Electronic Dipole Research Articles

Electric Dipole Moments as indirect probes of dark sectors

Dark sectors provide beyond Standard Model scenarios which can address unresolved puzzles, such as the observed dark matter abundance or the baryon asymmetry of the Universe. A naturally small portal to the dark sector is obtained if dark-sector interactions stem from a non-Abelian hidden gauge group that couples through kinetic mixing with the hypercharge boson. In this work, we investigate the phenomenology of such a portal of dimension five in the presence of CP violation, focusing on its signatures in fermion electric dipole moments. We show that, currently unbounded regions of the parameter space from dark photon searches can be indirectly probed with upcoming electron dipole moment experiments for dark boson masses in the range 1 − 100 GeV. We also discuss two particular scenarios where a SU(2)D dark gauge group spontaneously breaks into either an Abelian U(1)D or nothing. In both cases, we show that potentially observable electron dipole moments can be produced in vast regions of the parameter space compatible with current experimental constraints and observed dark matter abundance.

Experimental and computational analysis of poly(4-vinyl pyridine) and polyvinylpyrrolidone as effective corrosion inhibitors for low carbon steel in sulfuric acid

This study investigates the inhibitory effects of poly(4-vinyl pyridine) (P4VP) and polyvinylpyrrolidone (PVP) on the corrosion of low carbon steel (LCSt) in 1 M H2SO4. Protection efficacy (%PE) was measured using mass loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). Results showed %PE values increased with higher polymer concentration and lower temperature. At 450 mg/L, %PE reached 93.13% and 94.19% for P4VP and PVP, respectively. These polymers function as mixed inhibitors, adsorbing onto the LCSt surface per Langmuir’s model as a mode of physical adsorption. EIS indicated that higher polymer concentration increased charge transfer resistance and decreased effective double-layer capacitance. Both P4VP and PVP also reduced pitting corrosion in chloride-containing solutions. Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) optimized the molecular structures of the inhibitors, evaluating electronic parameters such as frontier molecular orbital (FMO) energies, energy gap, softness, hardness, electron transfer fraction, dipole moment, and hyperpolarizability ( β ° ). Monte Carlo (MC) and molecular dynamics (MD) simulations provided insights into adsorption mechanisms, corroborating experimental findings and highlighting the effect of protonation. This comprehensive study enhances our understanding of the relationship between molecular structure and function in polymer inhibitors, improving their application in corrosion protection.

A Chiral Propeller‐Shaped Triple Helicene Shows Multi‐Resonant Thermally Activated Delayed Fluorescence

Multi‐resonant thermally activated delayed fluorescence (MR‐TADF) helicenes show great potential as chiral emitters due to their typically high photoluminescence quantum yield and that they emit circularly polarized luminescence. Here, a new propeller‐shaped chiral MR‐TADF helicene DiKTa3, integrating three DiKTa moieties, was designed and synthesized aiming to achieve co‐parallel electronic and magnitude transition dipole moments that would lead to a high dissymmetry factor, g. It emits at λPL of 491 nm, with a full width at half maximum of 52 nm and has a moderate ΔEST value of 0.24 eV in toluene. The separated (P,P,P) enantiomer shows an absorption dissymmetry factor |gabs| of 6.8 × 10‐4 at 450 nm, which results from a lower symmetry conformation adopted by the compound in solution than the C3‐symmetric optimized structure. This work highlights the strong influence that geometry can have on the chiroptical properties of the emitter.

Unconventional superconductivity from electronic dipole fluctuations

Unconventional superconductivity from electronic dipole fluctuations

Smectogenic asymmetric naphthalene derived chalcones: Self-assembling behaviour and DFT studies

A series of new naphthalene derived asymmetric benzoates incorporating chalcone unit NPCH-(2–16) have been synthesized and investigated for their self-assembling behaviour. The naphthalene end of molecules linked to decyloxy long chain whereas the other end possess systematically substituted chalcone unit connected through ester and imine linking mesogenic units. New molecules have been found to exhibit smectogenic behaviour investigated by POM (polarising optical microscopy) and DSC (differential scaling calorimetry) investigations. Early members (C1 and C7) showed enantiotropic smectic-A (SmA) behaviour, whereas molecules with C8 and C10 showed enantiotropic SmA along with monotropic smectic-C (SmC) also during cooling scans. All afterwards molecules (C12-C16) with longer alkyl chains tend to exhibit enantiotropic SmC mesophase. For one of the representative compounds, the presence of mesophase was confirmed by VT-XRD (variable temperature X-ray-crystallography) analysis. Additionally, the density functional theory (DFT) method has been applied to provide an in-depth analysis of the relationship between the computed structural (length, aspect ratio) and electronic (dipole moment, polarizability) variables and the mesomorphic behaviour of investigated compounds.

PyArc: A python package for computing absorption and radiative coefficients from first principles

Light absorption and radiative recombination are two critical processes in optoelectronic materials that characterize the energy conversion efficiency. The absorption and radiative coefficients are thus key properties for device optimization and design. Here, we develop a python package named pyArc that allows rigorous computation of absorption and radiative coefficients from first principles. By integrating several interpolation strategies to augment k-point sampling in reciprocal space, our code is accurate yet highly efficient. In addition to evaluation of the coefficients, our code is capable of intuitive analysis of carrier distribution, facilitating a deeper understanding of the microscopic mechanisms underlying the radiative coefficients. Utilizing GaAs as a prototypical example, we demonstrate how to employ our package to compute absorption and radiative coefficients and to investigate the key features in the electronic structure that give rise to these coefficients. Program SummaryProgram title: PyArcCPC Library link to program files:https://doi.org/10.17632/5x9g9bvhcv.1Licensing provisions: MIT licenseProgramming language: Python 3Nature of problem: Light absorption and radiative recombination processes in semiconductors critically impact the energy conversion efficiency of optoelectronic devices. Developing a method to calculate coefficients of the two processes based on first-principles theory is essential, which not only can help to obtain the key properties of those semiconductor materials and guide the device design, but also can unveil the underlying microscopic mechanisms.Solution method: PyArc, written in the Python language, implements first-principles methodologies for the computation of absorption and radiative coefficients of semiconductors based on Fermi's golden rule. This package takes the electronic eigenvalues and dipole matrix elements of a material computed from first-principles codes such as VASP as input. Dense k-point sampling for the Brillouin zone is achieved through efficient interpolation schemes implemented in our code to acquire well converged results. The functionality of cross-sectional visualization of carrier distribution in our code provides intuitive insights into the fundamental mechanism beneath the charge-carrier radiative recombination process.

Collective rovibronic dynamics of a diatomic gas coupled by cavity

We consider an ensemble of homonuclear diatomic molecules coupled to the two polarization directions of a Fabry-Pérot cavity via fully quantum simulations. Accompanied by analytical results, we identify a coupling mechanism mediated simultaneously by the two perpendicular polarizations, and inducing polaritonic relaxation towards molecular rotations. This mechanism is related to the concept of light-induced conical intersections (LICIs). However, unlike LICIs, these nonadiabatic pathways are of a collective nature, since they depend on the intermolecular orientation of all electronic transition dipoles in the polarization plane. Notably, this rotational mechanism directly couples the bright upper and lower polaritonic states, and it stays in direct competition with the collective relaxation towards dark states. Published by the American Physical Society 2024

Screening and Antiscreening Effects in Endohedral Nanotubes.

Recently we investigated from first-principles screening properties in systems where small molecules, characterized by a finite electronic dipole moment, are encapsulated in different nanocages. The most relevant result was the observation of an antiscreening effect in alkali-halide nanocages characterized by ionic bonds: in fact, due to the relative displacement of positive and negative ions, induced by the dipole moment of the encapsulated molecule, these cages act as dipole-field amplifiers, different from what is observed in carbon fullerene nanocages, which exhibit instead a pronounced screening effect. Here we extend the study to another class of nanostructures: the nanotubes. Using first-principles techniques based on density functional theory, we studied the properties of endohedral nanotubes obtained by encapsulation of a water molecule or a linear HF molecule. A detailed analysis of the effective dipole moment of the complexes and of the electronic charge distribution suggests that screening effects crucially depend not only on the nature of the intramolecular bonds but also on the size and the shape of the nanotubes and on the specific encapsulated molecule. As observed in endohedral nanocages, screening is maximum in covalent-bond carbon nanotubes, while it is reduced in partially ionic nanotubes, and an antiscreening effect is observed in some ionic nanotubes. However, in this case, the scenario is more complex than in corresponding ionic nanocages. In fact the specific geometric structure of alkali-halide nanotubes turns out to be crucial for determining the screening/antiscreening behavior: while nanotubes with octagonal transversal section can exhibit an antiscreening effect, which quantitatively depends on the number of layers in the longitudinal direction, instead nanotubes with dodecagonal section are always characterized by a reduction of the total dipole moment so that a screening behavior is observed. Our results show that, even in nanotube structures, in principle one can tune the dipole moment and generate electrostatic fields at the nanoscale without the aid of external potentials.

Combined DFT and Monte Carlo simulation studies of potential corrosion inhibition properties of coumarin derivatives.

Corrosion, the degradation of materials due to chemical reactions with their environment presents significant challenges both economically and environmentally. It affects various industries, including construction, transportation, and manufacturing, leading to equipment failures, safety hazards, and increased maintenance costs. Coumarin derivatives have shown promise due to their inherent chemical properties and potential for biodegradability. In this study, a series of the coumarin derivatives were examined in silico to reveal their potential corrosion inhibition properties toward the Fe(110) and Cu(111) surfaces. The compounds investigated include coumarin (2H-chromen-2-one, 1), furanocoumarin (7H-furo[3,2-g]chromen-7-one, 2), dihydrofurano coumarin (2,3-dihydro-7H-furo[3,2-g]chromen-7-one, 3), pyrano coumarin-linear type (8,8-dimethyl-2H,8H-pyrano[3,2-g]chromen-2-one, 4), pyrano coumarin-angular type (8,8-dimethyl-2H,8H-pyrano[2,3-f]chromen-2-one, 5), bicoumarin (3,3'-methylenebis(2H-chromen-2-one), 6), and phenyl coumarin (4-phenyl-2H-chromen-2-one, 7). The findings suggest that the bicoumarin derivative 6 exhibits the lowest adsorption energy with the Fe(110) surface, while the same energy absolute value is about two times lower for the Cu(111) surface. This is due to the formation of a planar configuration of a molecule of 6 on the metal surfaces with the participation of both coumarin fragments upon interacting with the Fe(110) surface, while one coumarin fragment interacts with the Cu(111) surface. Density functional theory (DFT) calculations were employed to study the electronic properties of the coumarin derivatives. The specific computational method used was B3LYP, a hybrid functional that combines with the 6-311 + + G(d,p) basis set. Each coumarin derivative was first subjected to a geometry optimization to find the most stable molecular structure. Electronic properties, dipole moments, and molecular electrostatic potential surfaces were calculated. The Monte Carlo simulations were used to model the adsorption behavior of the coumarin derivatives on metal surfaces, namely, Fe(110) and Cu(111). These simulations allowed to visualize interaction of the studied molecules with the metal surfaces, which is crucial for their function as corrosion inhibitors. The present study provides a comprehensive understanding of the corrosion inhibition potential of the applied coumarin derivatives. The insights gained from these methods can inform the development of effective, sustainable corrosion inhibitors that are both environmentally friendly and highly efficient.

Isomeric effects on the electron impact scattering for selected five membered heterocyclic ring molecules

We present electron scattering cross-sectional data for selected isomers of the five-membered ring molecules, specifically oxazole and isoxazole, thiazole and isothiazole, and imidazole and pyrazole. The ab-initio R-matrix method, incorporating static exchange polarization approximations, is employed for this calculation from energy range 0.1 eV to 20 eV. Three shape resonances are identified and characterized in each system, consisting of two π* and one σ* shape resonances. Notably, thiazole and isothiazole exhibit additional σ* resonance which is which is at a lower energy than other σ* resonance. The calculated resonance positions align well with available experimental as well as theoretical data. We also performed electronic structure calculations to aid in characterization of resonances. Comparison of the scattering cross-sectional data with their respective isomers reveal marginal differences in the magnitude of the elastic cross section particularly below 1 eV. This discrepancy may be attributed to variations in the long-range electronic dipole contribution to the electron-molecule interaction process. Further, to understand dependency of dipole moment on elastic cross section, we performed a fitting procedure for the elastic cross sections at 0.1 eV with square of the dipole moment of all the five membered ring molecules studied here. The fitting formula so obtained was used to estimate the cross section for other three five membered ring molecules: Furan, Thiophene and Pyrrole. Additionally, total ionization cross sections are computed using the binary-encounter-Bethe (BEB) model, demonstrating nearly identical results when compared with their isomers. Our findings offer insights into the influence of structural changes on the electron scattering data, providing guidance for other theoretical investigations.

Quamtum Mechanical Study on Structural and Electronic Properties of Tert-Butyl Based Bridged Dithiophene Oxide Derivatives

Computational modeling is vital to designing and creating organic semiconductors used in solar cells, organic field-effect transistors, and other areas. This work studied the structural and electronic features of a group of substituted tert-butyl bridged dithiophene oxide derivatives using Density Functional Theory (DFT) calculations. Geometry improvements were carried out using the B3LYP hybrid functional and the 6-31G(d,p) basis set in Gaussian 09. Molecular shapes, bond lengths, bond angles, and dihedral angles were studied to find out how substitution patterns change the packing and conformation of molecules. Energy levels, distribution, and makeup of frontier molecular orbitals were found. This calculation also included finding other electronic qualities, such as electronic charges, dipole moments, and polarizabilities. Findings show that tert-butyl substitution makes the molecular backbone stiffer and limits its ability to twist compared to similar molecules that have not been replaced. The chemical geometry stays mostly the same when electron-withdrawing or electron-donating substituents are added to the tert- butyl groups. Nevertheless, the strength and location of substituents have a significant impact on frontier orbital energies. The HOMO-LUMO gap grew significantly when the nitro or cyano groups firmly pulled electrons away from derivatives. For successful charge transport, electron density plots show that the HOMO and LUMO are mainly located on the thiophene and substituent moieties, respectively. Molecular dipole moments are also strongly affected by the electronic features of substituents. This research shows how to change the optoelectronic properties of tert-butyl-based dithiophene oxide derivatives and how their structure-property relationships can be improved. The results help makes new organic semiconductors that work better in various electronic and optoelectronic uses.

Strain-dependent work function of metal surfaces: Insights from first-principles investigation

Establishing a fundamental understanding of the relationship between electronic work function (WF) and applied strain is crucial for the development flexible electrodes of and enhancement of metal corrosion resistance. The underlying mechanisms of this relationship have remained unknown, largely due to inconsistencies from previous studies caused by different strain states and the complex impact of anisotropic surface effects. In this study, we employ first-principles methods to investigate the work functions of strained metal surfaces. Our research findings suggest that lateral strain states significantly affect the WF, while strain perpendicular to the surface has minimal influence. Through subjecting the metal surface to linear elastic deformation, we establish a canonical relationship between the work function and strain. Further comparison of work functions under biaxial strain indicates that surfaces with high atom packing density exhibit greater susceptibility to strain. The mechanism behind the strain-dependent WF is attributed to the interplay of bulk electronic structure and surface dipole effects, which. These effects are influenced by volume changes and the redistributedion of charge density. To this end, we propose an effective strain-induced approach for engineering the WF of metal electrode is proposeds, with potential applications in other various materials.

Effect of the external electric fields on the polarization and vibrational spectrum of 1-ethyl-3-methylimidazolium bis(trifluormethylsulfonyl)imide on graphene surface

Ionic liquids, emerging as innovative solvents for energy harvesting, necessitate a comprehensive understanding of their structural characteristics at the graphene-ionic liquid interface. This work delves into the effects of external electric fields (EEFs) on the polarization and vibrational spectrum of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][NTf2]) on a graphene surface, employing density functional theory calculations. The analysis reveals that the geometrical configuration and stability of functional groups within the graphene-[Emim][NTf2] system are influenced by both the direction and intensity of the applied EEF. Notably, the threshold EEF strength required for dissociation varies based on the structural configuration of the anion. The electronic energy, dipole moment, and polarization rate under varying EEF conditions have been quantitatively assessed, providing insights into their EEF-dependent behaviors. Utilizing the independent gradient model approach, the inter-ion interactions, such as hydrogen bonding and van der Waals forces, under the influence of EEFs were analyzed, and how these interactions evolve with changes in the direction and intensity of the EEFs were also explored. Furthermore, the vibrational spectrum of [Emim][NTf2] on the graphene surface, spanning a range of 10–3500 cm−1, was meticulously calculated to systematically investigate the impact of the EEF on the vibrational spectra of the graphene-[Emim][NTf2] system. A key finding of this work is the distinct shifts in the vibrational peaks of the cis and trans isomers of [NTf2]− on the graphene surface, which can be attributed to differences in their exchange energies. Specifically, the exchange energy for the cis isomer of [NTf2]− is measured at 107.43 kJ∙mol−1, in contrast to 98.51 kJ∙mol−1 for the trans isomer.

Giant ab-Plane Birefringence in Quasi-1D Fibrous Red Phosphorus.

Quasi-one-dimensional (quasi-1D) van der Waals crystal fibrous red phosphorus (RP) exhibits pronounced in-plane optical anisotropy, positioning it as a potential candidate for polarization-related micro-nano devices. Unfortunately, a comprehensive investigation into the complex refractive index of fibrous RP and the structure-activity relationship connecting the distinctive quasi-1D structure with optical anisotropy is currently deficient. Herein, we have collectively determined the complex refractive index of the fibrous RP flakes within the ab-plane through Kramers-Kronig (KK) analysis and theoretical calculation. Notably, the maximum birefringence of fibrous RP reaches 0.642@475 nm with an absolute extinction coefficient of only 0.08, superior to the reported traditional optical crystals and the emerging low-dimensional materials as well. The remarkable birefringence can be attributed to the synergistic influence of the large electronic dipole polarizability, anisotropic electron density distribution and the distortion of stereochemically active lone pair (SCALP). This work demonstrates the potential of fibrous RP for polarization-sensitive devices, illuminating possibilities to exploit novel giant birefringent crystals based on the structure-activity relationship.

Giant ab‐Plane Birefringence in Quasi‐1D Fibrous Red Phosphorus

AbstractQuasi‐one‐dimensional (quasi‐1D) van der Waals crystal fibrous red phosphorus (RP) exhibits pronounced in‐plane optical anisotropy, positioning it as a potential candidate for polarization‐related micro‐nano devices. Unfortunately, a comprehensive investigation into the complex refractive index of fibrous RP and the structure–activity relationship connecting the distinctive quasi‐1D structure with optical anisotropy is currently deficient. Herein, we have collectively determined the complex refractive index of the fibrous RP flakes within the ab‐plane through Kramers–Kronig (KK) analysis and theoretical calculation. Notably, the maximum birefringence of fibrous RP reaches 0.642@475 nm with an absolute extinction coefficient of only 0.08, superior to the reported traditional optical crystals and the emerging low‐dimensional materials as well. The remarkable birefringence can be attributed to the synergistic influence of the large electronic dipole polarizability, anisotropic electron density distribution and the distortion of stereochemically active lone pair (SCALP). This work demonstrates the potential of fibrous RP for polarization‐sensitive devices, illuminating possibilities to exploit novel giant birefringent crystals based on the structure–activity relationship.

Toward Reliable Dipole Moments without Single Excitations: The Role of Orbital Rotations and Dynamical Correlation.

The dipole moment is a crucial molecular property linked to a molecular system's bond polarity and overall electronic structure. To that end, the electronic dipole moment, which results from the electron density of a system, is often used to assess the accuracy and reliability of new electronic structure methods. This work analyses electronic dipole moments computed with the pair coupled cluster doubles (pCCD) ansätze and its linearized coupled cluster (pCCD-LCC) corrections using the canonical Hartree-Fock and pCCD-optimized (localized) orbital bases. The accuracy of pCCD-based dipole moments is assessed against experimental and CCSD(T) reference values using relaxed and unrelaxed density matrices and different basis set sizes. Our test set comprises molecules of various bonding patterns and electronic structures, exposing pCCD-based methods to a wide range of electron correlation effects. Additionally, we investigate the performance of pCCD-in-DFT dipole moments of some model complexes. Finally, our work indicates the importance of orbital relaxation in the pCCD model and shows the limitations of the linearized couple cluster corrections in predicting electronic dipole moments of multiple-bonded systems. Most importantly, pCCD with a linearized CCD correction can reproduce the dipole moment surfaces in singly bonded molecules, which are comparable to the multireference ones.

Coumarin Schiff base derivatives with alkyl 4’-formyl-biphenyl-4-carboxylate: design, synthesis, mesomorphic studies and DFT calculations

ABSTRACT Symmetric and unsymmetric homologous series of coumarin Schiff base derivatives with alkyl 4’-formyl-biphenyl-4-carboxylate have been synthesised and studied for their mesomorphic behaviour. In the symmetric homologous series of Schiff base derivatives BPES(6–16), alkoxy chain length was varied at both ends of the molecules with n = 6,8,10,12,14,16, while in the unsymmetric homologous series of Schiff base derivatives 10BPEU(2–12), chain length was varied at coumarin end only (n = 2–8,10,12). In symmetric homologous series, compounds BPES(6–10) (n = 6,8,10) exhibited enantiotropic smectic A (SmA) mesophase, while smectic C (SmC) mesophase in cooling cycle only. SmC mesophase became prominent on increasing the chain length n = 12,14,16 in BPES(12–16). In the unsymmetric homologous series 10BPEU(2–12), compound with n = 2 showed monotropic nematic mesophase and highly stable (~165 °C) SmA mesophase. Higher analogues in unsymmetric series were turned biphasic and showed SmA as well as SmC mesophase during cooling scan only. Compound with n = 12 showed stable enantiotropic SmC mesophase (~92 °C). VT-XRD analysis of symmetric compound with n = 12, showed the tilted SmC mesophase. Further DFT calculations were investigated for un/symmetric series along with the literature molecules with similar variations and compared for various structural (length, aspect ratio) and electronic (dipole moment, polarisability) parameters to establish correlation with observed mesomorphic behaviour.

Coumarin Schiff base derivatives with 4′-alkoxy biphenyl-4-carboxaldehyde: Synthesis, mesomorphic studies and DFT calculations

Two homologous series of coumarin Schiff base derivatives with 4′-alkoxy biphenyl-4-carboxaldehyde have been designed and synthesized. All the compounds were analyzed IR, 1H NMR, 13C NMR, ESI-MS and CHN analysis followed by mesomorphic properties polarizing optical microscopy (POM) and differential scanning calorimetry (DSC) analysis. In the first homologous series BPS(6–16), Schiff base of 7-alkoxy-3-aminocoumarin with 4′-alkoxy biphenyl-4-carboxaldehyde, alkoxy chain length was varied systematically at both end of the molecules such as n = 6,8,10,12,14,16. In this series, BPS(6–10) (n = 6,8,10) exhibited enantiotropic nematic(N) and smectic C (SmC) mesophase and turned to monophasic on increasing the chain length n = 12,14,16 in BPS(12–16) with stable SmC mesophase. While in the second homologous series 10BPU(2–16), systemic variation of alkoxy chain length was carried out at coumarin end only (n = 2–18) and 4′-decyloxy-biphenyl-4-carboxaldehyde was used for Schiff base formation. In the this series, early member of the series with n = 2,3 showed enantiotropic very stable (∼ 145 °C) nematic mesophase, while N as well as SmC mesophase were observed for n = 4–8 at, whereas with increase of chain length stability of nematic mesophase was decreased and that of SmC was increased. Higher membered analogous 10BPU(12–16) exhibited SmC mesophase with stability in the rage of 130–160 °C. VT-XRD analysis was also confirmed the tilted SmC mesophase in this class of compounds. For both the series, all compounds were studied for the DFT calculations as well as literature molecules with similar variations. Based on the calculated structural (length, aspect ratio) and electronic (dipole moment, polarizability) parameters were correlated with mesomorphic behaviour observed for literature compounds and compounds from both the series followed by the detailed discussion.

Creation and characterisation of multi-charged cerium beams at TRIUMF’s OLIS

A novel 140Ce n+ stable ion beam was developed at TRIUMF’s Off-Line Ion Source (OLIS) facility for fundamental research into (i) astrophysical processes, and (ii) forming lanthanide molecules with O2 gas and halogens. This first creation of a multi-charged 140Ce beam at OLIS is a successful chemical analog for actinide beams and molecule formation at TRIUMF’s TITAN facility for future electron dipole moment (EDM) measurements with rare radioactive thorium molecules.

Asymmetric naphthalene centred bis-ester Schiff base: Self-assembling behaviour and DFT approach

New asymmetric 2,6-disubstituted naphthalene embedded Schiff base-bis esters NEKE-(2–18) synthesized and investigated for their mesomorphic behaviour. One end of naphthalene has been substituted by decyloxy long chain whereas the other end connected with imine-bis ester aromatic core with terminal long chains. New molecules have been found to exhibit polymorphic behaviour with good thermal stability and enhanced mesophase stability upon POM (polarising optical microscopy) and DSC (differential scaling calorimetry) investigations. Early members (C2 and C3) showed nematogenic behaviour along with SmA (smectic-A) mesophase, whereas molecules with C4 and C5 showed only SmA phase. Compounds with C6 and C7 showed monotropic SmC (smectic-C) upon cooling whereas molecules from C8-to-C18 exhibited enantiotropic SmC along with SmA mesophase. The presence of mesophase has been confirmed by VT-XRD (variable temperature X-ray-crystallography) analysis. For comparison and better understanding, the mesomorphic data of compounds from literature has been compared. The DFT (density functional theory) calculations were performed on both new compounds and structurally analogous molecules found in literature. A detailed discussion was carried out regarding the correlation between the mesomorphic behaviour observed in new compounds and literature, and the computed structural (length, aspect ratio) and electronic (dipole moment, polarizability) variables.