Optically isotropic liquid crystal medium and optical device

A liquid crystal composition exhibiting an optically isotropic liquid crystal phase, the liquid crystal composition comprising an achiral component T and a chiral dopant, wherein the achiral component T contains, as a first component thereof, at least one compound selected from the group consisting of compounds represented by formula (1),

• wherein R1 is C1-10 alkyl in which at least one —CH2— is optionally replaced by —O— and at least one —(CH2)2— is optionally replaced by —CH═CH—;
• ring A1, ring A2, ring A3, ring A4, ring A5 and ring A6 are independently 1,4-cyclohexylene or 1,4-phenylene, wherein in the 1,4-cyclohexylene at least one —CH2— is optionally replaced by —O— and least one —(CH2)2— is optionally replaced by —CH═CH—, and in the 1,4-phenylene at least one —CH═ is optionally replaced by —N═ and at least one hydrogen is optionally replaced by halogen;
• Z1, Z2, Z3, Z4, Z5, Z6 and Z7 are independently a single bond, —(CH2)2—, —COO—, —OCO—, —CF2O—, —OCF2— or —CH═CH—;
• X1 is fluorine, —CF3 or —OCF3;
• Y1 and Y2 are independently hydrogen or fluorine;
• i, j, k, m, n, p and q are independently 0 or 1;
• and i+j+k+m+n+p+q is 1, 2, 3 or 4.