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Transient EPR Reveals Triplet State Delocalization in a Series of Cyclic and Linear π-Conjugated Porphyrin Oligomers
[Image: see text] The photoexcited triplet states of a series of linear and cyclic butadiyne-linked porphyrin oligomers were investigated by transient Electron Paramagnetic Resonance (EPR) and Electron Nuclear DOuble Resonance (ENDOR). The spatial delocalization of the triplet state wave function in...
Autores principales: | , , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
American Chemical
Society
2015
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4569062/ https://www.ncbi.nlm.nih.gov/pubmed/26035477 http://dx.doi.org/10.1021/jacs.5b04511 |
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author | Tait, Claudia E. Neuhaus, Patrik Peeks, Martin D. Anderson, Harry L. Timmel, Christiane R. |
author_facet | Tait, Claudia E. Neuhaus, Patrik Peeks, Martin D. Anderson, Harry L. Timmel, Christiane R. |
author_sort | Tait, Claudia E. |
collection | PubMed |
description | [Image: see text] The photoexcited triplet states of a series of linear and cyclic butadiyne-linked porphyrin oligomers were investigated by transient Electron Paramagnetic Resonance (EPR) and Electron Nuclear DOuble Resonance (ENDOR). The spatial delocalization of the triplet state wave function in systems with different numbers of porphyrin units and different geometries was analyzed in terms of zero-field splitting parameters and proton hyperfine couplings. Even though no significant change in the zero-field splitting parameters (D and E) is observed for linear oligomers with two to six porphyrin units, the spin polarization of the transient EPR spectra is particularly sensitive to the number of porphyrin units, implying a change of the mechanism of intersystem crossing. Analysis of the proton hyperfine couplings in linear oligomers with more than two porphyrin units, in combination with density functional theory calculations, indicates that the spin density is localized mainly on two to three porphyrin units rather than being distributed evenly over the whole π-system. The sensitivity of the zero-field splitting parameters to changes in geometry was investigated by comparing free linear oligomers with oligomers bound to a hexapyridyl template. Significant changes in the zero-field splitting parameter D were observed, while the proton hyperfine couplings show no change in the extent of triplet state delocalization. The triplet state of the cyclic porphyrin hexamer has a much decreased zero-field splitting parameter D and much smaller proton hyperfine couplings with respect to the monomeric unit, indicating complete delocalization over six porphyrin units in this symmetric system. This surprising result provides the first evidence for extensive triplet state delocalization in an artificial supramolecular assembly of porphyrins. |
format | Online Article Text |
id | pubmed-4569062 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2015 |
publisher | American Chemical
Society |
record_format | MEDLINE/PubMed |
spelling | pubmed-45690622015-09-21 Transient EPR Reveals Triplet State Delocalization in a Series of Cyclic and Linear π-Conjugated Porphyrin Oligomers Tait, Claudia E. Neuhaus, Patrik Peeks, Martin D. Anderson, Harry L. Timmel, Christiane R. J Am Chem Soc [Image: see text] The photoexcited triplet states of a series of linear and cyclic butadiyne-linked porphyrin oligomers were investigated by transient Electron Paramagnetic Resonance (EPR) and Electron Nuclear DOuble Resonance (ENDOR). The spatial delocalization of the triplet state wave function in systems with different numbers of porphyrin units and different geometries was analyzed in terms of zero-field splitting parameters and proton hyperfine couplings. Even though no significant change in the zero-field splitting parameters (D and E) is observed for linear oligomers with two to six porphyrin units, the spin polarization of the transient EPR spectra is particularly sensitive to the number of porphyrin units, implying a change of the mechanism of intersystem crossing. Analysis of the proton hyperfine couplings in linear oligomers with more than two porphyrin units, in combination with density functional theory calculations, indicates that the spin density is localized mainly on two to three porphyrin units rather than being distributed evenly over the whole π-system. The sensitivity of the zero-field splitting parameters to changes in geometry was investigated by comparing free linear oligomers with oligomers bound to a hexapyridyl template. Significant changes in the zero-field splitting parameter D were observed, while the proton hyperfine couplings show no change in the extent of triplet state delocalization. The triplet state of the cyclic porphyrin hexamer has a much decreased zero-field splitting parameter D and much smaller proton hyperfine couplings with respect to the monomeric unit, indicating complete delocalization over six porphyrin units in this symmetric system. This surprising result provides the first evidence for extensive triplet state delocalization in an artificial supramolecular assembly of porphyrins. American Chemical Society 2015-06-02 2015-07-01 /pmc/articles/PMC4569062/ /pubmed/26035477 http://dx.doi.org/10.1021/jacs.5b04511 Text en Copyright © 2015 American Chemical Society This is an open access article published under a Creative Commons Attribution (CC-BY) License (http://pubs.acs.org/page/policy/authorchoice_ccby_termsofuse.html) , which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited. |
spellingShingle | Tait, Claudia E. Neuhaus, Patrik Peeks, Martin D. Anderson, Harry L. Timmel, Christiane R. Transient EPR Reveals Triplet State Delocalization in a Series of Cyclic and Linear π-Conjugated Porphyrin Oligomers |
title | Transient
EPR Reveals Triplet State Delocalization
in a Series of Cyclic and Linear π-Conjugated Porphyrin
Oligomers |
title_full | Transient
EPR Reveals Triplet State Delocalization
in a Series of Cyclic and Linear π-Conjugated Porphyrin
Oligomers |
title_fullStr | Transient
EPR Reveals Triplet State Delocalization
in a Series of Cyclic and Linear π-Conjugated Porphyrin
Oligomers |
title_full_unstemmed | Transient
EPR Reveals Triplet State Delocalization
in a Series of Cyclic and Linear π-Conjugated Porphyrin
Oligomers |
title_short | Transient
EPR Reveals Triplet State Delocalization
in a Series of Cyclic and Linear π-Conjugated Porphyrin
Oligomers |
title_sort | transient
epr reveals triplet state delocalization
in a series of cyclic and linear π-conjugated porphyrin
oligomers |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4569062/ https://www.ncbi.nlm.nih.gov/pubmed/26035477 http://dx.doi.org/10.1021/jacs.5b04511 |
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