``The Effect of Multiple Substituents on Sandwich and T-Shaped Pi-Pi Interactions,'' A. L. Ringer, M. O. Sinnokrot, R. P. Lively, and C. D. Sherrill, Chem. Eur. J. 12, 3821-3828 (2006).

Sandwich and T-shaped configurations of substituted benzene dimers were studied by second-order perturbation theory to determine how substituents tune pi-pi interactions. Remarkably, multiple substituents have an additive effect on the binding energy of sandwich dimers, except in some cases when substituents are aligned on top of each other. The energetics of substited T-shaped configurations are more complex, but nevertheless a simple model that accounts for electrostatic and dispersion interactions (and direct contacts between substituents on one ring and hydrogen atoms on the other), provides a good match to the quantum mechanical results. These results provide insight into the manner by which substituents can be utilized in supramolecular design.