Unifying Principles of the Reductive Covalent Graphene Functionalization

Covalently functionalized graphene derivatives were synthesized via benchmark reductive routes using graphite intercalation compounds (GICs), in particular KC₈. We have compared the graphene arylation and alkylation of the GIC using 4-<i>tert</i>-butylphenyldiazonium and bis­(4-(<i>tert</i>-butyl)­phenyl)­iodonium salts, as well as phenyl iodide, <i>n</i>-hexyl iodide, and <i>n</i>-dodecyl iodide, as electrophiles in model reactions. We have put a particular focus on the evaluation of the degree of addition and the bulk functionalization homogeneity (<i>H</i>_bulk). For this purpose, we have employed statistical Raman spectroscopy (SRS), and a forefront characterization tool using thermogravimetric analysis coupled with FT-IR, gas chromatography, and mass spectrometry (TGA/FT-IR/GC/MS). The present study unambiguously shows that the graphene functionalization using alkyl iodides leads to the best results, in terms of both the degree of addition and the <i>H</i>_bulk. Moreover, we have identified the reversible character of the covalent addition chemistry, even at temperatures below 200 °C. The thermally induced addend cleavage proceeds homolytically, which allows for the detection of dimeric cleavage products by TGA/FT-IR/GC/MS. This dimerization points to a certain degree of regioselectivity, leading to a low sheet homogeneity (<i>H</i>_sheet). Finally, we developed this concept by performing the reductive alkylation reaction in monolayer CVD graphene films. This work provides important insights into the understanding of basic principles of reductive graphene functionalization and will serve as a guide in the design of new graphene functionalization concepts