Photoemission study of a new electroluminescent material: trimer of N-arylbenzimidazoles (TPBI)

Electronic properties of ultra-thin films of an N-arylbenzimidazoles trimer (TPBI) vacuum-deposited on Ag substrates have been studied by ultraviolet photoelectron spectroscopy (UPS). It was found that the assumption of a com mon vacuum level at the metal/organic interface is not valid in the TPBI-me tal case. It was observed that there exists a gradual increase in energetic separation between the highest occupied molecular orbital (HOMO) of TPBI a nd the Fermi level, E-F, Of the metal during the formation of the TPBI-meta l interface. For monolayer-thick TPBI covered Ag surfaces, the barrier heig ht for electron injection (separation between EF and the lowest unoccupied molecular orbital (LUMO) was determined to be 0.6 eV. (C) 2000 Elsevier Sci ence B.V. All rights reserved.