Covering visible light region of fused rings-based D-A type electrochromic polymer with high-coloration efficiency

The colorful electrochromic polymers have been prepared, however, the neutral black or gray polymers are reported rarely due to the optical absorption region couldn’t cover the whole visible light region. Here, three donor-acceptor (D-A) type conjugated polymers PCDT-X (X = 1, 2, 3) based on two fused ring (FR) conjugated units cyclopentadithiophene (CPDT) and trithiophene-phenylhexyl (3TT) as donors and diketopyrrolopyrrole (DPP) as acceptor were synthesized. The difference of the three D-A type polymers focuses on donor/acceptor (D/A) molar ratio. Due to the introduction of FR units as donors, the optical absorption of PCDT-X (X = 1, 2, 3) cover the whole visible region, making them display gray color. Electrochromic studies demonstrate that the optical contrasts of PCDT-X (X = 1, 2, 3) in high- and low-energy absorption bands could be optimized specifically through adjusting D/A molar ratio. And, the prepared PCDT-X (X = 1, 2, 3) display good electrochromic properties, such as high optical contrast (57.25%), fast response time (0.59 s), and superior coloration efficiency (1342 cm2 C−1). These results demonstrate that the introduction of FR units as donors is an efficient strategy to construct gray or black D-A type electrochromic polymers.