2.4. Electrochemical, Spectroelectrochemical, and Conductometric Measurements

Solutions for electrochemical and spectroelectrochemical investigations were prepared by dissolving the polymer sample in chloroform (Sigma-Aldrich, CHROMASOLV, >99.9%, HPLC grade). Thin solid films on different working electrodes were prepared through spin-coating the polymer solution, typically at a concentration of 2.6 mg/cm³ onto an electrode.

Electrochemical and conductometric investigations were performed using a standard three-electrode cell, with an interdigitated array electrode (Pt–IAE) comprising two working electrodes (Pt path width of 5 μm and path spacing of 5 μm, produced by Dropsens (Herisau, Switzerland)), an Ag pseudo-reference electrode, and a Pt coil counter-electrode. Supplementary electrochemical (CVs) data was acquired for layers produced by drop-casting the copolymer solutions onto a Pt wire working electrode.

Measurements were carried out on a Metrohm-Autolab PGSTAT302N (Herisau, Switzerland) potentiostat equipped with a bipotentiostat module. Conductometric measurements were realised in cyclic voltammetric mode, scanning the potential, while maintaining a constant potential offset (0.005 V) between the two working electrodes.

UV-Vis-NIR spectroelectrochemical experiments were carried out in a 2 mm Hellma QS cuvette, equipped with an ITO/glass working electrode, an Ag pseudo-reference electrode, and a Pt mesh counter electrode. UV-Vis-NIR spectra were registered using an Ocean Optics (Largo, FL, USA) diode-array spectrometer set (QE65000 and NIRQuest 512). Optical contrast values were calculated using the transmittance of the polymer films in their most highly-doped and undoped states; these values were then averaged across all wavelengths in the spectral range of the spectrometer.

A solution of 0.1 M tetrabutylammonium tetrafluoroborate (Sigma-Aldrich, >99.0%, electrochemical analysis grade) in acetonitrile (Sigma-Aldrich, CHROMASOLV, >99.9%, HPLC grade) was used in all experiments as the supporting electrolyte. Prior to each measurement, each investigated sample was purged with inert gas, and the same gas was passed through the electrochemical cell during the measurement.

Applied potentials in all of the electrochemical experiments were calibrated versus the ferrocene/ferrocenium redox couple, as presented. In the case of spectroelectrochemical experiments, the applied potentials refer to the silver pseudo-reference electrode system. The silver pseudo-reference electrode was calibrated against ferrocene/ferrocenium redox couple, whose recorded potential versus this electrode was constant, amounting to +0.46 V.