Synthesis of poly(thiaheterohelicene)s and their conjugated helical structures

Thiaheterohelicenes were often characterized by unique optical activity and stable doped state due to their π-electron-excess conjugation on the thiophene ring. However there have been no reports of the thiaheterohelicene with a high molecular weight or a sufficient number of repeating units to form a helical structure. This paper described the electronic state and helicity-control of the polythiaheterohelicenes. The alkylsulfmyl-substituted poly(1,3-phenylene)s were synthesized. Red shift of the π-π transition absorption indicated that the ring-closing structure caused the extension of the π-conjugation. The MCD signal at the long-wavelength was assigned to the degeneration of the p-orbitals. A helical conformation was induced to one side in good and poor solvent mixtures, and the following ring-closing reaction afforded the same helical structure which was firmed by strong covalent bonds. The helical structure was very stiff as evidence by the independencies in the CD spectra of temperature and solvent species. The helical polymer with long alkyl chain exhibited a partially oriented structure in the polarized microscopy.