From Solid-State Structures and Superstructures to Self-Assembly Processes

An empirically-driven approach to the design and synthesis of highly ordered molecular assemblies and supramolecular arrays is described. In general, the approach is dependent upon a very close interplay between X-ray crystallography and synthetic chemistry. In particular, the approach is dependent upon π-π stacking interactions between π-donors, such as hydroquinone rings and 1,5-dioxynaphthalene residues, incorporated into both acyclic (e.g., 1,4-dimethoxybenzene) and macrocyclic (e.g., bisparaphenylene-34-crown-10 and 1,5-dinaphtho-38-crown-10) polyethers, and the π-accepting bipyridinium ring system, present either singly, as in the simple paraquat dication, or, as a pair in tetracationic cyclophanes, such as cyclobis-(paraquat-p-phenylene), cyclobis(paraquat-m-phenylene), and cyclobis(paraquat-4,4′-biphenylene). The molecular recognition associated with the π-π stacking interactions is augmented in the structures and superstructures by hydrogen bonding and other electrostatic interactions. The systems employed for the development of the concept of self-assembly in chemical synthesis have been mechanically-interlocked structures (e.g., catenanes) and mechanically-intertwined superstructures (e.g., pseudorotaxanes). The manner in which such intellectually-appealing molecules and supermolecules can contribute to an understanding of noncovalent bonding at both the structural and superstructural levels, during and after self-assembly processes, is described by reference to numerous solid-state structures and superstructures.