Phosphorescence Efficiency Originating from Spin–Orbit Coupling-Mediated Intensity Stealing from Low-Energy Singlet Excited States in Ru-(Aromatic Ligand) Phosphorescent Chromophore Series

This study investigates variations in phosphorescence rate constant (<i>k</i>_RAD) amplitude at low-temperature resulting from spin-orbit coupling-mediated intensity stealing from singlet excited states (SOCM-IS) among a series of Ru-(aromatic ligand) (Ru-L_Ar) phosphorescent chromophore series. The SOCM-IS model provides the theoretical basis for understanding the phosphorescence characteristics of the metal-to-ligand charge-transfer emitting states of the Ru-L_Ar phosphorescent chromophore series. The Amsterdam density functional (ADF) was employed to calculate the low-energy absorption transition parameters of 13 target complexes, with and without SOC perturbation, and calculated absorption spectra were calibrated against the corresponding observed absorption spectra. The strong linear relationship between observed phosphorescence efficiency (ι_em(p) = <i>k</i>_RAD/(ν_em)³, where ν_em denotes emission frequency) and SOCM-IS contributions revealed that ι_em(p) amplitude variations among the investigated Ru-L_Ar phosphorescent chromophores arose from their intrinsically low or high SOCM-IS contributions. To the best of our knowledge, this study presents a rare finding in the Ru-L_Ar phosphorescent chromophore series.