Effect of nitrated benzothiazole units on electro-optic properties of donor-acceptor monomers and their polymers

Abstract

Donor-acceptor (D-A) method is an effective strategy to synthesize high-performance conjugated polymers. In this work, a series of D-A pentameric hybrid monomers with EDOT as donor unit and nitrated benzothiazole as acceptor unit have been successfully synthesized by Stille coupling reaction (EDOT-Th-BT, EDOT-Th-NO2-BT and EDOT-Th-2NO2-BT). The effects of nitro groups on the electrochemical and electronic properties of the monomers and their corresponding polymers were systematically investigated by optical, CV, and spectroelectrochemistry techniques. As the number of nitro group increase, the electronic spectra were red-shifted for the mono-nitrated polymer but blue-shifted for the di-nitrated polymers, while the fluorescence quantum yield were stepwise reduced (from 0.64 to 0.02) and the oxidation peaks were positively shifted. The porous structure of the nitrated polymer film was very beneficial for their good redox behavior and favorable electrochemical stability. As a result, all of them exhibited favorable electrochromic properties, including fast switching time (0.74 s for oxidation and 0.4 s for reduction of P(EDOT-Th-2NO2-BT)), optical contrast up to 23.3 %, high coloration efficiency up to 129 C−1 cm2, and multi-color electrochromic property from brown to cyan, providing a new possibility for the preparation of nitrated polymers-based NIR electrochromic devices.