Ethyne derivatives

Ethyne derivatives of the formula I

• R.sup.1 --(A.sup.1 --Z.sup.1 --).sub.m --A.sup.3 --C.tbd.C--A.sup.4 --(Z.sup.2 --A.sup.2).sub.n --R.sup.2 I
• wherein
• R.sup.1 is an alkyl or alkenyl radical having 1 to 15 C atoms which is unsubstituted, monosubstituted by --CN or at least monosubstituted by halogen, it also being possible for one or more CH.sub.2 groups in these radicals in each case independently of one another to be replaced by --O--, --S--, --CO--, --O--CO--, --O--COO--, --CO--O-- or --C.tbd.C-- such that heteroatoms are not linked directly to one another, H, halogen, --CN or --NCS,
• R.sup.2 is --OCF.sub.3, --OC.sub.2 F.sub.5 or --OC.sub.2 F.sub.4 H,
• A.sup.1 and A.sup.2 in each case independently of one another are a
• a) 1,4-phenylene radical, wherein one or more CH groups can also be replaced by N,
• b) trans-1,4-cyclohexylene radical, wherein one or two non-adjacent CH.sub.2 groups can also be replaced by independently replaced by --O-- or --S--,
• c) radical from the group comprising 1,4-cyclohexenylene, 1,4-cyclohexadienylene or 1,4-bicyclo-(2.2.2)-octylene,
• it being possible for the radicals a) and b) to be substituted once or more than once by halogen, cyano and/or CH.sub.3,
• Z.sup.1 and Z.sup.2 in each case independently of one another are --CO--O--, --O--CO--, --CH.sub.2 O--, --OCH.sub.2 --, --CH.sub.2 CH.sub.2 --, --C.tbd.C-- or a single bond,
• m and n in each case independently of one another are 0 or 1,
• A.sup.3 and A.sup.4 in each case independently of one another are a
• a) 1,4-phenylene or 4,4'-biphenylene radical, wherein one or more CH groups can also be replaced by N,
• b) trans-1,4-cyclohexylene radical,
• c) radical from the group comprising 1,4-cyclohexenylene, 1,4-cyclohexadienylene or 1,4-bicyclo(2.2.2)octylene,
• it being possible for the radicals a) and b) to be substituted once or more than once by halogen, cyano and/or CH.sub.3,
• with the proviso that in at least one of the groups A.sup.3 or A.sup.4 at least one CH group is replaced by N and/or at least one of the groups A.sup.3 and A.sup.4 is trans-1,4-cyclohexylene or 1,4-bicyclo(2.2.2)octylene and/or at least one of the groups A.sup.1, A.sup.2, A.sup.3 and A.sup.4 is 1,4-cyclohexenylene or 1,4-cyclohexadienylene.