Coordination and electronic structure of ruthenium(II)-tris-2,2′- bipyridine in the triplet metal-to-ligand charge-transfer excited state observed by picosecond time-resolved Ru K-edge XAFS

Time-resolved X-ray absorption spectra of photoexcited ruthenium(II)-tris- 2,2′-bipyridine ([Ru ^II(bpy) ₃] ²⁺) in the triplet metal-to-ligand charge transfer ( ³MLCT) state are measured and analyzed to investigate transient structural changes directly related to the photophysical properties of the complex. The results from visible (400 nm) and UV (267 nm) excitation indicate that electrostatic interaction between the oxidized Ru atom and the reduced bipyridine ligand is the dominant factor affecting the Ru-N bond contraction. This thus leads to two groups of Ru ligand distances, one exhibiting the ground-state Ru-N distance and another yielding a slightly decreased Ru-N distance due to the localized MLCT excited state. The EXAFS analysis of the photoexcited complex was analyzed toward one single Ru-N distance, yielding a contraction of 0.04 (0.01) Å with an increased DW factor (corresponding to a 0.05 Å mean increase).