Effect of phenylamine moiety on the structure, optical properties, and phosphorescence efficiencies of some red-emitting iridium(III) complexes: A theoretical study

• The optical properties of meta and para substituted Ir complexes are investigated by density functional theory (DFT).
• The charge injection and transfer ability is evaluated by analysis of IP, EA, and λ.
• The quantum yield and efficiency of phosphorescence is evaluated by MLCT, 3MLCT, ΔES1–T1 and d-orbital splitting.
• The feasibility of using these Ir complexes as guest in the host of CBP is evaluated.

Quantum-chemistry methods are used to investigate the effect of phenylamine chromophore on the electronic structure, optical properties, and phosphorescence efficiencies of a series of fac-iridium(III) complexes, Ir-(g0)3(1), meta-substituted Ir compounds [Ir-(g0)2-(g1)1](1a), [Ir-(g0)1-(g1)2](1b), [Ir-(g1)3](1c) and para-substituted Ir compounds [Ir-(g0)2-(g1′)1](2a), [Ir-(g0)1-(g1′)2](2b), [Ir-(g1′)3](2c), where g0 = l-phenylisoquinolinato, g1 = 4-(isoquinolin-1-yl)-N,N-diphenylbenzenamine, g1′ = 3-(isoquinolin-1-yl)-N,N-diphenylbenzenamine. The calculations show that introduction of phenylamine chromophore at meta position of phenyl ring (1a–1c) slightly changes the ground-states geometries but largely increases the energy of HOMO and decreases IP values hence improves the ability of hole injection, which is consistent with the experimental report. The introduction of diphenylamine substitutions on the para position (2a–2c) is effective for extending the π-electron delocalization, which results in strengthening metal-ligand bond and dramatically increasing the HOMO energy. More important, the 2a–2c have enhanced metal-to-ligand charge transfer 3MLCT participation in the phosphorescent spectra, decreased the singlet-triplet splitting energy (ΔES1–T1), as well as dramatically small energy differences between the highest occupied orbitals splitting (Δddocc) and large lowest unoccupied d-orbitals splitting (Δdd*) at the both S0 and T1 geometries, these account for the quantum yield and efficiency of phosphorescence. The calculated ionization potentials (IPs), electronic affinities (EAs), and reorganization energy (λ) confirm that the hole and electron injection and transfer ability were enhanced by importing the diphenylamine. Furthermore, based on the analyses of triple energy differences between host and guest, charge carrier mobility, optical overlap, it is found that these Ir complexes maybe good guest materials in CBP. Thus, the introduction of phenylamine at para position is effective approach to obtain highly efficient red phosphorescent emitters.