LIQUID-CRYSTALLINE MEDIUM

Abstract

The invention relates to compounds of the formula I, and to a liquid-crystalline medium, preferably having a nematic phase and negative dielectric anisotropy, which comprises a) one or more compounds of the formula I

##STR00001## and b) one or more compounds of the formula II

##STR00002##

in which the parameters have the respective meanings indicated in Claim 1, to the use thereof in an electro-optical display, particularly in an active-matrix display based on the VA, ECB, PALC, FFS or IPS effect,

Claims

1. Liquid-crystalline medium comprising a) one or more compounds of the formula I, ##STR00249## in which n denotes an integer from 1 to 4, preferably 1, 2 or 3, particularly preferably 2 or 3, and very particularly preferably 2, m denotes (4-n), ##STR00250## denotes an organic radical having 4 bonding sites, preferably an alkanetetrayl unit having 1 to 20 C atoms, in which, in addition to the m groups R.sup.12 present in the molecule, but independently thereof, a further H atom may be replaced by R.sup.12 or a plurality of further H atoms may be replaced by R.sup.12, preferably a straight-chain alkanetetrayl unit having one valence on each of the two terminal C atoms, in which one CH.sub.2 group or a plurality of CH.sub.2 groups may be replaced by O or (CO) in such a way that two O atoms are not bonded directly to one another, or a substituted or unsubstituted aromatic or heteroaromatic hydrocarbon radical having 1 to 4 valences, in which, in addition to the groups R.sup.12 present in the molecule, but independently thereof, a further H atom may be replaced by R.sup.12 or a plurality of further H atoms may be replaced by R.sup.12, Z.sup.11 and Z.sup.12, independently of one another, denote O, (CO) or a single bond, but do not both simultaneously denote O, r and s, independently of one another, denote 0 or 1, R.sup.11 on each occurrence, independently of one another, denotes a straight-chain or branched alkyl chain having 1-20 C atoms, in which one CH.sub.2 group or a plurality of CH.sub.2 groups may be replaced by O or C(O), but two adjacent CH.sub.2 groups cannot be replaced by O, a cycloalkyl or alkylcycloalkyl unit, a hydrocarbon radical which contains a cycloalkyl or alkylcycloalkyl unit and in which one CH.sub.2 group or a plurality of CH.sub.2 groups may be replaced by O or C(O), but two adjacent CH.sub.2 groups cannot be replaced by O, an aryl or arylalkyl unit, a hydrocarbon radical which contains an aryl or arylalkyl unit and in which one CH.sub.2 group or a plurality of CH.sub.2 groups may be replaced by O or C(O), but two adjacent CH.sub.2 groups cannot be replaced by O, or ##STR00251## (cyclohexyl), in which one or more CH.sub.2 groups may be replaced by O or CO, or an acetophenyl, isopropyl or 3-heptyl radical, and R.sup.12 on each occurrence, independently of one another, denotes H, F, a straight-chain or branched alkyl chain having 1-20 C atoms, in which one CH.sub.2 group or a plurality of CH.sub.2 groups may be replaced by O or C(O), but two adjacent CH.sub.2 groups cannot be replaced by O, a hydrocarbon radical which contains a cycloalkyl or alkylcycloalkyl unit and in which one CH.sub.2 group or a plurality of CH.sub.2 groups may be replaced by O or C(O), but two adjacent CH.sub.2 groups cannot be replaced by O, or an aromatic or heteroaromatic hydrocarbon radical, b) one or more compounds of the formula II, ##STR00252## in which R.sup.21 denotes an unsubstituted alkenyl radical having 2 to 7 C atoms, R.sup.22 denotes an unsubstituted alkyl radical having 1 to 7 C atoms or an unsubstituted alkoxy radical having 1 to 6 C atoms, ##STR00253## denotes ##STR00254## p and q each, independently of one another, denote 0, 1 or 2 and (p+q) denotes 1, 2 or 3.

2. Medium according to claim 1, characterised in that, in formula I, the group ##STR00255## on each occurrence denotes ##STR00256##

3. Medium according to claim 1, characterised in that it comprises one or more compounds of the formula I selected from the compounds of the formulae I-1 to I-4, ##STR00257## in which the parameters have the meanings indicated in claim 1 and t denotes an integer from 1 to 12 and R.sup.11 and R.sup.11 each, independently of one another, have one of the meanings given for R.sup.11.

4. Medium according to claim 1, characterised in that it comprises one or more compounds of the formula I selected from the compounds of the formulae I-1-1 to I-1-3 and I-5-1, ##STR00258##

5. Liquid-crystalline medium according to claim 1, characterised in that it additionally comprises one or more compounds selected from the group of the compounds of the formulae II-1 to II-4, ##STR00259## in which R.sup.21 denotes an unsubstituted alkyl radical having 1 to 7 C atoms, R.sup.22 denotes an unsubstituted alkyl radical having 1 to 7 C atoms or an unsubstituted alkoxy radical having 1 to 6 C atoms, and m, n and o each, independently of one another, denote 0 or 1.

6. Liquid-crystalline medium according to claim 1, characterised in that it additionally comprises one or more compounds of the formula III-3, ##STR00260## in which alkoxy, alkoxy, independently of one another, denote an alkoxy radical having 1 to 5 C atoms.

7. Liquid-crystalline medium according to claim 1, characterised in that the total concentration of the compounds of the formula I in the entire medium is 1 ppm or more to 1000 ppm or less.

8. Medium according to claim 1, characterised in that it additionally comprises one or more compounds of the formula IV, ##STR00261## in which R.sup.41 denotes an unsubstituted alkyl radical having 1 to 7 C atoms or an unsubstituted alkenyl radical having 2 to 7 C atoms, and R.sup.42 denotes an unsubstituted alkyl radical having 1 to 7 C atoms, an unsubstituted alkoxy radical having 1 to 6 C atoms or an unsubstituted alkenyl radical having 2 to 7 C atoms.

9. Medium according to claim 1, characterised in that the total concentration of the compounds of the formula II in the entire medium is 25% or more to 45% or less.

10. Medium according to claim 5, characterised in that it comprises one or more compounds of the formula II-3.

11. Electro-optical display or electro-optical component, characterised in that it contains a liquid-crystalline medium according to claim 1.

12. Display according to claim 11, characterised in that it is based on the VA or ECB effect.

13. Display according to claim 11, characterised in that it has an active-matrix addressing device.

14. An electro-optical display or in an electro-optical component, comprising a medium according to claim 1.

15. Process for the preparation of a liquid-crystalline medium according to claim 1, characterised in that one or more compounds of the formula I are mixed with one or more compounds of the formulae II.

Description

EXAMPLES

[0308] The following examples explain the present invention without restricting it in any way. However, the physical properties make it clear to the person skilled in the art what properties can be achieved and in what ranges they can be modified. In particular, the combination of the various properties which can preferably be achieved is thus well defined for the person skilled in the art.

[0309] Liquid-crystal mixtures having the compositions and properties as indicated in the following tables are prepared and investigated. The improved stability of the mixtures comprising compounds of the formula I is demonstrated by comparison with unstabilised base mixtures as reference (Ref.).

Examples 1.1 to 1.4

[0310] The following mixture (M-1) is prepared and investigated.

TABLE-US-00009 Mixture M-1 Composition Compound Concentration/ No. Abbreviation % by weight Physical properties 1 CY-3-O2 15.0 T(N, I)= 80.1 C. 2 PY-3-O2 8.0 n.sub.e(20 C., 589 nm)= 1.5858 3 CCY-3-O1 6.0 n(20 C., 589 nm)= 0.1033 4 CCY-3-O2 8.0 .sub.(20 C., 1 kHz)= 7.6 5 CLY-3-O2 8.0 (20 C., 1 kHz)= 4.0 6 CPY-2-O2 8.0 .sub.1(20 C.)= 113 mPa .Math. s 7 CPY-3-O2 12.0 k.sub.11(20 C.)= 14.4 pN 9 CC-3-V 30.5 k.sub.33(20 C.)= 17.0 pN 10 CPP-3-2 4.5 V.sub.0*(20 C.)= 2.08 V 100.0 V.sub.10(20 C.)= 2.14 V V.sub.20(20 C.)= 2.43 V V.sub.30(20 C.)= 2.66 V V.sub.50(20 C.)= 3.07 V V.sub.70(20 C.)= 3.58 V V.sub.90(20 C.)= 4.46 V V.sub.100(20 C.)= 6.50 V Notes: *V.sub.0 capacitive measurement in homeotropic cells. The table with the electro-optical data indicates the voltage at which the transmission indicated in the index maximised to 100% is achieved. (Measurement temperature = 20 C., layer thickness of the cell = 3.5 m). Mixture M-1 is divided into five parts and investigated as described below. Firstly, the stability of the voltage holding ratio of the mixture (M-1) itself is determined. Mixture M-1 is investigated in a test cell having an alignment material for homogeneous alignment and flat ITO electrodes for its stability to light exposure, as caused by typical backlighting used, for example, in a television set (TV). To this end, the filled cells sealed with UV adhesive are firstly measured before exposure to the backlight. This represents the initial VHR value. To this end, the voltage holding ratio is in each case determined after an appropriate temperature equalisation time of about 15 min to 30 min, measured between room temperature and 100 C., with voltages between 1 V and 5 V and frequencies of 1 Hz and 100 Hz (depending on the indication in the results). The test cells are subsequently stored between two TV backlight units in each case a) at a temperature of about 40 C., b) at a higher temperature with additional exposure to alternating voltage of 10 V and c) at a higher temperature of 60 C. The results are summarised in Tables 1, 2 and 3. Here, as below, four to six test cells are filled and investigated in each case for each individual mixture. The values indicated are the average of the individual values.

[0311] Next, in each case 300 ppm each of a different compound of three compounds of the formula I-1 or I-5, more precisely of the corresponding sub-formulae I-1-1, I-1-2, I-1-3 or I-5-1,

##STR00247##

are added to the remaining four parts of mixture M-1, and the resultant mixtures (M-1-1, M-1-2, M-1-3 and M-1-4) are investigated for their stability, as described above. The results are shown in Tables 1 to 3 below.

[0312] The relative deviations of the voltage holding ratio values in various measurement series are typically in the range from about 3 to 4%.

TABLE-US-00010 TABLE 1 (exposure to backlighting, 40 C.) c(stab.)/ VHR(t, 70 C., 1 V, 1 Hz)/% Ex. Mixture Stabiliser ppm t = 0 h t = 72 h t = 168 h t = 480 h (Ref.) M-1 none 0 89.7 80.6 77.3 75.0 1.1 M-1-1 I-1-1 300 88.9 82.5 80.0 77.5 1.2 M-1-2 I-1-2 300 88.5 79.9 79.9 74.1 1.3 M-1-3 I-1-3 300 89.0 80.6 80.6 75.8 1.4 M-1-4 I-5-1 300 t.b.d. t.b.d. t.b.d. t.b.d. Note: t.b.d.: to be determined.

TABLE-US-00011 TABLE 2 (exposure to backlighting, 10 V (a.c.), 60 C.) c(stab.)/ VHR(t, 70 C., 1 V, 1 Hz)/% Ex. Mixture Stabiliser ppm t = 0 h t = 72 h t = 168 h t = 480 h (Ref.) M-1 none 0 90.8 71.5 74.2 72.4 1.1 M-1-1 I-1-1 300 89.6 74.1 75.4 78.2 1.2 M-1-2 I-1-2 300 89.0 71.8 73.4 75.0 1.3 M-1-3 I-1-3 300 89.8 73.9 76.3 77.5 1.4 M-1-4 I-5-1 300 t.b.d. t.b.d. t.b.d. t.b.d. Note: t.b.d.: to be determined.

TABLE-US-00012 TABLE 3 (exposure to backlighting, 60 C.) c(stab.)/ VHR(t, 70 C., 1 V, 1 Hz)/% Ex. Mixture Stabiliser ppm t = 0 h t = 72 h t = 168 h t = 480 h (Ref.) M-1 none 0 91.1 72.6 71.3 65.8 1.1 M-1-1 I-1-1 300 89.3 75.4 77.5 78.4 1.2 M-1-2 I-1-2 300 89.5 72.3 71.5 69.3 1.3 M-1-3 I-1-3 300 89.4 72.5 72.3 71.2 1.4 M-1-4 I-5-1 300 t.b.d. t.b.d. t.b.d. t.b.d. Note: t.b.d.: to be determined.

[0313] It is readily evident here that the compounds of the formulae I-1-1, I-1-2, I-1-3 and I-5-1 exhibit clearly stabilising properties, even in relatively low concentrations.

[0314] Compounds I-1-1 to I-1-3 and I-5-1 have excellent stabilisation activity in a concentration of 300 ppm. This results in a reduction in the risk of image sticking on exposure to backlighting.

Examples 2.1 to 2.4

[0315] The following mixture (M-2) is prepared and investigated.

TABLE-US-00013 Mixture M-2 Composition Compound Concentration/ No. Abbreviation % by weight Physical properties 1 CY-3-O2 15.0 T(N, I)= 79.1 C. 2 CY-5-O2 9.5 n.sub.e(20 C., 589 nm)= 1.5744 3 CCY-3-O1 4.0 n(20 C., 589 nm)= 0.0944 4 CCY-3-O2 6.0 .sub.(20 C., 1 kHz)= 7.7 5 CCY-3-O3 4.5 (20 C., 1 kHz)= 4.0 6 CCY-4-O2 6.0 .sub.1(20 C.)= 120 mPa .Math. s 7 CCY-5-O2 4.0 k.sub.11(20 C.)= 13.4 pN 8 CPY-2-O2 8.0 k.sub.33(20 C.)= 15.4 pN 9 CPY-3-O2 9.0 V.sub.0*(20 C.)= 2.06 V 10 PYP-2-4 2.0 11 CC-3-V 32.0 100.0 Notes: *V.sub.0 capacitive measurement in homeotropic cells. Mixture M-2 is divided into five parts, and 300 ppm of one of the four compounds of the formulae I-1-1, I-1-2, I-1-3 and I-5-1 are added to each of four of these five parts (mixtures M-2-1, M-2-2, M-2-3 and M-2-4), and all mixtures are investigated in test cells for their stability to UV exposure in the sun test analogously to the procedure described in Examples 1.1 to 1.4. The results of the VHR measurements after irradiation for 30 min are summarised in Table 4.

TABLE-US-00014 TABLE 4 c(stab.)/ VHR(t)/% Ex. Mixture Stabiliser ppm t = 0 h t = 30 min (Ref.) M-2 none 0 t.b.d. t.b.d. 2.1 M-2-1 I-1-1 300 t.b.d. t.b.d. 2.2 M-2-2 I-1-2 300 t.b.d. t.b.d. 2.3 M-2-3 I-1-3 300 t.b.d. t.b.d. 2.4 M-2-4 I-5-1 300 t.b.d. t.b.d. (VHR: 60 C., 1 V, 60 Hz) Note: t.b.d.: to be determined.

[0316] As can be seen from Table 4, even low concentrations of the compounds I-1-1, I-1-2, I-1-3 and I-5-1 result in a considerable improvement in the final value for the VHR after UV exposure.

Examples 3.1 to 3.4 and Comparative Example 3-V

[0317] The following mixture (M-3) is prepared and investigated.

TABLE-US-00015 Mixture M-3 Composition Compound Concentration/ No. Abbreviation % by weight 1 CY-3-O2 11.0 2 PY-3-O2 12.0 3 CCY-3-O2 4.0 4 CCY-3-O3 7.0 5 CCY-4-O2 8.0 6 CLY-3-O2 8.0 7 CPY-2-O2 7.0 8 CPY-3-O2 11.0 9 CC-3-V 23.5 10 CC-3O1 4.0 11 CPP-3-2 4.5 100.0 Physical properties T(N, I) = 86.0 C. n.sub.e(20 C., 589 nm) = 1.5962 n(20 C., 589 nm) = 0.1118 .sub.(20, 1 kHz) = 8.0 (20, 1 kHz) = 4.3 .sub.1(20 C.) = 143 mPa .Math. s k.sub.11(20 C.) = 15.0 pN k.sub.33(20 C.) = 16.7 pN V.sub.0* (20 C.) = 2.08 V V.sub.10(25 C.) = 2.17 V V.sub.20(25 C.) = 2.48 V V.sub.30(25 C.) = 2.71 V V.sub.50(25 C.) = 3.14 V V.sub.70(25 C.) = 3.67 V V.sub.90(25 C.) = 4.59 V V.sub.100(25 C.) = 6.80 V Notes: *) V.sub.0 capacitive measurement in homeotropic cells. The table with the electro-optical data indicates the voltage at which the transmission indicated in the index maximised to 100% is achieved. (Measurement temperature = 25 C., layer thickness of the cell = 3.2 m). Mixture M-3 is prepared and divided into six parts. 300 ppm of the compounds I-1-1, I-1-2, I-1-3 or I-5-1 are added to each part (mixtures M-3-1 to M-3-4). For comparison, 150 ppm of a stabiliser from the prior art (compound VII, mixture V-3) are added to a further part. [00248]

[0318] The VHR is investigated before and after an irradiation duration of 476 h with a light-emitting diode (LED) LCD backlight analogously to the experiments described above. The results are summarised in Table 5.

TABLE-US-00016 TABLE 5 c(stab.)/ VHR(t)/% Ex. Mixture Stabiliser ppm t = 0 h t = 476 h (Ref.) M-3 none 0 82.7 66.4 3.1 M-3-1 I-1-1 300 85.7 69.1 3.2 M-3-2 I-1-2 300 t.b.d. t.b.d. 3.3 M-3-3 I-1-3 300 t.b.d. t.b.d. 3.4 M-3-4 I-5-1 300 t.b.d. t.b.d. 3-V V-3 VII 150 79.8 71.6 (VHR: 100 C., 1 V, 60 Hz) Note: t.b.d.: to be determined.

Examples 4.1 to 4.4 and Comparative Example 4-V

[0319] The following mixture (M-4) is prepared and investigated.

TABLE-US-00017 Mixture M-4 Composition Compound Concentration/ No. Abbreviation % by weight Physical properties 1 CY-3-O2 12.0 T(N, I)= 86.5 C. 2 CY-3-O4 2.0 n.sub.e(20 C., 589 nm)= 1.5924 3 CY-5-O2 12.0 n(20 C., 589 nm)= 0.1092 4 CCY-3-O1 6.0 .sub.(20 C., 1 kHz)= 7.9 5 CCY-3-O2 8.0 (20 C., 1 kHz)= 4.2 6 CCY-4-O2 8.0 .sub.1(20 C.)= 155 mPa .Math. s 7 CPY-2-O2 9.0 k.sub.11(20 C.)= 14.6 pN 8 CPY-3-O2 9.0 k.sub.33(20 C.)= 16.6 pN 9 PYP-2-3 5.0 V.sub.0*(20 C.)= 2.08 V 10 CC-3-V1 5.0 11 CC-3-V 19.0 12 CPP-3-2 5.0 100.0 Notes: *V.sub.0 capacitive measurement in homeotropic cells. Mixture M-4 is prepared and divided into six parts. 300 ppm of the compounds I-1-1, I-1-2, I-1-3 or I-5-1 are added to each part (mixtures M-4-1 to M-4-4). For comparison, 100 ppm of a stabiliser from the prior art (compound VII, mixture V-4) are added to a further part.

TABLE-US-00018 TABLE 6 VHR(t)/% c(stab.)/ t = 30 min Ex. Mixture Stabiliser ppm t = 0 h sun test (Ref.) M-4 none 0 74.3 68.2 4.1 M-4-1 I-1-1 100 77.6 73.4 4.2 M-4-2 I-1-2 300 74.3 68.2 4.3 M-4-3 I-1-3 300 76.8 70.4 4.4 M-4-4 I-5-1 300 76.0 70.1 4-V V-4 VII 100 73.2 68.5 (VHR: 100 C., 1 V, 60 Hz) Note: t.b.d.: to be determined.

Examples 5.1 to 5.4 and Comparative Example 5-V

[0320] The following mixture (M-5) is prepared and investigated.

TABLE-US-00019 Mixture M-5 Composition Compound Concentration/ No. Abbreviation % by weight Physical properties 1 CCY-3-O1 8.0 T(N, I)= 76.0 C. 2 CCY-4-O2 3.0 n.sub.e(20 C., 589 nm)= 1.5830 3 CLY-3-O2 8.0 n(20 C., 589 nm)= 0.1025 4 CLY-3-O3 4.0 .sub.(20 C., 1 kHz)= 7.4 5 CPY-2-O2 6.5 (20 C., 1 kHz)= 3.7 6 CPY-3-O2 4.0 .sub.1(20 C.)= 90.0 mPa .Math. s 7 B-2O-O5 4.0 k.sub.11(20 C.)= 13.9 pN 8 CC-3-V 41.5 k.sub.33(20 C.)= 14.8 pN 9 PY-1-O4 5.0 V.sub.0*(20 C.)= 2.1 V 10 PY-3-O2 11.5 11 CCY-3-O2 4.5 100.0 Notes: *V.sub.0 capacitive measurement in homeotropic cells.

TABLE-US-00020 TABLE 7 c(stab.)/ VHR(t)/% Ex. Mixture Stabiliser ppm t = 0 h t = 476 h (Ref.) M-5 none 0 91.9 60.2 5.1 M-5-1 I-1-1 300 91.6 64.2 5.2 M-5-2 I-1-2 300 t.b.d. t.b.d. 5.3 M-5-3 I-1-3 300 t.b.d. t.b.d. 5.4 M-5-4 I-5-1 300 93.0 67.3 5-V V-5 VII 150 t.b.d. t.b.d. (VHR: 20 C., 1 V, 1 Hz) Note: t.b.d.: to be determined.

Examples 6.1 to 6.4 and Comparative Example 6-V

[0321] The following mixture (M-6) is prepared and investigated.

TABLE-US-00021 Mixture M-6 Composition Compound Concentration/ No. Abbreviation % by weight Physical properties 1 CC-3-V 30.5 T(N, I)= 80.1 C. 2 CC-3-V1 4.5 n.sub.e(20 C., 589 nm)= 1.5858 3 CCY-3-O1 6.0 n(20 C., 589 nm)= 0.1033 4 CCY-3-O2 8.0 .sub.(20 C., 1 kHz)= 7.6 5 CLY-3-O2 8.0 (20 C., 1 kHz)= 4.0 6 CPY-2-O2 8.0 .sub.1(20 C.)= 113 mPa .Math. s 7 CPY-3-O2 12.0 k.sub.11(20 C.)= 14.4 pN 8 CY-3-O2 15.0 k.sub.33(20 C.)= 17.0 pN 9 PY-3-O2 8.0 V.sub.0*(20 C.)= 2.16 V 100.0 Notes: *V.sub.0 capacitive measurement in homeotropic cells. Mixture M-6 is divided into six parts, and 300 ppm of one of the four compounds I-1-1, I-1-2, I-1-3 and I-5-1 are in each case added to four thereof. For comparison, 150 ppm of compound VII are added to a further part. The mixtures are subsequently subjected to an exposure test with an LCD backlight as described in Examples 1.1 to 1.4, and comparably good results are obtained.