Liquid crystalline compounds containing a biphenyl core

A method of stabilizing a smectic A phase in a liquid crystal mixture comprising the step of adding a liquid crystal compound of formula (I), to the liquid crystal mixture,

• or a dimer thereof;
• where R1 and R2 are independently selected from optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, a functional group selected from halo, cyano, nitro, oxo, C(O)n′Ra, ORa, S(O)tRa, NRbRc, OC(O)NRbRc, C(O)NRbRc, OC(O)NRbRc, —NRcC(O)n′Rb, —NRbCONRbRc, —NRaCSNRbRc, —C═NORa, —N═CRbRc, S(O)tNRbRc, or —NR S(O)tRa where Ra, Rb and Rc are independently selected from hydrogen or optionally substituted hydrocarbyl, or Rb and Rc together form an optionally substituted ring which optionally contains further heteroatoms such as S(O)s, oxygen and nitrogen, n′ is 1 or 2, s is 0, 1 or 2, t is 0 or an integer of 1-3, or a group of sub-formula (i) provided that at least one of R1 or R2 is a group of sub-formula (i);
• —(O)—(CH2)p—R7 (i)
• where m is 0 or 1;
• p is an integer of from 3 to 12;
• R7 is a group of formula —CqX2q+1 where q is an integer of from 2 to 12 and X is halogen, or R7 is a group of sub-formula (ii)
• where k is an integer of from 1 to 10, R8, R10 and R12 and each R9 and R11 are independently selected from alkyl, alkenyl or aryl;
• R3, R4, R5 and R6 are independently selected from hydrogen or halogen,
• n is 0 or 1, and A is a group of sub-formula (iii), (iv), (v), (vi) or (vii)
• where R13, R14, R15, R16, R17, R18 and R19 are independently selected from hydrogen or halo, and the group A may be orientated in either direction, so that the group R2 is attached at either of the available bonds in sub-formula (iii)-(vii);
• and further provided that where R2 is a group of sub-formula (i), m=1, n=0, p=3 and R3, R4, R5 and R6 are each hydrogen and R7 is a group of sub-formula (ii) in which k=1, R8, R9, R10 and R11 are each methyl and R12 is a phenyl group, then R1 shall not be either OMe or OBu;
• and further provided that at least one of the rings carries one or more halo atoms.

A liquid crystal compound of formula (I)

• or a dimer thereof;
• where R1 and R2 are independently selected from optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, a functional group selected from halo, cyano, nitro, oxo, C(O)Ra, ORa, S(O)tRa, NRbRc, OC(O)NRbRc, C(O)NRbRc, OC(O)NRbRc, —NRcC(O)n′Rb, —NRaCONRbRc, —NRaCSNRbRc, —C═NORa, —N═CRbRc, S(O)tNRbRc, or —NRbS(O)tRa where Ra, Rb and Rc are independently selected from hydrogen or optionally substituted hydrocarbyl, or Rb and Rc together form an optionally substituted ring which optionally contains further heteroatoms such as S(O)s, oxygen and nitrogen, s is 0, 1 or 2, t is 0 or an integer of 1-3, or a group of sub-formula (i) provided that at least one of R1 or R2 is a group of sub-formula (i);
• —(O)—(CH2)p—R7 (i)
• where m is 0 or 1;
• p is an integer of from 3 to 12;
• R7 is a group of sub-formula (ii)
• where k is an integer of from 1 to 10, R8, R10and R12 and each R9 and R11 are independently selected from alkyl, alkenyl or aryl;
• R3, R4, R5 and R6 are independently selected from hydrogen or halogen,
• n is 0 or 1, and A is a group of sub-formula (iii), (iv), (v), (vi) or (vii)
• where R13, R14, R15, R16, R17, R18 and R19 are independently selected from hydrogen or halo, and the group A may be orientated in either direction, so that the group R2 is attached at either of the available bonds in sub-formula (iii)-(vii);
• and further provided that where R2 is a group of sub-formula (i), m =1, n =0, p =3 and R3, R4, R5 and R6 are each hydrogen and R7 is a group of sub-formula (ii) in which k=1, R8, R9, R10 and R11 are each methyl and R12 is a phenyl group, then R1 shall not be either OMe or OBu;
• and further provided that at least one of the rings carries one or more halo atoms.