ABSTRACT
The concept of a macroscopic device and machine 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 position as a result of some external stimuli. In agreement with the definition of devices and machines of the macroscopic world, a molecular device is an assembly of a discrete number of molecular components designed to achieve a specific function. The operation time scale of molecular devices can range from less than picoseconds to seconds, depending on the type of rearrangement and the nature of the components involved. An important function at the molecular level is photoinduced energy- and electron-transfer over long distances and/or along predetermined directions.
