Specifically substituted aza-dibenzofurans and aza-dibenzothiophenes of formula (I) and their use in electronic devices, especially electroluminescent devices. When used as charge transport material, charge blocker material and/or host material in electroluminescent devices, the specifically substituted aza-dibenzofurans and aza-dibenzothiophenes may provide improved efficiency, stability, manufacturability, or spectral characteristics of electroluminescent devices and reduced driving voltage of electroluminescent devices. In formula (I) Y is S or O; one of X1-X8 is N; another X1-X8 is C-L(R9)—[X9X10X11]Ring; and the remaining X1-X8 are CR1-CR8 wherein R1-R8 are independently H, alkyl, alkenyl, aryl, etc.