Fluorine‐Free Colorless Polyimides with High Thermal Stability for Advanced Flexible Color Filters and Dye‐Based Photolithography

Addressing the fundamental trade‐off between thermal stability and optical transparency in polyimides (PIs) is pivotal for next‐generation flexible electronics. Herein, we report a fluorine‐free strategy to develop high‐performance colorless PIs by strategically engineering isomeric diamine monomers featuring meta‐substitutions and sterically bulky fluorenyl side groups. PI‐1 achieves an exceptional optical transmittance of 92.8% at 450 nm and a low yellowness index of 1.49, while maintaining a high glass transition temperature ( T g ) of 320°C. Theoretical simulations confirm that the highly distorted spatial conformation and high energy gap (5.05 eV) effectively suppress charge‐transfer complex (CTC) formation. Furthermore, PI‐1 demonstrates outstanding mechanical durability, sustaining 200 000 folding cycles at a 2 mm radius without structural failure. Finally, high‐fidelity RGB pixel arrays were successfully fabricated on flexible PI‐1 substrates using a simulated photolithography with thermally stable anthraquinone dyes, which offer superior homogeneity compared to conventional pigment‐based systems by eliminating particle‐induced light scattering. This work provides a sustainable and high‐performance material paradigm for advanced flexible displays and optoelectronic applications.