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

A new conjugated aromatic paly(azomethine) derivative, poly(3',4'-dibutyl-alpha-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 (lambda(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 lambda(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.