Compound of formula I wherein R 11 and R 12 are each independently H, F, Cl, CN, NCS or a straight-chain or branched alkyl group with 1 to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH 2 groups to be replaced, in each occurrence independently from one another, by -O-, -S-, -NH-, -N(CH 3)-, -CO-, -COO-, -OCO-, -O-CO-O-, -S-CO-, -CO-S-, -CH=CH-, -CH=CF-, -CF=CF- or -C≡C- in such a manner that oxygen atoms are not linked directly to one another, MG 11 is -A 11 -Z 11 -A 12 -, MG 12 is -A 13 -Z 12 -A 14 -Z 13 -A 15 -, Z 11 to Z 13 are, independently of each other in each occurrence, a single bond, -COO-, -OCO-, -O-CO-O-, -OCH 2 -, -CH 2 O-, -CH2CH2-, - 4 -, -CF 2 CF 2 -, -CH=CH-, -CF=CF-, -CH=CH-COO-, -OCO-CH=CH- or -C≡C-, optionally substituted with one or more of F, S and/or Si, A 11 to A 15 are each independently in each occurrence 1,4-phenylene, wherein in addition one or more CH groups may be replaced by N, trans-1,4-cyclo-hexylene in which, in addition, one or two non-adjacent CH 2 groups may be replaced by O and/or S, 1,4-cyclohexenylene, 1,4-bicyclo-(2,2,2)-octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydro-naphthalene-2,6-diyl, 1,2,3,4-tetrahydro-naphthalene-2,6-diyl, cyclobutane-1,3-diyl, spiro[3.3]heptane-2,6-diyl or dispiro[3.1.3.1] decane-2,8-diyl, it being possible for all these groups to be unsubstituted, mono-, di-, tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl groups with 1 to 7 C atoms, wherein one or more H atoms may be substituted by F or Cl, Sp 1 is a spacer group comprising 1, 3 or 5 to 40 C atoms, wherein one or more non-adjacent and non-terminal CH 2 groups may also be replaced by -O-, -S-, -NH-, -N(CH 3)-, -CO-, -O-CO-, -S-CO-, -O-COO-, -CO-S-, -CO-O-, -CH(halogen)-, -CH -, -CH=CH- or -C≡C-, however in such a way that no two O-atoms are adjacent to one another, no two -CH=CH- groups are adjacent to each other and no two groups selected from -O-CO-, -S-CO-, -O-COO-, -CO-S-, -CO-O- and -CH=CH- are adjacent to each other, X 11 and X 12 are independently from one another a linking group selected from -CO-O-, -O-CO-, -CH=CH-, -C≡C-, -O-, -S-CO-, -CO-S-, -S- and -CO- or a single bond, however under the condition that in -X 11 -Sp 1 -X 12 - no two O atoms are adjacent to one another, no two -CH=CH- groups are adjacent to each other and no two groups selected from -O-CO-, -S-CO-, -O-COO-, -CO-S-, -CO-O- and -CH=CH- are adjacent to each other. R 11 and R 12 are each independently H, F, Cl, CN, NCS or a straight-chain or branched alkyl group with 1 to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH 2 groups to be replaced, in each occurrence independently from one another, by -O-, -S-, -NH-, -N(CH 3)-, -CO-, -COO-, -OCO-, -O-CO-O-, -S-CO-, -CO-S-, -CH=CH-, -CH=CF-, -CF=CF- or -C≡C- in such a manner that oxygen atoms are not linked directly to one another, MG 11 is -A 11 -Z 11 -A 12 -, MG 12 is -A 13 -Z 12 -A 14 -Z 13 -A 15 -, Z 11 to Z 13 are, independently of each other in each occurrence, a single bond, -COO-, -OCO-, -O-CO-O-, -OCH 2 -, -CH 2 O-, -CH2CH2-, - 4 -, -CF 2 CF 2 -, -CH=CH-, -CF=CF-, -CH=CH-COO-, -OCO-CH=CH- or -C≡C-, optionally substituted with one or more of F, S and/or Si, A 11 to A 15 are each independently in each occurrence 1,4-phenylene, wherein in addition one or more CH groups may be replaced by N, trans-1,4-cyclo-hexylene in which, in addition, one or two non-adjacent CH 2 groups may be replaced by O and/or S, 1,4-cyclohexenylene, 1,4-bicyclo-(2,2,2)-octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydro-naphthalene-2,6-diyl, 1,2,3,4-tetrahydro-naphthalene-2,6-diyl, cyclobutane-1,3-diyl, spiro[3.3]heptane-2,6-diyl or dispiro[3.1.3.1] decane-2,8-diyl, it being possible for all these groups to be unsubstituted, mono-, di-, tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl groups with 1 to 7 C atoms, wherein one or more H atoms may be substituted by F or Cl, Sp 1 is a spacer group comprising 1, 3 or 5 to 40 C atoms, wherein one or more non-adjacent and non-terminal CH 2 groups may also be replaced by -O-, -S-, -NH-, -N(CH 3)-, -CO-, -O-CO-, -S-CO-, -O-COO-, -CO-S-, -CO-O-, -CH(halogen)-, -CH -, -CH=CH- or -C≡C-, however in such a way that no two O-atoms are adjacent to one another, no two -CH=CH- groups are adjacent to each other and no two groups selected from -O-CO-, -S-CO-, -O-COO-, -CO-S-, -CO-O- and -CH=CH- are adjacent to each other, X 11 and X 12 are independently from one another a linking group selected from -CO-O-, -O-CO-, -CH=CH-, -C≡C-, -O-, -S-CO-, -CO-S-, -S- and -CO- or a single bond,