Materials for organic electroluminescent devices

A compound of the formula (3a)

• where the symbols used are as follows:
• Ar is an aromatic ring system which has 6 to 30 aromatic ring atoms and may be substituted by one or more R3 radicals, or a dibenzofuran or dibenzothiophene group, each of which may be substituted by one or more R3 radicals, or a combination of an aromatic ring system having 6 to 18 aromatic ring atoms and a dibenzofuran or dibenzothiophene group, where these groups may each be substituted by one or more R3 radicals;
• Ar here may form a ring system together with the adjacent substituent R, which is bound on the same ring as Ar;
• R is the same or different at each instance and is H, D, a straight-chain alkyl or alkoxy group having 1 to 20 carbon atoms or a branched or cyclic alkyl or alkoxy group having 3 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms, where the alkyl, alkoxy or alkenyl group may in each case be substituted by one or more R3 radicals, where one or more hydrogen atoms may be replaced by D, or an aromatic ring system which has 6 to 30 aromatic ring atoms and may be substituted by one or more R3 radicals, or a dibenzofuran or dibenzothiophene group, each of which may be substituted by one or more R3 radicals;
• it is also possible here for two or more adjacent substituents R together to form a mono- or polycyclic aliphatic ring system;
• in addition, it is possible for R, which is bound on the same ring as Ar, with an adjacent Ar group to form a ring system;
• R1 is the same or different at each instance and is an aromatic ring system which has 6 to 30 aromatic ring atoms and may be substituted by one or more R3 radicals, or a dibenzofuran or dibenzothiophene group, each of which may be substituted by one or more R3 radicals;
• R2 is the same or different at each instance and is H, D, a straight-chain alkyl or alkoxy group having 1 to 20 carbon atoms or a branched or cyclic alkyl or alkoxy group having 3 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms, where the alkyl, alkoxy or alkenyl group may in each case be substituted by one or more R3 radicals, where one or more hydrogen atoms may be replaced by D, or an aromatic ring system which has 6 to 30 aromatic ring atoms and may be substituted by one or more R3 radicals, or a dibenzofuran or dibenzothiophene group, each of which may be substituted by one or more R3 radicals;
• in addition, it is possible for multiple adjacent substituents R2 together to form a ring system;
• R3 is the same or different at each instance and is H, D, a straight-chain alkyl or alkoxy group having 1 to 20 carbon atoms or a branched or cyclic alkyl or alkoxy group having 3 to 20 carbon atoms, where the alkyl or alkoxy group may in each case be substituted by one or more R4 radicals, where one or more hydrogen atoms may be replaced by D, or an aromatic ring system which has 6 to 30 aromatic ring atoms and may be substituted by one or more R4 radicals, or a dibenzofuran or dibenzothiophene group, each of which may be substituted by one or more R4 radicals;
• it is also possible here for two or more adjacent substituents R3 together to form a ring system;
• R4 is the same or different at each instance and is H, D or an aliphatic and/or aromatic hydrocarbyl radical having 1 to 20 carbon atoms.