Use of 4-fluoropyrimidine derivatives as component for ferroelectric liquid crystal mixtures

A ferroelectric liquid crystal mixture comprising 2 to 20 components and comprising at least one 4-fluoropyrimidine of the formula (I):

• ##STR19## in which the symbols have the following meaning:
• R.sup.1 and R.sup.2 independently of one another are straight-chain or branched alkyl having 1 to 16 carbon atoms, it being possible for one or two non-adjacent --CH.sub.2 -- groups to be replaced by --O--, --S--, --CO--, --CO--O--, --O--CO--, --CH.dbd.CH--, --OC(O)O--, --C.dbd.C--, ##STR20## or --Si(CH.sub.3).sub.2 --, or are one of the following groups:
• ##STR21## ##STR22## R.sup.3 and R.sup.4 independently of one another are H or alkyl having 1 to 16 carbon atoms or alkenyl having 2 to 16 carbon atoms, or R.sup.3 and R.sup.4 together are --(CH.sub.2).sub.4 -- or --(CH.sub.2).sub.5 --,
• --M.sup.1 -- is --CO--O, --O--CO--, --CH.sub.2 --O--, --O--CH.sub.2 --, --C.dbd.C--, --CH.dbd.CH--, --CH.sub.2 --CH.sub.2 --, --CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 --, --CH.sub.2 CH.sub.2 CH.sub.2 O--
• --M.sup.2 -- is CH.sub.2 --O--, --O--CH.sub.2, ##STR23## or a single bond a and b independently of one another are zero or one, on condition that a is zero if b is zero, and ##STR24## independently of one another are 1,4-phenylene, 1,4-cyclohexylene, 2,5-pyridinediyl or (1,3,4)thiadiazol-2,5-diyl.