Optical nonlinearity and photoinduced anisotropy of an azobenzene‐containing ionic liquid crystalline polymer

The nonlinear optical properties of an azobenzene‐containing ionic liquid crystalline polymer were investigated using single‐beam Z‐scan and optical Kerr effect (OKE). The polymer film exhibited large nonlinear absorption (～10^?6 cm W^?1) and nonlinear refraction (～10^?11 cm² W^?1) under 532 nm ps excitation. The femtosecond time‐resolved OKE results suggested that the nonlinear optical response time in off‐resonant region was as fast as 300 fs. Moreover, stable molecular reorientation and a large photoinduced birefringence ( ) were achieved in the polymer film with a 405 nm continous wave (CW) laser as pump light. The large optical nonlinearity, ultrafast response, and effective photoinduced molecular reorientation of the polymer films indicated their potential applications in nonlinear photonic devices and optical storage. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Photo‐induced birefringence phenomenon of a double azo polymer

Poly(glycidyl methacrylate) grafted with double azo bond 4[4′‐(phenylazo)phenylazo]phenol was synthesized and characterized. Photo‐induced birefringence phenomenon of this polymer was studied by static absorption and dynamic pump‐probe techniques, and was compared with that of another polymer Poly{(methyl methacrylate)‐co‐4‐[(3‐methacryloyloxy)} [P(MMA‐co‐MAZ)] containing mono azobenzene chromophore. The results showed that former polymer carrying two azo bonds, with a larger birefringence ratio, had a relatively faster optical switching response than the latter polymer under the same pump beam power. Copyright © 2003 Society of Chemical Industry     

Photoinduced birefringence in blends of a polyurethane bearing azobenzene moieties and a poly(amide–imide)

A polyurethane (MDI‐DR19Cl) bearing azobenzene moieties was prepared by condensation of 4,4′‐diphenylmethylenediisocyanate and an azobenzene compound, 2‐chloro‐4‐nitro‐4′‐[bis‐(2‐hydroxyethyl)]amine‐azobenzene (DR19Cl). Blends of MDI‐DR19Cl and a poly(amide‐imide) were prepared and characterized by UV‐visible and Fourier transform infrared spectroscopy and by DSC. The purpose of using the blends was to overcome the lack of stability of cast films of pure MDI‐DR19Cl, which tend to crack on storage under ambient conditions. This was successfully achieved and, depending on blend proportions, flexible self‐standing films could be prepared after thermal treatment. Optical storage experiments performed with the blends and pure MDI‐DR19Cl cast films showed a decrease in the remnant values of photoinduced birefringence in the blends (60 % for the blend with 5 wt% MDI‐DR19Cl) compared to pure MDI‐DR19Cl (75%), but, taking into account the low content of MDI‐DR19Cl used, the results obtained are probably sufficient to show the viability of these blends in optical storage applications. Copyright © 2006 Society of Chemical Industry     

Structural and photoresponsive behavior of a series of (phenylene)azobenzene‐containing liquid‐crystalline methacrylic copolymers

A series of side‐chain liquid‐crystalline methacrylic copolymers, having various amounts of 4′‐(4‐decyloxyphenyl)‐4‐(hexyloxy)‐azobenzene as the mesogenic group, were synthesized and characterized by differential scanning calorimetry, polarizing optical microscopy and X‐ray diffraction to determine their mesomorphic properties, and by UV?visible spectrometry to elucidate their optical absorption characteristics. Also, birefringence and surface relief gratings were photoinduced in the films using a laser beam of 413 nm. Copolymers with high mesogen contents display a polymorphic behavior of the smectic type. The smectic order tends to disappear as the content of mesogens in the copolymer decreases, going from extended lamellar domains of chromophores packed in a parallel position, typical for smectic liquid crystals, to small aggregates of chromophores dispersed in an amorphous matrix. Important hypsochromic shifts (Δλ_max ≈ 20 nm), associated with π interactions between neighboring aromatic groups, confirm the aggregation of chromophores in lamellar structures. The light‐induced birefringence (0.005 ? 0.06) is not as high as expected but it corroborates that there exists a tight interplay between photoinduced orientation and intrinsic molecular order. Surface relief gratings were recorded in copolymers with low mesogen content (15 ? 30 mol%), showing by atomic force microscopy sinusoidal profiles with an average depth of around 150 nm. © 2013 Society of Chemical Industry     

Synthesis and characterization of α‐methylstilbene‐ and azobenzene‐based thermotropic liquid crystalline polymers

A series of combined liquid crystalline poly(bis‐4,4′‐oxy‐α‐methylstilbene‐4‐substituted (X) phenylazo‐4′‐phenyloxydecylphosphate ester)s bearing photoreactive mesogenic units were synthesized. FTIR and ¹H NMR spectroscopy confirmed the structures of these polymers. The inherent viscosities of the polymers were found to be in the range 0.45–0.65 dL g^?1. Polarizing optical microscopy (POM) exhibited birefringent liquid crystalline melt properties. The thermal properties of all of the polymers were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The photochemical properties of these polymers were studied by UV‐visible and fluorescence spectroscopy. The influence of the photoinduced E–Z (trans–cis) isomerization of the various terminal substituents of the side‐chain azobenzenes was investigated. The kinetics of the photoisomerization process reveal the switching times for the conversion between the trans‐ and cis‐ forms of the azobenzene units. The photo‐optical properties of these polymers exhibited layered smectic phases and showed good photoinduced properties in their mesomorphic states. Copyright © 2005 Society of Chemical Industry     

Material design for polymer/azobenzene liquid crystal/metal salt composite films possessing thermo- and photoresponsive ionic conductivity

Various azobenzene derivatives and polymers were attempted as materials for thin composite films containing a polymer, a liquid crystal, and lithium perchlorate which can undergo ionic-conductivity switching induced by light or heat. Poly(vinyl chloride) -based composite films containing enantiotropic azobenzene liquid crystals 1 , exhibited significant ionicconductivity change based on thermo- and photoinduced phase transitions of 1 , the temperature dependence on the ionic conductivity reflecting the enantiotropic phase transition behavior of the liquid crystals. Marked, reversible ionic-conductivity switching on alternating irradiation of UV and visible lights was attained with the composite films containing 1 , especially 1 (n = 12). Incorporation of monotropic liquid crystals 3 to the composite films allowed bistability in the temperature dependence on the ionic conductivity. Employment of a polycarbonate resin and poly(methyl methacrylate) as the polymer material of the composite films gave similar ionic-conductivity changes to the poly(vinyl chloride) composite films, whereas polyethyleneoxide brought about some different results in the photoinduced ionic-conductivity change.     

Synthesis and physical properties of liquid‐crystalline copolymers with azobenzene segments

To investigate the effects of photoisomerizable azobenzene segments on the liquid‐crystalline characteristics and thermal properties of polymers, a series of liquid‐crystalline homopolymers and copolymers with azobenzene segments was synthesized. The azobenzene contents of the copolymers were estimated with elemental analysis. The photoisomerization of the azobenzene derivatives was studied with ultraviolet–visible (UV–vis) spectroscopy. The UV–vis absorption of the copolymers was found to be parallel with the content of the azobenzene segments. UV irradiation was found to cause a decrease in the copolymer transmittance around 355 nm due to the photoinduced isomerization from entgegen (E) to zusammen (Z). The phase‐transition temperatures and molecular weights of the polymers were investigated with differential scanning calorimetry and gel permeation chromatography, respectively. The variation in the phase‐transition temperature of the homopolymers before and after UV (365 nm) irradiation was investigated. The bended Z structure was found to disturb the order of the orientation of liquid crystals and to lower the phase‐transition temperature. The appearance of the polymer film was changed from opaque to clear after sufficient UV irradiation. The image recording of the polymer films was achieved after UV irradiation through a mask with pictures. The stability and reliability of the Nematic‐Isotropic phase transition of the homopolymers was evaluated with repeated cycles of 365‐nm UV irradiation and heating at 130°C. After the recycle phase transition was repeated nine times, no significant decay in the response and transmittance could be found. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 2006     

Optical switching behavior of polymer‐dispersed liquid crystal composite films with various novel azobenzene derivatives

Polymer‐dispersed liquid crystal (PDLC) composite films were fabricated by thermal polymerization with E7 liquid crystal, monomers, and novel azobenzene derivatives synthesized in this study. To investigate the effects of azocompounds on the optical switching of PDLC films, a series of novel azobenzene derivatives of 4‐alkyloxy‐4′‐methoxyazobenzene with carbon numbers of 3–6, chiral compounds of amyl‐4‐(4‐hexyloxyphenylazo)benzoate, and bornyl‐4‐(4‐hexyloxyphenylazo)benzoate were synthesized. The compounds synthesized in this investigation were identified using FTIR, NMR, and elemental analysis. The optical texture of the composite films was analyzed under crossed nicols with a polarizing microscope. The morphological observation of the solid polymer in the composite films was performed with a scanning electron microscope (SEM). The optical behavior of the composite films on UV irradiation and the effects of the curing time on the thermal stability of the composite films were investigated. Isomerization of the azobenzene derivatives due to UV irradiation was confirmed by a texture study and image recording method. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 789–799, 2004     

Post and prepolymerization strategies to develop novel photochromic poly(esterimide)s

This paper reports novel photoresponsive, processable poly(esterimide)s functionalized with the azobenzene and tricyanovinylene groups. Post and prepolymerization strategies were utilized for preparation of the new photochromic polymers with imide rings. The postpolymerization method of azopolymer synthesis included a functionalization of precursor poly(esterimide) containing dialkylaminophenyl groups with diazonium salt of aniline. The precursor poly(esterimide) was obtained from synthesized 2,2′[N‐phenylethyloaniline‐di(4‐estro‐1,2‐dicarboxylic)]anhydride and 4,4′‐methylene bis(2,6‐dimethylaniline). The prepolymerization strategy based on polycondesation of 2,4‐diaminoazobenzene with two dianhydrides, that is, with or without the azobenzene group. The new dianhydride with azobenzene unit was obtained. The reaction of post‐tricyanovinylation was carried out for substitution of prepared polymers with tricyanovinylene groups. The synthesized polymers were characterized and evaluated by FTIR, ¹H NMR, X‐ray, UV‐Vis spectroscopies, and DSC. The polymers exhibited glass transition temperatures in the range of 119–208°C and good solubilities in common organic solvents, providing optical‐quality films. Thermal stability of the polymers films was investigated by UV‐Vis spectroscopy. Preliminary investigations of the optical anisotropy in chosen poly(esterimide)s were carried out by photoinduced birefringence measurements. Relatively high photoinduced birefringence (Δn = 0.01) was measured for polyimide with covalently bonded azobenzene substituted with strong acceptor group. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

掺偶氮苯二氧化钛基复合薄膜的制备及光开关性能

通过低温溶胶-凝胶技术结合旋涂法制备了掺偶氮苯二氧化钛基有机-无机复合薄膜.研究了不同热处理温度对复合薄膜的表面形貌、传输模式、折射率与厚度和光化学结构特性的影响.结果表明:该复合薄膜在低于300℃的热处理温度时表面光滑致密、折射率可调,是良好的光波导材料.通过测试样品在365 nm紫外光和450 nm可见光照射下的吸...     

Photoresponse gas permeability of azobenzene‐functionalized glassy polymer films

The gas permeability of membranes composed of a polymer functionalized with azobenzene chromophores (azopolymer) was investigated under different conditions of light irradiation. A series of measurements with He gas showed that the permeability of the membranes increased by 5–10% upon irradiation with blue light, which caused cyclic photoisomerization of the azobenzene chromophores. In contrast, no significant change in gas permeability and no photoisomerization of the azobenzene chromophores were observed upon irradiation with red light. Moreover, using a digital video microscope, we observed that azopolymer irradiated with blue light spread out from localized particulate domains and thinly covered the surface of the base membrane. Together with the results of the photoresponse permeability measurements, this observation strongly suggested the existence of photoinduced plasticization as discussed in the study of photoinduced surface relief formation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2068–2072, 2003     

Synthesis of temporarily solubilised azo disperse dyes containing a β‐sulphatoethylsulphonyl group and dispersant‐free dyeing of polyethylene terephthalate fabric

Disperse dyes containing a β‐sulphatoethylsulphonyl group have temporary solubility and can be applied for dispersant‐free dyeing of hydrophobic fibre. Six novel temporarily solubilised azo disperse dyes having a β‐sulphatoethylsulphonyl group in their structures were synthesised, and their dyeing properties on polyester were investigated. As a dye intermediate, a diazo component having dibromo groups was prepared, and 4‐diethylamino‐4′‐(2‐sulphatoethylsulphonyl‐4,6‐dibromo)azobenzene dyes were prepared by a diazo‐coupling reaction. Then, the dyes containing dicyano groups were prepared by cyanation of corresponding dyes with dibromo groups. The absorption maxima of the dyes were affected by the substituents in the diazo and coupling component rings and varied from 434 to 616 nm in dimethylformamide. Polyethylene terephthalate woven fabric could be dyed with the synthesised temporarily solubilised dyes without using any dispersants. Dyebath pH affected the K/S value at maximum absorption as well as percentage exhaustion on polyethylene terephthalate fabric, and the optimum pH was 5. The dyes gave brownish orange, red, purple, and greenish blue hues on polyethylene terephthalate fabrics, and colour build‐up was good. Wash fastness was good to excellent, rubbing fastness was moderate to excellent, and light fastness was poor to moderate.     

Photoinduced optical anisotropy in new poly(amide imide)s with azobenzene units

Two series of new photosensitive poly(amide imide)s (PAIs) containing photochromic azobenzene moieties as side groups have been synthesized. For this purpose the following diamines with azobenzene groups have been prepared: 2,4-diamino-4′-fluoroazobenzene, 2,4-diamino-4′-methylazobenzene, 2,4-diamino-4′-trifluoromethoxy-azobenzene and 2,4-diamino-4′-nitroazobenzene. The poly(amide imide)s have been obtained from diamidedianhydrides and diamino-chromophores using high-temperature polycondensation. The resulting polyimides are characterized by good solubility in some solvents, high glass transition temperatures (257-280 °C), high thermal decomposition temperatures and good film forming properties. The irradiation with linearly polarized light (488 nm, 100 mW/cm²), causes a reorientation of the azobenzene groups by angular-selective EZ photoisomerization. In this way optical anisotropy is induced in the initially isotropic films casting from the amorphous polymers. The photoinduced dichroism in the films has been measured, and the results are discussed in relation to the structure of these polymers, whereas the substitution of the azobenzene moiety and the structure of the backbone are varied.     

Photoresponsive Crown Ethers. Part 11. Azobenzene-Pillared Cylindrical Macrocycle As a Photoresponsive Receptor

A cylindrical ionophore (1) in which two diaza-crown ethers are linked by two azobenzene pillars serves as a photoresponsive host molecule. In alkaline solution containing K⁺, (1) forms a cascade complex with dianionic guest molecules, but photoirradiated (1) which has a shortened cylinder cannot bind the guest molecules so effectively as (1). (1) solubilised in acidic aqueous solution by protonation of four tertiary nitrogens provides a hydrophobic cavity to bind several anionic azo dyes. The association is also suppressed by photoirradiation. The results indicate that parallel array of the azobenzene segments in (1) provides a host cavity and the photoinduced structural change is readily reflected by the association tendency. This is the first example for the photoresponsive inclusion complex.     

Deep‐coloured polyester/cotton blends with low concentrations of polymethylol dyes by a one‐pass continuous dyeing process

An obvious limitation of the one‐pass continuous dyeing process for polyester/cotton blends is its inability to achieve deep colour depth, which is caused by the low dye fixation yields of commercial reactive dyes. In this study, the performances of polyester/cotton blends dyed with high‐fixation polymethylol dyes and disperse dyes were compared with those of polyester/cotton blends dyed with a mixture of reactive dyes and disperse dyes. Polymethylol dyes were observed to be suitable for dyeing polyester/cotton blends when used in low concentrations; the required concentrations of polymethylol dyes were only 23–58% of the concentrations of commercial reactive dyes required to reach a given colour level on polyester/cotton blends. The wash and crocking fastness of polyester/cotton blends dyed with polymethylol dyes were similar to those of polyester/cotton blends dyed with reactive dyes.     

Investigation on stilbene‐ and azobenzene‐based liquid crystalline organophosphorus polymers

Two series of combined liquid crystalline polyphosphates bearing dual photoreactive mesogenic units (stilbene and azobenzene/α‐methylstilbene and azobenzene) were synthesized by solution polycondensation method. The structures of the synthesized polymers were confirmed by various spectroscopic techniques. Thermogravimetric analysis reveals that they are stable between 230 and 320°C. Differential scanning calorimetry studies were done to study the liquid crystalline property, and glass‐transition, melting, and isotropization temperatures for all the polymers. Polarizing optical microscope shows the birefringent melt for all the polymers exhibiting liquid crystalline property. The photochemical response was studied by UV–visible and fluorescence spectroscopy for all the polymers. The photocrosslinking reaction of the stilbene containing polymers was ascertained by spectroscopic and photolysis studies. The rate of the switching time for the conversion of trans to cis form of azobenzene unit was investigated by UV spectroscopy. The terminal substituents in the side chain affects the texture of liquid crystalline phase for all the polymers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

A novel photoactive hyperbranched poly(aryl ether ketone) with azobenzene end groups for optical storage applications

A novel hyperbranched poly(aryl ether ketone) terminated by azobenzene chromophores (azo-HPAEK) was prepared using 1,3,5-tris[4-(4-fluorobenzoyl)phenoxy] benzene (B₃) as a core molecule, 4,4′-(hexafluoroisopropylidene) diphenol as an A₂ monomer and 4-(4-hydroxyphenylazo) benzonitrile as an end-capping reagent. It is shown that azo-HPAEK exhibits a high glass transition temperature (Tg), excellent thermal stability and homogeneous photochromic behavior. By exposing the spin-coated film to a laser beam interference pattern, azo-HPAEK can be used for rapid (within 30 s) fabrication of surface relief gratings (SRGs), and the azo-HPAEK gratings cannot be totally erased by heating, even at 300 °C. In particular, azo-HPAEK shows a large photoinduced birefringence intensity and good reversible optical storage upon irradiation with 532 nm Nd:YAG laser.     

Chromophore concentration effect on holographic grating formation efficiency in novel azobenzene‐functionalized polymers

Optically active photochromic poly(amideimide)s containing azobenzene side groups in the repeating unit were prepared. The polymers were designed and synthesized specifically for this work in order to evaluate chromophore concentration effect on holographic grating recording. The poly(amideimide)s with mono‐ and bis‐azobenzene moieties were obtained via direct high temperature polycondensation and compared with respect to their ability of diffraction grating formation due to the light‐induced optical anisotropy effects. Holographic gratings were fabricated in polymer films upon exposure to an interference pattern of two polarized Ar⁺ laser beams at 514.5 nm wavelength. Different geometries of laser beams polarization were applied. It should be emphasized that although the azobenzene moieties are rigidly connected to the polymers backbone, some of polymers exhibited the unusually high light diffraction efficiency of around 40%. The created surface relief gratings (SRGs) were successfully observed using the atomic force microscopy (AFM). AFM images show regularly defined and aligned grating structures. It should be stressed that the SRGs with maximum of relief height up to 260 nm in polyimide derivatives with side azobenzene group were observed for the first time. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Syntheses and optical properties of hybrid materials containing azobenzene groups via sol–gel process for reversible optical storage

We focused on the synthesis and optical properties of new organic–inorganic hybrid materials containing azobenzene groups for rewritable optical recording media. Hybrid material (SGUR19‐n's) design has the structure of azobenzene group with urethane bonds in the silica network. The structures of the synthesized monomers and precursors were confirmed by FTIR and ¹H NMR spectrophotometer. Also, we reported on the effects of the direction of the polarized beam, the intensity of the induced beam, and the structures of SGUR19‐n's materials on the diffraction efficiency of SGUR19‐n's films. It was revealed that SGUR19‐n's films prepared by the sol–gel process have adequate writing–erasing–rewriting properties when used as a reversible optical storage material. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4811–4818, 2006     

One‐bath union dyeing of wool/polytrimethylene terephthalate blends†

The one‐bath dyeing of blends of polytrimethylene terephthalate (PTT) staple and wool has been investigated. The exhaustion of selected Terasil disperse dyes on PTT fibre and Lanasol reactive dyes on wool was measured as a function of temperature, together with the cross‐staining of the Terasil dyes on the wool component and the Lanasol dyes on PTT component. Most Terasil disperse dyes achieved satisfactory dye uptake on PTT at 110 °C, whereas on conventional polyester (polyethylene terephthalate) temperatures of up to 130 °C are required. An optimised union‐dyeing technique for wool/PTT blends was developed which minimised the staining of Terasil disperse dyes on wool and produced dyed goods with high levels of wet colour fastness. Carriers were not required to enhance the dyeability of PTT at low temperatures. The wool component appeared to be protected against damage at 110 °C by the reactive dyes. The results indicate the potential for blending PTT fibre and wool to produce fabrics that are easier to dye at lower temperatures than conventional wool/polyester blends.