Study On Excited States Of Stilbenoids And Chalcones For Natural UV Protective Compounds

The ultraviolet radiation of the solar energy has a large negative effect on the earth’s environment and human health.In order to alleviate the damage caused by ultraviolet radiation,various types of UV protective molecules have been developed on the market to implement photoprotective behavior.However,current UV protective molecules have many problems such as poor safety,single matrix type,narrow UV protective band,and single channel protective mechanism.Since natural plants could exposure to solar energy to resist ultraviolet radiation for a long time,this work is dedicated to develop the safe and efficient UV protective molecules from natural plants,using the calculation methods of density functional theory（DFT）and time-dependent density functional theory（TDDFT）combined with the steady-state spectroscopy experiments and ultrafast spectroscopy experiments to reveal the relationship between dynamic mechanism of the excited state and UV protective behavior.Based on natural compounds such as resveratrol,piceatannol,cardamom,isoliquiritigenin and pepper extracted molecules,this work elaborated the relationship between excited state dynamics and UV protective behavior.Resveratrol（RSV）and piceatannol（PIC）molecules of natural stilbenoids could absorb UVA and UVB energies efficiently,they could maintain the satisfactory photostability under the UV radiation.The excited stilbenoids will quickly relax the energy through trans-cis photoisomerization pathway via conical intersection position between potential energy curves（PECs）of S₁and S₀states within a few tens of picoseconds.The cardamom and isoliquiritigenin of natural chalcone compounds could relax the energy through dual-channels including excited state intramolecular proton transfer and trans-cis photoisomerization pathways.Their novel conjugated parent structure and hydroxyl effect could realize the adjustment of the position of absorbtion spectrum.The chalcone compounds could make up the shortcomings of low-energy UVA band absorbtion in the previous sunscreen products.Natural pepper extracted molecules could realize the regulation of steady-state absorbtion spectra through the substitution effect of the para position at benzene ring,which provides a reference for the development of new types of ultraviolet protective molecules.The strategy of spectrum regulation and the study of new protective matrix structure in this work will provide ideas for designing and developing novel ultraviolet protective molecules in future,and will lay the foundation for the expansion of broad-spectrum sunscreens.