Novel programmable functional polyimides: preparation, mechanism of CT induced memory, and ambipolar electrochromic behavior†
In this study, the new functional polyimides 9Ph-ODPI, 9Ph-DSPI, and 9Ph-PMPI consisting of electron-donating starburst triarylamine units and different dianhydrides were synthesized and used for memory device applications along with 9Ph-6FPI. To investigate the effects of donor moieties in polyimides on their memory behavior, the corresponding 3Ph- series polyimides (3Ph-PIs) and 5Ph-PIs were also discussed. With the intensity of electron donation increasing from 3Ph-PIs to 5Ph-PIs to 9Ph-PIs, the retention time of the memory device shows a systematic increase. The retention time of the memory device also increases with the increasing electron-withdrawing intensity of the dianhydrides. Furthermore, the in situ UV-vis absorption spectra of the memory devices during switching-ON were utilized as direct evidence to confirm the relationship between charge transfer (CT) complex stability and memory retention time. In electrochromic (EC) applications, the novel ambipolar 9Ph-PMPI exhibited a high contrast ratio and electroactive stability during EC operation with multiple colors at different applied potentials, due to its four oxidation and two reduction states. Finally, flexible colorful EC and volatile memory devices were fabricated for practical flexible electronics applications in the future.