Novel electrochromic polymers based on benzo[1,2-c:4,5-c']dithiophene-4,8-dione acceptor by varying different π-bridges and terminal active groups

Abstract

In this work, we designed and synthesized a series of donor (D)-π-acceptor (A)- π-donor (D) type monomers, namely ETBD, EEBD, TTBD and TEBD, by varying the different π-bridges and terminal active groups in monomeric backbone based on the benzo [1,2-c:4,5-c']dithiophene-4,8-dione acceptor. And then their corresponding polymers PTEBD, PETBD, PEEBD and PTTBD were synthesized by electrochemical polymerization. EEBD exhibited the most red-shifted absorption peak at 487 nm and the lowest E_onset of 0.44 V among these monomers. Notably, in comparison with PTEBD, polymers PETBD, PEEBD and PTTBD achieved much higher optical contrast of 50.93 % at 830 nm, 39.94 % at 660 nm and 45.65 % at 1100 nm, respectively. In addition, PTTBD possessed the best electrochromic performance and displayed a color transition from dark purple in the neutral state to grey in the oxidation state with the best coloration efficiency (CE) value of 570.84 cm² C⁻¹ at 1100 nm among these polymers. These results demonstrated that the strategy of varying the different π-bridges and terminal active groups in polymer backbone based on the benzo [1,2-c:4,5-c']dithiophene-4,8-dione acceptor could improve the electrochromic performance, offering a promising approach to the design of high-performance electrochromic polymers.