Compounds of the formula I in which A 3 denotes L 1, L 2 each, independently of one another, denote branched or unbranched alkyl, alkenyl or alkynyl having 1 to 12 C atoms, in which, in addition, one or more "-CH 2 -" groups may be replaced, independently of one another, by O, or denote substituted or unsubstituted cycloalkyl, cycloalkenyl, substituted or unsubstituted phenyl, substituted or unsubstituted arylethynyl, fluorinated alkyl or alkenyl, fluorinated alkoxy or alkenyloxy, F, Cl, Br, CN, NCS or SF 5, L 3, L 4 denote H, R 1 and R 2, independently of one another, denote a halogenated or unsubstituted alkyl radical having 1 to 15 C atoms, where, in addition, one or more CH 2 groups in these radicals may each be replaced, independently of one another, by -C≡C-, -CH=CH-, -CF=CF-, -CF=CH-, -CH=CF-, - - and -O- in such a way that O atoms are not linked directly to one another, F, Cl, Br, CN, CF 3, OCF 3, NCS or SF 5, R 2 also denotes H, A 1, A 2, A 4, A 5 each, independently of one another, denote a) 1,4-phenylene, in which one or more CH groups may be replaced by N, b) trans-1,4-cyclohexylene or cyclohexenylene, in which, in addition, one or two non-adjacent CH 2 groups may be replaced by -O- and/or -S-, and in which H may be replaced by F, c) a radical of the formula or or d) a radical from the group 1,4-bicyclo[2.2.2]octylene, cyclobutane-1,3-diyl, spiro[3.3]heptane-2,6-diyl, thiophene-2,5-diyl, thiophene-2,4-diyl, furan-2,5-diyl, furan-2,4-diyl, or and in which, in groups a), b), c) and d), in addition one or more H atoms may be replaced by Br, Cl, F, CN, -NCS, SF 5, C 1 -C 10 alkyl, C 1 -C 10 alkoxy or a mono- or polyfluorinated C 1 -C 10 alkyl or alkoxy group, k denotes 0 or 1, Z 1, Z 5, independently of one another, denote a single bond, -C≡C-, -CH=CH-, -CH 2 O- - O-, -CF 2 O-, -CF 2 CF 2 -, -CH 2 CF 2 -, -CH 2 CH 2 -, -(CH 2) 4 -, -CH=CF- or -CF=CF-, where asymmetrical bridges may be oriented to both sides, where, for k = 0, Z 5 is a single bond, and m, n, independently of one another, denote 0, 1 or 2. A 3 denotes L 1, L 2 each, independently of one another, denote branched or unbranched alkyl, alkenyl or alkynyl having 1 to 12 C atoms, in which, in addition, one or more "-CH 2 -" groups may be replaced, independently of one another, by O, or denote substituted or unsubstituted cycloalkyl, cycloalkenyl, substituted or unsubstituted phenyl, substituted or unsubstituted arylethynyl, fluorinated alkyl or alkenyl, fluorinated alkoxy or alkenyloxy, F, Cl, Br, CN, NCS or SF 5, L 3, L 4 denote H, R 1 and R 2, independently of one another, denote a halogenated or unsubstituted alkyl radical having 1 to 15 C atoms, where, in addition, one or more CH 2 groups in these radicals may each be replaced, independently of one another, by -C≡C-, -CH=CH-, -CF=CF-, -CF=CH-, -CH=CF-, - - and -O- in such a way that O atoms are not linked directly to one another, F, Cl, Br, CN, CF 3, OCF 3, NCS or SF 5, R 2 also denotes H, A 1, A 2, A 4, A 5 each, independently of one another, denote a) 1,4-phenylene, in which one or more CH groups may be replaced by N, b) trans-1,4-cyclohexylene or cyclohexenylene, in which, in addition, one or two non-adjacent CH 2 groups may be replaced by -O- and/or -S-, and in which H may be replaced by F, c) a radical of the formula or or d) a radical from the group 1,4-bicyclo[2.2.2]octylene, cyclobutane-1,3-diyl, spiro[3.3]heptane-2,6-diyl, thiophene-2,5-diyl, thiophene-2,4-diyl, furan-2,5-diyl, furan-2,4-diyl, or and in which, in groups a), b), c) and d), in addition one or more H atoms may be replaced by Br, Cl, F, CN, -NCS, SF 5, C 1 -C 10 alkyl, C 1 -C 10 alkoxy or a mono- or polyfluorinated C 1 -C 10 alkyl or alkoxy group, k denotes 0 or 1, Z 1, Z 5, independently of one another, denote a single bond, -C≡C-, -CH=CH-, -CH 2 O- - O-, -CF 2 O-, -CF 2 CF 2 -, -CH 2 CF 2 -, -CH 2 CH 2 -, -(CH 2) 4 -, -CH=CF- or -CF=CF-, where asymmetrical bridges may be oriented to both sides, where, for k = 0, Z 5 is a single bond, and m, n, independently of one another, denote 0, 1 or 2. k denotes 0 or 1, Z 1, Z 5, independently of one another, denote a single bond, -C≡C-, -CH=CH-, -CH 2 O- - O-, -CF 2 O-, -CF 2 CF 2 -, -CH 2 CF 2 -, -CH 2 CH 2 -, -(CH 2) 4 -, -CH=CF- or -CF=CF-, where asymmetrical bridges may be oriented to both sides, where, for k = 0, Z 5 is a single bond, and m, n, independently of one another, denote 0, 1 or 2.