Carbon Nanotubes and Graphene Promote Pyrolysis of Free-Base Phthalocyanine.

Unsubstituted phthalocyanines (including free-base HPc 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-HPc hybrid, an unexpected side effect of partial HPc pyrolysis was detected, phthalonitrile being a main decomposition product, under the conditions when HPc is supposed to be totally stable. By using density functional theory calculations, we offer an explanation for the thermal behavior of HPc 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.