Change In Dipole Moment Research Articles

Theoretical investigation on electronic structure and stability of some inverted cucurbiturils by density functional theory

ABSTRACTStructure and stability of diastereoisomers of cucurbit[n]urils (CB[n = 5–10]), the inverted CB[n]s, were investigated by density functional theory (DFT) computations. All the inverted CB[n]s were less stable than their normal CB[n]s and the mono-inverted ones with one inverted glycoluril unit in their structures were more stable than their doubly-inverted isomers. Relative change in dipole moments and molecular electrostatic potentials (MEP) were discussed with the deformation in geometric structure and charge distribution of the normal and inverted CB[n]s.

Probing the reverse micelle environment with a cationic dye by varying oil and water content of micelles.

In the present work, spectroscopic properties of crystal violet (CV) within water-in-hexane sodium base (2-ethyl hexyl) sulfosuccinate (AOT) reverse micellar environment was investigated as a function of water contents (W = [H2O]/[AOT] = 6,10) in AOT and also function of mass fraction of nanodroplet (MFD = 0.01, 0.04, 0.07, and 0.1) by using UV/visible, and fluorescence techniques. A deviation in the absorption spectra of crystal violet at the high CV concentration (0.002 M) was observed in the AOT reversed micelles. The Quenching in the emission intensity of crystal violet at high CV concentration and blue shift in λmax of fluorescence of dye was observed as a function of MFD in AOT RMs. At high concentration of dye, molecules of CV can be reside interfacial region but near core of AOT. At low dye concentration, the CV molecules also can be in interfacial region but far from core. The Stokes shift of CV at high concentration decreased with mass fraction of nano-droplet (MFD), whereas at the low CV concentration, its variation often increased. The ratio of ground state to the excited state dipole moment of crystal violet dye also affected by the change in W values and MFD values. The change in dipole moment and stokes shift indicates the different environment around CV for different W and MFD values.

Integral Method Analysis of Electroabsorption Spectra and Electrophotoluminescence Study of (C4H9NH3)2Pbl4 Organic–Inorganic Quantum Well

Electric-field-induced changes in absorption and photoluminescence (PL) spectra and in PL decay profile have been measured for two-dimensional hybrid organic–inorganic halide perovskite semiconductor, ((C4H9NH3)2Pbl4) (N1). Electroabsorption (E-A) spectra observed at room temperature and at a low temperature of 45 K were analyzed by assuming the Stark shift, and the magnitudes of the change in electric dipole moment and polarizability following photoexcitation were determined. The strong signal observed in the E-A spectra at 45 K was interpreted in terms of the weak absorption band which shows extremely large Stark shift resulting from the large change in polarizability following photoexcitation. Electrophotoluminescence spectra of this compound, that is, field-induced change in PL spectra, show that PL of N1 is quenched by the application of electric field. Field effects on PL decay profiles show that the quenching results both from the field-induced decrease of the population of the emitting state follo...

The effect of electron-donating substituents on tuning the nonlinear optical properties of pyrene-core arylamine derivatives: DFT calculations

Abstract Using the LC-DFT/M06 functional, we elucidate the structure-property relationship for the effect of electron-donating substituents on tuning the nonlinear optical (NLO) and optical properties of a series of pyrene-core (PY) arylamine derivatives. After successfully synthesizing N1,N1,N3,N3,N6,N6,N8,N8-octakis(4-methoxyphenyl)pyrene-1,3,6,8-tetraamine (PYOMe), its crystallographic data and photophysical properties were reported. By substituting/removing the terminal –OMe donors in PYOMe with groups with different electron donation abilities, we systematically designed novel derivatives with adjusted optical and NLO properties. Comparison between the obtained results and those of the prototypical NLO chromophore p-nitroaniline (pNA) were performed. The experimental data from PYOMe and pNA allowed us to validate the applied DFT functional among six tested functionals. Charge transfer descriptors, such as the charge transfer distance ( D CT ), the amount of charge transferred ( q CT ), and dipole moment change ( μ CT ), and other indices ( H and t ) were investigated. The trend observed for the β tot amplitudes was justified by the parameters in the two-level model and by the total term Δ μ f / Δ E 3 for two crucial transitions of the investigated systems. Our investigation reveals that substitution of these systems results in larger β tot amplitudes compared to that of the unsubstituted system. However, their β tot amplitudes are smaller than that of pNA, except that of PY substituted with phenoxy groups. Additionally, our results indicate that optimal combinations of the different (optical) parameters involved in two-level approximation affects the NLO properties of the systems under investigation to a larger extent.

Mechanisms underlying the shape effect on nano-piezoelectricity

Piezoelectric nanowires (NWs) or nanotubes (NTs) are a vital component in nano-electromechanical and piezo-electronic device development. With various cross-sectional geometries achievable, the piezoelectric property-cross sectional shape relation is of fundamental interest. As existing studies (primarily based on first-principles calculations) are limited to ultrathin NWs or analysis based on continuum theories, the present work employs molecular statics (MS) simulation, which enables the examination of NWs/NTs up to cross-sectional size of 20.6 nm and elucidation of the underlying mechanisms at the atomic level. Analyses are carried out for NWs/NTs with experimentally observed geometry by comparing their size-dependence of effective piezoelectric constant and the radial distribution of the average dipole moment change with strain. The fraction of strain-sensitive dipoles, initial volume contraction and surface piezoelectricity were shown to control the shape effect on the piezoelectricity of ZnO nanostructures.

On the change of paraelectric behavior of water at T = T* = 60 °C as a polar liquid

Curie-Weiss temperature dependence of the dielectric permittivity has been shown to take place in water. A bilinear change at has been reported recently. In this work an effective field statistical theory is developed for polar liquids such as water. A change of elementary dipole moment at describes well its behavior with temperature. It implies a change in dipole moment from a value close to that in ice to another close to that in water vapor. The Lindemann relationship is used to estimate the fractional oscillation of the water molecule from melting temperature T = 0 °C to in terms of the water Debye temperature and basic geometrical parameters.

BODIPY parent compound: Fluorescence, singlet oxygen formation and properties revealed by DFT calculations

The BODIPY (boron-dipyrromethene) parent compound is synthesized to measure its fluorescence properties and singlet oxygen generation ability. The ground state, excited singlet state S1 and triplet state T1 geometry and properties in gas, solid state and organic solvents are calculated by DFT method. This unsubstituted BODIPY (BDP) has good solubility in all solvents ranging from non polar n-hexane to highly polar water. BDP exhibits bright green fluorescence with high fluorescence quantum yield (Φf) and long fluorescence lifetime (τf) values in all solvents, Φf of BDP varies from the lowest 0.79 in toluene to the highest 0.98 in water, while τf varies from the shortest 6.02 ns in toluene to the longest 7.36 ns in water. τf and Φf show good linear correlation with the refractive index (n) of a solvent: τf = 17.13 – 7.36·n and Φf = 2.51–1.16·n (for air-saturated solution). The fluorescence lifetime in each solvent, however, becomes longer in deoxygenated solutions, suggesting that the presence of molecular oxygen leads to the formation of BDP T1 and singlet oxygen: BDP(S1)+O2 → BDP(T1)+1O2. Singlet oxygen formation quantum yield was measured to be up to 0.083. The absorption and emission maximum (λabs and λem), however, are only slightly changed by solvent nature: λabs= 500 ± 4 nm and λem= 510 ± 4 nm. The spectral shape and peak maximum for its absorption and emission are little affected by solvent nature. DFT calculation reveals that the geometry difference between S0 and S1 state of BDP is very small, so that the dipole moment change is also small. The calculated charges of carbon atoms, however, are very different and can well explain their different reactivity to nucleophiles. The calculated absorption spectra (peak maximum λcal) by TD-DFT method shows a good linear relation with experimental value λexp: λexp = 1.19 λcal. These results provide the basis for elucidating the mechanism or photophysical processes involving BODIPY as the functional units.

A leaning amine-ketone dyad with a nonconjugated linker: solvatofluorochromism and dual fluorescence associated with intramolecular charge transfer.

Dyad 4, comprising a triphenylamine (TPA) electron donor and 1,4-pentadien-3-one (pentadienone) electron acceptor tethered by a nonconjugated linker, displays solvatofluorochromism (SFC) and dual fluorescence associated with intramolecular charge transfer (ICT) in the excited state. While the fluorescence arises from a locally excited state of 4 (LE-4*) in saturated hydrocarbon solvents, the fluorescence from the ICT state of 4 (ICT-4*) occurs in aprotic solvents. ICT-4* has a much greater dipole moment than its corresponding ground state. The results of theoretical calculations suggest that the conversion of LE-4* to ICT-4* involves a unique structural change like a leaning of the pentadienone moiety. Two factors are responsible for the significant SFC displayed by 4, the first being the high electron-donating and -accepting abilities of the respective locally excited TPA and pentadienone moieties in LE-4* and the other being a rigid ethano bridge that links the two moieties in ICT-4*. The former property facilitates photoinduced electron-transfer (PET) and the latter prevents full single electron transfer (SET) by prohibiting direct π-conjugation and the spatial approach of the two dyad components. Consequently, these electronic and geometrical features lead to SFC arising from a large dipole moment change caused by ICT and partial intramolecular SET.

Theoretical study on twisted intramolecular charge transfer of 1-aminoanthraquinone in different solvents**Project supported by the Program of Outstanding Innovation Team of Hubei Normal University, China (Grant No. T201502), the Natural Science Foundation of Hubei Province, China (Grant Nos. 2014CFB349 and 2016CFC742), and the National Natural Science Foundation of China (Grant No. 11674355).

The twisted intramolecular charge transfer and the excited state relaxation of 1-aminoanthraquinone (1-NH2-AQ) in different solvents are investigated using quantum chemical calculations in this paper. The geometries of the ground state are optimized both in gas and solvents based on the high-level ab initio calculations, the lowest excited singlet state geometry is optimized only in gas for simplicity. An intramolecular charge transfer property is substantiated by the large change of dipole moments between the S0 and S1 states. The mechanism of twisted intramolecular charge transfer is proposed by the conformational relaxation on the potential surface of the S1 state. Quantum chemical calculations present that internal conversion and intersystem crossing are important approaches to the ultrafast deactivation of the S1 state via the twisting of the amino group. The smaller energy difference between the S0 and S1 state shows that the internal conversion process is much faster in a polar solvent than in a nonpolar solvent. Energy intersections between the T2 and S1 state in cyclohexane and dioxane indicate a faster intersystem crossing process in them than in ethanol. These theoretical results agree well with the previous experimental results. Energy barriers are predicted on the potential surface of the S1 state, and they have a positive correlation to solvent viscosity, and the timescale of twisted intra-molecular charge transfer in dioxane is predicted to be longer than in cyclohexane and ethanol.

Spectroscopic, DFT and antimicrobial activity of Zn(II), Zr(IV), Ce(IV) and U(VI) complexes of N,N‐ chelated 4,6‐bis (4‐chlorophenyl)‐2‐amino‐1,2‐dihydropyridine‐3‐carbinitrile

Four novel metal complexes of 4,6‐bis (4‐chlorophenyl)‐2‐amino‐1,2‐dihydropyridine‐3‐carbinitrile (H2L) with Zn(II), Zr(IV), Ce(IV) and U(VI) were synthesized. The structure was elucidated using elemental analysis, melting point, molar conductivity; spectroscopic techniques (IR, 1H NMR, UV–Vis., mass spectra) as well as thermo gravimetric analysis. The spectroscopic data proved that H2L chelated with the metal ions as a bidentate ligand through Namino and Ncarbinitrile atoms. The molecular structure of the complexes was determined using density functional theory (DFT). The central metal ion in each complex is six‐coordinate and the angles around it vary from 62.74° to 166.46°; these values agree with distorted octahedral geometry. The calculated total energy of the complexes found in the region – 406.342 to −459.717 au and the dipole moment change from 4.675 to 13.171D. The antibacterial and antifungal activities of the ligand, metal salts and complexes were estimated on some microorganisms. The complexes showed significant antibacterial profile in comparison to the free ligand.

Insights into the unusual dual fluorescence of the ortho-amino analogue of green fluorescent protein chromophore

Even though both p-aminobenzonitrile (p-ABN) and o-ABDI [o-amino analogue of green fluorescent protein (GFP)] have the same electron-donating amino group, o-ABDI displays dual fluorescence while p-ABN exhibits single fluorescence. Even though both o-AABDI (o-acetamido analogue of GFP) and o-ABDI have the similar intramolecular hydrogen bonding, o-ABDI displays dual fluorescence while o-AABDI shows single fluorescence. To explore the unusual phenomenon of dual fluorescence for o-ABDI, we used the time-dependent density functional theory (TD-DFT) method with the polarizable continuum model (PCM) to study the S1 excited state of o-ABDI in acetonitrile. What we found is that o-ABDI in acetonitrile has two isomeric conformations (minima) in the S1 excited state, the twisted intramolecular charge transfer (TICT) and the localized excited (LE) states. The TICT state involves a large dipole moment change during fluorescence emission, while the LE state with a flat structure involves only a slight dipole moment change without a charge transfer during fluorescence emission. Even though both o-DMABDI (o-dimethylamino analogue of GFP) and o-ABDI have the TICT excited state, o-DMABDI does not have the stabilized LE S1 state while o-ABDI does. It is because the intramolecular hydrogen bonding of o-ABDI makes its LE S1 state highly stabilized, and that leads its LE S1 state to become a global minimum. That is why o-ABDI displays dual fluorescence.

Electroabsorption Studies of Multicolored Lead Halide Perovskite Nanocrystalline Solid Films

Electroabsorption (E-A) spectra of lead halide perovskites, that is, CH3NH3PbI3–xBrx (x = 0–3), which show large spectral shift depending on the ratio between iodine and bromide, have been measured. By analyzing E-A spectra with the integral method, spectral shape of the absorption spectra for the first exciton band and binding energy of exciton have been determined. Magnitudes of the change in electric dipole moment and molecular polarizability following excitation into the exciton state have been also evaluated in these perovskites. The binding energy of electron and hole in exciton of these materials as well as the magnitude of change in electric dipole moment following exciton absorption is roughly the same, suggesting that the difference of the photoenergy conversion in photovoltaic cells using these materials comes from the difference in light harvesting effect and difference in carrier mobility, not from the difference in carrier generation efficiency. The frequency-dependent third-order nonlinear ...

Approximately 2400-Year Cycle in the Concentration of Cosmogenic Radionuclides: Sources of Variations

Cosmogenic isotopes, including 14C, 10Be, and 7Be, are produced in the Earth’s atmosphere under the effect of cosmic rays. The rate of their production is determined by several factors, such as the intensity of primary galactic cosmic rays, the level of solar activity, and the strength of the Earth’s magnetic field. Changes in the isotope concentrations and distributions receive contributions from mixing processes proceeding in the surrounding medium: the atmosphere, biosphere, and oceans. The isotopes 14C and 10Be are the most important for studying solar activity and climate. Investigation of isotope concentrations reveal that there are both long-term trends and cyclic components. As for 14C, the long-term component caused by the change in the magnetic dipole moment of the Earth with a characteristic time of about 104 years is the most commonly known. It is well known that the concentrations of cosmogenic isotopes change cyclically with time. The ~2400-year cycle (Hallstatt cycle) and the ~210-year cycle (de Vries cycle) are the most famous. In the present article, we discuss the possible origin of the ~2400-year cycle.

Dipole Moment and Polarizability of Tunable Intramolecular Charge Transfer States in Heterocyclic π-Conjugated Molecular Dyads Determined by Computational and Stark Spectroscopic Study.

The annulation of two redox-active molecules into a compact and planar structure paves the way toward a new class of electronically versatile materials whose physical properties can be tuned via a substitution of one of the constituting moieties. Specifically, we present tetrathiafulvalene-benzothiadiazole donor-acceptor molecules. The critical role played by the dielectric properties of these molecules is evident by the large spectral shifts of the ground-state absorption spectra in a range of solvents. Stark spectroscopy is performed to determine experimentally dipole and polarizability change over transitions in the visible range with particular attention to the transition from the highest-occupied molecular orbital (HOMO) to the lowest-unoccupied molecular orbital (LUMO). The experimental results are compared to the results of time-dependent density functional theory calculations, and we reciprocally validate results from calculation and experiment. This allows us to filter out effective models and reveal important insights. The calculations are initially performed in the gas phase and subsequently a polarizable continuum model is adopted to probe the influence of the solvent on the molecular dielectric properties. The results show a large charge displacement from the HOMO to the LUMO and confirm the intramolecular charge transfer nature of the lowest-energy transition. Substitution of the acceptor moiety with electron-withdrawing groups results in changes to the experimentally determined molecular properties consistent with the effects predicted by computational results. The dominant contribution to the electroabsorption signal is due to the change in dipole moment, which is measured to be roughly 20 D for all samples and forms a small angle with the transition dipole moment in a toluene solvent environment.

Spontaneous Symmetry Breaking Facilitates Metal-to-Ligand Charge Transfer: A Quantitative Two-Photon Absorption Study of Ferrocene-phenyleneethynylene Oligomers.

Change of the permanent molecular electric dipole moment, Δμ, in a series of nominally centrosymmetric and noncentrosymmteric ferrocene-phenyleneethynylene oligomers was estimated by measuring the two-photon absorption cross-section spectra of the lower energy metal-to-ligand charge-transfer transitions using femtosecond nonlinear transmission method and was found to vary in the range up to 12 D, with the highest value corresponding to the most nonsymmetric system. Calculations of the Δμ performed by the TD-DFT method show quantitative agreement with the experimental values and reveal that facile rotation of the ferrocene moieties relative to the organic ligand breaks the ground-state inversion symmetry in the nominally symmetric structures.

Charge-transfer excited state in pyrene-1-carboxylic acids adsorbed on titanium dioxide nanoparticles

The electronic structure of excited photosensitizer adsorbed at the surface of a solid is the key factor in the electron transfer processes that underlie the efficiency of dye-sensitized solar cells and photocatalysts. In this work, Stark effect (electroabsorption) spectroscopy has been used to measure the polarizability and dipole moment changes in electronic transitions of pyrene-1-carboxylic (PCA), -acetic (PAA) and -butyric (PBA) acids in ethanol, both free and adsorbed on colloidal TiO2, in glassy ethanol at low temperature. The lack of appreciable increase of dipole moment in the excited state of free and adsorbed PAA and PBA points that two or more single bonds completely prevent the expansion of π-electrons from the aromatic ring towards the carboxylic group, thus excluding the possibility of direct electron injection into TiO2. In free PCA, the pyrene's forbidden S0→S1 transition has increased intensity, exhibits a long progression in 1400cm−1 Ag mode and is associated with |∆μ| of 2 D. Adsorption of PCA on TiO2 causes a broadening and red shift of the S0→S1 absorption band and an increase in dipole moment change on electronic excitation to |∆μ|=6.5 D. This value increased further to about 15 D when the content of acetic acid in the colloid was changed from 0.2% to 2%, and this effect is ascribed to the surface electric field. The large increase of |∆μ| points that the electric field effect can not only change the energetics of electron transfer from the excited sensitizer into the solid, but can also shift the molecular electronic density, thus directly influencing the electronic coupling factor relevant for electron transfer at the molecule-solid interface.

Cis-to- Trans Isomerization of Azobenzene Derivatives Studied with Transition Path Sampling and Quantum Mechanical/Molecular Mechanical Molecular Dynamics.

Azobenzene-based molecular photoswitches are becoming increasingly important for the development of photoresponsive, functional soft-matter material systems. Upon illumination with light, fast interconversion between a more stable trans and a metastable cis configuration can be established resulting in pronounced changes in conformation, dipole moment or hydrophobicity. A rational design of functional photosensitive molecules with embedded azo moieties requires a thorough understanding of isomerization mechanisms and rates, especially the thermally activated relaxation. For small azo derivatives considered in the gas phase or simple solvents, Eyring's classical transition state theory (TST) approach yields useful predictions for trends in activation energies or corresponding half-life times of the cis isomer. However, TST or improved theories cannot easily be applied when the azo moiety is part of a larger molecular complex or embedded into a heterogeneous environment, where a multitude of possible reaction pathways may exist. In these cases, only the sampling of an ensemble of dynamic reactive trajectories (transition path sampling, TPS) with explicit models of the environment may reveal the nature of the processes involved. In the present work we show how a TPS approach can conveniently be implemented for the phenomenon of relaxation-isomerization of azobenzenes starting with the simple examples of pure azobenzene and a push-pull derivative immersed in a polar (DMSO) and apolar (toluene) solvent. The latter are represented explicitly at a molecular mechanical (MM) and the azo moiety at a quantum mechanical (QM) level. We demonstrate for the push-pull azobenzene that path sampling in combination with the chosen QM/MM scheme produces the expected change in isomerization pathway from inversion to rotation in going from a low to a high permittivity (explicit) solvent model. We discuss the potential of the simulation procedure presented for comparative calculation of reaction rates and an improved understanding of activated states.

First principles calculations on the influence of solute elements and chlorine adsorption on the anodic corrosion behavior of Mg (0001) surface

The influences of solute atoms (Li, Al, Mn, Zn, Fe, Ni, Cu, Y, Zr) and Cl adsorption on the anodic corrosion performance on Mg (0001) surface have been investigated based on first-principles calculations, which might be useful for the design of corrosion-resistant Mg alloys. Work function and local electrode potential shift are chosen as descriptors since they quantify the barrier for charge transfer and anodic stability. We found that at 25% surface doping rate, Y decreased the work function of Mg, while the impact of remaining doping elements on the work function of Mg was trivial due to the small surface dipole moment change. The adsorption of Cl destabilized the Mg atoms at surface by weakening the bonding between surface Mg atoms. We find that a stronger hybridization of d orbits of alloying elements (e.g. Zr) with the orbits of Mg can greatly increase the local electrode potential,which even overbalances the negative effect introduced by Cl adsorbates and hence improves the corrosion resistance of Mg alloys.

The origin of pyroelectricity in tourmaline at varying temperature

Although tourmaline is a common pyroelectric material, the origins of pyroelectricity in tourmaline at varying temperature are still unclear. In the present work, based on the crystallographic data obtained from X-ray diffraction refinement, we calculated the intrinsic electric dipole moments of the typical coordination polyhedra ([XO9], [YO6], [ZO6], [TO4], [BO3]) in tourmaline unit cell along c-axis at various temperature ranging from 25 °C to 300 °C. The theoretical pyroelectric coefficients obtained based on these intrinsic electric dipole moments were consistent with the experimental results, indicating that the pyroelectric coefficient of tourmaline at varying temperature is mainly originated from the intrinsic electric dipole moment changes of the [XO9], [YO6], [ZO6], [TO4], [BO3] polyhedra along c-axis. Furthermore, the deformations of the [SiO4] tetrahedra and [BO3] polyhedra along c-axis direction were dominant in the change of total intrinsic electric dipole moment in the tourmaline unit cell. These results were further supported by the analyses of the polarized Raman spectra and infrared spectra.

Synthesis, solvatochromism, photochemistry, DNA binding, photocleavage, cytotoxicity and molecular docking studies of a ruthenium(II) complex bearing photoactive subunit

A new pyrene-appended polypyridine ligand, wherein the 1,10-phenanthroline (phen) and the photoactive pyrene chromophore is connected via a CN bond; N-[1,10]phenanthrolin-5-yl-pyrenylmethanimine (ppym) and its complex [Ru(phen)2(ppym)]2+ was synthesized. Characterization of the ligand and the complex was investigated through elemental analysis, UV-vis, IR, 1H NMR, MALDI-TOF mass and cyclic voltammetry techniques. The change in dipole moment of the ground and the excited state of the chromophores with the different solvent polarity was examined. The dual emission (Excimer) characteristics observed for ligand ppym has been probed by detailed photophysical studies involving variable concentration, excitation wavelength and solvent experiments and also transition metal ion induced quenching data. 3MLCT emission was observed for [Ru(phen)2(ppym)]2+. Absorption, emission, thermal melting and viscosity studies reveal that [Ru(phen)2(ppym)]2+ bind to CT DNA avidly and that ruthenium-bound ppym intercalate inside the base sets of the duplex. Also, the DNA photonicking activity (pBR 322 DNA, λexc = 450 nm) of [Ru(phen)2(ppym)]2+ is almost four times higher than [Ru(phen)3]2+. Through inhibitor studies, we found that reactive oxygen species play a major role in the photo cleavage of [Ru(phen)2(ppym)]2+. The cytotoxicity of the complex was tested in Human cancer cell line (ZR-75-30) by MTT assay. In addition, modeling studies scaffold the intercalative binding to the d(CGCAATTGCG)2 sequence.