Photophysical and photochemical properties of resveratrol

• Photophysical and photochemical properties of trans-resveratrol have been investigated in water and acetonitrile solutions.
• The excited singlet state lifetime of resveratrol (ArOH) was determined to be 28.6 ps.
• Molar absorption coefficients of ArOH-derived radicals were measured using transient absorption techniques.
• Deprotonation of ArOH radical cation has been investigated in detail.

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 (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, ϵ(ArOH+, 500 nm, ACN) = 33400 M−1cm−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 × 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(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, ϵ(ArO, 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.