LIGHT MODULATION ELEMENT

Abstract

The invention relates to a device for the regulation of light transmission, preferably a window, more preferably a privacy window, comprising a liquid crystalline medium exhibiting a converse flexoelectric effect, and which is sandwiched between two substrates, wherein at least one substrate is provided with an electrode structure.

Claims

1. Device for the regulation of light transmission, comprising a liquid crystalline medium exhibiting a converse flexoelectric effect, which is sandwiched between two substrates, wherein at least one substrate is provided with an electrode structure.

2. The device according to claim 1, characterised in that the device utilizes a liquid crystalline medium comprising one or more bimesogenic compounds.

3. The device according to claim 1, characterised in that the device has two boundary states, one, a boundary state A with a corresponding transmission T.sub.A when no electrical field is applied the so-called off state or transparent state, and the other, a boundary state B with a corresponding transmission T.sub.B when an electrical field is applied the so-called on state or light scattering state, whereby:
T.sub.A>T.sub.B.

4. The device according to claim 1, characterised in that the liquid crystalline medium comprises one or more bimesogenic compounds which are selected from the group of compounds of formulae A-I to A-III, ##STR00128## and wherein R.sup.11 and R.sup.12, R.sup.21 and R.sup.22, and R.sup.31 and R.sup.32 are each independently H, F, Cl, CN, NCS or a straight-chain or branched alkyl group with 1 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 occurrence independently from one another, by O, S, NH, N(CH.sub.3), CO, COO, OCO, OCOO, SCO, COS, CHCH, CHCF, CFCF or CC in such a manner that oxygen atoms are not linked directly to one another, MG.sup.11 and MG.sup.12, MG.sup.21 and MG.sup.22, and MG.sup.31 and MG.sup.32 are each independently a mesogenic group, Sp.sup.1, Sp.sup.2 and Sp.sup.3 are each independently a spacer group comprising 5 to 40 C atoms, wherein one or more non-adjacent CH.sub.2 groups, with the exception of the CH.sub.2 groups of Sp.sup.1 linked to O-MG.sup.11 and/or O-MG.sup.12, of Sp.sup.2 linked to MG.sup.21 and/or MG.sup.22 and of Sp.sup.3 linked to X.sup.31 and X.sup.32, may also be replaced by O, S, NH, N(CH.sub.3), CO, OCO, SCO, OCOO, COS, COO, CH(halogen)-, CH(CN), CHCH or CC, however in such a way that no two O-atoms are adjacent to one another, no two CHCH groups are adjacent to each other, and no two groups selected from OCO, SCO, OCOO, COS, COO and CHCH are adjacent to each other and X.sup.31 and X.sup.32 are independently from one another a linking group selected from COO, OCO, CHCH, CC or S, and, alternatively, one of them may also be either O or a single bond, and, again alternatively, one of them may be O and the other one a single bond.

5. The device according to claim 1, characterised in that the liquid crystalline medium comprises one or more dyes.

6. The device according to claim 1, characterised in that the liquid crystalline medium comprises one or more dichroic dyes.

7. The device according to claim 1, characterised in that the liquid crystalline medium comprises one or more dichroic dyes selected from the group of compounds of formula I, ##STR00129## wherein, ##STR00130## are at each occurrence, identically or differently, selected from ##STR00131## and, in case i is 2 or more, the terminal one of group ##STR00132## may also be ##STR00133## and, in case j is 2 or more, the terminal one of group ##STR00134## may also be ##STR00135## Z.sup.11 and Z.sup.12 are, independently of each other, NN, OCO or COO, R.sup.11 and R.sup.12 are, independently of each other, alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl, alkylaminyl, dialkylaminy, alkylcarbonyl, alkyloxycarbonyl, alkylcarbonyloxy, alkyloxycarbonyloxy or alkylcyclohexylalkyl, and i and j are independently of each other 1, 2, 3 or 4.

8. The device according to claim 1, characterised in that the device comprises no polarizer.

9. The device according to claim 1, characterised in that the device comprises no alignment layer.

10. The device according to claim 1, characterised in that the device comprises one or more alignment layers capable of inducing a homeotropic orientation to the adjacent liquid-crystalline medium.

11. The device according to claim 1, characterised in that the device comprises one or more alignment layers capable of inducing a planar orientation to the adjacent liquid-crystalline medium.

12. Method for the regulation of light entry and/or energy input into an interior, comprising situating a device according to claim 1 so that the light entry and/or energy input passes through the device into the interior.

13. (canceled)

14. A display device, comprising a device of claim 1.

15. Process for the production of the device according to claim 1, comprising the steps of cutting and cleaning glass substrates, on which the electrodes are arranged, optionally, coating the substrates with an alignment layer or dielectric layer, assembling the cell using a UV curable adhesive, and filling the cell with the liquid-crystalline medium.

16. Optical or electro-optical device comprising the device according to claim 1.

17. Window comprising the device according to claim 1.

18. Window according to claim 17, characterized in that it is a privacy window.

Description

DETAILED DESCRIPTION

[0058] Suitable liquid crystalline media for the device for the regulation of light transmission according to the present invention typically comprise at least one bimesogenic compound. Preferably, the liquid crystalline media for the device for the regulation of light transmission according to the present invention substantially consists of one or more bimesogenic compounds.

[0059] Suitable bimesogenic compounds, exhibit typically relatively high values of the elastic constant K.sub.11, low values of the bend elastic constant K.sub.33 and the flexoelectric coefficient.

[0060] In view of the bimesogenic compounds, the Coles group published a paper (Coles et al., 2012 (Physical Review E 2012, 85, 012701)) on the structure-property relationship for dimeric liquid crystals.

[0061] Further bimesogenic compounds are known in general from prior art (cf. also Hori, K., Limuro, M., Nakao, A., Toriumi, H., J. Mol. Struc. 2004, 699, 23-29 or GB 2 356 629).

[0062] Symmetrical dimeric compounds showing liquid crystalline behaviour are further disclosed in Joo-Hoon Park et al. Liquid Crystalline Properties of Dimers Having o-, m- and p-Positional Molecular structures, Bill. Korean Chem. Soc., 2012, Vol. 33, No. 5, pp. 1647-1652.

[0063] EP 0 971 016 reports on mesogenic estradiols, which, as such, have a high flexoelectric coefficient.

[0064] Preferably, the liquid-crystalline medium utilized in a device for the regulation of light transmission in accordance with the present invention comprises one or more bimesogenic compounds which are preferably selected from the group of compounds of formulae A-I to A-III,

##STR00001##

and wherein [0065] R.sup.11 and R.sup.12, [0066] R.sup.21 and R.sup.22, [0067] and R.sup.31 and R.sup.32 are each independently H, F, Cl, CN, NCS or a straight-chain or branched alkyl group with 1 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 occurrence independently from one another, by O, S, NH, N(CH.sub.3), CO, COO, OCO, OCOO, SCO, COS, CHCH, CHCF, CFCF or CC in such a manner that oxygen atoms are not linked directly to one another, [0068] MG.sup.11 and MG.sup.12, [0069] MG.sup.21 and MG.sup.22, [0070] and MG.sup.31 and MG.sup.32 are each independently a mesogenic group, [0071] Sp.sup.1, Sp.sup.2 and Sp.sup.3 are each independently a spacer group comprising 5 to 40 C atoms, wherein one or more non-adjacent CH.sub.2 groups, with the exception of the CH.sub.2 groups of Sp.sup.1 linked to O-MG.sup.11 and/or O-MG.sup.12, of Sp.sup.2 linked to MG.sup.21 and/or MG.sup.22 and of Sp.sup.3 linked to X.sup.31 and X.sup.32, may also be replaced by O, S, NH, N(CH.sub.3), CO, OCO, SCO, OCOO, COS, COO, CH(halogen)-, CH(CN), CHCH or CC, however in such a way that no two O-atoms are adjacent to one another, no two CHCH groups are adjacent to each other, and no two groups selected from OCO, SCO, OCOO, COS, COO and CHCH are adjacent to each other and [0072] X.sup.31 and X.sup.32 are independently from one another a linking group selected from COO, OCO, CHCH, CC or S, and, alternatively, one of them may also be either O or a single bond, and, again alternatively, one of them may be O and the other one a single bond.

[0073] Preferably used are compounds of formulae A-I to A-III wherein [0074] Sp.sup.1, Sp.sup.2 and Sp.sup.3 are each independently (CH.sub.2).sub.n with [0075] n an integer from 1 to 15, most preferably an uneven integer, wherein one or more CH.sub.2 groups may be replaced by CO.

[0076] Especially preferably used are compounds of formula A-III wherein [0077] X.sup.31-Sp.sup.3-X.sup.32 is -Sp.sup.3-O, -Sp.sup.3-COO, -Sp.sup.3-OCO, O-Sp.sup.3-, O-Sp.sup.3-COO, O-Sp.sup.3-OCO, OCO-Sp.sup.3-O, OCO-Sp.sup.3-OCO, COO-Sp.sup.3-O or COO-Sp.sup.3-COO, however under the condition that in X.sup.31-Sp.sup.3-X.sup.32 no two O-atoms are adjacent to one another, no two CHCH groups are adjacent to each other and no two groups selected from OCO, SCO, OCOO, COS, COO and CHCH are adjacent to each other.

[0078] Preferably used are compounds of formula A-I in which [0079] MG.sup.11 and MG.sup.12 are independently from one another -A.sup.11-(Z.sup.1-A.sup.12).sub.m-
wherein [0080] Z.sup.1 is COO, OCO, OCOO, OCH.sub.2, CH.sub.2O, CH.sub.2CH.sub.2, (CH.sub.2).sub.4, CF.sub.2CF.sub.2, CHCH, CFCF, CHCHCOO, OCOCHCH, CC or a single bond, [0081] A.sup.11 and A.sup.12 are each independently in each occurrence 1,4-phenylene, wherein in addition one or more CH groups may be replaced by N, trans-1,4-cyclo-hexylene 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, decahydro-naphthalene-2,6-diyl, 1,2,3,4-tetrahydro-naphthalene-2,6-diyl, cyclobutane-1,3-diyl, spiro[3.3]heptane-2,6-diyl or dispiro[3.1.3.1]decane-2,8-diyl, it being possible for all these groups to be unsubstituted, mono-, di-, tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl groups with 1 to 7 C atoms, wherein one or more H atoms may be substituted by F or Cl, and [0082] m is 0, 1,2 or 3.

[0083] Preferably used are compounds of formula A-II in which [0084] MG.sup.21 and MG.sup.22 are independently from one another -A.sup.21-(Z.sup.2-A.sup.22).sub.m-
wherein [0085] Z.sup.2 is COO, OCO, OCOO, OCH.sub.2, CH.sub.2O, CH.sub.2CH.sub.2, (CH.sub.2).sub.4, CF.sub.2CF.sub.2, CHCH, CFCF, CHCHCOO, OCOCHCH, CC or a single bond, [0086] A.sup.21 and A.sup.22 are each independently in each occurrence 1,4-phenylene, wherein in addition one or more CH groups may be replaced by N, trans-1,4-cyclo-hexylene 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, decahydro-naphthalene-2,6-diyl, 1,2,3,4-tetrahydro-naphthalene-2,6-diyl, cyclobutane-1,3-diyl, spiro[3.3]heptane-2,6-diyl or dispiro[3.1.3.1]decane-2,8-diyl, it being possible for all these groups to be unsubstituted, mono-, di-, tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl groups with 1 to 7 C atoms, wherein one or more H atoms may be substituted by F or Cl, and [0087] m is 0, 1,2 or 3.

[0088] Most preferably used are compounds of formula A-III in which [0089] MG.sup.31 and MG.sup.32 are independently from one another -A.sup.31-(Z.sup.3-A.sup.32).sub.m-
wherein [0090] Z.sup.3 is COO, OCO, OCOO, OCH.sub.2, CH.sub.2O, CH.sub.2CH.sub.2, (CH.sub.2).sub.4, CF.sub.2CF.sub.2, CHCH, CFCF, CHCHCOO, OCOCHCH, CC or a single bond, [0091] A.sup.31 and A.sup.32 are each independently in each occurrence 1,4-phenylene, wherein in addition one or more CH groups may be replaced by N, trans-1,4-cyclo-hexylene 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, decahydro-naphthalene-2,6-diyl, 1,2,3,4-tetrahydro-naphthalene-2,6-diyl, cyclobutane-1,3-diyl, spiro[3.3]heptane-2,6-diyl or dispiro[3.1.3.1]decane-2,8-diyl, it being possible for all these groups to be unsubstituted, mono-, di-, tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl groups with 1 to 7 C atoms, wherein one or more H atoms may be substituted by F or Cl, and [0092] m is 0, 1,2 or 3.

[0093] Preferably, the compounds of formula A-III are asymmetric compounds, preferably having different mesogenic groups MG.sup.31 and MG.sup.32

[0094] Generally preferred are compounds of formulae A-I to A-III in which the dipoles of the ester groups present in the mesogenic groups are all oriented in the same direction, i.e. all COO or all OCO.

[0095] Especially preferred are compounds of formulae A-I and/or A-II and/or A-III wherein the respective pairs of mesogenic groups (MG.sup.11 and MG.sup.12) and (MG.sup.21 and MG.sup.22) and (MG.sup.31 and MG.sup.32) at each occurrence independently from each other comprise one, two or three six-atomic rings, preferably two or three six-atomic rings.

[0096] A smaller group of preferred mesogenic groups is listed below. For reasons of simplicity, Phe in these groups is 1,4-phenylene, PheL is a 1,4-phenylene group which is substituted by 1 to 4 groups L, with L being preferably F, Cl, CN, OH, NO.sub.2 or an optionally fluorinated alkyl, alkoxy or alkanoyl group with 1 to 7 C atoms, very 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 and OCF.sub.3, most preferably F, Cl, CH.sub.3, OCH.sub.3 and COCH.sub.3 and Cyc is 1,4-cyclohexylene. This list comprises the sub-formulae shown below as well as their mirror images

-Phe-Z-Phe-II-1

-Phe-Z-Cyc-II-2

-Cyc-Z-Cyc-II-3

-PheL-Z-Phe-II-4

-PheL-Z-Cyc-II-5

-PheL-Z-PheL-II-6

-Phe-Z-Phe-Z-Phe-II-7

-Phe-Z-Phe-Z-Cyc-II-8

-Phe-Z-Cyc-Z-Phe-II-9

-Cyc-Z-Phe-Z-Cyc-II-10

-Phe-Z-Cyc-Z-Cyc-II-11

-Cyc-Z-Cyc-Z-Cyc-II-12

-Phe-Z-Phe-Z-PheL-II-13

-Phe-Z-PheL-Z-Phe-II-14

-PheL-Z-Phe-Z-Phe-II-15

-PheL-Z-Phe-Z-PheL-II-16

-PheL-Z-PheL-Z-Phe-II-17

-PheL-Z-PheL-Z-PheL-II-18

-Phe-Z-PheL-Z-Cyc-II-19

-Phe-Z-Cyc-Z-PheL-II-20

-Cyc-Z-Phe-Z-PheL-II-21

-PheL-Z-Cyc-Z-PheL-II-22

-PheL-Z-PheL-Z-Cyc-II-23

-PheL-Z-Cyc-Z-Cyc-II-24

-Cyc-Z-PheL-Z-Cyc-II-25

[0097] Particularly preferred are the sub formulae II-1, II-4, II-6, II-7, II-13, II-14, II-15, II-16, II-17 and II-18.

[0098] In these preferred groups, Z in each case independently has one of the meanings of Z.sup.1 as given above for MG.sup.21 and MG.sup.22. Preferably Z is COO, OCO, CH.sub.2CH.sub.2, CC or a single bond, especially preferred is a single bond.

[0099] Very preferably the mesogenic groups MG.sup.11 and MG.sup.12, MG.sup.21 and MG.sup.22 and MG.sup.31 and MG.sup.32 are each and independently selected from the following formulae and their mirror images

[0100] Very preferably, at least one of the respective pairs of mesogenic groups MG.sup.11 and MG.sup.12, MG.sup.21 and MG.sup.22 and MG.sup.31 and MG.sup.32 is, and preferably, both of them are each and independently, selected from the following formulae IIa to IIn (the two reference Nos. II i and II I being deliberately omitted to avoid any confusion) and their mirror images

##STR00002## ##STR00003##

wherein
L is in each occurrence independently of each other F or Cl, preferably F and
r is in each occurrence independently of each other 0, 1, 2 or 3, preferably 0, 1 or 2.

[0101] The group

##STR00004##

in these preferred formulae is very preferably denoting

##STR00005##

furthermore

##STR00006##

[0102] Particularly preferred are the sub formulae IIa, IId, IIg, IIh, IIi, IIk and IIo, in particular the sub formulae IIa and IIg.

[0103] In case of compounds with a non-polar group, R.sup.11, R.sup.12, R.sup.21, R.sup.22, R.sup.31, and R.sup.32 are preferably alkyls with up to 15 C atoms or alkoxy with 2 to 15 C atoms.

[0104] If R.sup.11 and R.sup.12, R.sup.21 and R.sup.22 and R.sup.31 and R.sup.32 are 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.

[0105] 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.

[0106] In case of a compounds with a terminal polar group, R.sup.11 and R.sup.12, R.sup.21 and R.sup.22 and R.sup.31 and R.sup.32 are selected from CN, NO.sub.2, halogen, OCH.sub.3, OCN, SCN, COR.sup.x, COOR.sup.x or a mono-oligo- or polyfluorinated alkyl or alkoxy group with 1 to 4 C atoms. R.sup.x is optionally fluorinated alkyl with 1 to 4, preferably 1 to 3 C atoms. Halogen is preferably F or Cl.

[0107] Especially preferably R.sup.11 and R.sup.12, R.sup.21 and R.sup.22 and R.sup.31 and R.sup.32 in formulae A-I, A-II, respectively A-III are selected of H, 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 H, F, Cl, CN, OCH.sub.3 and OCF.sub.3, especially of H, F, CN and OCF.sub.3.

[0108] In addition, compounds of formulae A-I, A-II, respectively A-III containing an achiral branched group R.sup.11 and/or R.sup.21 and/or R.sup.31 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-methylpropoxy and 3-methylbutoxy.

[0109] The spacer groups Sp.sup.1, Sp.sup.2 and Sp.sup.3 are preferably a linear or branched alkylene group having 5 to 40 C atoms, in particular 5 to 25 C atoms, very preferably 5 to 15 C atoms, in which, in addition, one or more non-adjacent and non-terminal CH.sub.2 groups may be replaced by O, S, NH, N(CH.sub.3), CO, OCO, SCO, OCOO, COS, COO, CH(halogen)-, CH(CN), CHCH or CC.

[0110] Terminal CH.sub.2 groups are those directly bonded to the mesogenic groups. Accordingly, non-terminal CH.sub.2 groups are not directly bonded to the mesogenic groups R.sup.11 and R.sup.12, R.sup.21 and R.sup.22 and R.sup.31 and R.sup.32.

[0111] Typical spacer groups are for example (CH.sub.2).sub.o, (CH.sub.2CH.sub.2O).sub.pCH.sub.2CH.sub.2, with o being an integer from 5 to 40, in particular from 5 to 25, very preferably from 5 to 15, and p being an integer from 1 to 8, in particular 1, 2, 3 or 4.

[0112] Preferred spacer groups are pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, octadecylene, diethyleneoxyethylene, dimethyleneoxybutylene, pentenylene, heptenylene, nonenylene and undecenylene, for example.

[0113] Especially preferred are compounds of formulae A-I, A-II and A-III wherein Sp.sup.1, Sp.sup.2, respectively Sp.sup.3 are alkylene with 5 to 15 C atoms. Straight-chain alkylene groups are especially preferred.

[0114] Preferred are spacer groups with even numbers of a straight-chain alkylene having 6, 8, 10, 12 and 14 C atoms.

[0115] In another embodiment of the present invention are the spacer groups preferably with odd numbers of a straight-chain alkylene having 5, 7, 9, 11, 13 and 15 C atoms. Very preferred are straight-chain alkylene spacers having 5, 7, or 9 C atoms.

[0116] Especially preferred are compounds of formulae A-I, A-II and A-III wherein Sp.sup.1, Sp.sup.2, respectively Sp.sup.3 are completely deuterated alkylene with 5 to 15 C atoms. Very preferred are deuterated straight-chain alkylene groups. Most preferred are partially deuterated straight-chain alkylene groups. Preferred are compounds of formula A-I wherein the mesogenic groups R.sup.11-MG.sup.11- and R.sup.12-MG.sup.1- are different. Especially preferred are compounds of formula A-I wherein R.sup.1-MG.sup.11- and R.sup.12-MG.sup.12- in formula A-I are identical.

[0117] Preferred compounds of formula A-I are selected from the group of compounds of formulae A-I-1 to A-I-3

##STR00007##

wherein the parameter n has the meaning given above and preferably is 3, 5, 7 or 9, more preferably 5, 7 or 9.

[0118] Preferred compounds of formula A-II are selected from the group of compounds of formulae A-II-1 to A-II-4

##STR00008##

wherein the parameter n has the meaning given above and preferably is 3, 5, 7 or 9, more preferably 5, 7 or 9.

[0119] Preferred compounds of formula A-III are selected from the group of compounds of formulae A-III-1 to A-III-11

##STR00009## ##STR00010##

wherein the parameter n has the meaning given above and preferably is 3, 5, 7 or 9, more preferably 5, 7 or 9.

[0120] Particularly preferred exemplary compounds of formulae A-I are the following compounds:

symmetrical ones:

##STR00011##

and non-symmetrical ones:

##STR00012##

[0121] Particularly preferred exemplary compounds of formulae A-II are the following compounds:

symmetrical ones:

##STR00013##

and non-symmetrical ones:

##STR00014##

[0122] Particularly preferred exemplary compounds of formulae A-III are the following compounds:

symmetrical ones:

##STR00015##

and non-symmetrical ones:

##STR00016## ##STR00017## ##STR00018##

[0123] The bimesogenic compounds of formula A-I to A-III are particularly useful in flexoelectric liquid crystal displays as they can easily be aligned into macroscopically uniform orientation, and lead to high values of the elastic constant k.sub.11 and a high flexoelectric coefficient e in the applied liquid crystalline media.

[0124] The compounds of formulae A-I to A-III 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.

[0125] The liquid crystalline medium utilized in a device for the regulation of light transmission according to the present invention optionally comprises one or more dyes, preferably one or more dichroic dyes.

[0126] Preferably, the dichroic dyes are selected from the group of perylene dyes, anthrachinone dyes, and/or azo dyes.

[0127] More preferably, the dichroic dyes are selected from the group of compounds of formula I,

##STR00019## [0128] wherein,

##STR00020## [0129] are at each occurrence, identically or differently, selected from

##STR00021## [0130] and, in case i is 2 or more, the terminal one of group

##STR00022## [0131] may also be

##STR00023## [0132] and, in case j is 2 or more, the terminal one of group

##STR00024##

may also be

##STR00025## [0133] Z.sup.11 and Z.sup.12 are, independently of each other, NN, OCO or COO, [0134] R.sup.11 and R.sup.12 are, independently of each other, alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl, alkylaminyl, dialkylaminyl, alkylcarbonyl, alkyloxycarbonyl, alkylcarbonyloxy, alkyloxycarbonyloxy or alkylcyclohexylalkyl, and [0135] i and j are independently of each other 1, 2, 3 or 4.

[0136] In a preferred embodiment of the present invention, the liquid crystalline medium comprises one or more dichroic dyes preferably selected from the group of compounds of formulae I-1 to I-7,

##STR00026##

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

[0137] In a preferred embodiment of the present invention, the liquid crystalline medium comprises one or more dichroic dyes preferably selected from the group of compounds of formulae I-1 to I-7

##STR00027##

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

[0138] Further preferred compounds of formula I are represented by the following formulae

##STR00028##

[0139] Preferably the concentration of the dichroic dyes in the medium is in the range from 0.1% to 5%, more preferably from 0.2% to 4%, even more preferably from 0.3% to 3%, most preferably from 0.5% to 2% and in particular about 1%.

[0140] In a preferred embodiment, the medium comprises a mixture of two or more, preferably of three or more dichroic dyes. Most preferably three dichroic dyes are at present. Preferably, the dichroic dyes have mutually complementing absorption spectra to each other, i. e. complementary absorption colours and are preferably mixed in a ratio relative to each other which results in a neutral colour of the combined absorption of the mixture, i. e. in a black appearance. This means that the absorption is almost constant over the visible spectral range.

[0141] For example, the spectral characteristic of a preferred combination of three compounds I-1a, I-4a and I-5a are given in the following table:

TABLE-US-00002 Dye No. I-1a I-4a I-5a F593 F355 F357 ME-1107 ME-301 ME-540 Absorption Spectrum in CH.sub.2Cl.sub.2 (1/100,000) .sub.max/nm 621 536 426 .sub.max/nm 2 2 2 OD* 0.620 0.785 0.520 OD* 0.020 0.020 0.020 Colour Blue Red Yellow (Orange) Dichroic Properties Host LC.sup. No. ZLI- 2903 2452 DR** 16.2 13.7 13.0 S*** 0.83 0.81 0.80 *Optical Density: OD log.sub.10 (I.sub.i/I.sub.t), Ii = Intensity of incident light, It = Intensity of transmitted light, .sup.ZLI-mixtures available from Merck KGaA, Germany, **Dichroic Ratio of Dye in Host LC and ***Order Parameter of Dye in Host LC.

[0142] 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.

[0143] 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 bimesogenic compounds.

[0144] It goes without saying to the person skilled in the art that the LC media may also comprise compounds in which, for example, H, N, O, Cl, F have been replaced by the corresponding isotopes.

[0145] Typically, the amount of compounds of formula A-I to A-III in the liquid crystalline medium is preferably from 25 to 100%, in particular from 50 to 100%, very preferably 75 to 100% by weight of the total mixture.

[0146] Preferably the concentration of the dichroic dyes in the medium is in the range from 0.05% to 5%, more preferably from 0.1% to 4%, even more preferably from 0.2% to 3%.

[0147] The liquid-crystalline medium in accordance with the present invention optionally comprises further compounds, for example stabilisers, antioxidants, which are preferably employed in a concentration of 0% to approximately 20%, particularly preferably 0% to approximately 10%, and very particularly preferably 0% to approximately 5%, respectively.

[0148] In one preferred embodiment, the liquid-crystalline medium preferably exhibits positive values for the dielectric anisotropy . In this case, preferably has a value of approximately 0 to 8, more preferably approximately 0 to 5, even more preferably approximately 0 to 3.

[0149] In another preferred embodiment the liquid-crystalline medium preferably exhibits negative values for the dielectric anisotropy . In this case, preferably has a value of approximately 0 to 8, more preferably approximately 0 to 5, even more preferably approximately 0 to 3.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] The liquid crystal medium preferably exhibits a

k.sub.11>110-10 N and a flexoelectric coefficient
e>110-10 C/m.

[0154] 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.

[0155] The liquid-crystal media utilized in the device for the regulation of light transmission 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.

[0156] The functional principle of the device for the regulation of light transmission 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.

[0157] In a preferred embodiment of the invention, the layer of the liquid-crystalline medium is arranged between two substrate layers.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] In a further preferred embodiment of the invention, the layer of the liquid-crystalline medium is located between two flexible layers, for example flexible polymer films. The device for the regulation of light transmission according to the invention is consequently flexible and bendable and can be rolled up, for example. The flexible layers can represent the substrate layer, the alignment layer, and/or polarisers. Further layers, which are preferable flexible, may also, be present. For a more detailed disclosure of the preferred embodiments, in which the layer of the liquid-crystalline medium is located between flexible layers, reference is given to the application US 2010/0045924.

[0162] As used herein, the term polymer will be understood to mean a molecule that encompasses a backbone of one or more distinct types of repeating units (the smallest constitutional unit of the molecule) and is inclusive of the commonly known terms oligomer, copolymer, homopolymer and the like. Further, it will be understood that the term polymer is inclusive of, in addition to the polymer itself, residues from initiators, catalysts, and other elements attendant to the synthesis of such a polymer, where such residues are understood as not being covalently incorporated thereto. Further, such residues and other elements, while normally removed during post polymerisation purification processes, are typically mixed or co-mingled with the polymer such that they generally remain with the polymer when it is transferred between vessels or between solvents or dispersion media.

[0163] In a further preferred embodiment of the invention, the liquid-crystalline medium has a solid or gelatinous consistency. The term gelatinous refers to a consistency having the nature of or resembling jelly. The device for the regulation of light transmission according to the invention is consequently less susceptible to damage. If, furthermore, exclusively flexible, bendable and cuttable layers are present in addition to the layer of the liquid-crystalline medium, the device for the regulation of light transmission can not only be rolled up, but pieces of an area required in each case can also be cut out.

[0164] The device for the regulation of light transmission may furthermore have one or more alignment layers, which are in direct contact with the layer of the liquid-crystalline medium and induce homeotropic or planar orientation.

[0165] It is likewise possible in accordance with the present invention and advantageous under certain conditions for the device for the regulation of light transmission to comprise no alignment layers adjacent to the layer of the liquid-crystalline medium.

[0166] The term hybrid alignment or orientation of a liquid crystal or mesogenic material in a display cell or between two substrates means that the mesogenic groups adjacent to the first cell wall or on the first substrate exhibit homeotropic orientation and the mesogenic groups adjacent to the second cell wall or on the second substrate exhibit planar orientation.

[0167] By using a display cell with hybrid alignment conditions, a very high switching angle of flexoelectric switching, fast response times and a good contrast can be achieved.

[0168] Planar alignment can be achieved e.g. by means of an alignment layer, for example a layer of rubbed polyimide or sputtered SiOx, that is applied on top of the substrate.

[0169] Homeotropic alignment can be achieved e.g. by means of an alignment layer coated on top of the substrate. Suitable aligning agents used on glass substrates are for example, alkyltrichlorosilane or lecithine, whereas for plastic substrate thin layers of lecithine, silica or high tilt polyimide orientation films as aligning agents may be used. In a preferred embodiment of the invention silica coated plastic film is used as a substrate. However, it is also possible to add self-aligning agents to the liquid crystalline mixture in order to achieve homeotropic alignment, which are commonly known to the skilled person from prior art.

[0170] Further suitable methods to achieve planar or homeotropic alignment are described for example in J. Cognard, Mol. Cryst. Liq. Cryst. 78, Supplement 1, 1-77 (1981).

[0171] In a preferred embodiment, the alignment layers are rubbed by rubbing techniques known to the skilled person.

[0172] The device for the regulation of light transmission may furthermore comprise filters which block light of certain wavelengths, for example UV filters. In accordance with the invention, further functional layers, such as, for example, protective films, heat-insulation films or metal-oxide layers, may also be present.

[0173] Furthermore, electrodes and further electrical components and connections may be present in the device for the regulation of light transmission according to the invention in order to facilitate electrical switching of the light modulation element, comparable to the switching of an LC display.

[0174] Depending on the utilized electrode structure, preferably at least one substrate is provided with an electrode structure, but it is likewise preferred that 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.

[0175] 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, such as electrode layers covering the whole substrate.

[0176] 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.

[0177] Preferably, the electrodes of the device for the regulation of light transmission are associated with a switching element, such as a thin film transistor (TFT) or thin film diode (TFD).

[0178] 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.

[0179] The light transmission of the device for the regulation of light transmission according to the invention is dependent on the applied electric field. In a preferred embodiment, the light transmission of the device for the regulation of light transmission is high in the initial state when no electric field is applied and preferably, gradually decreases when an electric field is applied.

[0180] In a preferred embodiment, the device for the regulation of light transmission according to the invention has a boundary state A and a boundary state B.

[0181] The device for the regulation of light transmission preferably has the boundary state A with a transmission T.sub.A when no electrical field is applied, the so called off state.

[0182] The device for the regulation of light transmission preferably has another boundary state B when an characteristic electric field is applied, the so called on state, in which the liquid crystal medium is increasingly distorted away from the initial orientation towards the light scattering bend state, whereby

T.sub.A>T.sub.B.

[0183] The invention thus also relates to the use of the device according to the invention for the regulation of light entry and/or energy input into an interior.

[0184] As mentioned above, the invention is not restricted to buildings, but can also be used in transport containers, for example shipping containers, or vehicles. It is particularly preferred to install the device on glass panes of windows or to use it as a component of multipane insulating glass. The device according to the invention can be installed on the outside, the inside or, in the case of multipane glass, in the cavity between two glass panes, where the inside is taken to mean the side of a glass surface, which faces the interior. Preference is given to use on the inside or in the cavity between two glass panes in the case of multipane insulating glass.

[0185] The device according to the invention may completely cover the respective glass surface on which it is installed or only partly cover it. In the case of complete coverage, the influence on light transmission through the glass surface is at its maximum. In the case of partial coverage, by contrast, a certain amount of light is transmitted by the glass surface through the uncovered parts, even in the state of the device with low transmission. Partial coverage can be achieved, for example, by installing the devices on the glass surface in the form of strips or certain patterns.

[0186] In a preferred embodiment of the invention, the device regulates light trans-mission through the glass surface into the interior electrically.

[0187] The required applied electric field strength is mainly dependent on the electrode gap and the of the LC mixture.

[0188] The applied electric field strengths are typically lower than approximately 50 V/m.sup.1, preferably lower than approximately 30 V/m.sup.1 and more preferably lower than approximately 25 V/m.sup.1.

[0189] In a preferred embodiment, a DC electrical field is applied to the device in accordance with the present invention. Typically, the applied DC driving voltage is in the range from 0.1 V to approximately 25 V, more preferably in the range from approximately 0.3 V to approximately 20 V, and even more preferably in the range from approximately 0.5 V to approximately 15 V.

[0190] In another preferred embodiment, an AC electrical field is applied to the device in accordance with the present invention. Typically, the applied DC driving voltage is in the range from 0.1 V to approximately 150 V, more preferably in the range from approximately 0.3 V to approximately 125 V, and even more preferably in the range from approximately 0.5 V to approximately 100 V, each having a voltage frequency from 1 Hz to 100 Hz.

[0191] The way in which the devices according to the invention are produced is known to the person skilled in the art in the area of devices containing liquid-crystalline media.

[0192] However, a typical process for the production of a device for the regulation of light transmission according to the invention comprises the following steps: [0193] cutting and cleaning glass substrates, on which the electrodes are arranged, [0194] optionally, coating the substrates with an alignment layer or dielectric layer, [0195] assembling the cell using a UV curable adhesive, and [0196] filling the cell with the liquid-crystalline medium.

[0197] The device for the regulation of light transmission of the present invention can be used in various types of optical and electro-optical devices.

[0198] Said optical and electro optical devices include, without limitation electro optical displays, liquid crystal displays (LCDs), non-linear optic (NLO) devices, optical information storage devices and windows, preferably privacy windows.

[0199] Unless the context clearly indicates otherwise, as used herein plural forms of the terms herein are to be construed as including the singular form and vice versa.

[0200] The parameter ranges indicated in this application all include the limit values including the maximum permissible errors as known by the expert. The different upper and lower limit values indicated for various ranges of properties in combination with one another give rise to additional preferred ranges.

[0201] Throughout this application, the following conditions and definitions apply, unless expressly stated otherwise. All concentrations are quoted in percent by weight and relate to the respective mixture as a whole, all temperatures are quoted in degrees Celsius and all temperature differences are quoted in differential degrees. All physical properties are determined in accordance with Merck Liquid Crystals, Physical Properties of Liquid Crystals, Status November 1997, Merck KGaA, Germany, and are quoted for a temperature of 20 C., unless expressly stated otherwise. The optical anisotropy (n) is determined at a wavelength of 589.3 nm. The dielectric anisotropy () is determined at a frequency of 1 kHz or if explicitly stated at a frequency 19 GHz. The threshold voltages, as well as all other electro-optical properties, are determined using test cells produced at Merck KGaA, Germany. The test cells for the determination of have a cell thickness of approximately 20 m. The electrode is a circular ITO electrode having an area of 1.13 cm.sup.2 and a guard ring. The orientation layers are SE-1211 from Nissan Chemicals, Japan, for homeotropic orientation (e.sub.) and polyimide AL-1054 from Japan Synthetic Rubber, Japan, for homogeneous orientation (E.sub.). The capacitances are determined using a Solatron 1260 frequency response analyser using a sine wave with a voltage of 0.3 V.sub.rms. The light used in the electro-optical measurements is white light. A set-up using a commercially available DMS instrument from Autronic-Melchers, Germany, is used here.

[0202] Throughout the description and claims of this specification, the words comprise and contain and variations of the words, for example comprising and comprises, mean including but not limited to, and are not intended to (and do not) exclude other components. On the other hand, the word comprise also encompasses the term consisting of but is not limited to it.

[0203] 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.

[0204] Independent protection may be sought for these features in addition to, or alternative to any invention presently claimed.

[0205] Throughout the present application it is to be understood that the angles of the bonds at a C atom being bound to three adjacent atoms, e.g. in a CC or CO double bond or e.g. in a benzene ring, are 120 and that the angles of the bonds at a C atom being bound to two adjacent atoms, e.g. in a CC or in a CN triple bond or in an allylic position CCC are 180, unless these angles are otherwise restricted, e.g. like being part of small rings, like 3-, 5- or 5-atomic rings, notwithstanding that in some instances in some structural formulae these angles are not represented exactly.

[0206] 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. Alternative features serving the same, equivalent or similar purpose may replace each feature disclosed in this specification, unless stated otherwise. Thus, unless stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0207] 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).

[0208] Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following examples are, therefore, to be construed as merely illustrative and not limitative of the remainder of the disclosure in any way whatsoever.

[0209] The following abbreviations are used to illustrate the liquid crystalline phase behavior of the compounds: K=crystalline; N=nematic; N2=second nematic; S=smectic; Ch=cholesteric; I=isotropic; Tg=glass transition. The numbers between the symbols indicate the phase transition temperatures in C.

[0210] In the present application and especially in the following examples, the structures of the liquid crystal compounds are represented by abbreviations, which are also called acronyms. The transformation of the abbreviations into the corresponding structures is straightforward according to the following three tables A to C.

[0211] All groups C.sub.nH.sub.2n+1, C.sub.mH.sub.2m+1, and C.sub.1H2.sub.l+1 are preferably straight chain alkyl groups with n, m and l C-atoms, respectively, all groups C.sub.nH.sub.2n, C.sub.mH.sub.2m and C.sub.lH.sub.2l are preferably (CH.sub.2).sub.n, (CH.sub.2).sub.m and (CH.sub.2).sub.l, respectively and CHCH preferably is trans-respectively Evinylene.

[0212] Table A lists the symbols used for the ring elements, table B those for the linking groups and table C those for the symbols for the left hand and the right hand end groups of the molecules.

TABLE-US-00003 TABLE A Ring Elements [00029] C [00030] P [00031] D [00032] DI [00033] A [00034] AI [00035] G [00036] GI [00037] G(CI) [00038] GI(CI) [00039] G(1) [00040] GI(1) [00041] U [00042] UI [00043] Y [00044] M [00045] MI [00046] N [00047] NI [00048] np [00049] n3f [00050] n3fI [00051] th [00052] thI [00053] th2f [00054] th2fI [00055] o2f [00056] o2fI [00057] dh [00058] K [00059] KI [00060] L [00061] LI [00062] F [00063] FI

TABLE-US-00004 TABLE B Linking Groups n (CH.sub.2).sub.n E CH.sub.2CH.sub.2 V CHCH T CC W CF.sub.2CF.sub.2 B CFCF Z COO X CFCH O CH.sub.2O Q CF.sub.2O ZI OCO XI CHCF OI OCH.sub.2 OI OCF.sub.2 n is an integer except 0 and 2

TABLE-US-00005 TABLE C End Groups Left hand side, used alone or in Right hand side, used alone or combination with others in combination with others -n- C.sub.nH.sub.2n+1 -n C.sub.nH.sub.2n+1 -nO- C.sub.nH.sub.2n+1O -nO OC.sub.nH.sub.2n+1 -V- CH.sub.2CH -V CHCH.sub.2 -nV- C.sub.nH.sub.2n+1CHCH -nV C.sub.nH.sub.2nCHCH.sub.2 -Vn- CH.sub.2CHC.sub.nH.sub.2n -Vn CHCHC.sub.nH.sub.2n+1 -nVm- C.sub.nH.sub.2n+1CHCHC.sub.mH.sub.2m -nVm C.sub.nH.sub.2nCHCHC.sub.mH.sub.2m+1 -N- NC -N CN -S- SCN -S NCS -F- F -F F -CL- Cl -CL Cl -M- CFH.sub.2 -M CFH.sub.2 -D- CF.sub.2H -D CF.sub.2H -T- CF.sub.3 -T CF.sub.3 -MO- CFH.sub.2O -OM OCFH.sub.2 -DO- CF.sub.2HO -OD OCF.sub.2H -TO- CF.sub.3O -OT OCF.sub.3 -A- HCC -A CCH -nA- C.sub.nH.sub.2n+1CC -An CCC.sub.nH.sub.2n+1 -NA- NCCC -AN CCCN Left hand side, used in Right hand side, used in combination with others only combination with others only - . . . n . . . - C.sub.nH.sub.2n - . . . n . . . C.sub.nH.sub.2n - . . . M . . . - CFH - . . . M . . . CFH - . . . D . . . - CF.sub.2 - . . . D . . . CF.sub.2 - . . . V . . . - CHCH - . . . V . . . CHCH - . . . Z . . . - COO - . . . Z . . . COO - . . . ZI . . . - OCO - . . . ZI . . . OCO - . . . K . . . - CO - . . . K . . . CO - . . . W . . . - CFCF - . . . W . . . CFCF
wherein n und m each are integers and three points . . . indicate a space for other symbols of this table.

TABLE-US-00006 TABLE D Table D indicates possible stabilisers which can be added to the LC media (n here denotes an integer from 1 to 12, terminal methyl groups ar not shown). [00064] [00065] [00066] [00067] [00068] [00069] [00070] [00071] [00072] [00073] [00074] [00075] [00076] [00077] [00078] [00079] [00080] [00081] [00082] [00083] [00084] [00085] [00086] [00087] [00088] [00089] [00090] [00091] [00092] [00093] [00094] [00095] [00096] [00097] [00098]

[0213] The LC media preferably comprise 0 to 10% by weight, in particular 1 ppm to 5% by weight and particularly preferably 1 ppm to 3% by weight, of stabilisers. The LC media preferably comprise one or more stabilisers selected from the group consisting of compounds from Table D.

TABLE-US-00007 TABLE D Preferably the liquid crystalline media according to the present invention comprise, besides the compound(s) of formula A-I to A-III one or more compounds selected from the group of compounds of the formulae of the following table. [00099] F-PGI-O-n-O-GP-F [00100] F-PG-O-n-O-GIP-F [00101] N-PP-O-n-O-GU-F [00102] N-PP-O-n-O-PG-OT [00103] F-PGI-O-n-O-PP-N [00104] F-UIGI-ZI-n-Z-GU-F [00105] N-PGI-ZI-n-Z-GP-N [00106] F-UIGI-ZI-n-Z-GP-N [00107] F-UIGI-ZI-n-Z-GP-F [00108] N-PGI-ZI-n-Z-GP-F [00109] N-PP-ZI-n-Z-GP-F [00110] N-PP-ZI-n-Z-PG-OT [00111] F-PGI-ZI-n-Z-GP-F [00112] F-PGI-ZI-n-Z-PP-N [00113] F-PGI-ZI-n-Z-PU-N [00114] F-PGI-ZI-n-Z-PUU-N [00115] N-GIGIGI-n-GGG-N [00116] N-PGIUI-n-UGP-N [00117] N-GIUIGI-n-GUG-N [00118] N-GIUIP-n-PUG-N [00119] N-PGI-n-GP-N [00120] N-PUI-n-UP-N [00121] N-UIUI-n-UU-N [00122] N-GIGI-n-GG-N [00123] N-PGI(Me)-n-G(Me)P-N [00124] F-UIGI-n-GU-F [00125] UIP-n-PU [00126] N-PGI-n-GP-N [00127] N-PG(Me)-n-GI(Me)P-N

EXAMPLES

[0214] The following mixture M1 is prepared:

TABLE-US-00008 Amount Compound [%-w/w] N-PP-ZI-9-Z-PG-OT 4.0 F-PGI-ZI-7-Z-PP-N 15.0 F-PGI-ZI-9-Z-PU-N 8.6 F-PGI-ZI-9-Z-PUU-N 5.7 F-UIGI-ZI-9-Z-GP-N 11.4 N-PGI-ZI-5-Z-GP-F 12.9 N-PP-ZI-9-Z-GP-F 15.8 N-PP-O-7-O-PG-OT 26.7

[0215] The following mixture M2 is prepared:

TABLE-US-00009 Amount Compound [%-w/w] N-PP-ZI-9-Z-PG-OT 3.97 F-PGI-ZI-7-Z-PP-N 14.91 F-PGI-ZI-9-Z-PU-N 8.57 F-PGI-ZI-9-Z-PUU-N 5.66 F-UIGI-ZI-9-Z-GP-N 11.39 N-PGI-ZI-5-Z-GP-F 12.82 N-PP-ZI-9-Z-GP-F 15.69 N-PP-O-7-O-PG-OT 26.60 F357 (dye) 0.19 F593 (dye) 0.21

[0216] Experimental Set-Up

[0217] All measurements are made using a BX 51 microscope (Olympus) with sample mounted on a hotstage (Linkam) set to 25 C. The sample is positioned at the focal plane of an 10 objective lens with N.A:=0.25. The sample is rotated between crossed polarisers until maximum transmission is achieved then the top polarizer is removed from the optical path. The light intensity is measured using a SM1 PD1A photodiode and PDA-200C Photodiode Amplifier (supplied by Thor Labs) and signal captured and recorded via a computer interface in Labview 2013 (National Instruments).

Example 1

[0218] A test cell having a cell gap of 6 m and consisting of two glass substrates, an opposing electrode structure covered with anti-parallel rubbed homogeneous alignment layers (PI) is filled with the liquid crystal mixture M-1. The cell appears transparent with unpolarised light. Upon application of an electric field of 10 V (DC) the cell switches gradually to a translucent and then to a strongly scattering state exhibiting a clear white appearance. The reversible effect is depicted in FIGS. 1 and 2.

Example 2

[0219] A test cell having a cell gap of 6 m and consisting of two glass substrates, an opposing electrode structure covered with anti-parallel rubbed homogeneous alignment layers (PI) is filled with the liquid crystal mixture M-1. The cell appears transparent with unpolarised light. Upon application of an increasing electric field (AC) with a voltage frequency of 1 Hz the cell switches gradually to a translucent and then to a strongly scattering state exhibiting a clear white appearance. The effect is depicted in FIG. 3.

Example 3

[0220] A test cell having a cell gap of 6 m and consisting of two glass substrates, an opposing electrode structure covered with anti-parallel rubbed homogeneous alignment layers (PI) is filled with the liquid crystal mixture M-1. The cell appears transparent with unpolarised light. Upon application of an increasing electric field (AC) with a voltage frequency of 100 Hz the cell switches gradually to a translucent and then to a strongly scattering state exhibiting a clear white appearance. The effect is depicted in FIG. 4.

Example 4

[0221] A test cell having a cell gap of 3.5 m and consisting of two glass substrates, an IPS electrode structure having an electrode width of 3 m and an electrode spacing of 5 m, which is covered with a rubbed (Rubbing direction: 80 with respect to the electrodes) homogeneous alignment layers (PI) is filled with the liquid crystal mixture M-1. The cell appears transparent with unpolarised light. Upon application of an electric field of 15 V (DC) the cell switches gradually to a translucent and then to a scattering state exhibiting a hazy appearance. The reversible effect is depicted in FIGS. 5 and 6.

Example 5

[0222] A test cell having a cell gap of 3.5 m and consisting of two glass substrates, an IPS electrode structure having an electrode width of 3 m and an electrode spacing of 5 m, which is covered with a rubbed (Rubbing direction: 80 with respect to the electrodes) homogeneous alignment layers (PI)) is filled with the liquid crystal mixture M-1. The cell appears transparent with unpolarised light. Upon application of an increasing electric field (AC) with a voltage frequency of 1 Hz the cell switches gradually to a translucent and then to a strongly scattering state exhibiting a clear white appearance. The effect is depicted in FIG. 7.

Example 6

[0223] A test cell having a cell gap of 3.5 m and consisting of two glass substrates, an IPS electrode structure having an electrode width of 3 m and an electrode spacing of 5 m, which is covered with a rubbed (Rubbing direction: 80 with respect to the electrodes) homogeneous alignment layers (PI) is filled with the liquid crystal mixture M-1. The cell appears transparent with unpolarised light. Upon application of an increasing electric field (AC) with a voltage frequency of 100 Hz the cell switches gradually to a translucent and then to a scattering state exhibiting a hazy appearance. The effect is depicted in FIG. 8.

Example 7

[0224] A test cell having a cell gap of 10 m and consisting of two glass substrates, an IPS electrode structure having an electrode width of 10 m and an electrode spacing of 10 m, is filled with the liquid crystal mixture M-1. The cell appears transparent with unpolarised light. Upon application of an increasing electric field (AC) with a voltage frequency of 1 Hz the cell switches gradually to a translucent and then to a strongly scattering state exhibiting a clear white appearance. The effect is depicted in FIG. 9.

Example 8

[0225] A test cell having a cell gap of 10 m and consisting of two glass substrates, an IPS electrode structure having an electrode width of 10 m and an electrode spacing of 10 m, is filled with the liquid crystal mixture M-1. The cell appears transparent with unpolarised light. Upon application of an increasing electric field (AC) with a voltage frequency of 100 Hz the cell switches gradually to a translucent and then to a scattering state exhibiting a hazy appearance. The effect is depicted in FIG. 10.

Example 9

[0226] A test cell having a cell gap of 6 m and consisting of two glass substrates, an opposing electrode structure covered with anti-parallel rubbed homogeneous alignment layers (PI) is filled with the liquid crystal mixture M-2. The cell appears transparent with unpolarised light. Upon application of an electric field of 10 V (DC) the cell switches gradually to a translucent and then to a strongly scattering state exhibiting a clear white appearance. The reversible effect is depicted in FIGS. 11 and 12.

Example 10

[0227] A test cell having a cell gap of 6 m and consisting of two glass substrates, an opposing electrode structure covered with anti-parallel rubbed homogeneous alignment layers (PI) is filled with the liquid crystal mixture M-2. The cell appears transparent with unpolarised light. Upon application of an increasing electric field (AC) with a voltage frequency of 1 Hz the cell switches gradually to a translucent and then to a strongly scattering state exhibiting a clear white appearance. The effect is depicted in FIG. 13.

Example 11

[0228] A test cell having a cell gap of 6 m and consisting of two glass substrates, an opposing electrode structure covered with anti-parallel rubbed homogeneous alignment layers (PI) is filled with the liquid crystal mixture M-2. The cell appears transparent with unpolarised light. Upon application of an increasing electric field (AC) with a voltage frequency of 100 Hz the cell switches gradually to a translucent and then to a strongly scattering state exhibiting a clear white appearance. The effect is depicted in FIG. 14.