Carbon Nanotubes and Graphene Promote Pyrolysis of Free-Base Phthalocyanine

Unsubstituted phthalocyanines (including free-base H₂Pc and many of its metal complexes) are among the most stable organic compounds. They can sublime without decomposition under reduced pressure and temperatures of up to 550 °C. This property was previously employed to design a novel approach to noncovalent functionalization of pristine single-walled carbon nanotubes (SWNTs) with 3d metal(II) phthalocyanine complexes. However, when we attempted to use the same sublimation protocol to prepare a SWNTs-H₂Pc hybrid, an unexpected side effect of partial H₂Pc pyrolysis was detected, phthalonitrile being a main decomposition product, under the conditions when H₂Pc is supposed to be totally stable. By using density functional theory calculations, we offer an explanation for the thermal behavior of H₂Pc based on its covalent attachment to the pentagonal-ring topological defects, which are very common in all graphene-derived carbon nanomaterials and capable of reacting with amines via nucleophilic addition process.