Net Dipole Moment Research Articles

Theoretically grounded approaches to account for polarization effects in fixed-charge force fields.

Non-polarizable, or fixed-charge, force fields are the workhorses of most molecular simulation studies. They attempt to describe the potential energy surface (PES) of the system by including polarization effects in an implicit way. This has historically been done in a rather empirical and ad hoc manner. Recent theoretical treatments of polarization, however, offer promise for getting the most out of fixed-charge force fields by judicious choice of parameters (most significantly the net charge or dipole moment of the model) and application of post facto polarization corrections. This Perspective describes these polarization theories, namely the "halfway-charge" theory and the molecular dynamics in electronic continuum theory, and shows that they lead to qualitatively (and often, quantitatively) similar predictions. Moreover, they can be reconciled into a unified approach to construct a force field development workflow that can yield non-polarizable models with charge/dipole values that provide an optimal description of the PES. Several applications of this approach are reviewed, and avenues for future research are proposed.

Quantum phase transitions and cat states in cavity-coupled quantum dots

We study double quantum dots coupled to a quasistatic cavity mode with high mode-volume compression allowing for strong light-matter coupling. Besides the cavity-mediated interaction, electrons in different double quantum dots interact with each other via dipole-dipole (Coulomb) interaction. There is a first-order cavity-induced ferroelectric quantum phase transition when the attractive dipolar interaction is smaller than the critical value defined by the energy splitting in DQDs and a smooth transition, otherwise. We show that, in the smooth transition region, both the ground and the first excited states of an array of double quantum dots are cat states. Such states are actively discussed as high-fidelity qubits for quantum computing, and thus our proposal provides a platform for semiconductor implementation of such qubits. We also calculate gauge-invariant observables such as the net dipole moment, the optical conductivity, and the absorption spectrum beyond the semiclassical approximation. The results are robust against cavity losses and variations of system parameters. Published by the American Physical Society 2024

Janus-type BN-embedded perylene diimides via a “shuffling” strategy: Regioselective functionalizable building block towards high-performance n-type organic semiconductors

Regioselevtive functionalization of perylene diimides (PDIs) at bay area often requires multistep synthesis and strenuous recrys-tallization. Direct bromination of perylene diimides only afford the 1,6 and 1,7-regioisomers. More importantly, the 1,6-dibromo regioisomers could only be separated by preparative HPLC. Herein, we report a promising strategy for constructing Janus back-bones of BN-doped perylene diimide derivatives. This Janus-type configuration results in the unique regioselective functionalization of BN-JPDIs, which yields exclusively the 1,6-regioisomers. Further investigation shows that the Janus-type configuration leads to a net dipole moment of 1.94 D and intramolecular charge transfer, which causes substantial changes on the optoelectronic properties. Moreover, the single crystal organic field-effect transistors based on BN-JPDIs exhibit electron mobilities up to 0.57 cm2 V−1 s−1, showcasing their potential as versatile building block towards high-performance n-type organic semiconductors.

Segmental and Chain Dynamics of Polyisoprene-Based Model Vitrimers.

Polymer vitrimers are a new class of materials that combine the advantages of thermoplastics and thermosets. This is due to the dynamic nature of the chemical bonds linking different chains. However, how this property affects the polymer dynamics at different length scales is still an open question. Here, we investigate the dynamics of model vitrimers based on well-defined polyisoprene (PI) chains using broadband dielectric spectroscopy. In this way, we study the polymer dynamics from the segmental to the whole chain scale, taking advantage of the fact that PI belongs to the class of molecules that exhibit a net dipole moment associated with the end-to-end vector. Three distinct relaxation phenomena are identified. The fastest relaxation is attributed to the segmental PI dynamics with a small influence of the cross-linking. An intermediate relaxation attributed to the dipolar character of the cross-linker is also observed. The slower identified relaxation component, corresponding to limited fluctuations of the end-to-end PI chains, is found to be determined by the dynamics of the clusters formed by the cross-linkers with an average time scale orders of magnitude faster than that of the terminal relaxation as inferred from the viscous flow.

Probing the in-plane dipole moment vector between ground and excited state of single molecules by the Stark effect.

Single molecules, embedded inside a well-defined insertion site of a single-crystalline host matrix, are sensitive probes of electric field via the induced Stark shift on their lifetime-limited electronic transition. Though the response of molecules to electric field has been shown to be relatively homogeneous, crystal symmetry allows for several, spectroscopically-indistinguishable, orientations of the net permanent dipole moment between the ground and excited state - the dipole vector - and this is problematic for measuring field orientation and magnitude. In this work, we measure for each terrylene molecule, embedded inside a new host matrix, the dipole vector independently by an electric field that we can rotate in the plane of the crystal. This single crystal host matrix, called [1]BenzoThieno[3,2-b]BenzoThiophene, induces a moderate symmetry breaking of the embedded centrosymmetric terrylene molecule, and gives rise to a net dipole moment of 0.28±0.09 Debye. Based on quantum chemistry calculations we propose an insertion site that best matches the experimental findings.

Understanding Solvent‐Induced Delamination and Intense Water Adsorption in Janus Transition Metal Dichalcogenides for Enhanced Device Performance

AbstractRecently, there has been considerable interest in 2D Janus transition metal dichalcogenides owing to their unique structure that exhibits broken mirror symmetry along the out‐of‐plane direction, which offers fascinating properties that are applicable in various fields. This study investigates the issue of process instability in Janus MoSSe, which is mainly caused by its nonzero net dipole moments. It systematically investigates whether the built‐in dipole moments in Janus MoSSe make it susceptible to delamination by most polar solvents and increase its vulnerability to intense moisture adsorption, which leads to the deterioration of its semiconducting properties. To address these issues, as an example of device applications, field‐effect transistors (FETs) based on a van der Waals heterostructure are devised, where the bottom h‐BN (top h‐BN) insulating material is employed to prevent delamination (adsorption of moisture). The fabricated FETs exhibit improved electron mobility and excellent stability under ambient conditions.

Tunable high-Q metasurface for terahertz optical switching and sensing

We designed a metasurface for sensing and optical switching using an E-shaped bulk Dirac semimetal (BDS). The numerical results show that an extremely narrow Fano resonance can be achieved when terahertz waves are incident on the metasurface. At the Fano resonance frequency, the directions of the currents on the E-shaped BDS point towards the centre part, resulting in direct cancellation of the net dipole moment and suppression of electromagnetic dipole radiation. Owing to the overlap of the LSPR and diffraction mode frequencies on the E-shaped BDS, strong coupling can be achieved, resulting in photon energy confinement into the lattice units. In terms of tunable performance, by changing the Fermi energy of the BDS, narrowband optical switching with a modulation depth of 92.9% can be realised. In terms of sensing performance, our design is capable of achieving a sensitivity of 0.7 THz/RIU and FOM of 1178. In addition, our design is easier to prepare in the future by only consisting of E-shaped BDS and silicon substrate. The proposed design opens up possibilities for the development of multifunctional and ultrasensitive terahertz sensors, filters, and optical switching.

Thermodynamics and spectroscopic properties of C2H5CONH2 found in Sagittarius B2(N1)

Thermodynamics and spectroscopic properties of low-lying isomers of propionamide (C2H5CONH2) have been investigated employing density functional theory and high-level coupled-cluster (CC) method. Isomer 1 (Propionamide) is found to be the thermodynamically most stable, while 2 (N, N-dimethylformamide) and 3 (1-aminopropan-2-one) lie 0.63 and 0.79 eV, respectively above 1 at CCSD/cc-pVTZ level of theory. Spectroscopic parameters such as rotational and centrifugal distortion constants, inertial axis dipole moment components, net dipole moments have been calculated using ωB97XD/cc-pVQZ and ae-CCSD(T)/cc-pVTZ methods. Molecular properties such as ionization potential, electron affinity, chemical potential, electronegativity, global hardness and softness, electrophilicity index, etc. have also been evaluated at ae-CCSD(T)/cc-pVTZ level.

Nematic Phase of Polar Unsymmetrical Bent-Core Molecules.

In liquid crystalline systems, the presence of polar groups at lateral or terminal positions is fundamentally and technologically important. Bent-core nematics composed of polar molecules with short rigid cores usually exhibit highly disordered mesomorphism with some ordered clusters that favourably nucleate within. Herein, we have systematically designed and synthesized two new series of highly polar bent-core compounds comprised of two unsymmetrical wings, highly electronegative -CN and -NO2 groups at one end, and flexible alkyl chains at the other end. All the compounds showed a wide range of nematic phases composed of cybotactic clusters of smectic-type (Ncyb ). The birefringent microscopic textures of the nematic phase were accompanied by dark regions. Further, the cybotactic clustering in the nematic phase was characterized via temperature-dependent XRD studies and dielectric spectroscopy. Besides, the birefringence measurements demonstrated the ordering of the molecules in the cybotactic clusters upon lowering the temperature. DFT calculations illustrated the favourable antiparallel arrangement of these polar bent-core molecules as it minimizes the large net dipole moment of the system.

Dipole alignment of water molecules flowing through a carbon nanotube

The flow of water through nanochannels has promising applications in desalination, energy conversion, and nanomedicine. We have used molecular dynamics simulations to show that the water molecules passing through a wide single-walled carbon nanotube (CNT) get aligned by the flow to have a net dipole moment along the flow direction. With increasing flow velocity, the net dipole moment first increases and eventually saturates to a constant value. This behavior is similar to that of an Ising chain with the flow velocity acting as an effective aligning field. We show that the microscopic origin of this behavior is the preferential entry of water molecules with their dipole vectors pointing inward along the CNT axis.

Sign reversal of the spontaneous and induced polarisation in a mixture of achiral liquid crystal host and chiral azo dopant

ABSTRACT Achiral liquid crystal, possessing orthogonal smectic A and tilted smectic C phases in its phase sequence, was doped with a chiral photochromic azo dopant. It was found that the spontaneous and induced polarisation in the tilted smectic C* phase and in the orthogonal smectic A phase, respectively, change their sign, as well as their magnitude, under illumination with UV light. The origin of this sign reversal effect is considered to be the different sign of the molecular net dipole moment component µy of trans- and cis-isomers of the photochromic azo dopant, respectively. This light-induced sign reversal effect seems to have large potential for applications in the light-light controlled photonic liquid crystal devices, based on this effect.

Rational design of stapled antimicrobial peptides.

The global increase in antimicrobial drug resistance has dramatically reduced the effectiveness of traditional antibiotics. Structurally diverse antibiotics are urgently needed to combat multiple-resistant bacterial infections. As part of innate immunity, antimicrobial peptides have been recognized as the most promising candidates because they comprise diverse sequences and mechanisms of action and have a relatively low induction rate of resistance. However, because of their low chemical stability, susceptibility to proteases, and high hemolytic effect, their usage is subject to many restrictions. Chemical modifications such as D-amino acid substitution, cyclization, and unnatural amino acid modification have been used to improve the stability of antimicrobial peptides for decades. Among them, a side-chain covalent bridge modification, the so-called stapled peptide, has attracted much attention. The stapled side-chain bridge stabilizes the secondary structure, induces protease resistance, and increases cell penetration and biological activity. Recent progress in computer-aided drug design and artificial intelligence methods has also been used in the design of stapled antimicrobial peptides and has led to the successful discovery of many prospective peptides. This article reviews the possible structure-activity relationships of stapled antimicrobial peptides, the physicochemical properties that influence their activity (such as net charge, hydrophobicity, helicity, and dipole moment), and computer-aided methods of stapled peptide design. Antimicrobial peptides under clinical trial: Pexiganan (NCT01594762, 2012-05-07). Omiganan (NCT02576847, 2015-10-13).

Synthesis and Characterizations of Novel Isatin-s-Triazine Hydrazone Derivatives; X-ray Structure, Hirshfeld Analysis and DFT Calculations

A novel series of isatin-s-triazine hydrazone derivatives has been synthesized and reported herein. The synthetic methodology involved the reaction of s-triazine hydrazine precursors with isatin derivatives in the presence of CH3COOH as a catalyst and EtOH as solvent to afford the corresponding target products 6a-e in high yields and purities. The characterization data obtained from elemental analysis, FT-IR, NMR (1H- and 13C-) were in full agreement with the expected structures. Furthermore, an X-ray single crystal diffraction study of one of the target s-triazine hydrazone derivatives, 6c confirmed the structure of the desired compounds. It crystallized in the triclinic crystal system and P-1 space group with a = 10.3368(6) Å, b = 11.9804(8) Å, c = 12.7250(5) Å, α = 100.904(4)°, β = 107.959(4)° and γ = 109.638(6)°. The different non-covalent interactions which contributed in the molecular packing of 6c were analyzed using Hirshfeld analysis. The molecular packing of the organic part of the crystal structure showed important O…H (7.1%), C…H (16.4%), C…C (1.6%), H…H (34.8%), N…H (8.0%) and C…N (4.0%) interactions while for the crystal solvent, the O…H (21.3%), H…H (61.2%) and N…H (8.1%) contacts are the most significant. The studied compound 6c is polar and has a net dipole moment of 5.6072 Debye based on DFT study.

Density Functional Studies of Hydroxychloroquine and Chloroquine Reveals Higher Reactivity and Potential of Anionic Form of Hydroxychloroquine

AbstractDensity functional (B3LYP)/6‐31G calculations have been performed on the electronic structure of neutral, cationic, and anionic from of hydroxychloroquine and chloroquine. Net atomic charges, bond length, dipole moment, and total energy of hydroxychloroquine and chloroquine are compared in order to explore the finer details of these molecules. Comparison shows that redistribution of charges on anionic form of hydroxychloroquine is over larger range as compared to other forms hydroxychloroquine and chloroquine, which favors the experimental results of pharmacokinetic studies.

Orientation-Dependent Image Dipole Interaction for the Tuning of the Excitonic Properties of CdSe Nanoplatelets

The fundamental characteristics of semiconductor nanoplatelets (NPLs) have been intensively studied with a view to their use in various optoelectronic devices. In particular, the assembly of highly anisotropic NPLs into stacks allows their optical properties to be easily controlled. Here, we systematically investigate the radiative decay processes of NPL assemblies for two distinct configurations, face-down and edge-up, and find a new way of manipulating their excitonic properties by introducing metamaterial structures. While the exciton lifetime for face-down NPLs is not strongly affected by the metamaterials, a significant reduction in the exciton lifetime for edge-up NPLs is observed. We account for this interesting result in terms of orientation-dependent image dipole interactions by showing that the net transition dipole moments for the two NPL configurations can be affected inversely by metamaterials. These results will facilitate the development of optoelectronic applications requiring the active manipulation of exciton lifetimes.

CO2 Dipole Moment: A Simple Model and Its Implications for CO2-Rock Interactions

CO2 is a widespread fluid naturally occurring within the Earth crust or injected in deep strata for technological issues such as Carbon Capture and Storage (CCS). At STP conditions, CO2 is a gas, with a net zero dipole moment. Growing pressures produce an increase in its density. The reduced intermolecular distance causes a variation in the molecular structure, due to the intensification of mutual interactions. Some published spot data reveal the departure from the planarity of the bond angle while others provide few values of the CO2 dipole moment. Based on a small amount of literature-measured angle values, it was possible first to extrapolate a correlation between bond angle and density (R2 = 0.879). By fixing the partial charges distribution, we present a simple model that allows the calculation of the CO2 dipole moment directly from the geometry of the molecule, in the range of 179–162 degrees, 1-degree step. Results give values up to about 1 D. Being aware that this model is qualitative, it gives, however, an explanation of the experimental reactivity, and it also provides a valid tool in identifying zones in the crust where these reactions are likely to occur efficiently. Finally, we hypothesise the role of dry CO2 in the carbonate formation through the interactions with the basalts.

How far the chemistry of self-assembled monolayers on gold surfaces affects their work function?

Self-assembled monolayers composed of various long-chain aliphatic molecules and different tail functional groups have been synthesized on the Au(111) surface and characterized by Kelvin probe force microscopy and ultraviolet photoelectron spectroscopy. Carboxy, amino, thio and methyl terminal groups have been considered in the design of self-assembled monolayers with different aliphatic chain lengths (from C6 to C16). Work function measurements by Kelvin probe force microscopy have been carried out under a controlled and room atmosphere. Remarkably, a reduction of the relative humidity from 40% to 3% has induced a work function shift of up to 0.3 eV. As expected, the changes of the chain length of the aliphatic moiety and of the tail group have a significant impact on the tuning of the measured work function (3.90 eV for dodecanethiol versus 4.57 eV for mercaptohexadecylamine). Surprisingly, the change of the net dipole moment of the tail group (sign and amplitude) does not dominate the work function variations. In contrast, the change of the chain length and the possibility of the tail group to form a complex hydrogen bond network between molecules lead to significant modulations of the work function. In order to interpret these original findings, density functional theory models of equivalent self-assembled monolayers adsorbed on the Au(111) surface have been developed at an unprecedented level of description with large supercells including simultaneously 27 co-adsorbed molecules and weak van der Waals interactions between them. Such large systems have allowed the theoretical modeling of complex hydrogen bond networks between molecules when possible (carboxy tail group). The comparison between computed and measured work functions shows a striking agreement, thus allowing the disentanglement of the previously mentioned competing effects. This consistency between experiment and theory will help in designing the electronic properties of self-assembled monolayers in the context of molecular electronics and organic transistors.

Quantitative Relationships Between Structure and Activity of Gamma-Carboline Derivative Compounds as Anti-Bovine Viral Diarrhea Virus (BVDV) Using Semi-Empirical AM1 Method

This research aims to study the quantitative structure and activity relationship (QSAR) of gamma-carboline derivative compounds as anti-BVDV agents to get an equation that can predict the value of the anti-BVDV activity of gamma-carboline derived compounds. The research material is experimental EC50 data that convert to anti-BVDB activity. 14 gamma-carboline derivative compounds are divided into 2 groups, namely, 11 fitting compounds and 3 test compounds. QSAR analysis is based on multilinear regression calculations of the fitting compound by plotting the EC50 log as the dependent variable and the descriptor as the independent variable. The used descriptors are atomic net charge (q) and dipole moment (µ), which are involved in calculations using the AM1 semiempirical quantum mechanics method. In addition, the partition coefficient of n-octanol/water (Log P), molecular polarizability (α), molecular weight (BM), Van Der Waals surface area (A vdw), Van Der Waals volume (V vdw), and index of refraction (RD) are obtained from QSAR properties. The resulting QSAR equation is: Log pEC50 = -48.670 – 124.801 (qC11) – 12.661 (α) – 0.918 (µ) – 0.876 (RD) – 0.999 (Log P) + 1.863 (BM) + 0.043 (V vdw) with n = 14; r = 0.937; r2 = 0.878; SD = 0.244; Fcount/Ftable = 1.466; PRESS = 0.749; Sig. = 0.02 This equation can be used as an initial guide for designing the structure of new compounds of the gamma-carboline class by considering some of the most influential descriptors. Consequentially, new compounds can be designed that have a smaller predicted EC50 value than the known compounds derived from gamma-carboline.

Molecular Ordering and Nematic Character of Nonyloxy Benzoic Acid: Solvent and Thermodynamic Potentials Effect

Abstract: Benzoic acid derivative p-n-Nonyloxy Benzoic Acid (NOBA) has been chosen for the present investigation to analyze its properties under the effect of a polar aprotic solvent. Indication of stable phase has been examined by interaction-energy values both in pure form and in a polar aprotic solvent dimethylformamide (DMF, ε=38) for different modes of interaction. Complete neglect differential overlap (CNDO/2) method has been applied for net atomic charges and dipole moments at the atomic center. Modified version of Rayleigh–Schrödinger perturbation theory and multicentered-multipole expansion method have been used to regulate long-range intermolecular interactions, where short-range interactions have been studied by 6-exponential potential function. Details on phase behavior and phase stability of NOBA have been reported using statistical thermodynamic calculations of Helmholtz free energies and entropies in several modes of interaction. Keywords: NOBA, Interaction energy, Helmholtz free energy, Entropy, Stability.

Changes in polarization dictate necessary approximations for modeling electronic deexcitation intensity: Application to x-ray emission

We systematically investigate the underlying relations among different levels of approximation for simulating electronic de-excitations, with a focus on modeling X-ray emission spectroscopy (XES). Using Fermi's golden rule and explicit modeling of the initial, core-excited state and the final, valence-hole state, we show that XES can be accurately modeled by using orbital optimization for the various final states within a Slater-determinant framework. However, in this paper, we introduce a much cheaper approach reliant only on a single self-consistent field for all the final states, and show that it is typically sufficient. Further approximations reveal that these fundamentally many-body transitions can be reasonably approximated by projections of ground state orbitals, but that the ground state alone is insufficient. Furthermore, except in cases where the core-ionization induces negligible changes in polarization, linear-response approaches within the adiabatic approximation will have difficulty in accurately modeling de-excitation to the core level. Therefore, change in the net dipole moment of the valence electrons can serve as a metric for the validity of the linear-response approximation.