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Title: Hole localization and spin coupling in [pi]-mono- and [pi]-dications of [mu]-oxoporphyrin dimers, relevance to structure of oxidized [open quotes]special pair[close quotes] in photosynthetic reaction centers

Abstract

The antiferromagnetically coupled cofacial [mu]-oxoiron(III) dimers of octaethylporphyrin (OEP) and [alpha],[beta],[gamma],[Delta]-tetraphenylporphyrin (TPP) can be oxidized in two one-electron steps to yield [pi]-monocations and [pi]-dications. Hitherto unreported absorption bands are observed in the mid-infrared region in the spectra of the monocations. These are identified as intervalence transitions of dynamically trapped holes. The electron-phonon coupling energies (CH[sub 2]Cl[sub 2] solution, 295 K) are 0.31 [+-] 0.04 eV, and the inter-ring, predominantly through-space, electronic coupling constants J are 0.07 and 0.03 eV, respectively. The small values of J are a consequence of the large mean plane separation of the porphyrin rings (4.53 A). Since it is impossible that the electron-phonon coupling energies will vary greatly between cofacial porphyrin dimers, it is suggested that absorption hands around 1 eV in the [pi]-monocations of [open quotes]sandwich[close quotes] compounds such as M[sup III]P[sub 2] or M[sup IV]P[sub 2][sup +], where P is a porphyrin and M are lanthanide, actinide, or transition metals (3-12) observed under similar conditions will have electronic ground states that are delocalized on at least the vibrational time scale, with frequency maxima equal to 2J in the tight-binding approximation. The thermal inter-ring hole-transfer times in the [mu]-oxo dimer monocations are estimated to bemore » approximately 1 ps. The relevance of these results to the problem of the structure of the oxidized [open quotes]special pair[close quotes] in the photosynthetic reaction center is briefly discussed. 52 refs., 4 figs., 5 tabs.« less

Authors:
;  [1]
  1. Univ. of Sydney (Australia)
Publication Date:
OSTI Identifier:
5203377
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry; (United States)
Additional Journal Information:
Journal Volume: 97:50; Journal ID: ISSN 0022-3654
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; PORPHYRINS; ELECTRON TRANSFER; OXIDATION; CATIONS; DIMERS; ELECTRON-PHONON COUPLING; EXPERIMENTAL DATA; HOLES; INFRARED SPECTRA; IRON COMPOUNDS; PHOTOSYNTHESIS; PHOTOSYNTHETIC REACTION CENTERS; CARBOXYLIC ACIDS; CHARGED PARTICLES; CHEMICAL REACTIONS; COUPLING; DATA; HETEROCYCLIC ACIDS; HETEROCYCLIC COMPOUNDS; INFORMATION; IONS; NUMERICAL DATA; ORGANIC ACIDS; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; PHOTOCHEMICAL REACTIONS; SPECTRA; SYNTHESIS; TRANSITION ELEMENT COMPOUNDS; 140505* - Solar Energy Conversion- Photochemical, Photobiological, & Thermochemical Conversion- (1980-); 400201 - Chemical & Physicochemical Properties

Citation Formats

Binstead, R A, and Hush, N S. Hole localization and spin coupling in [pi]-mono- and [pi]-dications of [mu]-oxoporphyrin dimers, relevance to structure of oxidized [open quotes]special pair[close quotes] in photosynthetic reaction centers. United States: N. p., 1993. Web. doi:10.1021/j100152a023.
Binstead, R A, & Hush, N S. Hole localization and spin coupling in [pi]-mono- and [pi]-dications of [mu]-oxoporphyrin dimers, relevance to structure of oxidized [open quotes]special pair[close quotes] in photosynthetic reaction centers. United States. doi:10.1021/j100152a023.
Binstead, R A, and Hush, N S. Thu . "Hole localization and spin coupling in [pi]-mono- and [pi]-dications of [mu]-oxoporphyrin dimers, relevance to structure of oxidized [open quotes]special pair[close quotes] in photosynthetic reaction centers". United States. doi:10.1021/j100152a023.
@article{osti_5203377,
title = {Hole localization and spin coupling in [pi]-mono- and [pi]-dications of [mu]-oxoporphyrin dimers, relevance to structure of oxidized [open quotes]special pair[close quotes] in photosynthetic reaction centers},
author = {Binstead, R A and Hush, N S},
abstractNote = {The antiferromagnetically coupled cofacial [mu]-oxoiron(III) dimers of octaethylporphyrin (OEP) and [alpha],[beta],[gamma],[Delta]-tetraphenylporphyrin (TPP) can be oxidized in two one-electron steps to yield [pi]-monocations and [pi]-dications. Hitherto unreported absorption bands are observed in the mid-infrared region in the spectra of the monocations. These are identified as intervalence transitions of dynamically trapped holes. The electron-phonon coupling energies (CH[sub 2]Cl[sub 2] solution, 295 K) are 0.31 [+-] 0.04 eV, and the inter-ring, predominantly through-space, electronic coupling constants J are 0.07 and 0.03 eV, respectively. The small values of J are a consequence of the large mean plane separation of the porphyrin rings (4.53 A). Since it is impossible that the electron-phonon coupling energies will vary greatly between cofacial porphyrin dimers, it is suggested that absorption hands around 1 eV in the [pi]-monocations of [open quotes]sandwich[close quotes] compounds such as M[sup III]P[sub 2] or M[sup IV]P[sub 2][sup +], where P is a porphyrin and M are lanthanide, actinide, or transition metals (3-12) observed under similar conditions will have electronic ground states that are delocalized on at least the vibrational time scale, with frequency maxima equal to 2J in the tight-binding approximation. The thermal inter-ring hole-transfer times in the [mu]-oxo dimer monocations are estimated to be approximately 1 ps. The relevance of these results to the problem of the structure of the oxidized [open quotes]special pair[close quotes] in the photosynthetic reaction center is briefly discussed. 52 refs., 4 figs., 5 tabs.},
doi = {10.1021/j100152a023},
journal = {Journal of Physical Chemistry; (United States)},
issn = {0022-3654},
number = ,
volume = 97:50,
place = {United States},
year = {1993},
month = {12}
}