Obtained Langmuir-Blodgett Films Research Articles

Preparation of Langmuir-Blodgett composite films based on Bisphenol fluorene and Epoxy bisphenol fluorene with photovoltaic properties

The Langmuir-Blodgett (LB) technique can be used to obtain highly ordered arrangement and assembly of high polymer molecular chains, and the obtained LB films exhibit the controllable structures and special physicochemical properties. Here, we successfully prepared the composite LB films based on bisphenol fluorene (BPF) and epoxy bisphenol fluorene (DGPF) by LB technique, as well as explored the microstructures of the composite LB films by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The different aggregation states of various dye molecules in the composite LB films are investigated by UV–vis. Interestingly, the composite LB film electrodes exhibit promising photoelectrochemical properties. In particular, BPF/MB and DGPF/MB LB films show better photoelectric conversion efficiency. It is attributed to the ordered arrangement of BPF and DGPF and their effective aggregation with dye molecules, which improves the light absorption ability and charge transfer efficiency of the materials. Therefore, the prepared LB films based on the synthetic polymers BPF and DGPF are expected to play an important role in microelectronics.

Interfacial nanostructures and acidichromism behaviors in self-assembled terpyridine derivatives Langmuir-Blodgett films

Metal-ligand coordination is one of the most important interactions in supramolecular assembly. Terpyridine compounds demonstrate strong metal coordination ability and can coordinate with many transition metal ions to form complexes with unique optical and electrochemical properties. In this work, new self-assembled Langmuir films of three synthesized terpyridine derivatives with different spacers were prepared by Langmuir-Blodgett (LB) technique. The interfacial phase behaviors and coordination with K2PtCl4 and ZnCl2 subphases in the obtained LB films were studied. The spreading films from different subphases were transferred to corresponding solid substrates and their nanostructures and self-assembly features were characterized. The good acidichromism properties of the prepared LB films from present terpyridine derivatives were investigated by using UV–vis and FT-IR spectroscopy. The obtained results showed new clues for preparation of functional coordination polymers films and potential applications in molecular switches and biosensors fields.

Tuning ubiquinone position in biomimetic monolayer membranes.

Artificial lipid bilayers have been extensively studied as models that mimic natural membranes (biomimetic membranes). Several attempts of biomimetic membranes inserting ubiquinone (UQ) have been performed to enlighten which the position of UQ in the lipid layer is, although obtaining contradictory results. In this work, pure components (DPPC and UQ) and DPPC:UQ mixtures have been studied using surface pressure-area isotherms and Langmuir-Blodgett (LB) films of the same compounds have been transferred onto solid substrates being topographically characterized on mica using atomic force microscopy and electrochemically on indium tin oxide slides. DPPC:UQ mixtures present less solid-like physical state than pure DPPC indicating a higher-order degree for the latter. UQ influences considerably DPPC during the fluid state, but it is mainly expelled after the phase transition at [Formula: see text] 26 mN·m^-1 for the 5:1 ratio and at [Formula: see text] 21 mN·m^-1 for lower UQ content. The thermodynamic studies confirm the stability of the DPPC:UQ mixtures before that event, although presenting a non-ideal behaviour. The results indicate that UQ position can be tuned by means of the surface pressure applied to obtain LB films and the UQ initial content. The UQ positions in the biomimetic membrane are distinguished by their formal potential: UQ located in "diving" position with the UQ placed in the DPPC matrix in direct contact with the electrode surface ( -0.04±0.02 V), inserted between lipid chains without contact to the substrate ( 0.00±0.01 V) and parallel to the substrate, above the lipid chains ( 0.09±0.02 V).

Controlling the Structural and Electrical Properties of Diacid Oligo(Phenylene Ethynylene) Langmuir–Blodgett Films

The preparation, characterization and electrical properties of Langmuir-Blodgett (LB) films composed of a symmetrically substituted oligomeric phenylene ethynylene derivative, namely, 4,4'-[1,4-phenylenebis(ethyne-2,1-diyl)]dibenzoic acid (OPE2A), are described. Analysis of the surface pressure versus area per molecule isotherms and Brewster angle microscopy reveal that good-quality Langmuir (L) films can be formed both on pure water and a basic subphase. Monolayer L films were transferred onto solid substrates with a transfer ratio of unity to obtain LB films. Both L and LB films prepared on or from a pure water subphase show a red shift in the UV/Vis spectrum of about 14 nm, in contrast to L and LB films prepared from a basic subphase, which show a hypsochromic shift of 15 nm. This result, together with X-ray photoelectron spectroscopic and quartz crystal microbalance experiments, conclusively demonstrate formation of one-layer LB films in which OPE2A molecules are chemisorbed onto gold substrates and consequently -COO-Au junctions are formed. In LB films prepared on a basic subphase the other terminal acid group is also deprotonated and associates with an Na(+) counterion. In contrast, LB films prepared from a pure water subphase preserve the protonated acid group, and lateral H-bonds with neighbouring molecules give rise to a supramolecular structure. STM-based conductance studies revealed that films prepared from a basic subphase are more conductive than the analogous films prepared from pure water, and the electrical conductance of the deprotonated films also coincides more closely with single-molecule conductance measurements. This result was interpreted not only in terms of better electron transmission in -COO-Au molecular junctions, but also in terms of the presence of lateral H-bonds in the films formed from pure water, which lead to reduced conductance of the molecular junctions.

Optically anisotropic and photoconducting Langmuir–Blodgett films of neat poly(3-hexylthiophene)

Among the several types of conjugated polymers used in recent investigations, polythiophene and its derivatives have attracted considerable attention over the past 20 years due to their high mobility and other remarkable solid-state properties. They have potential applications in many fields, such as microelectronic devices, catalysts, organic field-effect transistors, chemical sensors and biosensors. There are two critical parameters that determine the polymer-based device performance: chemical structure and nanostructure of the conjugated polymer in solid state. Langmuir–Blodgett (LB) films may be an interesting alternative for producing the films used in the devices since they can be obtained with high degree of thickness control, low number of defects, and some degree of organization at the molecular scale. However, most of the polythiophene derivatives have poor film forming properties by LB method and need the use of film form aiding materials. In this work, we report on the fabrication and characterization of Langmuir and Langmuir–Blodgett films of neat poly(3-hexylthiophene). Although the LB technique is not suitable to obtain LB films with a great number of layers, good quality films, with thicknesses suitable for fabrication of opto-eletronic devices could be easily built by using the proper deposition conditions.

Langmuir–Blodgett films incorporating an ionic europium complex

Langmuir–Blodgett (LB) technique is a powerful tool to fabricate ultrathin films with highly ordered structures and controllable molecular array for efficient energy and electron transfer, allowing the construction of devices at molecular level. One method to obtain LB films consists in the mixture of classical film-forming molecules, for example Stearic Acid (SA) and functional metal complex. In this work NH 4[Eu(bmdm) 4], where the organic ligand bmdm is (butyl methoxy-dibenzoyl-methane) or (1-(4-methoxyphenyl)-3-(4-tert-butylphenyl)propane-1,3-dione) was used to build up Langmuir and LB films. Langmuir isotherms were obtained from (i) NH 4[Eu(bmdm) 4] complex and (ii) NH 4[Eu(bmdm) 4]/SA (1:1). Results indicated that (i) form multilayer structure; however the surface pressure was insufficient to obtain LB films, and (ii) can easily reproduce and build LB films. The dependence of number of layers in the UV absorption spectra suggest that the complex did not hydrolyze or show decomposition, UV spectral differences observed between the solution and the LB film indicate that the complex has a highly ordered arrangement in the film and the complex has an interaction with SA. Excitation spectra confirm a ligand-europium energy transfer mechanism. The transition lines of Eu 3+ ion were observed in emission spectra of all films, the photoluminescence spectra indicate a fluorescence enhanced effect with the number of LB layers.

Dye aggregates formed in Langmuir–Blodgett films of amphiphilic merocyanine dyes

Abstract The electronic absorption spectra of pure Langmuir (L) films of 6MeDS prepared upon MgCl2, CaCl2, CdCl2, and CuCl2 aqueous solutions have shown that the Mg2+, Ca2+, and Cd2+ cations promote the J-aggregation of the dye, but the Cu2+ cation inhibits it. Instead, the Cu2+ cation promotes the formation of another type of dye aggregate (D-aggregate), which exhibits a split electronic absorption band. These L films have been transferred onto solid substrates by the Langmuir–Blodgett (LB) technique. The vibronic absorption spectra observed for the obtained LB films have shown the similarity between the metal–cation-containing J-aggregate and the metal-free J-aggregate of the dye, the latter of which was characterized in the previous study [K. Ikegami, J. Chem. Phys. 121 (2004) 2337]. These spectra have also indicated that the bimolecular metal chelation plays an important role in the J-aggregation, like the intermolecular hydrogen bonding in the metal-free case.

Triazole-Based Magnetic Langmuir−Blodgett Films: Paramagnetic to Spin-Crossover Behavior

The behavior at the air−liquid interface of a series of metal(II) metallo-organic polymers of 4-octadecyl-1,2,4-triazole has been studied. Interactions between those amphiphilic compounds and metal ions in the subphase result in the formation of stable monolayers and well-defined Langmuir−Blodgett (LB) films incorporating oligomeric metal(II)/triazole units. Infrared, X-ray Photoelectron Microscopy, and magnetic measurements show that the obtained LB films are mostly resulting from recoordination of metal ions from the subphase with triazole ligands at the air−water interface. The relative stability of the polymers and the efficiency of association with 4-octadecyl-1,2,4-triazole have been found to follow the Ni > Fe ∼ Cu > Co and Cu > Ni > Fe > Co sequences, respectively. In the iron(II) cases, partial spin-crossovers are observed, demonstrating for the first time the feasibility of triazole-based LB films possessing interesting magnetooptical properties.

Langmuir–Blodgett Films Containing TCNQ Incorporated from the Aqueous Subphase

Films containing TCNQ (tetracyanoquinodimethane) anions were prepared by incorporating it from a LiTCNQ aqueous subphase. The TCNQ moiety was transferred from the subphase as the counterion of a positively charged monolayer of DPOP+ (diphenylbis(octadecylamino)phosphonium). The isotherm shape, the area per molecule, the collapse pressure, and the monolayer stability were dependent on the LiTCNQ concentration in the subphase. The obtained Langmuir–Blodgett films were classified into three types depending on the TCNQ oxidation state. The oxidation state depends on the transference pressure as well as on the monolayer age. The degree of both order and architecture of the films was studied by means of SEM, IR, UV–vis spectroscopy, and X-ray diffraction. Conductivity studies were also performed.

Structural change of Langmuir and Langmuir–Blodgett films of alkylDCNQI induced by charge-transfer reaction at the air–water interface

UV-visible absorption spectrum of pure 2-methyl-5-octadecyl-N,N′-dicyanoquinonediimine (C18MeDCNQI) Langmuir films and that of C18MeDCNQI–CuI mixed Langmuir films indicated the occurrence of charge-transfer (CT) reactions at the air–water interface in the latter case. These Langmuir films were deposited onto solid substrates as Langmuir–Blodgett (LB) films by the horizontal lifting method. Polarized UV–visible–IR absorption spectra and x-ray diffraction patterns recorded for the obtained LB films revealed a drastic structural change induced by the CT reactions: An interdigitated bilayer structure was suggested for the pure films, while a monolayer structure for the CT films. Furthermore, the CT degree of the major component of the mixed LB films was estimated at −1, unlike in the case of Cu–DCNQI crystals, for which the CT degree is −2/3.