Fast colour switching of asymmetric electrochromic devices

Abstract

Electrochromic (EC) devices based on conjugated polymers (CPs) with optical activity was developed. Asymmetric EC polymers are synthesised through electrochemical polymerisation in cholesteric liquid crystals (CLCs). This asymmetric polymerisation method transcribes the helical structure of CLCs to CPs. The EC performance of chiral EC polymers remains insufficiently explored. This study elucidated the impact of the electronic and structural properties of chiral EC polymers on their EC performances, focusing on optical contrast, response time, and cycle stability. Compared with 3,4-(ethylenedithia)thiophene (EDTT) units with an electron-withdrawing group, 3,4-(ethylenedioxy)thiophene (EDOT) units with an electron-donating group exhibited a stable oxidation state, enhanced cycle stability, and accelerated response time. Moreover, 3,4-(propylenedioxy)thiophene adorned with bulky methyl groups (dMProDOT) had a higher EC performance, characterised by a bleaching/colouring time of 1.1 s and high cycle stability. The EC performance of these asymmetric EC polymers was significantly influenced by the structural and electrical properties of the constituent units. The findings of this study provide valuable molecular design guidelines for the application and optimisation of the asymmetric EC polymers.