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

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.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

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.

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.

Change history

  • 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.

References

  1. 1.

    Lewis, N. S. & Nocera, D. G. Powering the planet: chemical challenges in solar energy utilization. Proc. Natl Acad. Sci. USA 103, 15729–15735 (2006).

    CAS  PubMed  Google Scholar 

  2. 2.

    Haegel, N. M. et al. Terawatt-scale photovoltaics: trajectories and challenges. Science 356, 141–143 (2017).

    CAS  PubMed  Google Scholar 

  3. 3.

    O’Regan, B. & Graetzel, M. A low-cost, high-efficiency solar cell based on dye-sensitized colloidal titanium dioxide films. Nature 353, 737–740 (1991).

    Google Scholar 

  4. 4.

    Hagfeldt, A., Boschloo, G., Sun, L., Kloo, L. & Pettersson, H. Dye-sensitized solar cells. Chem. Rev. 110, 6595–6663 (2010).

    CAS  PubMed  Google Scholar 

  5. 5.

    Bozic-Weber, B., Constable, E. C. & Housecroft, C. E. Light harvesting with earth abundant d-block metals: development of sensitizers in dye-sensitized solar cells (DSCs). Coord. Chem. Rev. 257, 3089–3106 (2013).

    CAS  Google Scholar 

  6. 6.

    Ardo, S. et al. Pathways to electrochemical solar-hydrogen technologies. Energy Environ. Sci. 11, 2768–2783 (2018).

    CAS  Google Scholar 

  7. 7.

    Larsen, C. B. & Wenger, O. S. Photoredox catalysis with metal complexes made from earth-abundant elements. Chem. Eur. J 24, 2039–2058 (2018).

    CAS  PubMed  Google Scholar 

  8. 8.

    Ponseca, C. S., Chábera, P., Uhlig, J., Persson, P. & Sundström, V. Ultrafast electron dynamics in solar energy conversion. Chem. Rev. 117, 10940–11024 (2017).

    CAS  PubMed  Google Scholar 

  9. 9.

    Schultz, D. M. & Yoon, T. P. Solar synthesis: prospects in visible light photocatalysis. Science 343, 985 (2014).

    CAS  Google Scholar 

  10. 10.

    Robertson, N. Optimizing dyes for dye-sensitized solar cells. Angew. Chem. Int. Ed. 45, 2338–2345 (2006).

    CAS  Google Scholar 

  11. 11.

    Prier, C. K., Rankic, D. A. & MacMillan, D. W. C. Visible light photoredox catalysis with transition metal complexes: applications in organic synthesis. Chem. Rev. 113, 5322–5363 (2013).

    CAS  PubMed  PubMed Central  Google Scholar 

  12. 12.

    Housecroft, C. E. & Constable, E. C. The emergence of copper(I)-based dye sensitized solar cells. Chem. Soc. Rev. 44, 8386–8398 (2015).

    CAS  PubMed  Google Scholar 

  13. 13.

    Zhang, Y., Lee, T. S., Petersen, J. L. & Milsmann, C. A zirconium photosensitizer with a long-lived excited state: mechanistic insight into photoinduced single-electron transfer. J. Am. Chem. Soc. 140, 5934–5947 (2018).

    CAS  PubMed  Google Scholar 

  14. 14.

    Pal, A. K., Li, C., Hanan, G. S. & Zysman-Colman, E. Blue-emissive cobalt(III) complexes and their use in the photocatalytic trifluoromethylation of polycyclic aromatic hydrocarbons. Angew. Chem. Int. Ed. 57, 8027–8031 (2018).

    CAS  Google Scholar 

  15. 15.

    Buldt, L. A. & Wenger, O. S. Chromium(0), molybdenum(0), and tungsten(0) isocyanide complexes as luminophores and photosensitizers with long-lived excited states. Angew. Chem. Int. Ed. 56, 5676–5682 (2017).

    Google Scholar 

  16. 16.

    Otto, S. et al. [Cr(ddpd)2]3+: A molecular, water-soluble, highly NIR-emissive ruby analogue. Angew. Chem. Int. Ed. 54, 11572–11576 (2015).

    CAS  Google Scholar 

  17. 17.

    Sattler, W., Henling, L. M., Winkler, J. R. & Gray, H. B. Bespoke photoreductants: tungsten arylisocyanides. J. Am. Chem. Soc. 137, 1198–1205 (2015).

    CAS  PubMed  Google Scholar 

  18. 18.

    Wenger, O. S. Photoactive complexes with earth-abundant metals. J. Am. Chem. Soc. 140, 13522–13533 (2018).

    CAS  PubMed  Google Scholar 

  19. 19.

    Galoppini, E. Light harvesting: strike while the iron is cold. Nat. Chem. 7, 861–862 (2015).

    CAS  PubMed  Google Scholar 

  20. 20.

    Juban, E. A., Smeigh, A. L., Monat, J. E. & McCusker, J. K. Ultrafast dynamics of ligand-field excited states. Coord. Chem. Rev. 250, 1783–1791 (2006).

    CAS  Google Scholar 

  21. 21.

    Liu, Y. et al. Towards longer-lived metal-to-ligand charge transfer states of iron(II) complexes: an N-heterocyclic carbene approach. Chem. Commun. 49, 6412–6414 (2013).

    CAS  Google Scholar 

  22. 22.

    Liu, L. et al. A new record excited state 3MLCT lifetime for metalorganic iron(II) complexes. Phys. Chem. Chem. Phys. 18, 12550–12556 (2016).

    CAS  PubMed  Google Scholar 

  23. 23.

    Liu, Y., Wärnmark, K., Liu, Y., Sundstrom, V. & Persson, P. Fe N-heterocyclic carbene complexes as promising photosensitizers. Acc. Chem. Res. 49, 1477–1485 (2016).

    CAS  PubMed  Google Scholar 

  24. 24.

    Duchanois, T. et al. An iron-based photosensitizer with extended excited-state lifetime: photophysical and photovoltaic properties. Eur. J. Inorg. Chem. 2015, 2469–2477 (2015).

    CAS  Google Scholar 

  25. 25.

    Harlang, T. C. B. et al. Iron sensitizer converts light to electrons with 92% yield. Nat. Chem. 7, 883–889 (2015).

    CAS  PubMed  Google Scholar 

  26. 26.

    Chábera, P. et al. A low-spin Fe(III) complex with 100-ps ligand-to-metal charge transfer photoluminescence. Nature 543, 695–699 (2017).

    PubMed  Google Scholar 

  27. 27.

    Chábera, P. et al. Fe(II) hexa N-heterocyclic carbene complex with a 528 ps metal-to-ligand charge-transfer excited-state lifetime. J. Phys. Chem. Lett. 9, 459–463 (2018).

    PubMed  Google Scholar 

  28. 28.

    Fatur, S. M., Shepard, S. G., Higgins, R. F., Shores, M. P. & Damrauer, N. H. A synthetically tunable system to control MLCT excited-state lifetimes and spin states in iron(II) polypyridines. J. Am. Chem. Soc. 139, 4493–4505 (2017).

    CAS  PubMed  Google Scholar 

  29. 29.

    Kjær, K. S. et al. Luminescence and reactivity of a charge-transfer excited iron complex with nanosecond lifetime. Science 363, 249–253 (2019).

    PubMed  Google Scholar 

  30. 30.

    Mukherjee, S., Torres, D. E. & Jakubikova, E. HOMO inversion as a strategy for improving the light-absorption properties of Fe(II) chromophores. Chem. Sci 8, 8115–8126 (2017).

    CAS  PubMed  PubMed Central  Google Scholar 

  31. 31.

    Betley, T. A., Qian, B. A. & Peters, J. C. Group VIII coordination chemistry of a pincer-type bis(8-quinolinyl)amido ligand. Inorg. Chem. 47, 11570–11582 (2008).

    CAS  PubMed  Google Scholar 

  32. 32.

    Mengel, A. K. C. et al. A heteroleptic push-pull substituted iron(II) bis(tridentate) complex with low-energy charge-transfer states. Chem. Eur. J. 21, 704–714 (2015).

    CAS  PubMed  Google Scholar 

  33. 33.

    Maksić, Z. B., Barić, D. & Müller, T. Clar’s sextet rule is a consequence of the σ-electron framework. J. Phys. Chem. A 110, 10135–10147 (2006).

    PubMed  Google Scholar 

  34. 34.

    Gibson, V. C., Redshaw, C. & Solan, G. A. Bis(imino)pyridines: surprisingly reactive ligands and a gateway to new families of catalysts. Chem. Rev. 107, 1745–1776 (2007).

    CAS  PubMed  Google Scholar 

  35. 35.

    Mondal, R., Giesbrecht, P. K. & Herbert, D. E. Nickel(II), copper(I) and zinc(II) complexes supported by a (4-diphenylphosphino)phenanthridine ligand. Polyhedron 108, 156–162 (2016).

    CAS  Google Scholar 

  36. 36.

    Hewage, J. S. et al. Homoleptic nickel(II) complexes of redox-tunable pincer-type ligands. Inorg. Chem. 53, 10070–10084 (2014).

    CAS  PubMed  PubMed Central  Google Scholar 

  37. 37.

    Frazier, B. A., Wolczanski, P. T., Lobkovsky, E. B. & Cundari, T. R. Unusual electronic features and reactivity of the dipyridylazaallyl ligand: characterizations of (smif)2M [M = Fe, Co, Co+, Ni; smif = {(2-py)CH}2N] and [(TMS)2NFe]2(smif)2. J. Am. Chem. Soc. 131, 3428–3429 (2009).

    CAS  PubMed  Google Scholar 

  38. 38.

    Reiff, W. M., Baker, W. A. & Erickson, N. E. Binuclear, oxygen-bridged complexes of iron(III). New iron(III)-2,2′,2′′-terpyridine complexes. J. Am. Chem. Soc. 90, 4794–4800 (1968).

    CAS  Google Scholar 

  39. 39.

    Dixon, I. M., Khan, S., Alary, F., Boggio-Pasqua, M. & Heully, J. L. Probing the photophysical capability of mono and bis(cyclometallated) Fe(II) polypyridine complexes using inexpensive ground state DFT. Dalton Trans. 43, 15898–15905 (2014).

    CAS  PubMed  Google Scholar 

  40. 40.

    Lever, A. B. P. Electrochemical parametrization of metal complex redox potentials, using the ruthenium(III)/ruthenium(II) couple to generate a ligand electrochemical series. Inorg. Chem. 29, 1271–1285 (1990).

    CAS  Google Scholar 

  41. 41.

    Braterman, P. S., Song, J. I. & Peacock, R. D. Electronic absorption spectra of the iron(II) complexes of 2,2′-bipyridine, 2,2′-bipyrimidine, 1,10-phenanthroline, and 2,2′:6′,2′′-terpyridine and their reduction products. Inorg. Chem. 31, 555–559 (1992).

    CAS  Google Scholar 

  42. 42.

    Brown, A. M., McCusker, C. E. & McCusker, J. K. Spectroelectrochemical identification of charge-transfer excited states in transition metal-based polypyridyl complexes. Dalton Trans. 43, 17635–17646 (2014).

    CAS  PubMed  Google Scholar 

  43. 43.

    Aubock, G. & Chergui, M. Sub-50-fs photoinduced spin crossover in [Fe(bpy)3]2+. Nat. Chem. 7, 629–633 (2015).

    CAS  PubMed  Google Scholar 

  44. 44.

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

    CAS  PubMed  Google Scholar 

  45. 45.

    Lever, A. B. P. in Inorganic Electronic Spectroscopy 2nd edn, 208–209 (Elsevier, 1986).

  46. 46.

    Ashley, D. C. & Jakubikova, E. Ironing out the photochemical and spin-crossover behavior of Fe(II) coordination compounds with computational chemistry. Coord. Chem. Rev. 337, 97–111 (2017).

    CAS  Google Scholar 

  47. 47.

    Francés-Monerris, A. et al. Synthesis and computational study of a pyridylcarbene Fe(II) complex: unexpected effects of fac/mer isomerism in metal-to-ligand triplet potential energy surfaces. Inorg. Chem. 57, 10431–10441 (2018).

    PubMed  Google Scholar 

  48. 48.

    Smeigh, A. L., Creelman, M., Mathies, R. A. & McCusker, J. K. Femtosecond time-resolved optical and Raman spectroscopy of photoinduced spin crossover: temporal resolution of low-to-high spin optical switching. J. Am. Chem. Soc. 130, 14105–14107 (2008).

    CAS  PubMed  Google Scholar 

  49. 49.

    Mondal, R., Lozada, I. B., Davis, R. L., Williams, J. A. G. & Herbert, D. E. Site-selective benzannulation of N-heterocycles in bidentate ligands leads to blue-shifted emission from [(P^N)Cu]2(μ-X)2 dimers. Inorg. Chem 57, 4966–4978 (2018).

    CAS  PubMed  Google Scholar 

  50. 50.

    Wenger, O. S. Is iron the new ruthenium? Chem. Eur. J. 25, 6043–6052 (2019).

    CAS  PubMed  Google Scholar 

  51. 51.

    Jiménez, J.-R., Doistau, B., Besnard, C. & Piguet, C. Versatile heteroleptic bis-terdentate Cr(III) chromophores displaying room temperature millisecond excited state lifetimes. Chem. Commun. 54, 13228–13231 (2018).

    Google Scholar 

Download references

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.

Author information

Affiliations

Authors

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.

Corresponding author

Correspondence to David E. Herbert.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

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

Download citation

Further reading