Optically isotropic liquid crystal medium and optical device

A liquid crystal composition that exhibits an optically isotropic liquid crystal phase, contains an achiral component T and a chiral agent, and contains at least one compound selected from the group of compounds represented by formula (1) as a first component of the achiral component T:

• wherein R1 is hydrogen or alkyl having 1 to 20 carbons, at least one —CH2— in the alkyl may be replaced by —O—, —S—, —COO— or —OCO—, at least one —CH2—CH2— in the alkyl may be replaced by —CH═CH—, —CF═CF— or —C≡C—, and in the alkyl, in the group formed by replacing at least one —CH2— in the alkyl by —O—, —S—, —COO— or —OCO—, or in the group formed by replacing at least one —CH2—CH2— in the alkyl by —CH═CH—, —CF═CF— or —C≡C—, at least one hydrogen may be replaced by halogen, provided that in R1, —O— and —CH═CH— are not adjacent and —CO— and —CH═CH— are not adjacent;
• L1, L2, L3, L4, L5, L6, L7 and L8 are independently hydrogen or fluorine;
• Z1, Z2 and Z3 are each independently a single bond, —COO— or —CF2O—, but at least one thereof is —COO—;
• n1 and n2 are each independently 0 or 1;
• and X1 is hydrogen, halogen, —SF5 or alkyl having 1 to 10 carbons, at least one —CH2— in the alkyl may be replaced by —O—, —S—, —COO— or —OCO—, at least one —CH2—CH2— in the alkyl may be replaced by —CH═CH—, —CF═CF— or —C≡C—, and in the alkyl, the group formed by replacing at least one —CH2— in the alkyl by —O—, —S—, —COO— or —OCO—, or the group formed by replacing at least one —CH2—CH2— in the alkyl by —CH═CH—, —CF═CF— or —C≡C—, at least one hydrogen may be replaced by fluorine, provided that in X1, —O— and —CH═CH— are not adjacent and —CO— and —CH═CH— are not adjacent.