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  Flexible Biradicals in Liquid and Supercritical Carbon Dioxide:  The Exchange Interaction, the Chain Dynamics, and a Comparison with Conventional Solvents

Forbes, M., Dukes, K., Avdievich, N., Harbron, E., & DeSimone, J. (2006). Flexible Biradicals in Liquid and Supercritical Carbon Dioxide:  The Exchange Interaction, the Chain Dynamics, and a Comparison with Conventional Solvents. The Journal of Physical Chemistry A, 110(5), 1767-1774. doi:10.1021/jp053183q.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0004-962C-2 Version Permalink: http://hdl.handle.net/21.11116/0000-0004-962D-1
Genre: Journal Article

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Forbes, MDE, Author
Dukes, KE, Author
Avdievich, NI1, Author              
Harbron, EJ, Author
DeSimone, JM, Author
Affiliations:
1Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497794              

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 Abstract: X-band time-resolved electron paramagnetic resonance (TREPR) spectra of three flexible biradicals of varying chain length and structure were obtained in liquid and supercritical carbon dioxide (CO2) solutions and compared to conventional solvents. For C16 acyl−alkyl biradical 1a, an average spin exchange interaction between the radical centers, Javg, was obtained by spectral simulation using a simple model for spin-correlated radical pairs (SCRPs) and a small amount of T2 relaxation from a previously established J modulation mechanism. A large solvent effect on Javg was observed for the first time, varying by almost 1 order of magnitude from CO2 (Javg = −120 ± 10 MHz) to heavy mineral oil (−11 ± 3 MHz) for 1a. For C15 bis(alkyl) biradical 1b, spectra obtained under supercritical conditions are only slightly different from those detected in liquid CO2 but differ from spectra taken in benzene. For C10 acyl−alkyl biradical 2a, more emissive spin polarization due to S−T- mixing is observed in CO2 than in benzene. These results are discussed in terms of solvent properties such as dielectric constant, viscosity, and specific interactions. Both chain dynamics and changes to the equilibrium distribution of end-to-end distances can alter Javg and the observed ratio of S−T0 to S−T- mixing; however, faster chain dynamics is concluded to be the most likely cause of the observed effects in these systems.

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 Dates: 2006-01
 Publication Status: Published in print
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 Rev. Method: -
 Identifiers: DOI: 10.1021/jp053183q
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Title: The Journal of Physical Chemistry A
  Other : J. Phys. Chem. A
Source Genre: Journal
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Publ. Info: Columbus, OH : American Chemical Society
Pages: - Volume / Issue: 110 (5) Sequence Number: - Start / End Page: 1767 - 1774 Identifier: ISSN: 1089-5639
CoNE: https://pure.mpg.de/cone/journals/resource/954926947766_4