Understanding of assembly phenomena by aromatic-aromatic interactions: benzene dimer and the substituted systems.
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.
Lee
Eun Cheol
EC
Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology, San 31, Hyojadong, Namgu, Pohang 790-784, Korea.
Kim
Dongwook
D
Jurecka
Petr
P
Tarakeshwar
P
P
Hobza
Pavel
P
Kim
Kwang S
KS
D001554:Benzene / Q000737:chemistry*; D001555:Benzene Derivatives / Q000737:chemistry*; D019281:Dimerization; D008433:Mathematics; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning; D008956:Models, Chemical; D008958:Models, Molecular; D037742:Nanotubes, Carbon / Q000737:chemistry / Q000648:ultrastructure; D013816:Thermodynamics
D001555:Benzene Derivatives; D037742:Nanotubes, Carbon; D001554:Benzene