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Iron(ii) coordination complexes with panchromatic absorption and nanosecond charge-transfer excited state lifetimes

Nature Chemistry volume 11, pages 1144–1150 (2019)Cite this article

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Abstract

Replacing current benchmark rare-element photosensitizers with ones based on abundant and low-cost metals such as iron would help facilitate the large-scale implementation of solar energy conversion. To do so, the ability to extend the lifetimes of photogenerated excited states of iron complexes is critical. Here, we present a sensitizer design in which iron(ii) centres are supported by frameworks containing benzannulated phenanthridine and quinoline heterocycles paired with amido donors. These complexes exhibit panchromatic absorption and nanosecond charge-transfer excited state lifetimes, enabled by the combination of vacant, energetically accessible heterocycle-based acceptor orbitals and occupied molecular orbitals destabilized by strong mixing between amido nitrogen atoms and iron. This finding shows how ligand design can extend metal-to-ligand charge-transfer-type excited state lifetimes of iron(ii) complexes into the nanosecond regime and expand the range of potential applications for iron-based photosensitizers.

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Fig. 1: Designing pseudo-octahedral iron(ii) coordination complexes with panchromatic absorption and long-lived CT excited states.
Fig. 2: Synthesis of ligands and Fe(ii) complexes.
Fig. 3: Solid-state and electronic structural characterization of 3a,b.
Fig. 4: Time-resolved absorption spectroscopy and excited state dynamics of 3b.

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Data availability

All data generated or analysed during this study are included in this published article or its Supplementary Information files, which include electrochemical data; the UV/Vis and multinuclear NMR spectra of all compounds; computational details, including comparisons of optimized/crystal structures, TD-DFT results and calculated spectra, extended MO diagrams, population analyses and potential energy surfaces, energies and reaction coordinates; crystallographic information files (CIFs) for 2a, 3a, 3b, [3a]PF6 and [3b]PF6. The crystallographic data for these structures have also been deposited at the Cambridge Crystallographic Data Centre, under deposition numbers 1589420 (2a), 1589421 (3a), 1589422 (3b), 1589423 ([3a]PF6) and 1589424 ([3b]PF6). Copies of these data can be obtained free of charge from www.ccdc.cam.ac.uk/structures.

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  • 16 December 2019

    In the version of this Article originally published, three lines of text beginning ‘tive cross-sections across’ and ending ‘design motif: two’ in the last paragraph of the right column on page 1 of the PDF were mistakenly transposed to the bottom of the left column. This has now been corrected.

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Acknowledgements

This work was supported by the Natural Sciences and Engineering Research Council of Canada [RGPIN-2014-03733 (D.E.H.), RGPIN-2018-05012 (J.v.L.)] and the Canada Foundation for Innovation and Research Manitoba (#32146). The University of Manitoba is acknowledged for GETS support (J.D.B., I.B.L.) and a UMGF Doctoral Fellowship (J.D.B.). CWRU is thanked for support for the Center for Chemical Dynamics. We are especially grateful to W. Sun and B. Liu for independent verification of the preliminary TA data, and to Y. Zatsikha and V. N. Nemykin for assistance setting up spectroelectrochemical experiments and helpful discussions.

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Authors and Affiliations

  1. Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, Canada

    Jason D. Braun, Issiah B. Lozada, Rebecca L. Davis & David E. Herbert

  2. Department of Chemistry, Case Western Reserve University, Cleveland, OH, USA

    Charles Kolodziej & Clemens Burda

  3. Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba, Canada

    Kelly M. E. Newman & Johan van Lierop

  4. Manitoba Institute for Materials, University of Manitoba, Winnipeg, Manitoba, Canada

    Johan van Lierop & David E. Herbert

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Contributions

J.D.B. and D.E.H. designed the research. J.D.B., C.K. (TA) and K.M.E.N. (Mössbauer) performed the experiments. K.M.E.N. and J.v.L. provided Mössbauer characterization and analysis. C.K. and C.B. provided TA characterization and analysis. I.B.L. and R.L.D. provided theoretical calculations. J.D.B. and D.E.H. wrote the paper with contributions from all authors.

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Correspondence to David E. Herbert.

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Supplementary Information

Supplementary Information

Methods containing experimental data, including electrochemical data; UV/Vis and multinuclear NMR spectra of all compounds; computational details, including comparisons of optimized/crystal structures, TD-DFT results and calculated spectra, extended MO diagrams, population analyses and potential energy surfaces, energies and reaction coordinates; extended transient absorption spectroscopy data and analysis for 3a and solvent dependence of time-resolved spectroscopy for 3a,b.

Crystallographic data

CIF for compound 2a; CCDC reference 1589420

Crystallographic data

CIF for compound 3a; CCDC reference 1589421

Crystallographic data

CIF for compound 3b; CCDC reference 1589422

Crystallographic data

CIF for compound [3a]PF6; CCDC reference 1589423

Crystallographic data

CIF for compound [3b]PF6; CCDC reference 1589424

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Braun, J.D., Lozada, I.B., Kolodziej, C. et al. Iron(ii) coordination complexes with panchromatic absorption and nanosecond charge-transfer excited state lifetimes. Nat. Chem. 11, 1144–1150 (2019). https://doi.org/10.1038/s41557-019-0357-z

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