Synthesis of Aniline Unit-Based Optically Active Magnetic Conjugated Polymers

In this study, we report the synthesis of polyaniline derivatives (para-, meta-, chiral meta-linked polyanilines, and a thiophene–aniline copolymer) using the Buchwald–Hartwig reaction. The electrical conductivity analysis results of sulfuric acid-doped meta- and para-linked polyanilines indicate the generation of polarons (radical and hole), whose delocalization is essential for electrical conduction. Furthermore, the delocalization of polarons in the main chain is associated with paramagnetism at high temperatures due to intramolecular interactions. A copolymer of thiophene and aniline, consisting of an electron-rich main chain affected by the lone pairs of S and N atoms, exhibits electrical conductivity despite the neutral electronic state. Chiral meta-linked polyaniline was synthesized via the combination of Mitsunobu (introduction of a chiral substituent into the monomer), Buchwald–Hartwig (Pd cross-coupling polycondensation), and Tokumaru (oxidation using m-chloroperoxybenzoic acid to generate nitroxyl radicals in the main chain) reactions. Circular dichroism measurement revealed that the chiral polymer exhibits optical activity. Magnetic measurements using a superconducting quantum interference device revealed magnetism for the resultant polymers at low temperatures. The differences in magnetic behaviors and electrical conductivities of polyaniline derivatives with different conjugated structures provide new avenues for molecular design in magnetic polymer science.