Theoretical study on the effect of different substituents on the electronic structures and photophysical properties of phosphorescent Ir(iii) complexes

Abstract

The electronic structure, absorption and emission spectra, as well as phosphorescence efficiency of (ppy)₂Ir(PPh₂^SiO) (1), (ppy)₂Ir(P(CH₃)₂^SiO) (2), (ppy)₂Ir(PH₂^SiO) (3), and (dfppy)₂Ir(PPh₂^SiO) (4) [where ppy = 2-phenylpyridne, dfppy = 2-(2,4-difluorophenyl)pyridine and (PR₂^SiO) is an organosilanolate ancillary chelate] were investigated by using density functional theory (DFT) and time-dependent DFT (TDDF) methods. The results revealed that the subtle differences in geometries and electronic structures result in different spectral properties and the quantum yields. Compared with 1, the substituent H in 3 leads to an obvious red shift in absorption spectra, while the substituent CH₃ leads to a blue shift for 2 in the emission spectra. Moreover, the S₁–T₁ splitting energy (ΔE_S1–T1), the transition dipole moment (μ_S1, transition from S₀ → S₁) and the energy gap between the metal-to-ligand charge transfer ³MLCT/π–π* and metal-centered ³MC/d–d states (ΔE_MC–MLCT) were also calculated. It was found that the designed complexes 2 and 3 have smaller ΔE_S1–T1, larger μ_S1 and ΔE_MC–MLCT, which make them have higher quantum yield compared with the experimentally synthesized complexes. Therefore, they are expected to be the potential candidates as emitting materials with high quantum yield.