Are Triphenylamine-Functionalized or Carbazole-Functionalized Iridium Complexes the More Effective Phosphorescent Materials? A Theoretical Perspective

The ground and excited states, charge injection/transport, and phosphorescence properties of eleven carbazole- and triphenylamine-functionalized Ir-III complexes were investigated by using the DFT method. By analyzing the spin-orbit coupling (SOC) matrix elements, radiative decay rate constants k(r), and the electronic structures and energies at the S-0(opt) and T-1(opt) states, it was possible to rationalize the order of the experimental phosphorescence quantum yields of a series of Ir-III complexes and to predict that [Ir(Nph-2-Cz-tz)(3)] has a higher phosphorescence quantum yield than [Ir(TPA-tz)(3)] (TPA=triphenylamine, tz=thiazolyl, Cz=carbazole, Nph=N-phenyl). Carbazole-functionalized Ir-III complexes were shown to be efficient phosphorescent materials that have not only fast but also balanced electron/hole-transport performance as well as high phosphorescence quantum yields. The phosphorescence emission spectra can be modulated by modifying or replacing a pyridyl substituent.