Synthesis and Characterization of Indole-Based Azomethine Compounds and Investigation of Their Dielectric Properties in Polyvinyl Alcohol Films

Abstract

The following study reports on the synthesis of a series of organo-Schiff bases (M1–M5) through condensation reactions between indole-3-carboxaldehyde and various aromatic and heterocyclic amines such as 4-aminoacetophenone, 2-aminobenzothiazole, 2-aminothiazole, 2-aminopyridine, and 5-amino-1,3,4-thiadiazole-2-thiol. The synthesized compounds were characterized by FTIR and ¹H-NMR techniques for confirmation of the proposed structures. Since these compounds do not form stable films in the solid state, they were incorporated into a polyvinyl alcohol matrix, and composite films were prepared using the solution casting technique to study their electrical properties. The measurements revealed that all composite films are characterized by a decrease in the true dielectric constant (ε′) with increasing frequency, whereas both imaginary permittivity (ε″) and alternating current conductivity (σ(ac)) increase with increasing frequency. The results also indicated that the electrical properties depend on the molecular structure of the Schiff base compounds. Among them, the film containing compound M4 showed the highest values of dielectric permittivity and conductivity, while the M1 and M2 films showed the lowest values of dielectric loss and conductivity.