Theoretical studies on the ground and excited states of blue phosphorescent cyclometalated Ir(III) complexes having ancillary ligand

The ground state and low-lying excited electronic states in the Ir(III) complexes, fac-Ir(dfpp)3, Ir(dfpp)2(acac) and FIrpic, are studied using the density functional theory, where dfpp = 2-(2,4-difluorophenyl)pyridine, acac = acetylacetonate, pic = picolinic acid and fac = facial. Herein, the electronic properties of these molecules are studied using the B3LYP functional and the structural analysis of the optimized geometries are done in comparison with the structures of the dfpp ligand and Ir complexes. Excited triplet and singlet states are examined using the time-dependent density functional theory (TD-DFT). The calculated energies of triplets are 2.8 eV, 2.69 eV and 2.73 eV, in the order described above, which are all higher than that of fac-Ir(ppy)3with 2.60 eV, where ppy = 2-phenylpyridine. Nearly all of the low-lying excitations calculated in this study are categorized as metal-to-ligand charge-transfer (MLCT) transitions because HOMOs are strongly mixed between the π orbital of the dfpp ligand and the d orbital of the centric Ir atom.