Investigation into the surface relief grating mechanism via XPS in new azobenzene based optical material

Research into azobenzene and its compounds focuses on the molecules ability to cis‐trans isomerize, this photoisomerization enables surface relief gratings (SRGs) to be formed on the azobenzene functionalized polymer films. SRG allows information to be written and then erased, an essential requirement of most modern electrical products. The interest into SRG photofabrication is thus rapidly increasing and is emerging at the forefront of photonic and nanotechnology research. The surface relief grating mechanism, however, is not fully understood, a photoplasticization process is postulated, which is thought to occur via the azo‐chromophores photoisomerization, so encouraging polymer chain migration to the surface. In comparison, suggestions have shown the SRG process does not involve a change in the film surface profile but in the local refractive index. Currently, no research has yet established the surface relief grating mechanism, this paper sets out to determine the mechanism and investigate those theories already postulated by observing the thin film surfaces prior to and after SRG using X‐ray photoelectron spectroscopy (XPS). By identifying the surface components, greater insight and understanding of the SRG mechanism can be achieved. In this paper, poly(4‐(N‐(2‐methacryloyloxyethyl)‐N‐ethylamino)‐4′‐nitroazobenzene)₉₀‐co‐(methylmethacrylate)₁₀ 50 : 50 PMMA blend was exposed to SRGs. Using XPS the surface composition was determined prior to and after SRG. Following SRG, the spectra for O 1s, N 1s and C 1s using XPS expressed a change in the components at the surface. This is most evident in the N 1s spectra, with PMMA not containing nitrogen, the N 1s becomes the determining factor. The nitrogen absence combined with a significant increase in the carbon and oxygen peak intensity concludes the azobenzene lies not on the surface but, in fact, within the bulk after SRG. The initial light irradiation process must be a consideration. However, on X‐ray analysis the sample showed the same spectra as the one prior to SRG. Copyright © 2002 John Wiley & Sons, Ltd.     

FT‐IR Investigation into the miscible interactions in new materials for optical devices

In this article we determine the miscibility of azobenzene derivative (poly(4‐(N‐(2‐methacryloyloxyethyl)‐N‐ethylamino)‐4′‐nitroazobenzene)₉₀‐co‐(methyl methacrylate)₁₀)/poly(vinyl acetate) (PVAc) and azobenzene derivative/poly(vinyl chloride) (PVC) blends using Fourier Transform infrared (FT‐IR) spectroscopy. With this method we can clearly identify the exact interactions responsible for miscibility. In the azobenzene derivative 50:50PVAc blend new peaks were evident at 2960, 2890, 1237 and 959 cm^?1, these peaks depict miscible interactions. These wavenumbers indicate that the miscible interactions occurring are from the C? H stretching band, the vinyl acetate C?O, conjugated to the ester carbonyl, the cis‐transformation N?N stretch frequency and the acetate ester weak doublet. The azobenzene derivative 80:20PVC blend display peaks identical in profile to the blend homopolymers, indicating no miscible interactions. However, this could be due to overlapping of peaks within the same wavenumber region, making resolution difficult. This research demonstrates FT‐IR can deduce favorable interactions for miscibility and therefore numerous miscible blends can successfully be calculated if possessing the same groups responsible for miscibility. This paves the way for a new generation of designer optical materials with the desired properties. Copyright © 2003 John Wiley & Sons, Ltd.     

偶氮苯掺杂聚合物光致双折射的一维空间分布

报道了偶氮苯掺杂聚合物光致双折射空间分布的实验研究。发现在光照区域外较大的范嗣内有双折射，证实了生色团分子的取向运动及其引起的周边分子相互运动的存在。对3种偶氮苯染料分散红1(DR1)。分散红13(DRl3)和分散黄7(DY7)掺杂的聚甲基丙烯酸甲酯(PMMA)聚合物进行了定性研究。发现生色团分子的取向运动及其引起的周边分子相互运动与抽运光强度和生色团分子的大小等因素有关。     

Stimuli Responsive Materials Supported by Orthogonal Hydrogen and Halogen Bonding or I···Alkene Interaction

Smart materials represent an elegant class of (macro)-molecules endowed with the ability to react to chemical/physical changes in the environment. Herein, we prepared new photo responsive azobenzenes possessing halogen bond donor groups. The X-ray structures of two molecules highlight supramolecular organizations governed by unusual noncovalent bonds. In azo dye I-azo-NO₂, the nitro group is engaged in orthogonal H···O···I halogen and hydrogen bonding, linking the units in parallel undulating chains. As far as compound I–azo–NH–MMA is concerned, a non-centrosymmetric pattern is formed due to a very rare I···π interaction involving the alkene group supplemented by hydrogen bonds. The Cambridge Structural Database contains only four structures showing the same I···CH₂=C contact. For all compounds, an ¹⁹F-NMR spectroscopic analysis confirms the formation of halogen bonds in solution through a recognition process with chloride anion, and the reversible photo-responsiveness is demonstrated upon exposing a solution to UV light irradiation. Finally, the intermediate I–azo–NH₂ also shows a pronounced color change due to pH variation. These azobenzenes are thereby attractive building blocks to design future multi-stimuli responsive materials for highly functional devices.     

Langmuir-Blodgett deposition and second-order non-linear optics of several azobenzene dye polymers

The Langmuir-Blodgett (LB) film-forming properties of a number of novel azobenzene dye polymers are reported. The linear and second-order non-linear optical properties of the films have been studied using ellipsometry, visible spectroscopy and Pockels effect measurements. As monolayers, the effective electro-optic r-coefficients ranged from 1 to 8.7 pm V.⁻¹ When one of the polymers was combined in an alternate layer film (230 layers in total), an r₁₃-coefficient of 13 pm V⁻¹ was achieved. This is one of the highest values reported for a ‘thick’ LB film.     

In situ immobilization on the silica gel surface and adsorption capacity of poly[4-methacroyloxy-(4′-carboxy-2′-nitro)-azobenzene] on toxic metals ions

Abstract

A new organo-mineral composite material has been synthesized by in situ immobilization of poly[(4-methacroyloxy-(4′-carboxy-2′-nitro)azobenzene on the silicagel surface. As a result of thermogravimetric analysis and DSC-MS analysis it has been found that the composition of synthesized composite includes 10,1?wt. % of polymer. It has been found that the synthesized composite exhibits the sorption ability in terms of microquantities of Cu (II), Cd (II), Pb (II) and Fe (III) ions in a neutral aqueous medium. The maximum degree of sorption of ions Cu (II), Pb (II) and Fe (III) is achieved during the first minutes of contact, and for Cd (II) ions the equilibrium is established within a day. The sorption capacity of silica gel as a result of modification by this polymer increases with respect to Cu (II) ions more than 14 times, with respect to Pb (II) ions - 5 times.     

含偶氮苯基元对称双噁二唑衍生物的合成及其发光性能

合成了含偶氮苯基元的对称双噁二唑衍生物Fn,利用IR、1H NMR方法确认了其分子结构,用荧光光谱研究了偶氮苯基元对噁二唑衍生物光致发光特性的影响。 F3、F6、F10的发射峰皆为双峰,分别位于348、356 nm和345、357 nm及345、357 nm,属于噁二唑基团的特征发射峰。 偶氮苯基元的引入,对噁二唑衍生物Fn在溶液中的最大发射峰位影响较小,对发光强度影响较大,其发光强度大大降低。 这主要是由于在光激发过程中偶氮苯基团与噁二唑基团间发生了分子内电子能量转移。     

一类功能D-π-A共轭偶氮苯化合物的合成及表征

采用偶氮反应合成了一系列对位分别连有不同吸电子和供电子功能基团的D-π-A共轭偶氮苯化合物,其结构经元素分析,IR,NMR,DSC等表征。     

Synthesis and chiroptical properties of optically active polymer liquid crystals containing azobenzene chromophores

A series of optically active methacrylic homopolymers, poly[(4‐{4′‐[(S)‐2‐methyl‐1‐butyloxycarbonyl]phenylazo}phenoxyl)x‐methylene methacrylate] (x = 0, 2, 6, or 11), were synthesized. The structures of the polymers were characterized by IR, ¹H NMR, UV, differential scanning calorimetry, and gel permeation chromatography. The chiroptical properties of the polymers in films were investigated with circular dichroism (CD) measurements. The CD and UV spectra of the films suggested that CD absorptions occurred in the films of the polymers with long spacers (x = 6 or 11) but not in the films of the polymers with short spacers (x = 0 or 2). After irradiation with linearly polarized light at 442 nm, the CD values were amplified in all the polymeric films. The amplificatory values of the CD bands in the absorption region (260–360 nm) of azobenzene chromophores suggested that the spacer length had an effect on both the transfer of chirality and photoinduced chirality in the polymeric films. The largest level of photoinduced chirality was induced in the polymer containing six methylene units. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3210–3219, 2006     

Atomic force microscopy study of self-organization of chiral azobenzene derived from amino acid

A kind of chiral azobenzene amphiphile, N-[4-(4-dodecyloxyphenylazo)benzoyl]- -glutamic acid (C₁₂-Azo- -Glu; as shown in Fig. 1), was synthesized and the self-organization properties on solid substrates were investigated. C₁₂-Azo- -Glu underwent a reversible trans–cis photoisomerization in dilute solution. While the photoisomerization was suppressed on solid substrate because of the H-aggregation, indicating the formation of compact film. When C₁₂-Azo- -Glu was cast from ethanol solution onto the hydrophilic surface of mica, a stable flat-layered structure formed spontaneously in large scale. High-resolution images allowed the identification of the relative orientation of molecular rows in the ordered thin film and the crystal lattice of mica. A molecular packing model of the layered structure was proposed. There was a template effect of mica to the self-organization process. Hydrogen bonding, π–π interaction and the chiral center in the molecule played the important roles in the self-organization process. The cooperative competitive effect between them led to the highly ordered structure.