The complete morphological,electro-optical and dielectric study of dichroic dye-doped polymer-dispersed liquid crystal

Polymerisation-induced phase separation method was used to prepare dye-doped polymer-dispersed liquid crystal (DPDLC) films consisting of nematic liquid crystal, photo-curable pre-polymer and a dichroic dye. The change occurring on droplets morphology with the change in dye concentration and voltage was investigated by means of polarising optical microscope and scanning electron microscope. Electro-optic behaviour of these composite films in the presence of an externally applied AC electric field (0–100 V, 200 Hz) and temperature range 25–50°C was evaluated using He–Ne laser. The maximum absorbance of dye and effect of electric field on the absorbance of dye was studied using UV-Vis spectrophotometer. Dielectric relaxation spectroscopy was carried out in the frequency range 20 Hz–20 MHz and over the temperature range 25°C–90°C. Dielectric parameters such as distribution parameter, relaxation frequency, relaxation strength and relaxation time of these DPDLC films were calculated, and the modelling of experimental data was done using Debye and Cole–Cole method.     

一种近红外光记录与存储材料——克酮酸染料的三阶非线性光学性质

克酮酸染料是一类新型的近红外吸收染料,由于具有良好的光热稳定性和荧光性能,因而在光记录与存储等领域有着潜在的应用价值.本文利用简并四波混频技术,在近红外区不同吸收波长,在脉宽为130 fs条件下研究了一种吲哚克酮酸染料在溶液和薄膜中的三阶非线性光学性质.该克酮酸染料在773 nm,四氢呋喃溶液中的共振三阶超分子极化率γ为5.3×10^-29esu,在薄膜中的共振三阶非线性极化率χ⁽³⁾值达到10^-8esu数量级.同时,对于三阶非线性光学响应及其动力学机制也进行了研究和探讨.     

Sensitization of the electrooptical effect by a merocyanine dye in polymers of azobenzene derivatives

Absorption spectra of poly[4-metacryloyloxy-(4′-carboxy-3′-oxy)azobenzene] films and their complexes with cobalt, without additives or doped with a merocyanine dye whose absorption spectrum lay in the near IR region, were studied before and after switching on an external electric field. An external electric field effect was found on the light transmittance of films within the dye absorption region, which indicated sensitization of the electrooptical effect. The electrooptical properties of the films resulted from spatial reorientation of dipole moments of azobenzene groups in an external electric field, which initiated turning of dye molecules. A phenomenological model was proposed to explain the sensitization of the electrooptical effect.     

Photopolymerisation kinetics and electro-optical properties in mixtures of dichroic dye-doped nematic liquid crystal and photocurable polymer

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 dichroic dye can be controlled in DPDLC to induce non-linearity and colour contrast without the use of polarisers.     

First Highly Efficient and Photostable E and C Derivatives of 4,4‐Difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) as Dye Lasers in the Liquid Phase,Thin Films,and Solid‐State Rods

A new library of E‐ and C‐4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) derivatives has been synthesized through a straightforward protocol from commercially available BODIPY complexes, and a systematic study of the photophysical properties and laser behavior related to the electronic properties of the B‐substituent group (alkynyl, cyano, vinyl, aryl, and alkyl) has been carried out. The replacement of fluorine atoms by electron‐withdrawing groups enhances the fluorescence response of the dye, whereas electron‐donor groups diminish the fluorescence efficiency. As a consequence, these compounds exhibit enhanced laser action with respect to their parent dyes, both in liquid solution and in the solid phase, with lasing efficiencies under transversal pumping up to 73 % in liquid solution and 53 % in a solid matrix. The new dyes also showed enhanced photostability. In a solid matrix, the derivative of commercial dye PM597 that incorporated cyano groups at the boron center exhibited a very high lasing stability, with the laser emission remaining at the initial level after 100 000 pump pulses in the same position of the sample at a 10 Hz repetition rate. Distributed feedback laser emission was demonstrated with organic films that incorporated parent dye PM597 and its cyano derivative. The films were deposited onto quartz substrates engraved with appropriate periodical structures. The C derivative exhibited a laser threshold lower than that of the parent dye as well as lasing intensities up to three orders of magnitude higher.     

混合溶剂对可录型光盘中吲哚类菁染料薄膜性能的影响

本文采用紫外可见光谱、FT-IR及AFM等手段,研究了混合溶剂对光盘记录介质吲哚类菁染料薄膜光学性能、稳定性和表面结构的影响.发现在不同混合溶剂下涂出的相同膜厚的染料薄膜,其光学性能和表面形貌都有很大的差异.不同的混合溶剂都存在一个最佳混合体积比,染料在此体积比下旋涂出膜的光学性能和表面形貌均优于单一溶剂下涂出的膜.对比不同混合溶剂涂出的膜的光学性质及AFM的观测结果,发现二丙酮醇与氯仿在等体积比混合、四氟丙醇与氯仿在7:3体积下混合时效果最好,易得到反射率高,表面较平整的染料薄膜.     

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 Δⁿ; maximum values of Δⁿ 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.     

Mesostructured Dye‐Doped Titanium Dioxide for Micro‐Optoelectronic Applications

Optically transparent, mesostructured titanium dioxide thin films were fabricated using an amphiphilic poly(alkylene oxide) block copolymer template in combination with retarded hydrolysis of a titanium isopropoxide precursor. Prior to calcination, the films displayed a stable hexagonal mesophase and high refractive indices (1.5 to 1.6) relative to mesostructured silica (1.43). After calcination, the hexagonal mesophase was retained with surface areas >300 m² g^?1. The dye Rhodamine 6G (commonly used as a laser dye) was incorporated into the copolymer micelle during the templating process. In this way, novel dye‐doped mesostructured titanium dioxide films were synthesised. The copolymer not only directs the film structure, but also provides a solubilizing environment suitable for sustaining a high monomer‐to‐aggregate ratio at elevated dye concentrations. The dye‐doped films displayed optical thresholdlike behaviour characteristic of amplified spontaneous emission. Soft lithography was successfully applied to micropattern the dye‐doped films. These results pave the way for the fabrication and demonstration of novel microlaser structures and other active optical structures. This new, high‐refractive index, mesostructured, dye‐doped material could also find applications in areas such as optical coatings, displays and integrated photonic devices.     

Effect of anti-parallel and twisted alignment techniques on various propertiesof polymer stabilised liquid crystal (PSLC) films

Thin composite films consisting of liquid crystal (LC) domains surrounded by polymer networks, termed as polymer stabilised liquid crystals (PSLCs), were prepared by photo-polymerisation of a pre-polymer dissolved in LC. Four composite films were prepared with different rubbing directions and with and without electric field during photo-polymerisation. Morphological characterisation carried our using a polarising optical microscope (POM) and a scanning electron microscope (SEM) reveal significant changes in LC domain morphology and associated polymer networks with the application of electric field during the fabrication of the films. The electro-optic (EO) properties of PSLC films placed between two crossed polarisers were studied using a He–Ne laser under an action of externally applied electric field. It was found that the PSLC film with twisted alignment and polymerised in the presence of electric field showed better EO properties than other films. Transmittance obtained by EO studies was verified with absorbance studies using a Ultraviolet-Visible spectrophotometer. The dielectric behaviour of PSLC films in the frequency range 20–20 MHz was investigated using a precision impedance analyser. The obtained data were modelled using Debye and Cole–Cole methods to calculate relaxation time and distribution parameter. The relaxation time calculated through the Cole–Cole model is in agreement with response time.     

Methylacrylate polymers with photochromic side chains containing heterocyclic sulfonamide substituted azobenzene

Methylacrylate monomers containing azobenzene groups with heterocyclic sulfonamide: sulfisomidyne (4-amino-N-[2,6-dimethylpyrimidyn-4-yl]benzenesulfonamide) and sulfamethoxazole (4-amino-N-[5-methylisoxazol-3-yl]benzenesulfonamide) substituents were synthesized. The monomers were used for preparation of homopolymers and copolymers with butyl 2-methylacrylate and 2-ethylhexyl acrylate. The materials obtained showed photochromic properties manifested by trans-cis isomerization of the side chain azobenzene fragments induced by illumination with unpolarized and polarized light. The decrease of the absorbance of the E(trans) form at ≈450 nm was observed and the materials tested were in form of thin films deposited onto glass.The isomerization of the polymers carried out during ellipsometric measurements showed the reversibility of the process in repeated illumination cycles with green laser light. The change of refractive index caused by illumination was in the range ≈0.005-0.008 as determined by ellipsometry.     

Thermokinetic study of CODA azoic liquid crystal and thin films deposition by matrix-assisted pulsed laser evaporation

Azoic dyes are compounds of interest from the point of view of their potential applications, such as the use of liquid crystals in optoelectronic and organic electroluminescent devices, or may be employed as template matrices for producing high-aspect ratio inorganic nanomaterials. Herein, 4-[(4-chlorobenzyl)oxy]-3,4′-dichloroazobenzene azoic dye, known as CODA, is selected as a choice compound among such materials due to its liquid crystalline properties and may be further used as nanostructured material in various applications. Thermokinetic study of CODA azoic dye thermal decomposition in air flow atmosphere was performed by employing thermogravimetric data; the kinetic parameters of the two decomposition steps were obtained under non-isothermal linear regimes, by means of multi-heating rates methods. Differential and integral “model-free” kinetic methods like Friedmann, Kissinger–Akahira–Sunose and Ortega, the invariant kinetic parameters method and the Perez-Maqueda et al. criterion (by Coats–Redfern and differential equations) were used. The kinetic study reveals very different behaviour related to the two decomposition steps of CODA, with complex processes composed of more than one kinetic mechanism for each of those, as indicated also by the Gotor et al. master plot method. Modern devices incorporating such materials tend to use them as thin films due to their specific properties; the CODA thin films were deposited on silicon substrates by matrix-assisted pulsed laser evaporation technique, using a Nd:YAG laser working at the wavelength of 266 nm. The preservation of the CODA compound after the transfer on the substrates was confirmed by Fourier transform infrared spectroscopy, while the morphology and topography of the deposited materials and of the thin film surfaces were investigated by atomic force microscopy and optical microscopy.     

Aggregation phenomena in polyelectrolyte multilayers made from polyelectrolytes bearing bulky functional,hydrophobic fragments

The functionalization of polyelectrolyte multilayers often implies the use of bulky functional fragments, attached to a standard polyelectrolyte matrix. Despite of the high density of non-charged, often hydrophobic substituents, regular film growth by sequential adsorption proceeds easily when an appropriate polyelectrolyte counter ion is chosen. However, the functional fragments may cluster or aggregate. This complication is particularly evident when using chromophores and fluorophores as bulky pendant groups. Attention has to be paid to this phenomenon for the design of functional polyelectrolyte films, as aggregation may modify crucially the properties. The use of charged spacer groups does not necessarily suppress the aggregation of functional side groups. Still, clustering and aggregation depend on the detailed system employed, and are not obligatory. In the case of cationic poly(acrylamide)s labeled with naphthalene and pyrene fluorophores, for instance, the polymers form intramolecular hydrophobic associates in solution, as indicated by strong excimer formation. But the polymers can undergo a conformational rearrangement upon adsorption so that they are decoiled in the adsorbed films. Analogous observations are made for polyanions bearing mesogenic biphenyls fragments. In contrast, polycations functionalized with the dye coumarin 343 show little aggregation in solution, but a marked aggregation in the ESA films.     

Photochromic characteristics of monodisperse microcapsules containing azobenzene derivative-doped nematic liquid crystals

Highly mono-sized dye-doped liquid crystal (LC) microcapsules were prepared by the solute codiffusion method for application in photoswitchable devices. Azobenzene derivatives, which can be photoisomerized by irradiation with UV (366 nm) and visible (433 nm) light, were used as a photoresponsive dichroic dye. The microcapsules have a spherical shape and a single dye-doped LC domain. After UV light (366 nm) irradiation, PDLC films prepared using the microcapsules attained a photostationary state within 10 min and this state maintained stability. PDLC films made by employing a dichroic dye having electron donor and acceptor groups in the molecule showed especially good photoisomerization properties. The reversible trans-cis -photoisomerization occurred sharply by irradiating alternately with visible and UV light.     

染料敏化的TiO2纳米晶多孔膜的性质及其光电转换

纳米材料由于粒径小而具有许多特殊的不同于块体材料的性质。用纳米技术制成ＴｉＯ２纳米晶多孔膜,能作为良好的光电转换的基质。通过选择合适的敏化染料,能达到很高的光电转换效率。本文介绍光电转换的原理,ＴｉＯ２纳米晶多孔膜的性质与制备及敏化染料的特性。     

Negative photoconductivity of ferrocenyl-containing oligomer films with a merocyanine dye

The effect of negative photoconductivity of ferrocenyl-containing oligomer films doped with a merocyanine dye based on ferrocene and tetranitrofluorene has been found. The decrease in the conductivity current and its recovery after switching off light are in agreement with the decrease and the recovery of the dielectric loss tangent in the films studied. The phenomenological model is suggested in which the buildup of space charge from nonequilibrium current carriers and its effect on electric conductivity of the films are taken into account. It is supposed that energetic traps for nonequilibrium charge carriers are formed due to proximity of the ferrocenyl fragments in the oligomer and a long distance between its end groups.     

Nonlinear studies of acid fuchsin dye in liquid and solid media

Solid-state dye-doped polymers are attractive alternative to the conventional liquid dye solutions. In this paper, nonlinear properties of the dye Acid Fuchsin has been studied. The third-order nonlinear optical properties of Acid Fuchsin dye in 1-butanol and dye-doped polymer film were measured by the Z-scan technique using 532 nm diode pumped Nd:Yag laser. This material exhibits negative optical nonlinearity. The dye at 0.4 mM concentration exhibited nonlinear refractive coefficient (n(2)=-8.72 x 10(-8) and -10.308 x 10(-8) (cm(2)/W) in liquid and solid media, respectively), nonlinear absorption coefficient (beta=-7.69 x 10(-4) and -8.294 x 10(-4)cm/W in liquid and solid media, respectively) and susceptibility (chi(3)=4.33 x 10(-6) and 5.13 x 10(-5)esu in liquid and solid media, respectively). These results show that Acid Fuchsin dye has potential applications in nonlinear optics.     

Photochromic characteristics of monodisperse microcapsules containing azobenzene derivative-doped nematic liquid crystals

Highly mono-sized dye-doped liquid crystal (LC) microcapsules were prepared by the solute codiffusion method for application in photoswitchable devices. Azobenzene derivatives, which can be photoisomerized by irradiation with UV (366 nm) and visible (433 nm) light, were used as a photoresponsive dichroic dye. The microcapsules have a spherical shape and a single dye-doped LC domain. After UV light (366 nm) irradiation, PDLC films prepared using the microcapsules attained a photostationary state within 10 min and this state maintained stability. PDLC films made by employing a dichroic dye having electron donor and acceptor groups in the molecule showed especially good photoisomerization properties. The reversible trans-cis -photoisomerization occurred sharply by irradiating alternately with visible and UV light.     

Multifunctional Langmuir-Blodgett film of an Amphiphilic Benziminazole Styryl Dye

IntroductionA considerable interest has been focused ondesigning organic crystals with multiproperty suchas conductivity,magnetism,and nonlinear opticalresponse[1,2 ] ,but there have been less reports ondesigning multifunctional Langmuir- Blodgett( LB)films[3 ] .In recent years,our group has found thatLB films of some dyes with a donor-π electronbridge- acceptor ( D-π- A ) structure such ashemicyanine dyes exhibit good photoelectricconversion properties besides their well- knownhigh secon…     

Nonlinear studies of Pararosanilin dye in liquid and solid media

Solid-state dye-doped polymers are attractive alternative to the conventional liquid dye solutions. In this paper, nonlinear properties of the dye Pararosanilin has been studied. The third-order nonlinear optical properties of Pararosanilin dye in 1-butanol and dye-doped polymer film were measured by the Z-scan technique using 532 nm diode pumped Nd:Yag laser. This material exhibits negative optical nonlinearity. The dye at 0.4 mM concentration exhibited nonlinear refractive coefficient (n(2) = -6.8 x 10(-8) and -7.11 x 10(-8) (cm(2)/W) in liquid and solid media, respectively), nonlinear absorption coefficient (beta = -7.7 x 10(-4) and -7.93 x 10(-4)cm/W in liquid and solid media, respectively) and susceptibility (chi((3))=3.38 x 10(-6) and 3.53 x 10(-5)esu in liquid and solid media, respectively). These results show that Pararosanilin dye has potential applications in nonlinear optics.     

Photoregulation of the optical properties of comb-shaped polymers with mesogenic side groups

A new approach for photoregulation of supramolecular structure and optical properties of polyacrylic copolymers bearing azobenzene and cyanobiphenyl mesogenic groups is presented. The detailed study of photooptical behaviour, kinetics of photoinduced optical birefringence and mechanism of structural transformations taking place during a laser illumination are discussed.