Cationic Iridium Complexes with 5-Phenyl-1-1,2,4-triazole Type Cyclometalating Ligands: Toward Blue-Shifted Emission.

Four cationic iridium complexes with 5-phenyl-1-1,2,4-triazole (phtz) type cyclometalating ligands (C^N) and different ancillary ligands (N^N), namely, [Ir(dphtz)(bpy)]PF (), [Ir(dphtz)(pzpy)]PF (), [Ir(Mephtz)(pzpy)]PF (), and [Ir(Mephtz)(dma-pzpy)]PF (), have been designed, synthesized, and fully characterized (dphtz = 1-(2,6-dimethylphenyl)-3-methyl-5-phenyl-1-1,2,4-triazole, Mephtz = 1,3-dimethyl-5-phenyl-1-1,2,4-triazole; bpy = 2,2'-bipyridine, pzpy = 2-(1-pyrazol-1-yl)pyridine, dma-pzpy = 4-dimethylamino-2-(1-pyrazol-1-yl) pyridine). In solution, complex emits efficient yellow light (λ = 547 nm), which is blue-shifted by nearly 40 nm (or by 1187 cm) compared with that from the archetypal complex [Ir(ppy)(bpy)]PF (Hppy = 2-phenylpyridine), owing to the stabilization of the highest occupied molecular orbital by the phtz-type C^N ligand. In the lightly doped rigid films, complex emits green light with a high luminescent efficiency of 0.89. Although complexes - with electron-rich N^N ligands are weakly emissive or nearly nonemissive in the solution, they emit relatively strong deep-blue light peaked around 435 and 461 nm in the lightly doped films, which is among the bluest reported for cationic iridium complexes. Theoretical calculations reveal that for complex , the emission always comes from the charge-transfer (CT) (Ir/C^N → N^N) state; for complexes and , the CT and C^N-centered π-π* states lie close in energy and the emission could originate from either or both of them; for complex , the emission comes predominantly from the C^N-centered π-π* state. For blue-emitting complexes -, metal-centered states play an active role in the nonradiative deactivation of the emitting triplet states. Solid-state light-emitting electrochemical cells (LECs) based on complexes - show yellow-green, blue, and blue-green electroluminescence, respectively, with the yellow-green LEC affording a peak current efficiency of 21.5 cd A.