Excited-state antioxidant capacity of Flavonoids based on solvent effect: A TD-DFT study

Abstract

Antioxidants have caught a widespread attention because of their applications in various fields such as biomedicine, food additives, cosmetics, and so on, but nevertheless studies on the antioxidant capacity of molecules after photoexcitation are still scarce and rare. In this work, by the application of the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods, based on the solvent effect, the antioxidant capacity of 4′-Hydroxyflavone (4′-HF), 6-Hydroxyflavone (6-HF), and 7-Hydroxyflavone (7-HF) in the S0 and S1 states are compared. In view of the frontier molecular orbitals (FMOs), depending on the HOMO energy, not only is it analyzed that the electron-donating capacity varies with the solvent, but also that the antioxidant capacity of the mostly molecules in the S1 state is better than those in the S0 state, in particular, the 6-HF in ACN in the S1 state shows a strong antioxidant capacity and is most susceptible to attack by electrophilic radicals, which is also in accordance with the conclusions drawn from the orbital weighted (OW) Fukui functions and OW double descriptors, and global indices including vertical ionization potentials (VIPs), softness (S),and so on. Moreover, absorption spectra indicate the potential of these molecules to resist UV radiation and diminished or even quenched fluorescence intensity is caused by intramolecular charge transfer as evidenced by hole-electron analysis. On the basis of the above photophysical properties, it is shown that these three molecules are expected to be one of the ingredients of sunscreens. In a nutshell, this work not only proposed the influence of solvent effect on antioxidant capacity, but also found the advantage of antioxidant capacity in the S1 state, which provides a strong support for exploring stronger antioxidant capacity.