Electrochemistry of redox active centres encapsulated by non-covalent methods

This manuscript presents a summary of recent research work on the electrochemical behaviour of redox active guests fully or almost fully encapsulated by suitable molecular receptors or molecular capsules. From the standpoint of their voltammetric behaviour the cyclodextrins have been shown to be very dynamic hosts, which hamper the observation of direct electron transfer to/from their inclusion complexes. Therefore, this Review is essentially concerned with research work on cucurbituril and cavitand-type hosts, which was mostly done in the author's laboratory. In general terms, the observed voltammetric behaviour for encapsulated guests covers a wide range of possibilities. Cucurbituril and cavitand-type hosts afford more kinetically stable complexes, whose direct electrochemical behaviour is observable and tends to be kinetically slower than that of the free guests. However, the degree of kinetic attenuation varies over a wide range and, in some cases, challenges our ability to rationalize the data. Clearly, more variation in the host structures and more research work are required to improve our understanding of encapsulation effects on these electron transfer reactions.