Understanding prominent effects of the intramolecular hydrogen bond on the photophysical properties and antiradical abilities of six flavonoids

The photophysical properties and antiradical abilities of 5-Hydroxyflavone, 3,5-Dihydroxyflavone, galangin, kaempferol, quercetin, and myricetin are explored using density functional theory and time-dependent density functional theory methods. The absorption spectra of the six flavonoids span the entire ultraviolet region, and their fluorescence peak intensities are faint, meeting the sunscreen requirements. Furthermore, their max absorption peaks are mainly affected by the hydroxyl groups in the A- and C-rings of the compounds. The hydrogen atom transfer, sequential proton loss electron transfer and single electron transfer followed by proton transfer mechanisms are used to evaluate their antiradical abilities. It can be concluded that the O4-H4 site of myricetin is the most active site to scavenge free radicals, revealing that the formation of intramolecular hydrogen bonds can significantly enhance molecular antiradical abilities. In a word, altering tactfully hydrogen group position is conducive to regulating the photophysical properties and antiradical abilities of flavonoids.