Microelectrode Voltammetry and Electron Transport in an Undiluted Room Temperature Melt of an Oligo(ethylene glycol)-Tailed Viologen

Abstract

This paper describes the synthesis, characterization, and voltammetry of a oligo(ethylene glycol) trimer derivative of 4,4‘-bipyridine, [N,N‘-(CH3(OCH2CH2)3)2-4,4‘-bipyridine][BF4]2 [V[E3M]2](BF4)2]. This “tailed” viologen is a room temperature molten salt. Its fast atom bombardment mass spectrum exhibits interesting aspects of cationation. Microelectrode voltammetry in the undiluted viologen melt shows the expected pair of reduction waves, but currents for the wave for the [V[E3M]2]2+/1+ are smaller than those for the [V[E3M]2]1+/0 couple. Analysis of the voltammetric behavior leads to the conclusion that the difference in currents arises from coupling of [V[E3M]2]1+/0 homogeneous electron exchanges to the physical diffusion of viologen species in the mixed-valent diffusion layer at the electrode interface. The physical diffusivity of the [V[E3M]2]2+ species, DPHYS, is much smaller than electron diffusivity through electron self-exchanges of the [V[E3M]2]1+/0 couple. kEX,1/0 is ∼106 M-1 s-1, or at least ...