UCLA

This dissertation involves explorations of on surfaces and on carbon-based nanomaterials, especially graphene, using quantum chemical calculations. The work evaluates energetics of cycloaddition reactions on different sites of graphene, improving the understanding of graphene chemistry and guiding experiments.

Chapter 1 to 3 describes theoretical investigations of 1,3-dipolar cycloadditions, Diels- Alder reactions, (2+2) cycloadditions, (4+4) cycloadditions and non-covalent interactions to graphene models. Reaction energetics have been obtained and showed that edge areas of graphene are much more favorable reaction sites than the center sites. Results indicate that graphene edges may be functionalized by a series of small molecule functional groups through cycloaddition reactions, while the interior regions cannot react. Non-covalent complexation is much more favorable than cycloaddition reactions on interior bonds of graphene. Furthermore, the Huckel molecular orbital (HMO) localization energy calculations could be used as a tool to estimate the reactivities of various polycyclic aromatic hydrocarbon molecules for experimental guidance.

Chapter 4 illustrates the Diels-Alder reactions of pentacene, bistetracene and their derivatives with fullerene. Reaction barriers and free energies have been obtained to assess the effects of frameworks and substituent groups on the Diels-Alder reactivity and product stability. Surprisingly, calculations predict that the bulky silylethynyl substituents of pentacene and bistetracene have only a small influence on reaction barriers. However, the silylethynyl substituents significantly destabilize the corresponding products due to steric repulsions in the adducts. This is confirmed by experimental results from collaborators.

Chapter 5 reports theoretical investigations of (1+2) cycloadditions of carbene, nitrene, and oxygen with fullerene, carbon nanotube and graphene models. The results suggest that closed bond adducts are much more preferred on graphene models.

Chapter 6 describes a new method to quickly estimate the reaction energetics on large carbon nanomaterials. For the same addition reaction or cycloaddition, the reaction energetics on benzene was found to perfectly correlate with those on carbon allotrope models. Based on these linear correlation equations, it is possible to quickly estimate cycloaddition or addition reaction energies on different sites of carbon-based nanomaterials by simply calculating these reactions on benzene.