Synthesis of novel dithienothiophene- and 2,7-carbazole-based conjugated polymers and H-bonded effects on electrochromic and photovoltaic properties

Abstract

Three kinds of dithienothiophene/carbazole-based conjugated polymers (P1–P3), which bear acid-protected and benzoic acid pendants in P2 and P3, respectively, were synthesized via Suzuki coupling reaction. Interestingly, P1–P3 exhibited reversible electrochromism during the oxidation processes of cyclic voltammogram studies, and P3 (with H-bonds) revealed the best electrochromic property with the most noticeable color change. According to powder X-ray diffraction (XRD) analysis, these polymers exhibited obvious diffraction features indicating bilayered packings between polymer backbones and π-π stacking between layers in the solid state. Compared with the XRD data of P2 (without H-bands), H-bonds of P3 induced a higher crystallinity in the small-angle region (corresponding to a higher ordered bilayered packings between polymer backbones), but with a similar crystallinity in the wide angle region indicating a comparable π-π stacking distance between layers. Moreover, based on the preliminary photovoltaic properties of PSC devices (P1–P3 blended individually with PCBM acceptor in the weight ratio of 1:1), P3 (with H-bonds) possessed the highest power conversion efficiency of 0.61% (with Jsc = 2.26 mA/cm2, FF = 29.8%, and Voc = 0.9 V). In contrast to P2 (without H-bands), the thermal stability, crystallinity, and electrochromic along with photovoltaic properties of P3 were generally enhanced due to its H-bonded effects. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012