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Titolo:
HOLE LOCALIZATION AND SPIN COUPLING IN PI-MONOCATIONS AND PI-DICATIONS OF MU-OXOPORPHYRIN DIMERS - RELEVANCE TO STRUCTURE OF OXIDIZED SPECIAL PAIR IN PHOTOSYNTHETIC REACTION CENTERS
Autore:
BINSTEAD RA; HUSH NS;
Indirizzi:
UNIV SYDNEY,DEPT THEORET CHEM SYDNEY NSW 2006 AUSTRALIA UNIV SYDNEY,DEPT THEORET CHEM SYDNEY NSW 2006 AUSTRALIA UNIV SYDNEY,DEPT BIOCHEM SYDNEY NSW 2006 AUSTRALIA
Titolo Testata:
Journal of physical chemistry
fascicolo: 50, volume: 97, anno: 1993,
pagine: 13172 - 13179
SICI:
0022-3654(1993)97:50<13172:HLASCI>2.0.ZU;2-S
Fonte:
ISI
Lingua:
ENG
Soggetto:
BISPORPHYRINATE DOUBLE-DECKERS; TETRAPYRROLE LIGANDS; METAL-COMPLEXES; PORPHYRIN SANDWICH; OXIDATION-PRODUCTS; FERRIC PORPHYRINS; CRYSTAL-STRUCTURE; REDOX POTENTIALS; RADICAL CATIONS; BACTERIOCHLOROPHYLL;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
52
Recensione:
Indirizzi per estratti:
Citazione:
R.A. Binstead e N.S. Hush, "HOLE LOCALIZATION AND SPIN COUPLING IN PI-MONOCATIONS AND PI-DICATIONS OF MU-OXOPORPHYRIN DIMERS - RELEVANCE TO STRUCTURE OF OXIDIZED SPECIAL PAIR IN PHOTOSYNTHETIC REACTION CENTERS", Journal of physical chemistry, 97(50), 1993, pp. 13172-13179

Abstract

The antiferromagnetically coupled cofacial mu-oxoiron(III) dimers of octaethylporphyrin (OEP) and 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-phononcoupling energies (CH2Cl2 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 aconsequence of the large mean plane separation of the porphyrin rings(4.53 angstrom). Since it is improbable that the electron-phonon coupling energies will vary greatly between cofacial porphyrin dimers, it is suggested that absorption bands around 1 eV in the pi-monocations of 'sandwich'' compounds such as M(III)P2 or M(IV)P2+, where P is a porphyrin and M are lanthanide, actinide, or transition metals (3-12) observed under similar conditions will have electronic ground states thatare 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 'special pair'' in the photosynthetic reaction center is briefly discussed. The pi-dications exhibit a band in the near-infrared region which is attributed to a transition between antiferromagnetically coupled pi-states, from which, using the Hubbard hamiltonian, inter-ring exchange integrals K are calculated to be 0.39 +/- 0.02 eV, and the singlet-triplet separations (S)DELTA(T) calculated to be 0.025 and 0.0024 eV, respectively. The monocations are stable to disproportionation in CH2Cl2 solution (K(com) (295 K) = 3 X 10(5) and 2 x 10(4), respectively).

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Documento generato il 24/11/20 alle ore 10:44:13