Issue 47, 2022

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

Abstract

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)2Ir(phim) (Ir1) and (dfdmapypy)2Ir(phim) (Ir2), were developed by employing 2-(2,4-difluorophenyl)-N,N-dimethylpyridin-4-amine (dfdmappy) and 2′,6′-difluoro-N,N-dimethyl-[2,3′-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.3LC). Meanwhile, the phim ligand with strong σ-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 (3MLCT/3LLCT) dominated emission from the T1 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 μs, 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.

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

Supplementary files

Article information

Article type
Paper
Submitted
17 Aug 2022
Accepted
02 Nov 2022
First published
02 Nov 2022

J. Mater. Chem. C, 2022,10, 17965-17973

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

Y. Lan, D. Liu, J. Li, Y. Mei and H. Tian, J. Mater. Chem. C, 2022, 10, 17965 DOI: 10.1039/D2TC03463H

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