Synthesis of the novel thienoisoindigo-based donor-acceptor type conjugated polymers and the stable switching performance of purple-to-transparent as the electrochromic materials

Three soluble conjugated polymers named PTINS-1, PTINS-2, and PTINS-3 were synthesized via Stille coupling reaction by employing different molar feed ratios of the donor units to the acceptor units. (E)-2,2' -dibromo-4,4'bis(2-ethylhexyl)-[6,6'-bithieno [3,2-b]pyrrolylidene]-5,5' (4H, 4H')-dione (TIIG, M2) was used as the acceptor unit, and 2,5-bis (trimethylstannyl)thieno [3,2-b] thiophene (M1) and tris(thienothiophene) (TTT, M3) were selected as the donor units. Electrochemical research demonstrates that three polymers could switch reversibly and stably between purple neutral states with different saturation and transparent oxidized states. Amid the three polymers, PTINS-1 exhibits the best comprehensive performance including the satisfying optical contrast of 41.28% in the visible region with the response time of coloring and bleaching in only 0.47 s and 0.93 s, respectively, and the optical contrasts up to 81.98% with the coloring and bleaching time in only 0.56 s and 1.18 s at the 1590 nm. Furthermore, the other two polymers display beyond 70% of the transmittance change in the near-infrared region (NIR), which endows three polymers with commendable prospects in NIR electrochromic applications, and deserves more attention and penetrating research.