Fine-tuning the color hue of the solution-processable electrochromic copolymers based on the diketopyrrolopyrrole, benzodithiophene and dithienosilole units

Abstract

Electrochromic materials (ECMs) have attracted increasing attentions on account of their extensive prospects and numerous demands. Here, the classical donor-acceptor (D-A) alternative copolymerization strategy was used to synthesize three kinds of novel conjugated polymers PBPS-1, PBPS-2, and PBPS-3. The diketopyrrolopyrrole (M1) unit with a long alkyl side-chain was employed as the core acceptor while the dithienosilole (M2) used as the donor units. More importantly, the benzodithiophene (M3) units which have the high skeleton coplanarity was selected as the bridge units to enhance the charge transport. Variations of the feed ratios of monomers was used to regulate the energy level and spectral absorption range of the solid films. Three polymers exhibited the abundant color hues in the redox process, which including grape purple/brownness/aircraft ash color (PBPS-1), dark grey/red soap/dusty blue color (PBPS-2) and marine blue/grayish/celadon color (PBPS-3). Electrochromic performances demonstrated that PBPS-2 possessed the fast discoloration speed as low as 0.26 s and the outstanding coloration efficiency (550.1 cm2·C−1), which portended a valuable material for smart ECMs applications. Furthermore, the effect of different feed ratios for three polymer in electrochemical, optical and kinetic properties were investigated in detail, which showed the satisfactory optical contrasts (>70% in the NIR region) and good kinetic stability (>97% retention in 1000 s). In general, this exploration supplied a handy design strategy for fine tuning of polymer color and conducive to strengthen the understanding of EC behaviors of the ternary polymers, which deserve further researches to explore more promising ECMs.