ELECTROCHEMICAL CHARACTERIZATION OF A VIOLOGEN-BASED REDOX-DEPENDENT RECEPTOR FOR NEUTRAL ORGANIC-MOLECULES

Cyclic voltammetry of the viologen-based cyclophane host (1) in acetonitrile by itself and in the presence of various para-substituted benzenes is described. Changes in peak separation and shifts in half-wave potentials of the viologen reduction waves are observed in the presence of excess benzene derivative. This behavior is shown to be due to preferential binding of the benzene guests in one oxidation state of 1. The oxidation state preferred depends on guest structure and can be predicted on the basis of donor-acceptor considerations and ion-dipole interactions. The strongest preference is observed with an ethoxy ether-substituted benzene that interacts strongly with positively charged sites on 1. Reduction of 1 leads to a >4000-fold decrease in binding strength with this guest. Further insight on the redox-dependent binding properties of 1 is gained from AM1 calculations on the host and host-guest complexes in the different oxidation states.