Tetrahydrothiophene derivatives of the formula (I) R1—X—(A1—M1)a—(A2—M2)b—A3—Y—T—Z—R2  (I) where the symbols and indices have the following meanings, for example: T is undirected and is tetrahydrothiophene-2,5-diyl or tetrahydrothiophene-2,4-diyl R1 is hydrogen or a straight-chain or branched C1-20-alkyl or C2-20-alkenyl radical (with or without asymmetric carbon atoms), R2 is hydrogen or a straight-chain or branched alkyl radical (with or without asymmetric carbon atoms) having 1 to 20 carbon atoms, X is a single bond, —O—, OC(═O)—, —C(═O)O— or —OC(═O)O— Y is —OC(═O)—, —SC(═O)—, —OCH2— or —CH2CH2— Z is a single bond or —O— A1, A2 and A3 are undirected different and are each, independently of one another phenylene-1,4-diyl, M1 and M2 are undirected and are each, independently of one another —OC(═O)—, —OCH2—, —CH2CH2—, —OC(═O)CH2CH2—, —OCH2CH2CH2—, —C≡C—, —CH2CH2CH2CH2— or a single bond; a and b are each, independently of one another, 0 or 1, can be used in liquid-crystal mixtures.