Molecular Dipole Moment Research Articles

Physical Mechanism of One-Photon Absorption, Two-Photon Absorption, and Electron Circular Dichroism of 1,3,5 Triazine Derivatives Based on Molecular Planarity.

We provide a method to regulate intramolecular charge transfer (ICT) through distorting fragment dipole moments based on molecular planarity and intuitively investigate the physical mechanisms of one-photon absorption (OPA), two-photon absorption (TPA), and electron circular dichroism (ECD) properties of the multichain 1,3,5 triazine derivatives o-Br-TRZ, m-Br-TRZ, and p-Br-TRZ containing three bromobiphenyl units. As the position of the C-Br bond on the branch chain becomes farther away, the molecular planarity is weakened, with the position of charge transfer (CT) on the branch chain of bromobiphenyl changing. The excitation energy of the excited states decreases, which leads to the redshift of the OPA spectrum of 1,3,5-triazine derivatives. The decrease in molecular plane results in a change in the magnitude and direction of the molecular dipole moment on the bromobiphenyl branch chain, which weakens the intramolecular electrostatic interaction of bromobiphenyl branch chain 1,3,5-triazine derivatives and weakens the charge transfer excitation of the second step transition in TPA, leading to an increase in the enhanced absorption cross-section. Furthermore, molecular planarity can also induce and regulate chiral optical activity through changing the direction of the transition magnetic dipole moment. Our visualization method helps to reveal the physical mechanism of TPA cross-sections generated via third-order nonlinear optical materials in photoinduced CT, which is of great significance for the design of large TPA molecules.

Deciphering the Effects of Molecular Dipole Moments on the Photovoltaic Performance of Organic Solar Cells.

The dielectronic constant of organic semiconductor materials is directly related to its molecule dipole moment, which can be used to guide the design of high-performance organic photovoltaic materials. Herein, two isomeric small molecule acceptors, ANDT-2F and CNDT-2F, are designed and synthesized by using the electron localization effect of alkoxy in different positions of naphthalene. It is found that the axisymmetric ANDT-2F exhibits a larger dipole moment, which can improve exciton dissociation and charge generation efficiencies due to the strong intramolecular charge transfer effect, resulting in the higher photovoltaic performance of devices. Moreover, PBDB-T:ANDT-2F blend film exhibits larger and more balanced hole and electron mobility as well as nanoscale phase separation due to the favorable miscibility. As a result, the optimized device based on axisymmetric ANDT-2F shows a JSC of 21.30mA cm-2 , an FF of 66.21%, and a power conversion energy of 12.13%, higher than that of centrosymmetric CNDT-2F-based device. This work provides important implications for designing and synthesizing efficient organic photovoltaic materials by tuning their dipole moment.

Density-Corrected Density Functional Theory for Molecular Properties.

Density-corrected (DC) density functional theory (DFT) has been proposed to overcome difficulties related to the self-interaction error. The procedure uses the Hartree-Fock electron density (matrix) non-self-consistently in conjunction with an approximate functional. DC-DFT has so far mainly been tested for total energy differences, whereas other types of molecular properties have not been evaluated systematically. This work focuses on the performance of DC-DFT for molecular properties, namely, dipole moments, static polarizabilities, and electric field gradients (EFGs) at atomic nuclei. Accurate reference data were generated from coupled-cluster theory to assess the performance of DC and self-consistent DFT calculations for twelve molecules, including diatomics with transition metals. DC-DFT does no harm in dipole moment calculations, but it negatively impacts the polarizability in at least one case. DC-DFT performs well for EFGs, even for the difficult case of CuCl.

Understanding and engineering spontaneous orientation polarization in organic light-emitting devices

Organic light-emitting devices (OLEDs) are a ubiquitous technology for displays with growing application in a variety of other spaces. The future success of this technology depends on further improvements in device efficiency and stability. One pathway for improvement relies on engineering molecular orientation in the organic thin films comprising an OLED. This review is focused on the subsequent spontaneous alignment of molecular electric dipole moments, known as spontaneous orientation polarization (SOP), a phenomenon observed for many common OLED materials. The magnitude of polarization fields associated with SOP rival what is experienced in an OLED under high injection and can significantly impact electronic and excitonic behavior. Here, we first review current work describing the mechanism for the formation of SOP, reflecting an interplay between several factors, such as molecular shape, intermolecular interactions, and processing conditions. We also consider several strategies to tune the polarization sign and magnitude, with emphasis on connecting observations to quantitative models of SOP formation. Building on this discussion of SOP in organic thin films, we review how polarization in OLED active layers impacts key aspects of device performance, including charge injection, luminescence efficiency, and stability. Finally, this review concludes with an outlook on areas of future development needed to realize broad control over SOP for a variety of applications, highlighting gaps in our current understanding of this phenomenon.

Charge Transfer and Level Lifetime in Molecular Photon-Absorption upon the Quantum Impedance Lorentz Oscillator.

On the strength of the new quantum impedance Lorentz oscillator (QILO) model, a charge-transfer method in molecular photon-absorption is proposed and imaged via the numerical simulations of 1- and 2-photon-absorption (1PA and 2PA) behaviors of the organic compounds LB3 and M4 in this paper. According to the frequencies at the peaks and the full width at half-maximums (FWHMs) of the linear absorptive spectra of the two compounds, we first calculate the effective quantum numbers before and after the electronic transitions. Thus, we obtain the molecular average dipole moments, i.e., 1.8728 × 10-29 C·m (5.6145 D) for LB3 and 1.9626 × 10-29 C·m (5.8838 D) for M4 in the ground state in the tetrahydrofuran (THF) solvent. Then, the molecular 2PA cross sections corresponding to wavelength are theoretically inferred and figured out by QILO. As a result, the theoretical cross sections turn out to be in good agreement with the experimental ones. Our results reveal such a charge-transfer image in 1PA near wavelength 425 nm, where an atomic electron of LB3 jumps from the ground-state ellipse orbit with the semimajor axis ai = 1.2492 × 10-10m = 1.2492 Å and semiminor axis bi = 0.4363 Å to the excited-state circle (aj = bj = 2.5399 Å). In addition, during its 2PA process, the same transitional electron in the ground state is excited to the elliptic orbit with aj = 2.5399 Å and bj =1.3808 Å, in which the molecular dipole moment reaches as high as 3.4109 × 10-29 C·m (10.2256 D). In addition, we obtain a level-lifetime formula with the microparticle collision idea of thermal motion, which indicates that the level lifetime is proportional (not inverse) to the damping coefficient or FWHM of an absorptive spectrum. The lifetimes of the two compounds at some excited states are calculated and presented. This formula may be used as an experimental method to verify 1PA and 2PA transition selection rules. The QILO model exhibits the advantage of simplifying the calculation complexity and reducing the high cost associated with the first principle in dealing with quantum properties of optoelectronic materials.

Relativistic calculations of molecular electric dipole moments of singly charged aluminium monohalides

In this work, we have studied the permanent electric dipole moments of singly charged aluminum monohalides in their electronic ground state, , using Kramers-restricted relativistic configuration interaction method. We report our results from this method in the singles and doubles approximation with those of Dirac–Fock calculations. For our finite field computations, quadruple zeta basis sets were employed. We discuss the electron correlation trends that we find in our calculated properties and have compared our results with those from literature, wherever available.

Photolysis mechanism of eleven insecticides under simulated sunlight irradiation: Kinetics, pathway and QSAR

Insecticides are widely used in crop protection against insects and frequently detected in aquatic environment. Photolysis kinetics are directly related with exposure assessment and risk assessment. However, the photolysis mechanism of neonicotinoid insecticides with different structures has not been studied and compared systematically in the literature. In this paper, the photolysis rate constants in water were determined for eleven insecticides under irradiation of simulated sunlight. At the same time, the photolysis mechanism and effect of dissolved organic matter (DOM) on their photolysis were studied. The results showed that photolysis rates of eleven insecticides vary in a large range. The photolysis rates of nitro-substituted neonicotinoids and butenolide insecticide are much faster than that of cyanoimino-substituted neonicotinoids and sulfoximine insecticide. The ROS scavenging activity assays reveal that direct photolysis dominates the degradation of seven insecticides and, on the other hand, self-sensitized photolysis dominates four insecticides. The shading-effect from DOM can reduce the direct photolysis rates, on the other hand, ROSs generated by triplet-state DOM (3DOM*) can also accelerate photolysis of insecticides. According to the photolytic products identified from HPLC-MS, these eleven insecticides have different photolysis pathways. Six insecticides are degraded from the removal of nitro group from their parent compounds and four insecticides are degraded through ·OH reaction or singlet oxygen (1O2) reaction. QSAR (quantitative structure-activity relationship) analysis showed that photolysis rate was directly related to the energy gap between the highest occupied molecular orbital to the lowest unfilled molecular orbital (Egap = ELUMO−EHOMO) and dipole moment (δ). These two descriptors reflect the chemical stability and reactivity of insecticides. The pathways developed from identified products and the molecular descriptors of QSAR models can well verify the photolysis mechanisms of eleven insecticides.

Interface modification of perovskite solar cell for synergistic effect of surface defect passivation and excited state property enhancement

The efficiency of perovskite solar cell (PSC) is significantly affected by the charge transport and recombination behaviors at the interfaces between the perovskite photoactive layer and charge transport intermediate layers. Especially, the defects, existing in those interfaces, induce non-radiative charge carrier recombination, reducing the stability of the device along with its performance. In this work, we newly design an imidazole- and methoxy-functionalized triphenylamine based hole-transport material (HTM), which has defect-passivating functionality together with proper carrier-transportation property, for the p-i-n PSC devices. Additionally, it is also designed to preserve its enhanced molecular dipole moment at the excited-state with longer lifetime through excited-state intramolecular proton transfer (ESIPT) process, consequently beneficial to improve the Vbi of the device. The designed HTM molecule, having a synergistic effect of defect-passivation and photo-enhanced dipole characteristic, is confirmed to be advantageous to produce PSCs with higher performance and stability.

A rapid aroma quantification method: Colorimetric sensor-coupled multidimensional spectroscopy applied to black tea aroma

Aroma affects the quality of black tea, and the rapid evaluation of aroma quality is the key to realize the intelligent processing of black tea. A simple colorimetric sensor array coupled with a hyperspectral system was proposed for the rapid quantitative detection of key volatile organic compounds (VOCs) in black tea. Feature variables were screened based on competitive adaptive reweighted sampling (CARS). Furthermore, the performance of the models for VOCs quantitative prediction was compared. For the quantitative prediction of linalool, benzeneacetaldehyde, hexanal, methyl salicylate, and geraniol, the CARS–least-squares support vector machine model's correlation coefficients were 0.89, 0.95, 0.88, 0.80, and 0.78, respectively. The interaction mechanism of array dyes with VOCs was based on density flooding theory. The optimized highest occupied molecular orbital levels, lowest unoccupied molecular orbital energy levels, dipole moments, and intermolecular distances were determined to be strongly correlated with interactions between array dyes and VOCs.

Development of Donor-π-Acceptor-Type Fluorinated Tolanes as Compact Condensed Phase Luminophores and Applications in Photoluminescent Liquid-Crystalline Molecules.

Fluorinated tolanes, produced by introducing fluorine atoms into one of the aromatic rings of tolane, emitted almost no fluorescence in a solution state, but the fluorescence intensity increased dramatically in the crystalline state because of intermolecular H⋅⋅⋅F hydrogen bonds. The photoluminescent (PL) colors depend on the molecular orbitals, dipole moments, and molecular aggregated structures can be varied by controlling terminal substituents along the major molecular axis. The introduction of a long alkoxy or semifluoroalkoxy unit as a flexible chain into the terminal positions along the major molecular axis induced the formation of a liquid-crystalline (LC) phase; fluorinated tolanes act both as luminophores and as mesogens, leading to the molecular design of new photoluminescent LC molecules (PLLCs). The results also indicated that a fluorinated tolane dimer, which consists of two fluorinated tolanes linked by a flexible alkylene spacer, also becomes a novel PLLC.

Molecular Packing and Dielectric Property Optimization through Peripheral Halogen Swapping Enables Binary Organic Solar Cells with an Efficiency of 18.77%

AbstractPeripheral halogen regulations can endow non‐fullerene acceptors (NFAs) with enhanced features as organic semi‐conductors and further boost efficient organic solar cells (OSCs). Herein, based on a remarkable molecular platform of CH14 with more than six halogenation positions, a preferred NFA of CH23 is constructed by synergetic halogen swapping on both central and end units, rendering the overall enlarged molecular dipole moment, packing density and thus relative dielectric constant. Consequently, the CH23‐based binary OSC reaches an excellent efficiency of 18.77% due to its improved charge transfer/transport dynamics, much better than that of 17.81% for the control OSC of CH14. This work demonstrates the great potential for further achieving state‐of‐the‐art OSCs by delicately regulating the halogen formula on these newly explored CH‐series NFAs.

Exploring Bethe-Salpeter Excited-State Dipoles: The Challenging Case of Increasingly Long Push-Pull Oligomers.

The change of molecular dipole moment induced by photon absorption is key to interpret the measured optical spectra. Except for compact molecules, time-dependent density functional theory (TD-DFT) remains the only theory allowing to quickly predict excited-state dipoles (μES), albeit with a strong dependency on the selected exchange-correlation functional. This Letter presents the first assessment of the performances of the many-body Green's function Bethe-Salpeter equation (BSE) formalism for the evaluation of the μES. We explore increasingly long push-pull oligomers as they present an excited-state nature evolving with system size. This work shows that BSE's μES do present the same evolution with oligomeric length as their CC2 and CCSD counterparts, with a dependency on the starting exchange-correlation functional that is strongly decreased as compared to TD-DFT. This Letter demonstrates that BSE is a valuable alternative to TD-DFT for properties related to the excited-state density and not only for transition energies and oscillator strengths.

Fluorination improves the mesomorphic and photovoltaic performance of rod-like liquid crystal molecules

Molecular modification engineering is an important pathway to develop novel multifunctional materials. In this work, we designed and synthesized compounds nN-1, nSN, nFN and nFSN to study the fluorination effect on the mesomorphic and photovoltaic performance of rod-like liquid crystal (LC) molecules. Their chemical structures were confirmed, and the instruments of differential scanning calorimetry and polarising optical microscopy were employed to investigate their mesomorphic properties. Their photovoltaic performance was assessed using dye-sensitized solar cells (DSSCs). Meanwhile, experimental results were explained by using molecular steric configuration, frontier orbital and dipole moment from DFT calculations. Research results indicate that the fluorination not only decreases the melting points and enhances the nematic phase temperature ranges, but also effectively improves molar extinction coefficients, further increasing photocurrent density and achieving higher efficiency. This study provides a scientific basis and experimental data for molecular engineering strategies to conduct bifunctional materials combining the excellent properties of LCs and dye sensitizers.

A Study of Abraham’s Effective Hydrogen Bond Acidity and Polarity/Polarizability Parameters, A and S, Using Computationally Derived Molecular Properties

AbstractAbraham’s hydrogen bond donor and polarity/polarizability parameters, A and S, respectively, are correlated with molecular properties derived from computational chemistry. The analyses show that A, like Kamlet and Taaft’s α, correlates only with the charge on the most positive hydrogen atom of the molecule but that there are marked steric effects. In contrast, S correlates with the molecular dipole moment, the partial charge on the most negative atom in the molecule and with the polarizability of single ring aromatic compounds but not those of aliphatic compounds. These results are compared with those for corresponding Kamlet and Taft parameters, α and π* and Reichardt’s ET(30) and discussed in terms of the experimental methods used to determine the parameters.

Infrared spectroscopy of isolated molecules having a dimethyl group in CCl4

The in-situ inclusion of acetone, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and 2-propanol into carbon tetrachloride (CCl4) were investigated by infrared vibrational spectroscopy. IR spectra in the CH stretch region were very different although the dimethyl group responsible for this region of the spectra is common for all these molecules. The difference between the spectra was explained in terms of the DFT calculations of the monomer molecules. The spectra changed appreciably in the in-situ inclusion process for acetone and 2-propanol, while did not change for DMSO and DMF, aside from an increase proportional to increased concentration. The structures of the molecules in the time series were verified by quantum chemical calculations of monomers and dimers for these molecules, and their vibrational spectra were also calculated. The results indicate that DMSO and DMF having large molecular dipole moments are included as a dimer (or multimer) into the CCl4 matrix due to the strong dipole interaction, while the other molecules first enter the CCl4 phase as monomers and take multimer structures afterwards.

On the computation of frequency‐dependent molecular magnetizabilities via dynamical charge and current electron densities

In the computation of molecular dynamic magnetizabilities and magnetic dipole moments, three different reference points are required: (i) origin of coordinate system, (ii) origin of vector potential , and (iii) origin of multipole expansion. This study shows that methods relying on continuous translation of origin of the current density induced by optical magnetic fields provide an effective solution to the problem of choices (i) and (ii), in that they yield origin independent within the algebraic approximation, for any basis set. Frequency-dependent magnetizabilities are also invariant with respect to (iii), as a consequence of symmetry, for a number of molecular point groups. In molecules of lower symmetries, computed magnetizabilities depend on origin of the multipole expansion. Large basis set computations carried out for water, ammonia, methane, ethane, ethylene, boranylborane, and hydroxilamine, at the DFT level, have been reported to document these statements. A comparison is made for results obtained within the conventional common origin approach for static magnetic field. Sum rules for invariance of computed properties are discussed. Representations of streamlines and stagnation graphs of dynamical current density vector field induced in the water molecule by monochromatic waves of four frequencies are displayed.

Polarizable Anionic Sublattices Can Screen Molecular Dipoles in Noncentrosymmetric Inorganic-Organic Hybrids.

We report the growth and photophysical characterization of two polar hybrid lead halide phases, methylenedianiline lead iodide and bromide, (MDA)Pb2I6 and (MDA)Pb2Br6, respectively. The phases crystallize in noncentrosymmetric space group Fdd2, which produces a highly oriented molecular dipole moment that gives rise to second harmonic generation (SHG) upon excitation at 1064 nm. While both compositions are isostructural, the size dependence of the SHG signal suggests that the bromide exhibits a stronger phase-matching response whereas the iodide exhibits a significantly weaker non-phase-matching signal. Similarly, fluorescence from (MDA)Pb2Br6 is observed around 630 nm below 75 K whereas only very weak luminescence from (MDA)Pb2I6 can be seen. We attribute the contrasting optical properties to differences in the character of the halide sublattice and postulate that the increased polarizability of the iodide ions acts to screen the local dipole moment, effectively reducing the local electric field in the crystals.

Dipole-Moment Modulation in New Incommensurate Ferrocene.

Despite 70 years of research on metallocenes and their applications, there are still unresolved regions in its phase diagram of the prototypic sandwich compound, ferrocene Fe2+[C5H5]-2 (FeCp2), and its molecular 5-fold symmetry cannot be reconciled with the dielectric response of this crystal. We found a new phase I″ of ferrocene, which reveals the relationships between the molecular conformation, intermolecular interactions, and electric permittivity of this compound. Between 172.8 and 163.5 K, the conformational disorder of ferrocene molecules transforms into the incommensurate modulation. The structure of phase I″ is described in the (3+2)-dimensional superspace, where the molecular conformations, rotations and inclinations of the Cp rings, molecular tilts, and displacements of the Fe2+ cations, as well as the CH···π bonds in the crystal environment, are modulated. These geometric changes combine into the FeCp2 bending distortion, breaking the 5-fold symmetry and generating waves of molecular dipole moments with their amplitudes approaching 4 × 10-30 C·m.

Heterocyclic Chromophore Amphiphiles and their Supramolecular Polymerization.

Supramolecular polymerization of π-conjugated amphiphiles in water is an attractive approach to create functional nanostructures. Here, we report on the synthesis, optoelectronic and electrochemical properties, aqueous supramolecular polymerization, and conductivity of polycyclic aromatic dicarboximide amphiphiles. The chemical structure of the model perylene monoimide amphiphile was modified with heterocycles, essentially substituting one fused benzene ring with thiophene, pyridine or pyrrole rings. All the heterocycle-containing monomers investigated underwent supramolecular polymerization in water. Large changes to the monomeric molecular dipole moments led to nanostructures with low electrical conductivity due to diminished interactions. Although the substitution of benzene with thiophene did not notably change the monomer dipole moment, it led to crystalline nanoribbons with 20-fold higher electrical conductivity, due to enhanced dispersion interactions as a result of the presence of sulfur atoms.

Heterocyclic Chromophore Amphiphiles and their Supramolecular Polymerization

AbstractSupramolecular polymerization of π‐conjugated amphiphiles in water is an attractive approach to create functional nanostructures. Here, we report on the synthesis, optoelectronic and electrochemical properties, aqueous supramolecular polymerization, and conductivity of polycyclic aromatic dicarboximide amphiphiles. The chemical structure of the model perylene monoimide amphiphile was modified with heterocycles, essentially substituting one fused benzene ring with thiophene, pyridine or pyrrole rings. All the heterocycle‐containing monomers investigated underwent supramolecular polymerization in water. Large changes to the monomeric molecular dipole moments led to nanostructures with low electrical conductivity due to diminished interactions. Although the substitution of benzene with thiophene did not notably change the monomer dipole moment, it led to crystalline nanoribbons with 20‐fold higher electrical conductivity, due to enhanced dispersion interactions as a result of the presence of sulfur atoms.