Anion-controlled redox process in a cross-linked polyviologen film toward electrochemical anion recognition

The highly selective recognition of halide ions by a cross-linked polyviolo gen film was demonstrated electrochemically. The film was prepared on an el ectrode by electropolymerization of a branched monomer with three polymeriz able groups, 1,3,5-tris(4'-cyanopyridinio-l'-methyl)-2,4,6-trimethylbenzene tribromide, to form a highly cross-linked polyviologen, through successive reductive coupling of the cyanopyridinium moieties. The highly cross-linke d structure is built up by the formed viologen skeleton, incorporating the electrolyte anion used as the template to fabricate a kind of cavity struct ure complementary in size to the electrolyte anion, called anion-imprinted electropolymerization. The resulting cross-linked polyviologen film exhibit s highly selective anion recognition in the redox process. The anion-contro lled redox process was investigated quantitatively by multilateral analyses with cyclic voltammetry, potential-step chronoamperometry, and electrochem ical quartz crystal microbalance measurement coupled with visible absorptio n spectrophotometry. A highly selective size exclusion effect by the cavity structure fabricated in the anion-imprinted electropolymerization was demo nstrated in the redox process of the viologen moiety in different kinds of aqueous electrolytic solutions. From the systematic study of the anion size recognition using a series of halide ions, not only the precisely fabricat ed cavity structure but also the anion diffusion dynamics in the cavities s uccessfully running are suggested.