Organic electroluminescent device

An organoelectroluminescent device comprising at least one compound of formula (1′),

• wherein:
• R is, identically or differently on each occurrence an aromatic or heteroaromatic ring system having 5 to 24 aromatic ring atoms optionally substituted by one or more radicals R2, or two or more substituents R together with the phosphorous atom to which they are bonded optionally define a mono- or polycyclic aliphatic or aromatic ring system with one another;
• R1 is, identically or differently on each occurrence, H, N(Ar1)2, CN, a straight-chain alkyl or alkoxy, group having 1 to 40 C atoms, or a branched or cyclic alkyl or alkoxy, group having 3 to 40 C atoms, each of which is optionally substituted by one or more radicals R2, or an aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms optionally substituted by one or more radicals R2, an aryloxy or heteroaryloxy group having 5 to 40 aromatic ring atoms optionally substituted by one or more radicals R2;
• R2 is selected from the group consisting of H, CN, aliphatic hydrocarbon radicals having 1 to 20 C atoms, and aromatic or heteroaromatic ring systems having 5 to 30 aromatic ring atoms, and wherein two or more adjacent substituents R2 optionally form a mono- or polycyclic, aliphatic, aromatic, or heteroaromatic ring system with one another.