Theoretical studies on photophysical properties and mechanism of phosphorescence in [fac-Ir(2-phenylpyridine)₃]

The photophysical properties of [fac-Ir(ppy)₃] have been studied using time-dependent density functional theory with one-center spin-orbit coupling approximation. The phosphorescent state of [fac-Ir(ppy)₃] was characterized by a mixture of 40% ³MLCT and 58% intra- and inter-ligand ³ππ* with charge distribution being partially localized to a single ligand. Zero-field splittings and oscillator strengths calculated for the sublevels of the lowest triplet state were in agreement with the observed values. The spin components in the sublevels and the mechanism of phosphorescence were well rationalized using a localized model for a hypothetical M-LL unit with C_2v symmetry similarly to the cases for [Ru(bpy)₃]²⁺ or [Os(bpy)₃]²⁺. Furthermore, it was revealed that the excited states were characterized by both high density-of-state (approximately 70 states per eV) and considerable mixing between singlet and triplet states due to strong spin-orbit coupling.