New symmetrical conjugated thiophene-azomethines containing triphenylamine or carbazole units: Synthesis, thermal and optoelectrochemical properties

Abstract

New oligo- and poly(azomethine)s containing 3,4-dicyanothiophene and triphenylamine or carbazole units were synthesized under condensation reaction conditions. Although the different amino group reactivity, a one-pot synthesis of symmetric conjugated oligoazomethines was possible by judicious choice of solvent and careful control of reagent stoichiometry. Different polycondensation strategies (in solution and bulk polymerization reactions) were applied in order to obtain soluble oligoazomethines and poly(azomethine)s. Their expected chemical structures were confirmed by 1H-NMR and Fourier transform infrared (FT-IR) characterization techniques. Electronic properties of the synthesized oligoazomethines were investigated in different solvents, using UV-Vis and photoluminescence spectroscopy (PL) and these revealed that there is a slight dependency between the solvent polarity and absorption wavelength, while the emissions peaks are shifted at higher wavelength with increasing the solvent polarity. The thermogravimetric and differential scanning calorimetry analysis showed a high thermal stability up to 350 °C and no glass transition temperature. Having in their structure electroactive sites, i.e., carbazole and triphenylamine units, cyclic voltammetry technique was used to investigate the oxido-reduction behavior and to determine the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels.