Direction Of Dipole Moment Research Articles

Electronic properties of Janus MXY/graphene (M = Mo, W; X ≠ Y = S, Se) van der Waals structures: a first-principles study.

Based on the first-principles calculations, we studied the intrinsic dipole moment and electronic properties of Janus MXY (M = Mo, W; X ≠ Y = S, Se) monolayers, bilayers and heterostructures with graphene, and the possibility of MXY encapsulating graphene. The results show that Janus MXY monolayer has an intrinsic dipole moment and a direct band gap. However, for MXY bilayers strong interlayer coupling will cause direct to indirect band gap transition, and the existence of the dipole moment leads to a significantly large interlayer band offset, being the driving force for the formation of interlayer excitons. In MXY/graphene heterostructures, changes in the direction of intrinsic dipole moment will cause a change in Schottky barrier height and even the transition between p- and n-type Schottky contacts. Independent of the interface atomic layer of Janus MXY, on one hand, the Dirac cone still exists in graphene, proving that MXY is an ideal coating material. On the other hand, the type-II band alignment will disappear as the intrinsic dipole moment disappears, confirming that the intrinsic dipole moment plays a vital role in the formation of a large band offset. Our results provide guidance for the study of interlayer excitonic states, the experimental construction of atomically thin p-n junctions and the encapsulation of graphene.

The investigation of the dipole-dipole action direction and molecular space configuration effect during the dipole–dipole induced azobenzene supramolecular self-assembly

In order to study the effect of dipole-dipole action direction and molecular space configuration on supramolecular self-assembly of azobenzene, three azobenzene dye molecules N1 (" linear "), N2 (" L ") and N3 (" U ") were designed. First, the feasibility of molecular design is verified by theoretical calculations and then synthesized by experiments. By adjusting the direction of the molecular dipole moment and the spatial configuration of the molecule, the three dye molecules self-assemble to form supramolecular self-assemblers with different structures. The properties of three azobenzene dye molecules were studied by IR、NMR、 X-ray diffraction and UV–vis spectra. Theoretical calculation and experimental results show that the direction of dipole dipole interaction and molecular space configuration have important effects on the supramolecular self-assembly morphology of azobenzene.

Microtubules lattice equal-frequency maps: The dynamics of relief changes in dependence on elastic properties, tubulins’ dipole–dipole interaction and viscosity

Microtubules lattice equal-frequency maps are obtained in the paper. Microtubule vibrational properties depending on their elastic properties, tubulins’ dipole–dipole interaction and the surrounding solution viscosity are analyzed in detail. Calculations have been made for different elastic constant values, damping coefficients and for different dipole moment directions. The relief of equal-frequency maps has also been investigated in accordance with a wave polarization direction. The dynamics of equal-frequency map relief changes have been analyzed. Its considerable dependence on viscosity, the direction of tubulins’ dipole–dipole moment and polarization has been demonstrated. The dynamics of changing the maps areas corresponding to damping harmonic oscillations and exponential damping law has been considered. Possible factors contributing to the microtubule’s structural damage are analyzed.

Using the Purcell effect for the modification of third-harmonic generation in a quantum dot near a metallic nanosphere

We study the modification of third-harmonic generation from a quantum dot close to a metallic nanosphere. We show that the strong variation of the spontaneous decay rate of the quantum dot near the metallic nanoparticle can be used for tailoring the third-harmonic generation coefficient of the quantum dot. Specifically, the strong enhancement or suppression of the quantum dot’s spontaneous emission rate can strongly modify the third-harmonic generation coefficient of the quantum dot depending on the distance of the quantum dot from the surface of the metallic nanosphere and on the direction of the electric dipole moment of the quantum dot. The alteration of the third-harmonic generation coefficient is also strongly dependent on the quantum dot’s pure dephasing rate.

Tailoring second-order nonlinear optical effects in coupled quantum dot-metallic nanosphere structures using the Purcell effect

We study the modification of second-order nonlinear optical processes, like nonlinear optical rectification and second-harmonic generation, of a quantum dot that is coupled to a metallic nanosphere. We show that the strong variation of the spontaneous decay rate of the quantum dot near the metallic nanosphere can lead to strong enhancement or suppression of the nonlinear optical rectification and second-harmonic generation coefficients depending on the distance of the quantum dot from the surface of the nanosphere and on the direction of the electric dipole moment of the quantum dot. The nonlinear optical coefficients are also strongly influenced by the pure dephasing rate of the quantum dot.

The response of electronic and energetic properties of conjugated vs aromatic molecules to an external uniform electric field

The susceptibility of electric and energetic properties of two sets of molecules to perturbation in a uniform electric field was investigated. The molecules of one set were deca-1,3,5,7-pentaene terminated with two functional groups, R1 and R2; those of the second set were 4-R1-4′-R2-p-diphenylbenzenes, with R1 and R2 being the same as in the polyene set. The polyene and aromatic molecules had similar lengths of the system of conjugated bonds between the two most extreme carbon atoms. Dipole moments were used as determinants of the overall charge transfer within the molecules. The electric field was directed along the main (longest) axes of the molecules from the negative pole to the positive. Comparison of the effect of the charge relocation in both sets of conjugated molecules revealed that the charge transfer imposed by the electric field was more efficient in the polyenes than in the aromatic compounds; however, for the molecule pairs with the same R1 and R2, reversal of the dipole moment direction falls at the same field strength. Parabolic dependence of the molecules’ energy as a function of field strength can also be interpreted in terms of the response of electron density to an electric field.

Control of Electric Dipole Moment using Deformation induced by Functionalization of (5, 0) Zigzag Carbon Nanotubes as Gigahertz Oscillators

Electric dipole moment (EDM) required for the relative motion of carbon nanotube (CNT) walls in nanoelectromechanical systems (NEMS) such as actuators and oscillators is studied by functionalization. Pristine (5,0) zigzag carbon nanotube with little inherent electric dipole moment (ì) were deformed by adding three -OH functional groups to its end rims. The properties of eight yielded isomers are studied. The Gibbs free energy calculations demonstrate that the eight structures are more stable than pristine CNT. The induced deformation resulted in charge imbalances which developed large electric dipole moments for each case. The values of dipole moments produced for all cases are calculated. The bandgap energy, conductivity, density of state (DOS) and IR spectra of these structures are also computed and analyzed. The study revealed that the location of the -OH positioning (site selectivity) which gives rise to different degrees of deformation has a significant impact on all of the above parameters, especially the magnitude and direction of the electric dipole moment. The functionalization produced large ì of about 6.9 D for 60 carbon atoms nanotube which is higher than in the previous study. Applying an external electric field to the isomers causes the CNTs with large dipole moments to either get attracted or repelled and hence physical movement or oscillation of the nanotube occurs. The frequency of this oscillation is in gigahertz scale. Keywords: Gigahertz oscillator, electric dipole moment, deformation, carbon nanotube, hydroxyl functionalization, site selectivity.

Modifying the linear and nonlinear optical susceptibilities of coupled quantum dot-metallic nanosphere systems with the Purcell effect

We study the modification of the linear, third-order, and fifth-order susceptibilities of a quantum dot that is coupled to a spherical metallic nanoparticle. We calculate the susceptibilities with a density matrix approach and calculate the modified spontaneous emission rate of the quantum dot due to the Purcell effect next to the metallic nanosphere using a boundary element method. We show that the strong variation of the spontaneous decay rates of the quantum dot near the metallic nanosphere can be used for tailoring the linear, third-order, and fifth-order susceptibilities. Specifically, the Purcell modified spontaneous decay rate leads to strong alteration (enhancement or suppression) of the linear and the nonlinear susceptibilities. The specific type of alteration depends on the distance of the quantum dot from the surface of the nanosphere and the direction of the electric dipole moment of the quantum dot. The strong influence of the pure dephasing rate of the quantum dot on the modification of the optical susceptibilities is also analyzed.

Understanding Keesom Interactions in Monolayer-Based Large-Area Tunneling Junctions.

Charge transport across self-assembled monolayers (SAMs) has been widely studied. Discrepancies of charge tunneling data that arise from various studies, however, call for efforts to develop new statistical analytical approaches to understand charge tunneling across SAMs. Structure-property studies on charge tunneling across SAM-based junctions have largely been through comparison of average tunneling rates and associated variance. These early moments (especially the average) are dominated by barrier width-a static property of the junction. In this work, we show that analysis of higher statistical moments (skewness and kurtosis) reveals the dynamic nature of the tunnel junction. Intramolecular Keesom (dipole-dipole) interactions dynamically fluctuate with bias as dictated by stereoelectronic limitations. Analyzing variance in the distribution of tunneling data instead of the first statistical moment (average), for a series of n-alkanethiols containing internal amide and aromatic terminal groups, we observe that the direction of dipole moments affects molecule-electrode coupling. An applied bias induces changes in the tunneling probability, affecting the distribution of tunneling paths in large-area molecular junctions.

Polarized infrared spectroscopy imaging applied to structural analysis of bilirubin aggregate at liquid-liquid interface

Fourier transform infrared spectroscopy imaging (FTIRSI) combined with spectral analysis and polarization approach was creatively used to investigate both structures of bilirubin (BR) precipitate and BR aggregate at liquid-liquid interface. It was found by spectral analysis that the internal hydrogen bonds of BR molecules all broke and the dihedral angles increased during the formation of BR aggregate at liquid-liquid interface. And the BR molecule might be of layer assembly along the long axis direction of CD half-group to form J-type aggregates, which could be parallel to the direction of the transition dipole moment of BR aggregate. The further study of polarized imaging/anisotropy revealed that the absorbance of 1570 and 1703 cm−1 bands of BR aggregate changed periodically at intervals of 90°, which were not shown in BR precipitate case, indicating that the CC of the corresponding lactam ring and the CO of the adjacent carboxyl groups formed ordered arrangement in BR aggregate. It also suggested that the two positions might be the active sites which J-type aggregates assembled on. The combined technique was firstly applied in interfacial aggregate research, which was helpful for further understanding and controlling the aggregation as well as structural transformation of BR molecules so as to decrease physiological hazard and facilitate the wide spread application in biomedicine.

Multigene Family of Pore-Forming Toxins from Sea Anemone Heteractis crispa.

Sea anemones produce pore-forming toxins, actinoporins, which are interesting as tools for cytoplasmic membranes study, as well as being potential therapeutic agents for cancer therapy. This investigation is devoted to structural and functional study of the Heteractis crispa actinoporins diversity. Here, we described a multigene family consisting of 47 representatives expressed in the sea anemone tentacles as prepropeptide-coding transcripts. The phylogenetic analysis revealed that actinoporin clustering is consistent with the division of sea anemones into superfamilies and families. The transcriptomes of both H. crispa and Heteractis magnifica appear to contain a large repertoire of similar genes representing a rapid expansion of the actinoporin family due to gene duplication and sequence divergence. The presence of the most abundant specific group of actinoporins in H. crispa is the major difference between these species. The functional analysis of six recombinant actinoporins revealed that H. crispa actinoporin grouping was consistent with the different hemolytic activity of their representatives. According to molecular modeling data, we assume that the direction of the N-terminal dipole moment tightly reflects the actinoporins’ ability to possess hemolytic activity.

Resveratrol Radical Repair by Vitamin C at the Micelle-Water Interface: Unexpected Reaction Rates Explained by Ion-Dipole Interactions.

Repair reactions of lipophilic phenoxy radicals by hydrophilic co-antioxidants at model membranes are important for understanding the factors that govern the interactions between radical scavengers in biological systems. By using near-UV photoionization, we have selectively generated the phenoxy radical of the famous antioxidant resveratrol inside anionic (SDS), cationic (DTAC), or neutral (TX-100) micelles, as well as in homogeneous aqueous solution, and have compared its repairs in these media by the water-soluble co-antioxidants ascorbic acid and ascorbate monoanion. With all surfactants, these reactions are dynamic processes at the micelle-water interface. Whereas for the combinations ascorbate monoanion/ ionic micelle the repair rates can be rationalized by the Coulombic interactions, unexpected effects were observed with the neutral ascorbic acid and the charged micelles: for the anionic micelles, this repair is three times faster than in homogeneous solution, and two orders of magnitude faster than for the cationic micelles. Given that the repair by a concerted proton-electron transfer demands a coplanar arrangement of the resveratrol phenoxy centre sticking out into the Stern layer and the co-antioxidant hydroxy moiety approaching from the aqueous bulk, we explain these results by ion-dipole interactions: only at a negatively charged micellar surface does the direction of the large dipole moment of ascorbic acid lead to an orientation favourable for the repair.

Spotlight on Excitonic Coupling in Polymorphic and Textured Anilino Squaraine Thin Films

Structural diffraction analysis of an anilino squaraine with branched isobutyl side chains shows crystallization into two polymorphic structures in the bulk and in spin-casted thin films. We observe multipeaked and pleochroic absorption spectra being blue-(red)-shifted for the monoclinic (orthorhombic) polymorph. We understand the packing as Coulombic molecular H-(J)-aggregates supporting Davydov splitting. Pictures of projected Davydov components in oriented thin films fit well to polarization resolved spectro-microscopy and crossed-polarized light microscopy investigations. By comparison with literature on anilino squaraines with linear alkyl side chains, we point out a general trend for steering the thin film excitonic properties by simple side chain and/or processing condition variation. Combined with the ability to locally probe the direction of transition dipole moments, this adds value to the rational design of functional thin films for optoelectronic applications, especially envisioning ultrastron...

Inhibition effect of opuntia stem extract on corrosion of mild steel: a quantum computational assisted electrochemical study to determine the most effective components in inhibition

The use of opuntia ficus indica stem extract as a mild steel corrosion inhibitor in 2.0 M HCl solution was investigated by weight loss measurements, potentiodynamic polarization and Electrochmical impedance spectroscopy (EIS) methods. The weight loss results showed that opuntia stem is an excellent corrosion inhibitor for mild steel immersed in 2.0 M HCl. EIS measurements showed an increase in the transfer resistance with the increase of inhibitor concentration. In addition, the inhibition action of the extract was discussed in view of Langmuir adsorption isotherm. It was found that the presence of extract increases the activation energy of the corrosion reaction. In order to explain which components of opuntia stem extract is the most efficient inhibitor, quantum chemical calculations of 8 constituent molecules of extract were applied. The correlation between inhibitive effect and molecular structures was investigated. Some parameters, such as EHOMO, ELUMO, gap energy (ΔE), electronegativity (χ), global hardness (η) and the fraction of electrons transferred from the inhibitor molecule to the metallic atom (ΔN) were calculated. The direction of dipole moment μ→, location of HOMO orbitals and NBO charges of atoms can determine how to connect the molecules on the surface of the metal.

Unusual Nonemissive Behavior of Rubrene J-Aggregates: A Rare Violation.

Structure-property correlations in rubrene (RB) colloidal J-aggregates were unravelled by steady state and time-resolved spectroscopy in conjunction with excited state density functional calculations. The RB J-aggregate with a slippage angle θ = 30.4°, estimated from the monomeric transition dipole moment directions, exhibited a broad fwhm of 1073 cm-1 and a 5 nm red-shifted absorption band carrying a transition dipole moment (M⃗λagg = 1.80 D) almost equivalent to the monomeric dye (M⃗λmon = 1.89 D). A significantly low magnitude of exciton coupling energy, ΔEexc = -358 cm-1 for the rhombic-RB colloidal J-aggregates resulted owing to the weaker electronic communication between the largely separated RB subunits (r = 7.2 Å) and a restricted exciton delocalization over the RB J-dimer (N = 2). The RB J-dimer exhibited a perfect balance between the computed singlet (2.53 eV) and the triplet (1.29 eV) exciton energies for singlet fission (SF). Supporting this, the PL decay profile of the J-aggregates revealed a delayed fluorescence, substantiating triplet pair formation via SF. The experimental evidence for the long-lived triplet formation was furthermore confirmed by its transient absorption (T1 → TN) at 530 nm. Consequently, a high probability for SF and a low probability for triplet-triplet recombination, leading to a dramatic lowering in photoluminescence quantum yield from 0.172 down to 0.035 was noted. The electronic structure calculations for the RB J-dimer followed TD-DFT-M062X/6-31G+(d,p) level of theory following integral equation formalism polarizable continuum model (IEFPCM) in water. S1 excited state for RB J-dimer was carefully analyzed using integral overlap of electron and hole density distribution (ϕ) and the defined t-indexes along all three spatial directions, and was found to be of locally excited in character.

Substituent Effects on the Absorption and Fluorescence Properties of Anthracene.

Substitution can be used to efficiently tune the photophysical properties of chromophores. In this study, we examine the effect of substituents on the absorption and fluorescence properties of anthracene. The effects of mono-, di-, and tetrasubstitution of electron-donating and -withdrawing functional groups were explored. In addition, the influence of a donor-acceptor substituent pair and the position of substitution were investigated. Eleven functional groups were varied on positions 1, 2, and 9 of anthracene, and on position 6 of 2-methoxyanthracene and 2-carboxyanthracene. Moreover, the donor-acceptor pair NH2/CO2H was added on different positions of anthracene for additional studies of doubly substituted anthracenes. Finally, we looked into quadruple substitutions on positions 1,4,5,8 and 2,3,6,7. Vertical excitation energies and oscillator strengths were computed using density functional theory with the hybrid CAM-B3LYP functional and 6-311G(d) basis set. Correlations between the excitation energies or oscillator strengths of the low-lying bright La state and the Hammett sigma parameter, σp+, of the substituents were examined. The energy is red-shifted for all cases of substitution. Oscillator strengths increase when substituents are placed along the direction of the transition dipole moment of the bright La excited state. Substitution of long chain conjugated groups significantly increases the oscillator strength in comparison to the cases for other substituents. In addition, the results of quadruply substituted geometries reveal symmetric substitution at the 1,4,5,8 positions significantly increases the oscillator strength and can lower the band gap compared to that of the unsubstituted anthracene molecule by up to 0.5 eV.

Overlapping Electronic States with Nearly Parallel Transition Dipole Moments in Reduced Anionic Flavin Can Distort Photobiological Dynamics.

Chromophoric biomolecules are exploited as reporters of a diverse set of phenomena, acting as internal distance monitors, environment and redox sensors, and endogenous imaging probes. The extent to which they can be exploited is dependent on an accurate knowledge of their fundamental electronic properties. Arguably of greatest importance is a precise knowledge of the direction(s) of the absorption transition dipole moment(s) (TDMs) in the molecular frame of reference. Such is the case for flavins, fluorescent redox cofactors utilized for ground- and excited-state redox and photochemical processes. The directions of the TDMs in oxidized and semiquinone flavins were characterized decades ago, and the details of charge redistribution in these forms have also been studied by Stark spectroscopy. The electronic structure of the fully reduced hydroquinone anionic state, FlH-, however, has been the subject of unfounded assumptions and estimates about the number and direction of TDMs in FlH-, as well the electronic structure changes that occur upon light absorption. Here we have used Stark spectroscopy to measure the magnitude and direction of charge redistribution in FlH- upon optical excitation. These data were analyzed using TD-DFT calculations. The results show unequivocally that not one but two nearly orientation-degenerate electronic transitions are required to explain the 340-500 nm absorption spectral range, demolishing the commonly held assumption of a single transition. The difference dipole moments for these states show that electron density shifts toward the xylene ring for both transitions. These measurements force a reappraisal of previous studies that have used erroneous assumptions and unsubstantiated estimates of these quantities. The results put future optical studies of reduced flavins/flavoproteins on a firm photophysical footing.

Giant permanent dipole moment of two-dimensional excitons bound to a single stacking fault

We investigate the magneto-optical properties of excitons bound to single stacking faults in high-purity GaAs. We find that the two-dimensional stacking fault potential binds an exciton composed of an electron and a heavy-hole, and confirm a vanishing in-plane hole $g$-factor, consistent with the atomic-scale symmetry of the system. The unprecedented homogeneity of the stacking-fault potential leads to ultra-narrow photoluminescence emission lines (with full-width at half maximum ${\lesssim 80~\mu \text{eV} }$) and reveals a large magnetic non-reciprocity effect that originates from the magneto-Stark effect for mobile excitons. These measurements unambiguously determine the direction and magnitude of the giant electric dipole moment (${\gtrsim e \cdot 10~\text{nm}}$) of the stacking-fault exciton, making stacking faults a promising new platform to study interacting excitonic gases.

Efficiency of Enzymatic O2 Reduction by Myrothecium verrucaria Bilirubin Oxidase Probed by Surface Plasmon Resonance, PMIRRAS, and Electrochemistry

Deciphering which parameters control the immobilization of enzymes on solid supports is essential for the development of biotechnological devices such as biosensors, bioreactors, and enzymatic fuel cells. In this work, we used surface plasmon resonance (SPR) coupled with electrochemistry and polarization modulated infrared reflection absorption spectroscopy (PMIRRAS) to correlate the loading, the conformation, and the activity of Myrothecium verrucaria bilirubin oxidase (Mv BOD) enzymes immobilized on two oppositely charged self-assembled monolayers (SAMs) on gold electrodes. The SPR signal showed that an enzyme layer close to a monolayer was formed by spontaneous adsorption on both negatively and positively charged SAMs. A different catalytic process for O2 reduction was obtained, however, being a direct catalysis at negative interfaces and a mediated catalysis at positive interfaces, in relation to the charge of the amino acids surrounding the surface of the Cu T1 and the dipole moment direction of Mv B...

Cold denaturation induces inversion of dipole and spin transfer in chiral peptide monolayers.

Chirality-induced spin selectivity is a recently-discovered effect, which results in spin selectivity for electrons transmitted through chiral peptide monolayers. Here, we use this spin selectivity to probe the organization of self-assembled α-helix peptide monolayers and examine the relation between structural and spin transfer phenomena. We show that the α-helix structure of oligopeptides based on alanine and aminoisobutyric acid is transformed to a more linear one upon cooling. This process is similar to the known cold denaturation in peptides, but here the self-assembled monolayer plays the role of the solvent. The structural change results in a flip in the direction of the electrical dipole moment of the adsorbed molecules. The dipole flip is accompanied by a concomitant change in the spin that is preferred in electron transfer through the molecules, observed via a new solid-state hybrid organic–inorganic device that is based on the Hall effect, but operates with no external magnetic field or magnetic material.