CONTROLLING SELF-ASSEMBLY

As a result of cooperative noncovalent bonding interactions (namely, p i-pi stacking, [CH ... O] hydrogen bonding, and [CH ...pi] interaction s) supramolecular complexes and mechanically interlocked molecular com pounds-in particular pseudorotaxanes (precatenanes) and catenanes-self -assemble spontaneously from appropriate complementary components unde r thermodynamic and kinetic control, respectively. The stereoelectroni c information imprinted in the components is crucial in controlling th e extent of the formation of the complexes and compounds in the first place; moreover, it has a very significant influence on the relative o rientations and motions of the components. In other words, the noncova lent bonding interactions-that is, the driving forces responsible for the self-assembly processes-live on inside the final superstructures a nd structures, governing both their thermodynamic and kinetic behavior in solution. In an unsymmetrical [2]catenane, for example, changing t he constitutions of the aromatic rings or altering the nature of subst ituents attached to them can drive an equilibrium associated with tran slational isomerism in the direction of one of two or more possible is omers both in solution and in the solid state. Generally speaking, the slower the components in mechanically interlocked compounds like cate nanes and rotaxanes move with respect to each other, the easier it is for them to self-assemble.