Synthesis and electrochromic properties of soluble 4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene-embedded conjugated polymers and their applications on preparing green-to-transmissive electrochromics via solution co-processing

In this work, six soluble polymers based on 4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene (IDT) and various electron-deficient moieties were synthesized via Stille coupling reaction. Aromatic cycles such as benzene (Ph), naphthalene (Na), and anthracene (An) incorporated into the polymer chain induce steric hindrance and generate strongly hypsochromic effect to achieve short-wavelength absorption band. As a result, one of the synthesized polymer (P(IDT-Na)) presents a single absorption peak at 433 nm and yellow color in the neutral state, which can turn into highly transmissive blue upon oxidation. On the other hand, due to the strong electron-deficient characteristics of 2,1,3-benzothidiazole (Tz), P(IDT-Tz) presents low band gap and very strong absorption located at long-wavelength visible band to give the neutral polymer a blue color. All these synthesized polymers also possess good properties. Then, these yellow and blue-to-transmissive ECPs are chosen for generating green-to-transmissive electrochromics via solution co-processing. The derived co-processed mixtures present desirably fine-tuning green color with the blending ratios, and excellent switching properties. Additionally, electrochromic devices based on these mixtures on ITO glass and flexible PET also give and confirm the fine-tuning of green color behavior and high-performance properties, implying that the blending strategy on soluble ECPs can be an efficient way for subtle green color control.