Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Tracking excited-state charge and spin dynamics in iron coordination complexes

Nature volume 509, pages 345–348 (2014)Cite this article

Subjects

Abstract

Crucial to many light-driven processes in transition metal complexes is the absorption and dissipation of energy by 3d electrons1,2,3,4. But a detailed understanding of such non-equilibrium excited-state dynamics and their interplay with structural changes is challenging: a multitude of excited states and possible transitions result in phenomena too complex to unravel when faced with the indirect sensitivity of optical spectroscopy to spin dynamics5 and the flux limitations of ultrafast X-ray sources6,7. Such a situation exists for archetypal polypyridyl iron complexes, such as [Fe(2,2′-bipyridine)3]2+, where the excited-state charge and spin dynamics involved in the transition from a low- to a high-spin state (spin crossover) have long been a source of interest and controversy6,7,8,9,10,11,12,13,14,15. Here we demonstrate that femtosecond resolution X-ray fluorescence spectroscopy, with its sensitivity to spin state, can elucidate the spin crossover dynamics of [Fe(2,2′-bipyridine)3]2+ on photoinduced metal-to-ligand charge transfer excitation. We are able to track the charge and spin dynamics, and establish the critical role of intermediate spin states in the crossover mechanism. We anticipate that these capabilities will make our method a valuable tool for mapping in unprecedented detail the fundamental electronic excited-state dynamics that underpin many useful light-triggered molecular phenomena involving 3d transition metal complexes.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Schematic depiction of ultrafast X-ray fluorescence detection of spin crossover dynamics.
Figure 2: Spin-dependent iron Kβ fluorescence spectra.
Figure 3: Time-dependent photo-induced iron Kβ difference spectra and kinetic modelling of spin crossover dynamics.

Similar content being viewed by others

References

  1. Gust, D., Moore, T. A. & Moore, A. L. Mimicking photosynthetic solar energy transduction. Acc. Chem. Res. 34, 40–48 (2001)

    Article  CAS  Google Scholar 

  2. Sato, O., Iyoda, T., Fujishima, A. & Hashimoto, K. Photoinduced magnetization of a cobalt-iron cyanide. Science 272, 704–705 (1996)

    Article  CAS  ADS  Google Scholar 

  3. Ferrere, S. & Gregg, B. A. Photosensitization of TiO2 by Fe-II(2,2′-bipyridine-4,4′-dicarboxylic acid)2(CN)2: band selective electron injection from ultra-short-lived excited states. J. Am. Chem. Soc. 120, 843–844 (1998)

    Article  CAS  Google Scholar 

  4. Heyduk, A. F. & Nocera, D. G. Hydrogen produced from hydrohalic acid solutions by a two-electron mixed-valence photocatalyst. Science 293, 1639–1641 (2001)

    Article  CAS  ADS  Google Scholar 

  5. Goldbeck, R. A., Kim-Shapiro, D. B. & Kliger, D. S. Fast natural and magnetic circular dichroism spectroscopy. Annu. Rev. Phys. Chem. 48, 453–479 (1997)

    Article  CAS  ADS  Google Scholar 

  6. Bressler, C. et al. Femtosecond XANES study of the light-induced spin crossover dynamics in an iron(II) complex. Science 323, 489–492 (2009)

    Article  CAS  ADS  Google Scholar 

  7. Huse, N. et al. Femtosecond soft X-ray spectroscopy of solvated transition-metal complexes: deciphering the interplay of electronic and structural dynamics. J. Phys. Chem. Lett. 2, 880–884 (2011)

    Article  CAS  Google Scholar 

  8. Gutlich, P. & Goodwin, H. A. in Spin Crossover in Transition Metal Compounds I Vol. 233, Topics in Current Chemistry (eds Gutlich, P. & Goodwin, H. A. ) 1–47 (Springer, 2004)

    Book  Google Scholar 

  9. Creutz, C., Chou, M., Netzel, T. L., Okumura, M. & Sutin, N. Lifetimes, spectra, and quenching of the excited-states of polypyridine complexes of iron(II), ruthenium(II), and osmium(II). J. Am. Chem. Soc. 102, 1309–1319 (1980)

    Article  CAS  Google Scholar 

  10. Hauser, A. Intersystem crossing in the Fe(PTZ)6 (BF4)2 spin crossover system (PTZ = 1-propyltetrazole). J. Chem. Phys. 94, 2741–2748 (1991)

    Article  CAS  ADS  Google Scholar 

  11. McCusker, J. K. et al. Subpicosecond 1MLCT-5T2 intersystem crossing of low-spin polypyridyl ferrous complexes. J. Am. Chem. Soc. 115, 298–307 (1993)

    Article  CAS  Google Scholar 

  12. Monat, J. E. & McCusker, J. K. Femtosecond excited-state dynamics of an iron(II) polypyridyl solar cell sensitizer model. J. Am. Chem. Soc. 122, 4092–4097 (2000)

    Article  CAS  Google Scholar 

  13. Gawelda, W. et al. Ultrafast nonadiabatic dynamics of [Fe(II)(bpy)3]2+ in solution. J. Am. Chem. Soc. 129, 8199–8206 (2007)

    Article  CAS  Google Scholar 

  14. Consani, C. et al. Vibrational coherences and relaxation in the high-spin state of aqueous [Fe-II(bpy)3]2+. Angew. Chem. Int. Edn 48, 7184–7187 (2009)

    Article  CAS  Google Scholar 

  15. Lemke, H. T. et al. Femtosecond X-ray absorption spectroscopy at a hard X-ray free electron laser: application to spin crossover dynamics. J. Phys. Chem. A 117, 735–740 (2013)

    Article  CAS  Google Scholar 

  16. Emma, P. et al. First lasing and operation of an angstrom-wavelength free-electron laser. Nature Photon. 4, 641–647 (2010)

    Article  CAS  ADS  Google Scholar 

  17. Harmand, M. et al. Achieving few-femtosecond time-sorting at hard X-ray free-electron lasers. Nature Photon. 7, 215–218 (2013)

    Article  CAS  ADS  Google Scholar 

  18. Haldrup, K. et al. Guest-host interactions investigated by time-resolved X-ray spectroscopies and scattering at MHz rates: solvation dynamics and photoinduced spin transition in aqueous [Fe(bipy)3]2+. J. Phys. Chem. A 116, 9878–9887 (2012)

    Article  CAS  Google Scholar 

  19. Vankó, G. et al. Probing the 3d spin momentum with X-ray emission spectroscopy: the case of molecular-spin transitions. J. Phys. Chem. B 110, 11647–11653 (2006)

    Article  Google Scholar 

  20. Krause, M. O. & Oliver, J. H. Natural widths of atomic K and L levels, K-alpha X-ray lines and several KLL Auger lines. J. Phys. Chem. Ref. Data 8, 329–338 (1979)

    Article  CAS  ADS  Google Scholar 

  21. de Graaf, C. & Sousa, C. Study of the light-induced spin crossover process of the [Fe(II)(bpy)3]2+ complex. Chemistry 16, 4550–4556 (2010)

    Article  CAS  Google Scholar 

  22. de Graaf, C. & Sousa, C. On the role of the metal-to-ligand charge transfer states in the light-induced spin crossover in Fe-II(bpy)3 . Int. J. Quantum Chem. 111, 3385–3393 (2011)

    Article  CAS  Google Scholar 

  23. Glatzel, P. & Bergmann, U. High resolution 1s core hole X-ray spectroscopy in 3d transition metal complexes — electronic and structural information. Coord. Chem. Rev. 249, 65–95 (2005)

    Article  CAS  Google Scholar 

  24. de Groot, F. High resolution X-ray emission and X-ray absorption spectroscopy. Chem. Rev. 101, 1779–1808 (2001)

    Article  CAS  Google Scholar 

  25. Lee, N., Petrenko, T., Bergmann, U., Neese, F. & DeBeer, S. Probing valence orbital composition with iron K β X-ray emission spectroscopy. J. Am. Chem. Soc. 132, 9715–9727 (2010)

    Article  CAS  Google Scholar 

  26. Cannizzo, A. et al. Light-induced spin crossover in Fe(II)-based complexes: the full photocycle unraveled by ultrafast optical and X-ray spectroscopies. Coord. Chem. Rev. 254, 2677–2686 (2010)

    Article  CAS  Google Scholar 

  27. Sousa, C. et al. Ultrafast deactivation mechanism of the excited singlet in the light-induced spin crossover of [Fe(2,2′-bipyridine)3]2+. Chemistry 19, 17541–17551 (2013)

    Article  CAS  Google Scholar 

  28. Alvarez, S. Relationships between temperature, magnetic moment, and continuous symmetry measures in spin crossover complexes. J. Am. Chem. Soc. 125, 6795–6802 (2003)

    Article  CAS  Google Scholar 

  29. Khalil, M. et al. Picosecond X-ray absorption spectroscopy of a photoinduced iron(II) spin crossover reaction in solution. J. Phys. Chem. A 110, 38–44 (2006)

    Article  CAS  Google Scholar 

  30. Nozawa, S. et al. Direct probing of spin state dynamics coupled with electronic and structural modifications by picosecond time-resolved XAFS. J. Am. Chem. Soc. 132, 61–63 (2010)

    Article  CAS  Google Scholar 

  31. Gawelda, W. Time-Resolved X-Ray Absorption Spectroscopy of Transition Metal Complexes. Ph.D. thesis, École Polytechnique Fédérale de Lausanne. (2006)

  32. Feng, Y. P. et al. A single-shot intensity-position monitor for hard X-ray FEL sources. Proc. SPIE 8140, 81400Q (2011)

    Article  Google Scholar 

  33. Alonso-Mori, R. et al. A multi-crystal wavelength dispersive X-ray spectrometer. Rev. Sci. Instrum. 83, 9 (2012)

    Article  Google Scholar 

  34. Koerner, L. J., Philipp, H. T., Hromalik, M. S., Tate, M. W. & Gruner, S. M. X-ray tests of a pixel array detector for coherent X-ray imaging at the Linac Coherent Light Source. J. Instrum. 4, P03001 (2009)

    Article  Google Scholar 

  35. Bionta, M. R. et al. Spectral encoding of X-ray/optical relative delay. Opt. Express 19, 21855–21865 (2011)

    Article  CAS  ADS  Google Scholar 

  36. Vankó, G. et al. Picosecond time-resolved X-ray emission spectroscopy: ultrafast spin-state determination in an iron complex. Angew. Chem. Int. Edn 49, 5910–5912 (2010)

    Article  Google Scholar 

  37. Vankó, G. et al. Spin-state studies with XES and RIXS: From static to ultrafast. J. Elec. Spec. Relat. Phenom. 188, 166–171 (2013)

    Article  Google Scholar 

  38. de Groot, F. M. F. & Kotani, A. Core Level Spectroscopy of Solids (CRC Press, Boca Raton, 2008)

    Book  Google Scholar 

  39. Stepanow, S. et al. Mixed-valence behavior and strong correlation effects of metal phthalocyanines adsorbed on metals. Phys. Rev. B 83, 220401 (2011)

    Article  ADS  Google Scholar 

  40. Kutner, M. H., Nachtsheim, C. J. & Neter, J. Applied Linear Regression Models (McGraw-Hill/Irwin, 2004)

    Google Scholar 

Download references

Acknowledgements

We thank P. Frank, B. Lin and S. DeBeer for discussion, S. DeBeer for some model iron complex X-ray fluorescence spectra, and D. Stanbury for providing some iron complexes. Experiments were carried out at LCLS and SSRL, which are National User Facilities operated for DOE and OBES respectively by Stanford University. W.Z., R.W.H., H.W.L., D.A.M., Z.S. and K.J.G. acknowledge support from the AMOS programme within the Chemical Sciences, Geosciences and Biosciences Division of the Office of Basic Energy Sciences, Office of Science, US Department of Energy. E.I.S. acknowledges support from the NSF (CHE-0948211). R.G.H. acknowledges a Gerhard Casper Stanford Graduate Fellowship and the Achievements Rewards for College Scientists (ARCS) Foundation. T.K. acknowledges the German Research Foundation (DFG), grant KR3611/2-1. K.S.K., M.M.N. and T.B.v.D. acknowledge support from the Danish National Research Foundation and from DANSCATT. K.K. thanks the Volkswagen Foundation for support under the Peter Paul Ewald fellowship program (I/85832). G.V. acknowledges support from the European Research Council (ERC-StG-259709) and the Lendület Programme of the Hungarian Academy of Sciences. C.B., W.G. and A.G. thank the DFG (SFB925), as well as the European XFEL, for financial support.

Author information

Authors and Affiliations

  1. PULSE Institute, SLAC National Accelerator Laboratory, Stanford University, Stanford, 94305, California, USA

    Wenkai Zhang, Robert W. Hartsock, Huiyang W. Liang, Drew A. Meyer, Carola Purser, Zheng Sun & Kelly J. Gaffney

  2. LCLS, SLAC National Accelerator Laboratory, Menlo Park, 94025, California, USA

    Roberto Alonso-Mori, Uwe Bergmann, Matthieu Chollet, Henrik T. Lemke, Joseph S. Robinson & Diling Zhu

  3. European XFEL, D-22761 Hamburg, Germany,

    Christian Bressler, Andreas Galler & Wojciech Gawelda

  4. Department of Chemistry, Stanford University, Stanford, 94305, California, USA

    Ryan G. Hadt, Robert W. Hartsock, Thomas Kroll, Huiyang W. Liang, Drew A. Meyer & Edward I. Solomon

  5. Centre for Molecular Movies, Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark,

    Kasper S. Kjær

  6. Department of Physics, Centre for Molecular Movies, Technical University of Denmark, DK-2800 Lyngby, Denmark,

    Kasper S. Kjær, Martin M. Nielsen & Tim B. van Driel

  7. Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany,

    Katharina Kubiček

  8. Deutsches Elektronen Synchrotron, Notkestraße 85, 22607 Hamburg, Germany,

    Katharina Kubiček

  9. SSRL, SLAC National Accelerator Laboratory, Menlo Park, 94025, California, USA

    Edward I. Solomon, Dimosthenis Sokaras & Tsu-Chien Weng

  10. Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, Hungary,

    György Vankó

Authors
  1. Wenkai Zhang
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Roberto Alonso-Mori
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Uwe Bergmann
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Christian Bressler
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Matthieu Chollet
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Andreas Galler
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Wojciech Gawelda
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Ryan G. Hadt
    View author publications

    You can also search for this author in PubMed Google Scholar

  9. Robert W. Hartsock
    View author publications

    You can also search for this author in PubMed Google Scholar

  10. Thomas Kroll
    View author publications

    You can also search for this author in PubMed Google Scholar

  11. Kasper S. Kjær
    View author publications

    You can also search for this author in PubMed Google Scholar

  12. Katharina Kubiček
    View author publications

    You can also search for this author in PubMed Google Scholar

  13. Henrik T. Lemke
    View author publications

    You can also search for this author in PubMed Google Scholar

  14. Huiyang W. Liang
    View author publications

    You can also search for this author in PubMed Google Scholar

  15. Drew A. Meyer
    View author publications

    You can also search for this author in PubMed Google Scholar

  16. Martin M. Nielsen
    View author publications

    You can also search for this author in PubMed Google Scholar

  17. Carola Purser
    View author publications

    You can also search for this author in PubMed Google Scholar

  18. Joseph S. Robinson
    View author publications

    You can also search for this author in PubMed Google Scholar

  19. Edward I. Solomon
    View author publications

    You can also search for this author in PubMed Google Scholar

  20. Zheng Sun
    View author publications

    You can also search for this author in PubMed Google Scholar

  21. Dimosthenis Sokaras
    View author publications

    You can also search for this author in PubMed Google Scholar

  22. Tim B. van Driel
    View author publications

    You can also search for this author in PubMed Google Scholar

  23. György Vankó
    View author publications

    You can also search for this author in PubMed Google Scholar

  24. Tsu-Chien Weng
    View author publications

    You can also search for this author in PubMed Google Scholar

  25. Diling Zhu
    View author publications

    You can also search for this author in PubMed Google Scholar

  26. Kelly J. Gaffney
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

W.Z., R.A.-M., U.B., R.W.H., D.A.M., T.-C.W. and K.J.G. designed the experiment. W.Z., R.A.-M., U.B., M.C., R.W.H., K.S.K., K.K., H.T.L., H.W.L., C.P., J.S.R., Z.S., D.S., T.B.v.D., T.-C.W., D.Z. and K.J.G. did the experiment. W.Z., T.K., K.S.K., T.B.v.D., G.V. and T.-C.W. analysed the data. W.Z., R.A.-M., U.B., C.B., W.G., A.G., R.G.H., R.W.H., T.K., K.S.K., K.K., D.A.M., M.M.N., E.I.S., D.S. and K.J.G. wrote the manuscript.

Corresponding author

Correspondence to Kelly J. Gaffney.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 Experimental and calculated Kβ fluorescence spectra for triplet spin states.

a, The calculated Kβ fluorescence spectra of iron complexes: triplet Fe(ii) in square planar crystal field (red) (calculation parameters based on Fe(ii)phthalocyanine), and triplet excited state in an octahedral crystal field (blue) (calculation parameters based on [Fe(2,2′-bipyridine)3]2+). b, The experimental Kβ fluorescence difference spectrum (red) obtained by subtracting the singlet [Fe(2,2′-bipyridine)3]2+ spectrum from the triplet Fe(ii)phthalocyanine spectrum, and the calculated Kβ fluorescence difference spectrum (blue) generated by subtracting the spectrum of the singlet state in an octahedral crystal field from the triplet state in a square planar crystal field.

Extended Data Figure 2 Time-dependent Kβ fluorescence spectra and fit using the sequential kinetic model with a triplet transient.

a, Experimental transient fluorescent amplitude difference spectra plotted with arbitrary units, and b, fit using the sequential kinetic model with a triplet transient. c, Residuals for the best fit, with the colour-scale maximum and minimum set to one-fifth of the value used in a and b. d, The excited state populations extracted from the best fit.

Extended Data Figure 3 Time-dependent Kβ fluorescence spectra and fit using the direct kinetic model without a triplet transient.

a, Experimental transient fluorescent amplitude difference spectra plotted with arbitrary units, and b, fit using the direct kinetic model without a triplet transient. c, Residuals for the best fit with the colour scale maximum and minimum set to one-fifth of the value used in a and b. d, The excited state populations extracted from the best fit.

Extended Data Figure 4 The 50 fs time delay normalized Kβ fluorescent amplitude difference spectrum (ΔI) and kinetic model fit plotted as a function of X-ray emission energy.

The measured data (black circles and line), along with the best global fit from the sequential kinetic model with a transient triplet state (red line).

Extended Data Figure 5 Absorption spectrum and pump power dependence measurements.

a, The ultraviolet–visible absorption spectrum of [Fe(2,2′-bipyridine)3]2+ in water. b, Power (fluence) dependence of the change in probe transmission measured at 520 nm, following excitation of an aqueous solution of [Fe(2,2′-bipyridine)3]Cl2 with a 520 nm pump pulse. The figure shows the change in transmission (ΔT) measured at a 10 ps time delay, a time long compared to the spin crossover and vibrational cooling timescales, but short compared to the lifetime of the high-spin excited state.

Extended Data Table 1 Fitted model parameters
Full size table

PowerPoint slides

Source data

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Zhang, W., Alonso-Mori, R., Bergmann, U. et al. Tracking excited-state charge and spin dynamics in iron coordination complexes. Nature 509, 345–348 (2014). https://doi.org/10.1038/nature13252

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature13252

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing