Magnetic field effects and time-resolved EPR studies on photogenerated biradical from intramolecular electron transfer reactions in zinc-tetraphenylporphyrin-C60 linked compounds: Contribution of relaxation mechanism due to spin-spin relaxation

H. Yonemura, S. Harada, S. Moribe, S. Yamada, H. Nakamura, Y. Fujiwara, Y. Tanimoto

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Abstract

Magnetic field effects (MFEs) and time-resolved EPR on photogenerated biradical from intramolecular electron-transfer reactions in zinc-tetraphenylporphyrin (ZnP)-C 60 linked compounds (ZnP(4)C 60 and ZnP(8)C 60 ) with flexible four and eight methylene groups have been investigated in benzonitrile. At low temperature (288K), the decay rate constant of the biradical decreased steeply in low magnetic fields (0.1 ≤ H ≤ 0.6 T) and finally became almost constant in high magnetic fields (0.6 ≤ H ≤ 1T) in both ZnP(4)C60 and ZnP(8)C60. At high temperature (323 K), in contrast, the decay rate constant decreased slightly in low magnetic fields (<0.1 T), and then increased gradually in higher magnetic fields (0.1 ≤ H ≤ 1 T). Interestingly, the decay rate constants in higher magnetic fields (0.4 ≤ H ≤ 1 T) were larger than that in zero magnetic field. The reverse phenomena of the MFEs around 0.1T and temperature dependence on the MFEs are explained by the contribution of spin-spin relaxation due to anisotropic Zeeman interaction to the relaxation mechanism and most likely ascribed to the properties of C60 anion radical due to the spherical π-system. The mechanism is also supported by the time-resolved EPR spectra.

Original languageEnglish
Pages (from-to)1559-1572
Number of pages14
JournalMolecular Physics
Volume104
Issue number10-11
DOIs
Publication statusPublished - May 20 2006

All Science Journal Classification (ASJC) codes

  • Biophysics
  • Molecular Biology
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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