Compound of the formula, where the following applies to the symbols and indices used: X is on each occurrence, identically or differently, CR 1 or N; or X is C if the group Ar is bonded at this position; Ar is on each occurrence, identically or differently, a phenylene group, which may be substituted by one or more radicals R; Ar 1 is an aromatic ring system having 6 to 24 aromatic ring atoms which contains no condensed aryl groups having more than 10 aromatic ring atoms and which may be substituted by one or more radicals R 1, or is a dibenzofuran or dibenzothiophene group, each of which may be substituted by one or more radicals R 1; Ar 2 is on each occurrence, identically or differently, an aryl group, a biaryl group, a triaryl group or quateraryl group, where each individual one of the aryl groups in the above-mentioned groups has 6 to 10 aromatic ring atoms and may be substituted by one or more radicals R 1, or is a dibenzofuran or dibenzothiophene group, each of which may be substituted by one or more radicals R 1; R is on each occurrence, identically or differently, H, D, F, CN, an aryl group, a biaryl group, a triaryl group or quateraryl group, where each individual one of the aryl groups in the above-mentioned groups has 6 to 10 aromatic ring atoms and may be substituted by one or more radicals R 1, or a carbazole group, which is linked via a carbon atom and which may also be substituted by one or more radicals R 1; R 1 is on each occurence, identically or differently, H, D, F, CN, a straight-chain alkyl or alkoxy group having 1 to 20 C atoms or a branched or cyclic alkyl or alkoxy group having 3 to 20 C atoms, where one or more non-adjacent CH 2 groups may be replaced by R 2 C=CR 2, C≡C or O and where one or more H atoms may be replaced by D or f, or an aryl group having 6 to 10 atoms, which may be substituted by one or more radicals R 2, or is dibenzofuran or dibenzothiophene group, each of which may be substituted by one or more radicals R 2, or a carbazole group, which is linked via a carbon atom and which may also be substituted by one or more radicals R 2, or an aralkyl group having 6 to 10 aromatic ring atoms, which may be substituted by one or more radicals R 2; two adjacent substituents R 1 here, together with the atoms to which they are bonded, may also form a mono- or polycyclic, aliphatic ring system with one another; R 2 is on each occurrence, identically or differently, H, D or an aliphatic hydrocarbon radical having 1 to 20 C atoms or an aryl group having 6 to 10 ring atoms; n is 1, 2, 3 or 4, preferably 1, 2 or 3. X is on each occurrence, identically or differently, CR 1 or N; or X is C if the group Ar is bonded at this position; Ar is on each occurrence, identically or differently, a phenylene group, which may be substituted by one or more radicals R; Ar 1 is an aromatic ring system having 6 to 24 aromatic ring atoms which contains no condensed aryl groups having more than 10 aromatic ring atoms and which may be substituted by one or more radicals R 1, or is a dibenzofuran or dibenzothiophene group, each of which may be substituted by one or more radicals R 1; Ar 2 is on each occurrence, identically or differently, an aryl group, a biaryl group, a triaryl group or quateraryl group, where each individual one of the aryl groups in the above-mentioned groups has 6 to 10 aromatic ring atoms and may be substituted by one or more radicals R 1, or is a dibenzofuran or dibenzothiophene group, each of which may be substituted by one or more radicals R 1; R is on each occurrence, identically or differently, H, D, F, CN, an aryl group, a biaryl group, a triaryl group or quateraryl group, where each individual one of the aryl groups in the above-mentioned groups has 6 to 10 aromatic ring atoms and may be substituted by one or more radicals R 1, or a carbazole group, which is linked via a carbon atom and which may also be substituted by one or more radicals R 1; R 1 is on each occurence, identically or differently, H, D, F, CN, a straight-chain alkyl or alkoxy group having 1 to 20 C atoms or a branched or cyclic alkyl or alkoxy group having 3 to 20 C atoms, where one or more non-adjacent CH 2 groups may be replaced by R 2 C=CR 2, C≡C or O and where one or more H atoms may be replaced by D or f, or an aryl group having 6 to 10 atoms, which may be substituted by one or more radicals R 2, or is dibenzofuran or dibenzothiophene group, each of which may be substituted by one or more radicals R 2, or a carbazole group, which is linked via a carbon atom and which may also be substituted by one or more radicals R 2, or an aralkyl group having 6 to 10 aromatic ring atoms, which may be substituted by one or more radicals R 2; two adjacent substituents R 1 here, together with the atoms to which they are bonded, may also form a mono- or polycyclic, aliphatic ring system with one another; R 2 is on each occurrence, identically or differently, H, D or an aliphatic hydrocarbon radical having 1 to 20 C atoms or an aryl group having 6 to 10 ring atoms; n is 1, 2, 3 or 4, preferably 1, 2 or 3.