Regioregular Polythiophene with Pendant Phenoxyl Radicals: A New High-Spin Organic Polymer

Poly[3-(3‘,5‘-di- tert -butyl-4‘-acetoxyphenyl)thiophene] ( 1a ) was regioselectively synthesized via simple oxidative polymerization of 3-(3‘,5‘-di- tert -butyl-4‘-acetoxyphenyl)thiophene ( 2a ) with ferric chloride. Head-to-tail content of 1a with a molecular weight of >10 4 reached 96% by modulating both the polymerization conditions and the purification procedure of the polymer. Visible absorption and fluorescence maxima were bathochromically shifted for both 1a and poly[3-(3‘,5‘-di- tert -butyl-4‘-hydroxyphenyl)thiophene] ( 1b ), which suggests an extended π-conjugation, i.e., a regioregular structure. Redox of the phenolate and of the thiophene residue of 1b was observed reversibly and independently under alkaline conditions. The polyphenoxyl 1 derived from the oxidation of 1b showed an electrical conductivity of 10 -5 S cm -1 . The polyradical 1 satisfies both an alternant but non-Kekulé-type π-conjugation and ferromagnetic connectivity of the unpaired electrons of the pendant phenoxyls. 1 with a spin concentration of 0.3 spin/unit displayed a spin quantum number ( S ) value of 2 / 2 to 3 / 2, indicating a high-spin ground state and an intramolecular ferromagnetic spin coupling through the polythiophene backbone.