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Updated: Sep 5, 2026
The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes
Published on: April 10, 2015
Conformationally-Gated Interligand Charge Transfer in a Ru-Polypyridine Complex
Kanyashree Jana1, Simil Thomas2, Naresh Duvva1
1Department of Chemistry, University of Texas at San Antonio, San Antonio, Texas78249, United States.
Abstract:
This study investigated the ultrafast excited-state dynamics in two ruthenium polypyridyl complexes, namely (bpy)2Ru(MQ)24+ and (bpy)2Ru(MQ')24+ (Ru-MQ and Ru-MQ'), where bpy = 2,2'-bipyridine, MQ = N-methyl-4,4'-bipyridine and MQ' = N-methyl-3,3'-dimethyl-4,4'-bipyridine. Broadband near-UV-visible transient absorption (TA) spectroscopy on Ru-MQ provides unequivocal evidence for bpy → MQ ligand-to-ligand electron transfer that occurs within 10 ps following 100 fs excitation of the Ru → bpy metal-to-ligand charge transfer (MLCT) state. Experimental results and density functional theory (DFT) calculations support the hypothesis that bpy → MQ electron transfer is gated by "flattening" of the MQ ligand mediated by torsion around the inter-ring C-C bond. Spin density plots obtained from the DFT calculations point toward the dihedral angle in MQ ligand being critical for the transition between the Ru → bpy and Ru → MQ3 MLCT states. The excited state model is further supported by parallel studies on Ru-MQ' in which the conformational change within MQ' is limited by steric constraints. Excitation wavelength-dependent TA studies on Ru-MQ indicate that the relative populations of the Ru → bpy and Ru → MQ3 MLCT states initially generated upon photoexcitation depend on the excitation wavelength. This behavior arises from the broad distribution of MQ conformers present in the ground state, which selectively absorb at different wavelengths.
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