Construction of Higher-Ordered Structures in Alkylpyridinium-Based Polymers via π-Conjugated Anion Pairing and Humid Annealing

In this study, π-conjugated anions were employed as counterions in poly(4-vinyl-N-alkylpyridinium) (P4VCxP⁺) polymers to construct highly ordered ionic microstructures. NMR, FT-IR, UV-vis spectroscopy, and differential scanning calorimetry were employed to characterize the resulting ion-pair polymers. Furthermore, thin films were fabricated and subjected to humidity annealing above the glass transition temperature. Grazing-incidence small-angle X-ray scattering (GI-SAXS) showed that humidity annealing promoted the formation of hexagonally packed cylindrical microdomains in P4VCxP⁺ with π-conjugated anion. The π-conjugated anions increased the effective hydrophilic volume and facilitated structural alignment via π–π and dipole–dipole interactions. Optical absorption analysis indicated that both the pyridinium and π-conjugated anions exhibited edge-on orientations and revealed the dynamic behavior of TCNQ·–, including dimerization and charge-transfer complex formation. Thus, π-conjugated ion pairs show significant promise for controlled self-assembly and functional optical properties in polymeric materials.