Unraveling The Marked Differences Of The Phosphorescence Efficiencies Of Blue-Emitting Iridium Complexes With Isomerized Phenyltriazole Ligands

Four structurally similar blue phosphorescent iridium complexes with isomerized phenyltriazole (ptz) ligands, [Ir(5-phenyl-1H-1,2,4-triazole)(3)] (1), [Ir(3-phenyl-4H-1,2,4-triazole)(3)] (2), [Ir(4-phenyl-1H-1,2,3-triazole)(3)] (3), and [Ir(2-phenyl-2H-1,2,3-triazole)(3)] (4), exhibit marked differences in their quantum efficiencies. In order to reveal the coordinating effect of these isomerized ptz ligands on the photophysical properties, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were performed to investigate the geometrical and electronic structures, absorption and emission properties, and radiative and nonradiative process of iridium complexes. The calculated results show that the transition nature of an emissive T-1 state can be assigned to the mixture of metal-to-ligand charge-transfer ((MLCT)-M-3) and intraligand charge-transfer ((ILCT)-I-3) states. The radiative decay rate constants are within the same order of magnitude, and thus the marked difference in the quantum efficiencies is ascribed to the different thermal deactivation pathways via the metal-centered ((MC)-M-3) states and the nonradiative vibrational relaxation. This work establishes the structure-property relationship for complexes with different ptz isomer ligands, and provides a better understanding of the excited-state behavior of the ptz-based iridium complexes.