Compound of the formula -, where the following applies to the symbols used: R is on each occurrence, identically or differently, H, F, C(=O)Ar, P(=O)(Ar) 2, CN, a straight-chain alkyl group having 1 to 10 C atoms or a branched or cyclic alkyl group having 3 to 10 C atoms, each of which may be substituted by one or more radicals R 1, where one or more H atoms may be replaced by F or CN, or an aromatic or heteroaromatic ring system having 5 to 40 aromatic ring atoms, which may in each case be substituted by one or more radicals R 1; R 1 is on each occurrence, identically or differently, H, D, F, Cl, Br, I, CHO, N(R 2) 2, N(Ar) 2, C(=O)Ar, P(=O)(Ar) 2 S(=O)Ar, S(=O) 2 Ar, CR 2 =CR 2 Ar, CN, NO 2, Si(R 2) 3, B(OR 2) 2, B(R 2) 2, B(N(R 2) 2) 2, OSO 2 R 2, a straight-chain alkyl, alkoxy or thioalkoxy group having 1 to 40 C atoms or a straight-chain alkenyl or alkynyl group having 2 to 40 C atoms or a branched or cyclic alkyl, alkenyl, alkynyl, alkoxy or thioalkoxy group having 3 to 40 C atoms, each of which may be substituted by one or more radicals R 2, where one or more non-adjacent CH 2 groups may be replaced by R 2 C=CR 2, C=C, Si(R 2) 2, Ge(R 2) 2, Sn(R 2) 2, C=O, C=S, C=S e, 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, I, CN or NO 2, or an aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may in each case be substituted by one or more radicals R 2, or an aryloxy or heteroaryloxy group having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R 2, or a combination of these systems; Ar is on each occurrence, identically or differently, an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms, which may be substituted by one or more non-aromatic radicals R 1; two radicals Ar which are bonded to the same nitrogen or phosphorus atom may also be linked to one another here by a single bond or a bridge selected from B(R 2), C(R 2) 2, Si(R 2) 2, C=O, C=NR 2, C=C(R 2) 2, O, S, S=O, SO 2, N(R 2), P(R 2) and P(=O)R 2; R 2 is on each occurrence, identically or differently, H, D or an aliphatic, aromatic and/or heteroaromatic hydrocarbon radical having 1 to 20 C atoms, in which, in addition, H atoms may be replaced by F; two or more adjacent substituents R 2 here may also form a mono- or polycyclic, aliphatic or aromatic ring system with one another. R is on each occurrence, identically or differently, H, F, C(=O)Ar, P(=O)(Ar) 2, CN, a straight-chain alkyl group having 1 to 10 C atoms or a branched or cyclic alkyl group having 3 to 10 C atoms, each of which may be substituted by one or more radicals R 1, where one or more H atoms may be replaced by F or CN, or an aromatic or heteroaromatic ring system having 5 to 40 aromatic ring atoms, which may in each case be substituted by one or more radicals R 1; R 1 is on each occurrence, identically or differently, H, D, F, Cl, Br, I, CHO, N(R 2) 2, N(Ar) 2, C(=O)Ar, P(=O)(Ar) 2 S(=O)Ar, S(=O) 2 Ar, CR 2 =CR 2 Ar, CN, NO 2, Si(R 2) 3, B(OR 2) 2, B(R 2) 2, B(N(R 2) 2) 2, OSO 2 R 2, a straight-chain alkyl, alkoxy or thioalkoxy group having 1 to 40 C atoms or a straight-chain alkenyl or alkynyl group having 2 to 40 C atoms or a branched or cyclic alkyl, alkenyl, alkynyl, alkoxy or thioalkoxy group having 3 to 40 C atoms, each of which may be substituted by one or more radicals R 2, where one or more non-adjacent CH 2 groups may be replaced by R 2 C=CR 2, C=C, Si(R 2) 2, Ge(R 2) 2, Sn(R 2) 2, C=O, C=S, C=S e, 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, I, CN or NO 2, or an aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may in each case be substituted by one or more radicals R 2, or an aryloxy or heteroaryloxy group having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R 2, or a combination of these systems; Ar is on each occurrence, identically or differently, an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms, which may be substituted by one or more non-aromatic radicals R 1; two radicals Ar which are bonded to the same nitrogen or phosphorus atom may also be linked to one another here by a single bond or a bridge selected from B(R 2), C(R 2) 2, Si(R 2) 2, C=O, C=NR 2, C=C(R 2) 2, O, S, S=O, SO 2, N(R 2), P(R 2) and P(=O)R 2; R 2 is on each occurrence, identically or differently, H, D or an aliphatic, aromatic and/or heteroaromatic hydrocarbon radical having 1 to 20 C atoms, in which, in addition, H atoms may be replaced by F; two or more adjacent substituents R 2 here may also form a mono- or polycyclic, aliphatic or aromatic ring system with one another.