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

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 ofmore » 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.« less
Authors:
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
Publication Date:
Grant/Contract Number:
AC02-76SF00515; DFF-4002-00272B; LP2013-59; StG-259709; K 109257; GINOP-2.3.6-15-2015-00001; VEKOP-2.3.2-16-2017-00015; 2014.0370; 158890
Type:
Accepted Manuscript
Journal Name:
Physical Chemistry Chemical Physics. PCCP (Print)
Additional Journal Information:
Journal Name: Physical Chemistry Chemical Physics. PCCP (Print); Journal Volume: 20; Journal Issue: 6; Journal ID: ISSN 1463-9076
Publisher:
Royal Society of Chemistry
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 14 SOLAR ENERGY
OSTI Identifier:
1426489