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)2n
(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)2n
(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)2n
(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.