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.

We recently reported that the photoisomerization of molecular motors used as chiral dopants in a cholesteric liquid crystal film induces a rotational reorganization which can be observed by optical microscopy and produces the motion of microscopic objects placed on top of the film (Feringa, B. L.; et al. Nature 2006, 440, 163; J. Am. Chem. Soc. 2006, 128, 14397). The mechanism underlying the mesoscopic manifestation of the molecular process was not fully understood, and here we present a joint theoretical and experimental investigation, which provides a detailed insight into the mechanism of texture rotation. This description allows us to identify the interplay between the chemical structure of the chiral dopant and the material properties of the liquid crystal host, and to quantify their role in the observed dynamic phenomenon. We have found that a crucial role is played by the hybrid anchoring of the liquid crystal, with the director parallel to the substrate and perpendicular to the interface with air; in this configuration an almost unperturbed cholesteric helix, with its axis normal to the substrate, is present in most of the film, with strong deformations only close to the free interface. The texture rotation observed in the experiment reflects the rotation of the director during the unwinding of the cholesteric helix, produced by the change in shape of the chiral dopant under photoisomerization. The rotational reorganization is controlled by the photochemical process, via the coupling between the chirality of the dopant and the elastic properties of the liquid crystal host.

A chiral poly(n-hexyl isocyanate) can form ordered mesoscale toroidal structures when drop-cast on a variety of surfaces.

Vesicular catalysis of the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate. The effects of sugars, long-tailed sugars, cholesterol and alcohol additives Jongejan, Mahthild G. M.; Klijn, Jaap E.; Engberts, Jan. B. F. N.; Kiijn, J.E. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. ABSTRACT: The effects of the addition of sugars, long-tailed n-alkyl pyranosides, n-alkyl glycerol ethers and nalcohols on the properties of di-n-hexadecyldimethylammonium bromide (DHAB) vesicles have been studied. Properties that were examined include the stability, morphology, phase of the tails, and catalytic rate acceleration of the unimolecular decarboxylation of the 6-nitrobenzisoxazole-3-carboxylate anion (6-NBIC). The kinetic data were analyzed on the basis of the pseudophase model and show a rate acceleration of a factor of about 1000 relative to the reaction in water. Upon addition of most additives an inhibiting effect on the decarboxylation reaction of 6-NBIC is observed relative to the reaction in vesicles without any additive. The largest inhibition was observed in the case of cholesterol. Contrastingly, n-dodecyl-b-maltoside (in the spherical vesicle region) and trehalose accelerate the reaction. The activation parameters show that the most significant contribution to the Gibbs energy of activation is the enthalpic factor, with a partly compensating entropic contribution.