Abstract
A new isocyanate monomer was synthesized which contains an azobenzene dye connected to the isocyanate group via a chiral spacer. Copolymers with the achiral hexyl isocyanate were prepared by anionic polymerization with NaCN. CD measurements in solution show that the chiral center in the spacer induces a shift in the equilibrium between P- and M-helical main chain conformations toward the left-handed conformation. The magnitude of this chiral induction can be varied reversibly by photochemical isomerization of the azo chromophore (trans → cis). The preference for one twist sense of the polymer chain is much larger than in previously studied systems, if copolymers with the same amount of chiral monomer units are compared. It is thus possible to build chirooptical switches with only small amounts of chiral monomers.
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