To elucidate the mechanism of the PCET between PiceH4 and O2 •-in DMF, DFT calculations were conducted using the B3LYP, M06-2X, and TPSSh hybrid functionals with the PCM method. We focus on the B3LYP results below unless otherwise noted, because the three functionals showed similar results. First, the stable conformations of PiceH4 (Figure ) and the structures of its anions ( a PiceH3 -, b PiceH3 -, c PiceH3 -, and d PiceH3 -) after the initial PT were obtained by energy scanning of the dihedral angle around the four OHs and stilbene moiety (Tables and). Figure shows the optimized structures and Gibbs free energy changes (ΔG°/kJ mol -1 , 298.15 K) along the initial PT (M06-2X and TPSSh results are shown in Figure ). Then, charge distribution on the OH protons of PiceH4 obtained using NBO analysis were indicated. The mechanistic analysis of PCET between O2 •-and PiceH4 was conducted using frontier molecular orbital analysis (Figure ). The HOMO-LUMO (hartree/a.u.) relation changes during the PCET (M06-2X and TPSSh results are shown in Figure ). Some reactant species, PiceH4, PiceH3 -, O2 •-, and HO2 • , coexist in the experimental solutions after the initial PT. The HOMO energies of PiceH4 (-0.21001) and its anions ( a PiceH3 -:-0.16988, b PiceH3 -:-0.16564) were much higher than the SOMO energy of HO2 • (-0.31659), indicating that HO2 • rather than O2 •- (-0.15933) was the electron acceptor. Meanwhile, CV revealed that PiceH4 scavenged O2 •-and HO2 • formed after the initial PT (Figure ). Therefore, PiceH3 -was the electron donor as shown in the downhill energy relation (bold red lines). The HOMO-LUMO energies changed during PT from PiceH4 to O2 •-, forming PicesH3 -and HO2 • , respectively. Moreover, the HOMO-LUMO relation between the products (i.e., a PiceH3 • / b PiceH3 • and HO2 -) upset after the subsequent ET (red dotted lines), suggesting that reverse ET proceed. However, the HOMO (-0.27731) of H2O2 is lower than that of HO2 -(-0.16694), indicating that the second PT prevents the reverse ET.