Self-assembly in chemical synthesis

The use of molecular recognition to activate the occurrence of self-assembly has become an important principle in the template-directed syntheses of molecular assemblies and supramolecular arrays. In our early lock-and-key systems, we investigated, as the lock, crown ethers like bisparaphenylene-34-crown-10 and, as the key, the 4,4'-bipyridinium dication. Now, they have been transformed into 'permanent' inclusion complexes, via a post-assembly modification pathway, leading to a range of mechanically-interlocked molecules in the shape of the catenanes and rotaxanes. The knowledge and experience gained by carrying out self-assembly on these relatively simple systems in solution go a long way toward establishing the fundamental rules for the elaboration of larger polymolecular assemblies. By modifying the nature of the components that make up the molecular assemblies, we have been able to gain a fundamentally better understanding of the limitations and the opportunities available for controlling self-assembly in a structural, geometric, and electronic sense during chemical synthesis. This account deals mainly with a carefully chosen selection of different molecular components in which the principle recognition sites have been varied to provide an opportunity for a predetermined bias in the translational isomerism of the [2]catenanes and [2]rotaxanes. These systems, which have been produced recently at Birmingham, are helping toward achieving an understanding of the processes of formation of, and the dynamics associated with, the mechanically-interlocked molecular compounds.