Associative π−π Interactions of Condensed Aromatic Compounds with Vanadyl or Nickel Porphyrin Complexes Are Not Observed in the Organic Phase

Association of vanadium and nickel petroporphyrin compounds with aromatic groups is commonly invoked as an important mechanism for aggregation of asphaltenes. In this study, the interaction of vanadium and nickel octaethylporphyrin with condensed aromatic compounds and bridged aromatic compounds was investigated. Neither UV−vis nor fluorescence spectroscopy detect any interactions between porphyrins and aromatic ring groups in either the ground or excited states. The lack of detectable binding of these model compounds suggests that the association of the majority of the vanadium and nickel petroporphyrins in crude oils with the asphaltene fraction may be due to other functionality appended to the porphyrin ring, rather than favorable π−π stacking interactions of aromatic rings with the porphyrin core itself.