Grafting π‑Conjugated Oligomers Incorporating 3,4-Ethylenedioxythiophene (EDOT) and Thiophene Units on Surfaces by Diazonium Electroreduction

The electrochemical reduction of diazonium salts, generated in situ, from 2-(4-aminophenyl)-3,4-ethylenedioxythiophene and two new amino functionalized π-conjugated oligomers incorporating 3,4-ethylenedioxythiophene (EDOT) and thiophene units, has been investigated. It coats the electrodes (glassy carbon (GC), gold or ITO) with an ultrathin organic layer (less than 10 nm thickness). The X-ray photoelectron spectroscopy (XPS) investigations confirm the presence of the starting oligomers deposited on the surface. As an important result, EDOT-based oligomer grafting was achieved on those surfaces which may be of general use as adhesion primer layers in all devices using PEDOT type materials. Furthermore, the coating is electroactive and the electrochemical investigations exhibit redox signal at potentials close to that obtained for short oligoEDOT in solution. The electrochemical responses of the modified GC electrodes were further studied in the presence of various reversible redox probes, showing that the attached layer acts as a conductive switch. The switching potential of the generated layer depends on the configuration of the starting oligomers and more precisely on the relative location of the EDOT unit. Such layer behave as a barrier to electron transfer when the standard redox potential of the redox probe is below the layer switching potential; in this case, a positive potential shift of the probe oxidation peak and a diode-like behavior are observed. However, for redox probes with redox potentials above the switching potential of the grafted film, the layer is transparent toward electron transfer, and no barrier effect is observed