Compound of the formula, where the following applies to the symbols used: Y is C=O or C(R 1) 2; X is on each occurrence, identically or differently, CR 2 or N, where all symbols X in a ring system either stand for CR 2 or where all symbols X in a ring system stand for N; R 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 radicals R 3, or an N(Ar) 2, C(=O)Ar or P (Ar) 2 group; 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 3; two radicals Ar here which are bonded to the same nitrogen or phosphorus atom may also be linked to one another by a single bond or a bridge selected from B(R 4), C(R 4) 2, Si(R 4) 2, C=O, C=NR 4, C=C(R 4) 2, O, S, S=O, SO 2, N(R 4), P(R 4) and P(=O)R 4; R 1 is on each occurrence, identically or differently, H or a linear alkyl group having 1 to 20 C atoms or a branched or cyclic alkyl group having 3 to 20 C atoms; a plurality of radicals R 1 here may form a ring system with one another; R 2 is H; R 3 is on each occurrence, identically or differently, H, D, F, Cl, Br, I, CHO, 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 4) 3, B(OR 4) 2, B(R 4) 2, B(N(R 4) 2) 2, OSO 2 R 4, a straight-chain alkyl, alkoxy or thioalkoxy group having 1 to 40 C atoms or a branched or cyclic alkyl, alkoxy or thioalkoxy group having 3 to 40 C atoms, each of which may be substituted by one or more radicals R 4, where one or more non-adjacent CH 2 groups may be replaced by R 4 C=CR 4, C=C, Si(R 4) 2, Ge(R 4) 2, Sn(R 4) 2, C=O, C=S, C=Se, C=NR 4, P(=O)(R 4), SO, SO 2, NR 4, O, S or CONR 4 and where one or more H atoms may be replaced by 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 4, or an aryloxy or heteroaryloxy group having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R 4, or a combination of these systems; two or more adjacent substituents R 3 here may also form a mono- or polycyclic, aliphatic or aromatic ring system with one another; R 4 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 4 here may also form a mono- or polycyclic, aliphatic or aromatic ring system with one another; the following compounds are excluded from the invention: where the following applies to the symbols R 1 to R 8 used: R 1 to R 8 are independent of one another and stand for a hydrogen atom, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a secondary butyl group or a tertiary butyl group. Y is C=O or C(R 1) 2; X is on each occurrence, identically or differently, CR 2 or N, where all symbols X in a ring system either stand for CR 2 or where all symbols X in a ring system stand for N; R 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 radicals R 3, or an N(Ar) 2, C(=O)Ar or P (Ar) 2 group; 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 3; two radicals Ar here which are bonded to the same nitrogen or phosphorus atom may also be linked to one another by a single bond or a bridge selected from B(R 4), C(R 4) 2, Si(R 4) 2, C=O, C=NR 4, C=C(R 4) 2, O, S, S=O, SO 2, N(R 4), P(R 4) and P(=O)R 4; R 1 is on each occurrence, identically or differently, H or a linear alkyl group having 1 to 20 C atoms or a branched or cyclic alkyl group having 3 to 20 C atoms; a plurality of radicals R 1 here may form a ring system with one another; R 2 is H; R 3 is on each occurrence, identically or differently, H, D, F, Cl, Br, I, CHO, 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 4) 3, B(OR 4) 2, B(R 4) 2, B(N(R 4) 2) 2, OSO 2 R 4, a straight-chain alkyl, alkoxy or thioalkoxy group having 1 to 40 C atoms or a branched or cyclic alkyl, alkoxy or thioalkoxy group having 3 to 40 C atoms, each of which may be substituted by one or more radicals R 4, where one or more non-adjacent CH 2 groups may be replaced by R 4 C=CR 4, C=C, Si(R 4) 2, Ge(R 4) 2, Sn(R 4) 2, C=O, C=S, C=Se, C=NR 4, P(=O)(R 4), SO, SO 2, NR 4, O, S or CONR 4 and where one or more H atoms may be replaced by 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 4, or an aryloxy or heteroaryloxy group having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R 4, or a combination of these systems; two or more adjacent substituents R 3 here may also form a mono- or polycyclic, aliphatic or aromatic ring system with one another; R 4 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 4 here may also form a mono- or polycyclic, aliphatic or aromatic ring system with one another;