network by direct C[double bond, length as m-dash]C bond opening. Commonly efficient functionalization methods were unsuccessful to functionalize astralenes while radicals generated from arylhydrazine could lead to functionalization of the outer surface of astralenes. The occurrence of functionalization could be shown by TGA coupled with MS and XPS. The reported method represents the first example of functionalization of astralenes. The efficiency of the applied functionalization methods is discussed considering the chemical reactivity of different carbon nanomaterials including graphene and carbon nanotubes.