A helical ladder polymer: Synthesis and magnetic circular dichroism of poly[phenylene-4,6-bis(methylsulfonio)-1,3-diyl triflate]

A helical ladder polymer composed of a fused-benzothiophenium ring was synthesized via the intramolecular ring-closing reaction of the methylsulfoxide-substituted poly(1,3-phenylene). The precursor polymer was prepared by the palladium-catalyzed polymerization of 1,3-dibromobenzene and 1,3-phenylenebisborate and the following quantitative oxidation. The intramolecular ring-closing of the precursor polymer yielded poly[phenylene-4,6-bis(methylsulfonio)-1,3-diyl triflate]. The polymer structure did not involve any structural defects based on NMR analysis, which was supported by the model dimers and the control reaction using the monomeric analogues. The obtained polymer is one of the new poly(thiaheterohelicene)s. Magnetic circular dichroism of the polymer suggested an electron transition ascribed to the fused-ring structure.