Mixture comprising two or more different compounds of the formula where the following applies to the compounds of the formula: Ar 1 is on each occurrence, identically or differently, an aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R 1; R 1 is on each occurrence, identically or differently, H, D, F, C(=O)R 2, CN, Si(R 2) 3, P(=O)(R 2) 2, S(=O)R 2, S(=O) 2 R 2, a straight-chain alkyl, alkoxy or thioalkyl group having 1 to 20 C atoms or a branched or cyclic alkyl, alkoxy or thioalkyl group having 3 to 20 C atoms or an alkenyl or alkynyl group having 2 to 20 C atoms, where the above-mentioned groups may each be substituted by one or more radicals R 2 and where one or more CH 2 groups in the above-mentioned groups may be replaced by -R 2 C=CR 2 -, -C≡C-, Si(R 2) 2, C=O, C=S, C=NR 2, -C(=O)O-, -C(=O)NR 2 -, P(=O)(R 2), -O-, -S-, SO or SO 2 and where one or more H atoms in the above-mentioned groups may be replaced by D, F or CN, or an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms, which may in each case be substituted by one or more radicals R 2, or an aryloxy or hetero-aryloxy group having 5 to 30 aromatic ring atoms, which may be substituted by one or more radicals R 2, where two or more radicals R 1 may be linked to one another and may form a ring; R 2 is on each occurrence, identically or differently, H, D, F or an aliphatic, aromatic or heteroaromatic organic radical having 1 to 20 C atoms, in which, in addition, one or more H atoms may be replaced by D or F; two or more substituents R 2 here may be linked to one another and may form a ring; where one, two or three groups Ar 1 are selected, identically or differently, from aromatic ring systems having 12 to 60 aromatic ring atoms, which may be substituted by one or more radicals R 1. Ar 1 is on each occurrence, identically or differently, an aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R 1; R 1 is on each occurrence, identically or differently, H, D, F, C(=O)R 2, CN, Si(R 2) 3, P(=O)(R 2) 2, S(=O)R 2, S(=O) 2 R 2, a straight-chain alkyl, alkoxy or thioalkyl group having 1 to 20 C atoms or a branched or cyclic alkyl, alkoxy or thioalkyl group having 3 to 20 C atoms or an alkenyl or alkynyl group having 2 to 20 C atoms, where the above-mentioned groups may each be substituted by one or more radicals R 2 and where one or more CH 2 groups in the above-mentioned groups may be replaced by -R 2 C=CR 2 -, -C≡C-, Si(R 2) 2, C=O, C=S, C=NR 2, -C(=O)O-, -C(=O)NR 2 -, P(=O)(R 2), -O-, -S-, SO or SO 2 and where one or more H atoms in the above-mentioned groups may be replaced by D, F or CN, or an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms, which may in each case be substituted by one or more radicals R 2, or an aryloxy or hetero-aryloxy group having 5 to 30 aromatic ring atoms, which may be substituted by one or more radicals R 2, where two or more radicals R 1 may be linked to one another and may form a ring; R 2 is on each occurrence, identically or differently, H, D, F or an aliphatic, aromatic or heteroaromatic organic radical having 1 to 20 C atoms, in which, in addition, one or more H atoms may be replaced by D or F; two or more substituents R 2 here may be linked to one another and may form a ring;