Novel helical conjugated polymers: synthesis and optical properties of polyarylenemethine derivatives bearing chiroptical substituents

We have synthesized chiral small-bandgap polymers by introducing chiroptical substituents into the methine moiety. The polymers showed Cotton effects in the region corresponding to the pi --> pi* transition of the conjugated polymer main chain; the polymers including bithiophene and quarterthiophene exhibited a positive Cotton effect and that including terthiophene a negative one. The results indicate that the polymers have helical structures, in which the screw direction should be varied with the number of thiophene ring of the unit cell.