Aggregation Of Dipoles Research Articles

An Adaptive Decomposition Approach with Dipole Aggregation Model for Polarimetric SAR Data

Polarimetric synthetic aperture radar (PolSAR) has attracted lots of attention from remote sensing scientists because of its various advantages, e.g., all-weather, all-time, penetrating capability, and multi-polarimetry. The three-component scattering model proposed by Freeman and Durden (FDD) has bridged the data and observed target with physical scattering model, whose simplicity and practicality have advanced remote sensing applications. However, the three-component scattering model also has some disadvantages, such as negative powers and a scattering model unfitted to observed target, which can be improved by adaptive methods. In this paper, we propose a novel adaptive decomposition approach in which we established a dipole aggregation model to fit every pixel in PolSAR image to an independent volume scattering mechanism, resulting in a reduction of negative powers and an improved adaptive capability of decomposition models. Compared with existing adaptive methods, the proposed approach is fast because it does not utilize any time-consuming algorithm of iterative optimization, is simple because it does not complicate the original three-component scattering model, and is clear for each model being fitted to explicit physical meaning, i.e., the determined adaptive parameter responds to the scattering mechanism of observed target. The simulation results indicated that this novel approach reduced the possibility of the occurrence of negative powers. The experiments on ALOS-2 and RADARSAT-2 PolSAR images showed that the increasing of adaptive parameter reflected more effective scatterers aggregating at the 45° direction corresponding to high cross-polarized property, which always appeared in the 45° oriented buildings. Moreover, the random volume scattering model used in the FDD could be expressed by the novel dipole aggregation model with an adaptive parameter equal to one that always appeared in the forest area.

Solvent Effects in Supramolecular Chemistry: Linear Free Energy Relationships for Common Intermolecular Interactions.

The proper choice of solvent is of major importance for all studies in supramolecular chemistry, including molecular recognition in host-guest systems, intramolecular folding, self-assembly, and supramolecular polymerization. In this Perspective, the usefulness of linear free energy relationships (LFERs) is highlighted to unravel the effect of solvents on coordinate bonding (e.g., cation-crown ether), hydrogen bonding, halogen bonding, dipolar aggregation, and π-π-stacking. For all of these intermolecular interactions widely applied in supramolecular systems, LFER relationships between the Gibbs binding energies and common solvent polarity scales including ET(30), π*, α or β based on solvatochromic dyes, scales derived from binding processes such as Gutmann donor and acceptor numbers or hydrogen bond donor and acceptor scales, or physical functions like the Kirkwood-Onsager or the Liptay-Onsager functions could be demonstrated. These relationships can now be applied toward a better understanding of the prevailing intermolecular forces for supramolecular interactions. They further enable a rational selection of the most suitable solvent for the preparation of self-assembled materials and the estimation of binding constants without the need for time-consuming comprehensive investigations of solvents.

Thermal and Optical Characterization of Multiple Hydrogen Bonded Liquid Crystals and Its Application in Display Devices

Novel homologous series of phloroglucinol (PG) and 4-n-alkyloxybenzoic acid (nOBA, n = 4 to 12) hydrogen bonded liquid crystal (HBLC) complex have been designed and synthesized. In the self-assembly process, intermolecular interaction between the molecules produce the multiple HBLCs with various shapes and structure. Existences of multiple hydrogen bonds in the PG+nOBA HBLC complex are confirmed by FT-IR spectroscopic method. Textural changes along with that phase transition temperature are identified by polarizing optical microscope (POM). Due to the polymerization, an induced stabilized smectic phase along with re-entrant disordered phase is noticed in the present PG+nOBA HBLC complex. The thermodynamic properties such as enthalpy values, thermal stability and thermal span width are analyzed by differential scanning calorimetry (DSC). An induced re-entrant phenomenon in the present HBLC complex is due to the dipolar aggregation has been discussed. The band gap energy is calculated by UV–Visible spectrometer (UV–Vis) which gives the clear evidence for the existence of band gap energy value (Eg = 3.5 eV) in the present HBLC complex. The desirable band gap in the present HBLC and its display device application is reported in the present communication. The other liquid crystal parameters (thermal stability, tilt angle, etc.) are also discussed.

Defined Merocyanine Dye Stacks from a Dimer up to an Octamer by Spacer-Encoded Self-Assembly Approach.

A series of well-defined chromophore stacks is obtained upon self-assembly of merocyanine and bis(merocyanine) dyes in nonpolar solvents. Careful design of the spacer moieties linking the dipolar chromophores within the bis(merocyanine) dyes allows one to direct the dipole-dipole interaction driven aggregation into stacks of desired size from dimer up to octamer. The spacer-encoded self-assembly process was investigated by UV/vis absorption spectroscopy showing an increase of the hypsochromic shift with increasing stack size. The structure of the largest aggregate comprising eight chromophores was analyzed by 1D and 2D nuclear magnetic resonance spectroscopic studies revealing a perfectly interdigitated centrosymmetric organization of the dipolar dyes and concomitant annihilation of the ground state dipole moment is observed in the UV/vis absorption spectra. This unprecedented series of dye stacks from dimer to octamer enabled a systematic study of the optical absorption properties in dependence of the stack size disclosing that the absorption features can be rationalized by molecular exciton theory. Our results show that the noncovalent synthesis approach based on dipolar aggregation is suitable for the design of well-defined dye aggregates of specific size, allowing in-depth studies to manifest structure-property relationships.

Orientational entropy and dipolar aggregation in mixtures of propylene carbonate + N,N-dimethylacetamide

The analysis of temperature behavior of the orientational entropy increment induced by the probing electric field, has been performed for two strongly polar liquids: propylene carbonate (PC) and dimethylacetamide (DMA), in the neat states as well as mixed together. It has been found that in the both neat fluids, the molecular dipoles self-assemble in a parallel, the head-to-tail way, wherein the effect is significantly higher in a less polar dimethylacetamide. This proves a better structural adjustment of DMA molecules to their effective self-association. In the mixtures of these two self-assembled liquids, the mixed dipolar aggregates consisting of molecules PC and DMA occur, in contrast to the mixtures of PC+DMSO (dimethyl sulfoxide), where the highly polar molecules of DMSO, being not capable for self-association, play only a neutral role of the filler the space between assemblies composed of PC molecules. The residual electrical conductivity in mixtures under investigation has been characterized.

Dipole-Dipole Interaction Driven Self-Assembly of Merocyanine Dyes: From Dimers to Nanoscale Objects and Supramolecular Materials.

π-Conjugation between heterocyclic donor (D) and acceptor (A) groups via a polymethine chain leads to dyes with dipole moments greater than 10 D. These dipole moments direct the self-assembly of the dyes into antiparallel dimer aggregates, even in dilute solution, with binding strengths that are far beyond those observed for other π-scaffolds whose self-assembly is driven primarily by dispersion forces. The combination of directionality and exceptional binding strength of dipolar interactions between D-π-A dyes indeed resembles the situation of the hydrogen bond. Thus, similar to the latter, dipolar interactions between merocyanine dyes, a unique class of D-π-A chromophores, can be utilized to construct sophisticated supramolecular architectures of predictable geometry, particularly in low polarity environments. For bis(merocyanine) dyes it has been demonstrated that the self-assembly pathway is encoded in the tether between the two constituent merocyanine chromophores. If the tether enables the antiparallel stacking of the two appended dyes, folding takes place, which may be followed by further self-assembly into extended H-aggregate π-stacks at higher concentrations in solvents of low polarity. For tethers that do not support folding, the formation of bimolecular complexes of four merocyanine units, cyclic oligomers, and supramolecular polymers has been observed. For the former case, that is, formation of a bimolecular stack of four merocyanine units from tweezer-type molecules, association constants >10(9) M(-1) were measured in chloroform. On the other hand, because only one π-face is utilized in the formation of supramolecular polymers from bis(merocyanine) dyes, higher hierarchical structures typically originate in which the other π-face is surrounded by an antiparallel π-stacked neighbor molecule. Among the observed self-assembled structures, nanorods in particular have attracted considerable attention because their self-assembly into well-defined H-aggregates falls under kinetic control and is slowed tremendously with decreasing solvent polarity. Co-assembly of achiral and chiral merocyanine building blocks or two enantiomers of a chiral merocyanine in different ratios provided insight into "majority rules" and "sergeant-and-soldiers" effects as well as the autocatalytic fiber growth process. With regard to materials applications, it is important to note that the high propensity for dipolar aggregation was disadvantageous for many envisioned applications of these dyes in the area of nonlinear optics. However, this aggregation behavior proved to be advantageous for the recently demonstrated applications of D-π-A dyes, in particular, merocyanines as p-type organic semiconductors in organic electronics and photovoltaics. Thus, organic transistors with hole mobilities >0.5 cm(2)/(V s) and organic solar cells with power conversion efficiencies >6% could be achieved with merocyanine-based organic semiconductor molecules.

Charge Relaxation and Stokes–Einstein Relation in Diluted Electrolyte Solution of Propylene Carbonate and Lithium Perchlorate

Impedance spectroscopy was used for studies of electrical conductivity and electric charge relaxation in a diluted solution of propylene carbonate and lithium perchlorate (mole fraction xLiClO4 = 6 × 10–5) in the temperature range from 250 to 350 K. It was found that the viscosity behavior of the conductivity as well as the charge relaxation time related to the Li+ and ClO4– ions immersed in propylene carbonate fulfill quite well the Stokes–Einstein hydrodynamic model. An essentially limited ion-pairing process in the studied solution of a low ion concentration and considerably limited dipolar aggregation of propylene carbonate molecules are considered to be essential factors determining the dynamic behavior of the ions immersed in that strongly polar liquid.

Self-Aggregation and Optical Absorption of Stilbazolium Merocyanine in Chloroform

Dipolar aggregation is in many cases detrimental for the functioning of optical materials. In this study we investigate self-aggregation and optical absorption of stilbazolium merocyanine (SM) in chloroform solution by performing classical Molecular Dynamics (MD) simulations under ambient conditions. The reversal solvatochromic shift, the large bathochromic shift, and the structured absorption band presented by SM in chloroform solution are all aspects of its optical absorption behavior for which the existence of self-aggregation is yet not completely understood. Moreover, the spectroscopic properties of SM oligomers and their occurrence in solvent of low polarity remain a relevant topic that deserves to be investigated. Our analysis of the aggregation behavior of SM in chloroform verified that the majority of the chromophores are involved in the formation of oligomers in solution, where the whole dimer and part of the trimer populations present a stable π-stacking structure. The optical properties of the monomers and oligomers in solution were evaluated by means of a discrete polarizable embedding quantum mechanical/molecular mechanical (PE-QM/MM) response scheme where the quantum part is described at the level of density functional theory. The visible absorption spectrum of SM in chloroform is simulated using time average values obtained for the monomeric and oligomeric forms of SM from the PE-QM/MM calculations performed on uncorrelated configurations extracted from the classical MD simulations. This study shows that the self-aggregation of SM in chloroform may exist, but it is not essential for reproducing the reversal solvatochromic shift in chloroform and that the process does not contribute to enhance the bathochromic shift nor explain the structure observed in its absorption band. Moreover, it is verified that since the electronic transitions of the monomer and oligomers are close together, changes in the interplane separation between the monomeric units of the stacked oligomers substantially affect the spectral resolution of their contribution to the optical absorption spectrum.

Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 2. Syntheses and Reactivities of Homo/HeteroMAAs

Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 2. Syntheses and Reactivities of Homo/HeteroMAAs

Aggregation of dipolar molecules in SiO2 hybrid organic–inorganic films: use of silver nanoparticles as inhibitors of molecular aggregation

The technological implementation of hybrid organic–inorganic materials in second order nonlinear optical photonic devices depends strongly on the ability of the host matrixes to contain high loads of dipolar molecules without aggregation. Some organic molecules are often used to diminish the attracting interactions between dipolar molecules in such kind of materials, but their efficiency as inhibitors of molecular aggregation is limited by their polarizability. In this work, we report the use of silver nanoparticles as inhibitors of molecular aggregation in hybrid organic–inorganic films doped with dipolar molecules. The large polarizability of the silver nanoparticles makes them ideal moieties for the inhibition of the electrostatic interactions between dipolar nonlinear optical molecules. The average size of the silver nanoparticles in this work was 70.5 nm in diameter, they were synthesized using silver nitrate (AgNO3) as precursor and aminoethylaminopropyltrimethoxysilane as reducing agent. These nanoparticles were immersed in SiO2 hybrid organic–inorganic sol–gel films doped with dipolar chromophores to study their effect as inhibitors of dipolar chromophores aggregation. The presence of the silver nanoparticles in the solid films was confirmed by transmission electronic microscopy and UV–Visible spectroscopy. UV–Visible spectroscopy was also used to monitor the dipolar chromophores aggregation in the SiO2 films. We found that, at room temperature, silver nanoparticles are good inhibiting chromophores aggregation in comparison with the performance of organic inhibitors.

Dipolar Aggregation and the Static Dielectric Permittivity of Some Liquid Crystalline Materials

In the paper, we show how some modifications in the chemical structure of mesogenic molecules can lead to an essential increase of the dielectric permittivity of liquid crystalline material due to the reduced molecular ability to the antiparallel dipolar aggregation. As an example, the static permittivities of two nematogenic homologous series, CnH2n+1PhPhCN and CnH2n+1PhCOOPhCN, are analyzed. However, the structural modifications of mesogenic molecules lead often to unfavorable changes in some important physical properties of liquid crystalline material, as a shift in the clearing temperature, for example, or can lead even to a disappearance of the mesophase. This paper presents such an event observed for the compound composed of C5H11PhPh(CH3)CN molecules, the methyl derivatives of C5H11PhPhCN molecules, which form a well-known nematic liquid crystal.

Optical Properties of NaCl:Sn2+ Phosphor Synthesized from Aqueous NaCl/SnCl2/HCl Solution

A NaCl:Sn2+ phosphor was synthesized from an aqueous NaCl/SnCl2/HCl solution. The optical properties of the as-synthesized phosphor material were investigated by diffuse reflectance spectroscopy, photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, and luminescence decay time measurement. The effects of temperature and excitation wavelength on the emission spectra were thoroughly studied in the present study. The temperature dependence of the PL spectra was examined between T = 20 and 300 K in 10 K increments, while the PLE spectra were obtained by excitation with λex ∼ 250–330 nm in the same temperature range. The PL spectra revealed four independent emission bands with peaks at ∼440 nm (B1), ∼490 nm (B2), ∼540 nm (G), and ∼635 nm (R). The B1 and G emission bands were assigned to the AT and AX emission bands typically observed in ns2-doped alkali halide phosphors, whereas the B2 and R emission bands were attributed to the Sn2 + − V−Na (cation vacancy) dipole aggregates.

Temperature Behavior of Electric Relaxational Effects due to Ionic Conductivity in Liquid Lactones

This paper concerns the studies of temperature and frequency behavior of the complex impedance, electric modulus, and electric conductivity due to an ionic current in liquid γ-butyrolactone (GBL) and γ-valerolactone (GVL). The frequency of the applied electric stimulus (500 Hz to 5 MHz) corresponds to the static dielectric regime of the lactones. The studies were performed in the temperature range of 263 K to 313 K. It was shown that in the static dielectric case, the dc ionic conductivity (σDC) and the static dielectric permittivity \({(\varepsilon_{\rm s})}\) determine the relaxational behavior of the impedance (Z*) and the electric modulus (M*) of the molecular liquids and both spectra are of the Debye-type characterized by the same conductivity relaxation time (τσ). Both σDC and τσ of GBL and GVL fairly well fulfill an Arrhenius temperature dependence with very similar values of the thermal activation energy \({{\rm E}_{\sigma_{\rm DC}} \approx {\rm E}_{\tau_\sigma} \approx 25 \,{\rm kJ} \, . \, {\rm mol}^{-1}}\) . The temperature dependence of the static dielectric permittivity and its temperature derivative is analyzed and interpreted in terms of the dipolar aggregation in the studied lactones.

Odd–Even Effects in the Static Dielectric Permittivity of a Homologous Series of Liquid Cycloalkanones, (CH2)n−1C═O, n = 4 to 8

Electric modulus spectra were used for the analysis of the static dielectric properties of liquid cycloalkanones: cyclobutanone, cyclopentanone, cyclohexanone, and cycloheptanone, studied in the temperature range from (243 to 313) K, and cyclooctanone, studied from (303 to 343) K. Odd–even effects with respect to the number of carbon atoms in the molecular ring of the compounds were found in the static dielectric permittivity value and in the dipolar aggregation ability, represented by the Kirkwood correlation factor.

Molecular Dynamics and Dipolar Aggregation in Some Fluoro-Substituted Liquid Crystals

The article presents the results of the molecular dynamics and dipolar aggregation studies performed with the use of dielectric spectroscopy for two differently fluoro-substituted nematogenic compounds: 4-cyano-3-fluorophenyl 4'-n-octyloxybenzoate [C8H17OPhCOOPh(F)CN] and 4-cyanophenyl 4'-n-octyloxy-3'-fluorobenzoate [C8H17OPh(F)COOPhCN]. The dielectric relaxation spectra recorded in the isotropic and nematic phases of the compounds as well as the activation energies corresponding to the molecular rotation around the short axis and the conductivity are analyzed. The role of the molecular structure in the aggregation ability of the compounds is discussed in relation to the dielectric anisotropy, the most important property of the nematic liquid crystals exploiting in opto-electronic devices.

Trimeric Cyclic Assemblies of Calix[4]arene‐Tethered Bismerocyanines

One ring to bind them: A cyclic complex containing three calixarene–bismerocyanine conjugates self-assembles by the pairing of chromophores (see picture). A simple mathematical model is introduced for the trimolecular association, and the potential of dipolar aggregation of merocyanine dyes as a directional and specific supramolecular binding motif is demonstrated. (Calixarenes: green; merocyanines: C pale blue, N dark blue, O red).

IMAGING MULTIPOLE SELF-POTENTIAL SOURCES BY 3D PROBABILITY TOMOGRAPHY

We present the theoretical development of the 3D multipole probability tomography applied to the electric Self-Potential (SP) method of geophysical exploration. We assume that an SP dataset can be thought of as the response of an aggregation of poles, dipoles, quadrupoles and octopoles. These physical sources are used to reconstruct, without a priori assumptions, the most probable position and shape of the true SP buried sources, by determining the location of their centres and critical points of their boundaries, as corners, wedges and vertices. At first, a few synthetic cases with cubic bodies are examined in order to determine the resolution power of the new technique. Then, an experimental SP dataset collected in the Mt. Somma-Vesuvius volcanic district (Naples, Italy) is elaborated in order to define location and shape of the sources of two SP anomalies of opposite sign detected in the northwestern sector of the surveyed area. The modelled sources are interpreted as the polarization state induced by an intense hydrothermal convective flow mechanism within the volcanic apparatus, from the free surface down to about 3 km of depth b.s.l.

Temperature Behavior of the Electric Field-Induced Entropy Increment within a Homologous Series of Nematogenic Compounds

Based on the temperature behavior of the entropy increment induced by the probing electric field in the isotropic phase of mesogenic compounds belonging to the homologous series C(n)H(2n+1)PhCOOPhCN ( n = 4-10), it is found that an ability to the dipolar aggregation of the molecules depends on the alkyl tail length, and, in particular, the ability is strongly reinforced when the number n changes from 7 to 8. The role of the molecular structure in the self-assembling process is discussed.

Synthesis of Merocyanine Dye Nanorods: The Importance of Solvent, Kinetic and Thermodynamic Control, and Steric Effects on Self-Assembly

Aggregation of dipolar merocyanine dyes into antiparallel dimers with high binding constant is an interesting binding motif for the construction of functional supramolecular architectures. This dipolar aggregation has been utilized for the formation of well-defined cylindrical nanorods. The self-assembly of these nanorods is profoundly influenced by solvent polarity which determines nanorod growth under kinetic or thermodynamic control. A newly synthesized series of bis(merocyanine) dyes bearing alkyl substituents of different chain lengths and branching further reveals that small structural changes of the monomeric building blocks have a considerable impact on the stability and structure of the aggregates. The knowledge acquired by the present study should be helpful for the development of self-assembled nanomaterials.

Contribution to Understanding of the Molecular Dynamics in Liquids

The dielectric relaxation spectroscopy is used for studying the orientational molecular dynamics in the isotropic (I) and nematic (N) phases of two mesogenic liquids composed of the molecules of similar structure and length, but of an essentially different polarity: n-heptylcyanobiphenyl, C(7)H(15)PhPhCN, 7CB (molecular dipole moment mu approximately 5D) and 4-(trans-4'-n-hexylcyclohexyl)isothiocyanatobenzene, C(6)H(13)CyHxPhNCS, 6CHBT (mu approximately 2.5D); advantageously, the temperatures of the I-N phase transition for the two compounds are very close to each other (T(NI) = 316.6 +/- 0.2 K). It is shown that regardless of the differences in polarity of 7CB and 6CHBT molecules and their abilities in dipolar aggregation, the values and temperature dependences of the relaxation time (corresponding to the rotational diffusion of the molecules around their short axis) are very close to each other, in both the isotropic and nematic phases of the liquids studied. Therefore, the data show that the dielectric relaxation processes occurring in dipolar liquids in the isotropic and nematic states lead through the rotational diffusion of individual molecules and the diffusion seems to be not influenced by the intermolecular interactions.