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Photophysical and photochemical properties of resveratrol

Resveratrol (ArOH, trans-3, 5, 4'- trihydroxystilbene) which can be mostly found in grapes and red wine, it has been investigated a lot in the last years because of its variety of biological effects including antioxidant properties. From the chemical point of view there are some uninvestigated photochemical properties, such as resveratrol intermediates radical cation (ArOH●+) and phenoxyl radical (ArO●) which can be helpful in the determination of resveratrol antioxidant reaction mechanisms. For that purpose some photophysical ArOH properties must be clarified as well. Photophysical and photochemical properties of ArOH have been investigated in H2O and acetonitrile (ACN). S1−Sn absorption spectrum with a peak around 530 nm was observed by femtosecond laser flash photolysis of ArOH in ACN. Fluorescence lifetime is determined to be 21.5 ps. The ArOH●+ with a peak at 500 nm, was generated by resonant two photon ionization in ACN by the energy of 50 mJ at 355 nm or 15 mJ at 266 nm Nd:YAG laser pulse. ArOH●+ deprotonates to the long lived ArO● with a peak at 390 nm. Absorption coefficient of ArOH●+ is determined to be, ε(ArOH● +, 500 nm, ACN) = 33400 M−1 cm−1. The ArOH●+ was not observed in H2O due to the fast deprotonation, but only ArO● with the peak at 410 nm. The rate constant of deprotonation of ArOH●+ in ACN by addition of small amount of H2O (0.10 – 0.75 %) is determined to be 1.3 x 108 M−1 cm−1. In order to calculate quantum yields and concentrations of the individual components, ArOH●+ and ArO● from the bi-component spectra after laser pulse, absorption coefficient of ArO● is determined, ε(ArO●, 390 nm, ACN) = 15 200 M-1 cm-1. The value obtained by LFP was comparable with the value obtained by pulse radiolysis, ε(ArO●, 410 nm, H2O) = 14 600 M-1 s-1.

resveratrol; resveratrol radical cation; absorption coefficient

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