Langmuir-Schaefer Films Research Articles

Enhanced Power Generation by Piezoelectric P(VDF-TrFE)/rGO Nanocomposite Thin Film

In this study we fabricated a piezoelectric nanogenerator (PENG) of nanocomposite thin film comprising a conductive nanofiller of reduced graphene oxide (rGO) dispersed in a poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) matrix that was anticipated to show enhanced energy harvest performance. For the film preparation we employed the Langmuir-Schaefer (LS) technique to provide direct nucleation of the polar β-phase without any traditional polling or annealing process. We prepared five PENGs consisting of the nanocomposite LS films with different rGO contents in the P(VDF-TrFE) matrix and optimized their energy harvest performance. We found that the rGO-0.002 wt% film yielded the highest peak-peak open-circuit voltage (VOC) of 88 V upon bending and releasing at 2.5 Hz frequency, which was more than two times higher than the pristine P(VDF-TrFE) film. This optimized performance was explained by increased β-phase content, crystallinity, and piezoelectric modulus, and improved dielectric properties, based on scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), x-ray diffraction (XRD), piezoelectric modulus, and dielectric property measurement results. This PENG with enhanced energy harvest performance has great potential in practical applications for low energy power supply in microelectronics such as wearable devices.

The structure, optical properties and photovoltaic effect in Langmuir-Schaefer films of nickel (II) bis-semiquinone complex derived from 3,6-di‑tert‑butyl‑benzoquinone annulated with a 1,3 -dithiole-2-thiocarbonyl fragment

Molecules with an extended conjugated π-electron system and a flat rigid topology have traditionally been considered as appropriate candidates for organic (semi-)conductors. With their potential for intramolecular charge transfer, these molecules can have bright prospects in optoelectronic device manufacturing. In this work we describe a novel bis-semiquinone complex of nickel and о-quinone annulated with a 1,3-dithiol-2-thiocarbonyl fragment and the peculiarities of thin-film deposition of this compound on different substrates. It is shown that a thin film can maintain the crystal structure of the original complex. A photovoltaic effect is detected in sandwich structures with an aluminum cathode. It is anticipated that further optimization of the structure of such sulfur-rich molecules will prodive solid-state ensembles with promising photovoltaic and/or photodetecting properties.

Proline Enantiomers Discrimination by (L)-Prolinated Porphyrin Derivative Langmuir–Schaefer Films: Proof of Concept for Chiral Sensing Applications

A porphyrin derivative functionalized with the L-enantiomer of proline amino acid was characterized at the air–pure water interface of the Langmuir trough. The porphyrin derivative was dissolved in dichloromethane solution, spread at the air–subphase interface and investigated by acquiring the surface pressure vs. area per molecule Langmuir curves. It is worth observing that the behavior of the molecules of the porphyrin derivative floating film was substantially influenced by the presence of L-proline amino acid dissolved in the subphase (10−5 M); on the contrary, the physical chemical features of the floating molecules were only slightly influenced by the D-proline dissolved in the subphase. Such an interesting chirality-driven selection was preserved when the floating film was transferred onto solid supports by means of the Langmuir–Schaefer method, but it did not emerge when a spin-coating technique was used for the layering of the tetrapyrrolic derivatives. The obtained results represent proof of concept for the realization of active molecular layers for chiral discrimination: porphyrin derivatives, due to their intriguing spectroscopic and supramolecular properties, can be functionalized with the chiral molecule that should be detected. Moreover, the results emphasize the crucial role of the deposition technique on the features of the sensing layers.

Subnanomolar Detection of Mercury Cations in Water by an Interfacial Fluorescent Sensor Achieved by Ultrathin Film Structure Optimization.

The objectives of this work were to develop and extend the previously proposed approaches to control the structure of nanoscale planar systems based on modular fluorophore compounds capable of efficient analyte binding and to optimize the architecture of ultrathin films formed from them to create a thin-film sensor element for mercury cations. The possibility of applying the ratiometric approach to the fluorescence measurements to obtain a quantitative analytical signal was shown. It was found that films with the Langmuir-Schaefer film architecture, in which the receptor crown ether groups of the fluoroionophore are oriented toward the studied solution, allow the quantitative determination of mercury cations in water at concentrations below the threshold limit value and are especially effective in the analyte concentration range of 10-10-10-5 M. High selectivity of the obtained thin-film sensitive elements with respect to mercury cations and the possibility of regeneration of such elements after quantitative determination of mercury cations in aqueous solutions are demonstrated.

Aggregation behavior and spectroscopic properties of red-emitting distyryl-BODIPY in aqueous solution, Langmuir-Schaefer films and Pluoronic® F127 micelles

Red-emitting distyryl substituted BODIPY dyes are among the most promising luminophors for bioimaging and optics applications. However, the practical application of BODIPYs is limited due to their high hydrophobicity and tendency to aggregate in aqueous organic solutions and solid phase. In this article, we propose an elegant solution to this problem. To this end, we carried out the detailed experimental and quantum-chemical study of the structural and spectral features of BF2-ms-phenyl-5,5′-bis(4-dimethylaminostyryl)-3,3′-dimethyl-2,2′-dipyrromethene (distyryl-BDP). The particular attention was paid to analysis of high sensitivity of the distyryl-BDP spectral characteristics to the solvent properties, and also the aggregation behavior features both in water-organic media and in mono- and multilayer Langmuir-Schaefer films. We selected the best conditions to obtain the hydrophilic micellar structures of distyryl-BDP with Pluronic® F127 having a high efficiency of dye solubilization. This method increasing the solubility improves the distyryl-BDP transport efficiency in physiological aqueous media. The aqueous solutions of distyryl-BDP–Pl micelles show the intense fluorescence in the phototherapy window region (λfl = 739 nm).

Using Langmuir-Schaefer deposition technique to improve the gas sensing performance of regiorandom polythiophene films

Polythiophene derivatives are one class of conducting polymers widely tested for application in organic electronics, such as photovoltaic devices, organic light-emitting diodes, and chemosensors to gas and liquid analysis. Polythiophenes can be classified as regioregular or regiorandom, which is determined by the position of their side chains in the polymer backbone, and the regioregular configuration is usually preferred for studies in organic electronic applications. There are few reports in the literature using regiorandom polythiophenes as active layers of devices, all with doped or composite materials. In this context, we have fabricated Langmuir-Schaefer films of neutral regiorandom polyalkylthiophenes (P3AT), aiming to evaluate their electrical characteristics compared to the drop-casting technique. The goal was to test whether the Langmuir deposition technique could yield a higher level of organization, while still being mindful of their intrinsic disorder at the molecular level. As a proof-of-concept, the thin films were evaluated as gas sensing devices relying on their resistivity modulation in the presence of ammonia. The devices based on Langmuir-Schaefer films of the regiorandom P3AT showed higher responses to the gas than the ones fabricated by drop-casting, indicating that the organization at the molecular level achieved by the deposition technique improved the gas sensing performance.

Influence of solvents on the morphology of Langmuir and Langmuir-Schaefer films of PCBM and PCBM-based oligomers and polymers.

Fullerene-based polymers and oligomers combined with non-fullerene acceptors show extremely high efficiencies in organic photovoltaic devices. Furthermore, fullerene-based materials are of interest for use in anti-cancer and anti-viral treatments, where their presence can enhance the efficacy of medication considerably. Therefore, it remains important to understand their morphology and electronic properties to improve devices and technological applications. The main goal of this study is to prepare and characterize Langmuir and Langmuir-Schaefer films of PCBM-based materials to investigate the influence of different solvents such as chloroform, toluene, and xylene, and co-components on their morphology. PCBM-based materials were thus studied either alone or in mixtures with a polythiophene derivative (poly(3-hexythiophene), P3HT) commonly used in organic photovoltaic devices. The formation of Langmuir films was studied using surface pressure isotherms and Brewster's angle microscopy (BAM), where the homogeneity, phase behavior, and morphology of the films were investigated. In addition, Langmuir-Schaefer films were characterized by UV-visible absorption spectroscopy, atomic force microscopy (AFM), and Raman spectroscopy, providing information on the morphology of the solid films. This study has shown that it is possible to successfully fabricate Langmuir and Langmuir-Schaefer films of PCBM and PCBM-based oligomers and polymers, both pure and in mixtures with P3HT, to compare their organization, roughness, and optical properties. With the Langmuir films, it was possible to estimate the area of the molecules and visualize their aggregation through BAM images, establishing a relationship between the area occupied by these materials and the solvent used. All characterization techniques corroborate that the use of chloroform significantly reduced the roughness of the LS films mixed with P3HT and also presented a higher ordering compared to films prepared with xylene solutions.

The efficiency of photothermal action of gold shell-isolated nanoparticles against tumor cells depends on membrane interactions

Photoinduced hyperthermia with nanomaterials has been proven effective in photothermal therapy (PTT) of tumor tissues, but a precise control in PTT requires determination of the molecular-level mechanisms. In this paper, we determined the mechanisms responsible for the action of photoexcited gold shell-isolated nanoparticles (AuSHINs) in reducing the viability of MCF7 (glandular breast cancer) and especially A549 (lung adenocarcinoma) cells in vitro experiments, while the photoinduced damage to healthy cells was much smaller. The photoinduced effects were more significant than using other nanomaterials, and could be explained by the different effects from incorporating AuSHINs on Langmuir monolayers from lipid extracts of tumoral (MCF7 and A549) and healthy cells. The incorporation of AuSHINs caused similar expansion of the Langmuir monolayers, but Fourier-transform infrared spectroscopy (FTIR) data of Langmuir-Schaefer films (LS) indicated distinct levels of penetration into the monolayers. AuSHINs penetrated deeper into the A549 extract monolayers, affecting the vibrational modes of polar groups and carbon chains, while in MCF7 monolayers penetration was limited to the surroundings of the polar groups. Even smaller insertion was observed for monolayers of the healthy cell extract. The photochemical reactions were modulated by AuSHINs penetration, since upon irradiation the surface area of A549 monolayer decreased owing to lipid chain cleavage by oxidative reactions. For MCF7 monolayers, hydroperoxidation under illumination led to a ca. 5% increase in surface area. The monolayers of healthy cell lipid extract were barely affected by irradiation, consistent with the lowest degree of AuSHINs insertion. In summary, efficient photothermal therapy may be devised by producing AuSHINs capable of penetrating the chain region of tumor cell membranes.

Study of Langmuir monolayers and Langmuir-Schaefer films based on symmetrical meso-aryl-substituted porphyrin derivative

This paper presents the results of a study of meso-aryl-substituted porphyrin Langmuir monolayers by the method of compression isotherms. Experimental data were used to plot the dependences of the compression modulus (C−1) on the specific area. Monolayers at specific surface pressure were transferred to solid substrates and investigated. The monolayers were transferred to the surface of monocrystalline silicon at surface pressures of 8, 25, and 60 mN/m and examined them by atomic force microscopy (AFM) in a semi-contact mode. It was found that with an increase in the transfer pressure, the coarsening of molecular aggregates occurs. The smallest roughness is observed for a porphyrin film formed and transferred at a pressure of 8 mN/m.

Supramolecular Organization and Optical Properties of Langmuir-Schaefer Films of N,N'-di(3,5-Dimethylphenyl)diimide 1,1'-Binaphthyl-4,4',5,5',8,8'-Hexacarboxylic Acid

Supramolecular Organization and Optical Properties of Langmuir-Schaefer Films of N,N'-di(3,5-Dimethylphenyl)diimide 1,1'-Binaphthyl-4,4',5,5',8,8'-Hexacarboxylic Acid

Helicenes at Air/Water Interface: Spreading Film and Metal Ion Induced a Helical Ring Nanostructure.

Two enantiomeric hydrohelicenes containing a hydroxyl group and a π-conjugated nonplanar structure are assembled at the air/water interface. These molecules are found to form spreading films with well-defined surface pressure-area isotherms. Upon transferring the spreading film onto the mica surface, porous nanostructures are observed. The spreading film can be transferred onto solid substrates by the Langmuir-Schaefer (LS) method and the transferred LS films display optical activity as revealed by the circular dichroism (CD) spectra. The P- and M-hydrohelicene enantiomers showed mirrored CD spectra, suggesting that the chirality of the LS films was controlled by molecular chirality. When these molecules are spread on the aqueous solution containing metal ions such as Ag+, Cu2+, and Zn2+, a clear twisted ring nanostructure, which is similar to the Möbius strip, is observed. It is suggested that the interaction between the hydroxyl groups of helicenes and metal ions induced such a ring nanostructure.

Self-Organization of A2B Type Boron Subphthalocyanine in Floating Layers and Langmuir-Schaefer Films

Self-Organization of A2B Type Boron Subphthalocyanine in Floating Layers and Langmuir-Schaefer Films

Langmuir-Schaefer Perylene Derivative Films: Influence of the Molecular Chemical Structure on the Supramolecular Arrangement.

Since the optical and electrical properties of organic thin films devices depend on their supramolecular arrangement and the molecular chemical structure, the understanding of such characteristics is essential for the optimization of these devices. In this study, we determine the supramolecular arrangement of thin films produced using the Langmuir-Schaefer (LS) technique and explain how its supramolecular arrangement is affected by the molecular chemical structure using two perylene derivatives: bis-butylimide (BuPTCD) and bis-phenethylimide (PhPTCD). The optical absorption measurements reveal that both films grow homogeneously and indicate that the presence of H aggregates (forbidden emission) is higher for BuPTCD LS film than for PhPTCD LS film. Atomic force microscopic analysis shows that the PhPTCD LS film is rougher than the BuPTCD film. In addition, FTIR analyses indicate that both films have head-on molecular organization. XRD patterns reveal that both the BuPTCD LS film and the PhPTCD LS film are crystalline, but that crystallinity is more prevalent in the BuPTCD LS film. Thus, the results show that the difference presented in the chemical structures leads the films to have different supramolecular arrangements, with consequences for their optical properties.

Effect of ms-substitution on aggregation behavior and spectroscopic properties of BODIPY dyes in aqueous solution, Langmuir-Schaefer and poly(methyl methacrylate) thin films

It is well known that boron-dipyrromethene (BODIPY) dyes have a remarkable combination of photophysical and photochemical properties, which are significant for practical use. Unfortunately, the application of BODIPYs in optical devices and biosensorics is severely limited due to the aggregation quenching effect (ACQ), the effects of the internal filter and/or the formation of excimers. One way to prevent fluorescence quenching is to synthesize new molecules BODIPY with a highly complicated structural organization or hybrid systems based on them. But in this paper, we demonstrate that the introduction of simple aliphatic or aryl substituents into the ms-position of the BODIPY molecule is an effective way to control the aggregation in various states: thin mono- and multilayer Langmuir-Schaefer (LS) films, polymer films and concentrated solutions, including aqueous ones. The results of experimental studies of the aggregation behavior of BODIPYs (BDP1-BDP3) are in good agreement with the theoretical calculations data of di- and tetramers, as well as multilayer packing. This allows to adjust the spectral properties of luminophores to the most possible types of their real applications in practical areas.

Modulating photochemical reactions in Langmuir monolayers of Escherichia coli lipid extract with the binding mechanisms of eosin decyl ester and toluidine blue-O photosensitizers

Photodynamic damage to the cell envelope can inactivate microorganisms and may be applied to combat super-resistance phenomenon, empowered by the indiscriminate use of antibiotics. Efficiency in microbial inactivation is dependent on the incorporation of photosensitizers (PS) into the bacterial membranes to trigger oxidation reactions under illumination. Herein, Langmuir monolayers of Escherichia coli lipid extract were built to determine the binding mechanisms and oxidation outcomes induced by eosin decyl ester (EosDEC) and toluidine blue-O (TBO) PSs. Surface-pressure isotherms of the E. coli monolayers were expanded upon EosDEC and TBO, suggesting incorporation of both PSs. Fourier-transform infrared spectroscopy (FTIR) of Langmuir-Schaefer (LS) films reveled that the EosDEC and TBO binding mechanisms are dominated by electrostatic interactions with the anionic polar groups, with limited penetration into the chains. Light-irradiation reduced the relative area of E. coli monolayer on TBO, indicating an increased loss of material to the subphase owing to the chain cleavage, generated by contact-dependent reactions with excited states of TBO. In contrast, the increased relative area of E. coli monolayers containing EosDEC suggests lipid hydroperoxidation, which is PS contact-independent. Even considering a small chain penetration, the saturated EosDEC may have partitioned towards saturated reach domains, avoiding direct contact with membrane unsaturations.

Modulating surface plasmon resonance response by an external electromagnetic wave

We fabricated a highly sensitive layered structure of organic molecules and studied the influence of polarization of the external electromagnetic (EM) wave on the surface plasmon resonance response from the layered structure. The layered structure was formed by depositing a self-assembled monolayer (SAM) of mercaptoundecanoic acid (MUA) followed by a single layer of Langmuir-Schaefer (LS) film of traditional calamitic liquid crystal molecule, 4-octyl-4-biphenylcarbonitrile (8CB). The SAM of MUA was found to be non-responsive towards the change in resonance angle (RA) of surface plasmon resonance (SPR) due to the change in polarization of the external EM wave. However, such layer provides a soft-surface platform for the single layer of 8CB molecules which gets perturbed locally due to the incidence of the external EM wave. We obtained an oscillatory modulation of the change in RA due to the change in polarization angle of the EM wave with respect to the plane of incidence. The magnitude of sensitivity was found to be ∼4 milli°/° angle of polarization of the external EM wave. This study strongly suggests that sensitivity of a SPR-based sensor can be controlled by altering the linear state of polarization of the incident external EM wave.

Ultrathin Langmuir–Schaefer films of slipped-cofacial J-type phthalocyanine dimer: Supramolecular organization, UV/Vis/NIR study and nonlinear absorbance of femtosecond laser radiation

Based on a comprehensive theoretical and experimental approach, a low-defect thin film of stable dimeric phthalocyanine zinc complex (bis-[2-hydroxy-9(10),16(17), 23(24)-tri-tert-butylphthalocyanine]zinc – J-[OHPctZn]2) was prepared. It is shown that the dye forms stable amorphous edge-on monolayers at the air/water interface with an insignificant content of cylindrical 3D aggregates. These floating layers keep their structure when transferred by the Langmuir-Schaefer method onto a solid substrate, demonstrating a tendency towards ordered H-aggregation with preserving their linear molecular properties. Mixed two- and three-photon absorption of femtosecond laser pulses (280 fs) was firstly detected on this sample, as well as the ability of a material to the nonlinear attenuation of the intense irradiation, which is important for optical limiting.

Study of the Effect of Solvent on the Conductivity of Langmuir-Schaefer Films of Poly(Fullerene)s

The present work aims to prepare and characterize very thin films of poly(fullerene)s in order to investigate their electrical properties and the influence of xylene and chloroform solvents on these materials. The fullerenes studied were phenyl-C61-butyric acid methyl ester (PCBM), oligo{(phenyl-C61-butyric acid methyl ester)-alt-[1,4-bis(bromomethyl)-2,5-bis(octyloxy)benzene]} (OPCBMMB) and poly{[bispyrrolidino(phenyl-C61-butyric acid methyl ester)]-alt-[2,5-bis(octyloxy) benzene]} (PPCBMB), along with poly(3-hexylthiophene) (P3HT). The Langmuir-Schaeffer technique was used to prepare films, which were deposited on interdigitated gold substrates, and electrically characterized, with emphasis on the study of transport, conductivity and mobility mechanisms with respect to the solvents used. We found that the addition of P3HT significantly increased the conductivity of these materials. The xylene cast PPCBM, in both pure and mixed forms under dark conditions, presented the best conductivity results with respect to the other materials. However, when chloroform was used, it was found that OPCBMMB in both pure and mixed forms under light, exhibited the best conductivities. This is the first treatment, to our knowledge, of the impact of solvents on the electronic properties of poly(fullerene)s.

Langmuir–Schaefer films based on highly hydrophobic Eu3+tetrakis-β-diketonate complexes containing amphiphilic counterions

Langmuir-Schaefer (LS) films based on [Q][Eu(dbm)4)] complexes — where dbm− = 1,3-diphenyl-1,3-propanedionate, Q = C26H56N+ (Q1), C19H42N+ (Q2), or C17H38N+ (Q3) — using amphiphilic counterions (Q) to organize the luminescent anionic complex on the subtract have been investigated. The amphiphilic counterions play an important role in the film fabrication by increasing the surface homogeneity and deposition quality as the carbonic chain increases, especially for the [Q1][Eu(dbm)4)] film, which showed root mean square surface roughness of 37.8 nm. All films displayed the characteristic Eu3+ red-light emission under excitation at 367 nm, and the best intrinsic emission quantum yield was achieved for the [Q1][Eu(dbm)4)] film (27.5%), confirming that the counterion also influences the luminescent features of the films due to changes in the anionic complex conformation compared to the respective bulk complexes.

Ultra-thin film sensors based on porphyrin-5-ylphosphonate diesters for selective and sensitive dual-channel optical detection of mercury(II) ions

Reusable dual-channel optical sensors for Hg2+ ions were prepared by Langmuir-Schaefer (LS) method from amphiphilic (trans-A2)BC-type porphyrins functionalized at meso-positions of the tetrapyrrolic macrocycle by sterically demanding diethoxyphosphoryl and mesityl groups as well as electron donating RO, RS or RNH substituents (R = n-C8H17). These three novel amphiphilic porphyrin derivatives were synthesized in good yields and their floating films at the air⎯water interface were investigated. In these monolayers, porphyrin molecules display a slipped stack-of-card orientation, but their strong π stacking is prohibited by bulky diethoxyphosphoryl and mesityl groups. The heteroatom substituent plays a key role in the molecular organization of the monolayers because it can participate in intermolecular hydrogen bonding, which influences the monolayer structure. Sensing properties of the porphyrins organized in Langmuir monolayers differ from those in the solution environment. Selective spectrophotometric detection of Hg2+ ions by these floating films is observed because interfering Cu2+, Zn2+, Cd2+, and Pb2+ ions are coordinated to donor centers located at the periphery of the macrocycle. Transfer of these floating films onto a polyvinyl chloride surface by LS technique affords perforated multilayer films with a tight molecular coverage of the solid support. The effect of the heteroatoms on the organization of these films was demonstrated by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Both absorption and emission studies provide a strong evidence that chromophore-chromophore interactions are rather weak in these LS films. Binding of mercury(II) ions by the films and the regeneration of the sensors were explored visually and using reflection absorbance and fluorescence spectroscopies and then confirmed by X-ray fluorescence analysis. Detection limit of these selective and reusable dual-channel (absorbance and fluorescence) thin-film sensors is about 10−8 M (2 ppb), that corresponds to the action level for Hg2+ ions in drinking water recommended by the U.S. Environmental Protection Agency (EPA).