Synthesis, characterization, optical and electrochemical properties of cyclopentadithiophene and fluorene based conjugated polymers containing naphthalene bisimide

•Polymers containing electron rich and electron deficient units have been prepared.•Increasing the conjugation length of copolymers leads to decrease the band gap.•No fluorescence can be found due to intramolecular charge transfer interaction.•The absorption band of copolymers covers the entire visible region.

Cyclopentadithiophene and fluorene based conjugated polymers containing naphthalene bisimide were synthesized through Suzuki cross-coupling polymerization. The resulting polymers exhibit good thermal stabilities and low crystallinities measured by thermogravimetric analysis and differential scanning calorimetry. The optical and electronic properties of polymers can be examined by UV–Vis spectroscopy and cyclic voltammetry. The UV–Vis absorption maxima of cyclopentadithiophene and naphthalene bisimide containing polymers showed longer wavelength than those of fluorene and naphthalene bisimide containing polymers. This is due to the stronger electron donating property of cyclopentadithiophene in the polymer backbone. The absorption maximum of cyclopentadithiophene and naphthalene bisimide containing polymers was red-shifted in comparison with those of low molecular weight analogous. Alternating polymers containing cyclopentadithiophene and naphthalene bisimide moieties showed a low band gap relative to that of the fluorene and naphthalene bisimide containing polymers presumably there is a strong charge transfer interaction between the electron-donating cyclopentadithiophene unit and the electron-accepting naphthalene bisimide.

Graphical abstractAlternating polymers containing cyclopentadithiophene and naphthalene bisimide moieties showed relative low band gap than fluorene and naphthalene bisimide containing polymers.Figure optionsDownload full-size imageDownload as PowerPoint slide