Dipole Moment Components Research Articles

Enhancing Circularly Polarized Luminescence Dissymmetry Factor of Chiral Cylindrical Molecules to -0.56 through Intramolecular Short-Range Charge Transfer.

High-performance circularly polarized luminescent (CPL) materials have received wide attention recently by virtue of broad application in circularly polarized light-emitting diodes, 3D display, and encryption. Reaching both high luminescence efficiency and strong luminescence dissymmetry factor (glum) is still a challenging goal that requires continuous efforts. Herein, we performed a systematic theoretical investigation on the chiroptical properties of helical cylindrical molecules (-)-[4]cyclo-2,6-anthracene [(-)-[4]CA2,6] and (P)-[4]cyclo-2,8-chrysenylene [(P)-[4]CC2,8], and found that the unique and symmetric cylindrical structure could make the transition dipole moment components offset along the cylindrical surface but concentrated along the vertical central axis. This structural superiority contributes the collinear electric and magnetic transition dipole moment vectors and thus the large glum. Based on the results of decomposed transition dipole moment vectors to individual atoms, an effective strategy to enhance the glum through introducing intramolecular short-range charge transfer by embedding B,N atoms is proposed. The decreased electric transition dipole moment and well-kept magnetic transition dipole moment enable the glum of B,N-embedded designed molecules (-)-[4]CA2,6-4BN and (P)-[4]CC2,8-4BN up to -0.31 and -0.56, respectively. This molecular-insight investigation deepens the understanding of the structure-property relationship and provides efficient guidance for improving glum of CPL materials.

Mechanism of submicron particle dendrite agglomeration growth and fracture in flow-electric coupling field

The research developed a new mechanism for particle agglomeration growth and fracture in the flow-electric coupling field. Microscopic visualization experiments reveal an optimum voltage range for controlling agglomerate growth dynamics. Additionally, we observed, for the first time, twisting behaviors of particle agglomerates during the growth and fracture process under the influence of the flow-electric field. A correlation between twist and fracture, varying with the increase in applied voltage, was identified. Moreover, we identified two distinct agglomeration modes: dendritic and chain agglomerates, each exhibiting unique growth characteristics. We discovered that the growth, twisting, and fracture of inclined dendritic agglomerates are influenced by two components of the electric dipole moment: the axial (Pg) and radial (Pt) components, with the aid of numerical simulation. Chain-like agglomerates exhibit growth followed by fracture. Our findings offer insights into the controlled growth of submicron particle agglomerates in gas phases using electric fields.

Jahn-Teller induced microwave spectra of the C70 + fullerene cation.

The C70 molecule is apolar. Upon ionization Jahn-Teller effects occur that distort the D5h neutral symmetry to Cs. This point group is polar thus ionization induces a permanent electric dipole moment in C70. The goal of the present calculations is to compute the equilibrium geometry and dipole moment of the C70 + cation by various DFT methods and to simulate microwave spectra. Using the Gaussian16 quantum chemistry program rotational constants, Cartesian dipole moment components, and the resultant dipole, as well as the Jahn-Teller stabilization energy and the HOMO-LUMO gaps were obtained. The microwave rotational spectra at gas phase temperatures 2.73 K and 10K were simulated using the Pgopher software. These spectra may serve as starting point for laboratory microwave measurements and as screening guide in radio astronomical searches. The static Jahn-Teller effect in C70 + is the consequence of the mixing of the two highest ground state occupied orbitals, thus it is a pseudo Jahn-Teller effect.

Unlocking the specificity of antimicrobial peptide interactions for membrane-targeted therapies

Antimicrobial peptides (AMPs) are increasingly recognized as potent therapeutic agents, with their selective affinity for pathological membranes, low toxicity profile, and minimal resistance development making them particularly attractive in the pharmaceutical landscape. This study offers a comprehensive analysis of the interaction between specific AMPs, including magainin-2, pleurocidin, CM15, LL37, and clavanin, with lipid bilayer models of very different compositions that have been ordinarily used as biological membrane models of healthy mammal, cancerous, and bacterial cells. Employing unbiased molecular dynamics simulations and metadynamics techniques, we have deciphered the intricate mechanisms by which these peptides recognize pathogenic and pathologic lipid patterns and integrate into lipid assemblies. Our findings reveal that the transverse component of the peptide's hydrophobic dipole moment is critical for membrane interaction, decisively influencing the molecule's orientation and expected therapeutic efficacy. Our approach also provides insight on the kinetic and dynamic dependence on the peptide orientation in the axial and azimuthal angles when coming close to the membrane. The aim is to establish a robust framework for the rational design of peptide-based, membrane-targeted therapies, as well as effective quantitative descriptors that can facilitate the automated design of novel AMPs for these therapies using machine learning methods.

System of metastable volume-localized electronic states in positively charged semiconductor single-wall carbon nanotubes

The volume-localized electronic states (SAMOs) with a maximum of their electron wave functions located in the cavity of nanomaterials have been experimentally and theoretically demonstrated in a fullerene. The existence of SAMOs in single-wall carbon nanotubes (SWCNTs) was also predicted theoretically. In the present paper, these volume states in semiconductor SWCNTs were theoretically investigated using numerical quantum modeling based on density functional theory (DFT). It is shown that the well appears in the center of the tube, whose depth increases with increasing positive charge, since the total potential of a positively charged structure can be represented as the sum of the Coulomb potential and the potential of the atoms of the tube wall. In this context, in addition to the well-studied surface-localized states, states localized in the volume of the cylinder also occur. Using the components of the electric transition dipole moment, the lifetime of the volume states was preliminarily estimated in comparison to the lifetime of the ordinary surface states.

Computational modelling of a triaxial vibrating sample magnetometer

Magnetic Field Assisted Additive Manufacturing (MFAAM) enables 3D printing of magnetic materials of various shapes which exhibit a complex anisotropy energy surface containing contributions generated from different origins such as sample, particle, and agglomerate shape anisotropy, flow and field induced anisotropy, and particle crystal anisotropy. These novel magnet shapes require the need to measure the x, y, and z components of the magnetic dipole moment simultaneously to fully understand the magnetic reversal mechanism and unravel the complex magnetic anisotropy energy surface of 3D printed magnetic composites. This work aims to develop a triaxial vibrating sample magnetometer (VSM) by adding a z-coil set to a pre-existing biaxial VSM employing a modified Mallison coil set. The optimum size and location of the sensing coils were determined by modeling the sensitivity matrix of the z-coil set. The designed coil set was implemented using 3D printed spools, a manual coil winder, and gauge 38 copper wire. A 3D printed strontium ferrite nylon composite sample was used to estimate the sensitivity of the z-coils (50 mV/emu). The results herein are applicable for any VSM using a modified Mallison biaxial coil configuration allowing for a quick implementation on pre-existing systems.

The influence of molecular shape on reorientation dynamics of sizable glass-forming isomers at ambient and elevated pressure

We used dielectric spectroscopy to access the molecular dynamics of three isomers with a structure based on a sizable, partially rigid, and non-polar core connected to a polar phenylene unit differing in the position of the polar group, and, consequently, the direction and magnitude of the dipole moment to address the question how unique molecular properties, in particular large size and elongated shape, affect the dynamics. The position of the polar group differentiates the molecular shape and isomer’s anisotropy and leads to different thermal and dynamic properties of the isomers. The shape of permittivity loss spectra was governed by magnitudes of the longitudinal and transverse components of dipole moment to a large extent. For para isomer with negligible traverse component of dipole moment, the narrowest loss peak was found while for meta isomer, the bimodal loss peak was observed at high temperatures. Its shape evolved on cooling limiting the possibility of individual mode separation near glass transition where the dynamics were more cooperative. High-pressure dielectric studies showed that sizable isomers were characterized by the pronounced sensitivity of glass transition temperature, Tg, to compression. Observed high activation volumes, such as 735 cm3/mol at Tg for para isomer, were found to correlate with the length scale of dynamic cooperativity. The number of dynamically correlated molecules depended on molecular shape and varied among isomers while the determined values were much smaller than that reported for other glass-forming liquids. We discussed here the obtained results in the context of the specific properties of the systems studied showing the overriding role of anisotropy.

Symmetry and reactivity of π-systems in electric and magnetic fields: a perspective from conceptual DFT.

The extension of conceptual density-functional theory (conceptual DFT) to include external electromagnetic fields in chemical systems is utilised to investigate the effects of strong magnetic fields on the electronic charge distribution and its consequences on the reactivity of π-systems. Formaldehyde, H2CO, is considered as a prototypical example and current-density-functional theory (current-DFT) calculations are used to evaluate the electric dipole moment together with two principal local conceptual DFT descriptors, the electron density and the Fukui functions, which provide insight into how H2CO behaves chemically in a magnetic field. In particular, the symmetry properties of these quantities are analysed on the basis of group, representation, and corepresentation theories using a recently developed automatic program for symbolic symmetry analysis, QSYM2. This allows us to leverage the simple symmetry constraints on the macroscopic electric dipole moment components to make profound predictions on the more nuanced symmetry transformation properties of the microscopic frontier molecular orbitals (MOs), electron densities, and Fukui functions. This is especially useful for complex-valued MOs in magnetic fields whose detailed symmetry analyses lead us to define the new concepts of modular and phasal symmetry breaking. Through these concepts, the deep connection between the vanishing constraints on the electric dipole moment components and the symmetry of electron densities and Fukui functions can be formalised, and the inability of the magnetic field in all three principal orientations considered to induce asymmetry with respect to the molecular plane of H2CO can be understood from a molecular perspective. Furthermore, the detailed forms of the Fukui functions reveal a remarkable reversal in the direction of the dipole moment along the CO bond in the presence of a parallel or perpendicular magnetic field, the origin of which can be attributed to the mixing between the frontier MOs due to their subduced symmetries in magnetic fields. The findings in this work are also discussed in the wider context of a long-standing debate on the possibility to create enantioselectivity by external fields.

Time characteristics of microsatellite attitude control at intervals between reac-tion wheels desaturations

The article is devoted to the processes study of changing the microsatellite reaction wheels angular velocities during its stabilization, turn and detumbling. Satellite control is considered under conditions of constant and harmonic external torques, as well as under gravitational, aerodynamic and magnetic disturbing torques. Expressions that describe the change in the reaction wheels angular velocities during satellite stabilization under the action of constant and harmonic torques at a frequency equal to the orbital angular velocity are given. The influence of the magnetic disturbing torque caused by the constant component of the satellite's dipole moment on the accumulation of the reaction wheels angular momentum has been studied. The formula for determining the magnitude of the reaction wheels angular velocities oscillations was obtained using a model of the Earth's magnetic field in the form of the straight dipole and taking into account a circular orbit. Moreover, its use for calculating the maximum values of angular velocities gives results that are very close to the results of modeling taking into account accurate models of the Earth’s magnetic field and the satellite’s center of mass trajectory. The maximum possible operating time intervals of the control system without forced desaturation of its controls are estimated.

Sweetness and light: computation of the rotational spectra of proto-saccharides

To date, four C 2 H 4 O 2 isomers have been identified in the interstellar medium: acetic acid, glycolaldehyde, methyl formate, and (Z)-1,2-ethenediol. The detection of these species raises the question of whether other related carbohydrates could be present in similar astrophysical environments. In this study, we report a systematic investigation of six C 2 H 4 O 2 isomers not previously observed spectroscopically in space: anti-(1)-, (2)- and (3)- CH 2 = CHOOH , methyldioxirane, and anti- and syn-(2S)-oxiran-2-ol. For each species, we employ coupled-cluster theory at the AE-CCSD(T)/cc-pCVQZ level to provide accurate equilibrium parameters, rotational constants, quartic centrifugal distortion parameters, and permanent electric dipole moment components. Anharmonic force fields were determined within vibrational perturbation theory to second order and evaluated using the MP2 method, thus allowing the evaluation of vibrational corrections. These computations provided, as a by-product, sextic centrifugal distortion constants. Rotational spectra have subsequently been simulated in the millimeter/submillimeter-wave frequency for the first time. It is hoped and anticipated that the accurate theoretical rovibrational spectral data presented herein will aid in experimental investigations of these title molecules in the interstellar medium.

Hydrogen-Atom Tunneling in a Homochiral Environment.

The role-exchanging concerted torsional motion of two hydrogen atoms in the homochiral dimer of trans-1,2-cyclohexanediol was characterized through a combination of broadband rotational spectroscopy and theoretical modeling. The results reveal that the concerted tunneling motion of the hydrogen atoms leads to the inversion of the sign of the dipole moment components along the a and b principal axes, due to the interchange motion that cooperatively breaks and reforms one intermolecular hydrogen bond. This motion is also coupled with two acceptor switching motions. The energy difference between the two ground vibrational states arising from this tunneling motion was determined to be 29.003(2) MHz. The corresponding wavefunctions suggest that the two hydrogen atoms are evenly delocalized on two equivalent potential wells, which differs from the heterochiral case where the hydrogen atoms are confined in separate wells, as the permutation-inversion symmetry breaks down. This intriguing contrast in hydrogen-atom behavior between homochiral and heterochiral environments could further illuminate our understanding of the role of chirality in intermolecular interactions and dynamics.

Hydrogen‐Atom Tunneling in a Homochiral Environment

AbstractThe role‐exchanging concerted torsional motion of two hydrogen atoms in the homochiral dimer of trans‐1,2‐cyclohexanediol was characterized through a combination of broadband rotational spectroscopy and theoretical modeling. The results reveal that the concerted tunneling motion of the hydrogen atoms leads to the inversion of the sign of the dipole moment components along the a and b principal axes, due to the interchange motion that cooperatively breaks and reforms one intermolecular hydrogen bond. This motion is also coupled with two acceptor switching motions. The energy difference between the two ground vibrational states arising from this tunneling motion was determined to be 29.003(2) MHz. The corresponding wavefunctions suggest that the two hydrogen atoms are evenly delocalized on two equivalent potential wells, which differs from the heterochiral case where the hydrogen atoms are confined in separate wells, as the permutation‐inversion symmetry breaks down. This intriguing contrast in hydrogen‐atom behavior between homochiral and heterochiral environments could further illuminate our understanding of the role of chirality in intermolecular interactions and dynamics.

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.

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.

Modelling of the torsional IR spectra of the HSSSH, DSSSH, and DSSSD molecules

Equilibrium configurations of trans- and cis- conformers of the HSSSH molecule (trisulfane), as well as the vibrational spectra of both conformers, were calculated at the MP2/Aug-cc-pVTZ, level of theory in the harmonic and anharmonic approximations. A more accurate analysis of torsional vibrations of thiol groups was performed by constructing 2D surfaces of a) potential energy, b) kinetic coefficients, and c) dipole moment components as functions of torsional coordinates of S-H groups. The values of b) and c) were calculated at the MP2/Aug-cc-pVTZ level of theory while the values of a) were calculated at the B3LYP/Aug-cc-pVTZ, MP2/cc-pVTZ, MP2/Aug-cc-pVTZ, MP2/cc-pVQZ, MP2/CBS(T,Q) and CCSD(T)/Aug-cc-pVTZ levels of theory. The energies of the stationary torsional states of the trisulfane molecule conformers were determined by numerically solving the vibrational Schrödinger equation of restricted dimensionality. The frequencies of torsional vibrations of S-H groups, as well as the splittings of torsional energy levels in trans- and cis-conformers due to tunneling between equivalent configurations of the molecule, were determined. The calculated values of tunneling frequencies in the ground torsional state of HSSSH and DSSSD trans-conformers (2.3 * 10−22 and 7.5 * 10−27 cm−1, respectively) are of particular interest due to the fact that trisulfane is considered to be one of the best candidates for establishing the effect of violation of parity conservation law in chiral molecules.

Electric Dipole Moments from Stark Effect in Supersonic Expansion: n-Propanol, n-Butanol, and n-Butyl Cyanide.

The orientation and magnitude of the molecular electric dipole moment are key properties relevant to topics ranging from the nature of intermolecular interactions to the quantitative analysis of complex gas-phase mixtures, such as chemistry in astrophysical environments. Stark effect measurements on rotational spectra have been the method of choice for isolated molecules but have become less common with the practical disappearance of Stark modulation spectrometers. Their role has been taken over by supersonic expansion measurements within a Fabry-Perot resonator cavity, which introduces specific technical problems that need to be overcome. Several of the adopted solutions are described and compared. Presently, we report precise electric dipole moment determinations for the two most stable conformers of the selected molecules of confirmed or potential astrophysical relevance: n-propanol, n-butanol, and n-butyl cyanide. All dipole moment components have been precisely determined at supersonic expansion conditions by employing specially designed Stark electrodes and a computer program for fitting the measured Stark shifts, inclusive of cases with resolved nuclear quadrupole hyperfine structure. The experimental values are compared with suitable quantum chemistry computations. It is found that, among the tested levels of computation, vibrationally averaged dipole moments are the closest to the observation and the molecular values are, as in the lighter molecules in the series, largely determined by the hydroxyl or nitrile groups.

Rotational spectroscopy of hydrogen-bonded binary trifluoro-propanol conformers: conformational diversity, preference and abundances in a jet expansion.

The rich conformational landscape including the associated conformational conversion paths of the hydrogen-bonded binary 3,3,3-trifluoropropanol (TFP) aggregate was explored using chirped pulse Fourier transform microwave spectroscopy and computational chemistry. To appropriately identify the binary TFP conformers responsible for the five sets of candidate rotational transitions assigned, we established a set of important conformational assignment criteria. These include an extensive conformational search, good agreement between the experimental and theoretical rotational constants, relative magnitude of the three dipole moment components, and quartic centrifugal distortion constants, and observation and non-observation of the predicted conformers. Extensive conformational searches were carried out using CREST, a conformational search tool, producing hundreds of structural candidates. The CREST candidates were screened using a multitier approach and subsequently the low energy conformers (<25 kJ mol-1) were optimized at the B3LYP-D3BJ/def2-TZVP level, leading to 62 minima within an energy window of 10 kJ mol-1. Good agreement with the predicted spectroscopic properties mentioned above allowed us to clearly identify five binary TFP conformers as the molecular carriers. Particularly, a combined kinetic and thermodynamic model was developed, which provides a satisfactory explanation for the observation and non-observation of the low energy conformers predicted. The role of the intra- and intermolecular hydrogen bonding interactions in the stability ordering of the binary conformers is discussed.

Alternating 1-Phenyl-2,2,2-Trifluoroethanol Conformational Landscape With the Addition of One Water: Conformations and Large Amplitude Motions.

The 1:1 adduct of 1-phenyl-2,2,2-trifluoroethanol (PhTFE), a chiral fluoroalcohol, with water was investigated using chirped pulse Fourier transform microwave spectroscopy and computational methods. While PhTFE itself was predicted to have three minima, I (gauche+), II (trans), and III (gauche-), only I and II were stable and only I was observed experimentally. A systematic search of the PhTFE···H2O conformational landscape identified 110 stable minima, 14 of which are within a 15 kJ mol-1 energy window. Rotational spectra of the two PhTFE···H2O conformers along with several deuterium and 18O isotopologues were assigned, and the isotopic data were used to verify the corresponding structures. In the two observed monohydrate conformers, one contains PhTFE I where the water subunit is inserted into the existing intramolecular OH···F contact of I, and the binary adduct is stabilized by two intermolecular contacts: OH···OW and HW···F, whereas the other contains PhTFE II where the water subunit interacts with both the alcohol hydrogen and phenyl ring of II, demonstrating that interaction with water sufficiently stabilizes II for its observation in a jet expansion. Interestingly, the predicted electric dipole moment components at the identified minima deviate considerably from the experimental ones. Such deviations were analyzed in terms of dynamic effects associated with the large amplitude motions of the unbound HW. In addition, tunnelling effects associated with the exchange of the bonded and nonbonded HW were also discussed.

Comprehensive Approach to the Interpretation of the Electrical Properties of Film-Forming Molecules.

This paper presents a general protocol for the interpretation of the electric surface potential of Langmuir monolayers based on a three-layer capacitor model. The measured values were correlated with the results from DFT molecular dynamics simulations, and, as a result, the local dielectric permittivities and dipole-moment components of molecules organized in the monolayer were obtained. The main advantage of the developed approach is applicability to amphiphiles of any type; irrespective of the structure of the polar head as well as the molecular organization and inclination in the surface film. The developed methodology was successively applied to an atypical surface-active compound, perfluorodecyldecane, and its derivatives containing the hydroxyl, thiol, and carboxyl moiety. The following contributions to the apparent dipole moments connected with the reorientation of water molecules and local dielectric permittivities in the vicinity of polar and apolar molecule parts, respectively, were determined: μw/εw = −0.85 D, εp = 5.00, and εa = 1.80. Moreover, the investigated perfluorodecyldecane derivatives were comprehensively characterized in terms of their surface activity, film rheology, and effective surface dissociation equilibria. The proposed methodology may be crucial for the process of the design and the preliminary characterization of molecules for sensor and material science applications.

Microwave spectra of two conformers of the (1R)-(–)-nopol monomer

The rotational spectrum of the (1R)-(-)-nopol monomer has been observed in the 6–18 GHz region using CP-FTMW spectroscopy. Transitions of two distinct conformers of the parent isotopologue have been observed and assigned. Density Functional Theory (DFT) calculations performed on the monomer predict nine distinct low-energy heavy atom geometries. The differences between these structures are attributed to changes in the orientation of two dihedral angles in the heavy atom R-CH2CH2OH functionalization, where R refers to the fixed bicyclic cage component of the molecule. Further optimization of these geometries found 27 distinct conformers associated with the hydroxyl hydrogen orientation. The rotational constants of the two lowest energy conformers were found to be in good agreement with the experimental constants of the two observed conformers and the predicted dipole moment components agree with the relative intensities of the observed transitions.