Synthesis, thermal, electrochemical, and photophysical characterization of 1,5-bis(diarylamino)naphthalene derivatives as potential hole transport OLED materials

Abstract

Novel 1,5-bis(diarylamino)naphthalene derivatives (1–9), which have potential as hole-transporting materials for electroluminescent devices, were obtained through palladium-catalyzed coupling of diarylamines and 1,5-dibromonaphthalene. The thermal, electrochemical, and photophysical properties of these compounds were examined and the effects of the N-aryl substituents on these properties were investigated. These materials possess glass transition temperatures (Tg) that range from 70–131 °C and these values are related to the identity of the aryl substituents. Cyclic voltammetric measurements demonstrated that these compounds possess two reversible oxidation processes and were further used to estimate the HOMO energy levels of these materials by comparison with the ferrocene/ferrocenium couple. The intramolecular charge mobility, as gauged by the difference between the two oxidation potentials, indicates that compounds 1–8 have a similar degree of delocalization as meta-diaminobenzene derivatives while that of 9 is similar to TPD. Compounds 1–9 emit in the blue-green region and optical absorption and emission data for these materials can be rationalized in terms of the electronic donating properties of the aryl substituents. This data when combined with the electrochemically determined HOMO energies allowed estimation of the LUMO energy levels.Key words: hole transport materials, diaminonaphthalene, thermal analysis, palladium-catalyzed arylation.