Theoretical study on electronic structures and phosphorescence properties of four tris-cyclometalated iridium(III) complexes

The geometry structures, electronic structures, absorption, and phosphorescence properties of four tris-cyclometalated iridium(III) complexes IrL₃, that is, 1 (L = 2-(4,6-difluorophenyl)pyridinato,N,C ^2′), 2 (L = 2-(4,6-difluorophenyl)pyridinato,N,C ^2′-5-phenyl), 3 (L = 2-(4,6-difluorophenyl)pyridinato,N,C ^2′-5-(p-tolyl)), and 4 (L = 2-(4,6-difluorophenyl) benzo[h]isoquinoline), have been investigated under the framework of the time-dependent density functional theory approach. For assumed 2 and 3, the emission energies are nearly the same, consistent with their similar HOMO-LUMO energy gaps. The calculated lowest energy emissions are localized at 523, 605, 616, and 642 nm for 1, 2, 3, and 4, respectively. Calculations of ionization potential and electron affinity were used to evaluate the injection abilities of holes and electrons into these complexes. For 2, the calculated results evidenced a larger ³MLCT contribution (27.0%), a large S₀ → S₁ transition dipole moment (μS1) of 1.43 D, and a small S₁-T₁ splitting energy (ΔES1-T1) of 0.33 eV, which could result in a large radiative decay rate (k_r). We hope that this theoretical work can provide a suitable guide to the future design and synthesis of novel phosphorescent materials for use in the organic light-emitting diodes.