Synthesis of carbazole-based copolymers containing carbazole-thiazolo[5,4-d]thiazole groups with different dopants and their fluorescence and electrical conductivity applications

Abstract

To improve the electrical conductivity of poly(carbazole-thiazolo[5,4-d]thiazole) (p-CzTT), five different dopants, such as HCl, Fe(III), Cu(II), H₃BO₃, and I₂, were introduced into its framework through protonation of a nitrogen atom or by complex formation. Carbazole-thiazolo[5,4-d]thiazole (CzTT) and poly(carbazole-thiazolo[5,4-d]thiazole) (p-CzTT) were synthesized by the reactions of carbazole aldehydes and dithiooxamide. The synthesized monomer and polymer were confirmed by FT-IR, UV-vis, ¹H, ¹³C-NMR, and GPC studies. The doped polymers were examined by FT-IR spectroscopy, UV-visible absorption, fluorescence, thermogravimetric analysis (TGA), cyclic voltammetry (CV), and electrical conductivity. The optical band gap (E^opt_g) of CzTT and p-CzTT were found to be 2.74 eV and 1.95 eV, respectively. The thermal stability of the polymer showed 5% weight loss at 358 °C. Based on CV analysis, the HOMO and LUMO energy levels and the electrochemical band gap (E^cv_g) of p-CzTT were obtained as −5.86 eV, −3.19 eV, and 2.67 eV, respectively. The CzTT and p-CzTT exhibited fluorescence emission at 461 nm and 448 nm, respectively. Among the dopants introduced, Fe(III)- and I₂-doped polymer showed excellent electrical conductivities of 6.8 × 10⁻⁵ S cm⁻¹ and 5.9 × 10⁻⁵ S cm⁻¹, respectively.