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Solvent control of charge transfer excited state relaxation pathways in [Fe(2,2′-bipyridine)(CN)4]2-

Kjær, Kasper S. LU ; Kunnus, Kristjan; Harlang, Tobias C.B. LU ; Van Driel, Tim B.; Ledbetter, Kathryn; Hartsock, Robert W.; Reinhard, Marco E.; Koroidov, Sergey; Li, Lin and Laursen, Mads G., et al. (2018) In Physical Chemistry Chemical Physics 20(6). p.4238-4249
Abstract

The excited state dynamics of solvated [Fe(bpy)(CN)4]2-, where bpy = 2,2′-bipyridine, show significant sensitivity to the solvent Lewis acidity. Using a combination of optical absorption and X-ray emission transient spectroscopies, we have previously shown that the metal to ligand charge transfer (MLCT) excited state of [Fe(bpy)(CN)4]2- has a 19 picosecond lifetime and no discernable contribution from metal centered (MC) states in weak Lewis acid solvents, such as dimethyl sulfoxide and acetonitrile.1,2 In the present work, we use the same combination of spectroscopic techniques to measure the MLCT excited state relaxation dynamics of [Fe(bpy)(CN)4]2- in water,... (More)

The excited state dynamics of solvated [Fe(bpy)(CN)4]2-, where bpy = 2,2′-bipyridine, show significant sensitivity to the solvent Lewis acidity. Using a combination of optical absorption and X-ray emission transient spectroscopies, we have previously shown that the metal to ligand charge transfer (MLCT) excited state of [Fe(bpy)(CN)4]2- has a 19 picosecond lifetime and no discernable contribution from metal centered (MC) states in weak Lewis acid solvents, such as dimethyl sulfoxide and acetonitrile.1,2 In the present work, we use the same combination of spectroscopic techniques to measure the MLCT excited state relaxation dynamics of [Fe(bpy)(CN)4]2- in water, a strong Lewis acid solvent. The charge-transfer excited state is now found to decay in less than 100 femtoseconds, forming a quasi-stable metal centered excited state with a 13 picosecond lifetime. We find that this MC excited state has triplet (3MC) character, unlike other reported six-coordinate Fe(ii)-centered coordination compounds, which form MC quintet (5MC) states. The solvent dependent changes in excited state non-radiative relaxation for [Fe(bpy)(CN)4]2- allows us to infer the influence of the solvent on the electronic structure of the complex. Furthermore, the robust characterization of the dynamics and optical spectral signatures of the isolated 3MC intermediate provides a strong foundation for identifying 3MC intermediates in the electronic excited state relaxation mechanisms of similar Fe-centered systems being developed for solar applications.

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Physical Chemistry Chemical Physics
volume
20
issue
6
pages
12 pages
publisher
Royal Society of Chemistry
external identifiers
  • scopus:85041855594
ISSN
1463-9076
DOI
10.1039/c7cp07838b
language
English
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yes
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7df6cf8f-a090-417f-abf0-160eb89ad49f
date added to LUP
2018-02-22 07:01:54
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2018-06-17 05:30:40
@article{7df6cf8f-a090-417f-abf0-160eb89ad49f,
  abstract     = {<p>The excited state dynamics of solvated [Fe(bpy)(CN)<sub>4</sub>]<sup>2-</sup>, where bpy = 2,2′-bipyridine, show significant sensitivity to the solvent Lewis acidity. Using a combination of optical absorption and X-ray emission transient spectroscopies, we have previously shown that the metal to ligand charge transfer (MLCT) excited state of [Fe(bpy)(CN)<sub>4</sub>]<sup>2-</sup> has a 19 picosecond lifetime and no discernable contribution from metal centered (MC) states in weak Lewis acid solvents, such as dimethyl sulfoxide and acetonitrile.<sup>1,2</sup> In the present work, we use the same combination of spectroscopic techniques to measure the MLCT excited state relaxation dynamics of [Fe(bpy)(CN)<sub>4</sub>]<sup>2-</sup> in water, a strong Lewis acid solvent. The charge-transfer excited state is now found to decay in less than 100 femtoseconds, forming a quasi-stable metal centered excited state with a 13 picosecond lifetime. We find that this MC excited state has triplet (<sup>3</sup>MC) character, unlike other reported six-coordinate Fe(ii)-centered coordination compounds, which form MC quintet (<sup>5</sup>MC) states. The solvent dependent changes in excited state non-radiative relaxation for [Fe(bpy)(CN)<sub>4</sub>]<sup>2-</sup> allows us to infer the influence of the solvent on the electronic structure of the complex. Furthermore, the robust characterization of the dynamics and optical spectral signatures of the isolated <sup>3</sup>MC intermediate provides a strong foundation for identifying <sup>3</sup>MC intermediates in the electronic excited state relaxation mechanisms of similar Fe-centered systems being developed for solar applications.</p>},
  author       = {Kjær, Kasper S. and Kunnus, Kristjan and Harlang, Tobias C.B. and Van Driel, Tim B. and Ledbetter, Kathryn and Hartsock, Robert W. and Reinhard, Marco E. and Koroidov, Sergey and Li, Lin and Laursen, Mads G. and Biasin, Elisa and Hansen, Frederik B. and Vester, Peter and Christensen, Morten and Haldrup, Kristoffer and Nielsen, Martin M. and Chabera, Pavel and Liu, Yizhu and Tatsuno, Hideyuki and Timm, Cornelia and Uhlig, Jens and Sundstöm, Villy and Németh, Zoltán and Szemes, Dorottya Sárosiné and Bajnóczi, Éva and Vankó, György and Alonso-Mori, Roberto and Glownia, James M. and Nelson, Silke and Sikorski, Marcin and Sokaras, Dimosthenis and Lemke, Henrik T. and Canton, Sophie E. and Wärnmark, Kenneth and Persson, Petter and Cordones, Amy A. and Gaffney, Kelly J.},
  issn         = {1463-9076},
  language     = {eng},
  number       = {6},
  pages        = {4238--4249},
  publisher    = {Royal Society of Chemistry},
  series       = {Physical Chemistry Chemical Physics},
  title        = {Solvent control of charge transfer excited state relaxation pathways in [Fe(2,2′-bipyridine)(CN)<sub>4</sub>]<sup>2-</sup>},
  url          = {http://dx.doi.org/10.1039/c7cp07838b},
  volume       = {20},
  year         = {2018},
}