Light modulation element

Abstract

The invention provides a light modulation element comprising a flexoelectric polarisable liquid-crystalline medium, characterized in that the switching from a boundary state A to a boundary state B comprises a combination of a distinct flexoelectric switching regime and a distinct dielectric switching regime upon application of an electric field. Furthermore, the present invention relates to the use of such a light modulation element in an electro-optical device, i.e. an LCD display device, and electrooptical devices comprising the light modulation element according to the present invention. Moreover, the invention relates to a method of production of the light modulation element according to the present invention.

Claims

1. Light modulation element comprising at least two substrates and a flexoelectric polarisable liquid-crystalline medium sandwiched between at least two substrates, wherein the liquid-crystalline medium is homeotropically aligned to both substrate surfaces it is sandwiched between in a boundary state A when no electric field is applied, and wherein the element effects switching from the boundary state A to a boundary state B through a combination of a flexoelectric switching regime and a dielectric switching regime upon application of an electric field, and wherein the liquid crystal medium comprises at least one bent core compound selected from the compounds of formula I,
R.sup.1-M.sup.1-Y.sup.1BY.sup.2-M.sup.2-R.sup.2I wherein Y.sup.1 and Y.sup.2 are in each case independently O, S, CO, COO, OCO, OCOO, CONR0-, NR.sub.0CO, OCH.sub.2, CH.sub.2O, SCH.sub.2, CH.sub.2S, CHCHCOO, OOCCHCH or a single bond, R.sup.0 is H or alkyl with 1 to 4 C atoms, M.sup.1 and M.sup.2 are independently of each other a mesogenic group, B is selected from the following groups: ##STR00180## where L.sup.1, L.sup.2 and L.sup.3 are selected from F, CN, NO.sub.2 , CH.sub.3 , C.sub.2H.sub.5 , OCH.sub.3 , OC.sub.2H.sub.5, COCH.sub.3 , COC.sub.2H.sub.5, COOCH.sub.3 , COOC.sub.2H.sub.5 , CF.sub.3 , OCF.sub.3 , OCHF.sub.2, and OC.sub.2F.sub.5 , and R.sup.1 and R.sup.2 denote, each and independently from another, H, F, Cl, CN, OCN, SCN, SF.sub.5, NO.sub.2 or a straight-chain or branched alkyl radical with up to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH.sub.2 groups to be replaced, in each case independently from one another, by O, S, NH, N(CH.sub.3), CO, COO, OCO, OCOO, SCO, COS, CHCH or CC in such a manner that oxygen atoms are not linked directly to one another.

2. The light modulation element according to claim 1, wherein the liquid-crystalline medium comprises a bent core liquid-crystalline compound having an absolute value of the bend flexoelectric coefficient |e.sub.3| in the range from 1 pCm.sup.1 to 60 pCm.sup.1.

3. The light modulation element according to claim 1, wherein the amount of compounds of formula I in the liquid-crystalline medium as a whole is in the range from 3 to 70%.

4. The light modulation element according to claim 1, wherein the liquid-crystalline medium comprises one or more compounds of formulae II and III, ##STR00181## in which R.sup.21 denotes alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms, ##STR00182## on each appearance, independently of one another, denote ##STR00183## L.sup.21 and L.sup.22 denote H or F, X.sup.21 denotes halogen, halogenated alkyl or alkoxy having 1 to 3 C atoms or halogenated alkenyl or alkenyloxy having 2 or 3 C atoms, m denotes 0, 1, 2 or 3, R.sup.31 denotes alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms, ##STR00184## on each appearance, independently of one another, are ##STR00185## L.sup.31 and L.sup.32 independently of one another, denote H or F, X.sup.31 denotes halogen, halogenated alkyl or alkoxy having 1 to 3 C atoms or halogenated alkenyl or alkenyloxy having 2 or 3 C atoms, Z.sup.31 denotes CH.sub.2CH.sub.2, CF.sub.2CF.sub.2, COO, trans-CHCH, trans-CFCF, CH.sub.2O or a single bond, and n denotes 0, 1, 2 or 3.

5. The light modulation element according to claim 1, wherein the liquid-crystalline medium comprises one or more compounds of formula IV ##STR00186## in which R.sup.41 and R.sup.42 independently of one another, denote alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms, L.sup.21 and L.sup.22 denote H or F, ##STR00187## independently of one another and, if ##STR00188## occurs twice, also these independently of one another, denote ##STR00189## Z.sup.41 and Z.sup.42 independently of one another and, if Z.sup.41 occurs twice, also these independently of one another, denote CH.sub.2CH.sub.2, COO, trans-CHCH, trans-CFCF, CH.sub.2O, CF.sub.2O, CC or a single bond, and p denotes 0, 1 or 2.

6. The light modulation element according to claim 1, wherein the liquid-crystalline medium comprises one or more compounds of the formula V, ##STR00190## in which R.sup.51 and R.sup.52 independently of one another, denote alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms, L.sup.21 and L.sup.22 denote H or F, ##STR00191## on each appearance, independently of one another, denotes ##STR00192## Z.sup.51 and Z.sup.52 independently of one another and, if Z.sup.51 occurs twice, also these independently of one another, denote CH.sub.2CH.sub.2, COO, trans-CHCH, trans-CFCF, CH.sub.2O, CF.sub.2O or a single bond, and r denotes 0, 1 or 2.

7. The light modulation element according to claim 4, wherein the amount of compounds of the formulae II and/or III in the liquid-crystalline medium as a whole is in the range from 2 to 90%.

8. The light modulation element according to claim 5, wherein the amount of compounds of the formulae IV in the liquid-crystalline medium as a whole is in the range from 2 to 70%.

9. The light modulation element according to claim 1, wherein the liquid-crystalline medium exhibits a dielectric positive anisotropy of 3.

10. The light modulation element according to claim 1, wherein the liquid-crystalline medium exhibits a birefringence in the range from 0.10 or more to 0.35 or more.

11. The light modulation element according to claim 1, wherein the element exhibits light modulation induced by an applied in-plane electric field.

12. The light modulation element according to claim 1, wherein the element exhibits flexoelectric switching at an applied electric field strength lower than 0.5 V/m1.

13. The light modulation element according to claim 1, wherein the boundary state B has a transmission T.sub.B when an electrical field is applied, which is termed in the on state, and the element exhibits an induced retardation in the on-state in the range from 1 nm to 300 nm.

14. Method for production of a light modulation element according to claim 1, comprising at least a step of filling a cell formed by the at least two substrates with the liquid-crystalline medium.

15. Electro-optical device comprising the light modulation element according to claim 1.

16. The light modulation element according to claim 5, wherein the amount of compounds of the formula IV in the liquid-crystalline medium as a whole is in the range from 2 to 70%.

17. A method comprising operating an electro-optical device wherein the operation of the device comprises light modulation as a result of application of an electric field and wherein the device comprises a light modulation element according to claim 1.

18. The light modulation element according to claim 1, wherein the boundary state A has a transmission T.sub.A when no electrical field is applied, which is termed the off state, and the boundary state B has a transmission T.sub.B when an electrical field is applied, which is termed the on state, and whereby: T.sub.A <T.sub.B .

19. The light modulation element according to claim 1, wherein L.sup.1, L.sup.2 and L.sup.3 are selected from F, CN, CH.sub.3, C.sub.2H.sub.5, OCH.sub.3, COCH.sub.3, CF.sub.3 and OCF.sub.3.

Description

DETAILED DESCRIPTION

(1) Suitable liquid crystal media in accordance with the present invention are a flexoelectric polarisable upon application of an in-plane electric field.

(2) A suitable liquid-crystalline medium in accordance with the present invention comprises 2 or more, preferably at least 3, particularly preferably at least 4 and very particularly preferably at least 5, different liquid-crystalline compounds. If only 2 liquid-crystalline compounds are employed, their typical concentration ranges from about 70% to 99% by weight of the total mixture.

(3) Preferably, the liquid-crystalline media used in the light modulation element according to the present invention exhibits an absolute value of the bend flexoelectric coefficient |e.sub.3|, which is in the range from approximately 1 pCm.sup.1 to approximately 60 pCm.sup.1, more preferably in the range from approximately 2 pCm.sup.1 to approximately 30 pCm.sup.1, and most preferably in the range from approximately 3 pCm.sup.1 to approximately 20 pCm.sup.1.

(4) In a preferred embodiment, the light modulation element according to the present invention comprises a liquid-crystalline medium, which comprises at least one liquid-crystalline compound having a dipole associated with a bend in the average molecular structure and which show suitable high values for the bend flexoelectric coefficient e3.

(5) Suitable bend flexoelectric coefficients |e3| are preferably in the range from approximately 1 pCm.sup.1 to approximately 100 pCm.sup.1, more preferably in the range from approximately 5 pCm.sup.1 to approximately 40 pCm.sup.1, most preferably in the range from approximately 13 pCm.sup.1 to approximately 18 pCm.sup.1.

(6) Molecules, which have a dipole associated with a bend in the average molecular structure, and which show suitable high values for e3 are preferably selected from the so-called bent-core liquid-crystalline compounds.

(7) Suitable bent-core liquid-crystalline compounds are preferably, selected from the group of compounds of formula I,
R.sup.1-M.sup.1-Y.sup.1BY.sup.2-M.sup.2-R.sup.2I
wherein Y.sup.1 and Y.sup.2 are in each case independently O, S, CO, COO, OCO, OCOO, CONR.sup.0, NR.sup.0CO, OCH.sub.2, CH.sub.2O, SCH.sub.2, CH.sub.2S, CHCHCOO, OOCCHCH or a single bond, R.sup.0 is H or alkyl with 1 to 4 C atoms, M.sup.1 and M.sup.2 are independently of each other a mesogenic group, B is a bivalent ring group that imparts a bent structure to the compound, and R.sup.1 and R.sup.2 denote, each and independently from another, H, F, Cl, CN, OCN, SCN, SF.sub.5, NO2 or a straight-chain or branched alkyl radical with up to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH.sub.2 groups to be replaced, in each case independently from one another, by O, S, NH, N(CH.sub.3), CO, COO, OCO, OCOO, SCO, COS, CHCH or CC in such a manner that oxygen atoms are not linked directly to one another.

(8) The bivalent ring group B in formula I is selected to impart to the inventive compound a bent or banana-shaped structure with a molecular bending angle as described above. The opening angle imparted to compounds of formula I by the bivalent ring group B is preferably from approximately 90 to approximately 165, in particular from approximately 105 to approximately 150, very preferably from approximately 115 to approximately 135, most preferably from approximately 120 to approximately 130.

(9) B is preferably a mono- or bicyclic aromatic group that may also contain up to three hetero atoms, and is for example selected from the following groups

(10) ##STR00002##
wherein U is CR or N, is CR.sub.2, NR, O or S, R is H or alkyl with 1 to 7 C atoms,
and the monocyclic five-membered groups can be substituted with 1, 2 or 3, the monocyclic six-membered groups with 1, 2, 3 or 4 and the bicyclic groups with 1, 2, 3, 4, 5 or 6 groups L, with L being in each case independently F, Cl, CN, SCN, NO.sub.2, SF.sub.5, alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl having 1 to 7 C atoms wherein one or more H atoms may be substituted by F or Cl.

(11) Preferably B is selected from the following groups

(12) ##STR00003##
wherein R and L have one of the meanings given above and r is 0, 1, 2 or 3. Preferably at least one of R denotes H.

(13) Very preferably B is 1,3-phenylene that is optionally substituted with L in the 4-, 5- and/or 6-position, in particular

(14) ##STR00004##
with L.sup.1, L.sup.2 and L.sup.3 preferably selected from F, Cl, CN, OH, NO.sub.2, CH.sub.3, C.sub.2H.sub.5, OCH.sub.3, OC.sub.2H.sub.5, COCH.sub.3, COC.sub.2H.sub.5, COOCH.sub.3, COOC.sub.2H.sub.5, CF.sub.3, OCF.sub.3, OCHF.sub.2, OC.sub.2F.sub.5, in particular F, Cl, CN, CH.sub.3, C.sub.2H.sub.5, OCH.sub.3, COCH.sub.3, CF.sub.3 and OCF.sub.3, most preferably F, Cl, CN, CH.sub.3, OCH.sub.3 and OCF.sub.3.

(15) M.sup.1 in formula I is preferably selected of formula I*1
-A.sup.1-(Z-A.sup.2).sub.m1-I*1
wherein Z is in each case independently O, S, CO, COO, OCO, OCOO, CONR.sup.0, NR.sup.0CO, OCH.sub.2, CH.sub.2O, SCH.sub.2, CH.sub.2S, CH.sub.2CH.sub.2, CHCH, CC, CHCHCOO, OCOCHCH or a single bond, A.sup.1 and A.sup.2 are each independently 1,4-phenylene in which, in addition, one or more CH groups may be replaced by N, 1,4-cyclohexylene in which, in addition, one or two non-adjacent CH.sub.2 groups may be replaced by O and/or S, 1,4-cyclohexenylene, 1,4-bicyclo(2,2,2)octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, or 1,2,3,4-tetrahydro-naphthalene-2,6-diyl, it being possible for all these groups to be unsubstituted, mono- or polysubstituted with F, Cl, SCN, CN, NO.sub.2, SF.sub.5 or optionally fluorinated alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl with 1 to 7 C atoms, R.sup.0 has the meaning of formula I, and m1 is 0, 1, 2 or 3. M.sup.2 in formula I is preferably selected of formula I*2
-A.sup.1-(Z-A.sup.2).sub.m2-I*2
wherein A.sup.1, Z and A.sup.2 have one of the meanings of formula I*1 and m2 is 0, 1, 2 or 3.

(16) Preferred compounds of formula I are those wherein m1 and m2 are independently of each other 1, 2 or 3. Further preferred are compounds wherein the mesogenic groups M.sup.1 and M.sup.2 comprise two or three five- or six-membered rings. Especially preferred are compounds wherein one of m1 and m2 is 2 or 3 and the other is 1, 2 or 3, very preferably both m1 and m2 are 2 or 3, in particular 2. Further preferred are compounds wherein m1+m2 is 3, 4, 5 or 6.

(17) Another preferred embodiment relates to compounds wherein at least one radical Z in formula I*1 and/or I*2 denotes CC. These compounds are especially suitable for uses where highly birefringent materials are needed.

(18) A smaller group of preferred mesogenic groups M.sup.1 and M.sup.2 is listed below. For reasons of simplicity, Phe in these groups is 1,4-phenylene that may also be substituted by 1 to 4 groups L, with L being F, Cl, CN, SCN, NO.sub.2, SF.sub.5 or an alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl group having 1 to 7 C atoms wherein one or more H atoms may be substituted by F or Cl, and Cyc is 1,4-cyclohexylene. Z has one of the meanings of formula I*1. The list comprises the following subformulae as well as their mirror images
-Phe-I*-1
-Cyc-I*-2
-Phe-Z-Phe-I*-3
-Phe-Z-Cyc-I*-4
-Cyc-Z-Cyc-I*-5
-Phe-Z-Phe-Z-Phe-I*-6
-Phe-Z-Phe-Z-Cyc-I*-7
-Phe-Z-Cyc-Z-Phe-I*-8
-Cyc-Z-Phe-Z-Cyc-I*-9
-Phe-Z-Cyc-Z-Cyc-I*-10
-Cyc-Z-Cyc-Z-Cyc-I*-11

(19) Particularly preferred are the subformulae I*-3, I*-4, I*-5, I*-7 and I*-10.

(20) Z is preferably COO, OCO, CH.sub.2CH.sub.2, CC or a single bond.

(21) Very preferably M.sup.1 and M.sup.2 are selected from the following formulae and their mirror images

(22) ##STR00005## ##STR00006##
wherein L has the meaning given above and r is 0, 1 or 2.

(23) ##STR00007##
in these formulae is preferably

(24) ##STR00008##
with L having one of the above meanings.

(25) Very preferred are subformulae I*d, I*g, I*h, I*i, I*k and I*o, in particular I*d and I*k.

(26) L is preferably F, Cl, CN, OH, NO.sub.2, CH.sub.3, C.sub.2H.sub.5, OCH.sub.3, OC.sub.2H.sub.5, COCH.sub.3, COC.sub.2H.sub.5, COOCH.sub.3, COOC.sub.2H.sub.5, CF.sub.3, OCF.sub.3, OCHF.sub.2, OC.sub.2F.sub.5, in particular F, Cl, CN, CH.sub.3, C.sub.2H.sub.5, OCH.sub.3, COCH.sub.3, CF.sub.3 and OCF.sub.3, most preferably F, Cl, CH.sub.3, OCH.sub.3 and OCF.sub.3.

(27) If R.sup.1 or R.sup.2 in formula I is an alkyl or alkoxy radical, i.e. where the terminal CH.sub.2 group is replaced by O, 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, 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.

(28) Especially preferably, R.sup.1 or R.sup.2 is straight chain alkyl or alkoxy with 1 to 8 C atoms.

(29) Oxaalkyl, i.e. where one CH.sub.2 group is replaced by O, 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-oxadecyl, for example.

(30) Halogen is F, Cl, Br, I, preferably F or Cl.

(31) R.sup.1 or R.sup.2 in formula I can be a polar or a non-polar group. In case of a polar group, R is selected from CN, NO.sub.2, halogen, OCH.sub.3, OCN, SCN, COR.sup.5, COOR.sup.5 or a mono-oligo- or polyfluorinated alkyl or alkoxy group with 1 to 4 C atoms. R.sup.5 is optionally fluorinated alkyl with 1 to 4, preferably 1 to 3 C atoms. Especially preferably polar groups R are selected of F, Cl, CN, NO.sub.2, OCH.sub.3, COCH.sub.3, COC.sub.2H.sub.5, COOCH.sub.3, COOC.sub.2H.sub.5, CF.sub.3, C.sub.2F.sub.5, OCF.sub.3, OCHF.sub.2, and OC.sub.2F.sub.5, in particular of F, Cl, CN, OCH.sub.3 and OCF.sub.3.

(32) In case of a non-polar group, R.sup.1 or R.sup.2 is preferably alkyl with up to 15 C atoms or alkoxy with 2 to 15 C atoms.

(33) R.sup.1 or R.sup.2 in formula I can be an achiral or a chiral group.

(34) Preferred chiral groups R.sup.1 or R.sup.2 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.

(35) Particularly preferred chiral groups R.sup.1 or R.sup.2 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-methylvaleroyloxy, 4-methylhexanoyloxy, 2-chlorpropionyloxy, 2-chloro-3-methylbutyryloxy, 2-chloro-4-methylvaleryloxy, 2-chloro-3-methylvaleryloxy, 2-methyl-3-oxapentyl, 2-methyl-3-oxahexyl, 1-methoxypropyl-2-oxy, 1-ethoxypropyl-2-oxy, 1-propoxypropyl-2-oxy, 1-butoxypropyl-2-oxy, 2-fluorooctyloxy, 2-fluorodecyloxy, 1,1,1-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-octyl and 1,1,1-trifluoro-2-octyloxy, for example.

(36) In addition, compounds of formula I containing an achiral branched group R.sup.1 or R.sup.2 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.

(37) Preferred compounds of formula I are the following

(38) ##STR00009## ##STR00010##
wherein L.sup.1 and L.sup.2 has each and independently from another one of the meanings of L, R.sup.1 and R.sup.2 have each and independently and in each occurrence one of the meanings as given above in formula I.

(39) Especially preferred are compounds of the above formulae, wherein L is CN, Cl, F, CF.sub.3 or OCF.sub.3, and R.sup.1 and R.sup.2 denote a straight chain or branched alkyl or alkoxy with 1 to 15 C atoms.

(40) 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. Some specific methods of preparation can be taken from the examples.

(41) In a preferred embodiment, the liquid-crystalline medium comprises one or more dielectrically positive compounds, preferably selected from the group of compounds of formulae II and III,

(42) ##STR00011##
in which R.sup.21 denotes alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms and preferably alkyl or alkenyl,

(43) ##STR00012## on each appearance, independently of one another, denote

(44) ##STR00013## L.sup.21 and L.sup.22 denote H or F, preferably L.sup.21 denotes F, X.sup.21 denotes halogen, halogenated alkyl or alkoxy having 1 to 3 C atoms or halogenated alkenyl or alkenyloxy having 2 or 3 C atoms, preferably F, Cl, OCF.sub.3, OCH.sub.2CF.sub.3, OCHCH.sub.2, OCHCF.sub.2 or CF.sub.3, very preferably F, Cl, OCHCF.sub.2 or OCF.sub.3, m denotes 0, 1, 2 or 3, preferably 1 or 2 and particularly preferably 1, R.sup.31 denotes alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms and preferably alkyl or alkenyl,

(45) ##STR00014##
on each appearance, independently of one another, are

(46) ##STR00015## L.sup.31 and L.sup.32, independently of one another, denote H or F, preferably L.sup.31 denotes F, X.sup.31 denotes halogen, halogenated alkyl or alkoxy having 1 to 3 C atoms or halogenated alkenyl or alkenyloxy having 2 or 3 C atoms, F, Cl, OCF.sub.3, OCH.sub.2CF.sub.3, OCHCF.sub.2, OCHCH.sub.2 or CF.sub.3, very preferably F, Cl, OCHCF.sub.2 or OCF.sub.3, Z.sup.31 denotes CH.sub.2CH.sub.2, CF.sub.2CF.sub.2, COO, trans-CHCH, trans-CFCF, CH.sub.2O or a single bond, preferably CH.sub.2CH.sub.2, COO, trans-CHCH or a single bond and very preferably COO, trans-CHCH or a single bond, and n denotes 0, 1, 2 or 3, preferably 1 or 3 and particularly preferably 1.

(47) Preferred compounds are selected from the group of compounds of subformulae II-1 and II-2:

(48) ##STR00016##
in which the parameters have the respective meanings indicated above under formula II, and L.sup.23 and L.sup.24, independently of one another, denote H or F, preferably L.sup.23 denotes F, and

(49) ##STR00017##
has one of the meanings given for

(50) ##STR00018##
and, in the case of formulae II-1 and II-4, X.sup.21 preferably denotes F or OCF.sub.3, particularly preferably F, and, in the case of formula II-3,

(51) ##STR00019##
independently of one another, preferably denote

(52) ##STR00020##
and/or selected from the group of the compounds of the formulae III-1 and III-2:

(53) ##STR00021##
in which the parameters have the meanings given under formula III.

(54) The media in accordance with the present invention preferably comprise, alternatively or in addition to the compounds of the formulae III-1 and/or III-2, one or more compounds of the formula III-3

(55) ##STR00022##
in which the parameters have the respective meanings indicated above, and the parameters L.sup.33 and L.sup.34, independently of one another and of the other parameters, denote H or F.

(56) The liquid-crystal medium preferably comprises compounds selected from the group of the compounds of the formulae II-1 to II-4 in which L.sup.21 and L.sup.22 and/or L.sup.23 and L.sup.24 both denote F.

(57) In a preferred embodiment, the liquid-crystal medium comprises compounds selected from the group of the compounds of the formulae II-2 and II-3 in which L.sup.21, L.sup.22, L.sup.23 and L.sup.24 all denote F.

(58) The liquid-crystal medium preferably comprises one or more compounds of the formula II-1. The compounds of the formula II-1 are preferably selected from the group of the compounds of the formulae II-1a to II-1e, preferably of formula II-1d:

(59) ##STR00023##
in which the parameters have the respective meanings indicated above, and L.sup.25 and L.sup.26, independently of one another and of the other parameters, denote H or F, and preferably in the formulae II-1a and II-1b, L.sup.21 and L.sup.22 both denote F, in the formulae II-1c and II-1d, L.sup.21 and L.sup.22 both denote F and/or L.sup.23 and L.sup.24 both denote F, and in formula II-1e, L.sup.21, L.sup.22 and L.sup.23 denote F.

(60) The liquid-crystal medium preferably comprises one or more compounds of the formula II-2, which are preferably selected from the group of the compounds of the formulae II-2a to II-2j, preferably of formula II-2j:

(61) ##STR00024## ##STR00025##
in which the parameters have the respective meanings indicated above, and L.sup.25 to L.sup.28, independently of one another, denote H or F, preferably L.sup.27 and L.sup.28 both denote H, particularly preferably L.sup.26 denotes H.

(62) The liquid-crystal medium preferably comprises compounds selected from the group of the compounds of the formulae II-1a to II-1e in which L.sup.21 and L.sup.22 both denote F and/or L.sup.23 and L.sup.24 both denote F.

(63) In a preferred embodiment, the liquid-crystal medium comprises compounds selected from the group of the compounds of the formulae II-1a to II-1i in which L.sup.21, L.sup.22, L.sup.23 and L.sup.24 all denote F.

(64) Especially preferred compounds of the formula II-2 are the compounds of the following formulae:

(65) ##STR00026## ##STR00027##
in which R.sup.21 and X.sup.21 have the meanings indicated above, and X.sup.21 preferably denotes F.

(66) The liquid-crystal medium preferably comprises one or more compounds of the formula III-1. Suitable compounds of the formula III-1 are preferably selected from the group of the compounds of the formulae III-1a to III-1j, preferably from formulae III-1c, III-1f, III-1g and III-1j:

(67) ##STR00028## ##STR00029##
in which the parameters have the meanings given above and preferably in which the parameters have the respective meanings indicated above, and the parameters L.sup.35 and L.sup.36, independently of one another and of the other parameters, denote H or F.

(68) The liquid-crystal medium preferably comprises one or more compounds of the formula III-1c, which are preferably selected from the group of the compounds of the formulae III-1c-1 to III-1c-5, preferably of formulae III-1c-3 and III-1c-4:

(69) ##STR00030##
in which R.sup.31 has the meaning indicated above.

(70) The liquid-crystal medium preferably comprises one or more compounds of the formula III-1f, which are preferably selected from the group of the compounds of the formulae III-1f-1 to III-1f-5, preferably of formulae III-1f-1, III-1 f-2, III-1 f-4 and III-1 f-5, more preferably of formulae III-1f-1, III-1f-4 and III-1f-5, more preferably:

(71) ##STR00031##
in which R.sup.31 has the meaning indicated above.

(72) The liquid-crystal medium preferably comprises one or more compounds of the formula III-1g, which are preferably selected from the group of the compounds of the formulae III-1g-1 to III-1g-5, preferably of formula III-1g-3:

(73) ##STR00032##
in which R.sup.31 has the meaning indicated above.

(74) The liquid-crystal medium preferably comprises one or more compounds of the formula III-1h, which are preferably selected from the group of the compounds of the formulae III-1h-1 to III-1h-3, preferably of the formula III-1h-3:

(75) ##STR00033##
in which the parameters have the meanings given above, and X.sup.31 preferably denotes F.

(76) The liquid-crystal medium preferably comprises one or more compounds of the formula III-1i, which are preferably selected from the group of the compounds of the formulae III-1i-1 and III-1i-2, preferably of the formula III-1i-2:

(77) ##STR00034##
in which the parameters have the meanings given above, and X.sup.31 preferably denotes F.

(78) The liquid-crystal medium preferably comprises one or more compounds of the formula III-1j, which are preferably selected from the group of the compounds of the formulae III-1 j-1 and III-1 j-2, preferably of the formula III-1j-1:

(79) ##STR00035##
in which the parameters have the meanings given above.

(80) The liquid-crystal medium preferably comprises one or more compounds of the formula III-2. The compounds of the formula III-2 are preferably selected from the group of the compounds of the formulae III-2a and III-2b:

(81) ##STR00036##
in which the parameters have the respective meanings indicated above, and the parameters L.sup.33 and L.sup.34, independently of one another and of the other parameters, denote H or F.

(82) The liquid-crystal medium preferably comprises one or more compounds of the formula III-2a, which are preferably selected from the group of the compounds of the formulae III-2a-1 to III-2a-6:

(83) ##STR00037##
in which R.sup.31 has the meaning indicated above.

(84) The liquid-crystal medium preferably comprises one or more compounds of the formula III-2b, which are preferably selected from the group of the compounds of the formulae III-2b-1 to III-2b-4, preferably III-2b-4:

(85) ##STR00038##
in which R.sup.31 has the meaning indicated above.

(86) Alternatively or in addition to the compounds of the formulae III-1 and/or III-2, the media in accordance with the present invention preferably comprise one or more compounds of the formula III-3

(87) ##STR00039##
in which the parameters have the respective meanings indicated above under formula III.

(88) These compounds are preferably selected from the group of the formulae III-3a and III-3b:

(89) ##STR00040##
in which R.sup.31 has the meaning indicated above.

(90) In another preferred embodiment, the liquid-crystalline medium comprises one or more, preferably dielectrically neutral, compounds of the formula IV

(91) ##STR00041##
in which R.sup.41 and R.sup.42, independently of one another, have the meaning indicated above for R.sup.21 under formula II, preferably R.sup.41 denotes alkyl and R.sup.42 denotes alkyl or alkoxy or R.sup.41 denotes alkenyl and R.sup.42 denotes alkyl,

(92) ##STR00042##
denote independently of one another and, if

(93) ##STR00043##
occurs twice, also these independently of one another, denote

(94) ##STR00044##
preferably one or more of

(95) ##STR00045##
denotes or denote

(96) ##STR00046## Z.sup.41 and Z.sup.42, independently of one another and, if Z.sup.41 occurs twice, also these independently of one another, denote CH.sub.2CH.sub.2, COO, trans-CHCH, trans-CFCF, CH.sub.2O, CF.sub.2O, CC or a single bond, preferably one or more thereof denotes/denote a single bond, and p denotes 0, 1 or 2, preferably 0 or 1.

(97) The liquid-crystalline media in accordance with the present invention preferably comprise one or more compounds selected from the group of the compounds of the formulae IV-1 to IV-6:

(98) ##STR00047##
in which R.sup.41 and R.sup.42 have the respective meanings indicated above under formula IV, and, in the formulae IV-1, IV-5 and IV-6, R.sup.41 preferably denotes alkyl or alkenyl, preferably alkenyl, and R.sup.42 preferably denotes alkyl or alkenyl, preferably alkyl, in formula IV-2, R.sup.41 and R.sup.42 preferably denote alkyl, and in formula IV-4, R.sup.41 preferably denotes alkyl or alkenyl, more preferably alkyl, and R.sup.42 preferably denotes alkyl or alkoxy, more preferably alkoxy.

(99) The liquid-crystalline media in accordance with the present invention preferably comprise one or more compounds selected from the group of the compounds of the formulae IV-1, IV-4, IV-5 and IV-6, preferably one or more compounds of the formula IV-1 and one or more compounds selected from the group of the formulae IV-4 and IV-5, more preferably in each case one or more compounds of the formulae IV-1, IV-4 and IV-5 and very preferably in each case one or more compounds of the formulae IV-1, IV-4, IV-5 and IV-6.

(100) In a preferred embodiment, the liquid-crystalline media in accordance with the present invention preferably comprise one or more compounds of the formula IV-1, more preferably selected from the respective sub-formulae thereof of the formulae CC-n-m and/or CC-n-Om and/or CC-n-V and/or CC-nV-m and/or CC-Vn-m, more preferably of the formulae CC-n-m and/or CC-n-V and/or CC-nV-m and very preferably selected from the group of the formulae CC-3-1, CC-3-2, CC-3-3, CC-3-4, CC-3-5, CC-3-01, CC-3-V, CC-4-V, CCSV and CC-3-V1. The definitions of these abbreviations (acronyms) are evident from Tables A to B.

(101) In a preferred embodiment, the liquid-crystalline media in accordance with the present invention preferably comprise one or more compounds of the formula IV-4, more preferably selected from the respective sub-formulae thereof of the formulae CP-V-n and/or CP-nV-m and/or CP-Vn-m, more preferably of the formulae CP-nV-m and/or CP-V2-n and very preferably selected from the group of the formulae CP-2V-1, CP-1V-2 and CP-V2-1. The definitions of these abbreviations (acronyms) are evident from Tables A and B.

(102) In a preferred embodiment, the liquid-crystalline media in accordance with the present invention preferably comprise one or more compounds of the formula IV-5, more preferably selected from the respective sub-formulae thereof of the formulae CCP-V-n and/or CCP-nV-m and/or CCP-Vn-m, more preferably of the formulae CCP-V-n and/or CCP-V2-n and very preferably selected from the group of the formulae CCP-V-1 and CCP-V2-1. The definitions of these abbreviations (acronyms) evident from Tables A and B.

(103) In a likewise preferred embodiment, the liquid-crystal medium preferably comprises one or more compounds of the formula IV-1, more preferably selected from the respective sub-formulae thereof of the formulae CC-n-m, CC-n-Om, CC-n-V, CC-n-Vm, CCVV, CCVVn and/or CC-nV-Vm, more preferably of the formulae CC-n-m and/or CC-n-V and/or CC-n-Vm and very preferably selected from the group of the formulae CC-3-1, CC-3-2, CC-3-3, CC-3-4, CC-3-5, CC-3-01, CC-3-V, CC-4-V, CC-5-V and CC-3-V1 and in particular selected from the group of the formulae CC-3-V, CC-4-V, CC-5-V CC-3-V1, CC-4-V1, CC-5-V1, CC-3-V2 and CCV-V1. The definitions of these abbreviations (acronyms) are evident from Tables A and B.

(104) In a further preferred embodiment of the present invention, which may be the same as the preceding one or another, the liquid-crystal mixtures in accordance with the present invention comprise the compounds of the formula IV selected from the group of the compounds of the formulae IV-1 to IV-6 as shown above and optionally of the formulae IV-7 to IV-14, preferably of formulae IV-7 and/or IV-14:

(105) ##STR00048##
in which
R.sup.41 and R.sup.42, independently of one another, denote alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms, and L.sup.4 denotes H or F.

(106) In a preferred embodiment, the liquid-crystal medium preferably comprises one or more compounds of the formula IV-7, more preferably selected from the respective sub-formulae thereof of the formulae CPP-3-2, CPP-5-2 and CGP-3-2, more preferably of the formulae CPP-3-2 and/or CGP-3-2 and very particularly preferably of the formula CPP-3-2. The definitions of these abbreviations (acronyms) are evident from Tables A and B.

(107) In a preferred embodiment, the liquid-crystal medium preferably comprises one or more compounds of the formula IV-14, more preferably selected from the respective sub-formulae thereof of the formulae CPGP-3-2, CPGP-5-2 and CPGP-3-4, more preferably of the formulae CPGP-3-2 and/or CPGP-3-2 and very particularly preferably of the formula CPGP-5-2. The definitions of these abbreviations (acronyms) are evident from Tables A and B.

(108) The liquid-crystalline media in accordance with the present invention preferably comprise one or more, preferably dielectrically neutral, compounds of the formula V,

(109) ##STR00049##
in which R.sup.51 and R.sup.52, independently of one another, have the meanings indicated above for R.sup.21 under formula II, preferably R.sup.51 denotes alkyl and R.sup.52 denotes alkyl or alkenyl,

(110) ##STR00050##
on each appearance, independently of one another, denotes

(111) ##STR00051##
preferably one or more

(112) ##STR00052## Z.sup.51 and Z.sup.52, independently of one another and, if Z.sup.51 occurs twice, also these independently of one another, denote CH.sub.2CH.sub.2, COO, trans-CHCH, trans-CFCF, CH.sub.2O, CF.sub.2O or a single bond, preferably one or more thereof denotes/denote a single bond, and r denotes 0, 1 or 2, preferably 0 or 1, particularly preferably 1.

(113) The liquid-crystalline media in accordance with the present invention preferably comprise one or more compounds selected from the group of the compounds of the formulae V-1 and V-2, preferably of formula V-1:

(114) ##STR00053##
in which R.sup.51 and R.sup.52 have the respective meanings indicated above under formula V, and R.sup.51 preferably denotes alkyl and in formula V-1, R.sup.52 preferably denotes alkenyl, preferably (CH.sub.2).sub.2CHCHCH.sub.3, and in formula V-2, R.sup.52 preferably denotes alkyl, (CH.sub.2).sub.2CHCH.sub.2 or (CH.sub.2).sub.2CHCHCH.sub.3.

(115) The liquid-crystalline media in accordance with the present invention preferably comprise one or more compounds selected from the group of the compounds of the formulae V-1 and V-2, in which R.sup.51 preferably denotes n-alkyl and, in formula V-1, R.sup.52 preferably denotes alkenyl and, in formula V-2, R.sup.52 preferably denotes n-alkyl.

(116) In a preferred embodiment, the liquid-crystal medium preferably comprises one or more compounds of the formula V-1, more preferably of the sub-formula PP-n-2Vm thereof, still more preferably of the formula PP-1-2V1. The definitions of these abbreviations (acronyms) are evident from Tables A and B.

(117) In a preferred embodiment, the liquid-crystal medium preferably comprises one or more compounds of the formula V-2, more preferably of the sub-formulae PGP-n-m, PGP-n-2V and PGP-n-2Vm thereof, still more preferably of the sub-formulae PGP-3-m, PGP-n-2V and PGP-n-V1 thereof, very preferably selected from the formulae PGP-3-2, PGP-3-3, PGP-3-4, PGP-3-5, PGP-1-2V, PGP-2-2V and PGP-3-2V. The definitions of these abbreviations (acronyms) are evident from Tables A and B.

(118) The liquid-crystalline media in accordance with the present invention preferably comprise compounds selected from the group of the compounds of the formulae I to V and more preferably of the formulae I to IV, more preferably predominantly consist, still more preferably essentially consist and very preferably completely consist thereof.

(119) Besides the compounds of the formula I, the liquid-crystal mixtures in accordance with the present invention preferably comprise compounds of the formulae II and/or III, preferably of the formula II and of compounds of the formula III. The liquid-crystal mixtures in accordance with the present invention particularly preferably additionally comprise one or more compounds of the formulae IV and/or V, particularly preferably of the formula IV.

(120) The mixtures in accordance with the present invention may of course also comprise in each case one or more compounds of a plurality of the five formulae, formulae I to V, and even all five formulae, formulae I to V.

(121) In this application, comprise in connection with compositions means that the entity in question, i.e. generally the medium, comprises the compound or compounds indicated, preferably in a total concentration of approximately 10% or more and very preferably approximately 20% or more.

(122) In this connection, predominantly consist of means that the entity in question comprises approximately 55% or more, preferably approximately 60% or more and very preferably approximately 70% or more of the compound or compounds indicated.

(123) In this connection, essentially consist of means that the entity in question comprises approximately 80% or more, preferably approximately 90% or more and very preferably approximately 95% or more of the compound or compounds indicated.

(124) In this connection, completely consist of means that the entity in question comprises approximately 98% or more, preferably approximately 99% or more and very preferably 100.0% of the compound or compounds indicated.

(125) Other mesogenic compounds, such as, for example dielectric negative compounds, which are not mentioned explicitly above, can optionally and advantageously also be used in the media in accordance with the present invention. Such compounds are known to the person skilled in the art.

(126) The compounds of formula I are preferably used in a concentration of approximately 3% to approximately 70%, more preferably approximately 5% to approximately 60% and very particularly preferably approximately 10% to approximately 50% of the mixture as a whole.

(127) The compounds of the formulae II and III are preferably used in a concentration of approximately 2% to approximately 90%, more preferably approximately 3% to approximately 80% and very particularly preferably approximately 4% to approximately 70% of the mixture as a whole.

(128) The compounds of the formulae IV and V are preferably used in a concentration of approximately 2% to approximately 70%, more preferably approximately 5% to approximately 65%, even more preferably approximately 10% to approximately 60% and very particularly preferably from approximately 10%, preferably from approximately 15%, to approximately 55% of the mixture as a whole.

(129) The media according to the invention may optionally comprise further liquid-crystal compounds in order to adjust the physical properties. Such compounds are known to the person skilled in the art. Their concentration in the media in accordance with the present invention is preferably 0% to approximately 30%, more preferably approximately 0.1% to approximately 20% and very preferably approximately 1% to approximately 15%.

(130) The liquid-crystal media preferably comprise in total approximately 50% to 100%, more preferably approximately 70% to 100% and very preferably approximately 80% to 100% and in particular approximately 90% to 100% preferably predominantly consist of and very preferably entirely consist of one or more of the compounds of the formulae I, II, III, IV and V, preferably of the formulae I, II, III and IV or V.

(131) In the following conditions for the liquid-crystalline media according to preferred embodiments of the present invention are given. These preferred conditions may be fulfilled individually or, preferably in combinations with each other. Binary combinations thereof are preferred, whereas ternary or higher combinations thereof are particularly preferred.

(132) The liquid-crystalline medium in accordance with the present invention optionally comprises further compounds, for example stabilisers, antioxidants, and/or as mentioned above self-alignment agents. They are preferably employed in a concentration of 0% to approximately 30%, particularly preferably 0% to approximately 15%, and very particularly preferably 0% to approximately 5%.

(133) In accordance with the invention, the liquid-crystalline medium preferably exhibits positive values for the dielectric anisotropy . In this case, preferably has a value of approximately 3, more preferably approximately 5, even more preferably approximately 8.

(134) The liquid-crystal media in accordance with the present invention preferably have a clearing point of approximately 65 C. or more, more preferably approximately 70 C. or more, still more preferably 80 C. or more, particularly preferably approximately 85 C. or more and very particularly preferably approximately 90 C. or more.

(135) The nematic phase of the media according to the invention preferably extends at least from approximately 0 C. or less to approximately 65 C. or more, more preferably at least from approximately 20 C. or less to approximately 70 C. or more, very preferably at least from approximately 30 C. or less to approximately 70 C. or more and in particular at least from approximately 40 C. or less to approximately 90 C. or more. In individual preferred embodiments, it may be necessary for the nematic phase of the media according to the invention to extend to a temperature of approximately 100 C. or more and even to approximately 110 C. or more.

(136) The n of a suitable liquid-crystal media is preferably as high as possible. Typically, the n of the liquid-crystal media in accordance with the present invention, at 589 nm (NaD) and 20 C., is preferably in the range from approximately 0.10 or more to approximately 0.35 or more, more preferably in the range from approximately 0.12 or more to approximately 0.35 or more, even more preferably in the range from approximately 0.15 or more to approximately 0.35 or more and very particularly preferably in the range from approximately 0.17 or more to approximately 0.35 or more.

(137) The liquid-crystal media used in the light modulation element according to the present invention preferably have an elastic constant K.sub.11 of approximately 18 pN or more, more preferably of approximately 20 pN or more, and even more preferably of approximately 25 pN or more.

(138) The liquid-crystal media used in the light modulation element according to the present invention preferably have an elastic constant K.sub.33 of approximately 30 pN or less, more preferably of approximately 15 pN or less, and even more preferably of approximately 10 pN or less.

(139) The rotational viscosity of a suitable liquid-crystal media is preferably as low as possible. Typically, the media according to the present invention, exhibit a rotational viscosity of approximately 90 mPas or less, preferably of approximately 80 mPas or less.

(140) The liquid-crystal media utilized in the light modulation element according to the present invention are prepared in a manner conventional per se. In general, the desired amount of the components used in lesser amount is dissolved in the components making up the principal constituent, preferably at elevated temperature. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, chloroform or methanol, and to remove the solvent again, for example by distillation, after thorough mixing. It is furthermore possible to prepare the mixtures in other conventional manners, for example using pre-mixes, for example homologue mixtures, or using so-called multibottle systems.

(141) The functional principle of the device according to the invention will be explained in detail below. It is noted that no restriction of the scope of the claimed invention, which is not present in the claims, is to be derived from the comments on the assumed way of functioning.

(142) In a preferred embodiment of the invention, the light modulation element comprises two or more polarisers, at least one of which is arranged on one side of the layer of the liquid-crystalline medium and at least one of which is arranged on the opposite side of the layer of the liquid-crystalline medium. The layer of the liquid-crystalline medium and the polarisers here are preferably arranged parallel to one another.

(143) The polarisers can be linear polarisers. Preferably, precisely two polarisers are present in the light modulation element. In this case, it is furthermore preferred for the polarisers either both to be linear polarisers. If two linear polarisers are present in the light modulation element, it is preferred in accordance with the invention for the polarisation directions of the two polarisers to be crossed.

(144) It is furthermore preferred in the case where two circular polarisers are present in the light modulation element for these to have the same polarisation direction, i.e. either both are right-hand circular-polarised or both are left-hand circular-polarised.

(145) The polarisers can be reflective or absorptive polarisers. A reflective polariser in the sense of the present application reflects light having one polarisation direction or one type of circular-polarised light, while being transparent to light having the other polarisation direction or the other type of circular-polarised light. Correspondingly, an absorptive polariser absorbs light having one polarisation direction or one type of circular-polarised light, while being transparent to light having the other polarisation direction or the other type of circular-polarised light. The reflection or absorption is usually not quantitative; meaning that complete polarisation of the light passing through the polariser does not take place.

(146) For the purposes of the present invention, both absorptive and reflective polarisers can be employed. Preference is given to the use of polarisers, which are in the form of thin optical films. Examples of reflective polarisers which can be used in the light modulation element according to the invention are DRPF (diffusive reflective polariser film, 3M), DBEF (dual brightness enhanced film, 3M), DBR (layered-polymer distributed Bragg reflectors, as described in U.S. Pat. No. 7,038,745 and U.S. Pat. No. 6,099,758) and APF (advanced polariser film, 3M).

(147) Examples of absorptive polarisers, which can be employed in the light modulation elements according to the invention, are the Itos XP38 polariser film and the Nitto Denko GU-1220DUN polariser film. An example of a circular polariser, which can be used in accordance with the invention, is the APNCP37-035-STD polariser (American Polarizers). A further example is the CP42 polariser (ITOS).

(148) In a preferred embodiment of the invention, the layer of the liquid-crystalline medium is arranged between two substrate layers.

(149) In accordance with the invention, the two substrate layers may consist, inter alia, each and independently from another of a polymeric material, of metal oxide, for example ITO and of glass, preferably each and independently of another of glass and/or ITO, in particular glass/glass.

(150) In a preferred embodiment, the substrates are arranged with a separation in the range from approximately 1 m to approximately 50 m from one another, preferably in the range from approximately 2 m to approximately 40 m from one another, and more preferably in the range from approximately 3 m to approximately 30 m from one another. The layer of the liquid-crystalline medium is thereby located in the interspace.

(151) The substrate layers can be kept at a defined separation from one another, for example, by spacers or electrodes, which extend through the full cell thickness or projecting structures in the layer. Typical spacer materials are commonly known to the expert, as for example spacers made of plastic, silica, epoxy resins, etc.

(152) The light modulation element may furthermore have one or more alignment layers, which are in direct contact with the layer of the liquid-crystalline medium, and preferably induce a homeotropic alignment throughout the entire liquid-crystalline medium. The alignment layers may also serve as substrate layers, so that substrate layers are not necessary in the light modulation element. If substrate layers are additionally present, the alignment layers are in each case arranged between the substrate layer and the layer of the liquid-crystalline medium. Typical alignment layer materials are commonly known to the expert, such as, for example, layers made of polyimide, alkoxysilanes, alkyltrichlorosilanes, CTAB, and chromium based Werner complexes, such as, for example, commercially available QuilonC from Zaclon.

(153) It is likewise possible in accordance with the present invention and advantageous under certain conditions for the light modulation element to comprise no alignment layers adjacent to the layer of the liquid-crystalline medium. In this case, a homeotropical alignment can be achieved by adding to the liquid-crystalline medium one or more so called self alignment agents. Suitable self alignment agents are, for example, described by Shie-Chang Jeng et al. Optics Letters (2009), 34, 455-457 or Shug-June Hwang et al. J. Phys D. Appl. Phys 2009, 42, 025102 or the self alignment agents disclosed in US 2008/0198301, JP 2010-170090 A, EP 2 593 529 A1 or EP 2 606 101 A1.

(154) The light modulation element may furthermore comprise filters, which block light of certain wavelengths, for example, UV filters. In accordance with the invention, further functional layers commonly known to the expert may also be present, such as, for example, protective films and/or compensation films.

(155) In a preferred embodiment, the light modulation element comprises a pattern of parallel electrodes, which are capable to allow the application of an electric field, which is substantially parallel to the substrates or the liquid-crystal layer.

(156) Depending on the utilized electrode structure, preferably both substrates carry patterns of opposing electrodes on their facing surfaces with the intervening liquid crystal medium there between. A suitable electrode structures is, for example, a comb-like electrode arrangement. Further preferred electrode structures are, for example, IPS, or FFS electrode structures.

(157) In another preferred embodiment, a through cell electrode structure is utilized, which serves as both spacer and electrode. Other suitable electrode structures are commonly known to the expert.

(158) Suitable electrode materials are commonly known to the expert, as for example electrodes made of metal or metal oxides, such as, for example transparent indium tin oxide (ITO), which is preferred according to the present invention.

(159) The spacing between the electrodes is preferably in the range from approximately 1 m to approximately 1000 m, more preferably in the range from approximately 10 m to approximately 1000 m, and even more preferably in the range from approximately 20 m to approximately 1000 m, in particular in the range from approximately 30 m to approximately 200 m.

(160) Preferably, the electrodes of the light modulation element are associated with a switching element, such as a thin film transistor (TFT) or thin film diode (TFD).

(161) The light transmission of the device according to the invention is dependent on the applied electric field. In a preferred embodiment, the light transmission of the device is high when an electric field is applied and low in the initial state when no electric field is applied.

(162) In a preferred embodiment, the device according to the invention has a boundary state A and a boundary state B. For the purposes of the present application, the term boundary state is taken to mean a state in which the transmission reaches a maximum or minimum value and changes no further or virtually no further on a further reduction or increase in the of the applied electric field.

(163) The light modulation element preferably has the boundary state A with a transmission T.sub.A when no electrical field is applied, the so called off state, in which the liquid crystal medium is essentially homeotropically aligned.

(164) The light modulation element preferably has another boundary state B when an electric field is applied, the so called on state, in which the liquid crystal medium is increasingly distorted away from the vertical towards the bend state, whereby the LC medium is initially homeotropically aligned and then becomes bent.
T.sub.A<T.sub.B.

(165) The light modulation element preferably exhibits an induced retardation in the on-state in the range from approximately 1 nm to approximately 300 nm, more preferably from approximately 1 nm to approximately 275 nm, even more preferably from approximately 1 nm to approximately 260 nm.

(166) The low applied electric fields required to switch the light modulation elements according to the present invention have several advantages. The inter-electrode spacing is substantially larger than the inter-electrode spacing found in current IPS devices. Accordingly, lower cost patterning of the electrodes, improved yields, increased optical apertures and lower driving voltages are some benefits from the light modulation element according to the present invention.

(167) The homeotropic off state of the device provides excellent optical extinction and therefore a favourable contrast.

(168) The optics of the device are to some degree self-compensating (similar to a conventional pi-cell) and provide better viewing angle than a conventional light modulation element according to the VA mode.

(169) The required applied electric field strength is mainly dependent on the electrode gap and the concentration of compounds of formula I as well as the e of the host mixture. The applied electric field strengths are typically lower than approximately 0.5 V/m.sup.1, preferably lower than approximately 0.2 V/m.sup.1 and more preferably lower than approximately 0.1 V/m.sup.1.

(170) Preferably, the applied driving voltage is in the range from 0 V to approximately 10 V, more preferably in the range from approximately 1 V to approximately 7V, and even more preferably in the range from approximately 1.5 V to approximately 4.V.

(171) The nature of the switching can also be inferred from the behaviour of the device under slow square wave driving. The switched state resulting from a Fredericksz transition has no polarity sensitivity, and the optical change as the voltage is reversed, is minimal. The bend state, however, changes the direction of its distortion in response to the applied voltage and the cell becomes optically extinct and then regains its previous appearance when the polarity changes. This provides a simple check on the nature of the distortion occurring in a particular cell/voltage combination.

(172) In preferred embodiment, three distinct switching regimes can be observed in a light modulation element according to the present invention: 1. At low applied electric fields, the induced retardation increases as a result from the induced flexoelectric bend distortion, 2. At fields approaching the Fredericksz critical field, the transmission increases rapidly. Even at fields appreciably above the Fredericksz threshold, the induced flexoelectric bend distortion remains a polarity dependent bend mode, 3. At still higher fields, a Fredericksz distortion grows into the cell from the electrodes. This results in a large increase in retardation, and the cell no longer responds to polarity changes.

(173) Accordingly, at low applied electric fields, the induced retardation increases as a result from the distinct flexoelectric switching regime and at higher applied electric fields approaching the Fredericksz critical field, the transmission increases rapidly as a result from the distinct dielectric switching regime.

(174) The light modulation element according to the present invention can be operated with a conventional driving waveform as commonly known by the expert.

(175) However, in a preferred embodiment according to the present invention an alternative driving waveform can be utilized. Therefore, a short duration kick or pre-pulse that is a number of times larger than the amplitude of the DC pulse required to obtain the desired amplitude of switching can be used to simulate the presence of a higher voltage, thus allowing a faster switching speed to be obtained.

(176) A typical process for the production of a light modulation element according to the invention comprises the following steps: cutting and cleaning glass substrates, on which the electrodes are arranged, coating the substrates with an alignment layer agent, assembling the cell using a UV curable adhesive, and filling the cell with the liquid-crystalline medium.

(177) The light modulation element of the present invention can be used in various types of optical and electro-optical devices.

(178) Said optical and electro optical devices include, without limitation electrooptical displays, liquid crystal displays (LCDs), non-linear optic (NLO) devices, and optical information storage devices.

(179) Especially preferred features of the invention are summarized in form of a numbered list: 1. Light modulation element comprising a flexoelectric polarisable liquid-crystalline medium, characterized in that the switching from a boundary state A to a boundary state B involves a combination of a flexoelectric switching regime and a dielectric switching regime upon application of an electric field. 2. The light modulation element according to note 1, characterized in that the liquid-crystalline medium which is sandwiched between at least two substrates, is homeotropically aligned to both substrate surfaces in the boundary state A. 3. The light modulation element according to note 1 or 2, wherein the liquid-crystalline medium comprises a bent core liquid-crystalline compound having an absolute value of the bend flexoelectric coefficient |e.sub.3| in the range from 1 pCm.sup.1 to 60 pCm.sup.1 4. The light modulation element according to one or more of notes 1 to 3, wherein the liquid crystal medium comprises at least one bent core compound selected from the compounds of formula I
R.sup.1-M.sup.1-Y.sup.1BY.sup.2-M.sup.2-R.sup.2I wherein the parameters R.sup.1, M.sup.1, Y.sup.1, Y.sup.2, M.sup.2 and R.sup.2 have the same meanings as given above for formula I. 5. The light modulation element according to one or more of notes 1 to 4, wherein the amount of compounds of formula in the liquid-crystalline medium as a whole is in the range from 3 to 70%. 6. The light modulation element according to one or more of notes 1 to 5, wherein the liquid-crystalline medium comprises one or more compounds of formulae II and III,

(180) ##STR00054## wherein the parameters have the same meaning as given above for formulae II and III. 7. The light modulation element according to one or more of notes 1 to 6, wherein the liquid-crystalline medium comprises one or more compounds of formula IV

(181) ##STR00055## wherein the parameters have the same meaning as given above for formula IV. 8. The light modulation element according to one or more of notes 1 to 7, wherein the liquid-crystalline medium comprise one or more compounds of the formula V,

(182) ##STR00056## wherein the parameters have the same meaning as given above for formula V. 9. The light modulation element according to one or more of notes 1 to 8, wherein the amount of compounds of the formulae II and/or III in the liquid-crystalline medium as a whole is in the range from 2 to 90%. 10. The light modulation element according to one or more of notes 1 to 9, wherein the amount of compounds of the formulae IV and/or V in the liquid-crystalline medium as a whole is in the range from 2 to 70%. 11. The light modulation element according to one or more of notes 1 to 10, wherein the liquid-crystalline medium exhibits a dielectric positive anisotropy of 3. 12. The light modulation element according to one or more of notes 1 to 11, wherein the liquid-crystalline medium exhibits a birefringence in the range from 0.10 or more to 0.35 or more. 13. The light modulation element according to one or more of notes 1 to 12, wherein the light modulation is induced by an applied in-plane electric field 14. The light modulation element according to one or more of notes 1 to 13, wherein the flexoelectric switching occurs at applied electric field strength lower than 0.5 V/m-1. 15. The light modulation element according to one or more of notes 1 to 14, wherein the induced retardation in the on-state is in the range from 1 nm to 300 nm. 16. Method for production of a light modulation element according to one or more of notes 1 to 15, comprising at least the step of filling the liquid-crystalline medium into a cell. 17. Use of a light modulation element according to one or more of notes 1 to 15 in an electro-optical device. 18. Electro-optical device comprising the light modulation element according to one or more of claims 1 to 15.

(183) It will be appreciated that variations to the foregoing embodiments of the invention can be made while still falling within the scope of the invention. Each feature disclosed in this specification, unless stated otherwise, may be replaced by alternative features serving the same, equivalent, or similar purpose. Thus, unless stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

(184) All of the features disclosed in this specification may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. In particular, the preferred features of the invention are applicable to all aspects of the invention and may be used in any combination. Likewise, features described in non-essential combinations may be used separately (not in combination).

(185) It will be appreciated that many of the features described above, particularly of the preferred embodiments, are inventive in their own right and not just as part of an embodiment of the present invention. Independent protection may be sought for these features in addition to or alternative to any invention presently claimed.

(186) In the present application and in the examples below, the structures of the liquid-crystal compounds are indicated by means of acronyms, with the transformation into chemical formulae taking place in accordance with Tables A and B below. All radicals C.sub.nH.sub.2n+1 and C.sub.mH.sub.2m+1 are straight-chain alkyl radicals having n and m C atoms respectively; n, m and k are integers and preferably denote 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12. The coding in Table B is self-evident. In Table A, only the acronym for the parent structure is indicated. In individual cases, the acronym for the parent structure is followed, separated by a dash, by a code for the substituents R.sup.1*, R.sup.2*, L.sup.1* and L.sup.2*:

(187) TABLE-US-00001 Code for R.sup.1*, R.sup.2*, L.sup.1*, L.sup.2*, L.sup.3* R.sup.1* R.sup.2* L.sup.1* L.sup.2* nm C.sub.nH.sub.2n+1 C.sub.mH.sub.2m+1 H H nOm C.sub.nH.sub.2n+1 OC.sub.mH.sub.2m+1 H H nO.m OC.sub.nH.sub.2n+1 C.sub.mH.sub.2m+1 H H n C.sub.nH.sub.2n+1 CN H H nN.F C.sub.nH.sub.2n+1 CN F H nN.F.F C.sub.nH.sub.2n+1 CN F F nF C.sub.nH.sub.2n+1 F H H nCl C.sub.nH.sub.2n+1 Cl H H nOF OC.sub.nH.sub.2n+1 F H H nF.F C.sub.nH.sub.2n+1 F F H nF.F.F C.sub.nH.sub.2n+1 F F F nOCF.sub.3 C.sub.nH.sub.2n+1 OCF.sub.3 H H nOCF.sub.3.F C.sub.nH.sub.2n+1 OCF.sub.3 F H n-Vm C.sub.nH.sub.2n+1 CHCHC.sub.mH.sub.2m+1 H H nV-Vm C.sub.nH.sub.2n+1CHCH CHCHC.sub.mH.sub.2m+1 H H

(188) Preferred mixture components are found in Tables A and B.

(189) TABLE-US-00002 TABLE A PYP PYRP BCH 0 CBC CCH CCP CPTP CEPTP ECCP CECP EPCH PCH CH 0 PTP CCPC CP BECH EBCH CPC B FET-nF CGG CGU 0 CFU

(190) TABLE-US-00003 TABLE B APU-n-OXF ACQU-n-F APUQU-n-F BCH-n.Fm CFU-n-F CBC-nmF ECCP-nm CCZU-n-F PGP-n-m 0 CGU-n-F CDUQU-n-F CDU-n-F DCU-n-F CGG-n-F CPZG-n-OT CC-nV-Vm CCP-Vn-m CCG-V-F CCP-nV-m 00 CC-n-V 01 CCQU-n-F 02 CC-n-Vm 03 CPPC-nV-Vm 04 CCQG-n-F 05 CQU-n-F 06 Dec-U-n-F 07 CWCU-n-F 08 CPGP-n-m 09 CWCG-n-F 0 CCOC-n-m CPTU-n-F GPTU-n-F PQU-n-F PUQU-n-F PGU-n-F CGZP-n-OT CCGU-n-F CCQG-n-F DPGU-n-OT 0 DPGU-n-F CUQU-n-F CCCQU-n-F CGUQU-n-F CPGU-n-OT PYP-n-F CPU-n-OXF CPGU-n-F CPGG-n-F CVCP-1V-OT 0 GGP-n-Cl PP-nV-Vm PP-1-nVm CWCQU-n-F PPGU-n-F PGUQU-n-F GPQU-n-F MPP-n-F PGP-n-kVm PP-n-kVm 0 PCH-nCl GP-n-Cl GGP-n-F PGIGI-n-F SUQU-n-F SPUQU-n-F

(191) In a preferred embodiment of the present invention, the LC media according to the invention comprise one or more compounds selected from the group consisting of compounds from Tables A and B.

(192) TABLE-US-00004 TABLE C Table C indicates possible stabilizers, which can be added to the LC media according to the invention. 0 0 0

(193) The LC media preferably comprise 0 to 10% by weight, in particular 0.01 to 5% by weight and particularly preferably 0.1 to 3% by weight, of dopants. The LC media preferably comprise one or more dopants selected from the group consisting of compounds from Table C.

EXAMPLES

(194) A cell is prepared by the following method: Two glass substrates are cleaned in deionised water in an ultrasound bath for 10 minutes, dried in a stream of air and immersed for 60 seconds in a solution of 20% KOH in deionised water. The substrates are rinsed in deionised water, dried under a stream of air, and dipped into a solution of a Quilon C, Chrome Complex solution for 60 seconds. The treated substrates are rinsed briefly in deionised water and dried at 150 C. for 60 minutes. Subsequently, two strips of aluminium foil of 30 m thickness were cut and placed parallel to each other on one of the substrates with a narrow gap of approximately 1 mm between the electrodes.

(195) A thin bead of Norland Optical Adhesive #65 is applied around the outside of the electrodes and the formed cell is subjected to pressure and Norland Optical Adhesive #65 was exposed to UV light (350 nm) to glue the cell together and to seal the edges leaving two gaps to allow filling with liquid crystal mixture.

Example 1

(196) A mixture containing 30% of compound (1) in ZLI-1132 (70%) is prepared and introduced into the cell by capillary filling at 80 C.

(197) ##STR00178##

(198) The cell is held at 60 C. for 30 minutes and cooled down to ambient temperature. Wires are attached to the aluminium foil electrodes using conductive adhesive (RS 186-3600, silver-loaded electrically conductive paint) and clips. A dc voltage is applied and the transmission of the cell is recorded using a standard photodiode on a polarising microscope. The transmission as a function of voltage is shown in table 1.

(199) TABLE-US-00005 TABLE 1 Transmission of the cell as a function of the applied electric field. Applied Field [Vm.sup.1] Transmission [%] 0.0000 0.2 0.0133 0.0 0.0263 0.3 0.0396 3.5 0.0459 7.8 0.0525 17.8 0.0584 36.5 0.0645 66.7

(200) As can be seen from the table, at low applied electric fields, the induced retardation increases as a result from the induced flexoelectric bend distortion.

(201) At fields approaching the Fredericksz critical field of 0.75 Vm.sup.1, the transmission increases rapidly. Even at fields appreciably above the Fredericksz threshold, the induced flexoelectric bend distortion remains a polarity dependent bend mode,

(202) At still higher fields above 0.75 Vm.sup.1, a Fredericksz distortion grows into the cell from the electrodes. This results in a large increase in retardation, and the cell no longer responds to polarity changes.

Example 2

(203) A mixture containing 63.6% ZLI-1132, 27.3% of compound (1) and 9.1% of compound (2) is prepared.

(204) ##STR00179##

(205) The cell is held at 60 C. for 30 minutes and cooled down to ambient temperature. Wires are attached to the aluminium foil electrodes using conductive adhesive (RS 186-3600, silver-loaded electrically conductive paint) and clips. A dc voltage is applied and the transmission of the cell is recorded using a standard photodiode on a polarising microscope (table 2).

(206) TABLE-US-00006 TABLE 2 Transmission of the cell as a function of the applied electric field. Applied Field/Vm.sup.1 Transmission % 0.000 0.00 0.034 0.15 0.056 0.58 0.068 0.90 0.079 1.60 0.090 2.44 0.102 4.00 0.113 6.38