Deep Blue Phosphorescence of the Iridium(III) Complexes Containing N-Heterocyclic Carbene Ligands

Previously, the iridium complexes containing N-Heterocyclic carbene (NHC) ligands have caught attention because of their phosphorescence for organic light-emitting diodes (OLEDs). It was reported that the use of strong-field ligands such as carbenes should result in an increase of the blue phosphorescent efficiency of their metal complexes. In this study, the new NHC ligands, 1-(4-fluorophenyl)-3-methyl benzimidazolate (fpmb) and 1-naphthyl-3-methyl benzimidazolate (nmb), were introduced to the iridium complexes to develop phosphorescent dyes for OLED. We investigated photoabsorption and photoluminescence (PL) properties of the iridium complexes and studied their bandgaps with cyclic voltammetry (CV). Deep blue and green phosphorescence was observed with these complexes, and the bandgaps between their highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) were correlated with CV data. We also studied the electroluminescence (EL) properties of the new iridium complexes as possible phosphors for the application to OLED.