Synthesis, characterization, and electronic and optical properties of donor-acceptor conjugated polymers based on alternating bis(3-alkylthiophene) and pyridine moieties

A novel series of conjugated polymers comprising alternating T-excessive bis(3-alkylthiophene) and pi-deficient 2,5-pyridine (or 2,6- or 3,5-pyridine) moieties were synthesized using a Stille coupling approach and characterized by FT-IR, NMR, UV-vis, fluorescence spectroscopy, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), electrochemical analysis, and X-ray photoelectron spectroscopy (XPS). The derived polymers were highly soluble in common organic solvents and trifloroacetic acid. The electronic and optical properties of these polymers were closely related to the polymer backbone structures. Polymers containing 2,6-/3,5-pyridine moieties exhibited blue shifts in UV and fluorescent spectra relative to those containing 2,5-pyridine analogues, and polymers containing 3,5-pyridine units depicted the highest thermal stability, UV absorption energy, fluorescence energy, and reduction potentials. The electrochemical behavior of these new polymers showed facile n-doping and p-doping properties. The lower reduction potential of these polymers implied their good electron-transporting and easy electron-injection properties due to the presence of the electron-withdrawing pyridine unit. The optical properties of the polymers in trifloroacetic acid were also investigated. XPS studies performed on both neutral and doped states implied the formation of charge carriers in the polymer backbones when doped.