Abstract
Three soluble conjugated polymers, named BEDPP, FLDPP, and CADPP, were prepared through the Suzuki polymerized reaction, and employed benzene (BE), fluorene (FL), and carbazole (CA) as the donor units, respectively. The electron-deficient molecule 2,5-bis-(2-octyldodecyl)-3,6-bis-(5-bromo-thiophene)-pyrrole[3-c]pyrrole-1,4-diketone(DPP) was introduced and used as the acceptor unit. The properties of these three copolymers were studied by a series of detailed characterization analysis, including X-ray photoelectron spectroscopy (XPS), colorimetry, electrochemical measurements, spectroelectrochemistry, kinetics, quantitative calculation, and thermogravimetric (TG) analysis, etc. The results revealed that BEDPP displayed a blue color in the neutral state and a light brown color in the oxidized state, FLDPP exhibited a cyan color in the neutral state and a gray color in the oxidized state, while CADPP displayed pure blue color in the neutral state and a light gray color in the oxidized state. All these polymers possess narrow optical band gaps lower than 1.80 eV and satisfactory thermal stability. The kinetic characterization showed that the optical contrasts (ΔT%) in the near-infrared region were superior to the visible region. The optical contrasts of BEDPP, FLDPP, and CADPP are 41.32%, 42.39%, and 45.95% in the near-infrared region, respectively, which made them a good application prospect in the near-infrared region. Amid the three polymers, CADPP has the highest coloration efficiency (around about 288 cm2·C−1) and fast switching times (0.77 s in the coloring process and 0.52 s in the bleaching process) in the visible region, and the comprehensive performance of CADPP can be comparable to that of the reported D-A (Donor-Acceptor) type blue color polymers. In general, based on the good performances and the stable neutral blue color, the three polymers had profound theoretical significance for the development of electrochromic material and the completion of the RGB (Red, Green, Blue) color space.
Highlights
Conjugated polymers have been considered as promising materials holding excellent optical and electrical properties with the charming benefits of being solution-processable, lightweight, having a facile synthesis, and good flexibility [1]
Through a series of detailed measurements, we found that the polymer films have a reversible electrochromism switching under a low driving potentials (
From the analysis of the infrared absorption spectra from the following diagram, we can determine that these polymers have similar absorption peaks, which is probably related to the same DPP acceptor unit, and the difference of donors may result in the changes of partial absorption peak intensity
Summary
Conjugated polymers have been considered as promising materials holding excellent optical and electrical properties with the charming benefits of being solution-processable, lightweight, having a facile synthesis, and good flexibility [1] These characteristics make them a rapid development in the fields of organic field-effect transistors (OFET) [2], electrochromic devices [3], organic Li-ion batteries [4], solar cells [5], polymer light-emitting diodes (PLEDs) [6], and so on. Our group synthesized some satisfactory electrochromic materials, such as a neutral green polymer containing indolo[3,2-b]carbazole donor and diketopyrrolopyrrole acceptor [15], and red color material based on benzotriazole, quinoxaline, and benzene units [25]. >900 cm2 /C accompanying the color changes from green to transparent These achievements indicated that diketopyrrolopyrrole unit is a promising acceptor for the construction of valuable electrochromic materials with the different donor units [31]. The properties of the three polymers have been investigated in detail and presented
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