Poly(thiaheterohelicene): Control of fused helical structure and its morphology

Helicenes are characterized by fused ring π-conjugation and its stiff structure, and have been expected to be stable magneto-optical molecules. However, they must be synthesized stepwise, therefore, there were no reports on synthesis of the helicenes having sufficient length as a π-conjugated polymer. We have developed the facile synthesis of the poly(thiaheterohelicene)s using ring-closing reaction via the sulfonium salts. Poly(1,3-phenylene)s bearing thioalkyl groups were polymerized with Pd(0) catalyst. Ring-closing reaction with strong acid followed oxidation reaction of the sulfide to produce the sulfonium derivatives. Poly(thiaheterohelicene)s were synthesized via dealkylation reaction of the sulfonium polymers with strong base. Its helicity was controlled with hydrophobic effect or inter-molecular interaction. Polarized optical micrographic imaging of poly sulfonium bearing dodecylthio groups revealed birefringence and it was changed with casting solvents. Radical formation on I₂-doped poly(thiaheterohelicene) was detected with UV-vis and ESR spectrum. The electrical conductivity of the doped poly(helicene) was developed than the undoped polymer.