2. Nanographenes

2.1 Allotropic forms of carbon

Diamond and graphite are the two most common allotropic forms of carbon (figure 1 ). In diamond, each carbon atom is tetrahedral (sp ³ hybridized) and thus covalently bonded to four neighboring atoms. Graphite, on the other hand, is a stack of parallel sheets composed of trigonal (sp ² -hybridized) carbon atoms bonded to just three neighboring coplanar atoms, creating a hexagonal tiling of the surface of each sheet. In graphite, each carbon atom contributes an additional delocalized electron, which is the source of the material's electrical conduction properties,...