Azo-dye Chromophores Research Articles

Lanthanide complexes with an azo-dye chromophore ligand: syntheses, crystal structures, and near-infrared luminescence by long-wavelength excitation.

Near-infrared (NIR) emissive probes are becoming increasingly popular in biological sensing and imaging due to the advantages of non-invasiveness and deep tissue-penetrating ability. Herein, a series of complexes of trivalent lanthanide ions (Ln = Yb, Er, and Gd) with the commercially available azo dye chromophore 2R (Na2H2C2R) as ligand and featuring respectively H2O and dimethylsulfoxide (DMSO) as ancillary ligands have been prepared. Formulated as [Ln2(HC2R)2(H2O)10]·8H2O (1-3, Ln = Yb, Er, Gd) and [Ln2(HC2R)2(DMSO)10]·2DMSO (4-6, Ln = Yb, Er, Gd), their structures have been determined by single-crystal X-ray diffraction studies. Photophysical property studies revealed NIR emissions of the DMSO complexes characteristic of Yb(III) and Er(III), effectively sensitized by the dye ligand arising mainly from the π-π* transition of the chromophore. The long-wavelength excitation of the complexes, covering the whole visible-light range and extending into the NIR region, portends the potential applications of such complexes for flexible bioimaging and sensing.

Optical Trapping of Photosoftened Solid Polymers

We present evidence of optical trapping of solid polymer films by a tightly focused near-infrared (NIR) laser beam (785 nm) when the polymer is softened by green laser (532 nm) irradiation, which is uniformly distributed over the film surface. While the whole film is softened by the green laser, only the part which is subjected to the NIR laser is trapped. The film, which is transparent in the NIR range and strongly absorbs the visible light, is deposited on a glass substrate. The NIR laser is focused at the sample plane and attracts the polymer to the laser focus, by the optical gradient force, during the green light irradiation, indicating that molecular mobility is strongly reduced and the optical gradient force of the NIR laser is inefficient in moving the polymer below the glass-transition temperature of the polymer without photosoftening. The observations are consistent with the theory of photochemical tweezing, which rests on the assumption that photosensitive polymers, containing azo dyes, are softened, i.e., molecular mobility is enhanced, by photoisomerization of the azo dyes during green light irradiation, and are moved in gradients of light fields. We also found that this two-color laser tweezing scheme is sensitive to light polarization, owing to the polarization sensitivity of the azo dye chromophores.

Synthesis and two-photon absorption property of novel salen complexes incorporated with two pendant azo dyes

New salen compounds have been developed to possess two pendant azo dye chromophores. The two-photon absorption properties have been observed which result from the chromophores. The additive property has been found to exist as a result of no detrimental dipole–dipole interaction between chromophores.

A STUDY ON THE SECOND-ORDER NONLINEAR OPTICAL PROPERTIES OF AZO-DYE CHROMOPHORES CONTAINING THE ELECTRON-ACCEPTOR GROUP

Two new azo-dye chromophores containing different electron-acceptor groups were synthesized and characterized by 1 H NMR, FT-IR and UV-vis spectra, respectively. The second-order nonlinearity of azo-dyes doped films in poly (methylmethacrylate) and the first hyperpolarizability of the azo molecules were investigated by the Maker Fringe method and the solvatochromic method, respectively. Experimental results showed that both of the two dyes exhibited large second-order nonlinearity (d33 > 30 pm/v) and the stronger electron-acceptor groups in dye molecules would induce larger second-order nonlinearity. This was confirmed by the measurement of the first hyperpolarizability.

Neutral and Cationic Cyclopentadienyliron Macromolecules Containing Azo Dyes

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Synthesis and properties of polymer containing azo-dye chromophores for nonlinear optical applications

Some thermal stable polyimides and polyimide/silica hybrid materials containing azo-dye have been synthesized. The resulting polyimides had high weight-average molecular weight ( M w) up to 49 300 and 53 900, respectively, and a large glass transition temperature ( T g) of 242 °C, and the decomposition temperature ( T d) of 350 °C. The resulting polyimide/silica hybrid materials had higher glass transition temperature and decomposition temperature than the pure polyimides. The silica content in the hybrid materials varied from 0 to 22.5 wt%. The electro-optic coefficients ( γ 33) at the wavelength of 832 nm for polymer thin films poled were in the range of 9–23 pm/V and the values remained well (retained >83% for more than 100 h). The heat capacities of some materials were in the range of 0.8433–1.2564 J K −1 g −1 for the temperature range from 273 to 363 K. No thermal anomaly was found in this temperature range.

Dielectric characteristic of photoinduced isomerization in azo-dye doped polymeric matrices

The dielectric permittivities and losses of poly(methyl methacrylate) doped with different concentrations of azo dye are investigated under the irradiation of 532nm light for the first time. The dielectric permittivities increase with the concentration of chromophores increasing, and the dielectric relaxation is mainly influenced by the doped azo-dye chromophores. Given the dye concentration, the dielectric permittivities depend on the pump power of 532nm light. With the increase of pumping light power, the low frequency dielectric losses increase while the high frequency dielectric losses decrease. The results are explained based on the photoinduced isomerization of chromophores and the interaction between the chromophores and polymer matrices.

MONTE CARLO SIMULATIONS OF TEMPERATURE DEPENDENCE OF THE KINETICS OF DIFFRACTION GRATINGS FORMATION IN A POLYMER MATRIX CONTAINING AZOBENZENE CHROMOPHORES

A simple kinetic model of temperature-dependent processes accompanying the writing and decay of diffraction gratings in a polymer matrix doped with azo-dye chromophores under illumination with spatially modulated and linearly polarized light is introduced and studied using Monte Carlo simulations. The model generalizes a recently proposed athermal kinetic model based on three-channel photoizomerization cycles of trans–cis type of azobenzene molecules and orientational redistribution and diffusion. These processes are influenced by a polymer matrix in a thermal equilibrium. The Monte Carlo simulations show the important role of temperature on the kinetic processes during building and erasure of diffraction gratings. We discuss some interesting applications for photonic devices, related to all-optical processing and storage of information using holographic methods.

Relaxational diffusion in guest–host polyphosphazene thin films: Temperature dependence

The relaxation of poled guest–host polyphosphazene (PPZ) films containing the 4-[(4′-nitrophenyl)azo]phenoxy (NPAP) azo-dye chromophore (Tg=144 °C) has been investigated by measuring the time decay of the nonlinear optical susceptibility tensor in the 80–120 °C temperature range. The kinetic data have been analyzed on the basis of the Legendre polynomial decomposition of the orientational distribution function. In the measuring time range, two components (fast and slow) of the decay have been found together with a constant component that disappears at temperatures close to Tg. This component accounts for the nonreorientable fraction of the molecules at each temperature. The temperature dependence of the two lifetimes has been determined and fitted to an Adam–Gibbs law. At a high temperature, (120 °C) the ratio of lifetimes closely follows the predictions of the orientational diffusion equation. This allows one to determine the two nonlinear components βzzz=−88.10−30 esu and βzxx=71.10−30 esu of the quadratic hyperpolarizability tensor in our rodlike (C∞v symmetry) molecules, showing the non-negligible contribution of the nondiagonal components.

Synthesis of iron‐containing polymers with azo dyes in the backbones or side chains

AbstractThe synthesis of cationic cyclopentadienyliron‐containing polymers with pendent azobenzene chromophores was accomplished via metal‐mediated nucleophilic aromatic substitution reactions. All of the desired polymers were isolated as vibrantly coloured materials and displayed excellent solubility in polar aprotic solvents. Cationic and neutral cyclopentadienyliron polymers incorporating azo dyes in the backbone were also prepared. Reactions of azo dyes with dichlorobenzene complexes allowed for the isolation of cationic cyclopentdienyliron (CpFe+) complexes with azo dye chromophores. These complexes were then reacted with 1,1′‐ferrocenedicarbonyl chloride to produce the trimetallic monomers with terminal chloro groups. These monomers contained two pendent CpFe+ cations and a neutral iron moiety in the backbone. Nucleophilic substitution reactions of these monomers with oxygen and sulfur containing dinucleophiles gave rise to a new class of polymeric materials. The pendent CpFe+ moieties could also be cleaved from the polymer backbones using photolysis to afford novel ferrocene based polymers. The UV‐vis spectra of the organoiron monomers and polymers display similar wavelength maxima however incorporating azobenzene chromophores with electron‐withdrawing substituent into the polymer chains resulted in bathochromic shifts of the λmax values.

Second-order nonlinearity and optical image storage in phenyl-silica hybrid films doped with azo-dye chromophore using optical poling technique

4-[ N-ethyl- N-(2-hydroxyethyl)]amino-4 ′-nitro-azobenzene (DR1)-doped phenyl group substituted silica films were prepared by a sol–gel method. The films were optically poled by the coherent superposition of 1064 and 532 nm beams from a Q-switched Nd:YAG laser. To discuss the effects of the modifier group, interaction between DR1 molecules and the matrix was investigated. The delocalization of π electrons occurred between DR1 molecules and the phenyl-silica hybrid matrix, and that consequently the polarized DR1 molecules could be stabilized. By use of the optimized optical poling technique, optical storage was successfully demonstrated for a phenyl-silica hybrid film doped with DR1.

A photorefractive organically modified silica glass with high optical gain

Photorefractive materials exhibit a spatial modulation of the refractive index due to redistribution of photogenerated charges in an optically nonlinear medium. As such, they have the ability to manipulate light and are potentially important for optical applications including image processing, optical storage, programmable optical interconnects and simulation of neural networks. Photorefractive materials are generally crystals, polymers and glasses with electro-optic or birefringent properties and noncentrosymmetric structure. Here we report the photorefractive effect in both non-centrosymmetric and centrosymmetric azo-dye-doped silica glasses, in which refractive index gratings that are spatially phase-shifted with respect to the incident light intensity pattern are observed. The effect results from a nonlocal response of the material to optical illumination, and enables the transfer of energy between two interfering light beams (asymmetric two-beam coupling). Although the writing time for the present grating is relatively slow, we have achieved a two-beam coupling optical gain of 188 cm(-1) in the centrosymmetric glasses, and a gain of 444 cm(-1) in the non-centrosymmetric structures. The latter are fabricated using a corona discharge process to induce a permanent arrangement of azo-dye chromophores.

Bismaleimide resins modified by bi- or tri-allyl-functionalized azo chromophores for second-order optical nonlinearity

Several novel azo dye chromophores with allyl groups at one or two ends of the molecules were synthesized. Differential scanning calorimetry and thermogravimetric analysis tracing showed that these chromophores can be thermally cured with bismaleimidodiphenyl methane to afford a series of crosslinked, and chromophore-modified bismaleimide resins without any appreciable decomposition up to >300°C, while IR spectra analysis indicated that it is not a trivial task to achieve highly-crosslinked BMI resins due to decomposition of the azo dye chromophores. The effects of different chromophores on the curing conditions and thermal stability of these modified BMI resins are discussed. It is noticeable that incorporating a chromophore into the network of BMI resins by its reactive groups at both ends facilitates improvement of the thermal stability of the materials.

Synthesis and characterization of accordion main-chain azo-dye polymers for second-order optical non-linearity

New type accordion polymers with azo-dye chromophores as the major segments (up to 70% by weight) of the main chain for second optical non-linearity (NLO) are designed and synthesized by the Knoevenagel polycondensation between bis(carboxaldehyde) containing azobenzene and bis(cyanoacetate) comonomers. Several important properties for NLO application, such as solubility and thermal stability, are investigated, and the effects of linkage groups on the physical properties of polymers are also discussed in some detail. Poled films of one of these polymers show a relatively high resonant d33 value of 33 pm V−1 by second harmonic generation (SHG) measurement, and their order parameter, which is determined to be 0.20 by UV–vis measurement, keep almost constant for 240 h at ambient temperature. © 2000 Society of Chemical Industry

Synthesis of a novel difunctional NLO azo-dye chromophore and characterizations of crosslinkable copolymers with stable electrooptic properties

Synthesis of a novel difunctional NLO azo-dye chromophore and characterizations of crosslinkable copolymers with stable electrooptic properties

Synthesis of a novel difunctional NLO azo‐dye chromophore and characterizations of crosslinkable copolymers with stable electrooptic properties

The synthesis and the nonlinear optical (NLO) properties of crosslinkable copolymers based on a novel NLO azo-dye chromophore bearing two functions: one used the free-radical copolymerization, that is, the methacrylate group, and the other one used for the crosslinking process, that is, the carboxylic acid function, are described. Copolymerization of this new monomer with glycidyl methacrylate leads to novel soluble crosslinkable NLO copolymers bearing free epoxy and carboxylic groups. The poling process, before crosslinking, is achieved at a temperature (Tp) close to the glass transition temperature, Tg (<70°C), of the copolymers. At this temperature, no reaction takes place between epoxy and carboxylic acid functions. In fact, crosslinking begins to start at a higher temperature, Tc (Tc ≫ Tp ≈ Tg). After the optimization of the poling and crosslinking processes, the NLO crosslinked polymer with 30 mol % of the chromophore exhibits a Tg of 157°C and a high quadratic susceptibility (d33) of 30 pm/V at 1320 nm. This coefficient is stable at 85°C for several weeks. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 974–982, 1999

Optical-Poling of an Azo-Dye Chromophore Doped Silica Hybrid Thin Films.

DR1 (4-[N-ethyl-N-(2-hydroxyethyl)]amino-4′-nitro-azobenzene) doped silica films were prepared by a solgel method, from a solution of tetraethyl orthosilicate and DR1. The films were optically poled and heat-treated to build a polarized structure for second-order optical nonlinearity. Two seed beams at 1064 and 532nm wavelengths from a Q-switched Nd: YAG laser were coaxially applied to the films. Second-harmonic generation was observed from the films after the optical-poling. We found that the rigid silica matrix prevented the relaxation of polarized structure.

Light-induced orientation in azo-polyimide polymers 325 °C below the glass transition temperature

We report on light-induced nonpolar orientation of sidechain nonlinear-optical polyimides [glass transition temperatures (Tg) up to 350 °C] containing no flexible connectors or tethers. The nonlinear-optical azo-dye chromophore is incorporated through the donor substituent as a part of the polymer backbone. This impressive photoinduced orientation occurs at room temperature, i.e., at least 325 °C below the Tg of one of the polymers that we investigated. Furthermore, it is shown that, after photoinduced ordering, this polymer must be heated to 350 °C to induce main-chain movement and to erase the orientation, whereas the direction of orientation of the chromophores can easily be controlled at room temperature simply by choice of the appropriate polarization of the irradiating light. This light-induced orientation process is shown to be useful for storing images in waveguides.

Synthesis of polymers bearing azo-dye chromophore with photocrosslinkable moiety for nonlinear optics

Novel photocrosslinkable second-order nonlinear optical(NLO) polymers were synthesized from radical homopolymerization of 4-[N-ethyl-N-(2-methacryloyloxyethyl)]amino-4′-(2-cinnamoyloxyethyloxycarbonyl)-2′-nitroazobenzene(MACN) or copolymerization of MACN with 2-(cinnamoxyloxy)ethyl methacrylate(CM), and from polycondensation of 4-[N,N-bis(2-hydroxyethyl)]amino-4′-(2-cinnamoyloxyethyloxycarbonyl)-2′-nitroazobenzene(HACN) with p-phenylenediacyloyl chloride(PD). For the purpose of obtaining an optimized condition of UV irradiation for poling treatment involving photocrosslinking, photoreactivity of these NLO polymer films was investigated. There was observed considerably different photoreaction behavior, especially in photofading of the NLO chromophore, between MACN polymer and HACNPD polycondensate; the latter faded more rapidly than the former. A reason for this phenomenon was considered.

Preparation of Langmuir-Blodgett Films of Methacrylate Copolymer Bearing Azo-dye Chromophores and Their Nonlinear Optical Properties.

A methacrylate copolymer, poly(MO), was prepared from radical copolymerization of octadecyl methacrylate and methacrylamide bearing DR-1 type azo-dye chromophore as NLO active group, which was synthesized through 7 reaction steps. Poly(MO) gave LB film on quartz substrate by the vertical dipping method. Transfer of the monolayer at the water-air interface was easier in upstroke than in down stroke. By SHG measurement for the multilayers it was found that only in the first monolayer exists an effective noncentrosymmetric structure of NLO chromophores, showing SHG. Unexpectedly, when a heat treatment wasperformed SH intensity of the monolayer decreased, whereas that of the multilayers increased significantly. More detailed investigations about this heat response behavior were carried out.