Long-Lived, Emissive Excited States in Direct and Amide-Linked Thienyl-Substituted RuII Complexes

The excited state behavior of a new series of homoleptic and heteroleptic RuII complexes bearing thienyl groups appended to a 2,2′‐bipyridine chelating ligand via direct, secondary and tertiary amide linkages is examined. The results of nanosecond transient absorption spectroscopy, emission lifetime measurements and bimolecular quenching experiments are correlated to determine that although the amide linkage does not act as a conjugated bridge to the peripheral substituents, it does not preclude possible electron transfer processes. Complexes bearing directly bound thienyl and bithienyl substituents exhibit long excited state and emission lifetimes (τem = 2 and 15 µs), with high emission quantum yields in solution (Φ = 0.35) and slow rates of non‐radiative decay. The photophysical properties of a series of RuII chromophores incorporating peripheral thienyl groups bound through secondary and tertiary amide linkages are compared to directly bound analogues. Nanosecond transient absorption and steady state optical spectroscopy data are correlated in an effort to elucidate the role of the amide linkage in photoinduced electron transfer from the periphery to the metal centre.