Four cationic iridium complexes with 5-phenyl-1H-1,2,4-triazole (phtz) type cyclometalating ligands (C^N) and different ancillary ligands (N^N), namely, [Ir­(dphtz)2(bpy)]­PF6 (1), [Ir­(dphtz)2(pzpy)]­PF6 (2), [Ir­(Mephtz)2(pzpy)]­PF6 (3), and [Ir­(Mephtz)2(dma-pzpy)]­PF6 (4), have been designed, synthesized, and fully characterized (dphtz = 1-(2,6-dimethylphenyl)-3-methyl-5-phenyl-1H-1,2,4-triazole, Mephtz = 1,3-dimethyl-5-phenyl-1H-1,2,4-triazole; bpy = 2,2′-bipyridine, pzpy = 2-(1H-pyrazol-1-yl)­pyridine, dma-pzpy = 4-dimethylamino-2-(1H-pyrazol-1-yl) pyridine). In solution, complex 1 emits efficient yellow light (λmax = 547 nm), which is blue-shifted by nearly 40 nm (or by 1187 cm–1) compared with that from the archetypal complex [Ir­(ppy)2(bpy)]­PF6 (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 1 emits green light with a high luminescent efficiency of 0.89. Although complexes 2–4 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 1, the emission always comes from the charge-transfer (CT) (Ir/C^N → N^N) state; for complexes 2 and 3, the 3CT and C^N-centered 3π–π* states lie close in energy and the emission could originate from either or both of them; for complex 4, the emission comes predominantly from the C^N-centered 3π–π* state. For blue-emitting complexes 2–4, 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 1–3 show yellow-green, blue, and blue-green electroluminescence, respectively, with the yellow-green LEC affording a peak current efficiency of 21.5 cd A–1.

Deep insight into the nonradiative deactivation pathways in phosphorescent cationic iridium complexes is critically important for developing efficient blue-emitting complexes toward advanced applications. Here, we report the synthesis and photophysical and electrochemical characterizations of a blue-green-emitting cationic iridium complex [Ir­(ppy)2­(bipzpy)]­PF6 (Hppy is 2-phenylpyridine, and bipzpy is 2,4-di­(1H-pyrazol-1-yl)­pyridine). The nonradiative deactivation pathways in [Ir­(ppy)2­(bipzpy)]­PF6 have been elucidated through extensive density functional theory calculations. The calculations reveal that the higher-lying charge-transfer (CT) state in [Ir­(ppy)2­(bipzpy)]­PF6, which arises from Ir/ppy → bipzpy transitions, favors nonradiative deactivation because of its large structural distortion compared to the ground state. Both the CT state and the dark metal-centered (3MC) state can be thermally accessed by the lowest-lying emitting triplet state at room temperature, with the former being much more easily accessible, which causes additional nonradiative deactivations for the emitting triplet state. The active roles of the CT and 3MC states in the nonradiative deactivation pathways are, for the first time, confirmed in such blue-emitting complexes with pzpy-type ancillary ligands (pzpy is 2-(1H-pyrazol-1-yl)­pyridine).