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Photoinduced Electron Transfer in Donor-Acceptor Complexes of Ethylene with Molecular and Atomic Iodine
Journal of Physical Chemistry A
  • Aimable Kalume
  • Lisa George
  • Andrew D. Powell
  • Richard Dawes, Missouri University of Science and Technology
  • Scott A. Reid
Building upon our recent studies of radical addition pathways following excitation of the I2 chromophore in the donor-acceptor complex of ethylene and I2 (C2H4··· I2), in this article, we extend our studies to examine photoinduced electron transfer. Thus, irradiation into the intense charge-transfer band of the complex (λmax = 247 nm) gave rise to a band at 366 nm that is assigned to the bridged ethylene-I radical complex on the basis of our prior work. the formation of the radical complex is explained by a mechanism that involves rapid back electron transfer leading to I-I bond fission. Excitation into the charge-transfer band of the radical complex led to regeneration of the parent complex and the formation of the final photoproduct, anti- and gauche-1,2-diiodoethane, which confirms that the reaction proceeds ultimately by a radical addition mechanism. This finding is contrasted with our previous study of the C2H4···Br2 complex, where CT excitation led to only one product, anti-1,2-dibromoethane, a result explained by a single electron-transfer mechanism proceeding via a bridged bromonium ion intermediate. For the I2 complex, the breakup of the photolytically generated I2 -· anion radical is apparently sufficiently slow to render it uncompetitive with back electron transfer. Finally, we report a detailed computational examination of the parent and radical complexes of both bromine and iodine, using high-level single- and multireference methods, which provide insight into the different behaviors of the charge-transfer states of the two radicals and the role of spin-orbit coupling.
Research Center/Lab(s)
Center for High Performance Computing Research
Keywords and Phrases
  • Charge transfer,
  • Chromophores,
  • Electron transitions,
  • Ethylene,
  • Iodine,
  • Back electron transfer,
  • Charge transfer state,
  • Charge-transfer bands,
  • Donor-acceptor complex,
  • Multireference methods,
  • Photo-induced electron transfer,
  • Single electron transfer,
  • Spin-orbit couplings,
  • Free radical reactions
Document Type
Article - Journal
Document Version
File Type
© 2014 American Chemical Society (ACS), All rights reserved.
Publication Date
Citation Information
Aimable Kalume, Lisa George, Andrew D. Powell, Richard Dawes, et al.. "Photoinduced Electron Transfer in Donor-Acceptor Complexes of Ethylene with Molecular and Atomic Iodine" Journal of Physical Chemistry A Vol. 118 Iss. 34 (2014) p. 6838 - 6845 ISSN: 1089-5639
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