Effect Of Molecular Orientation Research Articles

On the Order and Orientation in Liquid Crystalline Polymer Membranes for Gas Separation.

To prevent greenhouse emissions into the atmosphere, separations like CO2/CH4 and CO2/N2 from natural gas, biogas, and flue gasses are crucial. Polymer membranes gained a key role in gas separations over the past decades, but these polymers are often not organized at a molecular level, which results in a trade-off between permeability and selectivity. In this work, the effect of molecular order and orientation in liquid crystals (LCs) polymer membranes for gas permeation is demonstrated. Using the self-assembly of polymerizable LCs to prepare membranes ensures control over the supramolecular organization and alignment of the building blocks at a molecular level. Robust freestanding LC membranes were fabricated that have various, distinct morphologies (isotropic, nematic cybotactic, and smectic C) and alignment (planar and homeotropic), while using the same chemical composition. Single gas permeation data show that the permeability decreases with increasing molecular order while the ideal gas selectivity of He and CO2 over N2 increases tremendously (36-fold for He/N2 and 21-fold for CO2/N2) when going from randomly ordered to the highly ordered smectic C morphology. The calculated diffusion coefficients showed a 10-fold decrease when going from randomly ordered membranes to ordered smectic C membranes. It is proposed that with increasing molecular order, the free volume elements in the membrane become smaller, which hinders gasses with larger kinetic diameters (Ar, N2) more than gasses with smaller kinetic diameters (He, CO2), inducing selectivity. Comparison of gas sorption and permeation performances of planar and homeotropic aligned smectic C membranes shows the effect of molecular orientation by a 3-fold decrease of the diffusion coefficient of homeotropic aligned smectic C membranes resulting in a diminished gas permeation and increased ideal gas selectivities. These results strongly highlight the importance of molecular order and orientation in LC polymer membranes for gas separation.

Effect of morphology and molecular orientation on environmental water biodegradability of poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate

The biodegradation behaviors of several forms of poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] (P(3HB-co-3HV)) in seawater and freshwater, namely, powder, cast film, undrawn fiber, and fivefold-drawn fiber, were analyzed via biochemical oxygen demand, weight loss, and scanning electron microscopy measurements. The powder showed the highest degradation rate, attributed to its larger surface area, which allows microorganisms to attach to the surface and form a biofilm that begins to degrade sooner. The fivefold-drawn fibers degraded more slowly than the undrawn fibers owing to the higher crystallinity caused by the orientation of the former. Moreover, the degradation results of the fivefold-drawn fibers in seawater and freshwater showed that the degradation rate depended on the number of microorganisms in both environmental water types. The analysis of the degradation behavior in the freshwater revealed that the crystalline and amorphous phases in the film degraded simultaneously, whereas the degradation of the fibers started from the amorphous phase, followed by the crystalline phase.

Active Control of Spontaneous Orientation Polarization of Tris(8‐hydroxyquinolinato)aluminum (Alq3) Films and Its Effect on Performance of Organic Light‐Emitting Diodes

AbstractVacuum‐deposited amorphous organic films with an anisotropic amorphous structure are known to exhibit spontaneous orientation polarization (SOP). In this study, amorphous structures of tris(8‐hydroxyquinolinato)aluminum (Alq3) films are controlled by substrate temperature (Tsub) during vacuum deposition. The effect of density, molecular orientation, and SOP of Alq3 films on the performance of organic light‐emitting diodes (OLEDs) is comprehensively investigated. The SOP of Alq3 films is significant at low Tsub and becomes weaker as Tsub increases. The presence of SOP certainly improves electron injection from a metal cathode and, therefore, increases the current in OLEDs. External quantum efficiencies (EQEs) of OLEDs are increased by ≈40% when Tsub for the Alq3 deposition is increased from 260 to 328 K. The increased EQEs are attributed to several factors, which include not only increased photoluminescence quantum yields and light outcoupling efficiencies but also suppressed singlet‐polaron annihilation originating from the reduced SOP. Operational stability of OLEDs is also affected by Tsub and becomes the highest when Alq3 layers are vacuum‐deposited at Tsub = 299 K. These findings indicate the importance of controlling organic amorphous structures and SOP in films to maximize OLED performance and contribute to a better understanding of working mechanisms of OLEDs.

Precursor state of chemi-ionization reactions and confinement of valence electrons by anisotropic intermolecular forces

Modifications in atomic alignment and in molecular alignment/orientation determine a different structure of the adduct, formed by collisions of reagents, which represents the precursor state of many elementary chemical–physical processes. The following evolution of the system is directly controlled by the confinement of interacting partners in such a precursor state. However, a deep characterization of these phenomena is still today not fully available, especially when weak intermolecular forces are operative, although the inquiry is of general relevance for the control of the stereodynamics of processes, occurring under a variety of conditions both in gas phase and at surface. In this paper recent advances in the knowledge of the selective role of atomic alignment and molecular orientation effects on the stereodynamics of chemi-ionization reactions will be presented and discussed. These advances represent a basic step along a path whose final target is the complete and internally consistent rationalization and revaluation of the experimental findings already obtained, and published, in our and in other laboratories on chemi-ionization reactions involving as reagent molecules which are of great relevance in several fields. The basic idea is to export important guidelines provided by a recent detailed study of chemi-ionization of noble gas atoms to more complex reactions involving molecules. The main focus of the present paper is on the quantum confinement effects of valence electrons within the reaction transition state.Graphic abstract

KMap.py: A Python program for simulation and data analysis in photoemission tomography

Ultra-violet photoemission spectroscopy is a widely-used experimental technique to investigate the valence electronic structure of surfaces and interfaces. When detecting the intensity of the emitted electrons not only as a function of their kinetic energy, but also depending on their emission angle, as is done in angle-resolved photoemission spectroscopy (ARPES), extremely rich information about the electronic structure of the investigated sample can be extracted. For organic molecules adsorbed as well-oriented ultra-thin films on metallic surfaces, ARPES has evolved into a technique called photoemission tomography (PT). By approximating the final state of the photoemitted electron as a free electron, PT uses the angular dependence of the photocurrent, a so-called momentum map or k-map, and interprets it as the Fourier transform of the initial state’s molecular orbital, thereby gaining insights into the geometric and electronic structure of organic/metal interfaces.In this contribution, we present kMap.py which is a Python program that enables the user, via a PyQt-based graphical user interface, to simulate photoemission momentum maps of molecular orbitals and to perform a one-to-one comparison between simulation and experiment. Based on the plane wave approximation for the final state, simulated momentum maps are computed numerically from a fast Fourier transform (FFT) of real space molecular orbital distributions, which are used as program input and taken from density functional calculations. The program allows the user to vary a number of simulation parameters, such as the final state kinetic energy, the molecular orientation or the polarization state of the incident light field. Moreover, also experimental photoemission data can be loaded into the program, enabling a direct visual comparison as well as an automatic optimization procedure to determine structural parameters of the molecules or weights of molecular orbitals contributions. With an increasing number of experimental groups employing photoemission tomography to study molecular adsorbate layers, we expect kMap.py to serve as a helpful analysis software to further extend the applicability of PT. Program summaryProgram Title:kMap.pyCPC Library link to program files:https://doi.org/10.17632/tnrm9jcccc.1Developer’s respository link:https://github.com/brands-d/kMap/Code Ocean capsule:https://codeocean.com/capsule/5788845Licensing provisions: GPLv3Programming language: Python 3.xNature of problem: Photoemission tomography (PT) has evolved as a powerful experimental method to investigate the electronic and geometric structure of organic molecular films [1]. It is based on valence band angle-resolved photoemission spectroscopy and seeks an interpretation of the angular dependence of the photocurrent, a so-called momentum map, from a given initial state in terms of the spatial structure of molecular orbitals. For this purpose, PT heavily relies on a simulation platform which is capable of efficiently predicting momentum maps for a variety of organic molecules, which allows for a convenient way of treating the effect of molecular orientations, and which also accounts for other experimental parameters such as the geometrical setup and nature of the incident photon source. Thereby, PT has been used to determine molecular geometries, gain insight into the nature of the surface chemistry, unambiguously determine the orbital energy ordering in molecular homo- and heterostructures and even reconstruct the orbitals of adsorbed molecules [1–4].Solution method:kMap.py is a Python program that enables the user, via a PyQt-based graphical user interface, to simulate photoemission momentum maps of molecular orbitals and to perform a one-to-one comparison between simulation and experiment. Based on the plane wave approximation for the final state, simulated momentum maps are computed numerically from a fast Fourier transform (FFT) of real space molecular orbital distributions [2] which are used as program input and which are usually obtained from density functional calculations. The user can vary a number of simulation parameters such as the final state kinetic energy, the molecular orientation or the polarization state of the incident light field. Moreover, also experimental photoemission data can be loaded into the program, enabling a direct visual comparison as well as an automatic optimization procedure to minimize the difference between simulated and measured momentum maps. Thereby, structural parameters of the molecules [2] and the weights of molecular orbitals to experimentally observed emission features can be determined [3].

Revealing the effects of molecular orientations on the azo-coupling reaction of nitro compounds driven by surface plasmonic resonances.

A recent report on the azo coupling of 4-nitrobenzo-15-crown-ether (4NB15C) and 4-nitrothiophenol (4NTP) indicated that the reaction barrier could be reduced greatly with surface plasmonic effects on silver dendritic nanostructures in aqueous solution. Accordingly, an azo coupling reaction mechanism was proposed based on one or two SERS peaks. Toward a profound understanding of this azo coupling reaction mechanism, it is crucial to scrutinize the origin of the full SERS spectrum. Here, we construct a molecular model consisting of 4NTP and 4NB15C on an Ag7 cluster that simulates a silver dendritic nanostructure, and investigate the SERS spectra of the azo coupling of these two molecules. We propose five different adsorption sites and 13 different orientations of 4NTP on the Ag7 cluster and optimize the geometries of the five configurations. With each optimized configuration of 4NTP adsorbed on Ag7, we further consider the azo coupling product with a 4NB15C molecule and simulate the corresponding Raman spectra. Comparing the measured Raman spectra and model analysis, we conclude that the azo coupling reaction depends decisively on a parallel molecular orientation of the adsorbed 4NTP relative to the facets of Ag7, the orientation of which further directs the subsequent reaction for the product of 4NB15C-4NTP.

Computational Study of the Precursor Spectroelectrochemistry of Guanine

Precursor spectroelectrochemical behavior of guanine is investigated based on UV-Vis absorption and fluorescence, and IR and Raman spectra of guanine and its radical cation in the presence of a model electrode, computed using (TD)M06/6-31++G** method. Effects of electrode potential ( ), molecule-electrode distance (d) and molecular orientations (θ) on this behavior are investigated. Results indicate that application of electric potential causes changes in the molecular structure and distribution of charge and spin densities, which consequently changes the electronic and vibrational characteristics of the system. Also, perturbation due to the applied electric potential, changes both the intensities and frequencies of the vibrational bands of the studied species. The absorption wavelength, and the peak intensity and width of the electronic spectra of guanine and its radical cation also show sensitivity to the applied electrode potential. Presence of solvent both as electrostatic medium and as explicit solvent (molecules) have significant effects on the spectroelectrochemical properties of guanine, and change the chemical activity of guanine radical cation formed by the electrode reaction. Furthermore, population and orbital analyses show that for all orientations, application of the electric potential by the electrode increases contribution of the inter-molecular (guanine→water) charge density displacement to the UV-Vis transitions.

Effects of molecular axis orientation of MeV diatomic projectiles on secondary ion emission from biomolecular targets

We report first experimental results on the orientation effect of fast diatomic molecular projectiles on secondary ion emission processes for 3.6-MeV C2+ traversing a self-supporting target of phenylalanine (Phe) film evaporated on a carbon foil. Coincidence measurements were performed on the image of fragments resulting from the Coulomb explosion of C2+ projectiles and the time-of-flight mass spectrometry of secondary ions emitted from the Phe film. We compared the secondary ion yield for C2+ projectiles with parallel and perpendicular orientations to the beam direction. The parallel orientation was found to enhance the secondary ion yield by a factor of approximately 1.1 compared with that for the perpendicular orientation. This enhancement corresponds to an increase in the average charge of Coulomb-exploded fragments. This finding implies that there is a linear correlation between the electronic energy deposition causing secondary ion production and the effective charge number of the incident molecular ions which interact with biomolecular targets.

Multielectron Effect for High-Order Harmonic Generation From Molecule Irradiated by Bichromatic Counter-Rotating Circularly Polarized Laser Pulses

We investigated high-order harmonic generation in molecules N2 and C6H6 irradiated by bichromatic counter-rotating circularly polarized laser pulses by using time-dependent density-functional theory methods. It is found that $3N$ ( $N$ is an integer) order harmonics in C6H6 disappear. Whereas, $N$ order harmonics are obtained in N2. Analysis of the high harmonic generated from individual electronic orbital of the molecule, shows that, the characteristics of harmonic spectra are determined by the spatial distribution of electronic orbits. Moreover, effects of molecular orientation on harmonic emission are also presented.

Discrimination between two distinct nonlinear effects by polarization-resolved Z-scan measurements.

We investigated how the Z-scan technique can be explored to distinguish two types of nonlinear refractive effects by employing two distinct laser polarizations. It is possible that pure electronic, molecular orientation and thermal nonlinear effects may occur simultaneously during light-matter interaction. We found a way to discriminate and quantify two distinct nonlinear processes from Z-scan signals measured with linear and circular polarizations. This paper provides analytical equations for nonlinear refractions and in order to test them, we carried out measurements in CS2 and in a rhodamine-B solution, where electronic and orientational, and electronic and thermal nonlinearities mixing, respectively, are present.

Reconstruction of low-resolution molecular structures from simulated atomic force microscopy images

BackgroundAtomic Force Microscopy (AFM) is an experimental technique to study structure-function relationship of biomolecules. AFM provides images of biomolecules at nanometer resolution. High-speed AFM experiments produce a series of images following dynamics of biomolecules. To further understand biomolecular functions, information on three-dimensional (3D) structures is beneficial. MethodWe aim to recover 3D information from an AFM image by computational modeling. The AFM image includes only low-resolution representation of a molecule; therefore we represent the structures by a coarse grained model (Gaussian mixture model). Using Monte-Carlo sampling, candidate models are generated to increase similarity between AFM images simulated from the models and target AFM image. ResultsThe algorithm was tested on two proteins to model their conformational transitions. Using a simulated AFM image as reference, the algorithm can produce a low-resolution 3D model of the target molecule. Effect of molecular orientations captured in AFM images on the 3D modeling performance was also examined and it is shown that similar accuracy can be obtained for many orientations. ConclusionsThe proposed algorithm can generate 3D low-resolution protein models, from which conformational transitions observed in AFM images can be interpreted in more detail. General significanceHigh-speed AFM experiments allow us to directly observe biomolecules in action, which provides insights on biomolecular function through dynamics. However, as only partial structural information can be obtained from AFM data, this new AFM based hybrid modeling method would be useful to retrieve 3D information of the entire biomolecule.

Anisotropic photoconductivity of aromatic and semi-aliphatic polyimide films: Effects of charge transfer, molecular orientation, and polymer chain packing

The anisotropic photoconductive properties of polyimide (PI) films prepared using seven types of dianhydrides and a diamine containing a diphenyl-benzidine structure featuring rigid linear structure and strong electron-donating ability were analyzed. Photoirradiation wavelength dependences of the in-plane and out-of-plane photocurrents, which are known as anisotropic photocurrent spectra, were investigated in comparison with optical absorption spectra, the degrees of molecular aggregation, in-plane/out-of-plane orientation of PI chains, and ordered structures formed in film state. We have previously reported that intermolecular charge transfer (CT) interaction is a key factor for increasing the out-of-plane photoconductivity of PI films because they determine the efficiency of charge separation. However, when sufficient charge carriers are generated in thin PI films via photo irradiation, in which penetration depth of irradiated light is sufficiently larger than the film thickness, suppression of charge recombination by reducing molecular chain packing is rather effective at enhancing both the in-plane and out-of-plane photoconductivity. This is because the mobility of carriers is significantly increased in the dense aggregation structures, and thus collisions between carriers becomes more frequent, which led to higher recombination efficiency. Furthermore, the photocurrent anisotropy was increased as the degree of in-plane orientation of the main PI chains increased, which agrees with the fact that charged carriers are preferentially transported between PI chains. Accordingly, promoting charge transport efficiency by reducing PI chain packing and increasing the out-of-plane orientation of PI chains are essential to increase the in-plane photoconductivity of PI films.

Effect of Molecular Orientation to Proton Conductivity in Sulfonated Polyimides with bent backbones

Two organized sulfonated polyimides (ASPIs) with bent polymer backbones were synthesized to study a relation between structure and proton conductivity. Proton conductivity exhibited different values between the thin film and bulk pelletized forms. Results from small-angle X-ray scattering (SAXS) and attenuated total reflection measurements suggest that the orientation of backbones is different between the thin film and bulk forms. SAXS results suggest excess amount of water uptake in the bulk samples compared to the thin film form. These structure and water uptake property could contribute the difference of the proton conductivity between the thin film and bulk pelletized forms.

Silver films coated inverted cone-shaped nanopore array anodic aluminum oxide membranes for SERS analysis of trace molecular orientation

Abstract Reproducible surface enhanced Raman scattering (SERS) enhanced performance, affected by molecular orientations in plasmonic nanostructures, attracts more attention than SERS detection sensitivity for satisfying requirements of practical applications. In this work, by coating silver films on the inverted cone-shaped nanopore array anodic aluminum oxide membranes, we provide a way to study the effect of molecular orientations on SERS enhancement with mapping technology. SERS enhanced performance of the fabricated substrates is assessed with trace Rhodamine 6G detection, enhancement factor calculation and 3D finite-difference time-domain simulation respectively. It is found that inverted cone-shaped nanopore and silver films both contribute to the highly SERS enhancement. And special inverted cone-shaped nanopore plasmonic structures limit molecular vibrations so as to affect Raman scattering enhancement. These findings can help us to understand the electromagnetic mechanism of molecular orientations on SERS enhancement, so as to design highly reproducible SERS substrates for various applications.

Correction to Effects of Molecular Orientation of a Fullerene Derivative at the Donor/Acceptor Interface on the Device Performance of Organic Photovoltaics

Correction to Effects of Molecular Orientation of a Fullerene Derivative at the Donor/Acceptor Interface on the Device Performance of Organic Photovoltaics

Efficient high harmonic generation of bromine molecule by controlling the carrier-envelope phase and polarization of driving laser pulse

The generation of ultrashort attosecond pulse requires both an enhanced high harmonic generation and the spectral-phase control. In the present work, an efficient method is theoretically investigated for extending HHG cutoff energy in Br2 molecule using TDDFT. The effects of molecular orientation and carrier-envelope phase of the laser on the high harmonic spectrum are analyzed. As a result, by the fine modulations of the laser field, the harmonic plateau is enlarged and the position of structure-induced interference minimum shifts. We also provide a physical picture on the intensity dependence of the spectral minima in the harmonic spectra.

Effects of Molecular Orientation of a Fullerene Derivative at the Donor/Acceptor Interface on the Device Performance of Organic Photovoltaics

Designing donor/acceptor (D/A) interfaces that can efficiently generate free carriers is an attractive research target for organic photovoltaics (OPVs). While many reports suggest that the molecular orientation of the donor at the D/A interface influences the free-charge generation and recombination, the effects of the acceptor orientation on these processes remain elusive. In this work, we demonstrate that [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) changes its molecular orientation at the film surface on crystallization, resulting in the preferential surface exposure of the side chains. Photoelectron spectra of amorphous- and crystalline-PC61BM/sexithiophene (6T) interfaces and analysis of the external quantum efficiency and electroluminescence of bilayer OPVs in the charge-transfer absorption range reveal that the orientational change of PC61BM raises the energy of the charge-transfer state at the D/A interface. In addition, the PC61BM side chain at the crystalline-PC61BM/6T interface reduces t...

A Discrete Interaction Model/Quantum Mechanical Method for Simulating Plasmon-Enhanced Two-Photon Absorption.

In this work, we extend the discrete interaction model/quantum mechanical (DIM/QM) method to simulate plasmon-enhanced two-photon absorption (PETPA). The metal nanoparticle is treated atomistically by means of electrodynamics, while the molecule is described using damped cubic response theory within a time-dependent density functional theory framework. Using DIM/QM, we study the PETPA of para-nitroaniline ( p-NA) with a focus on the local and image field effects, the molecular orientation effects, and the molecule-nanoparticle distance effects. Our findings show that the enhancement is more complex than the simple | E|4 enhancement mechanism, where | E| is the local field at the position of the molecule. Because of specific interactions with the nanoparticle, we find that a TPA dark state of p-NA can be significantly enhanced through a coupling with the plasmon excitation. The results presented in this work illustrate that the coupling between molecular excitations and plasmons can give rise to unusual and complex behavior in nonlinear spectroscopy that cannot simply be understood by considering the optical properties of the individual molecules and nanoparticles separately. The method presented here provides detailed insights into the enhancement of nonlinear optical properties of molecules coupled to plasmonic nanoparticles.

Come Together: Molecular Details into the Synergistic Effects of Polymer-Surfactant Adsorption at the Oil/Water Interface.

The synergistic adsorption of polymers with surfactants at the oil/water interface has applications that range from oil remediation to targeted drug delivery. However, the inherent inaccessibility of the buried oil/water interface has challenged the development of a molecular-level understanding of the structure-function relationship of these systems. This study uses vibrational sum frequency spectroscopy to examine the molecular structure, orientation, and electrostatic effects of synergistic adsorption of the surfactant cetrimonium bromide (CTAB) and polymer poly(acrylic acid) (PAA) at a planar oil/water interface. Results demonstrate that coadsorption leads to a high degree of interfacial ordering of both the polymer and the surfactant and a subsequent alteration of the interfacial water bonding and orientation. Complementary zeta potential measurements provide further information about how surface partitioning of a charged polymer and a surfactant relates to their aggregation behavior in a bulk solution. With the CTAB concentration fixed but the PAA concentration variable, hydrophobic interactions result in a modest synergic coadsorption when CTAB is in excess. However, when the PAA carboxylate monomer concentration approaches that of CTAB, the electrostatic interactions between the components change the structure and increase the amount of adsorbed PAA until the interfacial charge is neutralized. This work reveals that the synergic adsorption behavior of this model polyacid/surfactant system arises from a combination of concentration-dependent hydrophobic and electrostatic forces working in tandem.

Effects of ultrasonic injection molding conditions on the plate processing characteristics of PMMA

Abstract Polymer processing is a crucial and diverse field in the manufacturing industry. We investigated the process characteristics and effects of injection molding using ultrasonic vibration. An ultrasonic device was installed in an injection mold; polymer was directly vibrated during injection. An ultrasonic oscillation device 45 mm in diameter was placed in the cavity and used to vibrate a poly(methyl methacrylate) melt at 19 kHz. The amplitude of the acoustic unit was set at 15 μm for the measurements. Moreover, cavity pressure sensors were positioned at the front and rear sides of the vibration region to determine the melt flow behavior under ultrasonic-assisted injection molding conditions. Because of the absorption of ultrasonic energy, local heat was generated inside the resin, thus improving the flow characteristics of the melt. Moreover, the melt flow behavior around the skin layer was changed; the molecular orientation and high shear effect were reduced. Furthermore, the freezing rate of the melt was reduced; thus, the amount of melt pressure lost through the cavity was decreased and the residual stress inside the injection-molded component generated during the photoelastic stress analysis was lower.