Cyclic secondary amine functionalized perylene diimide polymers for solution processed electrochromic devices

Abstract

To facilitate practical implementation of organic electrochromic devices in energy-efficient smart windows, displays, energy-storage, and sensors, it is important to consider factors such as switching speed and cycling stability. In this study, we report on the synthesis and characterization of two novel cyclic secondary amine functionalized perylene diimide-based polymers which utilize sterically hindering bulky functional groups as spacers that are either rotationally labile, X9, or are conformationally locked, F9. Furthermore, gel electrolyte-based electrochromic devices were solution-processed using these polymers and their switching time and cycling stability revealed that X9 exhibits a faster reduction to doubly reduced state and longer color retention time compared to F9-based electrochromic device. However, X9 displays inconsistent coloration during re-oxidation to the neutral state, which is attributed to dimer-type interactions, resulting in charge-trapped states within polymer films, whereas such interactions are impeded due to the rigid spacer of F9. Our results highlight the effectiveness of simple structural design strategies for fine-tuning self-assembly properties in electrochromic organic polymers to facilitate a balance between interchain charge transport and counter ion injection/extraction, which is essential for optimizing the performance and stability of electrochromic devices.