Synthesis and characterization of a new conjugated aromatic poly(azomethine) derivative based on the 3′,4′-dibutyl-α-terthiophene building block

A new conjugated aromatic poly(azomethine) derivative, poly(3′,4′-dibutyl-α-terthiophene-azomethine-1,4-phenylene- azomethine) (PBTPI), has been prepared by polycondensation of 2,5″-diformyl-3′,4′-dibutyl-2,2′:5′,2″- terthiophene with 1,4-phenylenediamine under the ethanothermal conditions. The red polycrystalline PBTPI was characterized by X-ray diffraction, NMR, FTIR, UV-visible-near-IR, photoluminescence, and ESR spectroscopies. PBTPI is partially soluble in tetrahydrofuran, giving an orange solution with an absorption maximum (λ_max) of 457 nm. In the solid state, PBTPI has an optical band gap of 2.06 eV, which is one of the lowest among poly(azomethines), and is highly sensitive to a strong acid environment. Protonation yields a blue polymer with an optical band gap of 1.61 eV. The polymer is completely soluble in concentrated sulfuric acid and nitromethane containing Lewis acids (e.g., AlCl₃), giving blue solutions with λ_max of 656 and 638 nm, respectively. Iodine-doped PBTPI shows low electrical conductivity at the order of 10^-7-10^-8 S/cm. The properties of PBTPI are compared to other, previously characterized, related polymers.