The present invention relates to compounds of formula (I), which are characterized in that they substituted by benzimidazo[1,2-a]benzimidazo-5-yl and/or benzimidazo[1,2-a]benzimidazo-2,5-ylene groups and in that at least one of the substituents B1, B2, B3, B4, B5, B6, B7 and B8 represents N; a process for their production and their use in electronic devices, especially electroluminescent devices. When used as host material for phosphorescent emitters in electroluminescent devices, the compounds of formula I may provide improved efficiency, stability, manufacturability, or spectral characteristics of electroluminescent devices.