Self-assembly in chemical systems

The development of a simple approach to studying self-assembly processes in the chemical laboratory began with an investigation of the donor/acceptor complexes formed between (a) crown ethers, like bisparaphenylene-34-crown-10, and 4,4′-bipyridinium dicalions, such as paraquat, and (b) tetracationic cyclophanes, like cyclobis(paraquat-p-phenylene). and neutral substrates, such as 1,4-dimethoxybenzene. Numerous template-directed syntheses that rely upon the post-assembly modification of the precursors, which lead to the tetracationic cyclophanes with their π-electron deficient components in the presence of macrocyclic or acyclic polyethers containing π-electron rich components, have afforded a wide range of catenanes and rotaxanes in recent years. By modifying the nature of the molecular recognition components, both sterically and electronically, it is possible to control the efficiency of the self-assembly process and also the proportions of the isomeric compounds present at equilibrium. This article gives a brief overview of some of the key molecular assemblies that have been constructed, as a result of an empirically-driven research programme, around interlocked molecules in which the components have been carefully selected to interact strongly and selectively with each other.