In this work, azobenzene-containing colloidal spheres have been fabricated and used to construct photoresponsive monolayers. The colloidal spheres were prepared from an amphiphilic azobenzene-containing random copolymer through hydrophobic aggregation of the polymer chains, which was induced by adding the selective solvent (H2O) into a THF solution of the polymer. The size and size distribution of the spheres depended on the initial concentration of the azo polymer in THF and the H2O/THF ratio. Adjusting those factors and optimizing other preparation conditions, uniform colloidal spheres could be obtained. Monolayers composed of hexagonally close-packed colloidal spheres were prepared by the capillary-force-driven method. The colloidal monolayers showed obvious dichroism after laser irradiation due to the photoinduced azo-chromophore orientation occurred in the spheres. The orientation order parameter was related to the irradiation time and estimated to be 0.09 at the photostationary state. The colloidal spheres and their monolayers can potentially be used as building blocks or media for reversible optical data storage, photo-switching, sensors, and other photo-driven devices. 相似文献
Hydrogen-bonded disk-shaped aggregates (rosettes) composed of azobenzene-appended melamine and barbiturate or cyanurate are investigated in view of their hierarchical organization and photoresponsive behavior by (1)H NMR and UV/vis spectroscopies, dynamic light scattering, and gelation behavior in aliphatic solvents and liquid crystalline behavior in bulk state. In the bulk state the rosette possessing a sterically bulky tridodecyloxyphenyl substituent in the barbiturate component stacks in an offset arrangement to form a rectangular columnar mesophase, whereas in aliphatic solvents it does not hierarchically organize into higher-order columnar aggregates. This drawback is improved by exchanging the barbiturate component into a more sterically nondemanding N-dodecylcyanurate component. The resulting new rosette stacks in a face-to-face arrangement to form a hexagonal columnar mesophase in the bulk state and hierarchically organizes into elongated fibrous aggregates in cyclohexane, which eventually leads to the formation of organogel. Dynamic light scattering and UV-vis experiments upon UV-irradiation of the columnar aggregates in cyclohexane revealed that the dissociation and the reformation of columnar aggregates can be controlled by the trans-cis isomerization of the azobenzene moiety. Molecular modeling indicates that the rosette possessing cis-azobenzene side chains loses its planarity. Using this photoinduced morphological change of the rosette, photoresponsive organogel is created by the use of a disk-shaped supramolecule the first time. 相似文献
The crosslinked polystyrene beads which immobilized two terminal azophenoxide groups of an azobenzene-crown(24-crown-8)-azobenzene unit were synthesized. The polymer beads adsorbed Cs+ in the dark while they rapidly released Cs+ into the solution under UV-light irradiation, and the photoresponsive complexation occurred reversibly. On the other hand, the crosslinked polystyrene beads which immobilized one terminal azophenoxide group of an azobenzene-crown (24-crown-8) unit scarcely (or only to a smaller extent) exhibited such a photoresponsive behavior. Similarly, the polymer beads which immobilized two terminal azophenoxide groups of an azobenzene-crown (18-crown-6) azobenzene unit reversibly adsorbed and desorbed K+ in response to UV-light irradiation. The novel photoresponsive behavior is ascribed to a conformational distortion of the crown rings which induced by the photoisomerization of the azobenzene moiety, although the photoinduced polarity change of the polymer beads is not completely ruled out. The results suggest that the polymer support is useful as a “fixed point” to enforce the conformational changes of immobilized functional molecules. 相似文献
The synthesis of an oriented liquid‐crystalline photoresponsive polymer, prepared by polymerization of mono‐ and di‐acrylates, both of which contain azobenzene chromophores, is reported. The prepared free‐standing polymer film shows strong reversible photoinduced deformation upon exposure to unpolarized UV light at 366 nm, as a result of an optically induced isomeric change of the azobenzene moieties in the polymer network. The synthesis process is relatively simple and more efficient compared to conventional ones, and can be used to synthesize other liquid‐crystalline photoresponsive polymers. The use of this photoresponsive polymer film as an optical high‐pass/low‐pass switch under UV or natural light irradiation for a laser beam is demonstrated. This photoresponsive polymer may have applications in robotic systems, artificial muscles, and actuators in microelectromechanical systems (MEMS) and labs on chips.
Photoisomerization in some azobenzene-containing polymers (azopolymers) results in reversible solid-to-liquid transitions because trans- and cis-azopolymers have different glass transition temperatures. This property enables photoinduced healing and processing of azopolymers with high spatiotemporal resolution. However, a general lack of knowledge about the influence of the polymer structure on photoinduced reversible solid-to-liquid transitions hinders the design of such novel polymers. Herein, the synthesis and photoresponsive behavior of new azopolymers with different lengths of spacers between the polymer backbone and the azobenzene group on the side chain are reported. Azopolymers with no and 20 methylene spacers did not show photoinduced solid-to-liquid transitions. Azopolymers with 6 or 12 methylene spacers showed photoinduced solid-to-liquid transitions. This study demonstrates that spacers are essential for azopolymers with photoinduced reversible solid-to-liquid transitions, and thus, gives an insight into how to design azopolymers for photoinduced healing and processing. 相似文献
