How important are dispersion interactions to the strength of aromatic stacking interactions in solution?† †Electronic supplementary information (ESI) available: Experimental details; X-ray and 1H/13C NMR data; details of substituent effect analyses and solvent studies. CCDC 1058828-1058830. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5sc01370d

In this study, the contributions of London dispersion forces to the strength of aromatic stacking interactions in solution were experimentally assessed using a small molecule model system. A series of molecular torsion balances were designed to measure an intramolecular stacking interaction via a conformational equilibrium. To probe the importance of the dispersion term, the size and polarizability of one of the aromatic surfaces were systematically increased (benzene, naphthalene, phenanthrene, biphenyl, diphenylethene, and diphenylacetylene). After correcting for solvophobic, linker, and electrostatic substituent effects, the variations due to polarizability were found to be an order of magnitude smaller in solution than in comparison to analogous computational studies in vacuo. These results suggest that in solution the dispersion term is a small component of the aromatic stacking interaction in contrast to their dominant role in vacuo.