Analyzing the Energetics of the Four Aromatic Ring Interactions: Theoretical Study

Despite the growing significance of noncovalent interactions in modern chemical studies, a comprehensive conception of fundamental noncovalent interactions remains elusive. The field still lacks a thorough understanding of these prototype interactions. Specifically, the nature of π-π and C-H···π interactions is not fully understood. These interactions are prevalent in biological systems, supramolecular chemistry, physics, and material science. Many aspects remain unclear, including their intensity, geometric dependencies, energetics, interactions, effects of substituents, and underlying physical principles. The dimers of four Fused Aromatic Rings (4FARs), Benz[<i>a</i>]anthracene (BA), Chrysene (Chy), Tetracene (Tet), and Triphenylene (Tri), have been investigated using Interaction Energy (IE), Stabilization Energy (E_<i>SAPT</i>), frontier orbital gaps, and aromaticity indices (FLU, PDI, HOMA, and PLR). Additionally, real-space analyses (QTAIM and NCI) and crystal-topology descriptors (Hirshfeld surfaces and 2D fingerprints) are employed. These methods facilitate the study of stability, energy, and strength of noncovalent interactions as well as the preferred structure of dimer arrangements. Theoretical computations of these homodimer complexes indicate a weak correlation between the interaction and stabilization energies, as well as results from the HOMO-LUMO energy gap and Clar π sextet rule. However, aromaticity, QTAIM, NCI, and Hirshfeld analyses were employed to investigate intermolecular interactions, yielding an agreement with the interaction and stabilization energies. These theoretical methods agree on conformers; therefore, cross-conformers are more stable than face conformers. In terms of 4FAR homodimer configurations, the Tet conformer with a linear geometry is the most stable. However, the Tri conformer with a compact geometry is the lowest stable. The 4FAR homodimer complexes are stabilized by the dominant π-π stacking, which is the critical point.