Organic synthesis on graphene.

Graphene is a two-dimensional crystalline carbon allotrope that has fascinated researchers worldwide and has extended the interest in carbon structures such as fullerenes and nanotubes. In this Account, we use electrical characterization tools to study chemistry on supported graphene. These experiments elucidate the way covalently bound phenyl units can change graphene's physical properties. Can we use chemistry to control electronic properties of graphene? What can we learn from well-known carbon allotropes like fullerenes? The surfaces of fullerenes and graphene show distinct differences in reactivity because of the high strain of sp² carbon in fullerenes compared with the complete lack of strain in graphene. Diazonium chemistry provides a versatile tool for attaching phenyl units covalently to carbon to produce advanced materials and electronic components, but diazonium-based carbon chemistry is strongly influenced by strain. Although fullerenes are highly reactive, graphite (stacks of graphene) remains relatively inert. We chemically introduce n- and p-like doping patterns in two-dimensional graphene using photolithography and extend the ability to chemically control doping to the chemical design of conducting and insulating areas. Thereby we can shape graphene surfaces into functional electronic devices. This Account also describes multistep synthesis on graphene-coated nanoparticles and the introduction of various functional groups on graphene surfaces. Only few functional groups can be produced directly via diazonium chemistry. To overcome this issue, we used these functional groups as starting points for more demanding organic reactions. We covalently attached chelating agents, catalysts, or polymers on the carbon surface. These more complex reactions facilitate the design of electronic modifications, intergraphene connections, and anchors for polymer incorporation. Diazonium chemistry forms strong covalent bridges between graphene and other areas of chemistry.