Excited state deactivation in phytochemical flavonoids: astragalin and kaempferol

Abstract

Femtosecond transient absorption experiments and ab initio and nonadiabatic dynamics (NAD) simulations have helped to explicate the photophysical dynamics of two ubiquitous members of the flavonoid family, astragalin and kaempferol. Differences between their excited state deactivation mechanisms have been observed and explained. Astragalin exhibits an ultrashort (∼10 ps) S₁ lifetime, whereas that of kaempferol extends approximately twice as long (∼20 ps), explained by the systems’ relative access to a S₁/S₀ conical intersection following excited state intramolecular proton transfer. These findings expound the unexpected role played by sugar substituents in photoprotective flavonoids and justify the use of similar natural derivatives for UV photothermal materials.