Applied Magnetic Resonance

, Volume 17, Issue 4, pp 577–586 | Cite as

FT-EPR study of the pH dependence of the photochemistry of sesamol in aqueous solution

  • A. Bussandri
  • H. van Willigen
  • K. Nakagawa


A Fourier transform electron paramagnetic resonance (FT-EPR) study was made of the photochemistry of 3,4-methylenedioxyphenol (sesamol, SEOH)) in aqueous solution. FT-EPR measurements show that in alkaline (pH 11) solution, pulsed-laser excitation of SECT leads to photoionization giving the hydrated electron and SEO free radical. Resonance signals from these paramagnetic species develop with instrument-controlled rise time. They exhibit a low-field emission/ high-field absorption (E/A) CIDEP pattern with the transition from emission to absorption occurring at the resonance of the hydrated electron. It is shown that the spin polarization stems from contributions from the ST0 radical pair mechanism (E/A) and triplet mechanism (A). From this it is concluded that photoionization of sesamol occurs via the triplet excited state. In neutral and acidic (pH 4–7) aqueous solution, photoexcitation generates SEO and cyclohexadienyl-type radicals. In this case, radicals grow in over a period of 1–2 μs and FT-EPR spectra display an E/A pattern with the inversion point in the center. The lowering of the pH of the solution apparently is accompanied by a strong reduction in the relative importance of photoionization. From the FT-EPR data it can be deduced that in neutral and acidic solutions the dominant reaction channel is H-atom transfer. In this respect, the photochemistry of sesamol differs from that of phenol andp-cresol. For these phenols the change in pH does not affect the appearance of the FT-EPR spectra. Apparently, the change in electronic structure caused by the methylenedioxy substituent strongly affects the excited state reactivity of sesamol.


Microwave Pulse Sesamol Triplet Excited State Phenoxyl Radical Hydrated Electron 


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  1. 1.
    Feitelson J., Hayon E.: J. Phys. Chem.77, 10 (1973)CrossRefGoogle Scholar
  2. 2.
    Feitelson J., Hayon E., Treinin A.: J. Am. Chem. Soc.95, 1025 (1973)CrossRefGoogle Scholar
  3. 3.
    Bent D.V., Hayon E.: J. Am. Chem. Soc.97, 2599 (1975)CrossRefGoogle Scholar
  4. 4.
    Zechner J., Köhler G., Grabner G., Getoff N.: Chem. Phys. Lett.37, 297 (1976)CrossRefADSGoogle Scholar
  5. 5.
    Grabner G., Köhler G., Zechner J., Getoff N.: Photochem. Photobiol.26, 449 (1977)CrossRefGoogle Scholar
  6. 6.
    Köhler G., Getoff N.: J. Chem. Soc. Faraday Trans.172, 2101 (1976)Google Scholar
  7. 7.
    Zechner J., Köhler G., Grabner G., Getoff N.: Can. J. Chem.58, 2006 (1980)CrossRefGoogle Scholar
  8. 8.
    Grabner G., Köhler G., Zechner J., Getoff N.: J. Phys. Chem.84, 3000 (1980)CrossRefGoogle Scholar
  9. 9.
    Grabner G., Köhler G., Marconi G., Monti S., Venuti E.: J. Phys. Chem.94, 3609 (1990)CrossRefGoogle Scholar
  10. 10.
    Anbar M., Meyerstein D., Neta P.: Nature208, 1348 (1966)CrossRefADSGoogle Scholar
  11. 11.
    Smaller B., Avery E.C., Remko J.R.: J. Chem. Phys.55, 2414 (1971)CrossRefADSGoogle Scholar
  12. 12.
    McLauchlan K.A. in: Modern Pulsed and Continuous Wave Electron Spin Resonance (Kevan L., Bowman M.K., eds.), pp. 285–364. New York: Wiley 1990.Google Scholar
  13. 13.
    van Willigen H., Levstein P.R., Ebersole M.H.: Chem. Rev.93, 173 (1993)CrossRefGoogle Scholar
  14. 14.
    Jeevarajan A.S., Fessenden R.W.: J. Phys. Chem.96, 1520 (1992)CrossRefGoogle Scholar
  15. 15.
    Clancy C.M.R., Forbes M.D.E.: Photochem. Photobiol.69, 16 (1999)CrossRefGoogle Scholar
  16. 16.
    Levstein P.R., van Willigen H.: J. Chem. Phys.95, 900 (1991)CrossRefADSGoogle Scholar
  17. 17.
    de Beer R., van Ormondt D. in: Advanced EPR: Applications in Biology and Biochemistry (Hoff A.J., ed.), pp. 135–173. Amsterdam: Elsevier 1989.Google Scholar
  18. 18.
    Dixon W.T., Murphy D.: J. Chem. Soc. Perkin Trans. II1976, 1823.Google Scholar
  19. 19.
    Cocivera M., Tomkiewicz M., Groen A.: J. Am. Chem. Soc.94, 6598 (1972)CrossRefGoogle Scholar
  20. 20.
    Molin Y.N. (ed.): Spin Polarization and Magnetic Effects in Radical Reactions. Amsterdam: Elsevier 1984.Google Scholar
  21. 21.
    Fessenden R.W., Schuler R.H.: J. Chem. Phys.38, 773 (1963)CrossRefADSGoogle Scholar

Copyright information

© Springer 1999

Authors and Affiliations

  • A. Bussandri
    • 1
  • H. van Willigen
    • 1
  • K. Nakagawa
    • 2
  1. 1.Department of ChemistryUniversity of Massachusetts at BostonBostonUSA
  2. 2.Radio Isotope Research CenterFukushima Medical UniversityFukushima-shiJapan

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