Photophysical and photochemical properties of resveratrol

Photophysical and photochemical properties of trans-resveratrol (trans-3, 5, 4′- trihydroxystilbene, ArOH) were investigated in water and acetonitrile (ACN). S1–Sn 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 (ArOHradical dot+) 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 ArOHradical dot+ was determined to be, ϵ(ArOHradical dot+, 500 nm, ACN) = 33400 M−1cm−1. The transient ArOHradical dot+ deprotonated yielding the long lived phenoxyl radical (ArOradical dot) 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 ArOHradical dot+ in ACN, by the addition of small amounts of water (0.10–0.75%), was estimated to be around 1 × 108 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, ϵ(ArOradical dot, 390 nm, ACN) = 15200 M−1 cm −1. The spectral properties of ArOradical dot 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, ϵ(ArOradical dot, 410 nm, H2O) = 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