form of a film.

The invention further relates to a chiral anisotropic polymer film obtained by polymerizing a compound of formula I or a polymerizable LC medium as described above and below in its oriented state, which has a pattern of at least two regions with different orientation and/or different optical properties.

The invention further relates to the use of a compound of formula I, a polymer or a polymer film as described above and below in electrooptical displays, liquid crystal displays, optical films, polarizers, compensators, beam splitters, reflective films, alignment layers, colour filters, holographic elements, hot stamping foils, coloured images, decorative or security markings e.g. for consumer objects or documents of value, LC pigments, adhesives, synthetic resins with anisotropic mechanical properties, cosmetics, diagnostics, nonlinear optics, optical information storage, as chiral dopants, in electronic devices like for example field effect transistors (FET) as components of integrated circuitry, as thin film transistors in flat panel display applications or for Radio Frequency Identification (RFID) tags, or in semiconducting components for organic light emitting diode (OLED) applications, electroluminescent displays or backlights of LCDs, for photovoltaic or sensor devices, as electrode materials in batteries, as photoconductors, for electrophotographic applications or electrophotographic recording or in lasing materials or devices.

The invention further relates to an LC device comprising a compound of formula I or an LC medium, polymer or polymer film as described above and below.

The invention further relates to an authentification, verification or security marking or a coloured image comprising a compound of formula I or an LC medium, polymer or polymer film as described above and below.

The invention further relates to an object or document of value comprising an authentification, verification or security marking or an image as described above and below.

Definition of Terms The terms 'liquid crystal or mesogenic material' or 'liquid crystal or mesogenic compound' means materials or compounds comprising one or more rod-shaped, lath-shaped or disk-shaped mesogenic groups, i.e., groups with the ability to induce LC phase behaviour.

The compounds or materials comprising mesogenic groups do not necessarily have to exhibit an LC phase themselves. It is also possible that they show LC phase behaviour only in mixtures with other compounds, or when the mesogenic compounds or materials, or the mixtures thereof, are polymerized.

The terms 'polymerizable' and 'reactive' include compounds or groups that are capable of participating in a polymerization reaction, like radicalic or ionic chain polymerization, polyaddition or polycondensation, and reactive compounds or reactive groups that are capable of being grafted for example by condensation or addition to a polymer backbone in a polymeranaloguous reaction.

The term 'film' includes self-supporting, i.e., free-standing, films that show more or less pronounced mechanical stability and flexibility, as well as coatings or layers on a supporting substrate or between two substrates.

Detailed Description of the Invention

The inventive chiral photoisomerizable compounds are mesogenic or liquid crystal, i.e. they can induce or enhance mesophase behaviour for example in a mixture with other compounds or exhibit one or more mesophases themselves. It is also possible that the inventive compounds show mesophase behaviour only in mixtures with other compounds, or, in case of polymerizable compounds, when being (co)polymerized. Mesogenic inventive compounds are especially preferred.

The inventive compounds have several advantages • they can easily be synthesized, also on large scale of several hundred grams, with a broad range of derivatives using standard methods that are known from the literature,

• the starting materials can be obtained commercially or synthesized cheaply using methods known from the literature

• they can be prepared enantiomerically pure as compounds of different handedness (left handed and right handed), enabling both left and right handed helices to be formed in a nematic host, • the availability of both helices is a considerable advantage, e.g. for the use in security applications, as it enables the production of chiral films or coatings reflecting circularly polarized light of a single handedness,

• they exhibit a high HTP,

• they exhibit a good solubility in liquid crystal mixtures,

• they are mesogenic or even liquid crystalline,

• when inventive compounds are used as chiral dopant in a liquid crystal mixture, due to their high solubility higher amounts of dopant can be used to produce a high twist (= a low pitch),

• in case high amounts of dopants are needed, due to the broad liquid crystal phases of the inventive dopants the liquid crystal phase of the host mixture is less negatively influenced, • due to their high HTP, lower amounts of inventive dopants are needed to achieve a high pitch, and thereby the liquid crystalline properties of the mixture are less negatively affected,

• liquid crystal mixtures comprising one or more inventive dopants show a considerably improved low temperature stability,

• cholesteric liquid crystal mixtures comprising one or more inventive dopants show a reduced temperature dependence of the reflection wavelength,

The compounds of formula I are especially suitable for use in polymerizable mixtures for the preparation of patterned chiral LC films which can be used as optical films, like colour filters in an LCD, or as decorative or security images.

It is also possible to co-polymerize compounds of formula I via group P with other polymerizable mesogenic monomers, in order to induce or enhance LC phase behaviour.

Particularly preferred are compounds of formula I, wherein

- A³ and A⁴ are substituted 1 ,4-phenylene,

- m1 = m2 = 0,

- ml = m2 = 1 ,

- Z¹ and Z² are -COO-, -OCO-, -C≡C- or a single bond, - R is P-Sp-,

- R is straight chain alkyl or alkoxy with 1 to 12, preferably 1 to 8 C- atoms or alkenyl with 2 to 12, preferably 2 to 7 C-atoms,

- Sp is alkylene with 1 to 12 C atoms which is linked to the neighboured ring group A³ or A⁴ via group selected from -0-, - COO-, -OCO-, -OCOO- or a single bond.

- Sp is a single bond,

L is preferably F, CI, Br, I, CN, N0₂ or straight chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl or alkylcarbonlyoxy with 1 to 8 C atoms, wherein one or more H atoms are optionally substituted by F or CI.

Very preferably L is selected from F, CI, CN, N0₂ or straight chain or branched aikyl, alkoxy or alkylcarbonyl with 1 to 4 C atoms, wherein the alkyl groups are optionally perfluorinated.

Especially preferred groups L are selected from F, CI, CN, N0₂, CH₃, C₂H₅, C(CH₃)_3J CH(CH₃)₂₎ CH₂CH(CH₃)C₂H₅, OCH₃, OC₂H_5> COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, OCF₃, OCHF₂ or OC₂F₅₎ in particular F, CI, CN, CH₃, C₂H₅, C(CH₃)₃, CH(CH₃)₂, OCH₃, COCH₃ or OCF₃, most preferably F, CI, CH₃, C(CH₃)₃, OCH₃ or COCH₃.

Preferred groups A¹ and A² are for example furan, pyrrol, thiophene, oxazole, thiazole, thiadiazole, imidazole, phenylene, cyclohexylene, cyclohexenylene, pyridine, pyrimidine, pyrazine, azulene, indane, naphthalene, tetrahydronaphthalene, anthracene and phenanthrene.

Particularly preferably A¹ and A² are selected from 1 ,4-phenylene, 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 in formula I.

Preferably the groups -(A¹-Z¹)_m1-A³- and -A⁴-(Z²-A²)_m2- in formula I contain only monocyclic groups A^1"4. Very preferably the groups -(A¹- 2_¹)mi-A³- and -A⁴-(Z²-A²)_m2- contain one or two 5- or 6-membered rings.

A smaller group of preferred mesogenic groups -(A¹-Z¹)_mrA³- and - A⁴-(Z²-A²)_m2- is listed below. For reasons of simplicity, Phe in these groups is 1 ,4-phenylene, PheL is 1 ,4-phenylene that is substituted with 1 to 4 groups L as defined in formula I, Cyc is 1 ,4-cyclohexylene and Z has one of the meanings of Z¹ formula I. The list is comprising the following subformulae as well as their mirror images

-PheL- 11-1

-PheL-Z-Phe- II-2 -PheL-Z-PheL- II-3

-PheL-Z-Cyc- II-4

Z is preferably -COO-, -OCO-, -CH₂CH₂- or a single bond.

Very preferably the groups -(A¹-Z¹ )_mrA³- and/or -A⁴-(Z²-A²)_m2- are selected from the following formulae and their mirror images

wherein L has the meanings given above, and r is 1 , 2, 3 or 4, preferably 1 or 2. The group in these preferred formulae is very preferably

denoting '

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

Especially preferred compounds of formula I comprise at least

10 two groups _ }>- wherein r is 1 and/or at least one group

wherein r is 2.

If R is an alkyl or alkoxy radical, i.e. where the terminal CH₂ group is replaced by -0-, this may be straight-chain or branched. It is preferably straight-chain, has 2, 3, 4, 5, 6, 7 or 8 carbon atoms and accordingly is preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl,

20 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.

25

Oxaalkyl, i.e. where one CH₂ group is replaced by -0-, is preferably straight-chain 2-oxapropyl (=methoxymethyl), 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-

30. oxadecyl, for example.

If R is an alkyl group wherein one or more CH₂ groups are replaced by -CH=CH-, this may be straight-chain or branched. It is preferably straight-chain, has 2 to 10 C atoms and accordingly is preferably

35 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-, 4-, 5-, 6-, 7- or non-8-enyl, dec-1-, 2-, 3-, 4-, 5-, 6-, 7-, 8- or dec-9-enyI.

Especially preferred alkenyl groups are C₂-C₇-1E-alkenyl, C₄-C₇-3E- alkenyl, C₅-C₇-4-alkenyl, C₆-C₇-5-alkenyl and C₇-6-alkenyl, in particular C₂-C₇-1 E-alkenyl, C₄-C₇-3E-alkenyl and C₅-C₇-4-alkenyl. Examples for particularly preferred alkenyl groups are vinyl, 1E-propenyl, 1 E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-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.

If R is 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 -0-CO-. Preferably this group R 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-propionyloxyethyl, 2-butyryloxyethyl, 3-acetyloxypropyl, 3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(propoxy- carbonyl)ethyl, 3-(methoxycarbonyl)propyl, 3-(ethoxycarbonyl)propyl, 4-(methoxycarbonyl)-butyl.

If R is 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.

If R is an alkyl or alkenyl group that is monosubstituted by CN or CF₃, it is preferably straight-chain. The substitution by CN or CF₃ can be in any desired position.

If R is an alkyl or alkenyl group that is at least monosubstituted by halogen, it is preferably straight-chain. Halogen is preferably F or CI, in case of multiple substitution preferably F. The resulting groups include also perfluorinated groups. In case of monosubstitution the F or CI 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 is preferably F or CI.

R can be a polar or a non-polar group. In case of a polar group, it is 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, CI, CN, OCH₃, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, CHF₂, CH₂F,

OCF₃, OCHF₂, OCH₂F, C₂F₅ and OC₂F₅, in particular F, CI, 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.

R can be an achiral or a chiral group. In case of a chiral group it is preferably selected of formula III: *

-Q¹-CH-Q²

Q³

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, CI, 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 -OC-, -0-, -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, CI, Br, CN or an alkyl or alkoxy group as defined for Q² but being different from Q².

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

Preferred chiral groups of formula III 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 are 2-butyl (=1-methylpropyl), 2- methylbutyl, 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 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-methylhexyl, 2-hexyl, 2-octyl, 2-nonyl, 2-decyl, 2-dodecyl, 6-methoxyoctoxy, 6- methyloctoxy, 6-methyloctanoyloxy, 5-methylheptyloxycarbonyl, 2- methylbutyryloxy, 3-methylvalerbyloxy, 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 -butoxypropyI-2-oxy, 2-fluorooctyloxy, 2- fluorodecyloxy, 1 ,1 ,1-trifluoro-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-octyI and 1 ,1 ,1- trifluoro-2-octyloxy.

In addition, compounds containing an achiral branched group R 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 P is preferably selected from

(O) ι-, CH₃-CH=CH-0-, (CH₂=CH)₂CH-OCO-, (CH₂=CH-CH₂)₂CH- OCO-, (CH₂=CH)₂CH-0-, (CH₂=CH-CH₂)₂N-, (CH₂=CH-CH₂)₂N-CO-, HO-CW²W³-, HS-CW²W³-, HW²N-, HO-CW²W³-NH-, CH₂=CW¹-CO- NH-, CH₂=CH-(COO)_k1-Phe-(0)_k2-, Phe-CH=CH-, HOOC-, OCN-, and W⁴W⁵W⁶Si-, with W¹ being H, CI, CN, phenyl or alkyl with 1 to 5 C- atoms, in particular H, CI 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 CI, oxaalkyl or oxacarbonylalkyl with 1 to 5 C-atoms, Phe being 1 ,4- phenylene that is optionally substituted by one or more groups L as defined above, and ki and k₂ being independently of each other 0 or 1.

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

Sp' is alkylene with up to 20 C atoms which may be unsubstituted, mono- or poly-substituted by F, CI, 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-, -NR⁰-, -SiR°R⁰⁰-, -CO-, -COO-, -OCO-, -OCO-0-, -S-

CO-, -CO-S-, -CH=CH- or -C≡C- in such a manner that O and/or S atoms are not linked directly to one another,

X is -0-, -S-, -CO-, -COO-, -OCO-, -0-COO-, -CO-NR⁰-, -NR°-CO- , -NR°-CO-NR°, -NR⁰-CO-O-, -O-CO-NR⁰-, -OCH₂-, -CH₂0-, -

SCH₂-, -CH₂S-, -CF₂0-, -OCF₂-, -CF₂S-, -SCF₂-, -CF₂CH₂-, - CH₂CF₂-, -CF₂CF₂-, -CH=N-, -N=CH-, -N=N-, -CH=CR⁰-, - CY¹=CY²-, -C≡C-, -CH=CH-COO-, -OCO-CH=CH- or a single bond, and

R >0 , R Γ-,00 , Y1 and Y have one of the meanings given in formula I.

X is preferably -0-, -S-, -OCH₂-, -CH₂0-, -SCH₂-, -CH₂S-, -CF₂0-, - OCF₂-, -CF S-, -SCF - -CH₂CH₂-, -CF₂CH₂-, -CH₂CF -, -CF₂CF -, - CH=N-, -N=CH-, -N=N-, -CH=CR⁰-, -CX¹=CX²-, -C≡C- or a single bond, in particular -0-, -S-, -C≡C-, -CX¹=CX²- or a single bond, very preferably a group that is able to from a conjugated system, such as -C≡C- or -CX¹=CX²-, or a single bond. Further preferred groups X are -O-COO-, -CO-NR⁰-, -NR°-CO-, -NR°-CO-NR°, -NR⁰-CO-O- and -O-CO-NR⁰-.

Typical groups Sp' are, for example, -(CH₂)_P-, -(CH₂CH₂0)_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 R° and R⁰⁰ having the meanings given above. Preferred groups Sp' 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.

Further preferred are compounds with one or two groups P-Sp- wherein Sp is a single bond. In case of compounds with two groups P-Sp, each of the two polymerizable groups P and the two spacer groups Sp can be identical or different.

In another preferred embodiment the group Sp' is a chiral group of formula IV:

4

-Q¹-CH-Q⁴

I

^Q3 ιv

wherein

Q¹ and Q³ have the meanings given in formula III, 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 polymerizable group P.

Particularly preferred compounds of formula I are those of the following formulae

wherein P and Sp are as defined above, and L^1"4 independently of each other denote H or have one of the meanings of L, with at least one of L^1"4 being different from H.

Particularly preferred are compounds of formula la-lc, wherein L³ and L⁴ are H and one or both of L¹ and L² are different from H. L¹ and L² in these preferred compounds are very preferably selected from F, CI, CN, N0₂, CH₃, C₂H₅₎ C(CH₃)₃, CH(CH₃)₂, CH₂CH(CH₃)C₂H₅, OCH₃, OC₂H₅, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, OCF₃, OCHF₂ and OC₂F₅.

The compounds of formula I can be synthesized according to or in analogy to methods which are known per se and which are described in standard works of organic chemistry such as, for example, Houben-Weyl, Methoden der organischen Chemie, Thieme-Verlag, Stuttgart. Preferably the compounds are synthesized according or in analgoy to reaction scheme 1 below. Further methods can be taken from the examples.

Scheme 1 :

pTSA DCM CICH₂CH₂C0₂H

The compounds of formula I can be used in a liquid crystal mixture for liquid crystal displays exhibiting a twisted molecular structure of the liquid crystal matrix like, for example, twisted or supertwisted nematic displays with multiplex or active matrix addressing, or in displays comprising a liquid crystal mixture with a chiral liquid crystal phase, like for example chiral smectic or chiral nematic (cholesteric) mixtures for ferroelectric or cholesteric displays.

The inventive compounds, mixtures and polymers are especially suitable for cholesteric displays, like for example surface stabilized or polymer stabilized cholesteric texture displays (SSCT, PSCT) as described in WO 92/19695, WO 93/23496, US 5,453,863 or US 5,493,430, in particular for liquid crystal devices with variable pitch, like multi-domain liquid crystal displays as described for example in WO 98/57223, or multicolour cholesteric displays as described for example in US 5,668,614.

The entire disclosure of the above mentioned documents is introduced into this application by way of reference. The inventive compounds of formula I are also suitable for use in photochromic liquid crystal media, which change their colour upon photoradiation.

Thus, another object of the invention is a liquid crystal mixture comprising at least one chiral compound of formula I.

Yet another object of the invention are cholesteric liquid crystal displays comprising cholesteric liquid crystal media containing at least one chiral compound of formula I.

The inventive compounds have a good solubility in liquid crystal host mixtures, and can be added as dopants to liquid crystal hosts in high amounts without significantly affecting the phase behaviour and electrooptical properties of the mixture. Undesired spontaneous crystallization at low temperatures is thereby reduced and the operating temperature range of the mixture can be broadened. Furthermore, these chiral compounds can be used for the preparation of a highly twisted liquid crystal medium even if they have a low HTP, because the dopant concentration can be increased to yield low pitch values (i.e. high twist) without affecting the mixture properties. The use of a second dopant, which is often added to avoid crystallization, can thus be avoided.

Also, the inventive chiral compounds of formula I exhibit high values of the HTP. A liquid crystal mixture with high helical twist, i.e. a low pitch, can be prepared by using these compounds as dopants, or a liquid crystal mixture with moderate helical twist can be achieved by using these inventive compounds as dopants already in very small amounts.

As mentioned above, the inventive compounds are furthermore advantageous because they are affecting the physical properties of the liquid crystal mixture only to a minor extent. Thus, when admixing the chiral compounds of formula I for example to a liquid crystal mixture with positive dielectric anisotropy that is used in a liquid crystal display, the dielectric anisotropy is only slightly reduced and the viscosity of the liquid crystal mixture is increased only to a small extent. This leads to lower voltages and improved switching times of the display when compared to a display comprising conventional dopants.

A liquid crystal mixture according to the invention comprises preferably 0.1 to 30 %, in particular 1 to 25 % and very particularly preferably 2 to 15 % by weight of chiral compounds of formula I.

A liquid crystal mixture according to the invention preferably comprises 1 to 3 chiral compounds of formula I.

In a preferred embodiment of the invention the liquid crystal mixture is consisting of 2 to 25, preferably 3 to 15 compounds, at least one of which is a chiral compound of formula I. The other compounds are preferably low molecular weight liquid crystal compounds selected from nematic or nematogenic substances, for example from the known classes of the azoxybenzenes, benzylidene-anilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl esters of cyclohehexanecarboxylic acid, phenyl or cyclohexyl esters of cyclohexylbenzoic acid, phenyl or cyclohexyl esters of cyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl esters of benzoic acid, of cyclohexanecarboxylic acid and of cyclo- hexylcyclohexanecarboxylic acid, phenylcyclohexanes, cyclohexyl- biphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, cyclohexylcyclohexenes, cyclohexylcyclohexylcyclohexenes, 1 ,4-bis- cyclohexylbenzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl- or cyclo- hexylpyrimidines, phenyl- or cyclohexylpyridines, phenyl- or cyclo- hexylpyridazines, phenyl- or cyclohexyldioxanes, phenyl- or cyclo- hexyl-1 ,3-dithianes, 1 ,2-diphenyl-ethanes, ,2-dicyclohexylethanes, 1- phenyl-2-cyclohexylethanes, 1-cyclohexyl-2-(4-phenylcyclohexyl)- ethanes, 1-cyclohexyl-2-biphenyl-ethanes, 1 -phenyl2-cyclohexyl- phenylethanes, optionally halogenated stilbenes, benzyl phenyl ether, tolanes, substituted cinnamic acids and further classes of nematic or nematogenic substances. The 1,4-phenylene groups in these compounds may also be laterally mono- or difluorinated.

The liquid crystal mixture of this preferred embodiment is based on the achiral compounds of this type.

The most important compounds that are posssible as components of these liquid crystal mixtures can be characterized by the following formula

R'-L'-G'-E-R"

wherein L' and E, which may be identical or different, are in each case, independently from one another, a bivalent radical from the group formed by -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -B-Phe- and -B-Cyc- and their mirror images, where Phe is unsubstituted or fluorine-substituted 1 ,4-phenylene, Cyc is trans- 1 ,4-cyclohexylene or 1 ,4-cyclohexenylene, Pyr is pyrimidine-2,5-diyl or pyridine-2,5-diyl, Dio is 1 ,3-dioxane-2,5-diyl abd B is 2-(trans-1 ,4- cyclohexyl)ethyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1 ,3-dioxane- 2,5-diyl.

G' in these compounds is selected from the following bivalent groups -CH=CH-, -N(0)N-, -CH=CY-, -CH=N(0)-, -C≡C-, -CH₂-CH₂-,

-CO-0-, -CH₂-0", -CO-S-, -CH₂-S-, -CH=N-, -COO-Phe-COO- or a single bond, with Y being halogen, preferably chlorine, or -CN.

R' and R" are, in each case, independently of one another, alkyl, alkenyl, alkoxy, alkenyloxy, alkanoyloxy, alkoxycarbonyl or alkoxycarbonyloxy with 1 to 18, preferably 3 to 12 C atoms, or alternatively one of R' and R" is F, CF₃, OCF₃, CI, NCS or CN.

In most of these compounds R' and R" are, in each case, independently of each another, alkyl, alkenyl or alkoxy with different chain length, wherein the sum of C atoms in nematic media generally is between 2 and 9, preferably between 2 and 7.

Many of these compounds or mixtures thereof are commercially available. All of these compounds are either known or can be prepared by methods which are known per se, as described in the literature (for example in the standard works such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), to be precise under reaction conditions which are known and suitable for said reactions. Use may also be made here of variants which are known per se, but are not mentioned here.

A preferred use of the inventive compounds is the preparation of polymerizable liquid crystal mixtures, anisotropic polymer gels and anisotropic polymer films, in particular polymer films that exhibit a helically twisted molecular structure with uniform planar orientation, i.e. wherein the helical axis is oriented perpendicular to the plane of the film, like oriented cholesteric films.

Anisotropic polymer gels and displays comprising them are disclosed for example in DE 195 04 224 and GB 2 279 659.

Oriented cholesteric polymer films can be used for example as broadband reflective polarizers, colour filters, security markings, or for the preparation of liquid crystal pigments.

Broadband cholesteric reflective polarizers are described for example in EP 0 606 940, WO 97/35219 or EP 0 982 605. Colour filters are described for example in EP 0 720 041 or EP 0 685 749 and R. Maurer et al., SID 1990 Digest, 110-113. Liquid crystal pigments are described for example in EP 0 601 483, WO 97/27251 , WO 97/27252, WO 97/30136 or WO 99/11719.

For the preparation of anisotropic polymer gels or oriented polymer films, the liquid crystal mixture should comprise at least one polymerizable compound, preferably a polymerizable mesogenic compound.

Thus, another object of the invention are polymerizable liquid crystal mixtures comprising at least two compounds, at least one of which is a chiral compound of formula I and at least one of which is a polymerizable compound. The polymerizable compound can be said at least one compound of formula I or an additional compound.

Preferably the polymerizable liquid crystal mixture comprises at least one polymerizable mesogenic compound having one polymerizable functional group and at least one polymerizable mesogenic compound having two or more polymerizable functional groups.

Polymerizable mesogenic mono-, di- and multireactive compounds used for the present invention can be prepared by methods which are known per se and which are described, for example, in standard works of organic chemistry such as, for example, Houben-Weyl, Methoden der organischen Chemie, Thieme-Verlag, Stuttgart.

Examples of suitable polymerizable mesogenic compounds that can be used as monomers or comonomers together with the compounds according to the present invention in a polymerizable LC mixture, are disclosed for example in WO 93/22397, EP 0 261 712, DE 195 04 224, WO 95/22586, WO 97/00600 and GB 2 351 734. The compounds disclosed in these documents, however, are to be regarded merely as examples that shall not limit the scope of this invention.

Examples of especially useful chiral and achiral polymerizable mesogenic compounds (reactive mesogens) are shown in the following lists which should, however, be taken only as illustrative and is in no way intended to restrict, but instead to explain the present invention: P-(CH₂)_xO // W COO // W-p R^O

(R1)

P-(CH₂)_χO- '/ - CeOO (R2)

P-(CH₂)_xO- // W COO- A R (R3)

In the above formulae, P is a polymerisable group, preferably an acryl, methacryl, vinyl, vinyloxy, propenyl ether, epoxy, oxetane or styryl group, x and y are identical or different integers from 1 to 12 , A is 1 ,4- phenylene that is optionally mono-, di- or trisubstituted by L¹, or 1 ,4- cyclohexylene, u and v are independently of each other 0 or 1 , Z° is - COO-, -OCO-, -OCOO-, -CH₂CH₂-, -CH=CH-, -C≡C- or a single bond, R° is a polar group or an unpolar group, Ter is a terpenoid radical like e.g. menthyl, Choi is a cholesteryl group, L, L¹ and L² are independently of each other H, F, CI, CN or an optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkylcarbonyloxy, alkoxycarbonyl or alkoxycarbonyloxy group with 1 to 7 C atoms, and r is 0, 1 , 2, 3 or 4. The phenyl rings in the above formulae are optionally substituted by 1 , 2, 3 or 4 groups L.

The term 'polar group' in this connection means a group selected from F, CI, CN, N0₂, OH, OCH₃, OCN, SCN, an optionally fluorinated alkycarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy group with up to 4 C atoms or a mono- oligo- or polyfluorinated alkyl or alkoxy group with 1 to 4 C atoms. The term 'unpolar group' means an optionally halogenated alkyl, alkoxy, alkycarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy group with 1 or more, preferably 1 to 12 C atoms which is not covered by the above definition of 'polar group'.

In addition to the compounds of formula I, the polymerizable LC mixtures according to the present invention may also comprise one or more further chiral dopants like for example the commercially available cholesteryl nonanoate (CN), CB15, R/S-811 , R/S-1011 , R/S-2011 , R/S-3011 , R/S-4011 or R/S-5011 (Merck KGaA,

Darmstadt). Particularly preferred are dopants with high twisting power comprising a chiral sugar group, in particular dianhydrohexitol derivatives like for example derivatives of sorbitol, mannitol or iditol, very preferably sorbitol derivatives as disclosed in WO 98/00428. Further preferred are dopants comprising a hydrobenzoin group as described in GB 2,328,207, chiral binaphthyl derivatives as described in WO 02/94805, chiral binaphthol acetal derivatives as described in WO 02/34739, chiral TADDOL derivatives as described in WO 02/06265, and chiral dopants with at least one fluorinated linkage group and a terminal or central chiral group as described in WO 02/06196 and WO 02/06195.

To prepare anisotropic polymer films, the polymerizable LC mixture is preferably coated onto a substrate, aligned and polymerized in situ, for example by exposure to heat or actinic radiation, to fix the orientation of the LC molecules. Alignment and curing are carried out in the LC phase of the mixture. This technique is well-known in the art and is generally described for example in D.J. Broer, et al., Angew. Makromol. Chem. 183, (1990), 45-66.

Alignment of the LC material can be achieved for example by treatment of the substrate onto which the material is coated, by shearing the material during or after coating, by application of a magnetic or electric field to the coated material, or by the addition of surface-active compounds to the LC material. Reviews of alignment techniques are given for example by I. Sage in "Thermotropic Liquid Crystals", edited by G. W. Gray, John Wiley & Sons, 1987, pages 75- 77, and by T. Uchida and H. Seki in "Liquid Crystals - Applications and Uses Vol. 3", edited by B. Bahadur, World Scientific Publishing, Singapore 1992, pages 1-63. A review of alignment materials and techniques is given by J. Cognard, Mol. Cryst. Liq. Cryst. 78,

Supplement 1 (1981), pages 1-77.

Polymerization takes place by exposure to heat or actinic radiation. Actinic radiation means irradiation with light, like UV light, IR light or visible light, irradiation with X-rays or gamma rays or irradiation with high energy particles, such as ions or electrons. Preferably polymerization is carried out by UV irradiation at a non-absorbing wavelength. As a source for actinic radiation for example a single UV lamp or a set of UV lamps can be used. When using a high lamp power the curing time can be reduced. Another possible source for actinic radiation is a laser, like e.g. a UV laser, an IR laser or a visible laser.

Polymerization is preferably carried out in the presence of an initiator absorbing at the wavelength of the actinic radiation. For example, when polymerizing by means of UV light, a photoinitiator can be used that decomposes under UV irradiation to produce free radicals or ions that start the polymerization reaction. When curing polymerizable materials with acrylate or methacrylate groups, preferably a radical photoinitiator is used, when curing polymerizable materials with vinyl, epoxide and oxetane groups, preferably a cationic photoinitiator is used. It is also possible to use a polymerization initiator that decomposes when heated to produce free radicals or ions that start the polymerization. As a photoinitiator for radical polymerization for example the commercially available Irgacure 651 , Irgacure 184, Darocure 1173 or Darocure 4205 (all from Ciba Geigy AG) can be used, whereas in case of cationic photopolymerization the commercially available UVI 6974 (Union Carbide) can be used. Preferably polymerization is carried out under an atmosphere of inert gas, preferably under a nitrogen atmosphere.

As a substrate for example a glass or quarz sheet as well as a plastic film or sheet can be used. It is also possible to put a second substrate on top of the coated mixture prior to, during and/or after polymerization. The substrates can be removed after polymerization or not. When using two substrates in case of curing by actinic radiation, at least one substrate has to be transmissive for the actinic radiation used for the polymerization. Isotropic or birefringent substrates can be used. In case the substrate is not removed from the polymerized film after polymerization, preferably isotropic substrates are used. Preferably at least one substrate is a plastic substrate such as for example a film of polyester such as polyethyleneterephthalate (PET) or polyethylenenaphthalate (PEN), of polyvinyialcohol (PVA), polycarbonate (PC) or triacetylcellulose (TAG), especially preferably a PET film or a TAG film. As a birefringent substrate for example an uniaxially stretched plastic film can be used. For example PET films are commercially available from ICI Corp. under the trade name Melinex.

The polymerizable mixture is preferably coated as a thin layer on a substrate or between substrate, and aligned in its chiral mesophase, e.g. the cholesteric or chiral smectic phase, to give a planar orientation, i.e. wherein the axis of the molecular helix extends transversely to the layer. Planar orientation can be achieved for example by shearing the mixture, e.g. by means of a doctor blade. It is also possible to apply an alignment layer, for example a layer of rubbed polyimide or sputtered SiO_x , on top of at least one of the substrates. Alternatively, a second substrate is put on top of the coated material. In this case, the shearing caused by putting together the two substrates is sufficient to give good alignment. It is also possible to apply an electric or magnetic field to the coated mixture.

In some cases it is of advantage to apply a second substrate not only to aid alignment of the polymerizable mixture but also to exclude oxygen that may inhibit the polymerization. Alternatively curing can be carried out under an atmosphere of inert gas. However, curing in air is also possible using suitable photoinitiators and high lamp power. When using a cationic photoinitiator oxygen exclusion most often is not needed, but water should be excluded.

An inventive polymerizable liquid crystal mixture for the preparation of anisotropic polymer films comprises preferably 0.1 to 35 %, in particular 0.5 to 15 % and very particularly preferably 0.5 to 5 % by weight of one or more polymerizable chiral compounds of formula I. Polymerizable liquid crystal mixtures are preferred that comprise 1 to 3 chiral compounds of formula I.

The polymerizable material can additionally comprise one or more other suitable components such as, for example, catalysts, sensitizers, stabilizers, inhibitors, chain-transfer agents, co-reacting monomers, surface-active compounds, lubricating agents, wetting agents, dispersing agents, hydrophobing agents, adhesive agents, flow improvers, defoaming agents, deaerators, diluents, reactive diluents, auxiliaries, colourants, dyes or pigments.

Preferably the inventive polymerizable mixture comprises a stabilizer that is used to prevent undesired spontaneous polymerization for example during storage of the composition. As stabilizers in principal all compounds can be used that are known to the skilled in the art for this purpose. These compounds are commercially available in a broad variety. Typical examples for stabilizers are 4-ethoxyphenol or butylated hydroxytoluene (BHT).

It is also possible, in order to increase crosslinking of the polymers, to add a non mesogenic compound with two or more polymerizable functional groups, preferably in an amount of up to 20% by weight, to the polymerizable mixture alternatively or additionally to multifunctional mesogenic polymerizable compounds. Typical examples for difunctional non mesogenic monomers are alkyldiacrylates or alkyldimethacrylates with alkyl groups of 1 to 20 C atoms. Typical examples for non mesogenic monomers with more than two polymerizable groups are trimethylpropanetrimethacrylate or pentaerythritoltetraacrylate.

Polymerization of inventive compositions comprising compounds with only one polymerizable functional group leads to linear polymers, whereas in the presence of compounds with more than one polymerizable functional group crosslinked polymers are obtained.

For the preparation of anisotropic polymer gels, the liquid crystal mixtures can be polymerized in situ as described above, however, in this case alignment of the polymerizable mixture is not always necessary.

The photoisomerizable compounds of formula I are particularly suitable for the preparation of cholesteric films or layers with planar alignment. Such layers or films show selective reflection of visible light that is circularly polarized, caused by interaction of incident light with the helically twisted structure of the cholesteric material. The central wavelength of reflection λ depends on the pitch p and average refractive index n of the cholesteric material according to equation (2) λ = n ^■ p (2)

The bandwidth Δλ of the reflected wavelength band depends on the pitch and the birefringence Δn of the cholesteric material according to equation (3)

Δλ = Δn - p (3)

The reflection wavelength λ of a cholesteric layer with planar orientation depends on the viewing angle in first approximation according to equation (4) λ(α) = λ(0) cos[arcsin((sinα)/n)] (4)

wherein λ(0) is the reflection wavelength at normal observation and λ( ) is the reflection wavelength at viewing angle α (see Eberle et al., Liq. Cryst. 1989, 5(3), 907-916). Thus, the reflection colour at larger viewing angles is shifted towards shorter wavelengths. This phenomenon is also known to the expert as "colour flop", and is exploited in decorative or security applications.

Due to the presence of a photoisomerizable group in the compounds of formula I, the chirality of the inventive compounds, and of liquid crystal materials comprising them, can be changed by photoirradiation. Photoirradiation can be achieved for example with irradiation by UV light or other high energy sources such as lasers. By using photomasking techniques it is possible to change the chirality only in selected regions of the material, which is then fixed e.g. by polymerization.

Thus, the invention further relates to a chiral anisotropic polymer film obtained by polymerizing a compound of formula I or a polymerizable LC medium as described above and below in its oriented state, which has a pattern of at least two regions with different orientation and/or different optical properties. Preferably, the film exhibits a pattern of at least two regions that differ in at least one property selected from helical pitch, reflection wavelength, handedeness of reflected light, and viewing angle dependence of reflected light (colour flop).

For example, the inventive compounds and mixtures can be used to prepare reflective cholesteric films wherein the optical properties, like the reflection wavelength λ and the reflection bandwidth Δλ, can be varied easily. For example, cholesteric reflective films with a horizontal pattern comprising regions of different reflection wavelength λ, or broadband reflective films with a broad bandwidth Δλ of the reflected wavelength band can be prepared. The preparation of such films is described for example in WO 00/34808 and in P. van de Witte et al., J. Mater. Chem. 9 (1999), 2087-2094, the entire disclosure of which is incorporated into this application by way of reference. The preparation of patterned cholesteric films and of broadband reflective films is also exemplarily described below.

A cholesteric film with variable wavelength can for example be prepared as follows:

A thin layer of a cholesteric polymerizable mixture comprising an inventive chiral photoisomerizable compound of formula I is coated onto a substrate and aligned into planar orientation as described above. The coated and aligned layer shows selective reflection of a wavelength λ that is depending on the helical pitch p according to above equation (2). If the coated layer is exposed to photoradiation of a suitable wavelength, the photoisomerizable group(s) in the compound of formula I is isomerized. This causes a shift of the HTP of the photoisomerizable compound and, according to above equation (1), a change in the helical pitch p and thus in the reflection wavelength λ of the layer. The degree of isomerization and the shift of λ can be controlled by varying e.g. the irradiation time and/or the radiation dose. The structure of the layer is then fixed by in-situ polymerization.

If only a part of the layer is exposed to photoradiation, the helical pitch and reflection wavelength will change only in the exposed parts, but remain unchanged in the non-exposed parts. This can be achieved for example by photoradiation through a photomask that is applied on top of the coated layer. Afterwards, the cholesteric structure is fixed in those parts where the pitch has changed by polymerization, for example by in-situ photopolymerization through the photomask. If the above steps of photoisomerization and (photo)polymerization are then repeated for the previously non- exposed parts of the coated layer under different conditions, e.g. different irradiation time and/or radiation dose, a patterned cholesteric film is obtained with different regions showing different reflection wavelengths. Such patterned films are suitable for example for use as colour filter in optical or electrooptical devices like liquid crystal displays or projectors. They can also be used for security markings, e.g. to identify or prevent falsification of credit cards, passports, bank notes or other documents of value.

A broadband reflective cholesteric film can for example be prepared as follows:

A layer of a cholesteric mixture with planar orientation comprising a photoisomerizable compound of formula I additionally comprises a dye having an absorption maximum at the wavelength where the isomerizable compound shows photoisomerization. For example, the mixture may comprise an isomerizable compound showing isomerization at a wavelength in the UV range together with a UV dye. If the mixture is exposed to UV radiation as described above, the dye will create a gradient in UV light intensity throughout the thickness of the layer. As a consequence, the isomerization is faster at the top of the layer than at the bottom and a pitch gradient is created, leading to a broadening of the reflected wavelength band. The pitch gradient and reflection bandwidth can be controlled for example by varying the film thickness, irradiation time, radiation dose and/or the concentration of the UV dye and the photoisomerizable compound. If the cholesteric mixture comprises one or more polymerizable components, the structure of the film can be fixed by in-situ polymerization.

The LC films or according to the present invention are useful as optical elements like polarizers, compensators, circular polarizers or colour filters in liquid crystal displays or projection systems, as alignment layers, decorative image, for the preparation of liquid crystal or effect pigments, and especially as reflective film with spatially varying reflection colours, e.g. as multicolour image for decorative, information storage or security uses, such as non- forgeable documents like identity or credit cards, banknotes etc..

Compounds of formula I that are photoorientable, i.e. which can be oriented into a preferred direction by irradiation with linearly polarized light and can thereby induce an alignment of liquid crystals, can be used, optionally in a mixture with other mono- or direactive mesogenic or liquid crystalline compounds, for the preparation of polymerized or crosslinked anisotropic films with unidirectional or locally varying orientation or orientating properties, as described for example in US 5,602,661 or EP 0 689 084 A2. Such films can be used as alignment layers for polymerizable or non-reactive LC mixtures that are provided on said film. Also, mixtures comprising photoorientable compounds of formula I can be used for the preparation of single polymer films with uniform or locally varying orientation for direct use as optical elements, without the need of a separate alignment layer.

The LC films according to the present invention can be used in displays of the transmissive or reflective type. They can be used in conventional LCDs, in particular those of the DAP (deformation of aligned phases) or VA (vertically aligned) mode, like e.g. ECB (electrically controlled birefringence), CSH (colour super homeotropic), VAN or VAC (vertically aligned nematic or cholesteric) displays, MVA (multi-domain vertically aligned) or PVA (patterned vertically aligned) displays, in displays of the bend mode or hybrid type displays, like e.g. OCB (optically compensated bend cell or optically compensated birefringence), R-OCB (reflective OCB), HAN (hybrid aligned nematic) or pi-cell (π-cell) displays, furthermore in displays of the TN (twisted nematic), HTN (highly twisted nematic) or STN (super twisted nematic) mode, in AMD-TN (active matrix driven TN) displays, or in displays of the IPS (in plane switching) mode which are also known as 'super TFT' displays. Especially preferred are VA, MVA, PVA, OCB and pi-cell displays.

The examples below serve to illustrate the invention without limiting it. In the foregoing and the following, all temperatures are given in degrees Celsius, and all percentages are by weight, unless stated otherwise.

Example 1 Compound (1a) was prepared according to reaction scheme 1 above.

The following compounds were prepared analoguously

Claims

Patent Claims

1. Compounds of formula I

P-Sp-(A¹-Z¹)_m1-A³-CH=CH-CO-G-CO-CH=CH-A⁴-(Z²-A²)_m2-R

wherein

P is a polymerizable or reactive group,

Sp is a spacer group or a single bond,

G is selected from the following groups

A¹ and A²are independently of each other an aromatic or alicyclic a group, which optionally contain one or more hetero atoms selected from N, O and S, and are optionally mono- or polysubstituted by L,

A³ and A⁴are independently of each other 1 ,4-phenylene in which one or more CH groups are optionally replaced by N, and which is optionally mono- or polysubstituted by L, L is F, CI, Br, I, CN, N0₂, OH, NCS, SF₅ or alkyl which is straight chain or branched, has 1 to 8 C-atoms, is unsubstituted, mono- or polysubstituted by F, CI, 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 -0-, -S-, -NH-, - NR⁰-, -SiR°R⁰⁰-, -CO-, -COO-, -OCO-, -OCO-0-, -S- GO-, -CO-S-, -CY¹=CY²- or -C≡C- in such a manner that O and/or S atoms are not linked directly to one another,

Z¹ and Z² are independently of each other -0-, -S-, -CO-, -COO-, -OCO-, -S-CO-, -CO-S-, -0-COO-, -CO-NR⁰-, -NR°- CO-, -NR°-CO-NR°, -NR°-CO-0-, -O-CO-NR⁰-, -OCH₂-,

-CH₂0-, -SCH₂-, -CH₂S-, -CF₂0-, -OCF₂-, -CF₂S-, - SCF₂-_ -CH₂CH₂-, -CF₂CH₂-, -CH₂CF₂-, -CF₂CF₂-, - CH=N-, -N=CH-, -N=N-, -CH=CR⁰-, -CY =CY²-, -C≡C-, -CH=CH-COO-, -OCO-CH=CH- or a single bond,

Y¹ and Y²are independently of each other H, F, CI or CN,

R is H, F, CI, Br, I, CN, N0₂, NCS, SF₅ or alkyl which is straight chain or branched, has 1 to 20 C-atoms, is unsubstituted, mono- or poly-substituted by F, CI, 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 -0-, -S-, -NH-, - NR⁰-, -SiR°R⁰⁰-, -CO-, -COO-, -OCO-, -OCO-0-, -S- CO-, -CO-S-, -CY¹=CY²- or -C≡C- in such a manner that O and/or S atoms are not linked directly to one another, or has one of the meanings of P-Sp,

R° and R⁰⁰ are independently of each other H or alkyl with 1 to 12 C-atoms, and m1 and m2 are independently of each other 0, 1 or 2,

2. Compounds according to claim 1 , characterized in that -(A¹- Z¹)mrA³- and/or -A⁴-(Z²-A²)_m2- are selected from the following formulae and their mirror images

wherein L has the meanings of formula I and r is 1 , 2, 3 or 4.

3. Compounds according to claim 1 or 2, characterized in that ml = m2 = 0.

4. Compounds according to at least one of claims 1 to 3, characterized in that R is P-Sp.

5. Compounds according to at least one of claims 1 to 4, characterized in that L is selected from F, CI, Br, I, CN, N0₂ or straight chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl or alkyicarbonlyoxy with 1 to 8 C atoms, wherein one or more H atoms are optionally substituted by F or CI.

6. Compounds according to at least one of claims 1 to 5, characterized in that they are selected from the following formulae

^ wherein P and Sp are as defined in formula I and L^1"4 independently of each other denote H or have one of the meanings of L in formula I, with at least one of L^1"4 being different from H.

^⁵

7. Liquid crystal medium, characterized in that it comprises at least one compound according to at least one of claims 1 to 6.

8. Liquid crystal medium according to claim 11 , characterized in that comprises at least one compound according to at least one 0 of claims 1 to 6 and at least one polymerizable mesogenic compound.

9. Polymer obtained by polymerizing a compound according to at least one of claims 1 to 6 or a iquid crystal medium according to claim 7 or 8.

10. Anisotropic polymer film obtained by polymerizing a compound according to at least one of claims 1 to 6 or a iquid crystal medium according to claim 7 or 8 in its oriented state. 0

11. Anisotropic polymer film according to claim 10, characterized in that it has a pattern of at least two regions with different orientation and/or different optical properties.

⁵ 12. Use of a compound, medium, polymer or polymer film according to at least one of claims 1 to 1 tin electrooptical displays, liquid crystal displays, optical films, polarizers, compensators, beam splitters, reflective films, alignment layers, colour filters, holographic elements, hot stamping foils, coloured images, decorative or security markings, liquid crystal pigments, adhesives, synthetic resins with anisotropic mechanical properties, cosmetics, diagnostics, nonlinear optics, optical information storage, as chiral dopants, in electronic devices like for example field effect transistors (FET) as components of integrated circuitry, as thin film transistors in flat panel display applications or for Radio Frequency Identification (RFID) tags, or in semiconducting components for organic light emitting diode (OLED) applications, electroluminescent displays or backlights of liquid crystal displays, for photovoltaic or sensor devices, as electrode materials in batteries, as photoconductors, for electrophotographic applications or electrophotographic recording or in lasing materials or devices.

13. Colour filter comprising a compound, medium, polymer or polymer film according to at least one of claims 1 to 11.

14. Liquid crystal device, characterized in that it comprises a compound, liquid crystal medium, polymer or polymer film according to at least one of claims 1 to 11 or a colour filter accor a colour filter according to claim 13.

15. Authentification, verification or security marking or coloured image comprising at least one compound, medium, polymer or polymer film according to at least one of claims 1 to 11.

16. Object or document of value comprising an authentification, verification or security marking or image according to claim 15.