Competitive binding for triggering a fluorescence response in a hydrazodicarboxamide-based [2]rotaxane

The design and synthesis of an interlocked receptor based on a hydrogen bonded [2]rotaxane containing a hydrazodicarboxamide binding site are reported. An anion recognition process with tetrabutylammonium benzoate triggers the submolecular translational movement of its benzylic amide macrocycle developing a progressive increase of the fluorescence intensity, effectively quenched at the original state. The binding of the anion competes with the hydrogen-bond-connected cyclic component for the bis(urea)-based station pushing it towards a stoppered alkyl chain. Moreover, this interlocked system is able to work as a molecular switch restoring its initial state in two ways, either by an ion exchange reaction or by a high yielding oxidation/reduction sequence.