Solvent Effects in Supramolecular Chemistry: Linear Free Energy Relationships for Common Intermolecular Interactions

The proper choice of solvent is of major importance for all studies in supramolecular chemistry, including molecular recognition in host-guest systems, intramolecular folding, self-assembly, and supramolecular polymerization. In this Perspective, the usefulness of linear free energy relationships (LFERs) is highlighted to unravel the effect of solvents on coordinate bonding (e.g., cation-crown ether), hydrogen bonding, halogen bonding, dipolar aggregation, and π-π-stacking. For all of these intermolecular interactions widely applied in supramolecular systems, LFER relationships between the Gibbs binding energies and common solvent polarity scales including E_T(30), π*, α or β based on solvatochromic dyes, scales derived from binding processes such as Gutmann donor and acceptor numbers or hydrogen bond donor and acceptor scales, or physical functions like the Kirkwood-Onsager or the Liptay-Onsager functions could be demonstrated. These relationships can now be applied toward a better understanding of the prevailing intermolecular forces for supramolecular interactions. They further enable a rational selection of the most suitable solvent for the preparation of self-assembled materials and the estimation of binding constants without the need for time-consuming comprehensive investigations of solvents.