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Transferring the entatic-state principle to copper photochemistry

Abstract

The entatic state denotes a distorted coordination geometry of a complex from its typical arrangement that generates an improvement to its function. The entatic-state principle has been observed to apply to copper electron-transfer proteins and it results in a lowering of the reorganization energy of the electron-transfer process. It is thus crucial for a multitude of biochemical processes, but its importance to photoactive complexes is unexplored. Here we study a copper complex—with a specifically designed constraining ligand geometry—that exhibits metal-to-ligand charge-transfer state lifetimes that are very short. The guanidine–quinoline ligand used here acts on the bis(chelated) copper(I) centre, allowing only small structural changes after photoexcitation that result in very fast structural dynamics. The data were collected using a multimethod approach that featured time-resolved ultraviolet–visible, infrared and X-ray absorption and optical emission spectroscopy. Through supporting density functional calculations, we deliver a detailed picture of the structural dynamics in the picosecond-to-nanosecond time range.

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Figure 1: Model complexes for the entatic state and their spectroscopic features.
Figure 2: Time-resolved UV/vis and infrared spectra of compound 1.
Figure 3: Schematic representation of the involved states.
Figure 4: Time-resolved X-ray absorption data.
Figure 5: Visualization of the ‘entatic’ coordinates for the optical excitation of compound 1.

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Acknowledgements

S.H.-P. acknowledges generous funding by the Deutsche Forschungsgemeinschaft (FOR1405 and SFB749, project B10) and M.R. thanks the Bundesministerium für Bildung und Forschung (BMBF VUV-FAST/05K2014 and 05K12GU1) and DFG (FOR1405). Also, W.Z. thanks the SFB749 (project A5) and the Cluster of Excellence ‘Munich-Center for Advanced Photonics’ and ‘Center for Integrated Protein Science (CIPSM)’. This work was supported by the project ELI (Extreme Light Infrastructure) phase 2 (CZ.02.1.01/0.0/0.0/15_008/0000162) from the European Regional Development Fund. J.A. acknowledges funding from the Röntgen Ångström Cluster and the Chalmers Area of Advance Materials Science. C.B. is grateful for funding by the European XFEL, the DFG via SFB925 (TP A4) and the Centre for Ultrafast Imaging. Parts of this research were carried out at beamline P11 at the PETRA III storage ring at DESY, a member of the Helmholtz Association. We thank the DESY beamline scientists B. Reime, A. Burkhardt, S. Panneerselvam and O. Lorbeer for their support. Moreover, we thank the XFEL team members C. Youngman, P. Gessler, A. Beckmann and A. Galler for the efficient integration of the MHz digitizer into our X-ray setup at P11.

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B.D., M.N., M.B., B.G.-L., S.H.-P., A.H., J.S., D.R., A.W. and J.B. performed the transient XAS measurements under the supervision of M.R.; the set-up for the transient XAS measurements was designed and developed by D.G., B.D., P.R. and A.M.; A.M., C.B., B.D., D.G., S.H.-P. and M.R. contributed to the improved data-acquisition technique; B.D. and M.N. analysed the transient XAS data; B.G.-L. performed the time-resolved optical emission experiments under the supervision of M.R.; J.A., F.B., H.N.C., K.R.B. and G.N. participated in the discussions about the data; A.H. and J.S. prepared the samples and A.H. performed the DFT calculations; the interpretation of the theoretical data in relation to the diverse experimental data was done by A.H. and S.H.-P.; M.S.R. and S.M.H. performed the transient infrared measurements under the supervision of W.Z.; B.M. accomplished the transient UV/vis measurements under the supervision of W.Z.; the interpretation of the entire experimental optical and XAS data was delivered by C.B., M.R., S.H.-P. and W.Z.; S.H.-P., W.Z. and M.R. designed the study and wrote the manuscript together with C.B., A.H. and B.D.

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Correspondence to W. Zinth, M. Rübhausen or S. Herres-Pawlis.

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Dicke, B., Hoffmann, A., Stanek, J. et al. Transferring the entatic-state principle to copper photochemistry. Nature Chem 10, 355–362 (2018). https://doi.org/10.1038/nchem.2916

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