Quantification
of the formation of molecular complexes between
simple organic aromatic molecules is straightforward for pure components
of definite composition; however, it becomes challenging when the
interacting species are complex, intractable mixtures of thousands
of polycyclic aromatic hydrocarbons (PAHs). Using the example of asphaltenes,
a complex mixture of oil-derived PAHs, we demonstrate the potential
of fluorescence spectroscopy for quantification of molecular processes
that are at the core of their aggregation. It is found that small
electron-deficient aromatic additives, especially surfactant-like
additives with electron-withdrawing functional groups, interact strongly
with the PAHs and lead to the formation of molecular complexes. Computational
modeling revealed that as we increase the number of PAH molecules
in the cluster, cohesive π–π stacking interactions
between PAHs dominate in preference to adhesive hydrogen bonding or
π–π stacking interactions between the PAHs and
additives.
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