The origin of phosphorescence in Iridium (III) complexes. The role of relativistic effects

A series of luminescent Ir(III) complexes of the type [Ir(F₂ppy)₂L] (where L = L^pytz, L^OMe, L^but) have been studied using relativistic two-component density functional theory considering the spin-orbit coupling. The absorption spectra of the three complexes were determined. The most important transition appears in the region between 250 and 350 nm, which is in good agreement with the experimental reports. The three complexes show phosphorescent properties due to a metal-ligand charge transfer (MLCT) process, where the spin-orbit coupling (SOC) plays a key role due to the introduction of a zero field splitting (ZFS) and the mixing of states with different spins which contributes to modify the emission selection rule. The lifetimes of the emission processes were calculated, and the values are in the same order of the experimental reports.