Synthesis and characterization of phenanthroimidazole derivatives for applications in organic electroluminescent devices

Abstract

A series of phenanthroimidazole derivatives have been synthesized, characterized and applied as non-doped emitters in organic light-emitting devices. The compounds show high fluorescent quantum yields up to 0.75 as well as good thermal and film-forming abilities. Crystal structures of the compounds were determined by X-ray crystallography. Correlations between optoelectronic properties, energy levels and molecular structures of the materials were investigated. It was found that introduction of a thiophene ring on the C2-position of phenanthroimidazole can effectively decrease the ionization potentials (Ip) of the compounds. Fluorescent properties of the materials were found to be related to the dihedral angles in the compounds with different substituents. The low Ip (from 5.00 to 5.21 eV) of the materials enables efficient hole-injection from the hole-transporting layer and results in low turn-on (<2.7 V) and operation voltages (<5.5 V to give 1000 cd m−2).