One of our primary aims is to understand how substituents can be used to tune the strength of non-covalent interactions. To this end, we have developed simple, qualitative models of substituent effects in general π-stacking interactions and prototypical cation/π and anion/π complexes. These models deviate significantly from prevailing ideas in the literature, but are beginning to gain traction among experimental and computational chemists. The prevailing model of substituent effects in π-stacking interactions hinges on the polarization of the aromatic π-system by the substituents. This has been used for decades to explain why electron-withdrawing substituents enhance π-stacking interactions while electron-donors hinder π-stacking.

We have developed an alternative model in which substituent effects arise solely from direct interactions between the substituents and the nearest vertex of the unsubstituted ring. Although this local, direct interaction model provides similar predictions to popular π-polarization models for simple monosubstituted benzene dimers, for more complex systems, including heteroaromatic dimers and polysubstituted systems, our model provides clear predictions that are in much better agreement with robust computational results.

Much of our current efforts are focused on applying what we've learned about π-stacking and other non-covalent interactions to more complicated systems in organocatalysis, organic electronic materials, and biological systems.