No abstract

Studies of how hydrogen bonding can be used to control molecular association continue to yield exciting discoveries in supramolecular chemistry. A simple way to make molecules that associate predictably is to link carefully selected cores to functional groups that form multiple hydrogen bonds according to reliable patterns. Bifunctional molecules constructed according to this strategy can associate to form linear aggregates robust enough to warrant the name supramolecular polymers, even though the bifunctional monomers are joined only by hydrogen bonds. More complex molecules with multiple hydrogen-bonding sites can be devised so that neighbors are held in predetermined positions, giving crystalline solids with predictable architectures and properties not previously seen in other materials. Initial studies of the ability of such compounds to associate in solution and in the molten state suggest that hydrogen-bonded networks can be purposefully designed to create novel par- tially ordered liquid materials, including liquid crystals, gels, and fluids with unusual rheological properties.