Direct measurement of photoinduced charge separation distances in donor-acceptor systems for artificial photosynthesis using OOP-ESEEM

Raanan Carmieli, Qixi Mi, Annie Butler Ricks, Emilie M. Giacobbe, Sarah M. Mickley, Michael R Wasielewski

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

(Graph Presented) The distance over which two photogenerated charges are separated in electron donor-acceptor systems for artificial photosynthesis depends on the structure of the system, while the lifetime of the charge separation and, ultimately, its ability to carry out useful redox chemistry depend on the electronic coupling between the oxidized donor and reduced acceptor. The radical ions produced by charge separation are frequently delocalized over the π systems of the final oxidized donor and reduced acceptor, so that there is often significant uncertainty as to the average distance between the separated charges, especially in low dielectric constant media, where the Coulomb attraction of the ions may be significant and the charge distribution of the ions may be distorted, so that the average distance between them may be shorter than that implied by their chemical structures. The charge separation distances between photogenerated radical ions in three donor-acceptor molecules having different donor-acceptor distances were measured directly from their dipolar spin-spin interactions using out-of-phase electron spin echo envelope modulation (OOP-ESEEM). The measured distances in toluene at 85 K compare favorably to the calculated distances between the centroids of the spin distributions of the radical ions within the radical ion pairs. These results show that despite the intrinsically nonpolar nature of medium, the spin (and charge) distributions of the RPs are not significantly distorted by Coulomb attraction over these long distances. This study shows that OOP-ESEEM is well-suited for probing the detailed structural features of charge-separated intermediates that are essential to understanding how to design molecular structures that prolong and control charge separation for artificial photosynthesis.

Original languageEnglish
Pages (from-to)8372-8373
Number of pages2
JournalJournal of the American Chemical Society
Volume131
Issue number24
DOIs
Publication statusPublished - Jun 24 2009

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Photosynthesis
Modulation
Electrons
Ions
Charge distribution
Toluene
Molecular Structure
Molecular structure
Uncertainty
Oxidation-Reduction
Permittivity
Molecules

ASJC Scopus subject areas

  • Chemistry(all)
  • Catalysis
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Direct measurement of photoinduced charge separation distances in donor-acceptor systems for artificial photosynthesis using OOP-ESEEM. / Carmieli, Raanan; Mi, Qixi; Ricks, Annie Butler; Giacobbe, Emilie M.; Mickley, Sarah M.; Wasielewski, Michael R.

In: Journal of the American Chemical Society, Vol. 131, No. 24, 24.06.2009, p. 8372-8373.

Research output: Contribution to journalArticle

Carmieli, Raanan ; Mi, Qixi ; Ricks, Annie Butler ; Giacobbe, Emilie M. ; Mickley, Sarah M. ; Wasielewski, Michael R. / Direct measurement of photoinduced charge separation distances in donor-acceptor systems for artificial photosynthesis using OOP-ESEEM. In: Journal of the American Chemical Society. 2009 ; Vol. 131, No. 24. pp. 8372-8373.
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abstract = "(Graph Presented) The distance over which two photogenerated charges are separated in electron donor-acceptor systems for artificial photosynthesis depends on the structure of the system, while the lifetime of the charge separation and, ultimately, its ability to carry out useful redox chemistry depend on the electronic coupling between the oxidized donor and reduced acceptor. The radical ions produced by charge separation are frequently delocalized over the π systems of the final oxidized donor and reduced acceptor, so that there is often significant uncertainty as to the average distance between the separated charges, especially in low dielectric constant media, where the Coulomb attraction of the ions may be significant and the charge distribution of the ions may be distorted, so that the average distance between them may be shorter than that implied by their chemical structures. The charge separation distances between photogenerated radical ions in three donor-acceptor molecules having different donor-acceptor distances were measured directly from their dipolar spin-spin interactions using out-of-phase electron spin echo envelope modulation (OOP-ESEEM). The measured distances in toluene at 85 K compare favorably to the calculated distances between the centroids of the spin distributions of the radical ions within the radical ion pairs. These results show that despite the intrinsically nonpolar nature of medium, the spin (and charge) distributions of the RPs are not significantly distorted by Coulomb attraction over these long distances. This study shows that OOP-ESEEM is well-suited for probing the detailed structural features of charge-separated intermediates that are essential to understanding how to design molecular structures that prolong and control charge separation for artificial photosynthesis.",
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