A stable, low band gap electroactive polymer: Poly(4,7-dithien-2-yl-2,1,3-benzothiadiazole)

A highly stable electrochromic polymer, poly(4,7-dithien-2-yl-2,1,3-benzothiadiazole), was electrochemically synthesized and its electrochemical, optical and morphological properties are reported. Poly(4,7-dithien-2-yl-2,1,3-benzothiadiazole) showed a very well-defined electrochemistry with a relatively low oxidation potential of the monomer at 0.9 V versus Ag/Ag+, E1/2 at 0.78 V and stability to long-term switching up to 1000 cycles. The band gap of the polymer films, 1.1 eV, was determined from electrochemistry. Spectroelectrochemistry for p-doped film indicated two absorption peaks at 560 (Vis range) and 1100 nm (NIR) corresponding to π–π* transition (onset 800 nm) band, and the bi-polarons band, respectively, and a band gap of 1.5 eV. The switching ability and kinetic studies of the polymer prove interesting optical properties in p- and n-doping case with a higher % ΔT at the 1100 nm peak, thus making the polymer a suitable material for NIR applications. Morphology studies on carbon fibers indicated a three-dimensional growth on carbon fibers with a large area determined by the pores suggesting the material to be used in storage devices and biosensors applications. The homogeneity of the polymer film on ITO-coated glass ensures that poly(4,7-dithien-2-yl-2,1,3-benzothiadiazole) is a potential material for electrochromic device applications.