Search

We report complex optical investigations of polymer-stabilised cholesteric photonic liquid crystal doped by a dichroic fluorescent dye. For the first time, we employed a combination of various expe...

The absorption properties of a dye molecule depend on its orientation relative to the light source. Thus the ability to predict how well a particular dye aligns with a liquid crystal host will impr...

Polymer dispersed ferroelectric liquid crystals (PDFLCs) have disclosed an enormous approach for use in electro-optic and display technology since ferroelectric liquid crystals (FLCs) have inherently fast switching speeds. In this work, we equipped dichroic PDFLC using dye-doped chiral SmC* liquid crystal (LC) and ultra-violet (UV) curable polymer by polymerization induced phase separation (PIPS) method. All fundamental material aspects like optical transmissions, spontaneous polarization, threshold voltage, contrast ratio and response time as a function of applied voltage, temperature, and dye concentration were examined. In the electro-optic study, 82% transmission with a threshold field value ∼0.6 V/μm was observed for PDFLC, however, 90% transmission was achieved with a threshold field ∼0.3 V/μm at the dye concentration of 0.125% (wt./wt.). As a result, present dichroic PDFLC device shows microseconds switching response, higher polarization value and superior contrast, at low dye concentration.

Light-emitting liquid crystal displays (LE-LCDs), serving as emissive displays, are considered as promising alternatives to conventional LCDs because of their superior power efficiency. A dichroic fluorescent dye (Z)-2-(4-aminophenyl)-3-(4-(fluorophenyl)acrylonitrile (CN-AFAN) is synthesised, which exhibits strong fluorescence in the solution and solid states. Moreover, an electrically switchable optical switch based on CN-AFAN and a cholesteric liquid crystal is demonstrated, which combines the internal scattering of excitation light and the dichroism of CN-AFAN to improve fluorescence contrast. The photoluminescence and transmittance of the optical switch is modulated by an electric field between the planar state, focal conic state, and homeotropic state. The resultant device is cost-effective and easy to fabricate, thereby demonstrating immense potential for security and display applications.

The opening installation in Colour and Vision: Through the Eyes of Nature is by the light artist Liz West, who uses dichroic glass to create spectrums of pure light (see Figure 1). Our Spectal Visi...

In order to study the droplet pattern and electro-optic (EO) behaviour of polymer dispersed liquid crystal (PDLC) with the addition of dye, dichroic polymer dispersed liquid crystal (DPDLC) films w...

A novel series of dichroic anthraquinone dyes have been successfully synthesised with conventional Sonogashira reaction. These synthesised anthraquinone dyes were found to have high dichroic ratios, good solubilities, excellent hues and to be potential candidates for guest–host liquid crystal displays. The dichroic ratio is as high as 13.26, which is in the top level of the anthraquinone dyes reported so far. In addition, this paper provides an effective method to modulate the optic properties of anthraquinone dyes from the molecular level via the introduction of different radicals on the anthraquinone cores.

The investigation of the helical pitch and the helical twist sense for several liquid crystal compounds in antiferroelectric phase have been performed. Electronic circular dichroic (ECD) and vibrational circular dichroic (VCD) spectroscopies have proved the existence of unwound helical structure in antiferroelctric phase. Obtained results may confirm the assumption connected via the inversion phenomena in liquid crystalline chiral phase with the change of the concentration of different conformers promoting opposite handedness. Two examples of such conformers, obtained by conformational analysis, have been proposed.

Low-band-gap polymers are promising materials for organic photovoltaic application. We prepared an oriented thin film of a low-band-gap polymer, PTB7, by friction transfer method. The oriented film showed a strong dichroic absorption in the whole visible range. The orientation of molecular chain was characterized by two-dimensional grazing incident X-ray diffraction (2D-GIXD) with synchrotron radiation. 2D-GIXD results showed PTB7 molecular plane parallel to the substrate plane, i.e., “face on orientation.”

Bistable or multi-stable displays have been attracting a great deal of attention owing to the demand for energy-efficient mobile devices as well as the arousal of environmental concerns. One of the candidates with the merit of bistability is the bistable chiral tilted-homeotropic nematic mode which can easily switch between the twist-like and homeotropic-like stable states. Introducing dichroic dyes into this optically bistable system, we demonstrated a bistable-liquid-crystal-display mode without the need of polarizers. A proper mixture of dichroic dyes of blue, orange, red, yellow and cyan colors that evenly cover the visible spectral range was considered and the electro-optical performance of the resulting device was addressed in this study.

Thin films of a nematic liquid crystal doped with three commercially available azobenzene dichroic dyes were successfully fabricated and their electro-optical properties as well as their selective optical absorptive characteristics were explored in detail. The experimental results showed that the films had a lower and higher transmittance of incident light across the whole visible region without and with an electric field applied, respectively. The transmittance of the light decreased with the increase in both the dye-doped concentration and the cell thickness. Moreover, the transmittances of the films from a continuous wave lasers (λ = 532 nm) were also studied, which exhibited the potential application as a laser protective material to protect against the damage to the sensor or human’s eye from a laser.

For more aggressive photo-decomposition of polyimide, the photoreactions employing triplet mechanism and the double fragmentation reactions were carried out. The polyimide was synthesized with cyclobutane-1, 2, 3, 4-tetracarboxylic dianhydride (CBDA) and 4, 4′-diaminobenzophenone (DABP) by condensation reaction. The benzophenone is well known triplet photo sensitizer, which was mixed with the equal mole ratio of the CBDA, The imidization reaction was confirmed by imide peak formation in FT-IR spectra. The orientation of polymer chains was confirmed by polar dichroic ratio of the liquid crystal cells. The benzophenone chromospheres shortened the UV irradiation time for the photodecomposition and induced the orientation of the polyimide chains.

The combination of synchrotron-based soft X-ray light sources and magnetism research has been very fruitful and productive in the last few decades and has led to numerous exciting results. This success is essentially based on resonant dichroic effects, which were employed to analyze magnetic order in an element-specific manner [11, 32]. Thanks to the short wavelength, magneto-dichroic effects could also be employed in microscopy, and within the available momentum transfer even magnetic scattering was developed [11]. Therefore, soft X-ray methods were and still are essential to develop the detailed understanding of magnetism and magnetic materials in the thermodynamic ground state available today.

This work reports the effect of dye on the photopolymerisation and electro-optical properties of polymer dispersed liquid crystal (PDLC) composite films. Dichroic PDLC (DPDLC) films based on a photocurable polymer and nematic liquid crystal (LC) with an azo dichroic dye were prepared by photopolymerisation-induced phase separation method. Polarising optical microscopy has been used for monitoring the phase separation kinetics and two-phase morphology evolution in the DPDLC system. LC domains with radial structures during initial period of phase separation adopted a resultant morphology of bipolar configuration over the course of polymerisation. The phase separation and morphology of LC domains was found to be dependent on the amount of dye used. Moreover, the addition of small amount of dye reduced the switching voltage, and enhanced the contrast ratio with improved switching time in the PDLC films. It was shown that, under the application of an electric field, the molecular orientation and absorbance of ...

Photoreactivity of photo-decomposible polyimde was studied with and without reactive monomer, RM257. Recently photo reactive monomers have been draw attention for better alignment of liquid crystals and broad viewing angle. Interfacial effects as well as macro molecular interaction have been studied to enhance anchoring energy of liquid crystal. After irradiation, polyimide film gives LC alignment, perpendicular to polarization direction of the UV irradiation. LC aligning direction is measured by polar diagram. We had time to adjust during 10min-30 min. And we exposed to linearly polarized UV the angle vertically or horizontally by measured the degree of LC alignment. And we used 253.7 nm UV light by the use of band pass filter. Because this photo-decomposition polyimide film when using the 253.7 nm UV light is active in the reaction. We are the best time of the photo-alignment can be found by dichroic ratio [= (Aper – Apara)/(Aper + Apara)]. Normal photo-decomposition polyimide films were 0.584 dichroic ...

Addition of the dichroic anthraquinone dye molecules in pure ferroelectric liquid crystal (FLC) matrix results in many improvement in the various vital parameters of the pure FLC. However, addition of anthraquinone dye molecules in pure FLC matrix is not advantageous every time. There are certain constraints which are crucial for the application of these systems into many devices. In this article, we have discussed the concentration and temperature dependence of vital properties of dye-doped FLC. In this study there is improvement in contrast ratio by dye doping due to enhancement in plane switching for dye-doped FLC.

Linear polyconjugated π-systems are rod-like molecular structures possessing mesogenic properties. Oriented layers of such materials demonstrate dichroic absorption of light. Prevailing absorption along long molecular axis of π-system, gives ground to study molecular distribution in the layer though polarizer light absorption. We derived equations to investigate light propagation in the layer with anisotropic absorption. If principle axes are known, series of polarized absorption spectra measurements in combination with sample rotation allow to measure volume absorption of the layer along x-, y-, z- axes to determine sx, sy, and sz order parameters of complex anisotropic structure. We investigated molecular reorientation dynamic of azo dyes (Reversible Intermolecular Bonding photoalignment materials) upon polarized light exposure. According to experimental results, for layers with thickness below quarter wavelength of observation, the Pointing vector (light energy) propagate through absorbing anisotropic ...

Dichroic dyes, based on anthraquinone chromophores, for incorporation into various liquid-crystalline host mixtures have been prepared. For each dye, which has been designed to absorb at different regions of the visible spectrum, we investigate liquid crystalline behaviour and prepare mixtures of dyes that also promote liquid-crystalline behaviour. The 2,6-disubstituted dyes, which are yellow and red, respectively, exhibit nematic and smectic C phase behaviour or smectic A and E phase behaviour over wide temperature ranges. In order to produce blue dyes we report a family of dyes derived from 1,5-dihydroxy-4,8-dinitroanthraquinone, which is similar in structure to known chromonic dyes. These dyes exhibit unusual optical textures by polarised optical microscopy, and display unusual mixing behaviour, which suggests the presence of a new type of liquid crystal.

The problem of the gain of dichroic devices is analysed in a framework based on a vectorial pure operatorial (non-matrix) Pauli algebraic approach to polarisation optics. We show that the partially polarised light and the partial polarisers can be described in this framework by absolutely similar, symmetric quantities. In this sense, a physically essential device parameter, the degree of dichroism, is defined. This symmetry between the description of the polarised light and of the polarisation devices leads to an expressive form of the generalised Malus’ law, the consequences of which are analysed in detail. Most importantly, one can for the first time describe and graphically illustrate the generalised structure of the gain of a dichroic device.

In recent past research on nanometal-glass hybrid composites has been the centre of attention across the globe particularly in the area of nanoscience and for the future nanotechnology. In this review, with a short historical background, its preparation by various multi-step techniques, properties and applications are briefly described. In addition, recently developed single-step in situ thermochemical reduction methodology by these authors for synthesis of various nanometal-glass hybrid nanocomposites are described in detail with their significant characteristic properties, relevant theories and applications. Here Au, Ag and Bi metals are considered and the synthesized glasses are mostly based on antimony, bismuth and phosphorus oxides. Some of them are dichroic in nature, that is, they exhibit blue to green colourations in transmitted light and brown to reddish brown colourations in reflected light. The appropriate reasons for their dichroic character are still remained unsolved. Nanometal-antimony oxide glass nanocomposites have been found to enhance the photoluminescence upconversion intensities up to 11 fold when co-doped with rare earth (RE) ions due to the plasmonic induced local field as enhanced by the effects of doped metal nanoparticles. The nanometal-glass hybrid nanocomposites, therefore, seem to be very promising for various nanophotonic applications (such as nanometal enhanced rare earth luminescence, solar cell, light emitting diode, plasmonic integrated circuit, plasmon slot waveguide, etc) that have presently emerged into a major field called `plasmonics'.

We have synthesized a class of blue-emitting polymers based on a donor-acceptor architecture composed of oxadiazole and carbazole moieties containing various substituted groups in the same side chain. Depending on the substituted group at carbazole, they showed different thermodynamic properties: two polymers containing N-methylcarbazole showed liquid-crystalline behavior. The single-layer polymer light-emitting diodes using these polymers exhibited blue emission with peaks from 430 to 440 nm. The device using the liquid-crystalline polymer with an alignment layer emitted polarized blue light with a dichroic ratio of 5.1.

The imbalance in the electronic density of states between spin-up and spin-down electrons characteristic of ferro(ferri)-magnetic materials gives rise to X-ray magnetic circular dichroism (XMCD) in the absorption of circularly polarized X-rays with opposite helicity. These dichroic effects are largest near element-selective atomic resonances and can be used to probe ferro(ferri)-magnetic ordering with element- and electronic orbital-selectivity. We describe recent developments at the Advanced Photon Source that allow measurements of XMCD in a diamond anvil cell. We discuss the challenges associated with these measurements as well as their potential to further our understanding of complex magnetic materials.

A novel layer‐by‐layer (LBL) film containing dual photoreaction groups, cinnamoyl and azobenzene, was prepared from poly(diallyldimethylammonium chloride) (PDDA) and a photosensitive polyanion, PCAzo, in aqueous solution via electrostatic attraction. The film was able to induce uniform alignment of liquid crystals (LCs) with good stability and 2.3° pretilt angle by oblique irradiation with linearly polarised ultraviolet light (LPUVL). UV absorption and FTIR spectroscopic results indicate that the photoreactions of the two photoreactive groups jointly participate in generating the anisotropy of the film. The dichroic ratio of the film was found to depend on the number of adsorbed layers. The thicker film has the larger dichroic ratio after the LPUVL irradiation. The reorientation behaviour of the LC molecules was found to be associated with the LBL film thickness. Experiment results revealed that the photo‐crosslinking of the cinnamoyl groups was responsible for the stability of the anisotropic orientation...

We fabricated highly-oriented thin films of 3,4,9,10-perylenetetracarboxylic-bis-benzimidazole (PTCBI), poly(9,9-dioctyl-fluorene) (PFO) and regioregular poly(3-hexylthiophene) (P3HT). Each material was aligned by the rubbing process, and high dichroic ratio of 4–6 was achieved. We also investigated application for organic p-n heterojunction type photovoltaic devices, which include the aligned layer. Aligned-PTCBI (n-type) stacked with unaligned-TiOPc (p-type) showed good photovoltaic performance equal to the conventional unaligned stacked devices. High power conversion efficiency of 0.8% was achieved.

The voltage dependencies of the dichroic properties for a homogeneously aligned sample of a partly fluorinated chiral smectic liquid crystal (S)-4-(1-methylheptyloxy carbonyl)phenyl 4′-[6-(3,4,4,4-tetrafluoro-3-trifluoromethylbutylcarbonyloxy) hexyloxy] biphenyl-4-carboxylate at various temperatures have been studied using polarized Fourier transform infrared spectroscopy. The temperature dependence of the molecular apparent tilt angle has also been determined. For the antiferroelectric SmC A * phase, the molecular apparent tilt angle is found to be close to 45° for a temperature range of 65–80°C. In the SmA* phase, an application of a sufficiently high electric fields causes a substantial increase in the orientational order parameter. This results probably from a change in the azimuthal distribution of the molecular directors around the tilt cone. The material is found to exhibit an extraordinary large surface electroclinic effect and its helix is considerably distorted by the surfaces.

A solid state, linear dichroic IR analysis of a mononuclear Au(III) complex of the tripeptide glycylmethioninylglycine (GlyMetGly) oriented in a nematic liquid crystal has been carried out. Structural results are compared with 1H and 13C NMR data. The ligand coordinates to Au(III) as a tridentate in [Au(C9H17N3O4S)Cl]Cl2, binding through S, and the N- and O-atoms of neighbouring CONH– and COO− groups. The fourth position is occupied by a terminal Cl− ligand.

In this work the influences of chain stiffness, solution concentration, and preparation methods on the formation and efficiency of highly oriented polyimide alignment layers are investigated. To quantify the performance of the alignment layers in liquid-crystalline (LC) cells, the orientation of a calamitic bis-azo dye in a low-molecular-weight nematic LC guest–host mixture was employed. The degree of orientation was quantified by measuring the dichroic ratio (DRUV) of the dye with polarized UV spectroscopy. Alignment layers were prepared from precursors of polyimide polymers with different chain stiffnesses. Additionally, the effect of polymer solution concentration, denoted as low (approx. 2 wt%) and high (50 wt%), and orientation techniques (casting and shearing) were systematically investigated. Cells assembled with buffed polyimide alignment layers originating from 1.5 wt% solutions in N-methyl-2-pyrrolidone (NMP) of a rigid para-linked poly(amic ethyl ester) precursor polymer resulted in a very high...

Emissive displays use additive color synthesis provided by two dimensional Red Green Blue pixels arrays; reflective displays would use the subtractive color synthesis from primary Cyan Magenta Yellow colors: several attempts show that photographic like structures using 3 active superposed color layers constitutes a very challenging objective. Beside the transflective mode compromise, most current attempts concern black and white or bicolor reflective displays, as well as reflective micro displays for image projectors. After reviewing these technologies, we consider some new approaches to reflective color displays, including the direct color synthesis using physical colors generation such as light dichroic reflection, diffraction and scattering.

Relationships between properties of dichroic dyes and performances of three layered Guest-Host Liquid Crystal Displays (GH-LCDs) with subtractive color mixing of yellow, magenta and cyan were studied by color mixing simulation. In the case of using the dyes we developed, it was found that the color reproduction areas were as much as 1.6 times larger than in the case of using only commercially available dyes. Performances of our prototype reflective three-layered GH-LCDs were high (the luminous reflectance of the white state was 43%, and the contrast was 5.3), indicating that three-layered GH-LCDs are practical for the display of full-color images.

An illustration of the possibilities of solid‐state linear‐dichroic infrared (IR‐LD) spectral analysis of a suspension of a sample in a nematic liquid crystal for supramolecular stereostructural characterization is demonstrated comparing the IR‐LD spectral results of solid adenine (Ade) and its new N1 protonated salt (AdeH). In addition, a detailed IR‐spectral characterization of the AdeH derivative that explains the corresponding frequencies that change as a result of the protonation process was also done.

In a nematic liquid crystal (LC), the excitation energy of an ultraviolet light (360 nm) is efficiently transferred to yellow fluorescent dye via blue fluorescent sensitizer, to enhance yellow fluorescence of the dichroic dye. The LC can emit white fluorescence when yellow and blue fluorescent dyes are mixed at suitable concentrations. In the homogeneously aligned cell with the fluorescent nematic LC, fluorescent dye molecules reorient along the applied electric field with LC molecules when the voltage is applied to the LC cell. With the increase of the voltage, the fluorescent intensity decreases without changing the fluorescent color. The contrast ratio at 0 and 8 V is about 6.5.

Interaction between the S-Phe–S-Phe dipeptide (PP) and Au(III) leads to the formation of a yellow complex, [Au(PP)Cl3]Cl (1), with monodentate coordination of the dipeptide with Au(III) through one O atom of the COO− group. Three Cl− anions bond to the metal center as terminal ligands. The structure of 1 was obtained by comparative solid-state linear-dichroic infrared (LD-IR) spectroscopic analysis of a solid sample and the pure dipeptide S-Phe–S-Phe, both oriented in a nematic liquid crystal suspension.

Langmuir–Blodgett (LB) films of some dichroic dyes, namely derivatives of naphthalenebicarboxylic acid and derivatives of naphthoylenebenzimidazole, and of their mixtures with mesogens: 4‐octyl‐4′‐cyanobiphenyl or 4‐pentyl‐4″‐cyano‐p‐terphenyl were prepared. Absorption and fluorescence studies using unpolarized and linearly polarized light were carried out. Both absorption and fluorescence spectra indicated the formation of aggregates of dye molecules in monomolecular layers. Moreover, it was found that dye molecules are more tilted to the quartz surface in LB films than to the plane of the air–water interface in Langmuir films.

Polarized electroluminescence is observed for a uniaxially aligned sample of a discotic compound in its crystalline state. The alignment was achieved by coating the ITO anode with an aligned film of poly(tetrafluoroethylene) (PTFE) deposited using the friction method. Organic light emitting devices with the layer sequence glass/ITO/PTFE/tetraethyl perylene-3,4,9,10-tetracarboxylate (55 nm)/aluminium (100 nm) show linearly polarized emission of light with a dichroic ratio up to 3.2.

We synthesized two kinds of side chain type polymers containing chalconyl moieties to investigate the alignment's capability of photo-crosslinked polymer films. One is methacrylate type polymer having the chalconyl moiety in the side chain, and the other is imide type polymer. A smectic phase was exhibited for the methacrylate type polymers, while no mesophases were observed for the imide type polymer. These polymer films were irradiated with linearly polarized UV (LPUV) light (350 nm) under different conditions. The liquid crystalline (LC) cell was fabricated from the polymer film irradiated with LPUV light to examine the alignment properties of low molecular liquid crystal on the film. A mixture of a low molecular liquid crystal and a dichroic dye was filled in the LC cells. Alignment behavior of the low molecular liquid crystal was discussed by the dichroic ratio of the dichroic dye in the LC cell.

Sensitization effects in a fluorescent nematic liquid crystal display (LCD) have been studied using a fluorescent dichroic dye or a fluorescent liquid crystal as a sensitizer. The sensitized fluorescence intensity can be increased by ten times and a dichroic ratio of the fluorescence is also increased. Moreover, the sensitized fluorescence intensity is controlled by applying the voltage across the cell. We applied these phenomena to the emissive type LCD. The luminance can be increased and the color switching properties are improved.

Polymer dispersed liquid crystals (PDLC) films doped by dichroic dyes (DD) with “polymer ball” morphology have been obtained. It has been shown that they possess a “memory effect”. The optical characteristics of PDLC films with the “memory effect” have been investigated. The possibility to use this effect for recording and storing an information has been established.

A detailed Mueller-Stokes analysis of an arbitrary elliptical dichroic polarizer is presented. Explicit expressions for the Jones matrix, the Stokes parameters, and the Mueller matrix for a distributed and localized dichroic polarizer acting as a polarization-dependent loss (PDL) element are derived. Application to wavelength-dependent PDL elements is discussed. The Poincare sphere representation and the application of the Mueller matrices for the study of randomly oriented concatenated PDL elements and PDL vector measurement are addressed.

Green and red fluorescence of dichroic dyes can be sensitized by adding blue fluorescent dyes in a nematic liquid crystal(LC). The excitation energy of a ultraviolet(UV)light transfers to an emitter through sensitizers and fluorescence intensity increases by 3 ∼ 13 times. Relations between absorption and emission dichroic ratios of sensitizers and emitters have been measured and discussed. The voltage dependence of fluorescence intensity is also measured in the fluorescent guest host LC cell. The brightness and contrast ratio can be enhanced by adding the sensitizer of which dichroic ratio is higher than that of the emitter.

Good correlation was found between the order parameter S of liquid crystal (LC) host-mixture and the dichroic ratio of its guest-host system. We investigated temperature dependence of the S value of several LC substances, focusing on its index β. The index β was determined by measuring the temperature dependence of refractive index. LC substances with a cyano terminal group have smaller β values than those with an alkoxy or a fluoro-substituted terminal. This means that the S value is expected to be larger for the cyano substances than the alkoxy or fluoro substances at a fixed reduced-temperature. There exists good correlation between the calculated S value of a host LC mixture and the measured dichroic ratio of its guest-host system. This enables us to design highly ordered LC mixtures for high contrast guest-host LC displays based on β values of LC substances.

We study dichroic effects in the two-photon ionization of hydrogen from its ground state due to the interaction with a bichromatic field of commensurate frequencies. The two field components have different polarization: one is linearly polarized and the other is circularly polarized. Circular dichroism in the angular distribution of the photoelectrons appears if the helicity of the circularly polarized field is reversed. Numerical results reveal the influence of the photon frequencies chosen on the circular dichroism in the azimuthal angular distribution of the ejected photoelectrons.

The structure of the chiral smectic C phase (SmC*) of the mesogen MHP10CBC in a homogeneously aligned thin cell, that exhibits V-shaped-like switching in a certain frequency range, was studied using polarized Fourier-transform infrared spectroscopy and optical microscopy. The molecular orientational distributions were analysed quantitatively in terms of dichroic parameters of the absorbance profiles, by taking into account the orientational properties of the transition moments for several phenyl and carbonyl bands. The polar angles of the transition moments, with respect to the molecular long axis and their azimuthal orientational parameters used in calculations, were determined from the infrared dichroic data for helical and electrically unwound structures in a thicker cell of this material. For a sufficiently thin cell in the SmC* phase at zero electric field, the results on the azimuthal orientational distribution of the director over a ferroelectric liquid crystal cone, with respect to the substrate n...

A photo-induced alignment layer for LCDs has been successfully fabricated using the polarized UV photoreaction of a photo-crosslinkable polymer with the incident UV light at some angle with respect to the cell normal. The surface alignment and electro-optic properties were investigated for various UV exposure times. The homeotropic alignment layer showed a discrete anisotropic dichroic ratio, its surface morphology became smoother as the UV exposure time increased, and the LCs were arranged in a perpendicular direction to the PUVL direction with a proper pretilt angle. The cell showed no defects under cross-polarized microscopy and the contrast ratio was as high as 550:1 in transmittance. The contrast ratio pattern was found to be very similar to that of dichroic ratio as a function of UV exposure time and depended upon the frequency change to some degree. The response time was also investigated.

The optical and electro-optical properties of filled nematic liquid crystals, nematic systems with added colloidal silica nanoparticles (⩽ 6%), have been studied. The macroscopic near IR birefringence of cells constructed from these materials was measured for wavelengths between 2 and 5 mum, and a wavelength independent value of 0.16 was obtained. The visible optical behaviour of cells formed with untreated ITO substrates using both filled nematic, and filled nematic and dichroic dyes was similar to those observed in polymer dispersed liquid crystals. At an electric field of 1–2 V μm -1, the cells were highly transmitting, while at low fields they were highly scattering. The effects of colloidal silica nanoparticle concentration, cell thickness, electric field and substrate preparation (rubbed polyimide versus no surface treatment) on the electro-optical behaviour of these cells were studied.

A study of dichroic dye-liquid crystal mixtures (guest-host systems) in monolayers formed at a gas-liquid interface (Langmuir films) and at a solid surface (Langmuir-Blodgett films) has been made. As a host 4- n -octyl-4′-cyanobiphenyl (8CB) or 4- n -pentyl-4″-cyano- p -terphenyl (5CT) were chosen, while three dichroic azo dyes with various molecular structures were used as guest species. The dyes were added to the liquid crystal matrices at a concentration corresponding to the whole range of molar fractions and the surface pressure-mean molecular area isotherms for Langmuir films were recorded. On the basis of the isotherms, conclusions about the molecular organization and the miscibility of the components in the ultrathin films were drawn. The Langmuir films were transferred onto the quartz plates at surface pressures below the collapse point. The polarized absorption spectra of the Langmuir-Blodgett films were recorded and information about the alignment and intermolecular interactions in the mixtures ...

Polymeric films of two types of rigid-flexible luminescent polyethers containing alkyloxy substituted quinquephenyl units and anthracene segments have been uniaxially drawn at temperatures above their glass transition (Tg). FT-IR linear dichroism measurements have been performed in order to evaluate the molecular orientation of the drawn polymers. It was found that the main chain of these polyethers orient parallel to the draw direction. In addition, both the main chain and the side chain for the alkyloxy substituted polyethers also orient parallel to the direction of stress, based on the analysis of the behavior of the ether groups. The concurrent polarized photoluminescence measurements confirm that the high degree of molecular orientation produces an enhancement of the dichroic ratio of the photoluminescence spectra which results in materials with polarized blue and yellow light emission.

The optical torque is experimentally studied in Disperse Red dichroic dye doped E7 nematic liquid crystal. Creation of a transitory out-of-plane (3D) anisotropy axis is observed in a geometry were in-plane reorientation is observed in pure nematics. The non-monotone behavior of dye absorption during the excitation and relaxation is correlated with the 3D reorientation. This shows that the photo-isomerization of the dye via transient excited states (particularly of Cis form) should be the mechanism, which gives a "pulse" for the creation of the 3D anisotropy axis.

Langmuir-Blodgett (LB) films of poly( p -phenylene vinylene) (PPV) were prepared using an amphiphilic precursor. These LB-PPV films are highly ordered along the dipping direction as demonstrated by linear dichroism experiments using linearly polarized optical absorption. The dichroic ratio between the intensity of the emitted light parallel and perpendicular to the dipping direction is Ca . 3.6. In addition, the LB films displayed circular polarization with a dissymmetry factor, g e , varying from 0.6 to −0.2 after increasing the sample temperature from 36 to 300 K.

The aim of the present paper is to show the mathematical model of light propagation through the liquid crystals display The numerical programme based on this model is constructed. The possibilities of this programme is shown.

Novel triphenodioxazines have been synthesized and evaluated. The dyes were not only highly dichroic in guest-host liquid crystal mixtures but also vivid because of a sharp peak in absorption spectra. Mesogenic substituents to the 2,9- position of the chromophore improve the order parameter in the mixture. Moreover, the mixtures also showed significant polarized photoluminescence. These results would reveal a few advantages of the novel dyes for some possible applications.