Variation Of Dipole Moment Research Articles

Origin of the π-stacking induced shifts in absorption spectral bands of the green fluorescent protein chromophore

We present the results of computational studies of the shifts in absorption bands in the 4-hydroxybenzylidene-1,2-dimethylimidazolinone (HBDI), a synthetic analogue of the green fluorescent protein chromophore, induced by its π-stacking interaction with aromatic compounds. The set of model systems composed of HBDI in the anionic form π-stacked with the substituted derivatives of benzene is considered. Ground state equilibrium geometry parameters are obtained at the MP2/cc-pvdz level of theory and the vertical S0,min-S1 excitation energies are estimated using the XMCQDPT2/sa2-CASSCF(12/12) approach. It is shown that the bathochromic shifts are obtained for systems with smaller values of the dipole moment variation while the hypsochromic shifts correlate with larger values of this quantity. We also demonstrate that absolute values of the S0,min-S1 transition energy shift well correlate with the calculated bond interaction energy parameter of π-stacked complexes.

Exploring the effect of aggregation-induced emission on the excited state intramolecular proton transfer for a bis-imine derivative by quantum mechanics and our own n-layered integrated molecular orbital and molecular mechanics calculations**Project supported by the National Natural Science Foundation of China (Grant Nos. 11574115 and 11704146).

We theoretically investigate the excited state intramolecular proton transfer (ESIPT) behavior of the novel fluorophore bis-imine derivative molecule HNP which was designed based on the intersection of 1-(hydrazonomethyl)-naphthalene-2-ol and 1-pyrenecarboxaldehyde. Especially, the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods for HNP monomer are introduced. Moreover, the “our own n-layered integrated molecular orbital and molecular mechanics” (ONIOM) method (TDDFT:universal force field (UFF)) is used to reveal the aggregation-induced emission (AIE) effect on the ESIPT process for HNP in crystal. Our results confirm that the ESIPT process happens upon the photoexcitation for the HNP monomer and HNP in crystal, which is distinctly monitored by the optimized geometric structures and the potential energy curves. In addition, the results of potential energy curves reveal that the ESIPT process in HNP will be promoted by the AIE effect. Furthermore, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) for the HNP monomer and HNP in crystal have been calculated. The calculation demonstrates that the electron density decrease of proton donor caused by excitation promotes the ESIPT process. In addition, we find that the variation of atomic dipole moment corrected Hirshfeld population (ADCH) charge for proton acceptor induced by the AIE effect facilitates the ESIPT process. The results will be expected to deepen the understanding of ESIPT dynamics for luminophore under the AIE effect and provide insight into future design of high-efficient AIE compounds.

Extending Global Continuous Geomagnetic Field Reconstructions on Timescales Beyond Human Civilization

AbstractStudy of the late Quaternary geomagnetic field contributes significantly to understanding the origin of millennial‐scale paleomagnetic secular variations, the structure of geomagnetic excursions, and the long‐term shielding by the geomagnetic field. A compilation of paleomagnetic sediment records and archeomagnetic and lava flow data covering the past 100 ka enables reconstruction of the global geomagnetic field on such long‐term scales. We use regularized inversion to build the first global, time‐dependent, geomagnetic field model spanning the past 100 ka, named GGF100k (Global Geomagnetic Field over the past 100 ka). Spatial parametrization of the model is in spherical harmonics and time variations with cubic splines. The model is heavily constrained by more than 100 continuous sediment records covering extended periods of time, which strongly prevail over the limited number of discrete snapshots provided by archeomagnetic and volcanic data. Following an assessment of temporal resolution in each sediment's magnetic record, we have introduced smoothing kernels into the forward modeling when assessing data misfit. This accommodates the smoothing inherent in the remanence acquisition in individual sediment paleomagnetic records, facilitating a closer fit to both high‐ and low‐resolution records in regions where some sediments have variable temporal resolutions. The model has similar spatial resolution but less temporal complexity than current Holocene geomagnetic field models. Using the new reconstruction, we discuss dipole moment variations, the time‐averaged field, and paleomagnetic secular variation activity. The new GGF100k model fills the gap in the geomagnetic power spectrum in the frequency range 100–1,000 Ma−1.

Evolutions on surface chemistry, microstructure, morphology and electrical characteristics of SnO2/p-Si heterojuction under various annealing parameters

The influences of annealing temperature and ambient on surface chemistry, microstructure, morphology and electrical characteristics of Tin Oxide (SnO2)/Si heterojuctions are systematically identified. Metallic and oxygen deficient SnO2-x bonds have been consistently treated to stoichiometric SnO2 with annealing temperatures up to 600 °C in nitrogen environment. It has been observed that further increase in the annealing temperature causes the formation of the silicate layer. Presence of hydrogen in forming gas environment causes formation of the oxygen deficient SnO2-x, while the presence of the oxygen contributes to the formation of the stoichiometric SnO2 layer in oxygen annealing ambient. Parasitic phases significantly affect the crystalline structure of the films. Surface roughness of the samples decreases up to 1.02 nm which is strongly correlated with stress and strain on the film. On the other hand, oxidations of the dangling bonds and/or hydrogen diffusion cause variations in the total dipole moments which significantly change the capacitance. Depending on the annealing parameters, effective charge densities and interface trap densities decrease to 1011 cm−2, while the ideality factor and barrier potential are improved to 1.43 and 0.59 eV, respectively. Owing to the crystallization of the SnO2 layer, leakage current increase at low temperature annealing. However, passivation of the dangling bonds becomes more effective than phase crystallization at higher temperatures on the leakage characteristics. The current study shows that any changes in the surface chemistry directly affect the device performance.

Theoretical Investigation on the Low-Lying States of LaP Molecule

The completely unexplored LaP molecule is investigated by ab initio methods. Potential energy curves for the low-lying states of LaP are constructed by means of the diffusion Monte Carlo method combined with three different trial functions. Spectroscopic constants are also numerically derived and the ground state is assigned, looking forward to experimental comparisons. Moreover, variations of the permanent dipole moments as a function of the internuclear separation for the two lowest states of the diatomic LaP are studied and analyzed.

Diffusion Monte Carlo calculations on LaB molecule

Potential energy curves for the lowest electronic states of LaB and LaB− have been calculated by ab initio calculations. The diffusion Monte Carlo method has been employed in combination with three different trial functions. Spectroscopic constants have also been numerically derived for the neutral molecule and compared with the only available theoretical work;[] however, predictions are provided for the corresponding constants for the anionic species which have not been reported yet. Our calculations suggest the high spin quintet state of LaB as the ground state with the triplet state higher in energy irrespective of the type of the functional used. This suggestion is in good accordance with the previous theoretical results calculated at B3LYP/LANL2DZ level of theory, whereas it contradicts with the prediction based upon B3LYP/SDD calculations in the same study. Moreover, variations of the permanent dipole moments as a function of the internuclear separations for the two electronic states of the neutral molecule have been studied and analyzed.

How Many Active Regions Are Necessary to Predict the Solar Dipole Moment?

Abstract We test recent claims that the polar field at the end of Cycle 23 was weakened by a small number of large, abnormally oriented regions, and investigate what this means for solar cycle prediction. We isolate the contribution of individual regions from magnetograms for Cycles 21, 22, and 23 using a 2D surface flux transport model, and find that although the top ∼10% of contributors tend to define sudden large variations in the axial dipole moment, the cumulative contribution of many weaker regions cannot be ignored. To recreate the axial dipole moment to a reasonable degree, many more regions are required in Cycle 23 than in Cycles 21 and 22 when ordered by contribution. We suggest that the negative contribution of the most significant regions of Cycle 23 could indeed be a cause of the weak polar field at the following cycle minimum and the low-amplitude Cycle 24. We also examine the relationship between a region’s axial dipole moment contribution and its emergence latitude, flux, and initial axial dipole moment. We find that once the initial dipole moment of a given region has been measured, we can predict the long-term dipole moment contribution using emergence latitude alone.

Tunable Resonance Coupling in Single Si Nanoparticle-Monolayer WS2 Structures.

Two-dimensional semiconducting transition metal dichalcogenides (TMDCs) are extremely attractive materials for optoelectronic applications in the visible and near-infrared range. Coupling these materials to optical nanocavities enables advanced quantum optics and nanophotonic devices. Here, we address the issue of resonance coupling in hybrid exciton-polariton structures based on single Si nanoparticles (NPs) coupled to monolayer (1L)-WS2. We predict a strong coupling regime with a Rabi splitting energy exceeding 110 meV for a Si NP covered by 1L-WS2 at the magnetic optical Mie resonance because of the symmetry of the mode. Further, we achieve a large enhancement in the Rabi splitting energy up to 208 meV by changing the surrounding dielectric material from air to water. The prediction is based on the experimental estimation of TMDC dipole moment variation obtained from the measured photoluminescence spectra of 1L-WS2 in different solvents. An ability of such a system to tune the resonance coupling is realized experimentally for optically resonant spherical Si NPs placed on 1L-WS2. The Rabi splitting energy obtained for this scenario increases from 49.6 to 86.6 meV after replacing air by water. Our findings pave the way to develop high-efficiency optoelectronic, nanophotonic, and quantum optical devices.

DFT and MP2 Calculations on Tautomers and Water-Assisted Proton Transfer on 1,2,5-Oxadiazol-4,3-diamine

In this work a detailed quantum-chemical comparison of the relative stability of six tautomers of 1,2,5-oxadiazol-4,3-diamine studied in the gas phase and solution. Theoretical calculations are carried out by the density functional theory (DFT/B3LYP) and MP2 methods using the standard 311++G(d,p) basis set. The results indicate that A is the most stable form in the gas phase and also is the predominant tautomer in solution at the DFT and MP2 methods. The transition states of proton transfer reaction are calculated. The variation of dipole moments and charges on atoms are studied in various solvent. Specific solvent effects with addition of one water molecule near the electrophilic centers of tautomer investigated. Also the transition state of proton transfer assisted by a water molecule was investigated.

Investigations on the charge transfer mechanism at donor/acceptor interfaces in the quest for descriptors of organic solar cell performance.

Herein, we theoretically and experimentally investigated the mechanisms of charge separation processes of organic thin-film solar cells. PTB7, PTB1, and PTBF2 have been chosen as donors and PC71BM has been chosen as an acceptor considering that effective charge generation depends on the difference between the material combinations. Experimental results of transient absorption spectroscopy show that the hot process is a key step for determining external quantum efficiency (EQE) in these systems. From the quantum chemistry calculations, it has been found that EQE tends to increase as the transferred charge, charge transfer distance, and variation of dipole moments between the ground and excited states of the donor/acceptor complexes increase; this indicates that these physical quantities are a good descriptor to assess the donor-acceptor charge transfer quality contributing to the solar cell performance. We propose that designing donor/acceptor interfaces with large values of charge transfer distance and variation of dipole moments of the donor/acceptor complexes is a prerequisite for developing high-efficiency polymer/PCBM solar cells.

Cosmogenic signature of geomagnetic reversals and excursions from the Réunion event to the Matuyama–Brunhes transition (0.7–2.14 Ma interval)

Long-term variations of the geomagnetic dipole moment (GDM) during periods of stable polarity and in transitional states (reversals and excursions) provide key information for understanding the geodynamo regime. Following several studies dealing with the Brunhes chron and the Matuyama–Brunhes transition, this study presents a new authigenic 10Be/9Be ratio (Be-ratio) record obtained from the MD97-2143 core (western Pacific Ocean). This new Be-ratio series yields a record of GDM variations covering the early Brunhes and mid to late Matuyama time period (i.e. 700–2140 ka), independently from the relative paleointensity (RPI) record obtained from the same core, that can be compared with available RPI records and stacks. Stratigraphic offsets measured between the Be-ratio peaks and the corresponding RPI minima reach 2 to 14 cm. They can be assigned to (post-) detrital remanent magnetization (pDRM) effects leading to magnetization locking-in delays varying from 2 to 12 ka in the studied core. 10Be overproduction episodes triggered by geomagnetic dipole moment lows (GDL) linked to polarity reversals and excursions confirm the global control exerted by the GDM on cosmogenic radionuclides production. A dipole moment reconstruction derived from the Beryllium-10 (BeDiMo) was compiled and calibrated using absolute paleointensity data. This independent record complements the available paleomagnetic RPI records, permitting 1) to overcome the pDRM lock-in offsets induced below the mixing layer, 2) to confront and increase the robustness and precision of GDM reconstructions and, 3) to better constrain the chronology of geomagnetic field instabilities during the mid to late Matuyama chron. Our new 10Be derived inventory is fully compatible with the GDL series linked to geomagnetic polarity reversals and events (Matuyama–Brunhes transition, Jaramillo and Olduvai subchron boundaries, Cobb Mountain, Réunion) and it strengthens the occurrence of several excursions (Kamikatsura, Santa Rosa, Punaruu, Bjorn, Gilsa, Gardar) that were until now reported from only sparse locations.

Improvement of solar-cycle prediction: Plateau of solar axial dipole moment

Aims. We report the small temporal variation of the axial dipole moment near the solar minimum and its application to the solar cycle prediction by the surface flux transport (SFT) model. Methods. We measure the axial dipole moment using the photospheric synoptic magnetogram observed by the Wilcox Solar Observatory (WSO), the ESA/NASA Solar and Heliospheric Observatory Michelson Doppler Imager (MDI), and the NASA Solar Dynamics Observatory Helioseismic and Magnetic Imager (HMI). We also use the surface flux transport model for the interpretation and prediction of the observed axial dipole moment. Results. We find that the observed axial dipole moment becomes approximately constant during the period of several years before each cycle minimum, which we call the axial dipole moment plateau. The cross-equatorial magnetic flux transport is found to be small during the period, although the significant number of sunspots are still emerging. The results indicates that the newly emerged magnetic flux does not contributes to the build up of the axial dipole moment near the end of each cycle. This is confirmed by showing that the time variation of the observed axial dipole moment agrees well with that predicted by the SFT model without introducing new emergence of magnetic flux. These results allows us to predict the axial dipole moment in Cycle 24/25 minimum using the SFT model without introducing new flux emergence. The predicted axial dipole moment of Cycle 24/25 minimum is 60--80 percent of Cycle 23/24 minimum, which suggests the amplitude of Cycle 25 even weaker than the current Cycle 24. Conclusions. The plateau of the solar axial dipole moment is an important feature for the longer prediction of the solar cycle based on the SFT model.

Substituent Effect on Intramolecular Charge Transfer of Symmetric Methoxy-Substituted Bi-1,3,4-oxadiazole Derivatives.

Intramolecular charge-transfer characteristics of a series symmetric methoxy -substituted bi-1,3,4-oxadiazole derivatives with various substituted positions and quantities have been studied with a combination of experimental techniques and theoretical calculations to investigate the substituent effect. Different degrees of fluorescence red shift in polar solvents are observed in these compounds. The meta-substituted molecule (BOXD-m-OCH3) exhibits a larger red shift (82 nm) than the other two monosubstituted molecules, BOXD-o-OCH3 (40 nm) and BOXD-p-OCH3 (37 nm); the polysubstituted molecules BOXD-D1 and BOXD-T1 show 80 and 104 nm red shifts, respectively, which are obviously larger than the monosubstituted molecules. The changes of molecular dipole moment between the ground state and charge transfer (CT) excited state are calculated to be on the same order with the degree of red shift (7.56 D in BOXD-o-OCH3, 12.07 D in BOXD-m-OCH3, 7.38 D in BOXD-p-OCH3, 14.79 D in BOXD-D1, and 16.80 D in BOXD-T1). Theoretical calculations at the density functional theory level reveal that the first singlet excited state of all of these compounds shows both π-π* and CT characteristics and the charge has been proven to transfer from the terminal methoxy phenyl group to the central bioxadiazole group. The analysis of charge transfer based on electron density shows that the greater the amount substituent, the more charge would be involved in the intramolecular charge transfer. In addition, the negative barycenter has a tendency to locate close to the methoxy substituent, which would cause the difference in the charge-transferred distance. The transferred charge and CT distance work jointly and finally lead to differences in dipole moment variation. These findings could provide very good guidance for the design of molecules with intramolecular charge-transfer characteristics.

Theoretical Study of the CO2 Adsorption by Zeolitic Imidazolate Frameworks (ZIFs)

Density functional theory with Grimme’s empirical correction, DFT-D3, has been used to examine the adsorption of a carbon dioxide molecule by different sets of zeolitic imidazolate framework materials (ZIF-1 to -4, -6 to -10, and -zni). We have calculated the interaction energy, the dipole moment variation, and the charge density difference for the different CO2@ZIF structures. Our study shows a strong relationship between the CO2 adsorption energy and the volume of the cavities of the ZIFs: the capture of carbon dioxide depends on the shape and size of the ZIFs pore in which CO2 has been inserted. The physisorption phenomena that govern the adsorption of CO2 molecule require both π-stacking interactions and hydrogen-like bonding. We have found that adsorption does not change the geometry of CO2, but it induces a significant structural change in some ZIF structures.

Origin of Solvent-independent Optical Property of Unsubstituted BODIPY Revisited

An unsubstituted BODIPY is revisited to clarify the origin of its characteristic nearly solvent-independent optical property based on the calculated results of the density functional theory (DFT) and time-dependent (TD)-DFT methods. Using the Kirkwood model, we provide a simple origin of the negligible difference in solvation energies between the S0 and S1 states based on their negligible variation in electric dipole moments, which are associated with the HOMO–LUMO transition and solvation effects on their structures.

Dipole moment and polarizability of impurity doped quantum dots driven by noise: Influence of hydrostatic pressure and temperature

Present study examines the pattern of variation of electric dipole moment (μ) and polarizability (αp) of impurity doped GaAs quantum dots (QDs) under combined presence of hydrostatic pressure and temperature and in presence of noise. Noise term carries a Gaussian white character and it has been introduced to the system via two different pathways; additive and multiplicative. Profiles of μ and αp have been monitored against the variations of hydrostatic pressure (HP), temperature and the noise strength. Under a given condition of HP and temperature, application of noise prominently influences the above two properties. However, the extent of influence depends on the noise strength and the pathway through which noise is introduced. The findings divulge feasible routes to control the dipole moment and polarizability of doped QD system through the interplay between HP, temperature and noise.

Second-order nonlinear optical switching with a record-high contrast for a photochromic and thermochromic bistable crystal.

Nonlinear optical (NLO) switchable materials are important for photonic and optoelectronic technologies. One important issue for NLO photoswitching, the most studied physical switching approach, is how to improve the switching contrast of second harmonic generation (SHG) in crystals, because the known values are generally below 3 times. Thermoswitching, as another approach, has shown impressive high SHG-switching contrasts (4-∞ times), but the fast decay of thermally induced states demands constant heat sources to maintain specific SHG intensities. We have synthesized a photochromic and thermochromic bistable acentric compound, β-[(MQ)ZnCl3] (MQ+ = N-methyl-4,4'-bipyridinium), which represents the first crystalline compound with both photo- and heat-induced SHG-switching behavior and the first example of a thermoswitchable NLO crystal that can maintain its expected second-order NLO intensity without any heat source. The SHG-switching contrast can reach about 8 times after laser irradiation or 2 times after thermal annealing. The former value is the highest recorded for photoswitchable NLO crystals. This work also indicates that higher SHG-switching contrasts may be obtained through increasing electron-transfer efficiency, variation of permanent dipole moment, and self-absorption.

Authigenic 10Be/9Be ratio signatures of the cosmogenic nuclide production linked to geomagnetic dipole moment variation since the Brunhes/Matuyama boundary.

Geomagnetic dipole moment variations associated with polarity reversals and excursions are expressed by large changes of the cosmogenic nuclide beryllium‐10 (10Be) production rates. Authigenic 10Be/9Be ratios (proxy of atmospheric 10Be production) from oceanic cores therefore complete the classical information derived from relative paleointensity (RPI) records. This study presents new authigenic 10Be/9Be ratio results obtained from cores MD05‐2920 and MD05‐2930 collected in the west equatorial Pacific Ocean. Be ratios from cores MD05‐2920, MD05‐2930 and MD90‐0961 have been stacked and averaged. Variations of the authigenic 10Be/9Be ratio are analyzed and compared with the geomagnetic dipole low series reported from global RPI stacks. The largest 10Be overproduction episodes are related to dipole field collapses (below a threshold of 2 × 1022 Am2) associated with the Brunhes/Matuyama reversal, the Laschamp (41 ka) excursion, and the Iceland Basin event (190 ka). Other significant 10Be production peaks are correlated to geomagnetic excursions reported in literature. The record was then calibrated by using absolute dipole moment values drawn from the Geomagia and Pint paleointensity value databases. The 10Be‐derived geomagnetic dipole moment record, independent from sedimentary paleomagnetic data, covers the Brunhes‐Matuyama transition and the whole Brunhes Chron. It provides new and complementary data on the amplitude and timing of millennial‐scale geomagnetic dipole moment variations and particularly on dipole moment collapses triggering polarity instabilities.

The interactional behaviors and photo-physical properties of two triarylmethane drugs in solvent media

Frequent use of triarylmethane and its derivatives in many drugs makes the investigation of specific and non-specific interactions and spatial configuration of these materials in their pharmaceutical behavior, very important. Therefore, in this paper absorption and fluorescence spectra of two triarylmethane drugs (E133 andE143) were studied in different solvents. The solute's photo-physical behavior depends strongly on the solvent–solute interactions and solvent's nature, along with attached groups on triphenylmethane skeleton in solvent media. In order to understand the effect of intermolecular and intramolecular interactions on spectral behaviors of these dyes, and to conceive the nature and extend of solvent-solute interactions, the spectral variations were analyzed via the linear solvation energy relationships concept, suggested by Kamlet and Taft. In addition, by means of solvatochromic method, ground and excited states dipole moments as well as dipole moment variations, from ground to excited states, were calculated, in different media.

Solvents effect on the stability and reactivity of Tamoxifen and its nano metabolites as the breast anticancer drug

The effect of protic and aprotic solvents polarity on optimized geometry and some chemical reactivity indices for Tamoxifen (TAM) and three of its important metabolites, i.e. 3-hydroxy Tamoxifen (3-HTAM), Droloxifen, 4-hydroxy Tamoxifen (4-HTAM), Afimoxifen, and Z-N-desmethyl-4-hydroxy Tamoxifen, Endoxifen (ENDX), antitumor are studied theoretically by density functional theory calculations (B3LYP) with 6-311++G(d, p) basis set in combination with polarizable continuum model (PCM) in selected non polar (CCl4), polar protic (H2O, Ethanol) and polar aprotic (DMSO, Acetone) solvents. The solvent-induced stretching vibrational frequency shifts (SFS) and the solvation influence on the DFT based chemical reactivity indices such as atomic charges, HOMO-LUMO energies, stabilization energies, variation of dipole moment of the conformers, ionization potential, electron affinity, chemical potential, hardness and softness have been investigated. The present results show the high kinetic stability and low chemical reactivity of Tam and its important active metabolite, Endoxifen, in water medium. So a drug carrier with good aqueous solubility should be applied to improve the bioavailability of these antitumor drugs.