Electrochemical Characterization of Polyacetylene Ionomers and Polyelectrolyte-Mediated Electrochemistry toward Interfaces between Dissimilarly Doped Conjugated Polymers

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Abstract
The electrochemical characterization of thin films of the ionically functionalized polyacetylene analogues poly(tetramethylammonium 2-cyclooctatetraenylethanesulfonate) (PA) and poly[(2-cyclooctatetraenylethyl)trimethylammonium trifluoromethanesulfonate] (PC) is reported along with an electrochemical approach to the fabrication of interfaces between dissimilarly doped conjugated polymers. Such interfaces are of interest because of the central role analogous interfaces based on silicon play in conventional microelectronics. The cationically functionalized PC can be both oxidatively (p-type) and reductively (n-type) doped to a conductive state, whereas the anionically functionalized PA can only be p-type doped. The voltammetry of PC displays relatively sharp waves with minimal history or relaxation effects. In contrast, the voltammetry of PA exhibits broader doping waves and a dependence on electrochemical history. The apparent formal potentials reported in 0.075 M Me4NBF4/CH3CN were −1.04 V versus SCE for the n-doping of PC and 0.40 and 0.30 V versus SCE for the p-doping of PC and PA, respectively. These values depend on electrolyte concentration consistent with a Donnan potential due to the selective partitioning of ions between the electrolyte and polymer. Electrochemical quartz crystal microbalance data demonstrate that the p-type doping of PA and the n-type doping of PC proceed with the loss of ions from the polymer film and the formation of the internally compensated state. Voltammetry in tetrabutylammonium poly(styrenesulfonate)/CH3CN supporting electrolyte is also reported. It is demonstrated how a polyanion supporting electrolyte in concert with a conjugated ionomer can be used to control redox chemistry by governing the sign of ions available for charge compensation. In particular, we demonstrate the self-limiting oxidation of PA to inhibit deleterious overoxidation and prepare the precisely internally compensated state; the selective oxidation of PA over PC, despite their similar apparent formal potentials; and the inhibition of the reoxidation of the n-doped form of PC. The use of such polyelectrolyte-mediated electrochemistry in the fabrication of interfaces between dissimilarly doped conjugated polymers is discussed.