A computational study of a reduced dye and its O2 reduction: Implication on H2O2 production with dye-sensitized photocathodes

Abstract Anion radicals of dyes (dye−•), including four coumarin 343 conformers and a perylenemonoimide derivative, as well as their reactions with the O2 molecule, were investigated by density functional theory. All the dye−• species reacted with O2 to form H∙∙∙O hydrogen bonds via C–H groups, followed by rigorous analysis by the natural bond orbital method. A complete atomic charge and spin transfer occurred upon the reaction, verifying that the reduction of O2 by dye−• occurred via a one-electron-transfer process. The exergonic reaction free energies revealed that an intermediate [dyeO2]−• complex can be easily formed and spontaneously dissociated into the neutral dye and O2−• subsequently. Most of the [dyeO2]−• intermediates did not react further with H+ and HO2•, and although some [dyeO2]−• species reacted, no atomic charge or spin transfer occurred. These results suggest that the dyes did not participate in the subsequent reactions of O2−• with H+ and HO2•, such as disproportionation, leading to the efficient production of H2O2 as the final product through HO2• and HO2− species.