Materials for organic light emitting devices

A compound of formula (1a) or (2a),

• where the following applies to the symbols and indices used:
• X is on each occurrence, identically or differently, CR or N, with the proviso that at least one group X stands for N;
• 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 R;
• Y1 is O or S
• Y2 is NR′;
• R′ is a 1,3,5-triazine group or a pyrimidine group, each of which may be substituted by one or more radicals R1, or is a phenylene group which is substituted with a 1,3,5-triazine group or a pyrimidine group, each of which may be substituted by one or more radicals R1;
• L is a single bond;
• R is selected on each occurrence, identically or differently, from the group consisting of H, D, F, Cl, Br, I, CN, NO2, N(Ar1)2, N(R1)2, C(═O)Ar1, C(═O)R1, P(═O)(Ar1)2, P(Ar1)2, B(Ar1)2, Si(Ar1)3, Si(R1)3, 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 group having 2 to 20 C atoms, each of which may be substituted by one or more radicals R1, where one or more non-adjacent CH2 groups may be replaced by R1C═CR1, Si(R1)2, C═O, C═S, C═NR1, P(═O)(R1), SO, SO2, NR1, O, S or CONR1 and where one or more H atoms may be replaced by D, F, Cl, Br, I, CN or NO2, 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 R1, an aryloxy or heteroaryloxy group having 5 to 40 aromatic ring atoms, which may be substituted by one or more radicals R1, or an aralkyl or heteroaralkyl group having 5 to 40 aromatic ring atoms, which may be substituted by one or more radicals R1;
• two substituents R which are bonded to the same carbon atom or to adjacent carbon atoms may optionally form a monocyclic or polycyclic, aliphatic, aromatic or heteroaromatic ring system here, which may be substituted by one or more radicals R1;
• Ar1 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 R1;
• two radicals Ar1 which are bonded to the same N atom, P atom or B atom may also be bridged to one another here by a single bond or a bridge selected from N(R1), C(R1)2, O or S;
• R1 is selected on each occurrence, identically or differently, from the group consisting of H, D, F, CN, an aliphatic hydrocarbon radical having 1 to 20 C atoms or an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms, in which one or more H atoms may be replaced by D, F, Cl, Br, I or CN and which may be substituted by one or more alkyl groups, each having 1 to 4 carbon atoms;
• two or more adjacent substituents R1 may form a mono- or polycyclic, aliphatic ring system with one another here.