Ultrafast Nonadiabatic Photoisomerization Dynamics Mechanism for the UV Photoprotection of Stilbenoids in Grape Skin

UV photoprotection behavior of natural life play a vital role for their physiological protection functions. It has been reported that UVC radiation can make resveratrol (RSV) and piceatannol (PIC) accumulated in grape skin. In this work, we demonstrated RSV and PIC could absorb UVA and UVB dramatically and confirmed their satisfactory photostability. Furthermore, we clearly clarified the UV photoprotection mechanism of typical stilbenoids of RSV and PIC for the first time by using combined femtosecond transient absorption (FTA) spectroscopy experiment and time-dependent density functional theory (TDDFT) calculation method. RSV and PIC can be photoexcited to the excited state after UVA and UVB absorption. Subsequently, the photoisomerized RSV and PIC quickly relax to the ground state via the nonadiabatic transition from S 1 state at a conical intersection (CI) position between the potential energy surfaces (PESs) of the S 1 and S 0 states. This ultrafast trans-cis photoisomerization will take place within a few tens of picoseconds. As a result, the UV energy absorbed by RSV and PIC could be dissipated ultrafast by nonadiabatic photoisomerization process.