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Title: Triplet states with unusual spin polarization resulting from radical ion pair recombination at short distances

Abstract

Covalently bound electron donor-acceptor, [D-A], molecules that undergo photoinduced charge separation from a photoexcited singlet state to form radical ion pairs that subsequently undergo back electron transfer to yield a triplet state are very rare. Apart from their importance in the general context of electro-transfer reactions, these molecules provide insights into the primary photochemistry of photosynthetic reaction centers. Photoexcitation of [D-A] produces {sup 1}*[D-A], which undergoes rapid charge separation to yield {sup 1}[D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}{minus}}]. At [D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}(minus)}] distances {ge}20 A, the exchange integral, J, between the two radicals is generally {le}10{sup {minus}4} cm{sup {minus}1}. This weak interaction allows radical pair intersystem crossing (RP-ISC) within {sup 1}[D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}(minus)}] to occur, which leads to the formation of a spin-correlated radical pair {sup 3}[D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}{minus}}]. Radical ion pair recombination within {sub 3}[D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}{minus}}]. In all of these reactions the spins remain correlated, which results in non-Boltzmann populations of the spin states within each intermediate. The authors report here the first example of a covalently bound [D-A] molecule in which a single electron-transfer step produces a [D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}{minus}}] pair at a short 11 {angstrom} distance with a large J value that leads to efficient {sup 3}*[D-A] formation.

Authors:
; ;
Publication Date:
Research Org.:
Argonne National Lab., IL (US)
Sponsoring Org.:
USDOE
OSTI Identifier:
20000136
DOE Contract Number:  
W-31109-ENG-38
Resource Type:
Journal Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 121; Journal Issue: 33; Other Information: PBD: 25 Aug 1999; Journal ID: ISSN 0002-7863
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; ION PAIRS; RECOMBINATION; TRIPLETS; COVALENCE; PHOTOCHEMISTRY; ELECTRON TRANSFER; HETEROCYCLIC COMPOUNDS

Citation Formats

Wiederrecht, G.P., Svec, W.A., and Wasielewski, M.R. Triplet states with unusual spin polarization resulting from radical ion pair recombination at short distances. United States: N. p., 1999. Web. doi:10.1021/ja991828s.
Wiederrecht, G.P., Svec, W.A., & Wasielewski, M.R. Triplet states with unusual spin polarization resulting from radical ion pair recombination at short distances. United States. doi:10.1021/ja991828s.
Wiederrecht, G.P., Svec, W.A., and Wasielewski, M.R. Wed . "Triplet states with unusual spin polarization resulting from radical ion pair recombination at short distances". United States. doi:10.1021/ja991828s.
@article{osti_20000136,
title = {Triplet states with unusual spin polarization resulting from radical ion pair recombination at short distances},
author = {Wiederrecht, G.P. and Svec, W.A. and Wasielewski, M.R.},
abstractNote = {Covalently bound electron donor-acceptor, [D-A], molecules that undergo photoinduced charge separation from a photoexcited singlet state to form radical ion pairs that subsequently undergo back electron transfer to yield a triplet state are very rare. Apart from their importance in the general context of electro-transfer reactions, these molecules provide insights into the primary photochemistry of photosynthetic reaction centers. Photoexcitation of [D-A] produces {sup 1}*[D-A], which undergoes rapid charge separation to yield {sup 1}[D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}{minus}}]. At [D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}(minus)}] distances {ge}20 A, the exchange integral, J, between the two radicals is generally {le}10{sup {minus}4} cm{sup {minus}1}. This weak interaction allows radical pair intersystem crossing (RP-ISC) within {sup 1}[D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}(minus)}] to occur, which leads to the formation of a spin-correlated radical pair {sup 3}[D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}{minus}}]. Radical ion pair recombination within {sub 3}[D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}{minus}}]. In all of these reactions the spins remain correlated, which results in non-Boltzmann populations of the spin states within each intermediate. The authors report here the first example of a covalently bound [D-A] molecule in which a single electron-transfer step produces a [D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}{minus}}] pair at a short 11 {angstrom} distance with a large J value that leads to efficient {sup 3}*[D-A] formation.},
doi = {10.1021/ja991828s},
journal = {Journal of the American Chemical Society},
issn = {0002-7863},
number = 33,
volume = 121,
place = {United States},
year = {1999},
month = {8}
}