Theoretical study on the electronic structures and optical properties of blue phosphorescent iridium(III) complexes

The ground- and excited-state geometries for a series of Ir(III) complexes were optimized including 5a, 5a1, 5a2, 5ax and 5ay at the B3LYP/LANL2DZ and CIS/LANL2DZ levels, respectively, and the results agree well with the corresponding experimental data. By means of the TD-DFT method, the absorption and the emission spectra were calculated based on the optimized ground-state and the excited-state geometries, respectively. It is found that the absorption and emission transition character can be altered by adjusting the position of the electron-withdrawing and electron-donating groups. These results indicate that both the absorption and emission are not dominated by the HOMO-LUMO gap (Δ_H-L) which is usually considered as the basis of the experimental design. In addition, the charge transport quality has been estimated approximately by the calculated reorganization energy (λ). The calculated results also show that the positions of the substitute groups also affect the charge transfer rate and balance. By summing up the results, we can conclude that the 5a2 and 5ax are good blue OLED materials with not only good charge transfer rates but also balance between hole and electron.