Photosensitive Functional Supramolecular Materials From Ionic Self-Assembly

Photosensitive polymers have attracted great interest in recent years due to their high potential application in smart response system and optical elements. Presently, various photosensitive materials have been exploited by doping dyes in polymers or covalent synthesis of photosensitive polymers. However, doping films usually have low dye loading and present unstable photoinduced property. Covalent photosensitive materials show better photoinduction stability, nevertheless the synthetic processes usually were rigorous and fussy and involved many steps with low yield. So the design of photosensitive polymer with optimizing properties to satisfy different applications is still the most attractive target. Ionic self-assembly (ISA) mainly employs the coulombic interaction to bind the oppositely charged tectonic units together and the complex architectures can be precisely tailored by selection of constituents according to the desire of different applications, which presents a promising situation for design of photosensitive materials with unique photochemical and photophysical properties. This dissertation describes research that is done aimed to obtain a series of photosensitive materials with improved and tunable properties by ISA technology. Their phase behavior, optical property and utility for LC alignment were investigated in detail. These preliminary studies may put more insight to the synthsis of photosensitive polymer with preferable properties.A new strategy based on ISA technology was provided for design of photosensitive material as liquid crystals (LC) alignment layer. The complex material was constructed by the coupling of poly(ionic liquid) and photosensitive unit methyl orange (MO). The structure, phase behavior and photoresponse were examined by a variety of techniques including FTIR, NMR, thermal analysis, polarized optical microscopy, X-ray diffraction, small-angle X-ray scattering and birefringence measurements. Highly ordered lamellar nanostructure and photosensitive character were confirmed. Under the irradiation of pulsed UV laser, the moderate optical anisotropic surface with the preferred direction perpendicular to the pulsed polarization or regular periodic grooves microstructure surface parallel to the pulsed polarization depend on laser fluence was obtained. The anisotropic surface of oriented molecular chain or topography was demonstrated to be resultful for the alignment of LC by the optical transmittance plot and polarizing microscopy images of LC cells with different rotation angle.Although the above photosensitive supramoleculethe prove to be useful in fabrication of anisotropic surface and subsequent LC alignment, its rigid structure results in poor mechanical property and also restricts photo-orientation. So we further elaborately design a series functional unit azobenzene ionic liquid crystal (azo-ILC) with a spacer length of 4, 6 or 12 methylene units, respectively, aim to obtain azobenzene thermotropic liquid crystalline polymer (LCP) for tunable phase behavior and improved optical orientation. The thermotropic LCP was fabricated by ISA of PAA and azo-ILC. Highly ordered liquid-crystalline structure with a lamellar morphology of different d-spacing was observed. The photo-induced orientation of azobenzene groups in thin films of the obtained ionic-bonding supramolecules was studied by polarized UV–Vis and FTIR. Under the irradiation of pulsed laser, very effective induction of optical anisotropy with the preferred direction perpendicular to the pulsed polarization was observed. Typically, the maximum in-plane orientation order of 0.93 for PAZO12 was achieved after irradiation and subsequent anneal, which was the reported crown valve up to now. It was found that the maximum S can be increased by increasing the clearing temperature of the photosensitive material. These results may provide guidelines for the design of effective photo-induced anisotropic materials. Supramolecular materials from ISA of polyelectrolyte and surfactant or elaborate amphiphilic molecules are mono-functional, while practical applications usually request material having multidimensional properties or functions. The design of difunctional and even multifunctional materials is becoming a trend of material development. Thus we proposed a concept of dual-functionalized supramolecules for effective optical anisotropy and tunable wettability. These complexes were fabricated by ISA technique that involved grafting different proportions of the photoresponsive units of MO and perfluorinated dodecanoic acid (FDA), as functional side-chains, onto a poly(ionic liquid). Surface wettability and photoinduced anisotropy could be tuned by changing of the molar ratio of MO and FDA. A pronounced anisotropic orientation with a birefringence valueΔn~10-2 was achieved at room temperature, and the complex films were found to possess the characteristics of long-term optical storage. Continuous tunable wetting properties were demonstrated and contact angles of the test liquids increased with an increase in the FDA content. Furthermore, LC orientational transition from planar to homeotropic alignment was achieved by adjusting the FDA content in the orientated complex alignment layers.Polymeric films composed of cinnamate derivatives are transparent in a visible region should be more attractive for optical devices and LC alignment. The photoreaction of cinnamate polymer includes a [2+2] photocross-linking reaction and photoisomerization of the cinnamic acid. The photocross linking make the film insluable and the photoinduced orientation very stable. In addition, it can be used to fabricate the photolithographic images for electronics applications. Herein, a kind of photosensitive polymer with photo-cross-linkable side chain group was devoloped based on ISA technology. The photo-cross-linkable supramolecules were constructed by the coupling of polyelectrolyte and cinnamate units with different spacer length (6 or 12 methylene units designated PCAM6 and PCAM12, respectively). Photochemical properties including photo-cross-linking and photoinduced orientation of complex materials were investigated by irradiating with a polarized laser. A clear photolithographic image was obtained by laser exposure. Its photoorientation result proved that long spacer length favors the photo-isomerization of the cinnamate group, which leads to higher photoinduced anisotropy for PCAM12 than that of PCAM6. Furthermore, a homogeneous and stable liquid crystals alignment was achieved on the resultant anisotropic orientation film.