Meta-linked CBP-derivatives as host materials for a blue iridium carbene complex

We present four derivatives of 4,4′-bis(9-carbazolyl)biphenyl (CBP) for the use as host materials in blue phosphorescent organic light emitting diodes. By replacing the para-linkage by a meta-linkage of the carbazole substituents at the central biphenyl unit materials with improved thermal and optical properties are obtained. The triplet energy of the meta-linked host materials is significantly increased to more than 2.90 eV compared to 2.58 eV for the para-linked CBP. Moreover, selective methyl substitution of the basic meta-CBP structure leads to materials with high glass transition temperatures up to 120 °C and electrochemical stability of the oxidised species against dimerisation. The high triplet energy allows the use of the meta-CBP derivatives as host materials for the carbene emitter mer-tris(N-dibenzofuranyl-N′-methylimidazole)iridium (III) (Ir(dbfmi)) with a pure blue emission at 450 nm.

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► Four carbazole based host materials for pure blue phosphors developed.
► Morphological stability with glass transition temperatures up to 120 °C.
► High triplet energy of more than 2.9 eV.
► Efficient blue OLEDs with the pure blue carbine emitter Ir(dbfmi) (λem = 450 nm).