Reactivity of Polycyclic Aromatic Hydrocarbon Soot Precursors: Implications of Localized π-Radicals on Rim-Based Pentagonal Rings

This paper presents a systematic study of the reactivity of polycyclic aromatic hydrocarbons (PAH), identifying crosslinks that permit the combination of physical pi-stacking interactions and covalent bonding. Hybrid density functional theory was used to identify the location of reactive sites on PAHs using the average local ionization potential. The bond energies formed between these various reactive sites were then computed. sigma-Radicals were found to be the most reactive, forming bonds with other radicals and some reactive closed shell edge types. Partially saturated rim-based pentagonal rings were found to form localized pi-radicals with high reactivity. This site, in addition to resonantly stabilized pi-radicals, was found to be capable of bonding and stacking, which is explored for a variety of larger species. Localized pi-radicals on rim-based pentagonal rings, in particular, were found to form strongly bound stacked complexes, indicating a potentially important role in soot formation.