Large Dipole Moment Research Articles

On a Specific Intermolecular Interactions in Nematic Liquid Crystal Systems

The aim of this study was the investigation of the molecular structure of Nematic Liquid Crystal Systems that are based on polar liquid crystals, whose molecules have a large dipole moment directed along the long axis of the molecule. The investigation has a practical importance in the development of the new LC materials for electro-optical systems. In this work, the investigation of a specific intermolecular interaction – the formation of charge transfer complexing (CTC) in LC systems − was carried out by UV and IR spectroscopy. A long−wavelength shift of the CTC absorption band is found. The complicated dependence of optical density of the absorption band of the donor and CTC on the initial donor concentration has been obtained. The correlation between the optical density of the absorption bands of the CTC and donor, on the one hand, and the phase diagram, on the other, was demonstrated to occur in the investigated systems. The analytical expressions for equilibrium constants of complexation process were derived, and the concentrations of the complexes were determined based on the absolute rates reaction theory.

The electronic structures and nonlinear optical properties of Alkali and Alkali earth metal atoms doped C6H6Cl6: A density functional theoretical study

The all-cis 1,2,3,4,5,6-hexafluorocyclohexane C6H6F6 (1) is a well-known molecule which has an unusually large molecular dipole moment (6.2 Debye), and plentiful novel excess electron compounds have been successfully designed on the basis of it recently. Inspired by 1, in this study, we tried to replace all the F atoms in molecule C6H6F6 with Cl atoms and obtained the all-cis 1,2,3,4,5,6-hexachlorocyclohexane C6H6Cl6 (2). By introducing alkali metal atoms and alkaline earth metal atoms, a novel series of alkalides and excess electron compounds, namely MA*+-2-MA− (MA* = Na, K; MA = Li, Na and K) and MA*-2-MAE (MA* = Na, K; MAE = Be, Mg and Ca), were theoretically constructed and studied in this work. Our results exhibit the apparent charge transfer in MA*+-2-MA− systems by NBO analysis. And these compounds all show good stability from the values of VIE and Gap. Especially, Na+-2-Li− compound exhibit the largest first hyperpolarizability value (3.4 × 106 au). The calculated results indicate these novel proposed species possess significantly large nonlinear optical responses. We hope this work will attract more experimental interests and efforts to design and synthesize new excellent NLO materials.

Probing the Local Polarity in Biocompatible Nanocarriers with Solvatofluorochromism of a 4-Carbazole-1,8-naphthalimide Dye

The study of local polarity at the nanoscale is of crucial importance for the development of smart drug delivery systems and photonic materials and is frequently accomplished with the use of luminescent tracer dyes. Nile Red is often used for this purpose, owing to its polarity-sensitive internal charge transfer transition, but its performance is affected by specific solute-solvent interactions that prevent its widespread applicability. Herein, we develop a new 1,8-naphthalimide dye with a strong charge-transfer transition that results in a large dipole moment change upon excitation. This leads to luminescence properties with high sensitivity to solvent polarity, that are independent of specific or inductive interactions. These properties are explored to probe the polarity of biocompatible nanocarriers. This dye was effective in probing the properties of polymeric nanoparticles, allowing the accurate calculation of polarity descriptors and dielectric constants.

Heptagon-Embedded π-Expanded Thieno- and N-Methylpyrrolo-Pyridazines with Substantial Out-of-Plane Dipole Moment.

Herein, we describe the synthesis and characterization of fully fused tetraphenylthieno[3,4-d]pyridazine 1 and N-methylpyrrolo[3,4-d]pyridazine 2 with two embedded seven-membered rings. Owing to the incorporated heptagon, 1 and 2 exhibited Cs-symmetric saddle conformations in the solid state with mean plane deviation around 0.38 Å. π-Expanded thienopyridazine 1 showed a one-dimensional (1-D) columnar packing along the b axis with net dipole moment aligning perpendicular to the b axis in the polar crystal system Pc. On the other hand, 2 formed a partially π-stacked brick-work structure. In addition to the Cs-symmetric saddle conformations found in the crystals, density functional theory (DFT) calculation found C2-symmetric twisted conformations of both 1 and 2 close in energy to the saddle conformations. The barrier of conformational interconversion was calculated to be 32 (1) and 31 kJ·mol-1 (2), and the interconversion occurs fast even at -60 °C as evidenced by variable-temperature (VT)-NMR studies. While 1 and 2 have moderately curved structures, optical and electrochemical studies revealed effective π-conjugation over the fused diphenylene units, which is also supported by DFT calculation. As the result of the intrinsic large dipole moment of thieno- and pyrrolo-pyridazines and the notably curved structure, 1 (2) has a substantial out-of-plane dipole moment of 2.0 (3.3) D in the saddle conformations.

The application of a molecular sieve for drying the insulation system of a power transformer in terms of improving its perational reliability

The first research objective was the assessment of the selectivity of water and hydrogen adsorption by the 3A molecular sieve (MS) in the terms of the safety of using the DGA (Dissolved Gas Analysis) method as a diagnostic technique. The second objective was to demonstrate the efficiency of drying the insulation system consisting of cellulose insulation impregnated with various insulating liquids in terms of improving safety and extending the service life of power transformers. In order to achieve the assumed objectives, measurement systems were prepared and material tests were carried out, based mainly on chromatographic analyzes and measurements of water content using the Karl Fischer titration method. On the basis of the obtained test results and the conducted physical analyzes, the selectivity of MS sorption was shown and it was explained that the facilitator of the adsorption of water molecules is their polar nature related to their large dipole moment. The high efficiency of drying cellulose insulation impregnated with various insulating liquids using MS was also demonstrated

Comprehensive Quantum Chemical Characterization of the Astrochemically Relevant HCnH Chain Family: An Attempt to Aid Astronomical Observations

AbstractIn this paper, the results of a comprehensive theoretical investigation of neutral HCnH0 and charged HCnH± chains are reported using state‐of‐the‐art compound model chemistries (W1BD, G4, CBS‐QB3, CBS‐APNO, CBS‐4M) and single point methods (including “gold standard” CCSD(T)). The properties envisaged include electronic and chemical bonding structure data, enthalpies of formation, adiabatic and vertical ionization (IP), and electron attachment (EA) energies, gas phase acidities, C−H bond strengths, and chain “deprotecting” (HCnH → H + Cn + H) energies. The best theoretical estimates based on composite models reported here for the various properties investigated agree with the available experimental data and are better than all previous theoretical estimates. To exemplify, for the enthalpies of formation, the G4 composite model achieves a RSMD (root square mean deviation) of 0.28 kcal mol−1 and a MUD (maximum unsigned deviation) of 0.45 kcal mol−1. Most importantly from the astrochemical perspective, it is predicted that the stable HCnH− anions with are nonlinear. Having sufficiently large dipole moments, the anion HCnH− cis conformers are potential candidates for detection in space via rovibrational spectroscopy.

Ultrafast Carrier Dynamics of Non-fullerene Acceptors with Different Planarity: Impact of Steric Hindrance.

Most high-performance non-fullerene acceptors are of the acceptor-donor-acceptor (A-D-A)-type structure. Under photoexcitation, the intramolecular charge transfer effect on the A-D-A framework results in a large dipole moment change, facilitating the efficient generation of charge carriers. Achieving more efficient intramolecular charge transfer by adjusting the molecular structure is one of the current research ideas. Recently, we found that the power conversion efficiency can be improved from 4.41 to 13.13% by tuning the planarity of the non-fused ring electron acceptor backbone through steric hindrance of lateral substituents. We found that the planar backbone can effectively improve the intramolecular charge transfer, which has a great influence on the power conversion efficiency of the device. Our results demonstrate that charge transfer dynamics can be controlled by optimizing steric hindrance, which plays a crucial role in the photovoltaic performance of organic solar cells.

Data-Driven and Multiscale Modeling of DNA-Templated Dye Aggregates.

Dye aggregates are of interest for excitonic applications, including biomedical imaging, organic photovoltaics, and quantum information systems. Dyes with large transition dipole moments () are necessary to optimize coupling within dye aggregates. Extinction coefficients () can be used to determine the of dyes, and so dyes with a large (>150,000 M−1cm−1) should be engineered or identified. However, dye properties leading to a large are not fully understood, and low-throughput methods of dye screening, such as experimental measurements or density functional theory (DFT) calculations, can be time-consuming. In order to screen large datasets of molecules for desirable properties (i.e., large and ), a computational workflow was established using machine learning (ML), DFT, time-dependent (TD-) DFT, and molecular dynamics (MD). ML models were developed through training and validation on a dataset of 8802 dyes using structural features. A Classifier was developed with an accuracy of 97% and a Regressor was constructed with an of above 0.9, comparing between experiment and ML prediction. Using the Regressor, the values of over 18,000 dyes were predicted. The top 100 dyes were further screened using DFT and TD-DFT to identify 15 dyes with a relative to a reference dye, pentamethine indocyanine dye Cy5. Two benchmark MD simulations were performed on Cy5 and Cy5.5 dimers, and it was found that MD could accurately capture experimental results. The results of this study exhibit that our computational workflow for identifying dyes with a large for excitonic applications is effective and can be used as a tool to develop new dyes for excitonic applications.

Asymmetrical and symmetrical naphthalene monoimide fused perylene diimide acceptors for organic solar cells

Perylene diimide (PDI) and its derivatives have received intensive research attention due to their promising applications in organic electronics, such as organic solar cells (OSCs) and organic field-effect transistors (OFETs). Fusing PDI with other arene imide is a robust strategy for the construction of high performance n-type organic semiconductors. In this work, we report two PDI derivatives (asymmetrical FPN and symmetrical FNPN) by fusing naphthalene monoimide (NMI) moieties at the bay regions. The optoelectronic characteristics of FPN and FNPN have been investigated. Using PBDB-T as donor material, FPN and FNPN based OSCs provide optimal power conversion efficiency (PCE) of 3.13% and 1.79%, respectively. The higher PCE of FPN based OSCs may be ascribed to the asymmetrical configuration-induced large natural dipole moment and the reinforced intermolecular forces, suggesting that the introduction of asymmetric structure is an effective strategy to improve the photovoltaic performance of PDI based OSCs.

Visualization of Macrophase Separation and Transformation in Immiscible Polymer Blends

Visualization of Macrophase Separation and Transformation in Immiscible Polymer Blends

Energy alignment manipulation at the C60/TiO2(110) interface using a blanket molecular dipole approach

Modifying the energy alignment between the frontier levels of a chromophore and the band edges of a semiconductor substrate using a “blanket layer” of molecular dipoles is explored. The electronic structure, measured with ultraviolet and x-ray photoemission spectroscopy, of C60 deposited directly onto the TiO2(110) surface is compared with that of C60 deposited onto the surface covered by a blanket layer of the custom-designed helical peptide Z-(Aib)6-Ipa, which has a large dipole moment of 18.6 D oriented along its molecular axis and pointing toward the substrate. The C60 HOMO level is shifted 600 meV to deeper binding energy in the presence of the blanket layer, in good agreement with what is expected from a simple parallel plate capacitor model. These results demonstrate a simple and versatile strategy for controlling energy level alignment at organic/inorganic interfaces.

Effect of gel additives on poly(vinylidene chloride‐co‐acrylontrile)‐based polymer membranes

AbstractFree standing films of gel polymer electrolytes with poly(vinylidene chloride‐co‐acrylontrile)/ poly(methyl methacrylate) are prepared and analyzed using ac impedance spectroscopy (EIS), infrared spectroscopy (FTIR), X‐ray diffraction technique (XRD), and thermogravimetric analysis (TGA). An enhanced ionic conductivity is observed for the polymer matrix on the addition of low‐molecular weight plasticizers. The obtained ionic conductivity is in the following order: EC + gBL > PC + gBL > EC + PC > EC + DMSO > PC + DMSO. The AC conductivity plot shows three well‐defined regions such as a low‐frequency deviation, a frequency independent plateau representing the DC conductivity and high‐frequency dispersion. The reduced dielectric value at higher frequencies is due to electrical relaxation process and the material electrode polarization. This is possibly associated with the large dipole moment of the carboxyl (C=O) group as well as nitrile (C ≡ N) group in the blend. The observed change in vibrational intensity of the C ≡ N group in each polymer membrane can be explained by the interaction between functional groups of both polymers and plasticizers.

Low-lying Dipole Resonances in FeCN−: A Viable Formation Pathway for FeCN− in Space

A low-lying resonance in FeCN− anion was identified through abrupt changes in the spectral dependence of the photoelectron angular distribution. Non-Franck–Condon transitions from the resonance to the neutral FeCN (4Δ), and the corresponding photoelectron angular distributions revealed that the resonance is a dipole scattering state. Significant thermionic electron emission was observed in the resonant photoelectron spectra, indicating a strong coupling of the resonance with the ground state of this triatomic anion and its competition over autodetachment. This low-lying resonance is identified to be an efficient pathway for the formation of FeCN− anion in the outer envelope of IRC+10216. The results in general reveal formation pathways in space for anions with low-lying resonances and large permanent dipole moment.

AlOSO: Spectroscopy and Structure of a New Group of Astrochemical Molecules

With the ever-increasing detection of sulfur-bearing molecules and the high abundance and refractory nature of aluminum, the [Al, S, O2] isomers may play an important role in the gas-phase chemistry of circumstellar envelopes and the chemistry on the surface of dust grains. High-level theoretical exploration of the [Al, S, O2] molecular system yielded five isomers, and predictions of their rotational, vibrational, and electronic spectroscopic properties are provided to inform experimental and observational searches. Cis-AlOSO and diamond isomers are isoenergetic and connected via a very small (∼1 kcal mol−1) transition-state barrier. These isomers may act as intermediates along the chemical pathway between Al + SO2 and AlO + SO. Other isomers OAlOS and SAlO2 are stable relative to their corresponding dissociation asymptotes. Large permanent dipole moments of 2.521 D (cis-AlOSO), 1.239 D (diamond), and 5.401 D (OAlOS) predict strong rotational transitions and indicate these molecules as prime candidates for experimental study. Due to the low transition-state barrier, mixing of the vibrational levels is anticipated, complicating the vibrational spectrum. Electronic spectroscopy may be used as a means to differentiate between the two isomers. Strong electronic transitions are predicted to occur in the 200–300 nm range for cis-AlOSO and diamond. Simulated electronic absorption spectra provide a starting point for experimental characterization and spectral deconvolution of these isomers.

Microscopic Insight into Water Desalination through Nanoporous Graphene: The Influence of the Dipole Moment.

Nanoporous graphene membranes with controllable pore size and chemical functionality may be one of the most desirable materials for water desalination. Herein, we investigate desalination performance of hydrogen-functionalized nanoporous graphene membranes. The charge values on hydrogen atoms (qH) and carbon atoms at the pore rim are systematically adjusted. For qH > 0, the flow rate decreases as qH increases, whereas for qH < 0, the flow rate tends to increase first and then decrease with increasing qH, yielding a peak at ∼ -0.2 e. Moreover, nanopores with large dipole moments at the rim have little effect on the salt rejection. The calculated oxygen and hydrogen density maps, the potential of mean force for water molecule and salt ion passage through the nanopores, and the coordination number unveil the mechanisms underlying water desalination in nanoporous graphene. This work may inspire the design and improvement of two-dimensional membranes for water desalination.

Mesophase behaviour of 1,2,3-triazole-based nematic liquid crystals influenced by varying alkyl chains and halogen atom substitution

ABSTRACT To develop novel nematic-phase liquid-crystal (LC) materials with practical potential in optical and photovoltaic devices, the alkyl chain and halogen atom substitution in 1,2,3-triazole-based compounds were varied, and the effects on the mesophase behaviour were investigated. The 4-(4-propylcyclohexyl)phenyl 4-(1-alkyl-5-hydro/halo-1,2,3-triazol-4-yl)benzoate series 1 was successfully synthesised through tandem aerobic oxidative halogenation and click reaction via in situ activation. Except for 5-thiophene-1,2,3-triazole compound 1c-Th displaying no mesomorphism, the other compounds 1 form enantiotropic nematic mesophases, among which compounds 5-hydro-1,2,3-triazole 1c-H (C10) and 1d-H (C12) (long straight chain compounds) form two mesophases (smectic C phase and nematic phase). For 5-halo-1,2,3-triazole compounds 1c-X (× = halide), the mesomorphic temperature range was wider than for the corresponding compound 1c-H because of the effect of the halogen atom substituent on the triazole. Density functional theory (DFT) analysis showed that the structure-property relation for series 1c-X(H) could be defined by using the calculated dihedral angles, dipole moment, polarisability, and molecular electrostatic potential as parameters. Notably, introducing halogen atoms at the 5-position of 1,2,3-triazole can greatly broaden the mesogenic temperature range, ascribed to the weak intermolecular forces and large dipole moment in this class of compounds.

Dendronized Hyperbranched Polymer: A New Architecture for Second-Order Nonlinear Optics

Organic/polymeric second-order nonlinear optical (NLO) materials, which rely on the poling-induced non-centrosymmetric arrangement of NLO chromophores, have played a very important role in laser technology and optical fiber communication, due to their ultra-fast response speed, excellent machining performance and low dielectric constant. However, the NLO chromophores have the large dipole moments with strong intramolecular charge transfer, which lead to the intermolecular electrostatic interactions to tend to the centrosymmetric arrangement and decrease the poling efficiency. Since the special three-dimensional spatial separation can minimize these strong intermolecular electrostatic interactions during poling process, dendrimers and hyperbranched polymers have been considered as better topology for the next generation of highly efficient NLO materials. In 2013, by the attachment of low generation dendrimers to the hyperbranched backbone, a new dendritic architecture of dendronized hyperbranched polymer (DHP) was proposed for improving the comprehensive performance of NLO materials. Recent results showed many advantages of DHPs in NLO field, such as easy syntheses, large NLO coefficients and high orientation stability, etc. In this review, the latest advancement of DHPs, including the design principle, synthesis, as well as their application as NLO materials is summarized. The new opportunities arising from DHPs are also summarized in the future perspective.

Pareto Optimization of Oligomer Polarizability and Dipole Moment Using a Genetic Algorithm.

High-performance electronic components are highly sought after in order to produce increasingly smaller and cheaper electronic devices. Drawing inspiration from inorganic dielectric materials, in which both polarizability and polarization contribute, organic materials can also maximize both. For a large set of small molecules drawn from PubChem, a Pareto-like front appears between the polarizability and dipole moment, indicating the presence of an apparent trade-off between these two properties. We tested this balance in π-conjugated materials by searching for novel conjugated hexamers with simultaneously large polarizabilities and dipole moments with potential use for dielectric materials. Using a genetic algorithm (GA) screening technique in conjunction with an approximate density functional tight-binding method for property calculations, we were able to efficiently search chemical space for optimal hexamers. Given the scope of chemical space, using the GA technique saves considerable time and resources by speeding up molecular searches compared to a systematic search. We also explored the underlying structure-function relationships, including sequence and monomer properties, that characterize large polarizability and dipole moment regimes.

Resolution of Intramolecular Dipoles and a Push-Back Effect of Individual Molecules on a Metal Surface

Molecules consisting of a donor and an acceptor moiety can exhibit large intrinsic dipole moments. Upon deposition on a metal surface, the dipole may be effectively screened and the charge distribution altered due to hybridization with substrate electronic states. Here, we deposit ethyl-diaminodicyanoquinone molecules, which exhibit a large dipole moment in the gas phase, on a Au(111) surface. Employing a combination of scanning tunneling microscopy and noncontact atomic force microscopy, we find that a significant dipole moment persists in the flat-lying molecules. Density functional theory calculations reveal that the dipole moment is even increased on the metal substrate as compared to the gas phase. We also show that the local contact potential across the molecular islands is decreased by several tens of meV with respect to the bare metal. We explain this by the induced charge-density redistribution due to the adsorbed molecules, which confine the substrate’s wavefunction at the interface. Our local measurements provide direct evidence of this so-called push-back or cushion effect at the scale of individual molecules.

Role of intermolecular interactions in formation of molecular clusters in liquid nitromethane and its solutions

Nitromethane molecules have a large dipole moment (3.54 D), so there is a possibility of dipole-dipole aggregation for them. Ab initio calculations show an additional possibility of molecular interaction for the nitromethane molecules—hydrogen bonding. In particular, the formation of H-bond is observed in the case of nitromethane dimers. The hydrogen bonds of the NO…HС type are formed between an oxygen atom of a nitromethane group of one molecule and a hydrogen atom of the C-H group of the adjacent one. These interactions have a significant effect on the formation of molecular clusters of nitromethane.