Investigation of Different Photochemical Reactions of Avobenzone Derivatives by Ultrafast Transient Absorption Spectroscopy
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 the photophysical and photochemical reactions of several AB derivatives. However, there is still a gap for the data of these compounds in the ultrafast time region. To help a better understanding of the photophysical and photochemical reaction mechanisms, selected AB derivatives of AB-Me, AB-Pr, AB-Br and AB-Cl were studied using ultrafast transient absorption spectroscopy and coupled with density functional theory calculations in the present study. It is unravelled that the alkylated substituted AB compounds of AB-Me and AB-Pr exhibit efficient intersystem crossing with the generation of the corresponding triplet state species, which leads to the further Norrish type II reaction for AB-Pr. On the other hand, AB-Br and AB-Cl prefer the photochemical reactions via the singlet state surface. Based on the DFT calculations, 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.