Differences in Photophysical Properties and Photochemistry of Ru(II)-Terpyridine Complexes of CH 3 CN and Pyridine

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2024-01, Vol.128 (3), p.599-610
• Main Authors: Dunbar, Marilyn N, Steinke, Sean J, Piechota, Eric J, Turro, Claudia
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.3c07432

A series of 22 Ru(II) complexes of the type [Ru(tpy)(L)(L')] , where tpy is the tridentate ligand 2,2';6,2″-terpyridine, L represents bidentate ligands with varying electron-donating ability, and L' is acetonitrile ( - ) or pyridine ( - ), were investigated. The dissociation of acetonitrile occurs from the MLCT state in - , such that it does not require the population of a LF state. Electrochemistry and spectroscopic data demonstrate that the ground states of these series do not differ significantly. Franck-Condon line-shape analysis of the 77 K emission data shows no significant differences between the emitting MLCT states in both series. Arrhenius analysis of the temperature dependence of MLCT lifetimes shows that the energy barrier ( ) to thermally populating a LF state from a lower energy MLCT state is significantly higher in the pyridine than in the CH CN series, consistent with the photostability of complexes - , which do not undergo pyridine photodissociation under our experimental conditions. Importantly, these results demonstrate that ligand photodissociation of pyridine in - does not take place directly from the MLCT state, as is the case for - . These findings have potential impact on the rational design of complexes for a number of applications, including photochemotherapy, dye-sensitized solar cells, and photocatalysis.