Improvement in color purity and lifetime of blue PHOLEDs using a homoleptic iridium(III) complex with fluorinated dibenzofuranyl-imidazole ligand

Abstract

To improve the color purity and device lifetime of Ir(dbi)3, where dbi is [1-(2,4-diisopropyldibenzo[b,d]furan-3-yl)-2-phenyl-1H-imidazole), a new iridium(III) compound (1) bearing a fluorinated-dbi ligand was prepared via a one-pot reaction with moderate yield. Compound (1) exhibits distorted octahedral structure around the Ir(III) metal ion with a facial geometry and an inverted triangular shape with significant curvature based on Hirshfeld analysis. There are several intra and intermolecular interactions involving C-H⋯F/N/O hydrogen bonds, which impart high thermal and chemical stability to compound 1. Additionally, compound 1 exhibits bright blue emission (λmax = 460 nm) with high photoluminescent quantum efficiency of 0.5. Further, a remarkable decrease in the energy level of highest occupied molecular orbital (HOMO) is observed, while no significant change is observed in the energy level of lowest unoccupied molecular orbital (LUMO), which is attributed to the stronger electronegativity of fluorinated-dbi compared to the parent Ir(dbi)3 compound. Phosphorescent organic light-emitting diodes (PHOLEDs) were successfully fabricated using 3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl (mCBP) as the host, with 17.5% external quantum efficiency achieved. Moreover, the absolute device lifetime of the compound 1 based device at 10 wt% doping concentration is measured to be 47 h at 1000 cd/m2 luminance, which is much better than that of the parent Ir(dbi)3-based device. The introduction of fluorine atom to the molecular structure provides not only improved device lifetime via strong intermolecular interactions but also improved color purity.