Electrochemical evaluation of conjugated oligophenylenimine in aqueous medium for bandgap determination

In the present work, three aqueous medium were used: sodium acetate (NaC₂H₃O₂), potassium nitrate (KNO₃) and sodium nitrate (NaNO₃) at two different scanning speeds, 50 and 100 mVs^-1, to evaluate the bandgap of the conjugated oligophenylenimine called DAFCHO by cyclic voltammetry (CV). DAFCHO was synthesized by solid-phase mechanosynthesis from 2, 7-diaminofluorene and 2, 5-bis(octyloxy)terephthalaldehyde and deposited as a film in a configuration a) glass/ITO (indium tin oxide)/DAFCHO and b) glass. The results showed an electrochemical bandgap range of 2.39 to 2.47 eV at 50 mVs^-1 and from 2.59 to 2.68 eV at 100 mVs^-1 on glass/ITO/DAFCHO. While the electrochemical bandgap on glass/DAFCHO in range of 2.58 to 2.64 eV at 50 mVs^-1; which are close to the optical bandgap and electrochemical bandgap of 2.56 eV and 2.35 eV reported in the literature, calculated by UV-vis absorption spectroscopy in solution acetonitrile (ACN) and electrochemically in a BU₄NPF₆/ACN electrolyte. In addition, a greater degradation of the film of the organic compound DAFCHO was observed in the three aqueous medium (NaC₂H₃O₂, KNO₃ and NaNO₃), compared with the anhydrous medium (BU₄NPF₆/ACN) from the literature. On the other hand, the electrical evaluation of semiconductor DAFCHO in an electronic device exhibits the characteristic behaviour of a P-N-type junction diode.

Keywords: mechanosynthesis, oligophenylenimine, cyclic voltammetry, organic semiconductor, diode.