Unraveling the Origin of Substituents Effects in π-Stacking Interactions

Abstract

Non-covalent interactions involving aromatic rings, which include π-stacking, anion-π, and cation-π interactions, among others, are central to modern chemical research. These interactions play vital roles in everything from protein-DNA interactions and the properties of organic electronic materials to stereoselective organocatalyzed reactions. We discuss recent efforts to understand the impact of substituents on the strength of π-stacking interactions through the application of modern tools of computational quantum chemistry. We first provide an account of previous efforts to develop qualitative physical models of these interactions, followed by apparent flaws in these previous models. We then present our local, direct interaction model of substituent effects in π-stacking interactions, and discuss recent extensions of this model based on the examination of electric fields of arenes. We also discuss related misconceptions regarding molecular electrostatic potentials (ESPs), and offer a simpler view of the origin of ESP differences arising from the incorporation of heteroatoms or substituents into aromatic rings. Finally, we conclude with an outlook for future advances in our understanding of π-stacking interactions.