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

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 3 MLCT participation in the phosphorescent spectra, decreased the singlet-triplet splitting energy (Δ E S1–T1 ), as well as dramatically small energy differences between the highest occupied orbitals splitting (Δdd occ ) and large lowest unoccupied d-orbitals splitting (Δdd*) at the both S 0 and T 1 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.