Spectro-Electro-Gravimetry of the Compactation Effect of Poly-(ortho-toluidine)

An example of an electroactive polymer is poly(ortho-toluidine) (POT), whose monomer has been widely used as aniline derivative for dyestuff, pesticides, pharmaceutical drugs and organic intermediates. POT’s properties can be looked into by spectroelectrochemical means, in that they are directly related to the variations of colour associated to the oxidation states of its active sites [1-4]. POT displays three main oxidation forms: fully reduced state (leucoemeraldine, LE), partially oxidized (emeraldine, EM), and fully oxidised (pernigraniline, PN). Among these, only the EM form is conductive. The 100 CV cycles obtained during electropolymerisation of o-toluidine are shown in Figure 1. At about 0.85 V, the sharp peaks observed correspond to the oxidation of o-toluidine and the fact that their maximum current density increases as cycling increases suggests that the polymer is forming. In this work, the behavior of POT during compaction and subsequent swelling has been reported on. Basically, electropolymerisation of a monomer, ortho-toluidine, was executed on a flat electrode. Then, Electrochemical Quartz Crystal Microbalance (EQCM) coupled with in situ Vis-NIR spectroscopy were employed to characterize the as-formed polymer. The compaction-decompaction process of poly(o-toluidine) (POT) films synthesized from H 2 SO 4 solution by cyclic voltammetry has been looked into. We present a detailed electrochemical mechanism for the insulating-to-conductor change of POT films. Oxidation of POT films involves their transformation into the conducting (i.e. emeraldine) form, with simultaneous anion insertion into the polymeric matrix. Coupling of electrochemical quartz crystal microbalance (EQCM) with vis-NIR spectroscopy provided singular information about the global response of current during the doping processes. Isolated polarons (P*) could form because of trapped anions when the film is reducing and shrinking (compaction). During the decompaction (i.e. relaxation), protons are expulsed when the isolated polarons detected at 420 nm are oxidized. Anions insert during the formation of conducting polarons (PC), which consist of coil structures due to the strong interaction of anions with the C-NH + -C group of polymer detected at 840 nm. This mechanism can be used to understand the relaxation process in other polyaniline-derived films. During the LE → EM change, POT can show two different intermediate states, known as polaron and bipolaron forms, which are conside