Cargando…

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...

Descripción completa

Detalles Bibliográficos
Autores principales: Tait, Claudia E., Neuhaus, Patrik, Peeks, Martin D., Anderson, Harry L., Timmel, Christiane R.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Chemical Society 2015
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
_version_ 1782389990729187328
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
work_keys_str_mv AT taitclaudiae transienteprrevealstripletstatedelocalizationinaseriesofcyclicandlinearpconjugatedporphyrinoligomers
AT neuhauspatrik transienteprrevealstripletstatedelocalizationinaseriesofcyclicandlinearpconjugatedporphyrinoligomers
AT peeksmartind transienteprrevealstripletstatedelocalizationinaseriesofcyclicandlinearpconjugatedporphyrinoligomers
AT andersonharryl transienteprrevealstripletstatedelocalizationinaseriesofcyclicandlinearpconjugatedporphyrinoligomers
AT timmelchristianer transienteprrevealstripletstatedelocalizationinaseriesofcyclicandlinearpconjugatedporphyrinoligomers