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Leveraging excited-state coherence for synthetic control of ultrafast dynamics

An Author Correction to this article was published on 20 August 2020

This article has been updated

Abstract

Design-specific control over excited-state dynamics is necessary for any application seeking to convert light into chemical potential. Such control is especially desirable in iron(ii)-based chromophores, which are an Earth-abundant option for a wide range of photo-induced electron-transfer applications including solar energy conversion1 and catalysis2. However, the sub-200-femtosecond lifetimes of the redox-active metal-to-ligand charge transfer (MLCT) excited states typically encountered in these compounds have largely precluded their widespread use3. Here we show that the MLCT lifetime of an iron(ii) complex can be manipulated using information from excited-state quantum coherences as a guide to implementing synthetic modifications that can disrupt the reaction coordinate associated with MLCT decay. We developed a structurally tunable molecular platform in which vibronic coherences—that is, coherences reflecting a coupling of vibrational and electronic degrees of freedom—were observed in ultrafast time-resolved absorption measurements after MLCT excitation of the molecule. Following visualization of the vibrational modes associated with these coherences, we synthetically modified an iron(ii) chromophore to interfere with these specific atomic motions. The redesigned compound exhibits a MLCT lifetime that is more than a factor of 20 longer than that of the parent compound, indicating that the structural modification at least partially decoupled these degrees of freedom from the population dynamics associated with the electronic-state evolution of the system. These results demonstrate that using excited-state coherence data may be used to tailor ultrafast excited-state dynamics through targeted synthetic design.

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Fig. 1: Structure and steady-state optical properties.
Fig. 2: Femtosecond time-resolved absorption data of [Fe(L)](PF6)2 (1) acquired in CH3CN solution.
Fig. 3: Vibronic coherence data for [Fe(L)]2+ (1) in CH3CN solution.
Fig. 4: Ultrafast time-resolved absorption data for [FeCu2(L)]4+ (2) in CH3CN solution.

Data availability

Crystal structures are in the Cambridge Crystallographic Data Centre (CCDC) with CCDC numbers 1904822 (1), 1875421 (2) and 1904820 (3). Additional data supporting the conclusions drawn in the main body of article can be found in Supplementary Information. Other data and the LPSVD code are available upon reasonable request to the corresponding author.

Change history

  • 08 July 2020

    The online publication date in the printed version of this article was listed incorrectly as 10 June 2020; the date was correct online.

  • 20 August 2020

    An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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Acknowledgements

We thank R. Staples for preparing the overlay figure of the two crystal structures shown in Supplementary Fig. 9, as well as A. M. Stettler and D. A. Proshlyakov of the Department of Chemistry at Michigan State University for assistance in the collection of resonance Raman data on compounds 1 and 2 (Supplementary Fig. 12). This work was supported by the Chemical Sciences, Geosciences, and Biosciences Program, Office of Basic Energy Science, Office of Science, US Department of Energy through grant number DE-FG02-01ER15282.

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Contributions

B.C.P. collected and analysed all ultrafast time-resolved absorption data, performed the DFT optimizations and frequency calculations, and created the vibrational mode figures. S.L.A. synthesized all complexes and carried out ground-state and nanosecond time-resolved characterization. B.C.P. and S.L.A. designed the experiments and co-wrote the paper with J.K.M. L.L.J. developed the initial synthetic route to producing the cage ligand and compound 2. J.K.M. conceived the central idea and directed the project.

Corresponding author

Correspondence to James K. McCusker.

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Peer review information Nature thanks Matthias Bauer, Katja Heinze and Julia Weinstein for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary methods with 32 display items to show the characterization of compounds 1-3, additional spectroscopic measurements, and further descriptions of the coherent vibrational modes of 1 and 2.

Supplementary Data 1

CIF Report for Compound 1 ([Fe(L)](PF6)2)

Supplementary Data 2

CIF Report for Compound 2 ([FeCu2(L)](PF6)4)

Supplementary Data 3

CIF Report for Compound 3 ([ZnCu2(L)](PF6)4)

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Paulus, B.C., Adelman, S.L., Jamula, L. et al. Leveraging excited-state coherence for synthetic control of ultrafast dynamics. Nature 582, 214–218 (2020). https://doi.org/10.1038/s41586-020-2353-2

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