Substituent effects in parallel-displaced π–π interactions

Abstract

High-quality quantum-mechanical methods are used to examine how substituents tune pi-pi interactions between monosubstituted benzene dimers in parallel-displaced geometries. The present study focuses on the effect of the substituent across entire potential energy curves. Substituent effects are examined in terms of the fundamental components of the interaction (electrostatics, exchange-repulsion, dispersion and induction) through the use of symmetry-adapted perturbation theory. Both second-order Møller-Plesset perturbation theory (MP2) with a truncated aug-cc-pVDZ' basis and spin-component-scaled MP2 (SCS-MP2) with the aug-cc-pVTZ basis are found to mimic closely estimates of coupled-cluster with perturbative triples [CCSD(T)] in an aug-cc-pVTZ basis. Substituents can have a significant effect on the electronic structure of the pi cloud of an aromatic ring, leading to marked changes in the pi-pi interaction. Moreover, there can also be significant direct interactions between a substituent on one ring and the pi-cloud of the other ring.

Noncovalent Interactions and Impact of Charge Penetration Effects in Linear Oligoacene Dimers and Single Crystals

“…Dispersion dominates the interaction energy at separations greater than 4.5 Å for co-facial arrangements and greater than 4.0 Å for T-shaped dimers; at even larger separations (i.e., greater 15 than ~7 Å), the electrostatics again take over due to the 5 1 R distance dependence of the quadrupole-quadrupole interactions compared to the approximately 6 1 R distance dependence of dispersion. The slower fall-off of the dispersion for co-facial dimers may be attributed to the large interaction of the π-clouds, and while exchange and charge penetration also depend on π-cloud interactions, their contribution falls off exponentially as distance increases, i.e., much faster than dispersion, which evolves as a power series in the form 1…”

“…[4][5][6][7][8] Recently, additional effects due to charge penetration -the electron-nucleus attraction due to the reduced screening of the nuclei of one monomer by its electrons as the electron clouds of two monomers overlap -have been shown to be significant at typical intermolecular separations in organic crystals. [9][10][11][12][13][14][15] In fact, without the inclusion of explicit charge penetration, 16 force fields using atom-centered charge models and semi-empirical models where only electrostatic interactions are considered for the 4 environment of a given subsystem, are of limited use to describe the complex interactions in noncovalently bound systems, especially for non-polar materials.…”

“…4,[17][18][19][20][21] In attempts to understand the packing behavior of oligoacenes in the solid state, a number of investigations have explored the nature and strength of the non-covalent interactions. 6,8,[22][23][24][25][26][27][28][29][30][31][32][33][34] These investigations generally have focused on a few representative dimer configurations (see Figure 1), in particular the cofacial (eclipsed or parallel-displaced) and T-shaped configurations, or only on the separation distance between dimers, though a few studies have also explored broader potential energy surfaces for oligoacene interactions as a function of the oligoacene length. [33][34] This issue is of interest since the crystalline packings change with oligoacene length, which is indicative of modifications in the non-covalent interactions.…”

Functional molecules and materials by π‐Interaction based quantum theoretical design

“…Consequently, most of reported findings in sandwich dimers would be applicable in parallel-displaced ones. [39,40] The benzene and perfluorobenzene have quadrupole moments with same magnitude and opposite sign. [41] Therefore, perfluorinated p-p dimers should have different characters compared with the nonfluorinated case as found experimentally.…”

Energetic factors determining the binding of type I inhibitors to c-Met kinase: experimental studies and quantum mechanical calculations

“…As a consequence of the Hunter-Sander model, an electron-deficit π system would show favorable interactions with an electronrich or benzene π system. This model was disputed by Sherrill and co-workers, as they found that both electron-donating substituents and electron-withdrawing substituents stabilize the benzene sandwich dimer [32][33][34][35] . The studies conducted by Sherrill et al led them to conclude that differential dispersion effects can dominate substituent effects in π-π stacking as well.…”