Liquid crystal compounds

A compound of formula I

• wherein
• A1 to A4 are independently selected from the group consisting of hydrogen, a methyl group and a hydrocarbon group containing from 2 to 80 carbon atoms in which one or more carbon atoms are optionally replaced by a heteroatom selected from the group consisting —O—, —S— and —N— and in which one or more hydrogen atoms are optionally substituted by a substituent selected from the group consisting of C1-20 alkyl, C2-20 alkenyl, C2-20 alkynyl, amino, cyano, epoxy, halogen, hydroxy, nitro or oxo, with the proviso that firstly no two oxygen atoms are joined together and secondly that at least one of A1 to A4 includes a polymerisable group;
• B1 represents a hydrocarbon group containing from 4 to 80 carbon atoms, in which one or more carbon atoms are optionally replaced by a heteroatom selected from the group consisting of —O—, —S— and —N— and in which one or more hydrogen atoms are optionally substituted by a substituent selected from the group consisting of C1-20 alkyl, C2-20 alkenyl, C2-20 alkynyl, amino, cyano, epoxy, halogen, hydroxy, nitro or oxo, with the proviso that no two oxygen atoms are joined together;
• MG1 and MG2 each independently are selected from a group of formula (IV)
• C1—(Z1—C2)a1—(Z2—C3)a2—(Z3—C4)a3 (IV),
• wherein
• C1 to C4 are each independently selected from the group consisting of an optionally substituted non-aromatic, aromatic, carbocyclic or heterocyclic group containing from 2 to 14 carbon atoms;
• Z1 to Z3 are each independently selected from the group consisting of —CH(OH)—, —CO—, —CH2(CO)—, —SO—, —CH2(SO)—, —SO2—, —CH2(SO2)—, —COO—, —OCO—, —COCF2—, —CF2CO—, —S—CO—, —CO—S—, —SOO—, —OSO—, —SOS—, —CH2—CH2—, —OCH2—, —CH2O—, —CH═CH—, —C≡C—, —CH═CH—COO—, —OCO—CH═CH— and a single bond;
• and
• a1, a2 and a3 are each independently 0 or an integer having a value of from 1 to 3, with the proviso that a1+a2+a3≦3, and with the proviso that firstly at least one of MG1 and MG2 comprises at least two ring systems and secondly when MG1 and MG2 are identical, either A1 and A2 or A3 and A4 are different or at least three of A1 to A4 are different,
• wherein groups A1, MG1, B1, MG2 and A2 are linearly arranged with respect to each other.