Fluorinated electron acceptors synthesized via an inverse electron demand Diels-Alder click reaction for electrochromic conjugated polymers

Abstract

Fluorinated electron acceptors play a vital role in the development of conjugated polymers. They enhance electronic and optical properties by increasing electron affinity and improving charge transport characteristics. This work reports the synthesis of two fluorinated electron acceptors using an inverse electron demand Diels–Alder reaction, a type of click reaction, involving tetrazine with 1-ethynyl-4-fluorobenzene and 1-allyl-2,3,4,5,6-pentafluorobenzene, achieving yields of (73–82 %). One non-fluorinated polymer (P1) as a reference and two fluorinated polymers (P2 and P3) were prepared via the Stille polymerization. Notably, fluorinated polymer P2 showed better electrochromic device stability compared to the non-fluorinated polymer P1. The electrochromic devices exhibited coloration efficiencies of 196.97 cm²/C for P1, 519.49 cm²/C for P2, and 273.37 cm²/C for P3, suggesting that increased fluorination, either in the polymer backbone or in the side chains of conjugated polymers, likely contributes to the incremental increase in coloration efficiency. Polymer P2 demonstrated the best overall performance, with rapid switching times of 0.99 s for coloring, along with better cyclic stability than other two polymers. This study highlights that conjugated polymers modified with appropriate fluorine substituents can significantly enhance the performance of electrochromic devices.