Excited state proton transfer dynamics of potential natural flavonoid sunscreens: Quercitrin and Hyperoside

In this work, we found the flavonoid molecules: quercitrin and hyperoside have potentiality as ultraviolet (UV) filters for the first time. The steady state spectra and time-dependent density functional theory (TDDFT) were used to prove the excited state intramolecular proton transfer (ESIPT) of the non-radiative relaxation. They are excellent potential UVA sunscreens, and they can also provide some UVB protection. We demonstrated the deactivation via ESIPT can be facilitated by the hydrogen bond strengthening in S 1 . In particular, when UV excited, the enol conformation can cross a small barrier to the keto conformation, then the proton transfer process can consumes energy through non-radiative path, and the other small part dissipates through the fluorescence path. Quercetin and hyperoside with a substituent caused 10 nm wavelength change, which opens up a way for the design of new broad-spectrum sunscreens: the adjustable absorption wavelength of sunscreen molecules can be achieved by adjusting the position and number of substituents.