Understanding of Assembly Phenomena by Aromatic−Aromatic Interactions:  Benzene Dimer and the Substituted Systems

Abstract

Interactions involving aromatic rings are important in molecular/biomolecular assembly and engineering. As a consequence, there have been a number of investigations on dimers involving benzene or other substituted pi systems. In this Feature Article, we examine the relevance of the magnitudes of their attractive and repulsive interaction energy components in governing the geometries of several pi-pi systems. The geometries and the associated binding energies were evaluated at the complete basis set (CBS) limit of coupled cluster theory with singles, doubles, and perturbative triples excitations [CCSD(T)] using a least biased scheme for the given data set. The results for the benzene dimer indicate that the floppy T-shaped structure (center-to-center distance: 4.96 A, with an axial benzene off-centered above the facial benzene) is isoenergetic in zero-point-energy (ZPE) corrected binding energy (D0) to the displaced-stacked structure (vertical interplanar distance: 3.54 A). However, the T-shaped structure is likely to be slightly more stable (D0 approximately equal to 2.4-2.5 kcal/mol) if quadruple excitations are included in the coupled cluster calculations. The presence of substituents on the aromatic ring, irrespective of their electron withdrawing or donating nature, leads to an increase in the binding energy, and the displaced-stacked conformations are more stabilized than the T-shaped conformers. This explains the wide prevalence of displaced stacked structures in organic crystals. Despite that the dispersion energy is dominating, the substituent as well as the conformational effects are correlated to the electrostatic interaction. This electrostatic origin implies that the substituent effect would be reduced in polar solution, but important in apolar media, in particular, for assembling processes.

Nanorings and rods interconnected by self-assembly mimicking an artificial network of neurons

“…However, ketimine-based Schiff base ligands and complexes present more advantages compared with their aldimine counterparts and represent ideal building units from a stability and chemical point of view 30,31 . Their chemical structure allows for an easy modulation of their molecular symmetry, shape, flexibility, aromaticity and charge distributions, which, upon combination, have a crucial role in programmable selfassembly and thus configurable 2D and three-dimensional (3D) geometries [32][33][34] . Additionally, their intermolecular interactions can be also modified by using solvents with different dielectric constants, whereas their electrochemical and magnetic properties can be easily modified by incorporating different metal centres in the Schiff base structures.…”

Communication: Benzene dimer—The free energy landscape

“…22 Recent studies where the stabilization energies were determined at the CCSD(T) (coupled cluster theory with singles, doubles, and perturbative triples excitations)/complete basis set (CBS) level or the DFTSAPT/ CBS level have convincingly shown that both structures are practically isoenergetic. [23][24][25][26][27] Computations also indicate that the energy barriers separating the T-shape and parallel displaced structure are very low (0.1 kcal/mol) suggesting that a dynamically averaged structure would be a more apt description especially for interpreting experimental results performed at nonzero temperatures where, in addition to the enthalpy term, entropy becomes important. In such situations it is the free energy landscape rather than the potential energy surface that provides a better description and it is, therefore, unlikely that single-point calculations even at the highest level of theory would be able to adequately reproduce experimental results.…”

Communication: Competition between π⋯π interaction and halogen bond in solution: A combined 13C NMR and density functional theory study

“…The hydrogen bond is probably the most important noncovalent bond. 1,2 Other important noncovalent driving forces for supramolecular assembly include π · · ·π stacking interaction, [3][4][5][6][7][8][9][10][11][12][13] halogen bond, [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] etc. Noncovalent bonds are much weaker than the covalent bonds.…”