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

We have synthesized chiral small-bandgap polymers by introducing chiroptica l 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 negat ive one. The results indicate that the polymers have helical structures, in which the screw direction should be varied with the number of thiophene ri ng of the unit cell.