Light-powered molecular-scale machines

The macroscopic concepts of a machine can be extended to the molecular level. Molecular-level machines are constructed by the molecule-by-molecule bottom-up approach following the guidelines of supramolecular chemistry. Like macroscopic machines, molecular machines are characterized by (i) the kind of energy supplied to make them work, (ii) the kind of movement performed by their components, (iii) the way in which their operation can be controlled and monitored, (iv) the possibility to repeat the operation, (v) the time needed to complete a cycle of operation, and (vi) the function performed. The most convenient way to supply energy to a molecular machine is through photochemical energy inputs. Photochemical techniques offer, indeed, several advantages: (i) photons can make a machine work without formation of waste products, (ii) light can be switched on/off easily and rapidly, (iii) lasers provide the opportunity of working in very small space and very short time domains, (iv) photons can be used to "read" the state of the system and to monitor the operation of the machine. The extension of the concepts of a machine to the molecular level is of interest not only for basic research, but also for the growth of nanoscience and the development of nanotechnology.