Compound of the formula or, where the following applies to the symbols and indices used: Ar is a heteroaromatic ring system having 5 to 40 aromatic ring atoms which is bonded to L via a carbon atom if L stands for a single bond, and which is bonded to L via a carbon atom or a nitrogen atom if L is not equal to a single bond, and which may be substituted by one or more radicals R 1; or Ar is an aromatic ring system having 6 to 40 aromatic ring atoms, which may be substituted by one or more radicals R 1, if L stands for C(=O); L is a single bond, C(=O) or an aromatic ring system having 5 to 24 aromatic ring atoms, which may be substituted by one or more radicals R; R, R 1 are selected on each occurrence, identically or differently, from the group consisting of H, D, F, Cl, Br, I, CN, Si(R 2) 3, a straight-chain alkyl, alkoxy or thioalkyl group having 1 to 40 C atoms or a branched or cyclic alkyl, alkoxy or thioalkyl group having 3 to 40 C atoms, which may in each case be substituted by one or more radicals R 2, where in each case one or more non-adjacent CH 2 groups may be replaced by Si(R 2) 2, C=NR 2, P(=O)(R 2), SO, SO 2, NR 2, O, S or CONR 2 and where one or more H atoms may be replaced by D, F, Cl, Br or I, an aromatic or heteroaromatic ring system having 6 to 40 C atoms, which may in each case be substituted by one or more radicals R 2, an aryloxy group having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R 2, or an aralkyl group having 5 to 60 aromatic ring atoms, which may in each case be substituted by one or more radicals R 2, where two or more adjacent substituents R or R 1 may optionally form a mono- or polycyclic, aliphatic ring system, which may be substituted by one or more radicals R 2; R 2 is selected from the group consisting of H, D, F, an aliphatic hydrocarbon radical having 1 to 20 C atoms or an aromatic or heteroaromatic ring system having 5 to 30 C atoms, in which one or more H atoms may be replaced by D or F, where two or more adjacent substituents R 2 may form a mono- or polycyclic, aliphatic ring system with one another; s is 0, 1 or 2; m is on each occurrence, identically or differently, 0, 1, 2, 3 or 4; n is on each occurrence, identically or differently, 0, 1, 2 or 3. Ar is a heteroaromatic ring system having 5 to 40 aromatic ring atoms which is bonded to L via a carbon atom if L stands for a single bond, and which is bonded to L via a carbon atom or a nitrogen atom if L is not equal to a single bond, and which may be substituted by one or more radicals R 1; or Ar is an aromatic ring system having 6 to 40 aromatic ring atoms, which may be substituted by one or more radicals R 1, if L stands for C(=O); L is a single bond, C(=O) or an aromatic ring system having 5 to 24 aromatic ring atoms, which may be substituted by one or more radicals R; R, R 1 are selected on each occurrence, identically or differently, from the group consisting of H, D, F, Cl, Br, I, CN, Si(R 2) 3, a straight-chain alkyl, alkoxy or thioalkyl group having 1 to 40 C atoms or a branched or cyclic alkyl, alkoxy or thioalkyl group having 3 to 40 C atoms, which may in each case be substituted by one or more radicals R 2, where in each case one or more non-adjacent CH 2 groups may be replaced by Si(R 2) 2, C=NR 2, P(=O)(R 2), SO, SO 2, NR 2, O, S or CONR 2 and where one or more H atoms may be replaced by D, F, Cl, Br or I, an aromatic or heteroaromatic ring system having 6 to 40 C atoms, which may in each case be substituted by one or more radicals R 2, an aryloxy group having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R 2, or an aralkyl group having 5 to 60 aromatic ring atoms, which may in each case be substituted by one or more radicals R 2, where two or more adjacent substituents R or R 1 may optionally form a mono- or polycyclic, aliphatic ring system, which may be substituted by one or more radicals R 2; R 2 is selected from the group consisting of H, D, F, an aliphatic hydrocarbon radical having 1 to 20 C atoms or an aromatic or heteroaromatic ring system having 5 to 30 C atoms, in which one or more H atoms may be replaced by D or F, where two or more adjacent substituents R 2 may form a mono- or polycyclic, aliphatic ring system with one another; s is 0, 1 or 2; m is on each occurrence, identically or differently, 0, 1, 2, 3 or 4; n is on each occurrence, identically or differently, 0, 1, 2 or 3.