Complex Langmuir-Blodgett Films Research Articles

Effect of surfactant micelle on the fluorescence efficiency of a water soluble anionic xanthene dye in complex Langmuir-Blodgett (LB) film

Present communication reports the micellar effect on the increased fluorescence efficiency of a fluorescent dye in the complex LB film. In the complex Langmuir monolayer and Langmuir-Blodgett films, anionic Xanthene dye molecules organized differently when the films were prepared below and above the critical micellar concentration (CMC) of Cetyltrimethylammonium Bromide (CTAB) in the mixed solution of the Langmuir Trough. In-situ Brewster Angle Microscopic (BAM) studies showed the visual images of the Langmuir monolayers during the formation of the films. UV–Vis absorption and Fluorescence Spectroscopic studies were employed to study the spectral characteristics of the complex films.

Micellar effect of surfactant on the aggregation pattern of a fluorescent dye in ultra-thin film

This communication reports the effect of micelles on the molecular organisation of an anionic fluorescent dye Fluorescein Sodium salt (FSS) in Langmuir-Blodgett (LB) film. FSS forms non-fluorescent H-aggregates in LB film when interact with Cetyltrimethylammonium Bromide (CTAB) molecules below critical micellar concentration (CMC). While above CMC, LB films of FSS adsorbed on the micellar surface of CTAB, show predominant J-aggregated sites. Complex LB films of FSS are also prepared by allowing it to adsorb onto a preformed Langmuir monolayer of cationic amphiphile octadecylamine (ODA) at the air-water interface and then depositing it onto the solid substrate. Complex ODA-FSS LB films are also investigated and a comparison is made with the SA-CTAB-FSS complex films. Unlike SA-CTAB-FSS complex LB films, ODA-FSS LB films can not effectively control the non-fluorescent H-aggregated sites. The films are characterised by UV–vis absorption and fluorescence spectroscopic studies and in-situ Brewster Angle Microscopic (BAM) studies. Thus CTAB micelles play an important role to decrease the H-aggregated sites in the SA-CTAB-FSS complex LB films. This complex LB film can act as efficient fluorescence probe for several biological systems due to the absence of non-fluorescent H-aggregated sites.

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.

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.

A new voltammetric sensor for sensitive and selective determination of xanthine based on DNA and polyaniline composite Langmuir–Blodgett film

DNA–polyaniline (PAn) complex Langmuir–Blodgett film modified glassy carbon electrode (GCE) was used as a new voltammetric sensor (DNA/PAn-LB/GCE) for xanthine (XA) detection. The characteristic of DNA/PAn-LB film was studied by electrochemical impedance spectroscopy and scanning electron microscope. Electrochemical behaviors of XA at the sensor were studied in pH 7.0 phosphate buffer solutions by cyclic voltammetry and differential pulse anodic voltammetry. The results showed that this new modified electrode exhibited an excellent immunity from uric acid and hypoxanthine interference and a new sensitive and selective electroanalytical method for XA was proposed with wider linear range. Under the optimum conditions, the calibration curve for XA was obtained over the range of 7.0×10−8–1.0×10−5molL−1, with the detection limit of 3.0×10−8molL−1. The practicability of this method was demonstrated by determining the concentration of XA in human serum samples.

Three Component Complex Langmuir - Blodgett Films of Water Soluble Eosin Y With Dodecyl Trimethyl Ammonium Bromide and Stearic Acid

In the present communication we report the formation of nano dimensional complex films of eosin Y (EY), stearic acid (SA) and dodecyl trimethyl ammonium bromide (DTAB) using Langmuir - Blodgett (LB) technique. By spreading SA onto the DTAB - EY mixed aqueous sub phase a complex monolayer of SA-DTAB-EY was formed. The adsorption kinetics in the complex monolayer was investigated by recording increase in surface pressure with time (S-t) graph at air - water interface. Initially the (S-t) graph shows steep rise and becomes flat at the end of the adsorption kinetics. More than 300 minutes were required to complete the adsorption process. In situ Brewster Angle Microscopy investigation gives compelling visual evidence of complex Langmuir monolayer formation at air-water interface. After transfer onto solid substrate the films were characterized by UV-Vis absorption and Atomic Force Microscopy (AFM). In the complex LB films the EY absorption bands were shifted and broadened with respect to pure EY solution and microcrystal spectrum due to the formation of nano dimensional aggregates. This was also supported by AFM investigations of the complex LB films.

Formation of Complex Langmuir and Langmuir-Blodgett Films of DNA with a Dichain Cationic Surfactant

Formation of complex monolayers between a dichain cationic surfactant, namely, dihexadecyldimethylammonium bromide (DHDAB) and deoxyribonucleic acid (DNA) at the air-water interface was first time systematically investigated here. The adsorption of DNA onto DHDAB monolayer was monitored by observing the surface pressure vs. time graph. The polyion-complex monolayers formed in situ through the electrostatic attraction between cationic DHDAB and the phosphate groups of anionic DNA. The organization of the DNA-DHDAB complex at the air-water interface deduced from surface pressure-area (π-A) isotherms was compared with the spectroscopic data in Langmuir-Blodgett films. Study of UV-Vis absorption spectra of pure DNA solution and DNA adsorbed DHDAB complex Langmuir-Blodgett films confirms the successful transfer of the films onto quartz substrates.

Discotic Mesogen – DNA Complex Films at Interfaces

In this article, we review our studies on discotic mesogen – DNA complex films at interfaces. Discotic molecules are known to form highly anisotropic structures at the air-water (A-W) interface. We have studied films of a novel ionic discotic mesogenic molecule, pyridinium salt tethered with hexaalkoxytriphenylene (PyTp) and its complex with DNA (PyTp-DNA) at A-W and air-solid interfaces. The PyTp monolayer was formed on the aqueous subphase containing small amount of DNA. The electrostatic interaction between PyTp and DNA molecules results in a PyTp-DNA complex monolayer. Compared to the pure PyTp monolayer, the PyTp-DNA complex monolayer exhibits higher collapse pressure and lower limiting area. Surface manometry and Brewster angle microscope studies of the PyTp-DNA complex monolayer film indicate the molecules to be in the edge-on configuration. With increase in surface pressure, the complex monolayer undergoes a transition from a loosely packed monolayer phase to a compactly packed monolayer phase. The PyTp-DNA complex films on silicon wafers were prepared using Langmuir-Blodgett (LB) technique. We find that several tens of layers of PyTp-DNA complex monolayer can be transferred with good efficiency. We have carried out nanoscale electrical conductivity measurements for the pure PyTp and PyTp-DNA complex LB films using current sensing atomic force microscope. We have studied the current-voltage (I-V) characteristics for the metal-LB film-metal junction and our analysis shows that the I-V curves followed the Fowler-Nordheim tunneling model.

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.

Complex Langmuir−Blodgett Films of SiO2 and ZnO Nanoparticles with Advantageous Optical and Photocatalytical Properties

Multifunctional Langmuir-Blodgett (LB) films were fabricated on the surface of glass substrates using sol-gel derived ZnO and SiO2 particles. ZnO particles of 6 and 110 nm diameter were synthesized according to the methods of Meulenkamp and Seelig et al. (Meulenkamp, E. A. J. Phys. Chem. B 1998, 102, 5566; Seelig, E. W.; Tang, B.; Yamilov, A.; Cao, H.; Chang, R. P. H. Mater. Chem. Phys. 2003, 80, 257). Silica particles of 37 and 96 nm were prepared by the Stober method (Stober, W.; Fink, A.; Bohn, E. J. Colloid Interface Sci. 1968, 26, 62). Alternate deposition of monoparticulate Langmuir films of SiO2 and ZnO nanoparticles provided complex (six- and nine-layered) LB films with both antireflective and photocatalytic properties. The LB films were investigated with scanning electron microscopy (morphology and structure) and UV-vis spectroscopy (optical properties and stability). The photocatalytic activity was measured by immersing the UV-irradiated films into an aqueous solution of Methyl Orange and following the photodegradation of the dye by optical spectroscopy. Adding ZnO particles to the silica films slightly lowered the antireflection property but ensured strong photocatalytic activity. Both the photocatalytic activity and antireflection properties were proved to be sensitive to the sequence of the silica and ZnO layers, with optimum properties in the case of nine-layered films with a repeated (SiO2-ZnO-ZnO) structure.

Discogen−DNA Complex Films at Air−Water and Air−Solid Interfaces

We have studied films of an ionic discogenic (discotic mesogenic) molecule (pyridinium salt tethered with hexaalkoxytriphenylene (PyTp)) and DNA complex at air-water (A-W) and air-solid interfaces. We have formed an PyTp monolayer on an aqueous subphase containing a small amount of DNA to obtain a PyTp-DNA complex at the A-W interface. Compared to the pure PyTp monolayer, the PyTp-DNA complex monolayer exhibits a higher collapse pressure and lower limiting area, indicating condensation and better stability. A Brewster angle microscope was used for in situ observation of the morphology of the film at the A-W interface. The PyTp-DNA complex films on silicon wafers were prepared using the Langmuir-Blodgett (LB) technique. We find that several tens of layers of the PyTp-DNA complex monolayer can be transferred with good efficiency. Fourier transform infrared spectroscopy studies confirm the presence of DNA in the LB films of the PyTp-DNA complex. Nanoindentation measurements using atomic force microscope reveal that the PyTp-DNA complex films are about two times harder as compared to the pure PyTp films.

Ultrathin Luminescent Films of Rigid Dinuclear Ruthenium(II) Trisbipyridine Complexes

Two asymmetric, luminescent, bimetallic ruthenium trisbipyridine complexes with the general formula [Ru(bpy)3-ph4-Ru(bpy) L 2 ](PF 6 ) 4 (bpy=2,2'-bipyridine, ph=phenyl, L=4,4'-di-n-undecyl-2,2'-bipyridine (1); 4,4'-di-non-1-enyl-2,2'-bipyridine (2)) have been synthesized and characterized. The introduction of two 4,4'-dialkyl-2,2'-bipyridine ligands on one of the ruthenium centers does not influence the electronic structure of the overall complexes to a large extent. Owing to the hydrophobic and hydrophilic nature of the two terminal metal complexes, the compounds 1 and 2 are expected to form Langmuir monolayers at the air/water interface. The film-forming properties of the amphiphilic complexes have been investigated by measuring surface-pressure-molecular-area (n-A) isotherms and recording Brewster-angle microscopy images. Complexes 1 and 2 were shown to form monolayer films at the air/water interface, which have subsequently been transferred to solid substrates using the Lang-muir-Blodgett (LB) technique. The homogeneity of the resulting LB films has been investigated using atomic force microscopy and has been compared with that of LB films of the reference compound [Ru(bpy)3-ph4-Ru(bpy)3](PF 6 )4 (3), which lacks the alkyl chains. The presence of the hydrocarbon chains on one side of the rigid bimetallic complexes was shown to be a prerequisite for the formation of homogeneous monolayers, as with 3 only multilayer formation was obtained. Confocal laser scanning microscopy measurements proved that the LB films of complexes 1 and 2 display a homogeneous red emission upon photoexcitation. Such important results represent the first step towards the fabrication of mono- or few-molecular-layer electroluminescent devices.

Complex Langmuir–Blodgett films from silica nanoparticles: An optical spectroscopy study

We prepared mono- and multiparticulate Langmuir–Blodgett (LB) films of Stöber silica nanoparticle samples in the particle size range of 20–80 nm. Multiparticulate films were prepared from particles with different diameters in the consecutive layers, creating a complex multiparticulate film on glass substrate. We were able to increase the antireflective properties of the multiparticulate films by decreasing the particles sizes in the covering layer.

Supramolecular chirality of the hydrogen-bonded complex Langmuir–Blodgett film of achiral barbituric acid and melamine

Complex monolayers of barbituric acid and melamine were formed by spreading a chloroform solution of amphiphilic barbituric acid on the subphase of melamine solution. It was confirmed that the complex monolayer was formed through in situ complementary hydrogen bonding at the air–water interface. It was interesting to find that the complex LB films showed supramolecular chirality although both of the molecules were achiral, as verified by the circular dichroism spectral measurements. It was suggested that the π– π stacking of the neighboring barbituric acid and melamine group in a helical sense resulted in the chirality of the molecular assemblies. Due to the directionality of the hydrogen bonding, the BA-M film could form regular aligned nanofibers on the AFM images. Increasing the subphase temperature will lead to the decrease of CD intensity and the change of the morphologies. We suggested that the strength of the hydrogen bonding resulted in the difference.

Low-dimensional hybrid organic–inorganic nanostructures via planar DNA–amphiphilic polycation complexes

New nanoscale organized planar complexes of DNA and amphiphilic polycation on the surfaces of solid substrates were obtained via the formation of Langmuir monolayer at the gas–aqueous phase interface composed by water-insoluble amphiphilic polycation poly(4-vinylpyridine) with 16% cetylpyridinium groups, then binding of DNA molecules from the aqueous phase with the amphiphilic polycation monolayer, and, finally, deposition of the planar complex structure. Those monolayer and multilayer DNA/polycation complex Langmuir–Blodgett films were used as nanotemplates and nanoreactors for synthesis of inorganic nanostructures. The obtained nanostructures were characterized by atomic force microscopy and transmission electron microscopy techniques. As a result, ultrathin planar polymeric nanocomposite films with integrated DNA molecules and organized inorganic semiconductor CdS and iron oxide nanoparticle quasi-linear arrays were formed successfully.

Interfacially organized DNA/polycation complexes: a route to new planar polymeric and composite nanostructures

Effects of nano-scale supramolecular organization and patterning in amphiphilic polycation monolayer formed by poly-4-vinilpyridine with 16% cetylpyridinium groups and in novel planar DNA/amphiphilic polycation complexes formed at the air-aqueous DNA solution interface and deposited on the solid substrates have been studied using AFM. Stable ordered quasi-crystalline planar polymeric monolayer structures were formed by amphiphilic polycation molecules. Extended net-like and quasi-circular toroidal condensed conformations of deposited planar DNA/amphiphilic polycation complexes were obtained in dependence on the amphiphilic polycation Langmuir monolayer state during the DNA binding. Those monolayer and multilayer DNA/polycation complex Langmuir–Blodgett films were used as templates and nanoreactors for generation of inorganic nanostructures. As a result, ultrathin polymeric nanocomposite films with integrated DNA building blocks and inorganic semiconductor (CdS) and iron oxide nanoparticle quasi-linear arrays or aggregates (nanorods) were formed successfully and characterized by TEM. The data obtained give evidence for effectiveness of the monolayer techniques for study mechanisms of DNA structural transformations caused by complexation with cationic compounds and demonstrate its perspectives for creation of new planar DNA-based self-organized stable polymeric complex nanostructures and nanocomposites with nano-scale structural ordering.

Preparation, Photo‐luminescence and Electro‐Luminescence Behavior of Langmuir−Blodgett Films of Bipyridylrhenium(I) Surfactant Complexes

AbstractSeveral bipyridylrhenium(I) surfactant complexes, fac‐[Re(CO)3(bpy)(L)]PF6 [bpy = 2,2′‐bipyridine, L = trans‐4‐dodecyloxy‐4′‐stilbazole (L1), trans‐4‐octadecyloxy‐4′‐stilbazole (L2), 4‐(4′‐dodecyloxyphenylethynyl)pyridine (L3)] were synthesized and characterised. The X‐ray crystal structure of fac‐[Re(CO)3(bpy)(L1)]PF6 has been determined. The complexes exhibited intense photo‐luminescence which has been ascribed to the dπ(Re) ⇄ π*(bpy) metal‐to‐ligand charge transfer (MLCT) triplet emission. The complexes were found to form stable Langmuir−Blodgett (LB) films with relatively high collapse pressures. The organic light‐emitting diodes (OLEDs) fabricated by employing the LB films of various complexes as the emitting layer exhibited electroluminescence (EL) behavior. The luminances of the EL devices were found to vary as a function of the number of LB film layers, hydrocarbon chain length and the deposition types. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The properties of praseodymium bis[octakis(octyloxy)phthalocyaninato] complex Langmuir–Blodgett films for NO 2 sensor

Langmuir–Blodgett (LB) films of general organic semiconductor materials may be used as gas sensors because the conductivity depends on the presence of some gas species. Praseodymium bis[phthalocyaninato] complex-based LB films are very sensitive to the change of nitrogen dioxide(NO 2) gas concentration. In the paper, a new kind of sandwich-like praseodymium bis[2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] complex Pr[Pc ∗] 2 ( Pc ∗= Pc (OC 8H 17) 8) was used as film-forming material. It is found that a mixture of Pr[Pc ∗] 2 and octadecanol (OA) with 1:6 molar ratio formed an excellent material for the fabrication of gas-sensing LB film. The sensitive property of Pr[Pc ∗] 2 LB films to NO 2 gas was monitored by the change of resistance during gas exposure. The detecting range was from 0 to 100 ppm, and the response time of 11-layer Pr[Pc ∗] 2 LB film to 20 ppm NO 2 was 27 s at room temperature. Factors affecting gas-sensing properties of Pr[Pc ∗] 2 LB films to NO 2 gas such as temperature, number of film layers and processing conditions were also discussed in the paper.

Studies of nanoscale structural ordering in planar DNA complexes with amphiphilic mono- and polycations

Formation of DNA complexes with Langmuir monolayers of cationic lipid octadecylamine (ODA) and new amphiphilic polycation poly-4-vinylpyridine with 16% cetylpyridinium groups (PVP-16) on the surface of native DNA aqueous solution with low ionic strength has been studied. AFM topographic images of DNA/ODA and DNA/PVP-16 complex Langmuir–Blodgett films deposited on the mica substrates were obtained. The complex structures and individual DNA molecules on the amphiphile monolayer surface were observed. The characteristic extended net-like structures and quasi-circular toroidal condensed conformations of the planar DNA complexes were formed in dependence on the polycationic amphiphile monolayer state during the DNA binding. The data obtained give evidence for the effectiveness of monolayer techniques for investigation the mechanisms of DNA complexation with amphiphilic mono- and polycations and demonstrate its perspectives for creation of supramolecular planar DNA-based self-organized nanostructures with nanoscale structural ordering.

Fabrication of Field-Effect Transistor Using Charge-Transfer-Complex Langmuir-Blodgett Films

Field-effect transistors (FETs) using charge-transfer (CT)-complex Langmuir-Blodgett (LB) films were fabricated and their FET characteristics were measured. Four-layer (2 bilayers), 3-layer (a bilayer and a monolayer) and monolayer of Y-type TMPD-CnTCNQ LB films were examined as active layers of the FET. The FET characteristics strongly depended on the number of CT-complex layers. The monolayer FET showed the highest dependence of drain-source current (IDS) on gate voltage (VG) although the film was the least conductive among the three. Elimination of bilayer units, of which the structure is symmetric against the substrate normal, was concluded to be essential for improving the VG dependence. The cutoff frequency of the CT-complex FET was estimated to be 5 Hz.