Transparent Polyimides with Near-UV Emission via Trace Incorporation of Pyridine-Based Diamines

The development of optically active polyimides (PIs) that retain the exceptional thermal robustness of high-performance polymers remains a significant challenge, particularly for emission in the near-UV region. Herein, we report the design and synthesis of pyridine-based diamine comonomers that function as efficient emissive units within polyimide backbones. In dilute THF solution, the diamines exhibit fluorescence in the blue region (433–454 nm). Incorporation of only 1 mol % of these comonomers into a semialicyclic CHDA–BAPP polyimide matrix induces a pronounced hypsochromic shift, yielding materials with near-UV/violet fluorescence in the solid state (emission maxima 359–376 nm; ΦPL = 8–13%). These films retain the thermal stability of the host polymer (Td5% = 454–471 °C, Tg = 258–264 °C). The emission wavelength and optical cutoff can be systematically tuned through comonomer structure, enabling control of photophysical behavior without sacrificing polymer processability or transparency. The combination of low comonomer loading, high thermal stability, and tunable near-UV emission positions these materials as promising candidates for advanced optoelectronics, including UV sensors and photonic coatings.