Low-Temperature Observation of the Excited-State Decay of Ruthenium-(Mono-2,2′:6′,2″-Terpyridine) Ions with Innocent Ligands: DFT Modeling of an (3)MLCT–(3)MC Intersystem Crossing Pathway

[Image: see text] The synthesis, electrochemistry, and photophysical characterization of five 2,2′:6′,2″-terpyridine ruthenium complexes (Ru-tpy complexes) is reported. The electrochemical and photophysical behavior varied depending on the ligands, i.e., amine (NH(3)), acetonitrile (AN), and bis(pyrazolyl)methane (bpm), for this series of Ru-tpy complexes. The target [Ru(tpy)(AN)(3)](2+) and [Ru(tpy)(bpm)(AN)](2+) complexes were found to have low-emission quantum yields in low-temperature observations. To better understand this phenomenon, density functional theory (DFT) calculations were performed to simulate the singlet ground state (S(0)), T(e), and metal-centered excited states ((3)MC) of these complexes. The calculated energy barriers between T(e) and the low-lying (3)MC state for [Ru(tpy)(AN)(3)](2+) and [Ru(tpy)(bpm)(AN)](2+) provided clear evidence in support of their emitting state decay behavior. Developing a knowledge of the underlying photophysics of these Ru-tpy complexes will allow new complexes to be designed for use in photophysical and photochemical applications in the future.