Birefringent layer with negative optical dispersion

A birefringent layer with R450/R550<1, wherein R450 is the optical on-axis retardation at a wavelength of 450 nm and R550 is the optical on-axis retardation at a wavelength of 550 nm, said layer comprising an LC medium that comprises one or more non-polymerizable compounds of formula I as a guest component

• wherein
• U1 and U2 are independently of each other selected from the group consisting of
• including their mirror images, wherein U1 and U2 are each bonded to the group —(B)q— via an axial bond, and in which one or two non-adjacent ring CH2 groups are optionally replaced by O and/or S, and U1 and U2 are optionally substituted by one or more groups L,
• L is, in case of multiple occurrence independently of one another, F, Cl, Br, I, —CN, —NO2, —NCO, —NCS, —OCN, —SCN, —O(═O)NR0R00, —C(═O)X, —C(═O)OR0, —C(═O)R0, —NR0R00, —OH, —SF5, optionally substituted silyl, aryl with 1 to 12 C atoms, or straight chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy with 1 to 12 C atoms, wherein one or more H atoms are optionally replaced by F or Cl,
• X is halogen,
• Q1 and Q2 are independently of each other CH or SiH,
• Q3 is C or Si,
• B is in each occurrence independently of one another —C≡C—, —CY1═CY2— or an optionally substituted aromatic or heteroaromatic group,
• Y1 and Y2 are independently of each other H, F, Cl, CN or R0,
• g is an integer from 1 to 10,
• A1, A2,
• A3 and A4 are independently of each other selected from the group consisting of non-aromatic carbocylic groups, heterocyclic groups, aromatic groups and heteroaromatic groups, which are optionally substituted by one or more L, and wherein each of -(A1-Z1)m—U1—(Z2-A2)n- and -(A3-Z3)o—U2—(Z4-A4)p- does not contain more aromatic groups than non-aromatic groups,
• Z1, Z2
• Z3 and Z4 are independently of each other —O—, —S—, —CO—, —COO—, —OCO—, —O—COO—, —CO—NR0—, —NR0—CO—, —NR0—CO—NR0—, —OCH2—, —CH2O— —SCH2—, —CH2S—, —CF2O—, —OCF2—, —CF2S—, —SCF2—, —CH2CH2—, —(CH2)3—, —)CH2)4—, —CF2CH2—, —CH2CF2—, —CF2CF2—, —CH═CH—, —CY1═CY2—, —CH═N—, —N═CH—, —N═N—, —CH═CR0—, —CH═CH—COO—, —OCO—CH═CH—, CR0R00 or a single bond,
• R0 and R00 are independently of each other H or alkyl with 1 to 12 C-atoms,
• m and n are independently of each other 0, 1, 2, 3 or 4,
• o and p are independently of each other 0, 1, 2, 3 or 4, and
• R1, R2, R3,
• R4 and R5 are independently of each other identical or different groups and are H, halogen, —CN, —NC, —NCO, —NCS, —OCN, —SCN, —C(═O)NR0R00, —C(═O)X0—C(═O)R0, —NH2, —NR0R00, —SH, —SR0, —SO3H, —SO2R0, —OH, —NO2, —CF3—SF5, optionally substituted silyl, or carbyl or hydrocarbyl with 1 to 40 C atoms that is optionally substituted and optionally comprises one or more hetero atoms, and wherein one or more H atoms are optionally replaced by D atoms,
• and further comprising one or more mesogenic or liquid crystalline compounds as a host component.