Hybrid Langmuir-Blodgett Films Research Articles

Interaction of hectorite clay with a phospholipid monolayer at air-saline interface in presence of a fluorescent dye

The effect of hectorite clay on the monolayer of 1, 2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) at air-saline interface in presence of fluorescent dye acridine orange (AO) is studied. Surface pressure–area isotherm and compressibility studies reveal the phase behavior and rheological properties of DPPC monolayer. Formation of DPPC/clay complex and their aggregation during monolayer compression partially remove DPPC molecules form the interface. UV-vis absorption and fluorescence emission techniques confirm the aggregation of AO in DPPC/clay/AO hybrid Langmuir-Blodgett film. As phospholipids act as lung surfactants, this model study has implication of realizing the detrimental effects of clay on phospholipids during alveolar surface compression while breathing.

Improvement of signal-to-noise ratio in oxygen sensitive emission from hybrid Langmuir–Blodgett films of amphiphilic iridium complexes with the exfoliated nanosheets using a metal layer

Cyclometalated Ir(III) complexes are attracting extensive attention due to their high emission properties in the visible region. Oxygen sensitive photoluminescence (PL) emissions from single- and multi-layered Ir(III) Langmuir–Blodgett (LB) films are measured. The single-layered LB film on a non-aluminum coated glass substrate shows oxygen sensitive PL emission but its intensity is very weak. In contrast, the multi-layered LB film shows higher intensity but their oxygen sensitivity is lower than that of the single-layered sample. To break the trade-off between intensity and sensitivity, PL characteristics from the LB film on an aluminum-coated glass substrate are investigated. The PL emission from the LB film on the metal layer show higher intensity and good oxygen sensitivity. The mechanism of the emission enhancement is also discussed in this paper.

Modified aggregation pattern of cresyl violet acetate adsorbed on nano clay mineral layers in Langmuir Blodgett film

Present work investigated the modified aggregation behavior of a cationic oxazine dye, Cresyl violet acetate (CVA) in presence of Laponite nano clay mineral layers in aqueous clay mineral dispersion as well as in ultra thin organo-clay hybrid Langmuir Blodgett (LB) films. The presence of non-fluorescent H-dimeric sites in aqueous solution of CVA even at very low concentration diminishes its fluorescence intensity and CVA ceases to emit any fluorescence in solid state and in the ultrathin films due to the abundance of H-dimeric sites. Incorporation of clay in aqueous solution drastically modified the absorption spectrum of CVA. Organo-clay hybrid film of CVA, fabricated at higher clay concentration, showed intense J-aggregated band due to the formation of J-aggregated species. UV–vis absorption and fluorescence spectroscopy as well as in-situ Brewster angle microscopic (BAM) studies were employed in this investigation.

Effect of clay in controlling the non-fluorescence H-dimeric states of a cationic dye Nile Blue Chloride (NBC) in hybrid Langmuir–Blodgett (LB) film

Present communication reports the effect of amphiphilic matrices and nano-clay platelets on the aggregation properties of a water soluble cationic fluorescent dye Nile Blue Chloride (NBC) in Langmuir-Blodgett (LB) films. In-situ Brewster Angle Microscopic (BAM) studies showed distinct domain structures of complex and hybrid Langmuir monolayer at the air-water interface. UV–vis absorption spectra showed non-fluorescent H-dimeric band in concentrated aqueous solution of NBC and in complex LB film of NBC with stearic acid. By changing various parameters, a great control over H-dimeric states has been achieved in clay incorporated hybrid LB films. These films can act as efficient fluorescence probe.

Oxygen Sensing by the Hybrid Langmuir-Blodgett Films of Iridium(III) Complexes and Synthetic Saponite on the Basis of Energy Transfer

An ultra-thin hybrid film of amphiphilic iridium(III) complexes and synthetic saponite was manipulated by means of the modified Langmuir-Blodgett method. In the film deposited onto a quartz substrate, the external mixed molecular layer of amphiphilic iridium(III) complexes was reinforced by the inner layer of exfoliated synthetic saponite. As components of the molecular layer, two iridium(III) complexes were used: [Ir(dfppy)2(dc9bpy)]+ (dfppyH = 2-(4′,6′-difluorophenyl) pyridine; dc9bpy = 4,4′-dinonyl-2,2′-bipyridine) (denoted as DFPPY) and [Ir(piq)2(dc9bpy)]+ (piqH = 1-phenyisoquinoline)) denoted as PIQ). The emission spectra from the films changed from blue to red maxima with the decrease of a ratio of DFPPY/PIQ due to the energy transfer from excited DFPPY to PIQ. The intensity of red decreased with the increase of oxygen pressure through the quenching of excited iridium(III) complexes, promising a possibility as an oxygen-sensing film.

Clay induced changes in the aggregation pattern of Safranine-O in hybrid Langmuir-Blogdgett (LB) films

Abstract In the present communication, detailed investigation has been carried out to study the clay mineral induced changes in aggregation of a well known cationic fluorescent dye Safranine-O (SO) in aqueous solution as well as in organo-clay hybrid Langmuir-Blodgett (LB) films. At higher dye concentration in aqueous solution, Safranine-O (SO) formed both H-dimers and J-aggregates and the corresponding UV–vis absorption spectra got distorted with increasing solution concentration. In clay mineral Laponite dispersed aqueous solution SO formed J-aggregates with increasing Laponite concentration resulting in an increase in fluorescence intensity. H-dimeric sites were also sufficiently decreased in organo-clay hybrid LB films of SO. UV–vis absorption and fluorescence spectroscopic as well as in-situ Brewster Angle Microscopic (BAM) studies were employed in our investigation.

Matrix dependent changes in metachromasy of crystal violet in Langmuir-Blodgett films

This communication reports the effect of building matrices and nano clay platelets on the aggregation pattern of a water soluble cationic fluorescent dye Crystal Violet (CV) in Langmuir-Blodgett (LB) Films. When stearic acid (SA) was used as a building matrix, pressure induced changes in metachromasy was observed in the SA-CV complex LB films with a characteristic J-band formed at the longer wavelength side. On the other hand, clay incorporated hybrid LB films showed high degree of control over H-dimeric band. Isotherm characteristics, Brewster Angle Microscopic (BAM) images, UV–vis absorption and fluorescence characteristic studies were employed to investigate this result.

Interfacial self-assembly, characterization, electrochemical, and photo-catalytic properties of porphyrin-ruthenium complex/polyoxomelate triad hybrid multilayers

Triad hybrid multilayers composed of tetrapyridylporphyrin (TPyP), bis(2,2′-bipyridyl)ruthenium chloride [Ru(bpy)2Cl2], and phosphomolybdic acid (PMA) have been prepared at the gas-liquid interface. The tetraruthenated porphyrin of TPyP-Rubpy complex was synthesized by the coordination interaction of TPyP with Ru(bpy)2Cl2. Surface pressure–area isotherms indicated that the average molecular area of the TPyP-Rubpy complex was in the range of 3.1–3.3nm2 when the PMA concentration was 0.1–0.3mg/mL in the subphases. Monolayers of the TPyP-Rubpy/PMA triad hybrids were transferred onto the substrate surfaces by using the Langmuir-Blodgett (LB) method. The absorption spectra of the hybrid LB films revealed several strong peaks between 300 and 440nm, attributed to the π–π* electron transfer of the Rubpy substituent and the Soret band of TPyP. Under radiation, the TPyP-Rubpy complex gave off strong luminescence in the wavelength between 600 and 700nm, attributed to the emissions from the Rubpy and TPyP substituents. These emissions largely weakened in the LB films of TPyP-Rubpy/PMA triad hybrids. Cyclic voltammograms showed six couples of redox waves in the potential range from −1.2 to 0.6V (vs Hg/HgCl2), which could be designated for the electron transfer processes of TPyP, Rubpy and PMA, respectively. Finally, it was revealed that the present triad hybrid LB films can be used as efficient light-harvesting units for the photo-catalytic oxidation of organic dyes and for light-induced photocurrent generation.

Energy transfer in hybrid Langmuir–Blodgett films of iridium complexes and synthetic saponite: dependence of transfer efficiency on the interlayer distance

Multi-layered hybrid films comprised of amphiphilic cationic iridium(III) complexes and the exfoliated layers of synthetic saponite were prepared by the modified Langmuir–Blodgett method. Two iridium(III) complexes, [Ir(dfppy)2(dc9bpy)]+ (dfppyH = 2-(4′,6′-difluorophenyl)pyridine; dc9bpy = 4,4′-dinonyl-2,2′-bipyridine) and [Ir(piq)2(dc9bpy)]+ (piqH = 1-phenyisoquinoline), were used as blue (donor) and red emitters (acceptor), respectively. A non-luminescent hybrid layer of stearylammonium and synthetic saponite was deposited in a layer-by-layer manner to vary the distance between the donor and acceptor layers. Energy transfer was analysed according to the Förster-type mechanism with a focus on the dependence of its efficiency on the interlayer distance.

The size control of nano-cluster formed on an inorganic nanosheet/cationic organic molecule hybrid Langmuir-Blodgett film.

Organic molecules adsorbed on an inorganic nanosheet often form a nanometer-sized cluster. In this study, we propose novel strategy for controlling the cluster size. We fabricated hybrid Langmuir-Blodgett (LB) films consisting of N-n-octadecyl-4-[2-(4-dimethylaminophenyl)ethenyl]-pyridinium bromide and a clay mineral, sodium montmorillonite, with varying subphase temperature. As a result, the size of the clusters was found to be decreased from 300 nm to 50 nm by increasing the subphase temperature from 10 degrees C to 40 degrees C.

Multi-emitting properties of hybrid Langmuir–Blodgett films of amphiphilic iridium complexes and the exfoliated nanosheets of saponite clay

Mono- and multi-layered films comprised of amphiphilic cationic iridium(III) complexes hybridized with the exfoliated nanosheets of synthetic saponite were prepared by the modified Langmuir–Blodgett method. Three iridium(III) complexes with different emission maxima (λmax) were used as incorporated complexes: [Ir(dfppy)2(dc9bpy)]+ (λmax = 500 nm) (dfppyH = 2-(4′,6′-difluorophenyl)pyridine; dc9bpy = 4,4′-dinonyl-2,2′-bipyridine) [Ir(ppy)2(dc9bpy)]+ (λmax = 550 nm) (ppyH = 2-phenylpyridine) and [Ir(piq)2(dc9bpy)]+ (λmax = 590 nm) (piqH = 1-phenylisoquinoline) for blue, yellow and red emissions, respectively. Six triple-layered films with different layer sequences were fabricated by layer-by-layer deposition onto quartz substrates. Stationary emission spectra were recorded on the prepared films under vacuum and at various oxygen pressures. Notably the change in the spectral shape at surrounding oxygen pressure depended remarkably on the layer sequence. Quenching by oxygen molecules was analyzed by applying a two-site model to the Stern–Volmer plots. The present nanometer-thick films were regarded as a benchmark for an optical device emitting different visible lights in response to oxygen pressure.

Langmuir–Blodgett films based on poly(p-phenylene vinylene) and protein-stabilised palladium nanoparticles: Implications in luminescent and conducting properties

In this paper, poly(p-phenylene vinylene) block copolymers (PPV) were immobilised in stearic acid (HSt) Langmuir–Blodgett (LB) films, and their conducting and luminescent properties were enhanced by the incorporation of palladium nanoparticles stabilised by glucose oxidase (GOx-PdNPs). The nanobiocomposite, based on HSt, PPV, and GOx-PdNPs, was transferred from the air-water interface onto solid supports using the LB technique. The films were characterised by surface pressure–area isotherms, polarisation modulation infrared reflection–absorption spectroscopy, fluorescence spectroscopy, and conductivity measurements. The results indicated that the incorporation of GOx-PdNPs in PPV-HSt LB films enhances the luminescence and conducting properties of the PPV. Based on the higher conductivity and emission obtained with the hybrid LB films and the ability to tune the molecular-level interactions between the film components by changing the experimental conditions, thus allowing for further optimisation, one may envisage applications for these films in optical and electronic devices, such as organic light-emitting diodes.

Preparation, characterization and photoelectric properties of dual-emissive Langmuir–Blodgett film of europium-substituted polyoxometalate and zinc(II) porphyrin platinum(II) complex

An organometallic/inorganic composite Langmuir–Blodgett (LB) film was prepared using a rigid-rod zinc(II) porphyrin platinum(II) complex coordinated with trans-bis(ethynylbenzene) (ZnPPt) as the π-conjugated organometallic molecule, and a europium-substituted polyoxometalate (POM), Na9EuW10O36 (EuW10) as the inorganic component. The structure and photophysical properties of the LB film was characterized by π–A isotherms, UV–vis absorption and photoluminescence spectra, atomic force microscopy imaging and scanning tunneling microscopy. The results indicate that stable, well-defined Langmuir and LB films were formed using pure water and POM as subphases. Luminescence spectra of the hybrid LB film showed that the emission spectra were obtained due to the dual-emissive nature of the mixed ZnPPt/EuW10 blends, and EuW10 was able to enhance the emission of ZnPPt. The ZnPPt-based LB film displayed an interesting electrical conductivity behavior. The 3-layer film formed by ZnPPt/EuW10 complex had a strong electrical response, giving rise to a tunneling current up to ±100nA when the voltage was monitored at −1.4–3.1V. When it was excited by light, the LB composite film generated a photovoltage of 24μV, indicating that the hybrid film had a strong photovoltage response as well.

Supported Ionic-Liquid “Semi-Heterogeneous Catalyst”: An Interfacial Chemical Study

The Langmuir–Blodgett (LB) technique has been employed for the construction of a model of interfacial supported ionic liquids (ILs) catalyst. In this model a hybrid LB film consists of three components: ionic liquids (imidazolium chloride with different length of substituent alkyl chain), catalyst carrier (saponite and laponite), and catalyst species (platinum nanocrystals). It was found imidazolium ILs with carbon number more than six in the alkyl substituents can form stable Langmuir monolayer over diluted clay dispersions. By recording surface pressure versus time (π–t) kinetic curves, we found that the adsorption of imidazolium ILs or platinum nanocrystals by clay elementary layers reaches equilibrium within 200 s, and the molar Gibbs free energy change −dG (kJ mol–1) for the adsorption lies in the range 0.34–5.6 kJ mol–1. Surface pressure versus area (π–A) isotherms revealed that platinum nanocrystals are adsorbed by the IL–clay Langmuir films at the air–water interface, and there are two phase trans...

Preparation, Characterization, and Photoelectric Properties of Langmuir–Blodgett Films of Some Europium-Substituted Polyoxometalates and 2-Aminofluorene with Tunable Emission Color

A new series of organic/inorganic composite Langmuir–Blodgett (LB) films consisting of 2-aminofluorene (Fl–NH2) as the π-conjugated organic molecule, an europium-substituted polyoxometalate (POM, POM = Na9EuW10O36, K13[Eu(SiW11O39)2] and K5[Eu(SiW11O39)(H2O)2], which are denoted by EuW10, EuW22 and EuW11, respectively) as the inorganic component, were prepared. Structural and photophysical characterization of these LB films were achieved by π–A isotherms, UV–Vis absorption and photoluminescence spectra, atomic force microscopy imaging, scanning tunneling microscopy, and surface photovoltage spectroscopy. Our experimental results indicate that stable Langmuir and LB films are formed in pure water and POM sub-phases. Luminescence spectra of the prepared hybrid LB films show that tunable emission color can be obtained due to the dual-emissive nature of the mixed Fl–NH2/POM blends. These 2-aminofluorene-based LB films displayed interesting electrical conductivity behavior. Among them, Fl–NH2/EuW11 3-layer films showed a good electrical response with the a tunneling current up to ± 100 nA when the voltage was monitored at −0.8 to 1.5 V. These LB composites show good photovoltage responses and a photovoltage of 2.7 μV can be obtained for the Fl–NH2/EuW22 system when it is excited by light.

Interaction of a Laser Dye with a Floating Phospholipid Monolayer

This communication reports the interaction of the well known laser dye RhB with a zwitterionic phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (abbreviated as DPPC). Reaction kinetics was studied at the air-water interface by measuring the increase in surface pressure with time while the Langmuir barrier was kept fixed. In-situ Fluorescence Imaging Microscopic (FIM) technique was employed to visualize the domain structure formed at the air-water interface with progress of reaction. After completion of the reaction, RhB-DPPC hybrid monolayer at the air-water interface was transferred onto solid substrates to form Langmuir-Blodgett (LB) films. UV-Vis absorption and fluorescence spectroscopic studies confirmed the presence of RhB molecules in the hybrid LB films.

Fabrication and Photochemical Characterization of Organic Dye-Metal Oxide Hybrid Langmuir Blodgett Film

Fabrication and Photochemical Characterization of Organic Dye-Metal Oxide Hybrid Langmuir Blodgett Film

Structure and Electrical Conductivity of Hybrid Langmuir–Blodgett Films from BEDO-TTF and Fatty Acid

Conducting Langmuir–Blodgett films are one of the candidates for molecular electronics. We investigated the structural and electrical properties of Langmuir–Blodgett films built up as a mixed molecular system of bis(ethylenedioxy)tetrathiafulvalene, in short BEDO-TTF, and fatty acid, as a function of (a) the alkyl chain length of the fatty acid and (b) the fatty acid: BEDO-TTF molar ratio in the starting solution from which the Langmuir film is prepared. The Langmuir–Blodgett films deposited from mixtures with molar ratio 1:2 showed better quality in terms of crystallinity and electrical conduction. Moreover, LB films with longer alkyl chain fatty acids were better ordered even at lower molar ratio.

Preparation, Characterization and Photoelectric Properties of Hybrid Langmuir–Blodgett Films of Alkynylplatinum(II)–Zinc(II) Porphyrinate/Heteropolyoxometalate

A new family of organometallic/inorganic hybrid Langmuir–Blodgett (LB) films, consisting of rigid-rod alkynylplatinum(II)–zinc(II) porphyrinate complex (OMA) as the π-conjugated donor–acceptor-type molecule, molybdophosphoric heteropolyacid and heteropolyacid salt (POM = H3PMo12O40, Na5IMo6O24, abbreviated as HPMo12 and NaIMo6, respectively) of the Keggin and Anderson structures as the inorganic composite, were prepared and characterized by π-A isotherms, UV–vis absorption and luminescence spectra, scanning tunneling microscopy and surface photovoltage spectroscopy. Our experimental results indicate that stable, well-defined and well-organized Langmuir and LB films have been formed in pure water and POM subphase. Luminescence spectra of these hybrid LB films show that HPMo12 can increase the emission intensity of OMA to some extent. These LB composites show good photovoltage responses and a photovoltage of 11.1 μV can be obtained for the OMA/HPMo12 system when it is excited by light. The 3-layer LB films on ITO wafer can also display intriguing electrical conductivity behavior and the tunneling current amounts to ±100 nA when the voltage is set at −0.7–2.5 and −1.3–0.8 V for OMA/HPMo12 and OMA/NaIMo6 hybrid LB films, respectively.

Graphene Oxide as a Monoatomic Blocking Layer

Monolayer graphene oxide (mGO) is shown to effectively protect molecular thin films from reorganization and function as an atomically thin barrier for vapor-deposited Ti/Al metal top electrodes. Fragile organic Langmuir-Blodgett (LB) films of C(22) fatty acid cadmium salts (cadmium(II) behenate) were covered by a compressed mosaic LB film of mGO flakes. These hybrid LB films were examined with atomic force microscopy (AFM) and X-ray reflectivity, both with and without the metal top electrodes. While the AFM enabled surface and morphology analysis, the X-ray reflectivity allowed for a detailed structural depth profiling of the organic film and mGO layer below the metal top layers. The structure of the mGO-protected LB films was found to be perfectly preserved; in contrast, it has previously been shown that metal deposition completely destroys the first two LB layers of unprotected films. This study provides clear evidence of the efficient protection offered by a single atomic layer of GO.