Red and Purple-to-Transmissive Electrochromic Copolymers Based on Fused Thiophene and 3,4-Di(cycloalkoxyl)thiophene with High Optical Contrast and Stability

The synthesis of high-performance electrochromic polymers remains a key research highlight in the field of electrochromism. Herein, a series of new solution-processable electrochromic polymers are designed and synthesized via direct arylation polymerization (DArP) of 4,9-dihydro-s-indaceno[1,2-b:5,6-b]dithiophene (IDT, M1) or tri(thienothiophene) (TTT, M2) and 3,4-bis(cycloalkoxyl)thiophene. All of these copolymers demonstrate outstanding electrochromic properties, such as high optical contrast, good switching stability, etc. The IDT-based copolymers present a red color in the neutral state and a highly transmissive oxidized state. Due to the stronger electron-rich character of TTT, the TTT-based copolymers can change from purple to highly transmissive. Additionally, due to the existence of methylene or ethylene units between the cycloalkyl and thiophene units, the different cycloalkoxyl side chains exhibit minor effects on the electrochromic properties of the copolymers. Finally, the fascinating properties of the electrochromic devices assembled based on these ECPs confirm their broad application potential in smart windows and as a color palette for color mixing.