Theoretical Study on Drum-Shaped Polymers (1,3,5-Triazine)₂ Composed of Nonplanar π-Extended Polymerization Units

A nonplanar extended π-system can be found not only in compounds formed by multiple ortho-fused benzenes, such as helicenes and corannulenes, but also in compounds formed by bonding of atoms on the large π-extended rings. (1,3,5-Triazine)₂ (n ≥ 3) are the latter type of compounds that are characterized by monomer units composed entirely of a 1,3,5-triazine core (general formula: C₃N₃). The first seven polymers (C₃N₃)₂ (n = 3-9) with a drum shape were investigated computationally. Analyses of natural bonding orbitals and atoms in molecules were applied to investigate the bonding properties. In contrast to the planar structure of the 1,3,5-triazine core, the monomer units in (C₃N₃)₂ (n = 3-9) are transformed from their planar π-system to a warped one. Similar to properties of the nonplanar π-system in [n]helicenes and corannulenes, the nonplanar heterocyclic aromatic configuration of the polymerization units is the determinant of the physical and chemical properties of these polymers. The discovery of nonplanar heterocyclic aromatic structures opens up a broad prospect for the study of azacyclic compounds. The results will be the supplement to the study of heterocyclic helicenes and corannulenes.