Light-powered molecular devices and machines.

One century ago Giacomo Ciamician predicted that photochemistry would have had a wealth of useful applications, starting from the conversion of solar energy into fuels. Most of Ciamician's predictions have not yet been achieved, but in the last decade outstanding progress concerning the interaction between light and molecules has led to the creation of artificial photochemical molecular devices and machines capable of using light as an energy supply (to sustain energy-expensive functions) or as an input signal (to be processed and/or stored). This paper illustrates (i) the principles of photochemical molecular devices for information processing, with a few examples of memories, logic functions, and encoding/decoding systems; (ii) the operational mechanisms of light-powered molecular machines, with some examples of rotary motors, shuttles, valves, and switchable boxes; and (iii) the recent progress made in the design and construction of the components of artificial photosynthetic systems. The use of photons to convert abundant low energy molecules into high energy valuable compounds, and to read, write, and erase smart molecular and supramolecular systems for information processing is likely to play a fundamental role for the progress of mankind.