Supramolecular chemistry is intrinsically a dynamic chemistry in view of the lability of the interactions connecting the molecular components of a supramolecular entity and the resulting ability of supramolecular species to exchange their components. Similarly, molecular chemistry becomes a dynamic covalent chemistry on introduction into the molecular entity of covalent bonds that may form and break reversibly, so as to allow for a continuous change in constitution by reorganization and exchange of building blocks. Taken together, these features define a Constitutional Dynamic Chemistry (CDC) covering both the molecular and supramolecular levels. CDC takes advantage of dynamic diversity to allow variation and selection and operates on dynamic constitutional diversity in response to either internal or external factors thus leading to an adaptive chemistry.
The field of artificial molecular machines has experienced a spectacular development, in relation to molecular devices at the nanometric level or as mimics of biological motors. In biology, motor proteins are of utmost importance in a large variety of processes essential to life (ATP synthase, a rotary motor, or the myosin-actin complex of striated muscles behaving as a linear motor responsible for contraction or elongation). Many examples published by many highly creative research groups are based on complex rotaxanes or catenanes acting as switchable systems or molecular machines. Particularly significant examples include “molecular shuttles” (Stoddart and others) as well as multi-rotaxanes reminiscent of muscles, able to contract or elongate under the action of a chemical signal. The molecules are set in motion using electrochemical, photonic or chemical signals. Particularly impressive light-driven rotary motors have been created by the team of Ben Feringa.