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

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).