Molecularly constrained conformation engineering suppresses charge hopping in polyetherimide for superior capacitive storage at elevated temperatures

Aromatic polyetherimide (PEI) emerges as a promising high-temperature dielectric for energy storage in demanding applications like electric vehicles and aerospace systems. However, at elevated temperatures (>140 °C), the delocalized π-conjugated backbone of PEI facilitates severe charge transport, causing significant performance degradation. Here, we overcome this limitation through a local constrained conformational architecture engineered via fluorene functionalization and methyl side-group modification in PEI. Despite exhibiting a reduced bandgap, the optimized PEI film achieves a remarkable 84 °C increase in glass transition temperature (T_g) and a 380 % surge in discharged energy density (U_e = 4.56 J cm⁻³ at 150 °C) while maintaining >95 % charge-discharge efficiency (η), surpassing the performance of most wide-bandgap polymer dielectrics and their composites. Mechanistically, the unique constrained non-planar conformation imposed by fluorene substituents and methyl groups reduces interchain electronic coupling by three orders of magnitude and restricts chain mobility. This synergistically suppresses both thermal molecular motion and intra/interchain charge hopping. Unlike conventional bandgap-engineering approaches that primarily limit charge excitation, our strategy directly targets the charge hopping mechanism by tailoring key local three-dimensional constrained conformations. Simultaneously, this work clarifies the interdomain relationships between molecular conformation and quantum charge-hopping processes, offering fundamental molecular-level design guidelines for developing next-generation high-temperature energy storage polymer dielectrics.