Modulating Electrochromic Properties via Thiophene Donors in Thieno[3,4-c]pyrrole-4,6-dione-based Conjugated Polymers

Abstract

Thieno [3,4-c]pyrrole-4,6-dione (TPD) is a strong imide-based electron-acceptor which has been less explored as a building block for the development of electrochromic (EC) conjugated polymers. To better assess the prospects of TPD-based conjugated polymers for high performance EC applications and to derive strategies to tune EC properties e.g. switching colours, seven TPD -based conjugated polymers bearing different thiophene-based electron donors were synthesized in this work for detailed structureproperty relationships study. From the findings, we noted how subtle change to the number and type of thiophene donors can result in variation of neutral colours from grey to purple and dark blue while the polymers exhibited different hues of grey in the oxidized state. Likewise, the introduction of stronger donors like 3,4-ethylenedioxythiophene (EDOT) and dithieno[3,2-b:2',3'-d]pyrrole (DTP) markedly improves EC properties such as optical contrasts (OC), response times, and open circuit memory retention. In particular, we are able to achieve up to 1000 switching cycles with only 8 % lost in OC, which is the most stable reported for TPD -based EC polymers to date. The electrofluorochromic (EFC) properties of five polymers were also studied with polymer bearing three thiophene donors showing the best contrasts of I OFF/ON 11.7 for fluorescence switching at 710 nm. Overall, this work provides critical insights into using TPD as a promising building block, to tune EC switching colours, and to develop future high performance EC materials to meet specific applicational needs.