Mechanically Interlocked Systems: Photoactive Rotaxanes and Catenanes

The mechanical bond offers novel and intriguing opportunities to connect together molecular components and arrange them in space. Mechanically interlocked molecules (MIMs) such as rotaxanes and catenanes can indeed be designed to operate as molecular devices, that is, to accomplish function(s) that arise(s) from the cooperation of their molecular components. In this chapter we will deal with rotaxane- and catenane-based architectures characterized by two main features: (i) the presence of inorganic moieties in the molecular structure and (ii) the integration of photoactive units. Here we focus on metal complexes as inorganic moieties, which can play the dual role of scaffolds for the construction of the molecules and for controlling the spatial arrangement of the components, and of functional units, because they present peculiar photophysical and electrochemical properties. The use of light to operate molecular devices and machines has long been acknowledged as a most valuable choice under several aspects. In this regard, for the sake of clarity, we have classified the selected examples in two main categories: photoactive systems, which are characterized by photoinduced processes within the components of the interlocked architecture, and photoactivated systems, wherein light is used to cause a mechanical rearrangement of the components. The examples discussed will show how the union of the structural control offered by the mechanical bond with the tools of inorganic chemistry can lead to the realization of complex structures with sophisticated functions.