Electrochemical evaluation of conjugated oligophenylenimine in aqueous medium for bandgap determination

In the present work, three aqueous media were used: sodium acetate (NaC2H3O2), potassium nitrate (KNO3) and sodium nitrate (NaNO3) at two different scanning speeds, i.e. 50 and 100 mVs−1, to evaluate the bandgap of the conjugated oligophenylenimine called DAFCHO by cyclic voltammetry (CV). DAFCHO was synthesised by solid-phase mechanosynthesis from 2,7-diaminofluorene and 2-5-bisocycloxyterephthaldehyde and deposited as a film on a glass substrate. 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, which are close to the optical bandgap and electrochemical bandgap of 2.56 eV and 2.35 eV obtained on the film, as calculated by UV–vis absorption spectroscopy and determined electrochemically in a BU4NPF6/ACN electrolyte in the literature. In addition, a greater degradation of the film of the organic compound DAFCHO was observed in the three aqueous media (NaC2H3O2, KNO3 and NaNO3), compared with the anhydrous medium (BU4NPF6/ACN) from the literature. On the other hand, the electrical evaluation of DAFCHO exhibits the characteristic behaviour of a P-N-type junction diode.