Unrevealing mechanism of the thermal tautomerization of avobenzone by means of quantum chemical computations

Abstract

Avobenzone (1-(4-tert-butylphenyl)-3-(4-methoxyphenyl)propane-1,3-dione) is one of the most widely used UV-A filters in cosmetic sunscreens. The reactivity of avobenzone is complex and challenging to understand, due to a presence of transient tautomers. In this contribution, the chelated enol, rotamer and keto tautomers of a reduced model of avobenzone, which are involved in keto-enol tautomerization, were studied. Two thermal tautomerization mechanisms are postulated and their transient structures are discussed. The computed vertical and adiabatic electronic excitation energies of the tautomers provide an additional insight into the excited state properties of the tautomers.