Photo-optical Properties Research Articles

Photopatternable fluorescent polymer composites based on stretched porous polyethylene and photopolymerizable liquid crystal mixture

A novel approach for the creation of photopatternable fluorescent polyethylene-based liquid crystal composites was developed. Stretched porous polyethylene (SPPE) films were used as the polymer matrices. A liquid crystalline (LC) photopolymerizable mixture containing nematogenic dimethacrylate, cholesterol-containing acrylate and perylene-containing methacrylate was introduced into the pores of SPPE and optical and photo-optical properties of such composite were studied. Polarized spectral data and dichroism calculations showed that the transition moment of perylene side groups and the liquid crystal director in composite films are oriented along a stretching direction of SPPE. UV irradiation induces photopolymerization of the LC mixture but does not lead to significant decrease in dichroism of the perylene groups, however it stabilizes the LC structure in composite films. A possibility of photopatterning of SPPE-based composite filled with LC photopolymerizable mixture was demonstrated. The novel composites can be considered as promising materials for photonic and optical applications.

Photochromic liquid-crystalline copolymers containing crown ether groups

An approach was developed for the synthesis of new multifunctional photosensitive liquid-crystalline copolymers of the acryl series containing azobenzene, ionophoric, and mesogenic groups in the same macromolecule. The phase behavior of the copolymers was studied. Most of these copolymers were demonstrated to form nematic mesophases. An increase in the concentration of crown-containing groups to 26 mol.% leads to amorphization of the copolymers. The influence of complexation of the crown ether groups of the copolymers with potassium perchlorate on the mesomorphic properties of the systems was investigated. A comparative study of the photooptical properties of the copolymers in solution and thin films was performed.

Construction of CdS quantum dots via a regioselective dendritic functionalized cellulose template

Using regioselective dendritic functionalized cellulose, CdS quantum dot nanoparticles were prepared and their photo-optical properties and morphology as well as the preliminary biocompatibility of the hybrid were investigated.

Thermal and photo optical properties of azoxybenzene/alkyloxy-azobenzene–cholesterol dimesogens with alkyl diacetylene linker

Thermal and photo-optical properties of azoxybenzene/alkyloxy-azobenzene containing chiral dimesogens are presented. Alkyloxyazobenzene containing dimesogenic materials exhibited two kinds of smectic A phases. Photoirradiation at temperatures exhibiting smectic phases of pure materials in azobenzene linked dimesogens resulted in formation of the isotropic phase, and this was systematically studied at different liquid crystalline temperatures. The efficacy of these compounds as a dopant in the glassy liquid crystalline material was also explored. Increasing concentration to 4 wt%/5 wt% in azobenzene/azoxy-benzene derivatives caused a dramatic red-shift in the wavelength of reflected light by the host cholesteric glassy liquid crystal. Photo-isomerization of these dopants led to a blue-shift of the reflected light, and this effect could be used to tune the light reflectivity of these mixtures over the visible region.

Phase Behavior and Photooptical Properties of Liquid Crystalline Functionalized Copolymers with Low-Molecular-Mass Dopants Stabilized by Hydrogen Bonds

The approach of deriving new photooptically active polymeric substances by hydrogen bonding between functionalized liquid crystalline (LC) copolymers and low-molecular-mass dopants, containing photochromic azobenzene fragments, is described. The formation of intermolecular hydrogen bonds between carboxylic groups of functionalized LC copolymers and the pyridine fragment of the dopant leads to stable, nonseparating mixtures in a broad interval of contents (up to 30 mol % dopant molecules). The phase behavior and structure of photochromic mixtures are investigated. Induction of a nematic mesophase is observed in the case of a smectic polymer matrix doped with low-molar-mass photochromic dyes.

Metallodendrimers Composed of Organometallic Building Blocks

AbstractFor Abstract see ChemInform Abstract in Full Text.

Light-responsive chiral photochromic liquid crystalline polymer systems

The authors reviewed their results obtained in recent years in the field of development of advanced optically controlled polymer systems based on photochromic cholesteric liquid crystalline (LC) polymers and their blends with each other and with low-molar-mass chiral and photochromic dopants. Recent advances in the research dealing with the design and study of photo-optical properties of photoresponsive LC polymers composed of nematogenic, chiral and one or two photochromic fragments incorporated in the same monomer units or entirely into the macromolecule as individual monomers are discussed. All polymer systems form cholesteric phase with a helical supramolecular structure. The light irradiation leads to the isomerization of one or two photochromic groups, which results in the variation in the helical twisting power of chiral fragments. This process is accompanied by dramatic changes in the supramolecular helical structure and optical properties of the LC polymer. This provides the possibility for controlling the pitch of helix, the rate of helix twisting and untwisting, spectral range, and the width of the selective light reflection. The photochromic LC systems offer new promising materials for reversible and irreversible colour data recording that can be used in optical memory systems (data storage), holography, colour projection techniques and give rise to a new generation of videodiscs, flat light guides and coatings with photocontrollable optical properties.

Photo-orientation phenomena in photosensitive chiral nematic copolymers

Photo-orientational phenomena have been studied for two comb-shaped cholesteric copolyacrylates containing azobenzene side groups. Copolymer I contains nematogenic phenyl benzoate groups and photosensitive chiral menthyl-containing azobenzene side groups. Copolymer II is composed of nematogenic phenyl benzoate groups, photosensitive cyanoazobenzene groups and chiral photochromic benzylidene- p -methan-3-one fragments. Under the action of polarized Ar+ laser light (488 nm), orientation of the side groups of the copolymers takes place, and this orientation is perpendicular to the vector of the electric field of the incident light. This process shows a co-operative character; that is, it involves both photosensitive azobenzene and phenyl benzoate groups. The kinetics of growth of the photoinduced orientational order parameter were studied as a function of film thickness, incident light intensity, and preliminary UV irradiation. For the planar oriented films of the copolymers, irradiation with polarized light leads to the development of photoinduced birefringence δ n ; maximum values of δ n reach 0.01. The photo-optical properties of copolymers I and II are compared. Such materials may be used for ‘dual’ data recording by varying the helix pitch, selective light reflection maximum, and photoinduced birefringence or linear dichroism.

Chiral Nematic Polymer Mixture Containing Crosslinker and Photosensitive Chiral Dopant: New Type of Materials with Tunable Photo-Optical Properties

Chiral Nematic Polymer Mixture Containing Crosslinker and Photosensitive Chiral Dopant: New Type of Materials with Tunable Photo-Optical Properties

Photochemical and Photoorientational Behavior of Liquid Crystalline Carbosilane Dendrimer with Azobenzene Terminal Groups

The photochemical and photooptical properties of the first-generation LC dendrimer with terminal azobenzene groups which forms a SmA mesophase in a wide temperature range have been studied. A comparative analysis of its photochemical behavior in a dilute solution and a thin film was carried out. Under the action of UV irradiation, the E/Z photoisomerization of the azobenzene group takes place both in the solution and in the film. This process is found to be photochemically and thermally reversible. The kinetics of the thermal Z/E process is studied, and the activation energy of the process is calculated. The process of the photoinduced orientation of the terminal azobenzene groups in films of the dendrimer upon irradiation with linearly polarized UV light (365 nm) and with the green light of an Ar+ laser (488 nm) was studied. Under irradiation with linearly polarized UV light, the E/Z isomerization takes place, but photoorientation is not observed. However, in the case of linearly polarized green light exposure (488 nm), a well pronounced linear dichroism is generated. The kinetics of the process was studied, and the photoinduced orientational order parameter was calculated.

The dysfibrinogenaemias.

The dysfibrinogenaemias.

Photosensitive cholesteric copolymers with spiropyran-containing side groups I. Phase behaviour and photo-optical properties

A number of terpolymers were synthesized by copolymerization of nematogenic, chiral and photochromic monomers with different contents of spiropyran photosensitive side groups. The synthesized copolymers possess selective light reflection in the visible region of the spectrum. Action of UV light on planarly-oriented films of the copolymers leads to the formation of the merocyanine form of the dye with a maximum of absorbance coinciding with the selective light reflection peak. The 'degeneration' of the selective light reflection is observed during this process. It was shown that such types of material can be used for reversible information storage; the principal scheme for the processes of optical data recording and reading is suggested.

Field-responsive chiral-photochromic side-chain liquid-crystalline polymers

A series of cholesteric copolymers containing combined chiral-photochromic side-groups has been obtained and their phase behaviour, optical and photo-optical properties have been studied. All copolymers are characterized by selective light reflection in the visible and IR spectral regions. It is shown that the light can be used as a very effective regulated 'external field' to control locally supramolecular structure and the optical properties of polymer films. The synthesized polymers are shown to be promising candidates for colour data recording.

New chiral photochromic menthone-containing homopolymers and copolymers - synthesis, phase behaviour and photo-optical properties

A new approach for the preparation of photosensitive materials for coloured data recording and storage is advanced. This approach involves the synthesis of copolymers containing nematogenic and combined (-)-arylidene-p-menthan-3-one chiral photochromic fragments in one monomer unit. The conditions for the formation of an LC phase in the chiral photochromic homopolymers as a function of the structure of the side groups have been identified; for a new series of copolymers, the effect of their composition on the phase behaviour and photooptical properties is considered. Planarly oriented films of the copolymers show selective light reflection in the UV, visible, and near IR spectral regions. The photochemical behaviour of the homopolymers and copolymers in dilute solution and as films has been studied. In these systems, under UV radiation, the E-Z isomerization of the (-)-arylidene-p-menthan-3-one fragment is the dominating process. The kinetic features of the photoprocess are revealed, and the effective quantum yields calculated. The isomerization process leads to dramatic changes in the anisometry of the chiral side groups, and the helical twisting power decreases. Therefore, as a result of UV radiation of films of the copolymers, the selective light reflection peak is shifted to a longer wavelength spectral region. This means that such polymeric films can be considered as promising materials for colour data recording and as storage media.

New Type of Chiral Photochromic Liquid Crystal Polymers for Colour Photo-Optical Recording

Photo-optical properties of a cholesteric copolymer based on nematogenic and photosensitive optical active lateral groups containing a benzeliden-p-mentan-3-on fragment have been investigated. The selective light reflection wavelength was found to be controlled by the UV irradiation that causes the photoisomerization of the chiral photochromic groups. As a result the selective reflection of light can be changed locally. That permits the recording of a color image on a color background. The copolymer's photo-optical properties are compared with properties of a blend of cholesterol-containing copolymer with a low-molar-mass chiral dopant based on menthone derivatives.

Photo-optical properties of new combined chiral photochromic liquid crystalline copolymers

For the first time, a series of cholesteric copolymers containing combined chiral photochromic side groups has been synthesized and the phase behaviour and optical properties of the copolymers have been characterized. Specific features of the photochemical and photo-optical behaviour of such systems were studied, and the quantum yields of the photo-induced process in solution and in the condensed state of the cholesteric copolymers were calculated. The selective light reflection wavelength was found to be controlled by the UV radiation. The synthesized polymers were shown to be promising candidates for colour data recording.

Tendency towards crystallization of Ge-As-Te system glasses

Recently, in the field of the physics of condensed systems, of special importance are investigations concerning the problem of the application of materials with predetermined, i.e. predictable, characteristics. Fundamental investigations of complex noncrystalline semiconductors have revealed some specificities of their spectral, optical refractive, photo-optical, elasto-optical and electrophysical properties. Of special importance are the materials containing chalcogenic elements (S, Se, Te), as the nature of the chalcogen and the character of the bonds formed in glasses of this type offer possibilities of varying relevant parameters of the obtained materials. In the frame of our systematic investigations of three-, fourand five-component glass systems, involving first of all S and Se [1-4], the aim of this work is to present some of the results of X-ray characterization of Te-containing glasses. Glasses of the type (AssoTes0)x (GelsTe85)t00-x were obtained by synthesis from high-purity elementary components involving heating in sealed evacuated quartz ampoules for many hours. Maximum temperature of synthesis was 950 °C, and the melt was held at this temperature for 20-25 h. Having in mind the fact that the area of glassy state of the Ge-As-Te system is relatively small, and that Te-containing glasses exhibit an increased tendency towards crystallization [5, 6], the process of melt cooling was carried out by annealing in cold water. To obtain more complete information about the relevant structural units of the three-component system, glass of stoichiometric composition As2Te3 and glass with equal percentage content of the components AsTe have been prepared by an analogous synthetic procedure. X-ray studies were performed using an automatic powder diffractometer PW 1373-PW 1065/50 (Philips) with high temperature attachment HTK 10 (Paar) and automatic control bar HTK 2-HC (Paar). Experiments were carried out up to a maximum temperature of 500 °C. The rate of sample heating was 1 or 2 °C/min. Fig. 1 shows X-ray diffraction spectra for two samples of the investigated three-component system at a number of characteristic temperatures. The amorphous character of the synthesized materials has been confirmed by the absence of maxima in the diffraction spectra of thermally untreated samples (curves 1 in Fig. l a and b).