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Title: Solvent control of charge transfer excited state relaxation pathways in [Fe(2,2'-bipyridine)(CN)4]2-

Journal Article · · Physical Chemistry Chemical Physics. PCCP
DOI: https://doi.org/10.1039/c7cp07838b · OSTI ID:1426489
ORCiD logo [1];  [2];  [3];  [4];  [2];  [2]; ORCiD logo [2];  [2];  [2];  [5]; ORCiD logo [6];  [5];  [5];  [5];  [5]; ORCiD logo [5];  [7];  [8];  [7];  [7] more »;  [7]; ORCiD logo [7];  [9]; ORCiD logo [9];  [9]; ORCiD logo [9];  [4];  [4];  [4];  [4];  [10];  [11];  [12];  [13]; ORCiD logo [14];  [2];  [15] « less
  1. SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., CA (United States). PULSE Institute; Technical University of Denmark, Lyngby (Denmark). Molecular Movies, Department of Physics; Lund Univ. (Sweden). Department of Chemical Physics
  2. SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., CA (United States). PULSE Institute
  3. Technical University of Denmark, Lyngby (Denmark). Molecular Movies, Department of Physics; Lund Univ. (Sweden). Department of Chemical Physics
  4. SLAC National Accelerator Lab., Menlo Park, CA (United States). LCLS
  5. Technical University of Denmark, Lyngby (Denmark). Molecular Movies, Department of Physics
  6. SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., CA (United States). PULSE Institute; Technical University of Denmark, Lyngby (Denmark). Molecular Movies, Department of Physics
  7. Lund Univ. (Sweden). Department of Chemical Physics
  8. Lund Univ. (Sweden). Department of Chemical Physics and Centre for Analysis and Synthesis, Department of Chemistry
  9. Hungarian Academy of Sciences, Budapest (Hungary). Wigner Research Centre for Physics
  10. SLAC National Accelerator Lab., Menlo Park, CA (United States). SSRL
  11. SLAC National Accelerator Lab., Menlo Park, CA (United States). LCLS; SwissFEL, Paul Scherrer Institut, Villigen (Switzerland)
  12. ELI-ALPS, ELI-HU Non-Profit Ltd. (Hungary); FS-ATTO, Deutsches Elektronen-Synchrotron (DESY ), Hamburg (Germany)
  13. Lund Univ. (Sweden). Centre for Analysis and Synthesis, Department of Chemistry
  14. Lund Univ. (Sweden). Theoretical Chemistry Division
  15. SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., CA (United States). PULSE Institute and SSRL
+ Show Author Affiliations

The excited state dynamics of solvated [Fe(bpy)(CN)4]2-, where bpy = 2,2'-bipyridine, show significant sensitivity to the solvent Lewis acidity. Using a combination of optical absorption and X-ray emission transient spectroscopies, we have previously shown that the metal to ligand charge transfer (MLCT) excited state of [Fe(bpy)(CN)4]2- has a 19 picosecond lifetime and no discernable contribution from metal centered (MC) states in weak Lewis acid solvents, such as dimethyl sulfoxide and acetonitrile. Here, in the present work, we use the same combination of spectroscopic techniques to measure the MLCT excited state relaxation dynamics of [Fe(bpy)(CN)4]2- in water, a strong Lewis acid solvent. The charge-transfer excited state is now found to decay in less than 100 femtoseconds, forming a quasi-stable metal centered excited state with a 13 picosecond lifetime. We find that this MC excited state has triplet (3MC) character, unlike other reported six-coordinate Fe(II)-centered coordination compounds, which form MC quintet (5MC) states. The solvent dependent changes in excited state non-radiative relaxation for [Fe(bpy)(CN)4]2- allows us to infer the influence of the solvent on the electronic structure of the complex. Lastly, the robust characterization of the dynamics and optical spectral signatures of the isolated 3MC intermediate provides a strong foundation for identifying 3MC intermediates in the electronic excited state relaxation mechanisms of similar Fe-centered systems being developed for solar applications.

Research Organization:
SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
Grant/Contract Number:
AC02-76SF00515
OSTI ID:
1426489
Journal Information:
Physical Chemistry Chemical Physics. PCCP, Journal Name: Physical Chemistry Chemical Physics. PCCP Journal Issue: 6 Vol. 20; ISSN 1463-9076; ISSN PPCPFQ
Publisher:
Royal Society of ChemistryCopyright Statement
Country of Publication:
United States
Language:
English

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Chemical interactions and dynamics with femtosecond X-ray spectroscopy and the role of X-ray free-electron lasers text January 2019
Hole dynamics in a photovoltaic donor-acceptor couple revealed by simulated time-resolved X-ray absorption spectroscopy text January 2019
Vibrational wavepacket dynamics in Fe carbene photosensitizer determined with femtosecond X-ray emission and scattering text January 2020
NHC-Based Iron Sensitizers for DSSCs journal June 2018
Covalency-Driven Preservation of Local Charge Densities in a Metal-to-Ligand Charge-Transfer Excited Iron Photosensitizer other January 2019
Excited-State Solvation Structure of Transition Metal Complexes from Molecular Dynamics Simulations and Assessment of Partial Atomic Charge Methods text January 2018

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