Materials for organic electroluminescent devices

A compound of formula I

• wherein
• R is selected on each occurrence, identically or differently, from the group consisting of F, CN, NO2, ArNAr2, NAr2, C(═O)Ar, C(═O)R2, P(═O)Ar2, S(═O)Ar, S(═O)2Ar, —CR2═C(R2)2 and a mono- or polycyclic aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, optionally substituted by one or more non-aromatic radicals R1;
• two radicals Ar which are bonded to the same nitrogen or phosphorus atom are optionally linked to one another by a single bond or a bridge selected from B(R2), C(R2)2, Si(R2)2, C═O, C═NR2, C═C(R2)2, O, S, S═O, SO2, N(R2), P(R2) and P(═O)R2;
• R1 is selected, identically or differently on each occurrence, from the group consisting of H, D, F, OH, CN, a straight-chain alkyl, alkoxy or thioalkoxy group having 1 to 40 C atoms and a branched or cyclic alkyl, alkoxy or thioalkoxy group having 3 to 40 C atoms or an alkenyl group having 2 to 40 C atoms, each of which is optionally substituted by one or more radicals R2, where one or more non-adjacent CH2 groups is optionally replaced by R2C═CR2, C≡C, Si(R2)2, C═O, C═S, C═NR2, P(═O)(R2), SO, SO2, NR2, O or S and where one or more H atoms is optionally replaced by D, F, Cl, Br, I, CN or NO2;
• where, in addition, the respective R1 which is located in the vicinal position to the radical R, in the case where R is an aromatic or heteroaromatic ring system, is optionally a divalent unit which is linked to the group R;
• 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 radicals R1;
• R2 is selected on each occurrence, identically or differently, from the group consisting of H, D, F, CN and an aliphatic, aromatic or heteroaromatic hydrocarbon radical having 1 to 20 C atoms, in which, in addition, one or more H atoms may be replaced by F, CN, 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;
• two or more adjacent substituents R2 may also be linked to one another by a covalent bond or also, in the case where the R2 involved are aromatic or heteroaromatic hydrocarbon radicals, by one or more divalent aliphatic hydrocarbon units.