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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.

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.

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.

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 ...

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 ...

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.

Alignment structure and optical properties of Langmuir-Blodgett (LB) films of urethane-substituted polydiacetylene (poly-4BCMU) was investigated. During compression, the coil to rod transition in molecular conformation of poly-4BCMU was induced and the polymer main chains were aligned perpendicular to the compressing direction. The dichroic ratio of absorption intensity of poly-4BCMU monolayer film was about 6. LC molecules were sandwiched with two glass plates covered with the poly-4BCMU monolayer films. LC molecules aligned spontaneously along the main chain direction of poly-4BCMU in the parallel cell. On the other hand, they formed a twisted structure of 90° in the crossed cell. The monolayer film of poly-4BCMU had a high potential as rubbing-free alignment layer of LC molecules.

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.

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.

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.

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.

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.

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.

This paper reviews the operational principle, construction and electro-optical performance of various types of dichroic liquid crystal displays such as Heilmeier, phase change, dye doped TN and polymer dispersed dichroic. It also discusses the double layer and positive mode dichroic LCDs. The impact of material properties such as birefringence, dielectric anisotropy, viscosity, elastic constant and cell construction such as alignment, cell gap, etc., on the electro-optical performance of these displays has been mentioned. The contrast ratio, viewing angle, switching speed, etc., of Heilmeier, phase change and dye doped TN have been discussed. The data indicate dye doped TN to be a display with very high contrast (> 100:1) and a much wider viewing angle compared to TN display. The colour shift with viewing angle is also found to be much less for dye doped TN than for normal TN liquid crystal displays. Some of the applications of current dichroic displays are shown, and potential future application...

Using data on geometry of molecules and direction of electronic oscillator a large series of dichroic dyes have been synthesized exhibiting positive, negative or zero dichroism, as well as two colour dichroic dyes with opposite signs of dichroism of absorption bands. Ways of obtaining dichroic dyes with a higher solubility have been proposed.

It has been found that contrast ratio of nematic liquid crystal (LC) on phthalocyanine (Pc) derivative Langmuir-Blodgett (LB) film cell has a correlation with dichroic ratio of the LB film. These results show that this homogeneous alignment force is originated from orientation of rod-like aggregates of the Pc derivative. On the other hand, the LC alignment changes from uniform homogeneous alignment to uniform homeotropic alignment through non-uniform tilted alignment, with the increase of the number of side chain carbon atoms of the Pc derivative. Such alignment change has been also observed with the increase of concentration ratio of a long side chain Pc in a mixed Pc LB film. These show that homeotropic alignment force originates from the ordered long side chain. Therefore, LC alignment is determined by Pc orientation and side chain length, and the feasibility of the tilted LC alignment is shown.

Exposure of photo-labile polyimide film to linearly polarized 254 nm UV incurred anisotropic dielectric orientation of film surface. The anisotropic surface resulted from the liquid crystal (LC) alignment is perpendicular to polarization direction of the UV irradiation. The polyimide (1,2,3,4-cycolbutanetetrcatboxylic dianhydride di(4 aminophenyl)methane-dianhydride)(CBDA-DAPM-DA) contains cyclobutane rings for photoinduced ring opening reaction. The LC alignments were obtained through polarized and unpolarized UV by exposing them to rubbed polyimide film. Dichroic ratio of LC cells increased with irradiation time until 20 min and was followed by disordering of further UV irradiation. Unpolarized UV irradiation on the rubbed polyimide film showed increased dichroic ratio compared to the films irradiated with a polarized UV light.

Oriented thin films of polyaniline (emeraldine base) were prepared by the friction transfer method by rubbing solid polyaniline against a glass substrate to form a thin coating film on the substrate. Characterization by polarized ultraviolet-visible-near infrared spectra showed the dichroic property of the films, suggesting that the polyaniline was oriented on the glass substrate. Hydrochloric acid treatment transformed the film into emeraldine salt without loss of orientation. Moreover, the oriented film of emeraldine base could be recovered by aqueous ammonia treatment of the emeraldine salt. The oriented film could also be doped with camphorsulfonic acid.

The ferroelectric liquid crystal displays normally suffers from less contrast ratio and vision angle. To produce high optical contrast and colours in FLC displays, Guest-host mode is widely used. Addition of small amount of dichroic dye in pure FLCs results in considerable change in its dielectric and electro-optical properties. In the present paper we have investigated the effect of two dichroic Anthraquinone dyes (D37 and D5) on the ferroelectric liquid crystal materials (Felix 17/100). Dye doped FLC mixtures have been prepared by the dispersion of each dye at five different concentrations about 1, 2, 3, 4 and 5%wt/wt in pure FLC. The planar aligned cells have been used to study dielectric and electro-optical properties in SmC* phase of all pure and the dye doped mixtures. Considerable change in various properties like Goldstone mode relaxation frequency and dielectric strength have been noticed for both the sets of dye doped mixtures. These effects have been discussed in the light of changes produced i...

Binary mixtures of the dichroic azo dye with the liquid crystal as Langmuir and Langmuir-Blodgett films have been studied. Four azo dyes with various molecular structure and liquid crystal materials: 4-octyl-4′-cyanobiphenyl (8CB) and trans-4-octyl(4′-cyanophenyl)-cyclohexane (PCH8) were used. The surface pressure as a function of the mean molecular area for Langmuir films were measured and the organization of molecules at the air-water interface was determined. Absorption spectra in situ for Langmuir films and absorption spectra by using both natural and linearly polarized light for Langmuir-Blodgett films were recorded and information about intermolecular interactions in the mixtures of the nonamphiphilic dye and the liquid crystal with polar terminal group was obtained. Conclusions about the formation of self-aggregates between dye molecules have been drawn.

Polarizing films doped with three kinds of dichroic azo dyes were prepared to investigate the effect of dye structures on the orientation behavior of dyes in stretched poly(vinyl alcohol) films. One reactive group exerted an unfavorable influence on the alignment of dye molecules toward the polymer segments orientation. However, two reactive groups resulted in the effective alignment and showed the best optical properties among three kinds of dyes.

In this work the mathematical model of a light propagation through the system of layers with dichroic properties are presented. This model makes it possible to obtain the spectral characteristics of transmission and reflection for any system of isotropic, anisotropic and dichroic layers. Additionally, the calculations takes into account real conditions of a display working. Basing of this model the computer program is done. This program makes it possible to conduct the complete optimization procedure for very complicated system such as for example color liquid crystals display.

Polarizing films were prepared using three dichroic dyes and iodine. The direction of transition moment in dichroic dyes was in accord with the orientation of the host polymer. The polarizing efficiency of PVA/dye polarizing films reached almost full contrast but their single-piece transmittances were rather low. PVA/dye polarizing films were superior to PVA/iodine polarizing film in their stability to high temperature and high humidity.

We have investigated the out-of-plane and the in-plane orientations of the transition dipole moments of merocyanine dye (MS) with various aggregation states including J- and H-aggregates in the mixed LB films by means of visible absorption spectroscopy. The results of the MS orientation estimated using the simple geometrical model suggest that the MS transition dipole moments lie in the film plane in all the aggregation states, and that the relationships between the dichroic behaviors observed and the in-plane order parameters obtained from the model are well recognized in the individual red-shifted and the blue-shifted aggregates.

The properties of three different classes of 2,3-substituted 1,4-diaminoanthraquinone dichroic greenish blue dyes with a maximum absorption peak in the long wavelength region from 660 nm up to 760 nm, which are useful as a guest dye in an achromatic black guest-host liquid crystal display, have been investigated. 1,4-Diaminoanthraquinone-(N-substituted-3-imino)-2,3-dicarboximidines (I) and 1,4-diaminoanthraquinone-(N-substituted-3-thioxo)-2,3-dicarboximidines (II) exhibit higher dichroic ratios and higher solubilities and moreover the latter class (II) shows a maximum absorption peak at a much longer wavelength, compared to 1,4-diaminoanthraquinone-(N-substituted)-2,3-dicarboximides (III). The order of various properties in the three classes of dyes are as follows: II > I > III for dichroic ratio, II > I > III for solubility, and II > III > I for maximum absorption wavelength, respectively.

When a voltage is applied to a twisted nematic cell (δe > 0) containing a positive dichroic dye, and the cell is illuminated by light with its polarisation plane perpendicular to the director of the front electrode, a decrease in light transmission is observed (i.e. positive contrast). In this paper we investigate the influence of different liquid crystal twist cell parameters such as the twist angle φ, the azimuthal angle γ between the polarization plane of the incident light and the director at the front substrate, the δnd/λ value, the dye order parameter S and the temperature τ on the transmission-voltage characteristics and the value of the positive contrast. The maximum positive contrast is found to correspond to γ and φ, values close to π/2, maximum dye order parameter, minimum temperature, and finally, δnd/λ = 2.1 ± 0.1.

We present novel measurements and correlations between the electric field-induced change of capacitance, optical appearance and material parameters of nematic as well as cholesteric guest-host layers. New guest-host mixtures comprising various dichroic dyes with transition moments parallel (L-dyes) and perpendicular (T-dyes) to the nematic director exhibiting large dichroic ratios and UV-stability were used. The material parameters determining the capacitive as well as the electro-optical characteristics, including all elastic constants, were measured. Good agreement was found between measureci and numerically calculated characteristics when using the experimentally determined material parameters in the formalism derived to calculate the transmission characteristics of homogeneous nematic guest-host displays. It is shown that the field-induced dielectric changes occurring in cholesteric guest-host layers with parallel and homeotropic wall alignment respectively differ considerably from their elec...

Continuing research of dichroic T-dyes we have obtained new 5-arylazo-2,6-diarylimidazo[2,I-b]-1,3,4-thiadiazoles (5,9–12). The compounds (2–5) have been synthesized by known methods.

Various yellow, red, and blue anthraquinone dyes have been synthesized. The structures of the dyes are presented and their properties are discussed with respect to the dichroic ratios, the color gamut, and the obtainable contrast in black colored liquid crystalline dye mixtures. Dichroic ratios of up to N = 10.2 in NP 1132 and ň = 12.3 in RO-TN 404 are calculated. The influence of the positions of the absorption bands on the perceived contrast is studied. It is shown that by shifting the absorption bands of the dyes, the effective dichoric ratio can be increased to N eff = 9.1 in NP 1132 and N eff = 11.4 in RO-TN 404

The nove approach is proposed to the synthesis of dyes with negative dichroism. The molecular models, which are adequate to the dichroic dyes, are shown. As an example of the approach, the synthesis and dischroic properties of some derivatives of the 2,2′-azomidazole are described. The time and contrast chracteristics of the displays, based on the guest-host effect, are presented.

New liquid-crystalline, dichroic 2,6-disubstituted cycloheptimidazoles (1.3-diazaazu-lenes) have been synthesized and their transition temperatures have been determined by differential scanning calorimetry (DSC). In view of the application of 6-arylazo-substituted cycloheptimidazoles as dyes for electrooptical displays (guest-host-cells), the order parameters of these compounds have been determined.

Anthraquinone dyes with negative dichroism in liquid crystals have been synthesized; value of the negative dichroism are of practical interest. The structural influence for the dichroic dyes on their dichroism in liquid crystals is discussed.

To clarify the relation between a molecular structure and an order parameter of a dichroic dye of a guest-host liquid-crystal cell, a ratio l/d of a length l to a diameter d of a circumscribed cylinder of the dichroic dye is used as a parameter. Experimental results clarify that there exists an obvious correlation between l/d and an order parameter of a long axis of the dye molecule; information is obtained on ordering state of the dye dissolved in the liquid crystal, especially the performance of flexible parts of the dye molecule.

When a uniaxial nematic phase is formed by biaxial molecules, in addition to S the order parameter D is necessary to describe the molecular order. It is shown here that D effects the dichroic ratio whenever the orientation of the transition moment differs from the molecular axis defining the director. The evaluation of experimental results with respect to D and its interpretation are discussed.

This paper reviews the present status, recent developments, future trend and market of liquid crystal displays. It also describes the historical developments very briefly. Today over 99% of LCDs are twisted nematic and their dominance is expected to continue in the near future. Recent developments in polarizers, glass plates, sealing, alignment, liquid crystal materials, etc., are described. Advances in multiplexing, thermally addressed S, displays and dichroic displays are discussed. Dye phase change and TFh may find considerable application in the future. Three major sectors of LCD market—calculator, watch and clock displays will remain almost static in terms of total dollar value though the number of units will be increasing. Trenendous growth rate of LCDs is expected in industrial and consumer items, office equipment, personal computers, business equipment, automobiles, avionics, military and telecommunications.

The liquid crystal display device using guest-host interactions has. attracted interest recently because of displaying color and wide viewing angle. This paper describes dyes with high dichroic ratio, and proposes two new types of the guest-host cell being more useful than usual one. One of them is the cell with twisted molecular alignment and has sharper threshold voltage than the usual cell with homogeneous alignment. The other one with small pretilt from homeotropic alignment is made of a host nematic with negative dielectric anisotropy and is the positive type display device with high color contrast. The optimal pretilt angle of this cell is also clarified.

A new fast optical shutter, based on the guest-host interaction, that uses a 2 mm optical path length, has been demonstrated. Using a suitable pleo-chroic dye as guest in a cyanobiphenyl nematic host it has been shown that the shutter can be turned on and off in a few milliseconds. The electro-optic cell uses transverse electric fields, and field strength, frequency and temperature studies have been made. It has been shown that both increases and decreases in transient light levels may be obtained by changing the polarisation state of the incident light.

Scientists working in the field of liquid crystals have become increasingly interested in the practical applications of dichroic dyes dissolved in liquid crystal matrices. This interest is due to a number of factors. Firstly an improved contrast of an image can be achieved in displays using this “guest-host” effect in comparison with displays solely using field effects or the “cholesteric-nematic” transition. Furthermore, utilization of dichroic dyes makes it possible to manufacture multi-coloured displays which do not require polarizers. This advance is a result of recent progress made in “quick-response” liquid crystalline materials and dichroic dyes with high order parameters in liquid crystal matrices.

Azo dye molecules are cylindrically shaped, and therefore, due to their resemblance to liquid crystal molecules, would seem to be suitable for use in guest-host mixtures. The dichroic ratio of a dye in a given nematic host depends on the molecular length of the dye molecules, the order parameter of the liquid crystal host and its molecular dimensions. It is possible to obtain a guest-host mixture with an order parameter which is higher than that of the pure host. Lateral substitution of mono-azo dyes lowers the order parameter, whilst lateral substitution of the corresponding bis-and tris-azo molecules results in only a slight change in their order parameter. The stability of these compounds to light is poor, and depends on the wavelength for maximum absorption, and on the host material. Whilst lateral substitution increases the fastness of azo compounds when used for textile dying, this is not the case when they are employed with liquid crystal mixtures. The kinetics of degradation are zero orde...

Three groups of liquid crystalline derivatives of 2,3-dicyanohydroquinone were synthesized. The dielectric anisotropy values, δe's, for these compounds were estimated to be around −20 by extrapolation. Some basic evaluations of these compounds, in view of their application as component materials for the practically usable nematic mixtures of highly negative δe, were made using their solution in a substituted phenyl cyclohexanecarboxylate nematic mixture; δ e. viscosity, dichroic ratio of dyes, driving voltages, and response times, are described in relation to their molecular length. By use of several selected members of these compounds in summe of about 20 wt% in low viscosity base nematics, one can make practical nematic compositions having δe of −5 and viscosity of 40 cp at 20°. The guest-host display device can be driven with 3 volts at acceptable response times of 100-200 milliseconds at room temperatures, to give positive color contrast, i. e. colored in on-state.

Light-stability of liquid-crystal color display devices using the guest-host interactions we investigated. It was found theoretically as well as experimentally that a decrease of absorbance of the guest-host cell was almost proportional to the exposed light intensity and time while the decrease was not large. Therefore, the lifetime can be calculated by extrapolation from the initial decreasing rate of absorbance obtained from accelerated life test using an intense light. Various azomethine-, disazo- and anthraquinone-dyes with large dichroic ratios were put to the test and some stable dyes were found.

Spectra of β-naphthol single crystals in the 5700-6800 cm−1 range in polarized light have been measured. Dichroic ratios of 2vCH and 2vOH. bands have been calculated and compared with experimental values. The results confirm the assumption concerning the linearity of a hydrogen bond in β-naphthol. It has also been found that it is possible to sum contributions of transition moments of different oscillators in the total intensity of a group of overlapping bands. This fact may be understood in terms of an effective charge model concept.

A series of N-substituted 1,4-diamino 2,3-dicarboximido-anthraquinone dyes has been synthesized. The location of the dicarboximido moiety in the 2,3-positions permits the elongation of the molecule in a direction collinear with the major axis of the anthraquinone nucleus by attaching substituents at the imido-N. The resulting dyes have improved order parameters, particularly when a phenyl group is directly bonded to the N.