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

Content Provider	Springer Nature Link
Author	Bussandri, A. Willigen, H. Nakagawa, K.
Copyright Year	1999
Abstract	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.
Starting Page	577
Ending Page	586
Page Count	10
File Format	PDF
ISSN	09379347
Journal	Applied Magnetic Resonance
Volume Number	17
Issue Number	4
e-ISSN	16137507
Language	English
Publisher	Springer-Verlag
Publisher Date	1999-01-01
Publisher Place	Vienna
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Solid State Physics Spectroscopy/Spectrometry Physical Chemistry Organic Chemistry
Content Type	Text
Resource Type	Article
Subject	Atomic and Molecular Physics, and Optics

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