Formation of highly ordered thin films of perfluorinated carboxylic acids and azobenzenes by thermal evaporation

Stearic acid, two short chain perfluorinated carboxylic acids, C₉F₁₉COOH and C₁₁F₂₃COOH, and two amphiphilic azobenzene derivatives were thermally evaporated onto a variety of substrates in vacuo. The resulting films (0.1–1.0 ωm thick) were studied by low angle X-ray diffraction and polarizing microscopy. Substrate temperature was a critical factor in determining film quality. For the azobenzenes, the structures obtained gave up to eight Bragg reflections and appeared to be identical to structures obtained by the much slower Langmuir-Blodgett (LB) technique. For the fluorocarbons up to 14 Bragg reflections were observed, corresponding to bilayer spacings of 2.79 nm (C₉) and 3.19 nm (C₁₁), indicating highly ordered structures which could not be achieved at all by the LB technique. The relative peak intensities before and after incorporating Ag⁺ ions into the structures confirm the bilayer-type structure. It is suggested that the thermal evaporation method has considerable potential for producing ordered films of non-polymeric organic materials where the LB technique is either too slow or unusable.     

Photochromism induced magnetization changes in Prussian Blue ultrathin films fabricated into the Langmuir-Blodgett films composed of an amphiphilic azobenzene and a deoxyribonucleic acid

A photomagnetic ultrathin film consisting of an azobenzene, a deoxyribonucleic acid, and Prussian Blue has been fabricated by the Langmuir-Blodgett method. Prussian Blue layers in the films were a two-dimensional structure with the height of 50 Å and the average coherence length of 210 Å. Reversible photoisomerization of the azobenzenes was observed even in the films. The films exhibit the long-range ferromagnetic order below 4.2 K and moreover, upon photoillumination at 2 K, reversible changes in the magnetization were realized with the value of ca. 1.0%. This photoswitching in the magnetization is due to changes in the electrostatic field induced by photoisomerization.     

Highly conducting Langmuir-Blodgett films of the TMTTF-CnTCNQ system

Highly conducting Langmuir-Blodgett (LB) films of the tetramethyltetrathia-fulvalene- alkyltetracyanoquinodimethane (TMTTF-C_n TCNQ, where C_n represents C_nH_2n+1) system are reported. The electron affinities of the acceptors C_nTCNQ (n=14, 18 or 22) in solution are almost the same and lie between those of TCNQ and dimethylTCNQ. These TCNQ derivatives form solid charge transfer complexes with TMTTF. The limiting areas of the complexes, normalized to the number of TCNQ derivatives at the air-water interface, are almost the same irrespective of the donor-to-acceptor ratio and of the length of the alkyl chain, indicating that the areas are governed by the TCNQ moiety. The monolayers of TMTTF-C_n TCNQ (n=14 or 18) are transferred onto solid substrates as LB films. Polarized UV-visible absorption spectra indicate that the long axis of TCNQ is parallel to the film surface. These LB films exhibit lateral conductivities as high as 0.4 S cm^-1 and 0.1 S cm^-1 when n=14 and n=18 respectively.     

Photovoltaic properties of purple membrane Langmuir-Blodgett films

Langmuir films of pure purple membranes with no added lipids were deposited on solid substrates by the horizontal transfer method. The photovoltaic properties of purple membrane Langmuir-Blodgett (LB) films were studied in correlation with the photochemical cycle of bacteriorhodopsin. The morphology of the air-water interface film transferred onto a chip of silicon wafer is briefly described as a characterization for purple membrane LB films.     

Synthesis and optical properties of photochromic perinaphthothioindigo

(1,2-naphtho)(1,8-naphtho)thioindigo (PNT) has been synthesized following a simple Friedel–Crafts route and its photochemical properties in toluene and polymethylmethacrylate (PMMA) have been characterized. PNT is a photochromic molecule capable of reversible photoisomerization between a yellow form (cis-PNT, λ_max = 484 nm) and a purple form (trans-PNT, λ_max = 595 nm). The stable purple form converts to the yellow form with a trans-PNT to cis-PNT conversion quantum yield of 0.027 in toluene and 0.062 in PMMA. The unstable yellow form exhibits a cis-PNT to trans-PNT quantum efficiency of conversion of 0.27–0.85 in toluene and 0.17–0.68 PMMA, with highest conversion efficiency occurring in the vicinity of its λ_max of 484 nm. trans-PNT has a strong fluorescence quantum yield, 0.14 (toluene) and 0.16 (PMMA). For samples prepared photochemically in the cis-PNT form, slow thermal relaxation to the trans form occurs in the dark, with a half life of about 17 h in toluene (25 °C) and even slower, 168 h, in PMMA. The property of photoswitching between fluorescent and non-fluorescent forms makes this material a candidate for many applications in imaging and data storage.     

Optical storage in azobenzene-containing epoxy polymers processed as Langmuir Blodgett films

In this study, azocopolymers containing different main-chain segments have been synthesized with diglycidyl ether of bisphenol A (DGEBA, DER 332, n = 0.03) and the azochromophore Disperse Orange 3 (DO3) cured with two monoamines, viz. benzylamine (BA) and m-toluidine (MT). The photoinduced birefringence was investigated in films produced with these azopolymers using the spin coating (SC) and Langmuir Blodgett (LB) techniques. In the LB films, birefringence increased with the content of azochromophore and the film thickness, as expected. The nanostructured nature of the LB films led to an enhanced birefringence and faster dynamics in the writing process, compared to the SC films. In summary, the combination of azocopolymers and the LB method may allow materials with tuned properties for various optical applications, including in biological systems were photoisomerization may be used to trigger actions such as drug delivery.     

Hybrid Langmuir and Langmuir–Blodgett films composed of amphiphilic cyclodextrins and hydrophobic azobenzene derivative

Hybrid Langmuir and Langmuir–Blodgett (LB) films consisting of amphiphilic cyclodextrins (CDs) and hydrophobic azobenzene were fabricated. Due to the larger cross-sectional area of the CD core compared with the sum of the cross-sectional areas of the attached alkyl chains, the films had free space in the hydrophobic regions. Azo(p-Hexyl) having hydrophobic terminal chains was accommodated in the free space, whereas the usage of an azobenzene derivative bearing hydrophilic groups led to the phase separation. The average tilt angle of Azo(p-Hexyl) gave minima when the free space was just filled with Azo(p-Hexyl). Photoisomerization of azobenzenes in the hybrid LB films was studied.     

C60/PVK/CdS纳米粒子功能复合 LB 膜研究

目的 尝试用Ｌａｎｇｍｕｉｒ－Ｂｌｏｄｇｅｔｔ（ＬＢ）技术组装Ｃ６０技术组装Ｃ６０功能复合体系的新方法。方法 采用（ＬＢ）技术制备Ｃ６０／ＰＶＫ／ＣｄＳ花生酸混合ＬＢ膜并利用界面化学反应技术将混合膜与硫化氢气体反应制得Ｃ６０／ＰＶＫ／ＣｄＳ纳米粒子功能复合ＬＢ膜并进行紫外光谱表征。结果 含不同比例Ｃ６０的Ｃ６０ＰＶＫ／ＡＡ体系可以在辐亚相上形成稳定的单层膜并转移到固体基片上得到了ＬＢ多层膜,ＬＢ混     

Photoisomerization of amphiphilic azobenzene derivatives in Langmuir Blodgett films prepared as polyion complexes, using ionic polymers

Polyion complexation in mixed Langmuir and Langmuir Blodgett (LB) films of photochromic amphiphilic azobenzene carboxylic acids, 11-[4-(4-hexylphenyl)azo] phenoxyundecanoic acid, 11-(4-phenylazo)phenoxyundecanoic acid, and diamine grafted poly(methylmethaacrylate) polymers has been studied. Monolayer behaviour of the pure components and mixed films was studied through pressure–area isotherms and LB films were characterized by spectroscopic, X-ray diffraction and Atomic force microscopy techniques. Aggregation (H-type), often observed in LB films of pure amphiphilic azo acids, was partly avoided in the mixed LB films as indicated by absorption spectral studies. Photoisomerization of the polyion complexed LB films was also studied. The results altogether demonstrate that amine grafted polymer enter into a polyion complexation with azo acid carboxylate group. LB films could be obtained by transfer of the composite monolayers and these LB films exhibited different levels of aggregation of the azo acids. Reversible photoisomerization was observed in LB films with unaggregated azo acid.     

基于超分子结构的光电子材料的制备与表征(英文)

为实现短波长光存储材料,提出一种基于金属纳米粒子与染料共掺杂的复合材料制备新方法.采用透射电子显微镜(TEM)、紫外-可见吸收光谱(UV-Vis)以及傅立叶变换红外光谱(FT-IR)对所制备的复合薄膜进行表征.实验发现,与未掺杂银的薄膜相比,掺杂银的复合薄膜中甲基橙的吸收蓝移了6nm.提出并利用超分子结构模型分析了该吸收蓝移的机理.研究结果显示,本研究所提出的这种新的材料制备方法具有制备吸收波长在400～500nm,且可望与GaN激光器在光存储技术中匹配的能力.     

Langmuir-Blodgett films of ethylenedithiotetrathiafulvalene derivative containing hydroxyl groups

Langmuir-Blodgett (LB) films of an ethylenedithiotetrathiafulvalene (EDT-TTF) derivative containing hydroxyl groups, 4, 5-bis(11-hydroxyundecylthio)-4′, 5′-ethylenedithiotetrathiafulvalene were deposited without using stabilizer molecules. Doping of the film with iodine leads to oxidation of EDT-TTF moiety as evidenced by UV-vis and IR spectroscopy. X-ray diffraction studies reveal the presence of layered arrangement of the EDT-TTF derivative molecules in the LB film. Cyclic voltammetry studies indicate that the electrochemical oxidation of the EDT-TTF derivative in its LB film is irreversible. Due to the insulating nature of the alkyl chains, only the first layer of the LB film was found to be redox-active. The electrical conductivity of the 25 layer LB film was found to increase by two orders of magnitude on doping with iodine. On equilibrating the doped film in air, the conductivity gradually reduced with time and finally reached the conductivity of undoped film. This reversibility could be because of the steric hindrance induced by the two long alkyl groups. The alkyl chains help in rendering the EDT-TTF molecule amiable to LB film formation but are found to reduce the electrical conductivity of the films and also cause instability of the doped state. The hydroxyl groups at the end of the alky chain impart amphiphilic nature to the molecules and help in stabilizing the film at the air-water interface.     

Optical and electrical properties of merocyanine dye LB films by various time of UV irradiation and heat treatment

The Langmuir-Blodgett (LB) technique provides many possibilities for the control of film thickness, dimensions, and molecular structures on the nanometer scale. Various kinds of dye molecules have been found to form the J-aggregation which has been used as sensitizers of silver halide photography for long time. In recent years, they attract attention as model systems for investigating the ultra-fast exciton dynamics, materials for ultra-fast nonlinear optical devices, fluorescence probes for mitochondrial membranes. We fabricated the merocyanine dye LB films with arachidic acid (AA). In order to observe the J-aggregation of the merocyanine dye LB films, CdCl2 and KHCO3 solutions were added in subphase. From the optical absorption spectra of the mixed dye LB films (6Me-Ds:AA = 1:2) at different layers, the optical absorption peak was about 520 nm. However, the optical absorption peak of the LB films was shifted to 600 nm, when CdCl2 and KHCO3 solutions were added. This is the consequence result to the J-aggregation of the merocyanine dye. We also investigated the optical absorption peak of the LB films according to various time at 60 degrees C and 275 nm UV. We measured the STM morphology of the merocyanine dye LB film (1 layer) before UV irradiation and heat treatment. The morphology size of the LB film on HOPG was 5 nm. The roughness and molecular size were about 66.163 pm and 0.176 nm, respectively. The J-aggregation of this type was also accompanied by large morphological changes. We analyze the morphology and electrical properties of the LB films by the scanning tunneling microscopy (STM).     

Construction and electrochemistry of Langmuir-Blodgett films of fullerene lipid composite/hybrid materials

Studies of the electrochemistry of Langmuir-Blodgett (LB) films of C70/artificial lipids including tridodecylmethylammonium bromide (3C12N+Br-, 1), didodecylphosphate (2C12PO4H, 2), and dioleoylphosphatidylcholine (DOPC, 3) and of LB films of a fullerene lipid (4) bearing triple alkyl chains on a C60 moiety on electrodes were carried out in aqueous media. Stable Langmuir monolayers of fullerene C70/artificial lipid composites and the fullerene lipid (4) were formed at the air-water interface and these monolayers were transferred onto electrodes as LB films. Here, we focus on the importance of cationic matrix lipid films to the facile electrochemistry of C70 embedded in a LB film of cationic lipids on an electrode in aqueous media. On the basis of the electrolyte dependence and the charge dependence of the matrix lipids, a possible electron-transfer mechanism of the C70/artificial lipid LB film-modified electrodes is presented. Electrochemistry of a LB film of 4 was also obtained in an aqueous medium. We demonstrate that the introduction of the chemistry of lipid bilayer membranes to the LB films of fullerenes guides us toward the construction of fullerene/lipid bilayer devices.     

Electrical properties of a novel 1,3-bis-(p-iminobenzoic acid) indane Langmuir-Blodgett films containing ZnS nanoparticles

ZnS nanoparticles have been formed in a newly synthesized 1,3-bis-(p-iminobenzoic acid) indane (IBI) by exposing Zn2+ doped multilayered Langmuir-Blodgett (LB) film to H2S gas after the growth. The formation of ZnS nanoparticles in the LB film structure was verified by measuring UV-Visible absorption spectra. DC electrical measurements were carried out for thin films of IBI prepared in a metal/LB films/metal sandwich structure with and without ZnS nanoparticles. It was observed that ZnS nanoparticles in the LB films cause a blue-shift in the absorption spectra as well as a decrease in both capacitance and conductivity values. By analysing I-V curves and assuming a Schottky conduction mechanism the barrier height was found to be about 1.13 eV and 1.21 eV for IBI LB films without and with ZnS nanoparticles, respectively. It is thought that the presence of ZnS nanoparticles influences the barrier height at the metal-organic film interface and causes a change in electrical conduction properties of LB films.     

X-ray diffraction analysis of 10,12-pentacosadiynoic acid Langmuir-Blodgett films during polymerization

10,12-pentacosadiynoic acid (PCDA) LB films were deposited on two different subphases of CdCl₂ and TbCl₃ respectively and polymerized under UV-irradiation. It is found that the different subphase influenced the molecular packing, and in turn, influenced the polymerization behavior in the LB films. The molecular arrangement structures of unpolymerized and photopolymerized LB films were investigated by low angle X-ray diffraction. The periodic spacing of molecules in the LB films and the inclination angle of molecules on the substrate were calculated from the X-ray diffraction profiles. The unpolymerized PCDA LB film had one set of diffraction peaks, however, two sets of diffraction peaks were clearly observed in partly-polymerized PCDA LB films deposited on CdCl₂ subphase and reduced to one set of diffraction peaks corresponding to the polymerized LB films. On the other hand, the PCDA LB films deposited on TbCl₃ subphase had only one set of diffraction peaks throughout. This is interpreted to correspond to different mechanisms of chain propagation, i.e., heterogeneous chain propagation for the PCDA LB film deposited on CdCl₂ subphase and homogeneous polymerization for the LB film deposited on TbCl₃ subphase. A molecular arrangement model in LB film was employed to explain the phenomenon of the even-odd intensity oscillation qualitatively.     

C60—聚苯乙烯LB膜摩擦学性能的初步研究

介绍了Ｃ６０－聚苯乙烯（Ｃ６０－Ｐｓｔ）ＬＢ膜的部分研究结果：合成方法、ＬＢ膜制备、用原子力／摩擦力显微镜测试的Ｃ６０－聚苯乙烯ＬＢ膜的表面微观形貌及轻载荷下的摩擦力等微观摩擦学性能。     

An optical chemical sensor using a fluorophor- embedded Langmuir-Blodgett film

An optical sensor with a Langmuir-Blodgett (LB) film was developed for simultaneous recognition of amino acids in an aqueous solution. Anthroyloxy- stearate-containing stearate LB films and perylene-containing arachidate LB films were deposited on a quartz glass. The fluorescence of these LB films in an aqueous solution was quenched in response to amino acids. Amino acids were classified into five groups by the pattern of fluorescence quenching of anthroyloxy stearate and perylene LB films.     

Langmuir-Blodgett films of Cu(II)-tetrakis (3,3-dimethylbutoxycarbonyl) phthalocyanine: a spectrophotometric and TEM analysis of their structure and morphology

Langmuir-Blodgett (LB) films of copper(II)-tetrakis (3,3-dimethylbutoxycarbonyl) phthalocyanine [Cu(dmbc)Pc] have been prepared from toluene solutions; multilayers (up to 80 layers) were deposited onto hydrophobic quartz substrates. The refractive index n and extinction coefficient κ at normal incidence have been determined from both transmission and reflection measurements carried out in the 400–800 nm spectral range. The optical absorption spectrum as a function of the incident photon energy was also registered in order to determine the optical transition type in Cu(dmbc)Pc LB films by using a band model approach. Linearly polarised light absorbance measurements were performed at room temperature in the same spectral range. The average orientation of the phthalocyanine molecular rings in the LB film, with respect to the normal to the substrate and the dipping direction, has been evaluated. We have found that such orientation differs from that determined for LB films deposited from ethyl acetate solutions.

Structural and morphological analysis were also carried out by transmission electron microscopy techniques. Small ordered domains in a low range order matrix were observed by high resolution images. The structure of the material in the substrate plane has been determined by electron diffraction performed on single ordered domains.     

Preparation and colossal magnetoresistance in a trilayer La0.67Sr0.33MnO3/La0.75MnO3/La0.67Sr0.33MnO3 device by dc magnetron sputtering

Epitaxial trilayer films of La_0.67Sr_0.33MnO₃ (LSMO)/La_0.75MnO₃ (L0.75MO)/La_0.67Sr_0.33MnO₃ (LSMO) have been prepared on (0 0 1) oriented LaAlO₃ substrates by dc magnetron sputtering. The structure and MR are studied. All as-deposited trilayer films exhibit a semiconductor to metal transition at temperature ranging from 116 to 185 K. The MR is also shown to be dependent on the thickness of the middle oxide layer. A maximum MR value of 32% (ΔR/R₀) has been obtained at 132 K under 0.4 T magnetic field for a LSMO (300 nm)/L0.75MO (70 nm)/LSMO (300 nm) trilayer film. The MR of trilayer film prefers to that of both LSMO and L0.75MO single layer films.     

Controls of photochromic reactions in spiropyran Langmuir-Blodgett films

The possibility of controlling photochromic reactions has been investigated in Langmuir-Blodgett (LB) films. The formation of J aggregates of a spiropyran (SP1822) with two long chains has been found previously. We have studied another possibility using LB films of 1′-octadecyl-3′,3′-dimethyl-6-nitro-8-methoxy- spiro[2H-1-benzopyran-2,2′-indoline] (SP1801). SP1801 at the air-water interface gave a monolayer which showed the photomerocyanine form. The LB film of the compound returned to the spiropyran form in the dark. The LB film of the hetero structure with SP1801 and stearic acid, however, turned to J aggregates from the photomerocyanine form spontaneously in the dark. The absorption of the J aggregates was a sharp and intense band, and the half-decay period in the dark was 10⁴ times longer than that of conventional spiropyrans. SP1801, in addition to SP1822, is suggested as a candidate for a multifrequency optical memory system with several J-aggregated photochromic compounds having different sharp absorption bands.