Development of Blue Phosphorescent Pt(II) Materials Using Dibenzofuranyl Imidazole Ligands and Their Application in Organic Light-Emitting Diodes.

Organic light-emitting diodes (OLEDs) are energy-efficient; however, the coordinating ligand can affect their stability. Sky-blue phosphorescent Pt(II) compounds with a C^N chelate, fluorinated- dbi ( dbi = [1-(2,4-diisopropyldibenzo [b,d]furan-3-yl)-2-phenyl-1 H -imidazole]), and acetylactonate (acac) ( 1 )/picolinate (pic) ( 2 ) ancillary ligands were synthesized. The molecular structures were characterized using various spectroscopic methods. The Pt(II) Compound Two exhibited a distorted square planar geometry, with several intra- and inter-molecular interactions involving C π ⋯H/C π ⋯C π stacking. Complex One emitted bright sky-blue light (λ max = 485 nm) with a moderate photoluminescent quantum efficiency (PLQY) of 0.37 and short decay time (6.1 µs) compared to those of 2 . Theoretical calculations suggested that the electronic transition of 1 arose from ligand(C^N)-centered π-π* transitions combined with metal-to-ligand charge-transfer (MLCT), whereas that of 2 arose from MLCT and ligand(C^N)-to-ligand(pic) charge-transfer (LLCT), with minimal contribution from C^N chelate to the lowest unoccupied molecular orbital (LUMO). Multi-layered phosphorescent OLEDs using One as a dopant and a mixed host, mCBP/CNmCBPCN, were successfully fabricated. At a 10% doping concentration of 1 , a current efficiency of 13.6 cdA -1 and external quantum efficiency of 8.4% at 100 cdm -2 were achieved. These results show that the ancillary ligand in phosphorescent Pt(II) complexes must be considered.