New insights into ESIPT mechanism of three sunscreen compounds in solution: A combined experimental and theoretical study.

[Display omitted] • Apigenin, Luteolin and Steppogenin were used as sunscreens to study in solution. • Site-selective electron transfer in the excited state is induced by hydrogen bond. • A certain theoretical basis for the application of plant flavonoids in sunscreen cosmetics. • This work clarified the excited state kinetic behavior of Apigenin, Luteolin and Steppogenin in solvent. In this present work, we have successfully designed and investigated three flavonoid sunscreen compounds. Based on steady-state spectroscopy and time-dependent density functional theory (TDDFT), the mechanism of excited state intramolecular proton transfer (ESIPT) of sunscreen compounds was studied. The calculated UV–vis absorption spectra and fluorescence emission spectra are in good agreement with the experimental results in methanol solution. The potential energy curve demonstrates that the ESIPT process can easily occur in the three sunscreen compounds without energy barrier. Therefore, the absorbed excitation energy can get back to the ground state through a non-radiative relaxation process. Light stability tests ensure that the three flavonoids have the potential as sunscreens. This work provides not only an application of the ESIPT process in sunscreen mechanisms, but also a theory basis for the development of novel sunscreen molecules. [ABSTRACT FROM AUTHOR]