Electrochromic polymers based on 2,5-di(thiophen-2-yl)thieno[3,2-b]thiophene and thiophene derivatives as potential anodic layers for high performance electrochromic devices

Abstract

A 2,5-di(2-thienyl)thieno[3,2-b]thiophene (dTT)-containing homopolymer (PdTT) and four dTT-containing copolymers (P(dTT-co-bTp (2,2′-bithiophene)), P(dTT-co-TF), P(dTT-co-CPdT) and P(dTT-co-CPdTK)) were polymerized using electrochemical method and their electrochromic switching properties were explored. dTT shows lower onset oxidized potential (Eonset) than that of bTp, conjecturing that dTT displays more extended conjugated degree than that of bTp ring. PdTT film presents camel, olive green, and dark blue at 0.0, 0.8 and 1.0 V, respectively. Colorful-to-colorless switching investigations of polymeric films display that P(dTT-co-bTp) has high △T (41.3% at 1070 nm) and η (149.4 cm2/C at 1070 nm) in 0.2 M LiClO4/ACN/DCM solution. Five dual-layer complementary electrochromic devices based on PdTT, P(dTT-co-bTp), P(dTT-co-TF), P(dTT-co-CPdT) or P(dTT-co-CPdTK) as the anodic layer and PEDOT-PSS as the cathodic layer are assembled. P(dTT-co-TF)/PEDOT-PSS ECD exhibits high △T (44.7% at 680 nm) and satisfactory electrochemical redox stability, while P(dTT-co-CPdT)/PEDOT-PSS ECD displays high η (656.5 cm2/C at 686 nm) and rapid switching time (≤ 0.9 s). On the basis of these findings, the present work offers new structural insights for significant design of large contrast and multicolored electrochromic electrodes.Background: The thieno[3,2-b]thiophene (TT) unit is a fused heterocyclic ring, its coplanar structure and electron-donating ability can enhance carrier transporting properties of polymer chain. A 2,5-di(2-thienyl)thieno[3,2-b]thiophene (dTT) unit displays more extended conjugated degree than that of bTp, it is interesting to explore the multichromic behaviors of five dTT-based polymers and their corresponding ECDs upon applying various potentials.Methods: A dTT-containing homopolymer (PdTT) and four dTT-containing copolymers (P(dTT-co-bTp), P(dTT-co-TF), P(dTT-co-CPdT) and P(dTT-co-CPdTK)) are polymerized using electrochemical method. The spectral properties, kinetic characterizations, open-circuit memory, and electrochemical redox stability of PdTT/PEDOT-PSS, P(dTT-co-bTp)/PEDOT-PSS, P(dTT-co-TF)/PEDOT-PSS, P(dTT-co-CPdT)/PEDOT-PSS and P(dTT-co-CPdTK)/PEDOT-PSS ECDs are systematically studied.Significant Findings: The present work offers new structural insights for significant design of large contrast and multicolored electrochromic electrodes.