Homoleptic Iridium(III) Carbene Complexes with gem-Dimethyl-1,2,4-triazolo[4,3-a]indole Chelates for Blue Organic...

Iridium(III) carbene complexes represent the advanced structure of efficient blue phosphorescent emitters to date, yet the refinement of the carbene group is not easy to realize in a large-scale synthesis route. In this study, we develop a series of deep-blue emissive homoleptic Ir(III) carbene complexes bearing the novel gem-dimethyl-1,2,4-triazolo[4,3-a]indole ligand. The carbene ligand can be produced on a large scale without purification by column chromatography, and the cyclometalation can be completed in a high yield without the use of Ag₂O. The gem-dimethyl and fused-ring in this unconventional carbene ligand endow Ir(III) complexes with the insensitivity to dopant concentration and high rigidity. The inclusion of a large steric electron-donating tert-butyl group in these phosphors promotes the radiative transition rates and increases their photoluminescence quantum yields (PLQYs). As a result, these complexes exhibit great promise as deep-blue phosphors with the emission maxima at ∼435 nm. We successfully fabricated phosphorescent organic light-emitting diodes (OLEDs) based on these blue emitters, in which a tert-butyl-functionalized mer-Ir(III) phosphor (mer-TzDm-t)-based device achieves a maximum external quantum efficiency (EQE) up to 11.75% and Commission Internationale de I'Eclairage (CIE_x,y) coordinates of (0.161, 0.117).