Abstract
Photoinduced charge-transfer is an important process in nature and technology and is responsible for the emergence of exotic functionalities, such as magnetic order for cyanide-bridged bimetallic coordination networks. Despite its broad interest and intensive developments in chemistry and material sciences, the atomic-scale description of the initial photoinduced process, which couples intermetallic charge-transfer and spin transition, has been debated for decades; it has been beyond reach due to its extreme speed. Here we study this process in a prototype cyanide-bridged CoFe system by femtosecond X-ray and optical absorption spectroscopies, enabling the disentanglement of ultrafast electronic and structural dynamics. Our results demonstrate that it is the spin transition that occurs first on the Co site within ~50 fs, and it is this that drives the subsequent Fe-to-Co charge-transfer within ~200 fs. This study represents a step towards understanding and controlling charge-transfer-based functions using light.
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Data availability
The datasets generated and analysed during the current study are available in the HAL repository at https://hal.archives-ouvertes.fr/hal-02996531 or from the authors upon request.
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Acknowledgements
E.C. and M.C. acknowledge the support of Rennes Métropole, ANR (ANR-13-BS04-0002 FEMTOMAT, ANR-19-CE30-0004 ELECTROPHONE, ANR-19-CE29-0018 MULTICROSS and ANR-15-CE32-0004 Bio-XFEL), Centre National de la Recherche Scientifique (CNRS, PEPS SASLELX), Fonds Européen de Développement Régional (FEDER) and Région Bretagne (ARED 8925/XFELMAT). S.Z, L.C., T.M. and S.F.M. acknowledge the support of ANR (ANR-13-BS04-0002 FEMTOMAT). T.M. thanks the IUF (Institut Universitaire de France) for financial support. M.C., L.B., M.L., C.E. and M.T. acknowledge the support of European Union Horizon2020 under the Marie Skłodowska-Curie Project ‘X-Probe’ grant no. 637295. We thank A. Bleuzen for sharing the published XANES data used in Supplementary Fig. 7. Use of the Linac Coherent Light Source, SLAC National Accelerator Laboratory, is supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under contract no. DE-AC02-76SF00515.
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Contributions
E.C. and M.C., in collaboration with T.M. and S.F.M., conceived the project. S.M., L.C. and T.M. synthesized and characterized the CoFe sample. M.C., S.Z., L.B., G.A., C.E., M.T., M.L., R.A.M., J.M.G., S.S. and E.C. performed the femtosecond XANES experiment. S.Z. and G.A. performed the optical study. S.Z., M.C. and E.C. analysed the data. S.F.M. performed the DFT and TD-DFT calculations. E.C. and M.C. set the physical picture for interpreting the data. E.C. and M.C. wrote the paper. All authors contributed to discussions and gave comments on the manuscript.
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Supplementary Information
Supplementary Figs. 1–10, Discussion and Table 1.
Supplementary Video 1
Torsion mode at 1.62 THz for the (CN)5–Coii–N–C–Feiii–(CN)5 state.
Supplementary Video 2
Torsion mode at 1.44 THz for the (CN)5–Coii–N–C–Feiii–(CN)5 state.
Supplementary Video 3
Torsion mode at 1.85 THz for the (CN)5–Coiii–N–C–Feii–(CN)5 state.
Supplementary Video 4
Torsion mode at 1.56 THz for the Co2iiiFe2ii square.
Supplementary Video 5
Breathing mode at 11.2 THz for the (CN)5–Coii–N–C–Feiii–(CN)5 state.
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Cammarata, M., Zerdane, S., Balducci, L. et al. Charge transfer driven by ultrafast spin transition in a CoFe Prussian blue analogue. Nat. Chem. 13, 10–14 (2021). https://doi.org/10.1038/s41557-020-00597-8
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DOI: https://doi.org/10.1038/s41557-020-00597-8
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