Guidelines to calculate non-radiative deactivation mechanisms of ruthenium tris(bipyridine) derivatives

The applicability of ruthenium tris(bipyridine) complexes in fields like photoactivated chemotherapy or photocatalysis requires in-depth understanding of their excited state deactivation mechanism. In particular, the quenching of luminescence from the lowest triplet metal-to-ligand charge-transfer ([Formula presented]) excited state or the ligand photorelease relies on the fine-tuning of the energetics of the higher-lying metal-centered excited states ([Formula presented]). In this contribution, we critically review different kinetic models commonly used to interpret the thermal activation of the [Formula presented] excited states from the lowest [Formula presented] minimum. Further, we extend our recently introduced kinetic model (Angew. Chem. Int. Ed. 2023, 62, e202308803) for [Formula presented] (bpy = 2,2'-bipyridine) to a set of homoleptic tris(bipyridine)ruthenium (II) derivatives. This set has been selected to cover a wide range of electron -withdrawing/-donating substituents in the periphery of the bipyridyl ligands (4,4'-[Formula presented]-2,2'-bpy; R= [Formula presented], [Formula presented], [Formula presented], [Formula presented], [Formula presented] [Formula presented], and [Formula presented]), on the basis of the Hammett's constant of the R functional group. Our calculations show that complexes with electron donating groups decay predominantly via one Jahn-Teller isomer (the so-called [Formula presented] -trans conformation), while those with electron withdrawing ligands tend to decay through a different one (the [Formula presented]-cis Jahn-Teller isomer). We discuss structure/property relationships with focus on how to steer the energetics of the [Formula presented] excited states. This work opens the pathway to rationally use ligand substitution to enhance or quench the lifetimes of the [Formula presented] state and also provides guidelines to understand better non-radiative deactivation mechanisms in metal complexes.