Langmuir-Blodgett films of cyclopalladated ferrocenylimine: preparation, characterization, and application in Suzuki coupling reaction

Langmuir monolayer and Langmuir-Blodgett (LB) films of cyclopalladated ferrocenylimine 1 were prepared and characterized. The surface pressure (π)-area (A) isotherm of complex 1 indicated the formation of highly condensed monolayer on the subphase. Ultraviolet-visible (UV-vis) and Fourier transform infrared (FTIR) spectroscopy showed that complex 1 monolayer was transferred successfully onto solid supports. Atomic force microscopy (AFM) image suggested that LB films transferred on the solid substrate were well-ordered, homogeneous. Cyclic voltammograms of LB films deposited on glassy carbon electrodes showed quasi-reversible oxidation/reduction waves of ferrocene moiety. From the average thickness of monolayer, the hydrocarbon chain could be fairly directed perpendicular to the substrates. Finally, LB films of complex 1 presented a largely improved catalytic efficiency for Suzuki reaction with respect to its cast films and homogeneous reactions under the same conditions. The results might have an implication on the catalytic mechanism of this reaction.     

A novel amphiphilic push-pull ferrocene derivative: Langmuir–Blodgett films and second-order optical nonlinearity

The Langmuir–Blodgett (LB) films built from the mixture of an amphiphilic push–pull ferrocene derivative (P) and behenic acid were investigated. Langmuir films of P diluted by behenic acid exhibit a very good cohesion and the mixed films can easily be transferred onto solid substrates. Linear dichroism UV-visible and IR spectroscopy measurements of the mixed LB multilayers confirm that the molecules (P) are oriented to the substrate. The nonlinear optical experiments on the mixed monolayer deposited on the CaF₂ slide showed that P displayed efficient optical second harmonic generation (SHG) with a molecular hyperpolarizability (β) as high as 6.0×10^-29 e.s.u.     

Spectroscopic studies on molecular recognition capabilities of a nucleolipid bearing thymine headgroup to adenosine

The Langmuir-Blodgett (LB) films of octadecanoyl ester of 1-(2-carboxyethyl) thymine deposited from pure water and aqueous adenosine subphases were investigated by ultraviolet-visible (UV-vis), Fourier transform infrared-attenuated total reflection (FTIR-ATR), and Fourier transform surface-enhanced Raman scattering (FT-SERS) spectroscopy. The obtained spectral results indicate that the adenosine molecules in the subphase can be transferred onto solid substrates by LB techniques as a result of the formation of base pairs at the air/water interface. UV-vis spectra alternations indicated that, with increasing adenosine concentration in subphase, more adenosine molecules were recognized by nucleolipid monolayer and were transferred onto the quartz substrates. The closed-packing of the constituent molecules facilitates the photodimerization of the thymine moieties in the headgroup under ultraviolet irradiation. FTIR-ATR results suggest that the hydrocarbon chains of nucleolipid in the LB films deposited from pure water and aqueous adenosine take on a close-packed all trans conformation. By analyzing the FT-SERS spectra results, it can be deduced that the orientation of nucleobase in the headgroup is different before and after the recognition effect occurred. For LB film deposited from pure water, the nucleobases are lying flat on the silver substrates; whereas for LB film deposited from aqueous adenosine, the base pairs take an end-on adsorption on silver substrate.     

稀土三酞菁夹心化合物混合LB膜的研究

将不对称三明治型夹心化合物(Pc)Dy[Pc(OC₈H₁₇)₈]Dy[Pc(OC₈H₁₇)₈]与硬脂酸混合成膜，表面压-面积（π-A）曲线表明形成了稳定的单层膜，由透射电子显微镜（TEM）观察,表明硬脂酸的加入有效地改善了分子的聚集行为，分子形成了取向高度有序的结构。用紫外-可见光谱、偏振紫外可见光谱、低角X射线衍射等对LB膜进行了研究，发现该取代稀土三酞菁分子在气/液界面上长链向上伸展，分子之间均以面对面（face-to-face）排列，以一边接触（edge-on）方式取向,大环平面与基片夹角约为52°，每层厚度为2.41 nm。     

Manipulation of Multicomponent Langmuir-Blodgett Films of Electrically Conductive Polymers: Polypyrrole and Poly(3-Hexylthiophene)

Abstract

Multicomponent Langmuir-Blodgett (LB) films containing poly-pyrrole, 3-octadecanoyl pyrrole, and poly(3-hexylthiophene) were fabricated via a novel in-situ polymerization process. In this process, pyrrole monomer is polymerized at the air-subphase interface in the presence of poly(3-hexylthiophene) by using a subphase containing 1 wt% FeCl₃. The resultant electrically conductive films could be readily deposited onto solid substrates as Z-type films by the vertical lifting method. By using visible absorption, x-ray diffraction, and FTIR measurements, it was found that all three components were present within the transferred films, with the polypyrrole chains assuming a preferential orientation parallel to the film surface. The conductivities of the mixed LB films were as high as 1.0 S/cm, and the stability of the conductivity was very good. Chemical doping of poly(3-hexylthiophene) within the film with strong oxidizing agents such as I₂ further enhanced the conductivity of the film.     

Preparation and characterization of 5,10,15,20‐tetraphenylporphyrin Langmuir films for gas chemsensor applications

In this work is reported the preparation and characterization of 5,10,15,20‐tetraphenylporphyrin (H₂TPP) films at the water‐air interfaces. The surface pressure‐area isotherms (π‐A) and UV‐Vis spectroscopy were used to investigate the effect of the spreading methods and parameters on the porphyrin monolayer formation. Also, Langmuir‐Blodgett (LB) and Langmuir‐Schaefer (LS) films were deposited onto glass substrates in order to study the conformation changes in porphyrin molecular packing. Quartz crystal microbalance (QCM) was utilized as the active solid substrate for the development of the NO₂ gas sensor based on the H₂TPP molecular films. The results of π‐A curves have clearly shown the significant contribution of the preparation methods and processing parameters on the conformation of porphyrin molecular films. The UV‐Vis spectroscopy results using polarized absorption dichroism have indicated different molecular packing for porphyrin films deposited by LB and LS methods, with relative tilted angles of 50° ± 5° and 35° ± 5°, respectively. Moreover, the QCM response has given strong evidence that H₂TPP porphyrin molecular films have performed as NO₂ chemsensor. Copyright © 2011 John Wiley & Sons, Ltd.     

Studies on Mixed Monolayers and Langmuir–Blodgett Films of Schiff-Base Complex Cu(SBC18)2 and Calix[4]arene

Mixed monolayers of Schiff-base complex Cu(SBC₁₈)₂ with an octadecyl hydrocarbon chain and Calix[4]arene without a long alkyl chain at an air/water interface were studied in ultrapure water at different temperatures. Interface behavior and thermodynamic estimation of the mixed monolayer indicate that a strong intermolecular interaction exists between the mixed components (Cu(SBC₁₈)₂ and calix[4]arene) and the two-dimensional miscibility decreases with the molar fraction of Cu(SBC₁₈)₂. It is noticeable that the calix[4]arene monolayer can be transferred successfully onto solid substrates due to the introduction of Cu(SBC₁₈)₂. FTIR transmission and UV-Vis absorption spectra of mixed LB films provide further evidence of molecular interaction between the headgroups.     

Preparation and Characterization of 6-<Emphasis Type="Italic">O</Emphasis>-(4-stearyloxytrityl)Cellulose acetate Langmuir–Blodgett Films

Multilayer films of 2,3-di-O-acetyl-6-O-(4-stearyloxytrityl)cellulose (ASTC) were prepared and investigated. The fairly high surface pressure (π)–area (A) isotherms (36– 47 mN/m) suggest that the balky and hydrophobic trityl group contribute to form a condensed monolayer. The cellulose derivative formed a homogeneous monolayer at 10 mN/m. The monolayer on the water surface was transferred successfully at 10 mN/m onto various substrates by modifying the preparation methods, to form Z-type multilayer films. The ultraviolet–visible (UV–Vis) absorbance was independent of the number of layers, indicating that each layer is made of definite number of anhydroglucose unit (AGU). The monolayer thickness determined from atomic force microscope (AFM) and ellipsometry was calculated to be about 1.9 nm, suggesting that the long alkyl chain in the film has a so-called hairy-rod type structure. This is the first paper about the Z-type LB film prepared from cellulose derivatives having long mono-alkyl chain only at 6-O-position.     

An infrared study on Langmuir–Blodgett films of octadecylammonium octadecanoate: FWHM and the vibrational coupling

The monolayer of the mixture of octadecanoic acid and octadecylamine with molar ratio 1:1 has been investigated at the air–water interface. It was found that the monolayer shows a rather stable state at the surface pressure of 30 mN/m and this monolayer can be transferred onto a CaF₂ plate by Langmuir–Blodgett (LB) technique. The infrared spectra of LB films indicated that octadecylammonium octadecanoate is formed by an intermolecular proton exchange between adjacent carboxylic and aminic groups (COO⁻ and NH₃⁺). In three-layer LB film, the CH₂ scissoring mode of the long hydrocarbon chains of octadecylammonium octadecanoate shows a broad band feature at about 1468 cm⁻¹ while this vibrational mode of three-layer LB film of the mixture (1:1) of deuterated stearic acid and octadecylamine (octadecylammonium octadecanoate-d35, C₁₈H₃₇NH₃⁺C₁₇D₃₅COO⁻) only shows a narrow band. The broad feature of the CH₂ scissoring mode in octadecylammonium octadecanoate probably originates from the coupling between the chain of stearic acid and that of octadecylamine while this kind of coupling could be completely removed in octadecylammonium octadecanoate-d35. Another conclusion presented in this paper is that there are no couplings among the chains of fatty acid or among the chains of octadecylamine in LB films of octadecylammonium octadecanoate.     

A Novel Amphiphilic Push-pull Ferrocene Derivative: Langmuir-Blodgett Films and Second-order Optical Nonlinearity

We investigated Langmuir-Blodgett(LB) films built from the mixture of an amphiphilic push-pull ferrocene derivative(P) and behenic acid. Langmuir films of P diluted by behenic acid exhibit a very good cohesion, and the mixed films can easily be transferred onto solid substrates. Linear dichroism UV-visible and IR spectroscopy measurements of the mixed LB multilayers confirm that the molecules(P) are oriented to the substrate. The nonlinear optical experiments on the mixed monolayer deposited on the CaF₂ slide showed that P displays efficient optical second harmonic generation(SHG) with a molecular hyperpolarizability (β)h, high as 6.0×10^-29e. s. u..     

Resorcinol calixarenes (resorcarenes): Langmuir-Blodgett films and optical properties

Specially synthesized amphiphilic resorcinol calixarene (resorcarene 2) molecules have been deposited as Langmuir-Blodgett (LB) films on a variety of substrates including hydrophobically treated glass slides, silicon and gold-coated glass slides. A value of 1.9 nm² is obtained for the area per molecule from measurements of pressure/area isotherms of the floating layer. Optical absorption studies within the ultraviolet-visible frequency region have been performed on these molecules in both LB films and in solution of resorcarene 2 in chloroform, containing 10% ethanol. Molecular aggregation in the form of dimerization is believed to take place during film formation. Further analysis has been carried out for Langmuir-Blodgett films of resorcarene 2 by using Fourier transform infra-red spectroscopy, low-angle X-ray diffraction and surface plasmon resonance (SPR) techniques. The monolayer thickness of 1.6 nm found from SPR measurements is consistent with that from other experimental observations.     

Interfacial properties of a novel pyrimidine derivative and poly(ethylene glycol)-grafted phospholipid floating monolayers

4-amino-2-phenyl, 6(p-fluor-phenyl)-5-carbonitrile-pyrimidine (APCP) is a new derivative of pyrimidine with low solubility in water and anti-inflammatory properties. We compared the interfacial behaviors of spread films of poly(ethylene glycol)-grafted phospholipid (DSPE-PEG₂₀₀₀), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and APCP and a mixture of these molecules. The surface pressure–area (Π–A) isotherm showed that APCP and DSPE-PEG₂₀₀₀ molecules were stable at the air/water interface and could be evenly inserted into a DPPC floating monolayer. The introduction of APCP into the DPPC/(DSPE-PEG₂₀₀₀) binary monolayer generally causes an overall increase in surface potential. Analyses of distance variation between the grafted sites are associated with a change of mushroom to brush conformation and this behavior is observed for the DPPC/(DSPE-PEG₂₀₀₀) and DPPC/(DSPE-PEG₂₀₀₀)/APCP monolayers. Langmuir–Blodgett (LB) films of molecules of biological interest were transferred onto mica in order to investigate their interaction. AFM images do not show any regular shape or size and are randomly distributed.     

Electrochemical and coupled XPS studies on Langmuir–Blodgett mixed films of behenic acid and over-grafted platinum nanoparticles: Effect of the behenic acid removal

We report on the behavior of Pt nanoparticles functionalized with 4-mercaptoaniline over-grafted with 2-thiophenecarbonyl chloride. Stable Langmuir–Blodgett (LB) mixed films were built up from these particles with behenic acid (BHA). Such ultra-thin films were transferred onto gold substrates, which allowed the study of their electrochemical response towards Fe[(CN)₆]³⁻ and their XPS chemical analysis before and after the BHA removal. After washing, XPS analysis showed that the signals corresponding to the metal core and the capping agent were almost unchanged. Moreover, the layers became more compact, as shown by the Pt/Au intensity ratio decrease, because of the apparent decrease of length escape of electrons coming from gold, evidencing the removal of the fatty acid in the LB film structure. After BHA removal, the resulting electrochemical activity slightly increased. This result, in agreement with XPS analysis, showed the structural rearrangement within the film that facilitated the percolation between the particle domains.     

Organic vapor sensing properties and characterization of α-naphthylmethacrylate LB thin films

Determination of organic vapor sensing properties of α-Naphthylmethacrylate (α-NMA) monomer based Langmuir-Blodgett (LB) thin films was aimed in this study. LB thin film fabrication was performed on quartz glass and quartz crystal substrates in order to investigate the characterization and organic vapor properties of α-NMA materials by using UV-Visible, Atomic Force Microscopy (AFM) and Quartz Crystal Microbalance (QCM) techniques. π-A isotherm graph was taken and a suitable surface pressure value were primarily determined as 13?mN m^?1 for successful α-NMA LB thin film fabrication. Transfer ratio value was found to be ≥ 0.93 for quartz glass and quartz crystal substrates. The typical frequency shift per layer was obtained as 16.93?Hz/layer and the deposited mass onto a quartz crystal was calculated as 271.30?ng/layer (1.02?ng mm^?2). The sensing responses of α-NMA LB films against dichloromethane, chloroform, toluene and m-xylene were measured by QCM system. Dichloromethane created the maximum shift in the resonance frequency than other organic vapors used in this study. Results exhibited that α-NMA LB thin films were potential candidates for organic vapor sensing applications, especially high sensitive detection of dichloromethane at room temperature.     

Biomimetic synthesis of the arachidic acid/Ag<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>S nanocomposite films

Ag _x Cd _y S nanoparticles were obtained in arachidic acid (AA) monolayer containing Ag⁺ and Cd²⁺ under H₂S flow. The AA/Ag _x Cd _y S monolayers were deposited onto solid substrate to prepare LB films. The UV-vis spectrum showed that the LB film exhibited notable quantum-size effect. The small-angle X-ray diffraction revealed periodic structure of the LB films. The molar ratio of Ag to Cd in AA/Ag _x Cd _y S film was ca. 1 : 5 as measured by the XPS. TEM and FTIR spectroscopy showed that the head-groups of arachidic acid molecules controlled formation of Ag _x Cd _y S nanoparticles in the monolayer.     

Surface-enhanced spectroscopy of Langmuir—Blodgett films of N-octyl,N′-isobutyl-3,4:9,10-perylene-bis(dicarboximide)

The infrared, resonant Raman and surface-enhanced resonant Raman spectra of N-octyl, N′-isobutyl-3,4:9,10-perylene-bis(dicarboximide) (PBDC) were obtained and the aggregation of PBDC molecules was studied using surface-enhanced fluorescence. Langmuir—Blodgett (LB) films of the neat dye as well as mixed layers with arachidic acid, were prepared and transferred to glass slides and surface-enhanced active surfaces for spectroscopic characterization. A strong red shifted excimer emission was characteristic of LB layers of the neat material and of the thin solid films formed by dipping a glass slide into a solution containing the dye and a volatile solvent. However, using mixed LB monolayers of PBDC and arachidic acid, the surface-enhanced fluorescence of the monomer was observed. The surface-enhanced scattering was measured for both neat and mixed LB layers.     

Conducting LB films based on metal complexes of sulphur donor ligands

Preliminary studies are reported on the film forming characteristics of compounds such as dialkyldimethylammonium-M (dmit)₂ and dialkyldimethylammonium-M (mnt)₂ where M = Ni, Pt or Pd. All materials investigated show good monolayer behaviour and deposit readily onto evaporated aluminium or gold films. This is confirmed by surface potential and FTIR measurements. The lateral conductivity of deposited films increases by many orders of magnitude when exposed to bromine vapour.     

Ultrathin films of functionalised single-walled carbon nanotubes: a potential bio-sensing platform

ABSTRACT

The Langmuir monolayer is a special class of lyotropic liquid crystalline system wherein phase transition essentially depends on surface density, temperature and ion-content in the aqueous medium. The variety of surface phases can be transferred onto devices by the Langmuir–Blodgett (LB) technique. The Langmuir monolayer of pristine single-walled carbon nanotubes (SWCNTs) exhibited gas and liquid-like phases. The LB film of SWCNTs shows target surface pressure dependent interesting morphologies. The methane gas sensing using parallel alignment of SWCNTs was found to be better than that of randomly oriented SWCNTs. The SWCNTs can be functionalised chemically to enhance the ease of film processability and affinity towards analytes. These are essential parameters for the development of a sensor. In this article, we present our work on Langmuir monolayer and LB films of octadecylamine functionalised SWCNTs (ODACNTs) and its sensing application towards bio-analytes, e.g. L-aspartic acid and bovine serum albumin. The sensing performance of LB film of ODACNTs was compared with that of spin-coated films of ODACNTs. The sensing performance of LB films of ODACNTs indicated a potential platform for bio-sensing application.     

Electrodeposition of PbO2 onto Au and Ti substrates

The electrodeposition of lead dioxide (PbO₂) onto Au and Ti substrates was anodically executed at 65°C and the electrochemical characteristics and the mechanism in the PbO₂ films deposition were investigated by the using an in-situ electrochemical quartz crystal microbalance, cyclic voltammogram, and chronoamperometry experiments. An X-ray diffractometer and scanning electron microscope were also used for investigation of the formed lead dioxide films onto both substrates. Considering the experimental and theoretical mass/charge ratios, PbO₂ deposition on Au by applying constant potential was in excellent agreement with the theoretical value, while relatively higher values of the mass/charge ratio due to film hydration were found when Ti was used as substrate. Analysis of X-ray diffractometer and scanning electron microscope show different film structures on each substrate, especially the additional hydration of the lead dioxide film deposited on Ti leads to some structural effects, identified as Sky-Lotus PbO₂.     

Patterned langmuir-blodgett films of monodisperse nanoparticles of iron oxide using soft lithography

Langmuir-Blodgett (LB) films of monodisperse iron oxide nanoparticles have been successfully deposited onto patterned poly(dimethylsiloxane) surfaces. These patterned LB films of iron oxide nanoparticles were transferred onto solid substrates using micro contact printing.