Light-Controlled Supramolecular Helicity of a Liquid Crystalline Phase Using a Helical Polymer Functionalized with a Single Chiroptical Molecular Switch

Control over the preferred helical sense of a poly(n-hexyl isocyanate) (PHIC) by using a single
light-driven molecular motor, covalently attached at the polymer's terminus, has been accomplished in
solution via a combination of photochemical and thermal isomerizations. Here, we report that after
redesigning the photochromic unit to a chiroptical molecular switch, of which the two states are thermally
stable but photochemically bistable, the chiral induction to the polymer's backbone is significantly improved
and the handedness of the helical polymer is addressable by irradiation with two different wavelengths of
light. Moreover, we show that the chiral information is transmitted, via the macromolecular level of the
polyisocyanate, to the supramolecular level of a lyotropic cholesteric liquid crystalline phase consisting of
these stiff, rodlike polymers. This allows the magnitude and sign of the supramolecular helical pitch of the
liquid crystal film to be fully controlled by light.