Photophysical and photochemical properties of resveratrol Iva Džeba b , Tomasz Pedzinski a, *, Branka Mihaljevi  c b a Adam Mickiewicz University, Faculty of Chemistry, 89b Umultowska Str., 61-614 Poznan, Poland b Ruper Boškovi c Institute, Divison of Materials Chemistry, Radiation Chemistry and Dosimetry Laboratory, Bijeni9 cka 54, 10000 Zagreb, Croatia A R T I C L E I N F O Article history: Received 31 July 2014 Received in revised form 15 November 2014 Accepted 18 November 2014 Available online 20 November 2014 Keywords: Resveratrol Phenoxyl radical Laser flash photolysis A B S T R A C T Photophysical and photochemical properties of trans-resveratrol (trans-3,5,4 0 -trihydroxystilbene, ArOH) were investigated in water and acetonitrile (ACN). S 1 –S n transient absorption spectrum with a peak around 530 nm was observed by a femtosecond transient absorption technique for ArOH in ACN. The excited singlet state lifetime was determined to be 28.6 ps. The radical cation of resveratrol (ArOH  +) was generated by resonant two photon ionization in ACN using nanosecond Nd:YAG laser pulses at 355 nm with an energy of 50 mJ. The molar absorption coefficient of ArOH  + was determined to be, e(ArOH  +, 500 nm, ACN) = 33400 M 1 cm 1 . The transient ArOH  + deprotonated yielding the long lived phenoxyl radical (ArO  ) with a peak at 390 nm. This deprotonation was found to occur rapidly in the presence of water. The rate constant for the deprotonation of ArOH  + in ACN, by the addition of small amounts of water (0.10–0.75%), was estimated to be around 1 10 8 M 1 s 1 . In comparison with molar absorption coefficients of the other phenoxyl radicals, an unexpectedly large value of the molar absorption coefficient of phenoxyl radicals of resveratrol was determined, e(ArO  , 390 nm, ACN) = 15200 M 1 cm 1 . The spectral properties of ArO  were confirmed with pulse radiolysis, and the value of the molar absorption coefficient obtained by laser flash photolysis was found to be in a good agreement with the value obtained by pulse radiolysis, e(ArO  , 410 nm, H 2 O) = 14600 M 1 s 1 . These spectral and kinetic data of the transients could contribute to the understanding of mechanisms of resveratrol reactions with biologically relevant radical species. ã 2014 Elsevier B.V. All rights reserved. 1. Introduction trans-Resveratrol (trans-3,5,4 0 -trihydroxystilbene, ArOH)is a natural compound present in plant species such as grapes, peanuts and berries [1]. ArOH is produced in response to stressor agents like fungi so it can be classified as a phytoalexin [2]. In the last several years ArOH has been widely investigated because of its various beneficial biological activities like: anticancer, anti-inflammatory, cardioprotective and antioxidative activity [1,3,4]. The antioxidant activity of resveratrol is related to the ability of its stilbenic and polyphenolic structure to scavenge free radicals by different mechanisms: (1) a one-step hydrogen atom transfer from resveratrol to active radicals, (2) a sequential proton loss electron transfer process from the resveratrol anionic form (phenoxide anion), (3) an electron-transfer process from resveratrol to active radical followed by proton transfer, (4) the addition of an appropriate radical on the double bond of resveratrol [5,6]. Despite previous extensive studies of its biological activity, it is somewhat surprising that some spectral and kinetic data of resveratrol and its transients are still unknown. Also mechanisms of resveratrol reactions with most relevant radical species are scarce. In order to investigate the mechanism of its antioxidative action, it is important to fully characterize all ArOH transients in excited states and intermediates which can be formed in the reactions with different free radicals. The aim of this study was to investigate systematically properties of the ArOH intermediates. We determined that ArOH is unexpectedly a very reactive compound photochemically which undergoes a biphotonic process with the formation of ArOH  +. In order to avoid misinterpretation with the ArOH products of monophotonic reactions, we have characterized ArOH excited states and determined ArOH photophysical properties. This is, to our knowledge, the first comprehensive characterization of the resveratrol-derived transients (both qualitative and quantita- tive). The findings collected in this paper should help in better understanding of the mechanisms of antioxidative action of resveratrol and its other beneficial activities in living organisms. 2. Experimental 2.1. Materials Resveratrol, sodium azide (NaN 3 ), 1,4-dicyanoanthracene (1,4-DCA), biphenyl (Bph), di-phenyl methanol ((C 6 H 5 ) 2 CHOH), * Corresponding author. Tel.: +48 61 829 1327; fax: +48 61 829 1555. E-mail address: tomekp@amu.edu.pl (T. Pedzinski). http://dx.doi.org/10.1016/j.jphotochem.2014.11.019 1010-6030/ ã 2014 Elsevier B.V. All rights reserved. Journal of Photochemistry and Photobiology A: Chemistry 299 (2015) 118–124 Contents lists available at ScienceDirect Journal of Photochemistry and Photobiology A: Chemistry journal home page : www.elsevier.com/locat e/jphotochem