To obtain a greater understanding of computed redox potentials, the highest occupied molecular orbitals (HOMOs) of 1-6 were analyzed. As displayed in Fig. , 1 exhibited the lowest HOMO level among 1-6, which is correlated with the calculated E° value. The orbital lobes localized at the C5-C7 positions in the HOMOs of 1-3 showed that electron-donating groups at those positions may effectively elevate the HOMO level. In good agreement with this expectation, the HOMO level of 4 carrying three hydroxyl groups at all the C5, C6, and C7 positions was reached at -5.924 eV, which became lower (for 5) when an electron-withdrawing moiety was substituted at the C8 position. To determine the ability of 1-6 to quench free organic radicals, we performed the Trolox equivalent antioxidant capacity (TEAC) assay employing the cationic radical form of 2,2'-azinobis(3-ethylbenzthiazoline-6-sulphonic acid). As presented in Fig. and, compounds were tested, except for 1 that has limited solubility in ethanol under our experimental conditions.