Poly(thiaheterohelicene) derived from the long-alkylated polysulfonium precursor

Poly[4,6-bis(dodecylthio)-1,3-phenylene-alt-2-methyl-1,3-phenylene] (Poly-S) was synthesized via Suzuki-Miyaura coupling of 1,3-dibromo-2,6-bis(dodecylthio)benzene and 2-methyl-1,3-phenylenebis (pinacol borate). After quantitative oxidation of the pendant sulfide moiety to the sulfoxide derivative (Poly-SO), the m-linked benzene rings were fused via intramolecular ring-closing condensation with excess triflic acid to form the corresponding poly(sulfonium cation) (Poly-S⁺) with a helical structure. Poly-S⁺ was quite soluble in non-polar solvents due to the long alkyl dodecyl chain. The Poly-S⁺ film, especially the film cast from its acetone solution, gave a polarized optical micrograph, suggesting an oriented structure of the helical poly(sulfonium) derivative. The X-ray diffraction pattern of the film supported a hexagonal columnar packing of the polymer. The polysulfonium derivative in the film state was converted to the corresponding poly(thiaheterohelicene) (Poly-TH) via the dealkylation with a basic potassium hydroxide methanol solution or pyridine. The Poly-TH film was doped with iodine. Its conductivity was enhanced about 30 times when compared to that of the undoped film.