Theoretical Study of Electronic Properties of Phenalenyl Radical and Zethrene Diradical Species: Possibility of Triplet Oxygen Adsorption onto Graphene Surface

摘要

Phenalenyl, zethrene, and extended zethrene molecules were employed to study the change in electronic properties of graphene surfaces upon exposure to oxygen atmosphere. These hydrocarbons are the smallest systems that can be used to evaluate intermolecular interaction with triplet oxygen molecules. The phenalenyl radical can simulate the radical nature of an edge structure and defect site of graphene sheets. Zethrene and extended zethrene molecules (n = 0, 1, 2, 3, and 4), which possess open-singlet diradical character, are also good models for studying chemisorption phenomena. From the calculated results for phenalenyl, the reaction path from the dissociation limit to the final products was found with chemisorbed structures (SS1 and SS2) and transition states (TS1, TS2, and TS3). Calculated adsorption energies were 7.72 (SS1) and 6.58 (SS2) kcal mol(-1). An oxygen molecule can form a contact with phenalenyl radical in a weak chemisorption process, which is endothermic and has very low energy barriers to transition states. For the zethrene series, the diradical character index y, used to describe coupling between two radical spins, was evaluated using the broken symmetry approach. The values were 0.00, 0.01, 0.10, 0.23, and 0.32, for n = 0, 1, 2, 3, and 4, respectively. Although diradical nature was absent in ordinary zethrene, other extended zethrene molecules exhibited cliraclical character. The radical spin induced in phenalenyl unit A can contribute to the chemisorption of triplet oxygen molecules. The calculated adsorption energy for the first 02 adsorption onto heptazethrene was 5.38 kcal mol(-1). Concomitantly, the radical electron on unit B revived and played an important role in the radical activity. The required adsorption energy for the second 02 adsorption became lower at -0.64 kcal mol(-1).