Investigation Of Different Photochemical Reactions Of Avobenzone Derivatives

Avobenzone(AB)is one of the most widely used UVA sunscreens,and it is viewed as a model compound for studying the photoisomerization process.In recent years,Miranda and co-workers studied photophysical and photochemical reactions of several AB derivatives.The AB derivatives were found to exhibit different photochemical behaviors in different solvents upon irradiation.To get a detailed understanding of the photophysical and photochemical reaction mechanisms,selected AB derivatives of AB-Me,AB-Pr,AB-Br and AB-Cl were studied by using ultrafast transient absorption spectroscopy and density functional theory calculations in this paper.It is unraveled that alkylated substituted AB compounds of AB-Me and AB-Pr exhibit an efficient intersystem crossing with the generation of the corresponding triplet state species,which further leads to the Norrish type II reaction for AB-Pr.On the other hand,AB-Br and AB-Cl prefer photochemical reactions via the singlet state surface.Based on the DFT calculations,the spin-orbit coupling constant between the singlet and triplet states,the energy difference between the singlet and triplet states and the natural transition orbital separations of the studied AB compounds were found to be the leading reasons accounting for their corresponding photochemical activities via singlet and triplet states.This paper provides very important information for the application of AB derivatives in the fields of photochemistry,biology,and medicine,and provides important theoretical guidance for the design and synthesis of safer and more effective UVA absorbers.The paper consists of four chapters.The first chapter is the introduction part,which summarizes the significance of photochemistry,UV absorbers,avobenzone derivatives,time-resolved spectroscopy,density functional theory and related research background.The second chapter deals with the photophyscial and photochemical reaction of alkyl substituted avobenzone derivatives;The third chapter deals with the photophyscial and photochemical reaction of halo-substituted avobenzone derivatives.The last chapter deals with the reasons why AB-Me,AB-Pr and AB-Br,AB-Cl have different photochemical behaviors.