Synthesis, structure and electroluminescent properties of cyclometalated iridium complexes possessing sterically hindered ligands

Abstract

New CN donor ligands incorporating pyridine or benzoimidazole N donors and a sterically hindered cyclometalating aromatic core featuring a polyphenylenephenyl, fluoranthene, or triphenylene segment are prepared and successfully converted into heteroleptic iridium(III) cyclometalated complexes with acetylacetone auxiliary ligands. The X-ray structure of the complex, derived from a ligand containing a fluoranthene fragment, has been solved to unveil the corresponding structure. The results clearly demonstrate that the nature of the σ-coordinating ligand segment plays a key role in dictating the emission profile and peak position, such that the emission hue has been successfully tuned ranging from green to red. Supplementary support of this viewpoint is also rendered by computational (DFT) approaches. Electroluminescent devices fabricated using a complex as dopant in the PVK matrix were found to exhibit bright greenish yellow emission with promising device characteristics (maximum brightness 26450 cd m⁻² at 30 V and a maximum current efficiency of 40 cd A⁻¹).