Liquid crystal composition containing dibenzo derivatives and liquid crystal display device

A liquid crystal composition containing a dibenzo derivative, including at least one compound of general formula I and at least one compound of general formula II:

• in which,
• R represents —H, halogen, —CN, C1-12 linear alkyl, C3-12 branched alkyl,
• one or at least two nonadjacent —CH2— in the C1-12 linear alkyl, C3-12 branched alkyl,
• may be respectively and independently replaced by —CH—CH—, —C═C—, —O—, —S—, —CO—, —CO—O— or —O—CO—, one or at least two —H in the aforesaid groups may be respectively and independently substituted by —F or —Cl;
• Rx represents —H, C1-12 linear alkyl, C3-12 branched alkyl, one or at least two nonadjacent —CH2— in the C1-12 linear alkyl, C3-12 branched alkyl may be respectively and independently replaced by —CH—CH—, —C═C—, —O—, —S—, —CO—, —CO—O— or —O—CO—, one or at least two —H in the C1-12 linear alkyl, C3-12 branched alkyl may be respectively and independently substituted by —F or —Cl, Rx is attached to an arbitrary carbon atom in ring
• R1 and R2 each independently represents C1-12 linear alkyl, C3-12 branched alkyl,
• one or at least two nonadjacent —CH2— in the C1-12 linear alkyl, C3-12 branched alkyl may be respectively and independently replaced by —CH—CH—, —C═C—, —O—, —CO—, —CO—O— or —O—CO—;
• ring
• represents
• one or at least two single bond within the ring of the aforesaid groups may be replaced by double bond;
• ring
• represents
• one or at least two —CH2— in
• may be replaced by —O—, one or at most two single bond within the ring may be replaced by double bond;
• one or at least two —H in
• may be substituted by —F or —Cl, one or at least two —CH═ within the ring may be replaced by —N═;
• ring
• represents
• one or at least two —CH2— in
• may be replaced by —O—, one or at most two single bond within the ring may be replaced by double bond;
• one or at least two —H in
• may be substituted by —F or —Cl, one or at least two —CH═ within the ring may be replaced by —N═;
• Z1 represents —(CH2)aO— or —(CH2)aS—, wherein a represents an integer of 0 to 7;
• Z2 represents —O—, —S—, —CO—O—, —O—CO—, —CF2O—, —OCF2—, —CH2O—, —CH2S—, —OCH2—, —SCH2—, —CH2—, —CH2CH2—, —(CH2)4—, —CH═CH—CH2O—, —C2F4—, —CH2CF2—, —CF2CH2—, —CF=CF—, —CH═CF—, —CF═CH—, —CH═CH—, —C≡C— or single bond;
• Z3 represents single bond, —CO—O—, —O—CO—, —CH2O—, —OCH2—, —CH═CH—, —C≡C—, —CH2CH2—, —(CH2)4—, —CF2O—, —OCF2— or —CF2CF2—;
• L1 and L2 each independently represents —F, —Cl, —CF3 or —CHF2;
• X represents —CO—, —S— or —O—;
• n represents 0, 1 or 2, wherein when n represents 2, ring
• is same or different, Z2 is same or different;
• m represents 0, 1 or 2, wherein when m represents 2, ring
• is same or different, Z3 is same or different;
• and
• at least one group of the following three groups:
• R1, ring
• and Z3, contains at least one of —CH═CH— or —C≡C—.