Difluoromethoxy-bridge liquid crystal compound containing methyl-substituted 2,3-difluorophenyl and crystal composition

Abstract

Provided are a difluoromethoxy-bridge liquid crystal compound containing methyl-substituted 2,3-difluorophenyl, a liquid crystal composition containing the compound, and a liquid crystal display element and a liquid crystal display, wherein said liquid crystal composition is represented by the following formula I: ##STR00001##
wherein the difluoromethoxy-bridge liquid crystal compound containing methyl-substituted 2,3-difluorophenyl not only has a high clearing point (CP) and a prominent low-temperature miscibility with other liquid crystals, but also has a good stability to ultraviolet light, stability to high temperatures, and particularly also a high vertical dielectric constant (ε.sub.⊥), and may be applied to the formulation of various types of liquid crystal compositions, and it is particularly prominent that the compound has the advantages of both a good low-temperature miscibility and a high vertical dielectric constant (ε.sub.⊥).

Claims

1. A difluoromethoxy-bridge liquid crystal compound containing methyl-substituted 2,3-difluorophenyl, represented by formula I3, I5 to I18, ##STR00074## ##STR00075## ##STR00076## wherein R.sub.1 represents H, an alkyl group having a carbon atom number of 1-5, an alkenyl group having a carbon atom number of 2-6 or an alkoxy group having a carbon atom number of 1-5, with any CH.sub.2 in R.sub.1 being optionally substituted with cyclopentyl, cyclobutyl or cyclopropyl, any CH.sub.2 not connected to O being optionally substituted with O and any one or more hydrogen atoms being optionally replaced with fluorine atom; and Y represents H, F, Cl, CN, an alkyl group having a carbon atom number of 1-5, an alkenyl group having a carbon atom number of 2-6 or an alkoxy group having a carbon atom number of 1-5, with any CH.sub.2 not connected to O being optionally substituted with O and any one or more hydrogen atoms being optionally replaced with fluorine atom; ##STR00077## represents ##STR00078##

2. A liquid crystal composition, wherein said liquid crystal composition comprises one or more difluoromethoxy-bridge liquid crystal compounds containing methyl-substituted 2,3-difluorophenyl of claim 1.

3. The liquid crystal composition according to claim 2, wherein said liquid crystal composition further comprises one or more compounds represented by formula II, ##STR00079## wherein R.sub.2 and R.sub.3 each independently represent an alkyl group having a carbon atom number of 1-5, an alkenyl group having a carbon atom number of 2-6 or an alkoxy group having a carbon atom number of 1-5; m represents 1 or 2; and ##STR00080## and ##STR00081## each independently represent one or more selected from phenylene, cyclohexylene and cyclohexenylene.

4. The liquid crystal composition according to claim 3, wherein the content in mass percentage of the compound represented by formula I is 1-40%, and the content in mass percentage of the compound represented by formula II is 1-65%.

5. The liquid crystal composition according to claim 3, wherein said one or more compounds represented by formula II are selected from the group consisting of compounds represented by formulas II1 to II22 below: ##STR00082## ##STR00083##

6. The liquid crystal composition according to claim 2, wherein said liquid crystal composition comprises one or more of compounds represented by formulas III1 to III14 below: ##STR00084## ##STR00085## R.sub.4 represents H, an alkyl group having a carbon atom number of 1-5, an alkenyl group having a carbon atom number of 2-6 or an alkoxy group having a carbon atom number of 1-5, with any CH.sub.2 in R.sub.4 being optionally substituted with cyclopentyl, cyclobutyl or cyclopropyl; (F) represents F or H; and (O) represents —O— or a single bond.

7. The liquid crystal composition according to claim 2, wherein said liquid crystal composition further comprises one or more compounds represented by formula IV, ##STR00086## R.sub.5 represents H, an alkyl group having a carbon atom number of 1-5, an alkenyl group having a carbon atom number of 2-6 or an alkoxy group having a carbon atom number of 1-5, with any CH.sub.2 in R.sub.5 being optionally substituted with cyclopentyl, cyclobutyl or cyclopropyl; o represents 0 or 1; ##STR00087## represents phenylene, cyclohexylene, cyclohexenylene or a group formed by substituting one or two non-connected CH.sub.2 in cyclohexylene with O; and (F) each independently represents H or F.

8. The liquid crystal composition according to claim 2, wherein said liquid crystal composition further comprises one or more negative compounds represented by formula V, ##STR00088## wherein R.sub.6 and R.sub.7 represent H, an alkyl group having a carbon atom number of 1-5, an alkenyl group having a carbon atom number of 2-6 or an alkoxy group having a carbon atom number of 1-5, with any CH.sub.2 in R.sub.6 and R.sub.7 being optionally substituted with cyclopentyl, cyclobutyl or cyclopropyl; p and q each independently represent 0, 1 or 2, with 1≤p+q≤3; Z.sub.3 and Z.sub.4 each independently represent a single bond, —CH.sub.2CH.sub.2—, —CH.sub.2O— or —OCH.sub.2—; and ##STR00089## each independently represent one or more of ##STR00090##

9. The liquid crystal composition according to claim 2, wherein said liquid crystal composition further comprises one or more compounds represented by formula VI ##STR00091## wherein R.sub.8 represents H, an alkyl group having a carbon atom number of 1-5, an alkenyl group having a carbon atom number of 2-6 or an alkoxy group having a carbon atom number of 1-5, with any CH.sub.2 in R.sub.8 being optionally substituted with cyclopentyl, cyclobutyl or cyclopropyl; ##STR00092## represents phenylene, cyclohexylene, cyclohexenylene or a group formed by substituting one or two non-connected CH.sub.2 in cyclohexylene with O; r represents 0 or 1; (F) represents F or H; and R.sub.9 represents F, an alkyl group having a carbon atom number of 1-6 or an alkoxy group having a carbon atom number of 1-6.

10. A liquid crystal display element or liquid crystal display comprising a liquid crystal compound of claim 1, wherein said liquid crystal display element or liquid crystal display is an active matrix display element or liquid crystal display, or a passive matrix display element or liquid crystal display.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The sole FIGURE is a mass spectrum of a PUQYi-3-F compound in Example 1.

DETAILED DESCRIPTION OF EMBODIMENTS

(2) The present invention is further described in conjunction with particular examples below, but the present invention is not limited to the following examples. Said methods are all conventional methods, unless otherwise specified.

(3) The specific meanings of symbols and the test conditions in the examples are as follows:

(4) Cp: represents the clearing point of a liquid crystal, with a unit of ° C.

(5) S-N: represents the melting point of a liquid crystal from a crystal state to a nematic phase, with a unit of ° C.

(6) Δn: represents optical anisotropy, with Δn=n.sub.o−n.sub.e, in which n.sub.o is the refractive index of an ordinary light, and n.sub.e is the refractive index of an extraordinary light, with the test conditions being 589 nm and 25±0.5° C.

(7) Δε: dielectric anisotropy, with Δε=ε.sub.//−ε.sub.⊥, in which ε.sub.// is the dielectric constant parallel to the molecular axis, and ε.sub.⊥ is the dielectric constant perpendicular to the molecular axis, with the test conditions being 25±0.5° C., 1 KHz, HP4284A, and a 5.2 μm TN left-hand cell.

(8) γ.sub.1: rotatory viscosity, with a unit of mPa.Math.s, the test conditions being 25±0.5° C.

(9) VHR: voltage holding ratio (%), with the test conditions being 20±2° C., a voltage of ±5 V, a pulse width of 10 ms, and a voltage holding time of 16.7 ms. The test equipment is a TOYO Model 6254 liquid crystal performance comprehensive tester.

(10) It should be noted that the process of the subsequent reaction for the synthesis of a liquid crystal compound is generally monitored by means of TLC, and treatments after the completion of the reaction are generally water washing, extraction, organic phase combination and drying, solvent evaporation under reduced pressure, as well as recrystallization and column chromatography; and a person skilled in the art would be able to implement the present invention according to the following description.

(11) The synthesis route of the compound represented by formula I is

(12) ##STR00034##

(13) and specifically comprises the following two steps, i.e., steps a and b,

(14) a) a raw material

(15) ##STR00035##
is dissolved in toluene,

(16) ##STR00036##
is added, the temperature is raised to 60° C. under stirring, CF.sub.3SO.sub.3H is dropwise added, the temperature is raised to reflux after the addition is complete, water is separated, a reaction under refluxing is carried out for 12 hours, the temperature is reduced, the toluene is evaporated to dryness, methyl tert-butyl ether is added for washing, and after suction filtration, a product

(17) ##STR00037##
is obtained.

(18) ##STR00038##
In, R.sub.1 represents H, an alkyl group having a carbon atom number of 1-5, an alkenyl group having a carbon atom number of 2-6 or an alkoxy group having a carbon atom number of 1-5, with any CH.sub.2 in R.sub.1 being optionally substituted with cyclopentyl, cyclobutyl or cyclopropyl, any CH.sub.2 not connected to O being optionally substituted with O and any one or more hydrogen atoms being optionally substituted with fluorine atom; n represents 1, 2, 3 or 4;

(19) ##STR00039##
and represents one or more of phenylene, a fluoro-substituted phenylene group, cyclohexenylene, cyclohexylene and a group formed by substituting one or two non-connected CH.sub.2 in cyclohexylene with O.

(20) b) The resulting

(21) ##STR00040##
from step a) is dissolved in dichloromethane, the temperature is reduced to −75° C. under the protection of an inert gas, a solution of triethylamine and

(22) ##STR00041##
in dichloromethane is dropwise added, a reaction is carried out at a maintained temperature for 1 hour after the addition is complete, triethylamine tris(hydrogen fluoride) is dropwise added, a reaction is carried out at a maintained temperature for 30 minutes after the dropwise addition is complete, Br.sub.2 is further dropwise added, a reaction is carried out at a maintained temperature for 30 minutes after the dropwise addition is complete, the temperature is naturally raised to −20° C., the reaction solution is poured to a saturated solution of sodium bicarbonate, and after liquid separation, extraction, water washing, passing through a silica gel column and concentration, a target product

(23) ##STR00042##
is obtained, wherein

(24) ##STR00043##
represents

(25) ##STR00044##
Y represents H, F, Cl, CN, an alkyl group having a carbon atom number of 1-5, an alkenyl group having a carbon atom number of 2-6 or an alkoxy group having a carbon atom number of 1-5, with any CH.sub.2 not connected to O being optionally substituted with O and any one or more hydrogen atoms being optionally substituted with a fluorine atom.

(26) The key intermediates

(27) ##STR00045##
in the synthesis of the compound represented by formula I may be purchased from commercial approaches.

(28) In the examples of the present invention application, liquid crystal monomer structures are represented by codes, wherein the code representation methods of ring structures, end groups and linking groups of the liquid crystals are shown in tables (I) and (II) below

(29) TABLE-US-00001 TABLE (I) Corresponding code for ring structure Ring structure Corresponding code C U P A 0 G Gi Y Yi Yii

(30) TABLE-US-00002 TABLE (II) Corresponding code for end group and linking group End group and Corresponding linking group code C.sub.nH.sub.2n+1— n- C.sub.nH.sub.2n+1O— nO— —OCF.sub.3 —OT —CF.sub.2O— —Q— —CH.sub.2O— —O— —F —F —CN —CN —CH.sub.2CH.sub.2— —E— —CH═CH— —V— —C≡C— —W— —COO— —COO— —CH═CH—C.sub.nH.sub.2n+1 Vn— C(5)— C(3)1—

Example

(31) ##STR00057##

Example 1

(32) ##STR00058##

(33) The synthesis route is:

(34) ##STR00059##

(35) and specifically comprises two steps, i.e., steps 1-a) and 1-b):

(36) 1-a) 115 g (0.42 mol) of a raw material

(37) ##STR00060##
is dissolved in 1.0 L of toluene, 54 g (0.5 mol) of

(38) ##STR00061##
is added, the temperature is raised to 60° C. under stirring, 75 g (0.5 mol) of trifluoromethanesulfonic acid (CF.sub.3SO.sub.3H) is dropwise added, the temperature is raised to reflux after the addition is complete, water is separated, reaction under refluxing is carried out for 12 hours, the temperature is reduced, the toluene is evaporated to dryness, 0.6 L of methyl tert-butyl ether is added for washing, and after suction filtration, 150 g of a product

(39) ##STR00062##
is obtained with a yield of 60%.

(40) 1-b) 48 g (0.10 mol) of the resulting

(41) ##STR00063##
from step 1-a) is dissolved in 0.2 L of dichloromethane, the temperature is reduced to −75° C. under the protection of an inert gas, 0.2 L of a solution of 19.4 g (0.2 mol) of triethylamine and 16.2 g (0.1 mol) of

(42) ##STR00064##
in dichloromethane is dropwise added, a reaction is carried out at a maintained temperature for 1 hour after the addition is complete, 161 g (0.29 mol) of triethylamine tris(hydrogen fluoride) (NEt.sub.3.3HF) is dropwise added, a reaction is carried out at a maintained temperature for 30 minutes after the dropwise addition is complete, 32.2 g (0.29 mol) of Br.sub.2 is further dropwise added, a reaction is carried out at a maintained temperature for 30 minutes after the dropwise addition is complete, the temperature is naturally raised to −20° C., the reaction solution is poured to 0.4 L of a saturated solution of sodium bicarbonate, and after liquid separation, extraction, water washing, passing through a silica gel column, concentration and recrystallization, 15 g of a target product PUQYi-3-F

(43) ##STR00065##
is obtained with GC=99.88% and a yield of 34%.

(44) The parameters of PUQYi-3-F are as follows: Δn=0.1402, Cp=30.5° C., ε.sub.⊥=6.8 and Δε=12.0.

(45) The following compound is synthesized in the same manner as in the synthesis method of Example 1, except that the starting materials in Example 1 are replaced, and the synthesis method therefor will not be repeated below:

Example 2 PUQYi-2-F

(46) ##STR00066##

(47) The parameters of PUQYi-2-F are as follows: Δn=0.1381, CP=31.3° C., ε.sub.⊥=6.7 and Δε=11.8.

Example 3 PUQYii-3-F

(48) ##STR00067##

(49) The parameters of PUQYii-3-F are as follows: Δn=0.1394, CP=30.1° C., ε.sub.⊥=6.6 and Δε=12.0.

Example 4 PUQYi-3-02

(50) ##STR00068##

(51) The parameters of PUQYi-3-02 are as follows: Δn=0.1702, CP=71.0° C., ε.sub.⊥=7.9 and Δε=1.2.

Example 5 PUQYi-3-04

(52) ##STR00069##

(53) The parameters of PUQYi-3-04 are as follows: Δn=0.1650, CP=67.2° C., ε.sub.⊥=8.8 and Δε=0.2.

Example 6 PGUQYi-3-F

(54) ##STR00070##

(55) The parameters of PGUQYi-3-F are as follows: Δn=0.2105, CP=140.5° C., ε.sub.⊥=6.2 and Δε=15.8.

Example 7 PGUQYi-3-02

(56) ##STR00071##

(57) The parameters of PGUQYi-3-02 are as follows: Δn=0.2307, CP=205.5° C., ε.sub.⊥=6.9 and Δε=3.5.

Example 8 APUQYi-3-F

(58) ##STR00072##

(59) The parameters of APUQYi-3-F are as follows: Δn=0.1572, CP=123.6° C., ε.sub.⊥=6.4, and Δε=14.2.

Example 9 CPUQYi-3-F

(60) ##STR00073##

(61) The parameters of CPUQYi-3-F are as follows: Δn=0.1502, CP=130.5° C., ε.sub.⊥=6.8 and Δε=12.8.

(62) Liquid Crystal Composition Examples:

Example 10

(63) TABLE-US-00003 Category Liquid crystal monomer code Content (%) I APUQYi-3-F 10 I PUQYi-3-F 10 I PGUQYi-3-F 10 I PUQYi-3-O2 10 II CC-3-V 30 II CC-3-V1 5 II CP-3-O2 5 II CCP-3-3 7 II CCP-V-1 8 II CPP-V1-2 5 Δε[1 KHz, 25° C.]: 4.3 ε.sub.⊥: 4.1 Δn[589 nm, 25° C.]: 0.1211 Cp: 88° C. γ.sub.1: 85 mPa .Math. s.

(64) After the composition of Example 10 is stored at −20° C. for 120 hours, there is also no precipitation of the crystal of the compound of formula I.

Example 11

(65) TABLE-US-00004 Category Liquid crystal monomer code Content (%) I PUQYi-2-F 5 I CPUQYi-3-F 10 I PGUQYi-3-F 10 I PUQYii-3-F 5 II CC-3-V 25 II CC-5-V 5 II CP-3-O1 3 II PP-5-1 2 II CCP-2V-1 5 III CCP-3-F 10 III CCU-3-F 10 III CPU-3-F 5 III PGP-C(3)1-3 5 Δε[1 KHz, 25° C.]: 6.3 ε.sub.⊥: 4.0 Δn[589 nm, 25° C.]: 0.1175 Cp: 85° C. γ.sub.1: 85 mPa .Math. s.

(66) After the composition of Example 11 is stored at −20° C. for 120 hours, there is also no precipitation of the crystal of the compound of formula I.

Example 12

(67) TABLE-US-00005 Category Liquid crystal monomer code Content (%) I PGUQYi-3-O2 3 I PUQYi-3-O4 8 I PUQYi-3-O2 9 II CC-3-V 30 II CC-2-3 5 II PP-1-5 5 II PP-2V-1 3 II CCP-3-1 2 II CPP-3-2V1 5 III CCG-3-F 5 III CGU-3-F 5 III CCP-3-OT 5 III PPGi-3-F 5 IV PUQU-C(5)-F 1 IV PUQU-C(3)1-F 1 IV PGUQU-3-F 1 IV PGUQU-C(3)-F 2 IV PGUQU-C(5)-F 2 IV CPUQU-C(5)-F 3 Δε[1 KHz, 25° C.]: 4.1 ε.sub.⊥: 4.2 Δn[589 nm, 25° C.]: 0.1195 Cp: 74° C. γ.sub.1: 88 mPa .Math. s.

(68) After the composition of Example 12 is stored at −20° C. for 120 hours, there is also no precipitation of the crystal of the compound of formula I.

Example 13

(69) TABLE-US-00006 Category Liquid crystal monomer code Content (%) I PUQYi-3-O2 7 I PGUQYi-3-F 7 I PUQYi-3-F 7 I PUQYii-3-F 7 I PUQYi-2-F 7 II CC-3-V 10 II CC-V-V1 5 II PP-2V-1 7 II CCP-V-1 8 III PGU-3-F 2 III CGU-3-F 3 III CPUP-3-OT 2 III PGP-3-F 3 IV APUQU-C(5)-F 10 IV DUQU-C(5)-F 5 IV CPUQU-C(5)-F 5 V CPY-3-O2 5 Δε[1 KHz, 25° C.]: 9.6 ε.sub.⊥: 5.1 Δn[589 nm, 25° C.]: 0.1414 Cp: 78° C. γ.sub.1: 115 mPa .Math. s.

(70) After the composition of Example 13 is stored at −20° C. for 120 hours, there is also no precipitation of the crystal of the compound of formula I.

Example 14

(71) TABLE-US-00007 Category Liquid crystal monomer code Content (%) I PUQYi-2-F 5 I PGUQYi-3-O2 2 I PUQYi-3-O4 3 II CC-3-V 30 II CC-V-V1 20 II CPP-3-2 10 II CCP-V-1 5 III CPGU-C(5)-F 2 III PPGU-C(5)-F 3 IV PUQU-C(5)-F 5 IV PGUQU-3-F 5 IV CPUQU-C(5)-F 5 V CPY-3-O2 2 V CY-3-O4 3 Δε[1 KHz, 25° C.]: 4.9 ε.sub.⊥: 3.8 Δn[589 nm, 25° C.]: 0.109 Cp: 80° C. γ.sub.1: 63 mPa .Math. s.

(72) After the composition of Example 14 is stored at −20° C. for 120 hours, there is also no precipitation of the crystal of the compound of formula I.

Example 15

(73) TABLE-US-00008 Category Liquid crystal monomer code Content (%) I PUQYi-3-O2 2 I PUQYi-3-F 3 II CC-3-V 20 II CCP-V-1 5 III CCU-4-F 15 III CPUP-3-OT 10 III CPU-5-F 15 IV PUQU-C(5)-F 10 IV PGUQU-3-F 5 IV CPUQU-C(5)-F 5 V CPY-3-O2 2 V CCY-3-O2 2 V PPY-3-O2 3 V COY-3-O2 3 Δε[1 KHz, 25° C.]: 9.2 ε.sub.⊥: 4.7 Δn[589 nm, 25° C.]: 0.122 Cp: 90° C. γ.sub.1: 115 mPa .Math. s.

(74) The liquid crystal composition of Example 15 has a moderate Δε, a larger Δn, a lower γ.sub.1 and an appropriate Cp, and is suitable for a liquid crystal material of a rapid response, a low cell thickness TN, IPS or FFS-TFT display. After the composition of Example 15 is stored at −20° C. for 120 hours, there is also no precipitation of the crystal of the compound of formula I.

Example 16

(75) TABLE-US-00009 Category Liquid crystal monomer code Content (%) I PGUQYi-3-F 2 I PUQYi-3-F 2 I PGUQYi-3-O2 1 II CC-3-V 20 II CCP-V2-1 5 III CCU-4-F 15 III CCG-4-F 10 III CPU-5-F 15 IV PUQU-C(5)-F 10 IV PGUQU-3-F 5 IV PGUQU-C(3)1-F 5 V CPY-3-O2 5 V CCY-3-O2 5 Δε[1 KHz, 25° C.]: 8.9 ε.sub.⊥: 4.6 Δn[589 nm, 25° C.]: 0.111 Cp: 87° C. γ.sub.1: 115 mPa .Math. s.

(76) The liquid crystal composition of Example 16 has a larger Δε, a larger Δn, a moderate Cp and a larger ε.sub.⊥, and is suitable for a liquid crystal material of a high transmittance, a rapid response and a TN, IPS or FFS-TFT display.

(77) After the composition of Example 16 is stored at −20° C. for 240 hours, there is also no precipitation of the crystal of the compound of formula I.

Example 17

(78) TABLE-US-00010 Category Liquid crystal monomer code Content (%) I APUQYi-3-F 5 I PUQYi-2-F 5 I PUQYi-3-F 10 II CC-3-V 31 II CCP-V-1 5 III CCU-4-F 5 III CCP-2-OT 2 III CPU-3-F 5 III PGP-C(3)1-1 3 III PPGi-2-F 3 III PGP-3-F 4 VI PUQY-3-O4 10 VI PGUQY-3-O2 4 VI APUQY-3-O2 5 VI PUQY-3-F 3 Δε[1 KHz, 25° C.]: 4.7 ε.sub.⊥: 4.7 Δn[589 nm, 25° C.]: 0.122 Cp: 76° C. γ.sub.1: 110 mPa .Math. s.

(79) After the composition of Example 17 is stored at −20° C. for 240 hours, there is also no precipitation of the crystal of the compound of formula I.

Example 18

(80) TABLE-US-00011 Category Liquid crystal monomer code Content (%) I APUQYi-3-F 5 I PUQYii-3-F 5 I PGUQYi-3-F 10 II CC-3-V 31 II CC-3-V1 5 III CCU-4-F 5 III CCP-2-OT 2 III CPU-3-F 5 III CPUP-3-OT 3 III PPGU-C(5)-F 3 V CPY-3-O2 4 VI PUQY-3-O4 10 VI PGUQY-3-O2 4 VI APUQY-3-O2 5 VI PUQY-3-F 3 Δε[1 KHz, 25° C.]: 5.2 ε.sub.⊥: 4.0 Δn[589 nm, 25° C.]: 0.1105 Cp: 84° C. γ.sub.1: 75 mPa .Math. s.

(81) After the liquid crystal composition of Example 18 is stored at −20° C. for 240 hours, there is also no precipitation of the crystal of the compound of formula I.

Example 19

(82) TABLE-US-00012 Category Liquid crystal monomer code Content (%) I PUQYi-3-F 15 II CC-3-V 36 II CCP-V2-1 5 III CCP-3-F 5 III CCP-2-OT 7 III CCG-5-F 5 IV APUQU-C(5)-F 3 IV PGUQU-C(5)-F 2 IV PGUQU-C(3)1-F 3 V CPY-3-O2 5 VI PUQY-3-O4 2 VI PGUQY-3-O2 4 VI APUQY-3-O2 5 VI PUQY-3-F 3 Δε[1 KHz, 25° C.]: 5.1 ε.sub.⊥: 4.4 Δn[589 nm, 25° C.]: 0.1056 Cp: 85° C. γ.sub.1: 105 mPa .Math. s.

(83) After the liquid crystal composition of Example 19 is stored at −20° C. for 240 hours, there is also no precipitation of the crystal of the compound of formula I.

Comparative Example 1

(84) The PUQYi-3-F compound in Example 10 is replaced with a PUQY-3-F compound in the prior art; the ε.sub.⊥ data is reduced to 3.8 and the Cp is reduced to 86° C.; after the liquid crystal composition is placed in a flask at −20° C. and maintained for 100 hours, the PUQY-3-F is precipitated;

Comparative Example 2

(85) The 10% PGUQYi-3-F compound of formula I in Example 10 is replaced with PGUQY-3-F; the ε.sub.⊥ data is 3.9 and the Cp is reduced to 85° C.; after being maintained at −20° C. for 100 hours, the PGUQY-3-F is precipitated; and

Comparative Example 3

(86) The 10% PUQYi-3-02 compound of formula I in Example 10 is replaced with PUQY-3-02; the ε.sub.⊥ data is 3.7 and the Cp is reduced to 87° C.; after being maintained at −20° C. for 100 hours, the PUQY-3-02 is precipitated.