Active-template synthesis of small functionalised rotaxanes for sensing applications

Interlocked molecules, the archetypal examples of which are catenanes, and rotaxanes, have progressed over the last half-century from a significant synthetic challenge to readily accessible chemical species. The interest for these supramolecular architectures, which started from a purely aesthetic point of view, has further developed due to the high degree of freedom between its individual components. Controlling this motion via chemical or physical stimuli has resulted in the development of many stimuli-responsive interlocked systems with applications in wide range of field such as switches, molecular machinery and sensing. The latter is of particular interest as the mechanical bond within a catenane or rotaxane molecule creates a well-defined three-dimensional environment that can be readily functionalised to accommodate a variety of guest molecules. This thesis presents an investigation into the design and synthesis of novel functional rotaxane receptors and their application in the sensing of metal ions, anions and small chiral molecules. The introductory chapter presents the active template approach to interlocked molecules. It highlights its key advantages and outline recent advances that have been made using this methodology. The following three chapters focus on the study of rotaxane receptors synthesised using this approach. Chapter two reports the synthesis of a sulfur-functionalised rotaxane and the investigation of its selective response for Zn2+ ion over other transition metal cations. Chapter three on the other hand focuses on a urea-based rotaxane that binds ion-pairs. This section will introduce preliminary results obtained with a simple model rotaxane before presenting its evolution into a stimuli-responsive receptor. The binding behaviour of both the rotaxane and related non-interlocked axle will be investigated to demonstrate the impact of the mechanical bond on the properties of the receptor. In the fourth chapter, the project was expanded toward chirality and more specifically enantioselective sensing. The development of a novel synthetic route to access functionalised mechanically planar chiral rotaxanes will be presented and it will conclude on preliminary binding studies of simple chiral anionic guest that shows enantioselectivity.