Electronic structure of tris(2-phenylpyridine)iridium: electronically excited and ionized states

A computational study of tris(2-phenylpyridine)iridium, Ir(ppy)3, is presented. The perspective is that of using organo-transition-metal complexes as phosphorescent species in light-emitting diodes (OLED's). Quantum yields approaching 100% are possible through a triplet harvesting mechanism. Complexes such as Ir(ppy)3 are amenable to exacting experimental and theoretical studies: small enough to accommodate rigor, yet large enough to support bulk phenomena in a range of host materials. The facial and meridional isomers differ by ∼220 meV, with fac-Ir(ppy)3 having the lower energy. Because fac-Ir(ppy)3 dominates in most environments, focus is on this species. Time-dependent density functional theory using long-range-corrected functionals (BNL and ωB97X) is used to calculate excited states of Ir(ppy)3 and a few low energy states of . The calculated T1 – S0 energy gap (2.30 eV) is in reasonable agreement with the experimental value of 2.44 eV. Only a few percent of singlet character in T1 is needed to explai...