Multifunctional 3,3'-bicarbazole-based polyimides for electrochromic and sodium-ion battery applications

Organic polymeric materials constitute essential components for next-generation intelligent optoelectronic and green energy storage devices. Carbazole and its derivatives have demonstrated substantial application potential in electrochromic (EC) and sodium-ion batteries (SIBs) fields by virtue of their reversible redox activity and superior hole-transport characteristics. However, achieving synergistic optimization of optoelectronic and energy storage performances within a single material system remains challenging. Herein, we report the synthesis of a diamine monomer centered on 3,3'-bicarbazole (BCBTAA-NH₂), which was subsequently polymerized with pyromellitic dianhydride, naphthalene tetracarboxylic dianhydride, and perylene tetracarboxylic dianhydride to afford a series of polyimide (PI) materials. The 3,3'-bicarbazole unit, comprising two carbazole moieties directly linked through a C-C single bond, ensures efficient π-electron delocalization while introducing moderate molecular torsion. By systematically modulating the π-conjugated systems of the dianhydride monomers, we achieved tailored control over the energy level structures, molecular packing morphologies, and ion transport kinetics of the resulting PIs. All PIs exhibited pronounced EC behavior, with PI-BA achieving a significant optical contrast (ΔT) of 73% at 769 nm and a coloration efficiency (CE) of 184 cm² C⁻¹. As an anode material for SIBs, PI-PTCA exhibits the most favorable energy storage performance, delivering a reversible capacity of 141.7 mAh g⁻¹ after 600 stable cycles at 0.5 A g⁻¹, and retaining 130.9 mAh g⁻¹ even after 1500 cycles at 1 A g⁻¹. These results demonstrate that the developed series of PIs possesses certain potential for applications in EC and SIBs.