Molecular design of multifunctional integrated conjugated polymers with photoluminescence and electrochromic properties and constructing the electrochromic devices

Three conjugated donor-π-acceptor-π (D-π-A-π) type polymers PBBT-X (X = 1, 2, 3), possessing 3,4-propylenedioxy-thiophene (ProDOT) with solubilizing side chain as donor units, benzothiadiazole (BT) with alkoxy side chains as acceptor units and benzene as π-linkers, were designed and synthesized via regulating the feed ratios of the donor to acceptor. And the synthetic procedures are fulfilled with palladium-catalyzed Suzuki coupling reaction. Three polymers all exhibit yellow hue in the neutral state while switching different shades of black in the oxidation states. We found that the electrochromic (EC) performances of conjugated polymers could be enhanced through designing the skeleton structure and optimizing feed ratios of donor to acceptor units, achieving high optical contrast (82 %) and high coloration efficiency (623 cm2 C-1), which is more excellent than that of reported neutral state yellow polymers. Interestingly, PBBT-3 reveals good emission performance with photoluminescence quantum yields (PLQY) of beyond 56 %. Based on the above analysis, the electrochromic device (ECDs) based on PBBT-3 was constructed by solution processing and achieved fast color switching between yellow and blue in low voltage driving force, which offering a valuable material choice for advanced multi-functional electronic devices in the future. The results show that the molecular design of D-π-A-π type polymers and the optimization of feed ratios can significantly enhance their potential for intelligent applications, particularly where multifunctional compatibility of electrochromic and photoluminescence behaviors is crucial. © 2024 Elsevier B.V.