Liquid crystal compound, liquid crystal composition and liquid crystal display device

1. A liquid crystal compound represented by formula (a):

wherein R a and R b are independently hydrogen, alkyl having 1 to 10 carbons, alkenyl having 2 to 10 carbons, alkoxy having 1 to 9 carbons, alkoxyalkyl having 2 to 9 carbons or alkenyloxy having 2 to 9 carbons; the ring A 1 and the ring A 2 are independently 1,4-phenylene, trans-1,4-cyclohexylene, 1,4-cyclohexenylene, tetrahydropyran-2,5-diyl, 1,3-dioxane-2,5-diyl, pyrimidine-2,5-diyl or pyridine-2,5-diyl, and the ring A 1 and the ring A 2 are not simultaneously 1,4-phenylene; L 1 , L 2 , L 3 and L 4 are independently hydrogen or fluorine, and at least three of them are fluorine; and Z 1 and Z 2 are independently a single bond, —CH 2 CH 2 —, —CH═CH—, —C≡C—, —CH 2 O—, —OCH 2 —, —COO— or —OCO—.

2. The liquid crystal compound according to claim 1 , wherein in formula (a), the ring A 1 and the ring A 2 are independently 1,4-phenylene, trans-1,4-cyclohexylene, 1,4-cyclohexenylene or tetrahydropyran-2,5-diyl.

3. The liquid crystal compound according to claim 2 , wherein the compound is represented by formula (a-1):

wherein Ra 1 and Rb 1 are independently alkyl having 1 to 10 carbons, alkenyl having 2 to 10 carbons, alkoxy having 1 to 9 carbons, alkoxyalkyl having 2 to 9 carbons or alkenyloxy having 2 to 9 carbons; the ring A 3 is 1,4-phenylene, trans-1,4-cyclohexylene, 1,4-cyclohexenylene or tetrahydropyran-2,5-diyl; the ring A 4 is trans-1,4-cyclohexylene, 1,4-cyclohexenylene or tetrahydropyran-2,5-diyl; L 5 , L 6 , L 7 and L 8 are independently hydrogen or fluorine, and at least three of them are fluorine; and Z 3 is independently a single bond, —CH 2 CH 2 —, —CH═CH—, —CH 2 O—, —OCH 2 —, —COO— or —OCO—.

4. The liquid crystal compound according to claim 2 , wherein the compound is represented by formula (a-2):

wherein Ra 2 and Rb 2 are independently alkyl having 1 to 10 carbons, alkenyl having 2 to 10 carbons, alkoxy having 1 to 9 carbons, alkoxyalkyl having 2 to 9 carbons or alkenyloxy having 2 to 9 carbons; the ring A 5 and the ring A 6 are independently 1,4-phenylene, trans-1,4-cyclohexylene, 1,4-cyclohexenylene or tetrahydropyran-2,5-diyl, and independently hydrogen or fluorine, and at least three of them are fluorine; and Z 4 is independently —CH 2 CH 2 —, —CH═CH—, —CH 2 O—, —OCH 2 —, —COO— or —OCO—.

5. The liquid crystal compound according to claim 3 , wherein the compound is represented by any one of formulas (a-3) to (a-8):

wherein Ra 3 and Rb 3 are independently alkyl having 1 to 10 carbons, alkenyl having 2 to 10 carbons, alkoxy having 1 to 9 carbons, alkoxyalkyl having 2 to 9 carbons or alkenyloxy having 2 to 9 carbons; and Z 5 is a single bond, —CH 2 CH 2 —, —CH═CH—, —CH 2 O—, —OCH 2 —, —COO— or —OCO—.

6. The liquid crystal compound according to claim 4 , wherein the compound is represented by any one of formulas (a-9) to (a-15):

wherein Ra 4 and Rb 4 are independently alkyl having 1 to 10 carbons, alkenyl having 2 to 10 carbons, alkoxy having 1 to 9 carbons, alkoxyalkyl having 2 to 9 carbons or alkenyloxy having 2 to 9 carbons; and Z 6 is independently —CH 2 CH 2 —, —CH═CH—, —CH 2 O—, —OCH 2 —, —COO— or —OCO—.

7. The liquid crystal compound according to claim 1 , wherein in formulas (a-3) to (a-8), Z 5 is a single bond.

8. A liquid crystal composition including at least one of the compounds according to claim 1 as a first component and at least one of the compounds represented by formulas (e-1) to (e-3) as a second component:

wherein Ra 11 and Rb 11 are independently alkyl having 1 to 10 carbons, and in the alkyl, arbitrary —CH 2 — may be nonadjacently replaced by —O—, and arbitrary —CH 2 CH 2 — may be nonadjacently replaced by —CH═CH—, and hydrogen may be replaced by fluorine; the ring A 11 , the ring A 12 , the ring A 13 and the ring A 14 are independently trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, pyrimidine-2,5-diyl, 1,3-dioxane-2,5-diyl or tetrahydropyran-2,5-diyl; and Z 11 , Z 12 and Z 13 are independently a single bond, —CH 2 CH 2 —, —CH═CH—, —C≡C—, —COO— or —CH 2 O—.

9. A liquid crystal composition, wherein a first component is at least one compound selected from the compounds represented by formula (a-1) and a second component is at least one compound selected from formulas (e-1) to (e-3):

wherein Ra 1 and Rb 1 are independently alkyl having 1 to 10 carbons, alkenyl having 2 to 10 carbons, alkoxy having 1 to 9 carbons, alkoxyalkyl having 2 to 9 carbons or alkenyloxy having 2 to 9 carbons; the ring A 3 is 1,4-phenylene, trans-1,4-cyclohexylene, 1,4-cyclohexenylene or tetrahydropyran-2,5-diyl; the ring A 4 is trans-1,4-cyclohexylene, 1,4-cyclohexenylene or tetrahydropyran-2,5-diyl; L 5 , L 6 , L 7 and L 8 are independently hydrogen or fluorine, and at least three of them are fluorine; and Z 3 is independently a single bond, —CH 2 CH 2 —, —CH═CH—, —CH 2 O—, —OCH 2 —, —COO— or —OCO—, and then

wherein Ra 11 and Rb 11 are independently alkyl having 1 to 10 carbons, and in the alkyl, arbitrary —CH 2 — may be nonadjacently replaced by —O—, and arbitrary —CH 2 CH 2 — may be nonadjacently replaced by —CH═CH—, and hydrogen may be replaced by fluorine; the ring A 11 , the ring A 12 , the ring A 13 and the ring A 14 are independently trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, pyrimidine-2,5-diyl, 1,3-dioxane-2,5-diyl or tetrahydropyran-2,5-diyl; and Z 11 , L 12 and Z 13 are independently a single bond, —CH 2 CH 2 —, —CH═CH—, —C≡C—, —COO— or —CH 2 O—.

10. A liquid crystal composition, wherein a first component is at least one compound selected from the compounds represented by formula (a-2) and a second component is at least one compound selected from formulas (e-1) to (e-3):

wherein Ra 2 and Rb 2 are independently alkyl having 1 to 10 carbons, alkenyl having 2 to 10 carbons, alkoxy having 1 to 9 carbons, alkoxyalkyl having 2 to 9 carbons or alkenyloxy having 2 to 9 carbons; the ring A 5 and the ring A 6 are independently 1,4-phenylene, trans-1,4-cyclohexylene, 1,4-cyclohexenylene or tetrahydropyran-2,5-diyl, and the ring A 5 and the ring A 6 are not simultaneously 1,4-phenylene; L 9 , L 10 , L 11 and L 12 are independently hydrogen or fluorine, and at least three of them are fluorine; and Z 4 is independently —CH 2 CH 2 —, —CH═CH—, —CH 2 O—, —OCH 2 —, —COO— or —OCO—; and then

wherein Ra 11 and Rb 11 are independently alkyl having 1 to 10 carbons, and in the alkyl, arbitrary —CH 2 — may be nonadjacently replaced by —O—, and arbitrary —CH 2 CH 2 — may be nonadjacently replaced by —CH═CH—, and hydrogen may be replaced by fluorine; the ring A 11 , the ring A 12 , the ring A 13 and the ring A 14 are independently trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, pyrimidine-2,5-diyl, 1,3-dioxane-2,5-diyl or tetrahydropyran-2,5-diyl; and Z 11 , Z 12 and Z 13 are independently a single bond, —CH 2 CH 2 —, —CH═CH—, —C≡C—, —COO— or —CH 2 O—.

11. The liquid crystal composition according to claim 8 , wherein the ratio of the first component is in the range of 5 to 60% by weight, and the ratio of the second component is in the range of 40 to 95% by weight, based on the total weight of the liquid crystal composition.

12. The liquid crystal composition according to claim 9 , wherein the ratio of the first component is in the range of 5 to 60% by weight, and the ratio of the second component is in the range of 40 to 95% by weight, based on the total weight of the liquid crystal composition.

13. The liquid crystal composition according to claim 10 , wherein the ratio of the first component is in the range of 5 to 60% by weight, and the ratio of the second component is in the range of 40 to 95% by weight, based on the total weight of the liquid crystal composition.

14. The liquid crystal composition according to claim 8 , including at least one compound selected from the group of compounds represented by formulas (g-1) to (g-6) and the group of compounds represented by formulas (i-1) to (i-4) as a third component, in addition to the first component and the second component:

wherein Ra 21 and Rb 21 are independently hydrogen or alkyl having 1 to 10 carbons, and in the alkyl, arbitrary —CH 2 — may be nonadjacently replaced by —O—, and arbitrary —CH 2 CH 2 — may be nonadjacently replaced by —CH═CH—, and hydrogen may be replaced by fluorine; the ring A 21 , the ring A 22 and the ring A 23 are independently trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene, pyrimidine-2,5-diyl, 1,3-dioxane-2,5-diyl or tetrahydropyran-2,5-diyl; Z 21 , Z 22 , and Z 23 are independently a single bond —CH 2 CH 2 —, —CH═CH—, —C≡C—, —OCF 2 —, —CF 2 O—, —OCF 2 CH 2 CH 2 —, —CH 2 CH 2 CF 2 O—, —COO—, —OCO—, —OCH 2 — or —CH 2 O—; Y 1 , Y 2 , Y 3 and Y 4 are independently fluorine or chlorine; q, r and s are independently 0, 1 or 2, q+r is 1 or 2, and q+r+s is 1, 2 or 3; and t is 0, 1 or 2; and then

wherein Ra 23 and Rb 23 are independently alkyl having 1 to 8 carbons or alkoxy having 1 to 7 carbons; the ring A 24 is trans-1,4-cyclohexylene, 1,4-cyclohexenylene, 1,4-phenylene or tetrahydropyran-2,5-diyl; the ring A 25 is trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene or 3-fluoro-1,4-phenylene; Z 27 is independently a single bond, —CH 2 O—, —COO— or —CF 2 O—; and both X 1 and X 2 are fluorine, or one of them is fluorine and the other is hydrogen.

15. The liquid crystal composition according to claim 14 , wherein the third component is at least one compound selected from the group of compounds represented by formulas (g-1-1) to (g-2-3):

wherein Ra 22 and Rb 22 are independently alkyl having 1 to 8 carbons, alkenyl having 2 to 8 carbons or alkoxy having 1 to 7 carbons; Z 24 , Z 25 and Z 26 are independently a single bond, —CH 2 CH 2 —, —COO—, —OCO—, —CH 2 O— or —OCH 2 —; and both Y 1 and Y 2 are fluorine, or one of them is fluorine and the other is chlorine.

16. The liquid crystal composition according to claim 14 , wherein the ratio of the first component is in the range of 5 to 60% by weight, the ratio of the second component is in the range of 20 to 75% by weight, and the ratio of the third component is in the range of 20 to 75% by weight, based on the total weight of the liquid crystal composition.

17. The liquid crystal composition according to claim 15 , wherein the ratio of the first component is in the range of 5 to 60% by weight, the ratio of the second component is in the range of 20 to 75% by weight, and the ratio of the third component is in the range of 20 to 75% by weight, based on the total weight of the liquid crystal composition.

18. A liquid crystal display device containing the liquid crystal composition according to claim 16 .

19. A liquid crystal display device containing the liquid crystal composition according to claim 17 .

20. The liquid crystal display device according to claim 18 , wherein an operating mode of the liquid crystal display device is a VA mode, an IPS mode or a PSA mode, and a driving mode of the liquid crystal display device is an active matrix mode.

21. The liquid crystal display device according to claim 19 , wherein an operating mode of the liquid crystal display device is a VA mode, an IPS mode or a PSA mode, and a driving mode of the liquid crystal display device is an active matrix mode.