We employ femtosecond X-ray absorption spectroscopy of [Ru(m-bpy)3]2+ (m-bpy = 6-methyl-2,2′-bipyridine) to elucidate the time evolution of the spin and charge density upon metal-to-ligand charge-transfer (MLCT) excitation. The core-level transitions at the Ru L3-edge reveal a very short MLCT lifetime of 0.9 ps and relaxation to the lowest triplet metal-centered state (3MC) which exhibits a lifetime of about 300 ps. Time-dependent density functional theory relates ligand methylation to a lower ligand field strength that stabilizes the 3MC state. A quarter of the 3MLCT population appears to be trapped which may be attributed to intramolecular vibrational relaxation or further electron transfer to the solvent. Our results demonstrate that small changes in the ligand field allow control of the photophysical properties. Moreover, this study underscores the high information content of femtosecond L-edge spectroscopy as a probe of valence charge density and spin-state in 4d transition metals.
|Number of pages||8|
|Journal||Journal of Physical Chemistry Letters|
|Publication status||Published - 2021 Dec 30|
Bibliographical noteFunding Information:
The experiments at the XSS end-station, PAL-XFEL, were approved by the Korean Synchrotron Users Association and supported by the Ministry of Science and ICT, Republic of Korea (Proposal Nos. 2019-2nd-XSS-025 and 2020-2nd-XSS-024). Funding from the following organizations are acknowledged: Ministry of Science and ICT, Republic of Korea, and the National Research Foundation of the Republic of Korea (NRF-2016K1A4A4A01922028, NRF-2018R1D1A1B07049917, NRF-2019R1A6B2A02098631, NRF-2020R1A4A1017737, and NRF-2021R1F1A1051444). This work was supported by an NRF (National Research Foundation of the Republic of Korea) Grant funded by the Korean Government (NRF-2018-Global Ph.D. Fellowship Program). This work was also supported by the Cluster of Excellence ‘CUI: Advanced Imaging of Matter’ of the Deutsche Forschungsgemeinschaft (DFG) - EXC 2056 - project ID 390715994.
© 2021 The Authors. Published by American Chemical Society
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Physical and Theoretical Chemistry