Structural Effects on Thermal Stability and Photoluminescence of Novel Aromatic Poly(amide-imide)s Based on 3,4′-Bis(3-N-trimellitimido)chalcone and Various Aromatic Diamines

Abstract A novel series of aromatic poly(amide-imide)s (PAI-01–PAI-04) was synthesized from a novel asymmetric chalcone-based diimide-diacid and four structurally different aromatic diamines to investigate the effects of chain asymmetry and conjugation on thermal and optical properties. The key monomer, 3,4′-bis(3-N-trimellitimido)chalcone (6), was prepared in a two-step route: aldol condensation of 3-nitrobenzaldehyde and 4-nitroacetophenone to yield 4,3′-dinitrochalcone, followed by reduction with Fe/acetic acid to the corresponding diaminochalcone and subsequent imidization with trimellitic anhydride. The resulting PAIs were characterized by FT-IR and ¹H NMR, and their properties were evaluated by UV–Vis, photoluminescence (PL), XRD, TGA, and DTG. UV–Vis spectra exhibited primary absorption in the 250–264 nm range. Upon excitation at 365 nm, PAI-01, PAI-03, and PAI-04 emitted primarily at 404.5 nm, whereas PAI-02 showed a red-shifted emission at 425.8 nm. Thermal analysis revealed that PAI-02 possessed the highest char yield (59.8% at 800°C) and a maximum degradation temperature (DTG_max) of 528.3°C, while PAI-01 showed the highest T₁₀% (508°C). XRD patterns indicated predominantly amorphous structures with localized short-range order. These findings demonstrate that the asymmetric chalcone-based diacid, combined with the diamine architecture, governs chain packing, thermal degradation pathways, and excited-state behavior. Among the synthesized polymers, PAI-02 is identified as the most promising candidate for applications requiring a combination of high thermal stability and blue-violet photoluminescence.