Permanent Dipole Moment Research Articles

Static or dynamic pear shapes in radioactive nucleus 224Rn?

We report a comprehensive study on low-lying parity doublet states of 224Rn by mixing both quadrupole- and octupole-shaped configurations in multireference covariant density functional theory, in which broken symmetries in configurations are restored using projection techniques. The low-lying energy spectrum is reasonably reproduced when the shape fluctuations in both the quadrupole and octupole shapes are considered. Electric octupole transition strength in 224Rn is found to be B(E3;31-→01+)=43\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B(E3; 3^-_1 \\rightarrow 0^+_1)=43$$\\end{document} W.u., comparable to that in 224Ra, whose data are 42(3) W.u.. Our results indicate that 224Rn shares similar low-energy structure with 224Ra despite the excitation energy of first 3-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$3^-$$\\end{document} state of the former nucleus is higher than that of the latter. This study suggests 224Rn is a candidate for the search for permanent electric dipole moment.

Three-Dimensional Magneto-Optical Trapping of Barium Monofluoride.

As a heavy molecule, barium monofluoride (BaF) presents itself as a promising candidate for measuring permanent electric dipole moment. Here we report the realization of three-dimensional magneto-optical trapping (MOT) of BaF molecules. Through the repumping of all the vibrational states up to v=3, and rotational states up to N=3, we effectively close the transition to a leakage level lower than 10^{-5}. This approach enables molecules to scatter a sufficient number of photons required for laser cooling and trapping. By employing a technique that involves chirping the slowing laser frequency, BaF molecules are decelerated to near-zero velocity, resulting in the capture of approximately 3×10^{3} molecules in a MOT. Our findings represent a significant step towards the realization of ultracold BaF molecules and the conduct of precision measurements with cold molecules.

Active string fluids and gels formed by dipolar active Brownian particles in 3D.

Self-propelled particles possessing permanent magnetic dipole moments occur naturally in magnetotactic bacteria and can be built into man-made systems such as active colloids or micro-robots. Yet, the interplay between self-propulsion and anisotropic dipole-dipole interactions on dynamic self-assembly in three dimensions (3D) remains poorly understood. We conduct Brownian dynamics simulations of active dipolar particles in 3D, focusing on the low-density regime, where dipolar hard spheres tend to form chain-like aggregates and percolated networks with increasing dipolar coupling strength. We find that strong active forces override dipolar attractions, effectively inhibiting chain-like aggregation and network formation. Conversely, activating particles with low to moderate forces results in a fluid composed of active chains and rings. At strong dipolar coupling strengths, this active fluid transitions into an active gel, consisting of a percolated network of active chains. Although the overall structure of the active gel remains interconnected, the network experiences more frequent configurational rearrangements due to the reduced bond lifetime of active dipolar particles. Consequently, particles exhibit enhanced translational and rotational diffusion within the active fluid of strings and active gels compared to their passive counterparts. We quantify the influence of activity on aggregate topology as they transition from branched structures to unconnected chains and rings. Our findings are summarized in a state diagram, delineating the impact of dipolar coupling strength and active force magnitude on the system.

Tuning Two-Photon Absorption in Rhodopsin Chromophore via Backbone Modification: The Story Told by CC2 and TD-DFT.

We investigate here a systematic way to tune two-photon transition strengths (δ2PA) and two-photon absorption (2PA) cross sections (σ2PA) of the rhodopsin's chromophore 11-cis-retinal protonated Schiff base (RPSB) via the modulation of the methyl groups pattern along its polyene chain. Our team employed the resolution of identity, coupled cluster approximate second order (RI-CC2) method with Dunning's aug-cc-pVDZ basis set, to determine the structural impact on δ2PA, as well as its correlation to both transition dipole moments and permanent electric dipole moments. Seven structures were probed in vacuo, including five-double-bond-conjugated model of the native chromophore, shortened by the β-ionone ring (RPSB5), and its de/methylated analogues: 9-methyl, 13-methyl, planar and twisted models of 9,10-dimethyl and 9,10,13-trimethyl. Our results demonstrate that the magnitude of δ2PA is dictated by both the position and number of methylated groups attached to its polyene chain as well as the degree of dihedral twist that is introduced due to the de/methylation. In fact, a strong correlation between δ2PA enhancement and the presence of a C13-methyl group in the planar RPSB5 species is found. Trends in δ2PA values follow the trends observed in their corresponding changes in the permanent dipole moment upon the S0-S1 excitation nearly exactly. The assessment of four DFT functionals, i.e., M11, MN15, CAM-B3LYP, and BHandHLYP, previously found most successful in predicting 2PA properties in biological chromophores, points to a long-range-corrected hybrid meta-GGA M11 as the top-performing functional, albeit still delivering underestimated δ2PA and σ2PA values by a factor of 3.3-5.3 with respect to the CC2 results. In the case of global-hybrid meta-NGA (MN15), as well as CAM-B3LYP and BHandHLYP functionals, this factor deteriorates significantly to 6.7-20.9 and is mostly related to significantly lower quality of the ground- and excited-state dipole moments.

Emergent Ferroelectric Nematic and Heliconical Ferroelectric Nematic States in an Achiral "Straight" Polar Rod Mesogen.

Ferroelectric nematic liquid crystals (NFLCs) are distinguished by their remarkable polarization characteristics and diverse physical phenomena, sparking significant interest and excitement within the scientific community. To date, over 150 NFLC molecules are developed; however, there are no reports regarding straight linear polar molecules with a parallel alignment of the permanent dipole moment and the molecular axis. The straight polar mesogen nBOE exhibits an enantiotropic NF phase with a wide temperature window (up to 100 K) despite having a longer alkyl chain (up to n = 6) than the critical alkyl chain length of conventional models. Interestingly, nBOE with a medium-length alkyl chain displays an exotic phase sequence of NF-HCNF-SmXF during the elimination of positional displacement among adjacent molecules. Furthermore, the reflective color modulation of the HCNFLC over the entire VIS-NIR spectral regime by ultralow E-field (up to 0.14V µm-1) is demonstrated.

Dynamics of discrete solitons in the fractional discrete nonlinear Schrödinger equationwith the quasi-Riesz derivative.

We elaborate a fractional discrete nonlinear Schrödinger (FDNLS) equationbased on an appropriately modified definition of the Riesz fractional derivative, which is characterized by its Lévy index (LI). This FDNLS equationrepresents a novel discrete system, in which the nearest-neighbor coupling is combined with long-range interactions, that decay as the inverse square of the separation between lattice sites. The system may be realized as an array of parallel quasi-one-dimensional Bose-Einstein condensates composed of atoms or small molecules carrying, respectively, a permanent magnetic or electric dipole moment. The dispersion relation (DR) for lattice waves and the corresponding propagation band in the system's linear spectrum are found in an exact form for all values of LI. The DR is consistent with the continuum limit, differing in the range of wave numbers. Formation of single-site and two-site discrete solitons is explored, starting from the anticontinuum limit and continuing the analysis in the numerical form up to the existence boundary of the discrete solitons. Stability of the solitons is identified in terms of eigenvalues for small perturbations, and verified in direct simulations. Mobility of the discrete solitons is considered too, by means of an estimate of the system's Peierls-Nabarro potential barrier, and with the help of direct simulations. Collisions between persistently moving discrete solitons are also studied.

Spin-dependent linear confinement in a magnetic medium

The linear confinement in two-dimensions can yield an analogue of a triangular well or a quantum bouncer. We discuss a way of achieving a linear confinement of a neutral particle with a permanent magnetic dipole moment in a magnetic medium by dealing with a two-dimensional system with cylindrical symmetry. This linear confinement is characterized by being spin-dependent. Then, by including the Aharonov–Casher geometric quantum phase, we show that bound states analogous to those of the quantum bouncer can be achieved, where the energy levels are infinitely degenerated with regard to the ℓ-waves. Further, we obtain the revival time of the system.

Theoretical investigation of the electronic structure of the Rhodium Halides molecules RhF and RhCl with dipole moment calculation

The current study involves an ab initio exploration of the ground and low-lying excited electronic states of the rhodium halide molecules RhF and RhCl using the complete active space self-consistent field (CASSCF) with multireference configuration interaction (MRCI+Q) method including single and double excitations and with Davidson corrections. We investigated the potential energy curves, the transition and permanent electric dipole moments, the electronic energy relative to the ground state Te, the harmonic frequency ωe, the internuclear distance Re, and the rotational constant Be corresponding to each of the bounded states. Our findings demonstrate good agreement with the available experimental data. Notably, this work represents the inaugural theoretical investigation of the excited states of RhF and RhCl molecules, identifying the ground state of both to be X3Π, as observed in the sole two experimental investigations.

Simultaneous control of carrier transport and film polarization of emission layers aimed at high-performance OLEDs

The orientation of a permanent dipole moment during vacuum deposition results in the occurrence of spontaneous orientation polarization (SOP). Previous studies reported that the presence of SOP in organic light-emitting diodes (OLEDs) lowers electroluminescence efficiency because electrically generated excitons are seriously quenched by SOP-induced accumulated charges. Thus, the SOP in a host:guest-based emission layer (EML) should be finely controlled. In this study, we demonstrate the positive effect of dipole-dipole interactions between polar host and polar emitter molecules on the OLED performance. We found that a small-sized polar host molecule that possesses both high molecular diffusivities and moderate permanent dipole moment, well cancels out the polarization formed by the SOP of the emitter molecules in the EML without a disturbance of the emitter molecules’ intrinsic orientation, leading to high-performance of OLEDs. Our molecular design strategy will allow emitter molecules to pull out the full potential of the EMLs in OLEDs.

Harnessing Ion‐Dipole Interactions for Water‐Lean Solvation Chemistry: Achieving High‐Stability Zn Anodes in Aqueous Zinc‐Ion Batteries

AbstractThe reversibility and stability of aqueous zinc‐ion batteries (AZIBs) are largely limited by water‐induced interfacial parasitic reactions. Here, dimethyl(3,3‐difluoro‐2‐oxoheptyl)phosphonate (DP) is introduced to tailor primary solvation sheath and inner‐Helmholtz configurations for robust zinc anode. Informed by theoretical guidance on solvation process, DP with high permanent dipole moments can effectively substitute the coordination of H2O with charge carriers through relatively strong ion‐dipolar interactions, resulting in a water‐lean environment of solvated Zn2+. Thus, interfacial side reactions can be suppressed through a shielding effect. Meanwhile, lone‐pair electrons of oxygen and fluorinated features of DP also reinforce the interfacial affinity of metallic zinc, associated with exclusion of neighboring water to facilitate reversible zinc planarized deposition. Thus, these merits endow the Zn anode with a high‐stability performance exceeds 3800 hours at 0.5 mA cm−2 and 0.5 mAh cm−2 for Zn||Zn batteries and a high average Coulombic efficiency of 99.8 % at 4 mA cm−2 and 1 mAh cm−2 for Zn||Cu batteries. Benefiting from the stable zinc anode, the Zn||NH4V4O10 cell maintains 80.3 % of initial discharge capacity after 3000 cycles at 5 A g−1 and exhibits a high retention rate of 99.4 % against to the initial capacity during the self‐discharge characterizations.

UNDULATING POTENTIALS OF RYDBERG Σ+-STATES OF ME-RG MOLECULES: NON-EMPIRICAL TREATMENT OF NA-HE EXCIPLEX

The multi-reference con guration interaction method based on single and double excitations (MR-CISD), l-independent core polarization potential (CPP) and diffuse function-saturated cc-pVQZ and aug-cc-pV5Z basis sets for Na and He atoms, respectively, have been used to perform non-relativistic calculations of potential energy curves and permanent dipole moment functions for the ground and excited electronic states of the exciplex Na-He molecule up to the Na(62S) state. The ab initio results obtained in a wide range of internuclear distances R [1.7, 20.0] (Å) have quantitatively claimed the undulating behavior of interatomic potentials, predicted within the framework of the inelastic scattering theory. It has been established that at large R the interatomic potentials and dipole moments of highly excited (3,6,10)2Σ+ states, converging to Na (n = 4, 5, 62S)+He(22S) atomic limits, are modulated by the nodal structure of the radial Rydberg wave function (n > 3) s-electron of Na atom during its scattering on the remote He atom.

Effect of molecular permanent dipole moment on guest aggregation and exciton quenching in phosphorescent organic light emitting diodes.

This study explores the effect of molecular permanent dipole moment (PDM) on aggregation of guest molecules in phosphorescent host-guest organic light-emitting diodes (OLEDs). Through a combination of photoluminescence measurements, high-angle annular dark-field scanning transmission electron microscopy analysis, and an Ising model based physical vapor-deposition simulation, we show that higher PDM of tris[2-phenylpyridinato-C2,N]iridium(III) guest can actually lead to a reduced aggregation relative to tris[bis[2-(2-pyridinyl-N)phenyl-C] (acetylacetonato)iridium(III) when doped into a non-polar host 1,3,5-tris(carbazol-9-yl)benzene. This study further explores the effect of host polarity by using a polar host 3',5'-di(carbazol-9-yl)-[1,1'-biphenyl]-3,5-dicarbonitrile, and it is shown that the polar host leads to reduced guest aggregation. This study provides a comprehensive understanding of the impact of molecular PDM on OLED material efficiency and stability, providing insights for optimizing phosphorescent OLED materials.

A theoretical model considering the photochemical and photothermal behavior of arc radiation-induced gassing materials ablation

In this study, we introduce a theoretical model designed to explore both the photochemical and photothermal behavior of arc plasma radiation-induced ablation in gassing materials. We employ time-dependent density functional theory to analyze the photochemical behavior, while reactive force field molecular dynamics are used to explore the photothermal behavior. The phenomena, behavior and consequences of valence shell electronic excitation are analyzed in terms of ultraviolet (UV) absorption, electron-hole distribution, and Mayer bond order. Based on the photochemical findings, we apply a periodic electric field that corresponds to the vibration frequency of the permanent dipole moment to simulate infrared radiation, and convert UV photon energy into atomic kinetic energy to analyze UV radiation. This atomic-scale insight into photothermal behavior enables us to identify the final composition of ablation gases, including H2, CO, H2O, NH3, as well as specific cyanides, amines, and hydrocarbons. The results of the theoretical model and physical properties indicate that the concentration of hydrogen-containing gases in the ablation gas significantly affects the arc extinguishing capabilities of different polymers. Finally, we propose modification schemes suitable for polymers in power circuit breakers, considering UV absorption and smoke black production. Additionally, we present the potential application of theoretical models for calculating the ablation rate, necessitating further in-depth re-search.

Liquid crystalline behaviour of symmetrical thermotropic Schiff base compounds

A series of new symmetrical liquid crystal compounds with Schiff base as a linking unit attached to different terminal alkyl chains were synthesized and characterized. The intermediates of 4-(decyloxy)benzaldehyde, 4-(dodecyloxy)benzaldehyde, and 4-(tetradecyloxy)benzaldehyde were synthesized through alkylation reaction between 4-hydroxybenzaldehyde with three series of bromoalkanes. Next, it further reacted with 1,4-phenylenediamine through condensation reaction to produce symmetrical Schiff base linkage with different terminal group chain which indicated as N-(substitutedbenxylidene)benzene-1,4-diamine. The compounds were characterized using Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and CHN elemental analysis. The Schiff base linkages are detectable in the FTIR spectra within the range of 1601–1604 cm⁻¹ and in the NMR spectra at δ 8.47–8.48 ppm. The mesophase transition phase of this compounds were determined using polarized optical microscope (POM) and further confirmed using differential scanning calorimetry (DSC). The Schiff base compounds were found to be mesogenic with smectic C and nematic transitions phases. These compounds attached to decyl, dodecyl, and tetradecyl terminal chains were found to exhibit smectic C phase at 142.47, 135.60, and 131.90 °C and nematic phase at 199.62, 197.11, and 188.76 °C, respectively. The incorporation of a Schiff base linking unit with a symmetrical alkyl chain induces the mesogenic effect in the molecules. A long alkyl chain allows the compounds to adopt a lamellar packing, facilitating the formation of a smectic phase. Incorporating the Schiff base into the molecules maintains an appropriate permanent dipole moment, which enables the homologs to arrange in a parallel orientational order, thereby adopting a nematogenic character.

Impact of Spontaneous Orientational Polarization on Triplet-Triplet Upconversion-Based Blue Organic Light-Emitting Diodes.

The spontaneous orientation polarization (SOP) of a permanent dipole moment of the molecule induces a giant surface potential (GSP) in an organic semiconductor film, and GSP is expected to be a crucial parameter for understanding the operational mechanism of organic light-emitting diodes (OLEDs). This study demonstrates that the voltage-dependent migration of a carrier recombination zone induced by a polar electron transporting layer (ETL) having a positive SOP causes a decline in the overall performance of the OLED in triplet-triplet upconversion (TTU) based on OLEDs. Specifically, the TTU efficiency in an OLED with 2,2',2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) as the ETL decreased by 20% due to the reduction of electrically generated triplet exciton density. This decrease resulted in a lower external electroluminescence (EL) quantum efficiency (EQE) of 5.4% at 1 mA cm-2, while the OLED with a nonpolar ETL resulted in an EQE of around 8.1% at 1 mA cm-2. We confirmed a shift in the recombination zone from the current density dependence of the EL spectra in the OLEDs. Our results indicate that the fixed carrier recombination zone near a hole transport layer and an emitting layer (HTL/EML) strongly enhanced the TTU process, while the polar EML/ETL interface induced the migration of the recombination zone depending on voltage, resulting in the decrease of triplet exciton density.

Harnessing Ion-Dipole Interactions for Water-Lean Solvation Chemistry: Achieving High-Stability Zn Anodes in Aqueous Zinc-Ion Batteries.

The reversibility and stability of aqueous zinc-ion batteries (AZIBs) are largely limited by water-induced interfacial parasitic reactions. Here, dimethyl(3,3-difluoro-2-oxoheptyl)phosphonate (DP) is introduced to tailor primary solvation sheath and inner-Helmholtz configurations for robust zinc anode. Informed by theoretical guidance on solvation process, DP with high permanent dipole moments can effectively substitute the coordination of H2O with charge carriers through relatively strong ion-dipolar interactions, resulting in a water-lean environment of solvated Zn2+. Thus, interfacial side reactions can be suppressed through a shielding effect. Meanwhile, lone-pair electrons of oxygen and fluorinated features of DP also reinforce the interfacial affinity of metallic zinc, associated with exclusion of neighboring water to facilitate reversible zinc planarized deposition. Thus, these merits endow the Zn anode with a high-stability performance exceeds 3800 hours at 0.5 mA cm-2 and 0.5 mAh cm-2 for Zn||Zn batteries and a high average Coulombic efficiency of 99.8 % at 4 mA cm-2 and 1 mAh cm-2 for Zn||Cu batteries. Benefiting from the stable zinc anode, the Zn||NH4V4O10 cell maintains 80.3 % of initial discharge capacity after 3000 cycles at 5 A g-1 and exhibits a high retention rate of 99.4 % against to the initial capacity during the self-discharge characterizations.

Multifunctional Applications Enabled by Fluorination of Hexagonal Boron Nitride.

2D materials exhibit exceptional properties as compared to their macroscopic counterparts, with promising applications in nearly every area of science and technology. To unlock further functionality, the chemical functionalization of 2D structures is a powerful technique that enables tunability and new properties within these materials. Here, the successful effort to chemically functionalize hexagonal boron nitride (hBN), a chemically inert 2D ceramic with weak interlayer forces, using a gas-phase fluorination process is exploited. The fluorine functionalization guides interlayer expansion and increased polar surface charges on the hBN sheets resulting in a number of vastly improved applications. Specifically, the F-hBN exhibits enhanced dispersibility and thermal conductivity at higher temperatures by more than 75% offering exceptional performance as a thermofluid additive. Dispersion of low volumes of F-hBN in lubricating oils also offers marked improvements in lubrication and wear resistance for steel tribological contacts decreasing friction by 31% and wear by 71%. Additionally, incorporating numerous negatively charged fluorine atoms on hBN induces a permanent dipole moment, demonstrating its applicability in microelectronic device applications. The findings suggest that anchoring chemical functionalities to hBN moieties improves a variety of properties for h-BN, making it suitable for numerous other applications such as fillers or reinforcement agents and developing high-performance composite structures.

Dielectric response of metal-organic frameworks as a function of confined guest species investigated by molecular dynamics simulations.

When using metal-organic frameworks (MOFs) as electric field-dependent sensor devices, understanding their dielectric response is crucial as the orientation of polar groups is largely affected by confinement. To shed light on this at the molecular level, the response to a static field was computationally investigated for two structurally related MOFs, depending on their loading with guest molecules. The pillared-layer MOFs differ in their pillar moiety, with one bearing a rotatable permanent dipole moment and the other being non-polar. Two guest molecules with and without polarity, namely, methanol and methane, were considered. A comprehensive picture of the response of the guest molecules could be achieved with respect to both the amount and polarity of the confined species. For both MOFs, the dielectric response is very sensitive to the introduction of methanol, showing an anisotropic and non-linear increase in the system's relative permittivity expressed by a strongly increasing polarization response to external electric fields scaling with the number of confined methanol molecules. As expected, the effect of methane in the non-dipolar MOF is negligible, whereas subtle differences can be observed for the dipolar response of the MOF with rotatable dipolar linker groups. Taking advantage of these anisotropic and guest-molecule-specific confinement effects may open pathways for future sensing applications. Finally, methanol-induced global framework dynamics were observed in both MOFs.

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.

Theoretical investigation of the silver chalcogenide molecules AgSe and AgTe electronic structure with dipole moment calculation

The spectroscopic constants (Re, Te, ωe, Be) are determined for 46 doublet and quartet low-lying states of the molecules AgTe and AgSe using CASSCF/MRCI (single and double excitations plus Davidson correction) calculations. The equilibrium bond length Re, and the vibrational frequency ωe of the ground state of both molecules have also been investigated using the density functional theory (DFT) incorporating eight different functionals along with different basis sets. The potential energy and permanent dipole moment curves of 23 states of each molecule have been investigated and depicted. This study represents the first theoretical investigation of the molecules AgSe and AgTe.