Design Strategy for Efficient Solution-Processable Red Electrochromic Polymers Based on Unconventional 3,6-Bis(dodecyloxy)thieno[3,2-b]thiophene Building Blocks

In the quest for solution-processable red electrochromic material with high performance, a series of 3,6-bis(dodecyloxy)thieno[3,2-b]thiophene (DOTT)-based polymers have been designed by combining DOTT with different aromatic building blocks (bithiophene, benzene, and dimethoxybenzene) and prepared through Pd-catalyzed chemical copolymerization. Among them, the solution-processable polymer poly(2,5-dimethoxyphenyl-1,4-diyl-3,6-bis(dodecyloxy)thieno[3,2-b]thiophene) (P3) showed obvious yellow-green fluorescence in chloroform and demonstrated a rapid reversible switching (1.1 s/0.9 s for doping/dedoping process) between the red and bleached states. This brilliant red polymer exhibited moderate contrast (46% at 510 nm) and excellent cycling stability (in film: 78% for total amount and 63% for reduction after 12000 cycles; in device: 85.6% after 3000 cycles) which qualify it for further device fabrications. This study reveals that this polymer (P3) would be a promising high performance red electrochrome and could be a good candidate for flexible and large-scale organic electrochromic devices as well as for smart indicators or display applications.