Solvent effects on the redox-dependent binding properties of a viologen-based receptor for neutral organic molecules

Abstract

Cyclic voltammetry of a viologen-based cyclophane receptor, VH, in water, 10% acetonitrile/water, and acetonitrile is described. Minimal electrolyte was necessary in order to prevent precipitation of the reduced VH in aqueous solutions. Shifts in the half-wave potential of the first viologen reduction are observed in the presence of various substituted benzenes. The direction and magnitude of the shifts are explained in terms of two competing factors : (i) the change in the electron donor-acceptor character of the host that occurs upon reduction and (ii) the change in the hydrophobic/hydrophilic character of the host upon reduction. The first factor promotes binding of acceptor-substituted guests to the reduced host and donorsubstituted guests to the oxidized host The second factor promotes binding of all the guests to the reduced host in aqueous solution. Large potential shifts are observed when both factors work in the same direction