Investigation of the effect of different π-bridge units on the optical and electrical properties of carbazole-based polymers

Recent advances in science and technology have increased interest in the synthesis of new materials and their potential applications. The choice of bridge units in molecular architecture plays a crucial role in obtaining conjugated materials with desired properties. The main highlight of this work is to study of the effect of two different π-bridges on the structural, optical, electrical, and electronic properties of carbazole-based compounds. Herein, two monomers with structurally donor-π-conjugated linker-donor (D-π-D) architecture containing carbazole as the D unit and glyoxal or terephthalaldehyde as π-conjugated linkers were designed and synthesized.The structural properties of (1E,2E)-N¹,N²-bis(9-ethyl-9H-carbazol-3-yl)ethane-1,2-diimine (namely Cz-Gly) and 1,1′-(1,4-phenylene)bis(N-(9-ethyl-9H-carbazol-3-yl)methanimine) (namely Cz-Tpa) were successfully characterized by different spectroscopic techniques (NMR, FT–IR, UV–Vis, fluorescence, and mass) and elemental analysis. Also, the structure-property relationships of monomers with different π-bridges were investigated by density functional theory (DFT) with the Beck3-Lee-Yang-Parr (B3LYP) hybrid functional level and 6-31G(d,p) basis set. The pCz-Gly and pCz-Tpa polymer thin films were synthesized using electropolymerization on indium‑tin-oxide (ITO) substrates. The role of different bridge units on the electrochemical, optical, and morphological properties of the polymers was investigated in detail. The pCz-Tpa with the rigid and conjugated bridge unit exhibited higher optical contrast and coloration efficiency, faster switching time, and better electrochemical stability than pCz-Gly. Furthermore, the pCz-Tpa polymer film also revealed distinct color changes from a transparent at neutral state to light pink, orangey brown, light green, and green oxidized forms. These superior properties make the prepared pCz-Tpa polymer film a potential candidate for next-generation applications such as electrochromic devices, supercapacitors, photovoltaic cells, etc. The present work provides an effective strategy to obtain high-performance materials by selecting the appropriate donor and π-bridge units.