Functional Supramolecular Systems Controlled by Light

Molecules can be used as building blocks for the assembly of multicomponent (supramolecular) structures exhibiting novel and complex functions that derive from the cooperation of simpler functions performed by each component. These systems, if suitably designed, behave as devices and machines of nanometric size. In analogy to their macroscopic counterparts, molecular devices and machines need energy to operate and signal to communicate with the operator. Light provides an answer to this dual requirement: photons are indeed both quanta of energy and elements of information (by means of the spectroscopic techniques). In this chapter we describe a few recent examples developed in our laboratory with the aim to show that, in the frame of research on supramolecular photochemistry, the design and construction of nanoscale devices and machines capable of performing useful light-induced functions can indeed be attempted. They are (a) molecular machines capable of undergoing light-controlled unidirectional linear movements, (b) dendrimers in which predetermined energy transfer processes occur, (c) quantum dots that behave as luminescent chemosensors, and (d) assemblies of molecules that upon light inputs and/or outputs can perform logic functions. These systems represent some small, although interesting, advancements in exploiting the peculiar properties of light and its interaction with matter to obtain useful functions.