Devices and machines at the molecular Level

The concept of (macroscopic) device can be extended to the molecular level. A molecular-level device can be defined as an assembly of a discrete number of molecular components designed to achieve a specific function. A molecular-level machine is a particular type of molecular-level device in which the component parts can display changes in their relative positions as a result of some external stimulus. The extension of the concept of a device to the molecular level is of interest not only for basic research, but also for the growth of nanoscience and the development of nanotechnotogy. A few examples of molecular-level devices and machines are illustrated.