Oksana Nadtoka

Nonlinear Optical Effects In Polymeric Azoesters

The methacrylic monomers containing azobenzene moiety with flexible alkyl spacers of different lengths and groups of different nature are synthesized, and their physicochemical properties were determined by electronic absorption, 1H NMR spectroscopy, and element analysis. In the present work, the homopolymers built with the use of the free radical polymerization of methacrylic monomers incorporating an azobenzene side-group have been synthesized and structurally characterized. The results of photochemical and optical activities of the corresponding polymers are presented. Third-order nonlinear optical (NLO) properties of the azopolymer solutions are studied by the degenerate four wave mixing (DFWM) method.

Photochromic Polymers Based on Methacrylic Azoesters

ABSTRACT The new polymers and copolymers based on methacrylic acid azoesters with substituents of different nature and spacer length were synthesized. The difference in chemical structure of the side chains was expected to influence on the difference in the supramolecular structure of azobenzene moieties. Due to flexibility of alkyl spacers, the azobenzene fragments can rotate relatively freely in the polymeric matrix.

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

ABSTRACT 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 Tg 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 azochromophores concentration in polymers reduces the anisotropy rate but not influence the trends described above. The observed regularities were earlier described for several other classes of photosensitive polymers and so they may be common rules for photoordering in the photochromic media.

Factors in liquid crystal photoalignment on polymer films: photoorientation versus self‐assembly

We demonstrate that photostimulated self‐assembly, running in parallel with molecular photoorientation in the top layer of the aligning polymer film, breaks the bulk molecular order mainly determined by the symmetry of irradiation. This may substantially modify liquid crystal (LC) alignment. Depending on the chemical composition of the liquid crystal, the self‐assembled layers may influence either homeotropic or planar LC alignment with extremely weak azimuthal anchoring. Effective self‐assembly occurs in polymers having side chain chromophores with flexible spacers and polar terminal groups.

Photoinduced Orientation of Azobenzene Groups in Polymer Films. Characterization by UV/Visible Spectroscopy

We study the kinetics of the photoinduced orientational ordering of two methacrylic polymers containing different azobenzene groups with both electron-donor and electron-acceptor substituents under irradiating them at two different wavelengths. For the experimental study of the orientational distribution in polymer films, we use the method based on absorption measurements. It is found that azofragments are oriented by either the photoorientation or photoselection mechanism depending on the wavelength. The components of the order parameter tensor of azobenzene fragments are estimated for the initial state and after different doses of irradiation.

The influence of matrix material on the spectral dependence of the photosensitivity of polymer nanocomposites

ABSTRACT The influence of matrix material on optical and photovoltaic properties of nanocomposite dyes-containing films is analyzed. The H-aggregates of the polymethine dyes with different energies are formed in the films. The efficiency of charge-carrier photogeneration of some H-aggregates is higher than that of quasi-isolated dyes molecules. This results in an essential widening of the spectral region absorption and the photosensitivity to the region 1.6-2.0 eV. The energy maxima for H-aggregates weakly depend on the matrix molecular structure, whereas their photosensitivity maxima mainly depend on the dyes molecular structure. The effective charge carrier photogeneration and the photovoltage in these films in the region 2.0–3.0 eV are verified.

The photochemical behavior of polyhydroxy styrene with azofragments containing free methacrylic double bounds

ABSTRACT Polymer material which combines advantages of photoaligning azo-compounds with thermal stability of the induced anisotropy provided by free methacryloyl groups was synthesised. FTIR spectroscopy was employed for clarification its photochemical behavior. Two Fries rearrangements in arylester groups and photoinitiated cross-linking in methacryloyl functional groups were established after the action of UV-irradiation.

Polymer dye-containing nanocomposites as photocatalysts

ABSTRACT A significant improvement of photocatalytic efficiency is achieved by the synthesis of TiO2/SiO2 nanocomposites where silica matrix provides the transport of reagents to TiO2 nanoparticles via porous structure, generation of the new active sites and thermal stability. The semiconductive films contained 10 or 30% of TiO2 in silica matrix are synthesized by sol-gel method using concentrated anatase titania colloid. The complex composites consisted of i) the Acridine Yellow dye molecules and the polyepoxypropyl carbazole; ii) the azobenzene containing polymer covered onto the titania/silica films are obtained as photocatalytic materials. Photocatalytic activity of the composites is tested via the reduction of dichromate ions.

Some Multifunctional Methacrylic Polymers with Azobenzene Fragments and Free Double Bonds in Side Chains as Liquid Crystal Alignment Agents

Two series of polymers based on the polymethacrylic acid were obtained and investigation of their orientation ability was carried out: “azobenzene-containing” polymers; “azobenzene-oxyethylmethacrylate-containing” polymers. Under the action of actinic UV light photosensitive fragments of these materials are undergone the orientation and crosslinking due to trans-cis isomerization of azofragments and photopolymerization of free C˭C bonds. Liquid crystal photoalignment ability of these materials is investigated.

Investigation of selected polymers with different azobenzene moieties for NLO application

The polymers with different azobenzene moiety were synthesized. The results of photochemical and optical activities of the corresponding polymers are presented. The third order nonlinear optical susceptibilities of studied compounds have been investigated in solutions using degenerate four wave mixing (DFWM) method at 532 nm.