Blue heteroleptic iridium(iii) complexes for OLEDs: simultaneous optimization of color purity and efficiency

作者：Lan, Ying; Liu, Di^*; Li, Jiuyan^*; Mei, Yongqiang; Tian, Houru

来源：Journal of Materials Chemistry C, 2022, 10(47): 17965-17973.

DOI：10.1039/d2tc03463h

• HIGHLY EFFICIENT
• HOST MATERIALS
• FLUORINE-FREE
• EMISSION
• LIGANDS

High-performance blue phosphorescent iridium(iii) complexes having good efficiency and color purity simultaneously are still a huge challenge. Two blue phosphorescent iridium(iii) complexes, (dfdmappy)(2)Ir(phim) (Ir1) and (dfdmapypy)(2)Ir(phim) (Ir2), were developed by employing 2-(2,4-difluorophenyl)-N,N-dimethylpyridin-4-amine (dfdmappy) and 2 & PRIME;,6 & PRIME;-difluoro-N,N-dimethyl-[2,3 & PRIME;-bipyridin]-4-amine (dfdmapypy) as cyclometalating ligands and N-heterocyclic carbene (phim) as an ancillary ligand. The introduction of a strong electron-donating dimethylamino (dma) group onto the N-coordinating pyridine ring of the main ligands and the adoption of high field-strength phim effectively raise the cyclometalating ligand-centered emitting triplet states (i.e.(LC)-L-3). Meanwhile, the phim ligand with strong sigma-donating electron character destabilizes the non-radiative d-d*state as well. These strategies make both complexes achieve charge transfer (CT) state dominated emission, i.e., metal-to-ligand/ligand-to-ligand charge transfer ((MLCT)-M-3/(LLCT)-L-3) dominated emission from the T-1 state and resulted in Ir1 and Ir2 single-peak blue phosphorescence with high photoluminescence quantum yields (PLQYs) of 91% and 60%, respectively, and shorter excited-state lifetimes of 1.10 and 3.33 mu s, respectively. Quantum chemical calculations verified the CT-dominated feature and lower root-mean-square displacement/deviation (RMSD) value of Ir1versus more metal centered d-d*transition and larger RMSD value of Ir2, well accounting for the higher PLQY and superior color purity of Ir1. Pure blue organic light-emitting diodes (OLEDs) of Ir1 exhibit a maximum external quantum efficiency (EQE) of 28% with Commission Internationale de I'Eclairage (CIE) coordinates of (0.16, 0.21), which is one of the best performances for blue phosphorescent OLEDs reported so far.