U.S. Department of Energy Office of Scientific and Technical Information
Revealing Parallel Inter‐ and Intra‐Ligand Charge Transfer Dynamics in [Ru(L)2(dppz)]2+ Molecular Lightswitch with N K‐Edge X‐Ray Absorption Spectroscopy
Journal Article·· Angewandte Chemie (International Edition)
SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States). Photon Ultrafast Laser Science and Engineering Institute (PULSE); Stanford Univ., CA (United States)
Univ. of Washington, Seattle, WA (United States)
SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Stanford Univ., CA (United States)
Argonne National Laboratory (ANL), Argonne, IL (United States)
Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States). Linac Coherent Light Source (LCLS)
In photoactive metal complexes the localization of photoexcited charges dictates the site of chemical reactivity, but few studies measure the charge redistribution in these systems with spatial precision. Herein, we track the inter- and intra-ligand charge transfer processes that underpin light-driven charge separation in the well-studied “molecular lightswitch” [Ru(bpy)2dppz]2+ (aqueous [RutheniumII(2,2′-bipyridine)2(dipyrido[3,2-a:2′,3′-c]phenazine)]2+[Cl−]2) by probing the electronic structure of ligand nitrogen atoms in real-time using ultrafast X-ray absorption spectroscopy and first principles calculations. We confirm the localization of excited electron density on the phenazine N atoms of dppz and we newly identify two parallel electron transfer pathways to populate this state. Sub-70 fs electron transfer to the phenazine portion of dppz is observed and attributed to intra-ligand electron transfer following Ru-to-dppz metal-to-ligand charge transfer (MLCT) excitation. This fast charge transfer was not reported in prior ultrafast studies. The slower (ca. 2 ps) charge transfer reported extensively in time-resolved optical absorption and emission studies is reassigned here to inter-ligand electron “hopping” between nearly isoenergetic ligand moieties following Ru-to-bpy MLCT excitation. In conclusion, the results demonstrate much faster charge separation than previously identified in this well-studied system, highlighting how extended azaacene ligand motifs promote the competitive charge transfer processes needed to drive light-driven electron transfer chemistry.
Ryland, Elizabeth S., et al. "Revealing Parallel Inter‐ and Intra‐Ligand Charge Transfer Dynamics in [Ru(L)<sub>2</sub>(dppz)]<sup>2+</sup> Molecular Lightswitch with N K‐Edge X‐Ray Absorption Spectroscopy." Angewandte Chemie (International Edition), vol. 64, no. 36, Jul. 2025. https://doi.org/10.1002/anie.202509496
Ryland, Elizabeth S., Yang, Xinzheng, Garratt, Douglas, et al., "Revealing Parallel Inter‐ and Intra‐Ligand Charge Transfer Dynamics in [Ru(L)<sub>2</sub>(dppz)]<sup>2+</sup> Molecular Lightswitch with N K‐Edge X‐Ray Absorption Spectroscopy," Angewandte Chemie (International Edition) 64, no. 36 (2025), https://doi.org/10.1002/anie.202509496
@article{osti_2583411,
author = {Ryland, Elizabeth S. and Yang, Xinzheng and Garratt, Douglas and Henke, Wade C. and Kahraman, Abdullah and Taub, Maxwell and Sachs, Michael and Biasin, Elisa and Hampton, Christina Y. and Hoffman, David J. and others},
title = {Revealing Parallel Inter‐ and Intra‐Ligand Charge Transfer Dynamics in [Ru(L)<sub>2</sub>(dppz)]<sup>2+</sup> Molecular Lightswitch with N K‐Edge X‐Ray Absorption Spectroscopy},
annote = {In photoactive metal complexes the localization of photoexcited charges dictates the site of chemical reactivity, but few studies measure the charge redistribution in these systems with spatial precision. Herein, we track the inter- and intra-ligand charge transfer processes that underpin light-driven charge separation in the well-studied “molecular lightswitch” [Ru(bpy)2dppz]2+ (aqueous [RutheniumII(2,2′-bipyridine)2(dipyrido[3,2-a:2′,3′-c]phenazine)]2+[Cl−]2) by probing the electronic structure of ligand nitrogen atoms in real-time using ultrafast X-ray absorption spectroscopy and first principles calculations. We confirm the localization of excited electron density on the phenazine N atoms of dppz and we newly identify two parallel electron transfer pathways to populate this state. Sub-70 fs electron transfer to the phenazine portion of dppz is observed and attributed to intra-ligand electron transfer following Ru-to-dppz metal-to-ligand charge transfer (MLCT) excitation. This fast charge transfer was not reported in prior ultrafast studies. The slower (ca. 2 ps) charge transfer reported extensively in time-resolved optical absorption and emission studies is reassigned here to inter-ligand electron “hopping” between nearly isoenergetic ligand moieties following Ru-to-bpy MLCT excitation. In conclusion, the results demonstrate much faster charge separation than previously identified in this well-studied system, highlighting how extended azaacene ligand motifs promote the competitive charge transfer processes needed to drive light-driven electron transfer chemistry.},
doi = {10.1002/anie.202509496},
url = {https://www.osti.gov/biblio/2583411},
journal = {Angewandte Chemie (International Edition)},
issn = {ISSN 1433-7851},
number = {36},
volume = {64},
place = {United States},
publisher = {Wiley},
year = {2025},
month = {07}}