Organic light‐emitting materials based on iridium(III) complexes bearing phenanthroimidazole ligands

Abstract

We present the elegant synthesis and the photophysical and electroluminescent properties of a series of cyclometalated iridium(III) complexes [Ir(PPI) 2 (pic), PPI: 1,2-diphenyl-1H-phenanthro[9,10-d]imidazole; pic: picolinic acid]. The Ir(PPI) 2 (pic) complexes showed characteristic phosphorescence with an emission range of 556-579 nm and a high quantum efficiency with microsecond lifetimes. The strongly allowed phosphorescence in these complexes is the result of significant spin-orbit coupling of the Ir center. All bis(PPI) derivatives exhibit intense triplet metal-to-ligand charge transfer (MLCT) photoluminescence in the fluid solutions at room temperature. The impact of different solvents, substituents on the phenanthroimidazole ligands and complex concentrations upon their emissive behavior have been examined and demonstrate that their emission energies can be systematically modified. Weak bands located at longer wavelength have been assigned to the 1 MLCT ← S 0 and 3 MLCT ← S 0 transitions of iridium complexes. Application of the 3 MLCT excited state of the [Ir(PPI) 2 (pic)] materials in organic light-emitting devices are described.