Superstructured Porphyrins as Effectors in Dynamic Supramolecular Assemblies: Receptors, Rotaxanes and Catenanes

The development of porphyrinic systems specifically functionalised to recognise photoactive and electroactive substrates has been a study in the evolution of supramolecular assemblies, from receptors, through pseudorotaxanes to catenanes, to thermodynamically-controlled synthesis, and eventually to solid-appended self-assembling supermolecules. We describe how crown ether-capped porphyrins act as efficient receptors for bipyridinium dications, where the complexes have an in-built addressability through the porphyrin, and are monitored through physical and chemical stimuli. Conceptual extension allows production of porphyrin[2]- and -[3]-catenanes, and a series of these offers opportunities for a structure-activity profile through a variety of dynamic processes, including motional, translational, chemical (acid/base), photochemical and electrochemical methods. Related design concepts extend the study into neutrally-charged diimide-based catenanes. The recognition processes responsible for their synthesis have then been extended into equilibrating conditions, so that the thermodynamically most favourable rotaxanes can be assembled by simple mixing of components. Finally, these concepts have led to the direct real-time study by gel-phase HRMAS methodology of the self-assembly of porphyrin rotaxanes on polymer supports, under equilibrating conditions between solid and solution phases.