Mesogenic media based on a mixture of positive dielectrically compounds, characterised in that it comprises a) at least one compound of the formula I, wherein L 11 to L 14 are, independently of each other, H or F, is an aromatic and/or alicyclic ring, or a group comprising two or more fused aromatic or alicyclic rings, wherein these rings optionally contain one or more hetero atoms selected from N, O and/or S, and are optionally mono-, di- or polysubstituted by R, R is halogen, CN, NCS, SCN, SF 5, SO 2 CF 3 or alkyl, which is straight chain or branched, has 1 to 20 C-atoms, is unsubstituted, mono- or poly-substituted by F, Cl, or CN, and in which one or more CH 2 groups are optionally replaced, in each case independently from one another, by -O-, -S-, -NH-, -NR 01 -,-SiR 01 R 02 -, -CO-, -COO-, -OCO-, -OCO-O-, -S-CO-, -CO-S-, -CY 01 =CY 01 - or -C≡C- in such a manner that O and/or S atoms are not linked directly to one another, R 1 has the meaning given for R Z 1 is -CO-O-, -O-CO-, -S-CO-, -CO-S-, -CO-NR 01 -, -NR 01 -CO-, -OCH 2 -, -CH 2 O-, -SCH 2 -, -CH 2 S-, -CF 2 O-, -OCF 2 -, -CF 2 S-, -SCF 2 -, -CH 2 CH 2 -, -CF 2 CH 2 -, -CH 2 CF 2 -, -CF 2 CF 2 -, -CH=N-, -N=CH-, -N=N-, -CH=CR 01 - -CR 01 =CH- -CY 01 =CY 02 -, -C≡C-, -(CH 2) 4 -, -CH=CH-CO-O-, -O-CO-CH=CH-or a single bond, Y 01 and Y 02 are, independently of each other, F, Cl or CN, and alternatively one of them may be H, R 01 and R 02 are, independently of each other, H or alkyl with 1 to 12 C-atoms, n is 0 or 1, X 1 is halogen, OCF 3, CF 3, OCHF 2, CN, NCS, SCN, SF 5 or SO 2 CF 3, and b) 1-20 % by weight of at least one chiral compound or more chiral compounds with a HTP of ≥ 20 μm -1, and said mesogenic media of a) and b) exhibiting a Blue Phase. a) at least one compound of the formula I, wherein L 11 to L 14 are, independently of each other, H or F, is an aromatic and/or alicyclic ring, or a group comprising two or more fused aromatic or alicyclic rings, wherein these rings optionally contain one or more hetero atoms selected from N, O and/or S, and are optionally mono-, di- or polysubstituted by R, R is halogen, CN, NCS, SCN, SF 5, SO 2 CF 3 or alkyl, which is straight chain or branched, has 1 to 20 C-atoms, is unsubstituted, mono- or poly-substituted by F, Cl, or CN, and in which one or more CH 2 groups are optionally replaced, in each case independently from one another, by -O-, -S-, -NH-, -NR 01 -,-SiR 01 R 02 -, -CO-, -COO-, -OCO-, -OCO-O-, -S-CO-, -CO-S-, -CY 01 =CY 01 - or -C≡C- in such a manner that O and/or S atoms are not linked directly to one another, R 1 has the meaning given for R Z 1 is -CO-O-, -O-CO-, -S-CO-, -CO-S-, -CO-NR 01 -, -NR 01 -CO-, -OCH 2 -, -CH 2 O-, -SCH 2 -, -CH 2 S-, -CF 2 O-, -OCF 2 -, -CF 2 S-, -SCF 2 -, -CH 2 CH 2 -, -CF 2 CH 2 -, -CH 2 CF 2 -, -CF 2 CF 2 -, -CH=N-, -N=CH-, -N=N-, -CH=CR 01 - -CR 01 =CH- -CY 01 =CY 02 -, -C≡C-, -(CH 2) 4 -, -CH=CH-CO-O-, -O-CO-CH=CH-or a single bond, Y 01 and Y 02 are, independently of each other, F, Cl or CN, and alternatively one of them may be H, R 01 and R 02 are, independently of each other, H or alkyl with 1 to 12 C-atoms, n is 0 or 1, X 1 is halogen, OCF 3, CF 3, OCHF 2, CN, NCS, SCN, SF 5 or SO 2 CF 3, and L 11 to L 14 are, independently of each other, H or F, is an aromatic and/or alicyclic ring, or a group comprising two or more fused aromatic or alicyclic rings, wherein these rings optionally contain one or more hetero atoms selected from N, O and/or S, and are optionally mono-, di- or polysubstituted by R, R is halogen, CN, NCS, SCN, SF 5, SO 2 CF 3 or alkyl, which is straight chain or branched, has 1 to 20 C-atoms, is unsubstituted, mono- or poly-substituted by F, Cl, or CN, and in which one or more CH 2 groups are optionally replaced, in each case independently from one another, by -O-, -S-, -NH-, -NR 01 -,-SiR 01 R 02 -, -CO-, -COO-, -OCO-, -OCO-O-, -S-CO-, -CO-S-, -CY 01 =CY 01 - or -C≡C- in such a manner that O and/or S atoms are not linked directly to one another, R 1 has the meaning given for R Z 1 is -CO-O-, -O-CO-, -S-CO-, -CO-S-, -CO-NR 01 -, -NR 01 -CO-, -OCH 2 -, -CH 2 O-, -SCH 2 -, -CH 2 S-, -CF 2 O-, -OCF 2 -, -CF 2 S-, -SCF 2 -, -CH 2 CH 2 -, -CF 2 CH 2 -, -CH 2 CF 2 -, -CF 2 CF 2 -, -CH=N-, -N=CH-, -N=N-, -CH=CR 01 - -CR 01 =CH- -CY 01 =CY 02 -, -C≡C-, -(CH 2) 4 -, -CH=CH-CO-O-, -O-CO-CH=CH-or a single bond, Y 01 and Y 02 are, independently of each other, F, Cl or CN, and alternatively one of them may be H, R 01 and R 02 are, independently of each other, H or alkyl with 1 to 12 C-atoms, n is 0 or 1, X 1 is halogen, OCF 3, CF 3, OCHF 2, CN, NCS, SCN, SF 5 or SO 2 CF 3, and b) 1-20 % by weight of at least one chiral compound or more chiral compounds with a HTP of ≥ 20 μm -1, and said mesogenic media of a) and b) exhibiting a Blue Phase.