Hydrogen-bonded synthetic molecular machines

This thesis reports on: 1) the development of two new methods to provoke the translation of the macrocycle along the thread (“shuttling”) in hydrogen bonded, fumaramide-based [2]rotaxanes and 2) the utilization of that movement to provoke a potentially useful response. The fumaramide template is perfectly preorganised to form four intercomponent hydrogen bonds with a benzylic amide macrocycle, affording [2]rotaxanes in “world record” yields. This preorganisation can be disrupted by photo-isomerisation (254 nm) of the E double bond to its Z counterpart. The newly formed maleamide template shows little affinity for the macrocycle. This has previously been exploited to synthesise a light and heat switchable molecular shuttles. A unique tristable molecular shuttle in which the macrocycle can be located in three different “stations” by means of thermal and photochemical stimuli is described in Chapter Two. In Chapter Three an alternative mechanism of shuttling for fumaramide-based molecular shuttles is reported. The reversibility of Diels-Alder chemistry is exploited to synthesise a chemically driven molecular shuttle. A chiral two-station [2]rotaxane in which translational motion of the macrocycle along the thread results in a profound change in its optical properties (CD spectrum) is described in Chapter Four. Finally, a light-switchable optically-addressable molecular shuttle is discussed. A [2]rotaxane with a thread containing a fluorophore and a macrocycle functionalised to quench its fluorescence was synthesised. Shuttling of the macrocycle along the thread switched the fluorescence “on” and “off”.