Compound of formula where the symbols and indices used are as follows: A is selected from the structures of the formulae (A-1) to (A-6) where the dotted bond represents the attachment of these groups and where a benzo group may optionally be fused to the (A-5) and (A-6) groups and may be substituted by one or more R radicals; B is an aromatic ring system having 6 to 30 aromatic ring atoms or an electron-rich heteroaromatic ring system having 13 to 30 aromatic ring atoms, each of which may be substituted by one or more nonaromatic R radicals; X is the same or different at each instance and is CH or N, where not more than one X is N; Ar is the same or different at each instance and is an aromatic or heteroaromatic ring system which has 5 to 30 aromatic ring atoms and may be substituted by one or more nonaromatic R radicals; R, R 1 is the same or different at each instance and is selected from the group consisting of H, D, F, Cl, Br, I, Si(R 2) 3, a straight-chain alkyl, alkoxy or thioalkyl group having 1 to 20 carbon atoms or a branched or cyclic alkyl, alkoxy or thioalkyl group having 3 to 20 carbon atoms or an alkenyl or alkynyl group having 2 to 20 carbon atoms, each of which may be substituted by one or more R 2 radicals, where one or more nonadjacent CH 2 groups may be replaced by R 2 C=CR 2, C=C, Si(R 2) 2, C=O, C=NR 2, P(=O)(R 2), SO, SO 2, NR 2, O, S or CONR 2 and where one or more hydrogen atoms may be replaced by D, F, Cl, Br, I, CN or NO 2, an aromatic or heteroaromatic ring system which has 5 to 40 aromatic ring atoms and may be substituted in each case by one or more R 2 radicals, or an aryloxy or heteroaryloxy group which has 5 to 40 aromatic ring atoms and may be substituted by one or more R 2 radicals; at the same time, it is optionally possible for two adjacent R 1 substituents to form a monocyclic or polycyclic, aliphatic, aromatic or heteroaromatic ring system which may be substituted by one or more R 2 radicals; R 2 is the same or different at each instance and is selected from the group consisting of H, D, F, CN, an aliphatic hydrocarbyl radical having 1 to 20 carbon atoms and an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms in which one or more hydrogen atoms may be replaced by D, F, CN or an alkyl group having 1 to 10 carbon atoms, where two or more adjacent R 2 substituents together may form a mono- or polycyclic, aliphatic ring system; n is 0 or 1. where the dotted bond represents the attachment of these groups and where a benzo group may optionally be fused to the (A-5) and (A-6) groups and may be substituted by one or more R radicals; B is an aromatic ring system having 6 to 30 aromatic ring atoms or an electron-rich heteroaromatic ring system having 13 to 30 aromatic ring atoms, each of which may be substituted by one or more nonaromatic R radicals; X is the same or different at each instance and is CH or N, where not more than one X is N; Ar is the same or different at each instance and is an aromatic or heteroaromatic ring system which has 5 to 30 aromatic ring atoms and may be substituted by one or more nonaromatic R radicals; R, R 1 is the same or different at each instance and is selected from the group consisting of H, D, F, Cl, Br, I, Si(R 2) 3, a straight-chain alkyl, alkoxy or thioalkyl group having 1 to 20 carbon atoms or a branched or cyclic alkyl, alkoxy or thioalkyl group having 3 to 20 carbon atoms or an alkenyl or alkynyl group having 2 to 20 carbon atoms, each of which may be substituted by one or more R 2 radicals, where one or more nonadjacent CH 2 groups may be replaced by R 2 C=CR 2, C=C, Si(R 2) 2, C=O, C=NR 2, P(=O)(R 2), SO, SO 2, NR 2, O, S or CONR 2 and where one or more hydrogen atoms may be replaced by D, F, Cl, Br, I, CN or NO 2, an aromatic or heteroaromatic ring system which has 5 to 40 aromatic ring atoms and may be substituted in each case by one or more R 2 radicals, or an aryloxy or heteroaryloxy group which has 5 to 40 aromatic ring atoms and may be substituted by one or more R 2 radicals; at the same time, it is optionally possible for two adjacent R 1 substituents to form a monocyclic or polycyclic, aliphatic, aromatic or heteroaromatic ring system which may be substituted by one or more R 2 radicals; R 2 is the same or different at each instance and is selected from the group consisting of H, D, F, CN, an aliphatic hydrocarbyl radical having 1 to 20 carbon atoms and an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms in which one or more hydrogen atoms may be replaced by D, F, CN or an alkyl group having 1 to 10 carbon atoms, where two or more adjacent R 2 substituents together may form a mono- or polycyclic, aliphatic ring system; n is 0 or 1.