[2 + 2] Cycloadditions onto graphene

Abstract

Herein, we study [2 + 2] cycloadditions reactions onto graphene. We have found that owing to stacking, CH–π interactions and steric hindrance existing between the aromatic rings, the addition of benzyne molecules follows a characteristic pattern. For a 4 × 4 graphene unit cell, the optimum level of functionalization is achieved when one benzyne group per 4.0 carbon atoms is attached. Although the addition of benzyne molecules does not result in unpaired electrons (as observed for free radicals), the attachment of benzyne molecules in pairs on opposite sides of the sheet and on neighboring carbon atoms dramatically increases binding energies. We observed that reaction energies were increased by more than three times, as compared with the addition of an isolated benzyne molecule. The preferred structure has a band gap close to 1.5 eV. The uniformity of the properties found for aryne modified graphene, the ease whereby this is achieved (due to non bonded interactions, cooperative effects and steric hindrance between the benzyne molecules) and the fact that the reaction occurs in solution, turns the nanomaterial into a very attractive species for electronics. Lastly, we have shown that the addition of larger benzyne molecules as well as the addition of biscyclopropyl alkenes is favored from a thermodynamical stand point.