Pyridine vs N-Hydrogenated Pyridine Moieties: Theoretical Study of Stability and Spectroscopy of Nitrogen-Contained Heterocyclic Aromatic Compounds and Graphene Nanoflakes.

Nitrogen is one of the most common heteroatom appearing in heterocyclic aromatic compounds (HACs) as well as the frequently applied dopant in graphene nanoflakes/nanoribbons. The pyridine moiety is an intuitive and stable common feature of these compounds; but interestingly, using density functional theory calculations, we found that the N-hydrogenated pyridine moiety could be even more stable in large HACs and in N-doped graphene nanoflakes considering their formation reaction energies. The hydrogenation reaction of the pyridine moiety was calculated to be exothermic for models of four and more fused aromatic rings with specific substitutional positions of nitrogen. This theoretical investigation provides energetic and spectroscopic hints to the existence of the N-hydrogenated pyridine moiety under proper conditions.