The Initial and Photoinduced 3D Orientational Order in Polymethacrylates with Azobenzene Side Groups

The combination of the transmission null ellipsometry and total absorption method, earlier approved for several polymer classes, is applied to study 3D orientational configurations of azochromophores in polymethacrylates with azobenzene side groups. The transformation of the initial orientation due to the photoexcitation of azochromophores is investigated. The dependence of the orientational configuration on the structure of azochromophore fragments and its concentration in the polymers are also studied. In the non-irradiated films, azochromofores strive to be aligned normally to the film plate. Under irradiation, if reorientation mechanism of the photoinduced ordering prevails, the azochromophores reorient perpendicularly to the polarization direction of the exciting light, E ex , and in the saturation state they are randomly distributed in the plane perpendicular to E ex . This implies that the induced structure is mainly influenced by the photoordering, while selfordering of polymer chains is not effective or overcome, presumably because of high T g of polymethacrylates. In case when photoselection ordering mechanism dominates, 3D distribution of azochromophores in the saturation state of irradiation is isotropic due to a strong exhaustion of the number of anisotropic trans isomers. The transient photoinduced orientations are biaxial independently on the dominating ordering mechanism. The reduction of the azochromophore's concentration in polymers reduces the anisotropy rate but not influence the trends described above. The observed regularities were earlier described for several other These studies were carried out within the framework of the project ''Ordering regularities and properties of nano-composite systems'' of the NA Sci. of Ukraine. Partially, they were also supported by

Photoinduced 3D orientational order in side chain liquid crystalline azopolymers

We apply experimental technique based on the combination of methods dealing with principal refractive indices and absorption coefficients to study the photoinduced 3D orientational order in the films of liquid crystalline (LC) azopolymers. The technique is used to identify 3D orientational configurations of trans azobenzene chromophores and to characterize the degree of ordering in terms of order parameters. We study two types of LC azopolymers which form structures with preferred in-plane and out-of-plane alignment of azochromophores, correspondingly. Using irradiation with the polarized light of two different wavelengths we find that the kinetics of photoinduced anisotropy can be dominated by either photo-reorientation or photoselection mechanisms depending on the wavelength. We formulate the phenomenological model describing the kinetics of photoinduced anisotropy in terms of the isomer concentrations and the order parameter tensor. We present the numerical results for absorption coefficients that are found to be in good agreement with the experimental data. The model is also used to interpret the effect of changing the mechanism with the wavelength of the pumping light.Comment: uses revtex4 28 pages, 10 figure

Photoluminescence of Liquid-Crystal Azo Derivatives in Nanopores

The properties of organic nanocomposites are of much interest from the point of view of both basic research and practical application. This interest has increased significantly in recent years, when nanotechologies allowing production of nanoobjects with unique physical properties have been developing very rapidly. The class of organic nanocomposites under study is very wide. It includes organic media filled with nanoparticles [1], porous media containing fine-grained particles of organic materials In this paper, we report the results of studying the photoluminescence (PL) of a system formed by a liquid crystal (LC) and a porous glass. The object and the method of study were chosen for several reasons. First, it is well known that LCs form a unique class of materials. They are characterized by intermediate phases (mesophases) in the temperature range between the solid and liquid states and combine anisotropy (typical of solid crystals) with fluidity (typical of liquids). Such materials show LC properties in both macroscopic volumes and microvolumes. At the same time, according to EXPERIMENTAL Objects of Study Porous glasses with different pore sizes, prepared at the Institute of Technical and Macromolecular Chemistry of Martin Luther University (Halle, Germany), were used as porous matrices. Porous glasses were obtained from initial sodium borosilicate glasses by the technique described i