Synthesis and photophysical studies on cyclometalated iridium complexes containing various monodentate phenyl-azole ancillary ligands

In this study, five cyclometalated iridium complexes containing phenyl-azole ancillary ligands were synthesized and characterized by X-ray crystallography, and their photophysical properties were studied. The reaction of [Ir (ppy)(2)(mu-Cl)](2) (ppy: 2-phenylpyridine) with pim (4-phenylimidazole), ptr4h (4-phenyl-4H-1,2,4-triazole), and ptr1h (1-phenyl-1H-1,2,4-triazole) ligands furnished mononuclear [Ir(ppy)(2)ClL] complexes (1-3; L = pim, ptr4h, ptr1h) featuring monodentate neutral N -> Ir coordination. In contrast, the corresponding reaction with ptz (5phenyl-1H-tetrazole) ligand yielded a hetero-bridged dimeric iridium complex, [Ir(ppy)(2)(mu-Cl)(mu-ptz)Ir(ppy)(2)] (4). Notably, adding dimethylsulfoxide (DMSO) solvent to complex 4 resulted in its division to [Ir(ppy)(2)(ptz) (DMSO)] (5) and [Ir(ppy)(2)Cl(DMSO)]. Complexes 1-4 exhibited blue-green phosphorescence in solution with marginal shifts in the emission wavelengths. Complex 1, having a pim ligand, exhibited a significantly higher phosphorescence quantum efficiency (Phi(PL) = 31%) than those of complexes 2-4 (Phi(PL) = 4-9%), which was attributed to the relatively small non-radiative decay rate constant in 1. Density functional theory calculations confirmed that the phosphorescence has originated from both the metal-ligand charge transfer ((MLppyCT)-M-3) and the ligand-centered ((LCppy)-L-3) states. An increased LC character was observed in the phosphorescence of the dinuclear complex 4.

Automated summary

In this study, five cyclometalated iridium complexes with phenyl-azole ancillary ligands were synthesized and their photophysical properties were studied. Complex 1 showed a higher phosphorescence quantum efficiency compared to complexes 2-4, attributed to its relatively small non-radiative decay rate constant.