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

Abstract

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.