Nano meccano

Switchable catenanes and rotaxanes, as well as a class of self-complexing donor-acceptor cyclophanes, can generate molecular motions when appropriate redox conditions are applied, thus turning them into functional nanoscale machines for a range of different applications. The key to switching lies in the fact that the redox states of the molecular components determine the vast preference of one (co-)conformation over all others. The switching of these molecular machines has been investigated in considerable detail in solution using ¹HNMR and UV-visible spectroscopic methods, as well as by cyclic voltammetry and spectroelectrochemistry. Such machines have been demonstrated to switch in electronic devices, in the context of which molecular switch tunnel junctions and an 8 × 8 molecular memory have been constructed. The machines' abilities to generate induced molecular motions in closely packed Langmuir-Blodgett films have been established under redox conditions. Mechanical devices have been constructed from these molecular machines by attachment to the surfaces of different substrates. In one example, switchable tikya[2]rotaxanes have been shown to function as molecular valves for regulating the release of guest molecules embedded in porous silica materials. In another example, specially designed molecular machines function as biomimetic molecular muscles that are capable of bending an array of microscopic cantilever beams up and down under redox control. Such examples suggest that their cooperative ability to generate nanoscale mechanical motions when married with different substrates means that molecular machines can be utilized to move objects around across length scales that reach up to, and possibly into, the world of their macroscopic counterparts.