Light‐Driven Molecular Machines

In the last 40 years, the opinion of most researchers has moved from considering artificial molecular machines as simple laboratory curiosities to viewing them as valuable tools to impart novel functionalities and properties to advanced materials and multicomponent systems. In this chapter, we present an overview of the progress on the design and realization of light-activated molecular machines and on their different applications. This research field has always been in close relationship with the study of photoswitchable and photochromic compounds. Indeed, it can be confidently said that at the heart of any light-activated nanomachine, a photoswitchable moiety is at work. After a brief description of the basic type of photoinduced processes that light-activated nanomachines exploit for their operation, a concise description of the main classes of nanomachines is presented. The chapter follows with examples in which the nanoscale motion of the machine is translated in an advanced functionality. These include switchable catalysts, linear and rotary transporters of small molecular cargos, and supramolecular pumps. Furthermore, examples in which the collective operation of an assembly of molecular machines is harnessed to perform tasks at the microscale and macroscale in hard and soft materials are also reviewed. In particular, functionalized surfaces, metal–organic frameworks, polymers, and self-assembled nanostructures are described wherein the nanoscale movement of embedded molecular machines is amplified, allowing the realization of muscle-like actuators, microfluidic devices, and polymeric materials for light energy transduction and storage.