Dipole Moment Vector Research Articles

Deep Blue Phosphorescent Organic Light-Emitting Diodes with CIEy Value of 0.11 and External Quantum Efficiency up to 22.5.

Organic light-emitting diodes (OLEDs) based on red and green phosphorescent iridium complexes are successfully commercialized in displays and solid-state lighting. However, blue ones still remain a challenge on account of their relatively dissatisfactory Commission International de L'Eclairage (CIE) coordinates and low efficiency. After analyzing the reported blue iridium complexes in the literature, a new deep-blue-emitting iridium complex with improved photoluminescence quantum yield is designed and synthesized. By rational screening host materials showing high triplet energy level in neat film as well as the OLED architecture to balance electron and hole recombination, highly efficient deep-blue-emission OLEDs with a CIE at (0.15, 0.11) and maximum external quantum efficiency (EQE) up to 22.5% are demonstrated. Based on the transition dipole moment vector measurement with a variable-angle spectroscopic ellipsometry method, the ultrahigh EQE is assigned to a preferred horizontal dipole orientation of the iridium complex in doped film, which is beneficial for light extraction from the OLEDs.

Визначення дипольних моментів ковалентних зв’язків за допомогою CLPO-аналізу

Basing on the orbitals localization method which provides the most accurate (in a Frobenius norm sense) approximation for the reduced one-particle density matrix of the molecule, the model is proposed for partitioning the dipole moment of the molecule into additive contributions, defined in CLPO basis. By augmenting the proposed model with the Ruedenberg scheme for partitioning the nuclear contribution to the dipole moment, the contributions to the dipole moment associated with particular covalent bonds and lone pairs of the atoms were determined. Using the datasets composed of 11410 12-atomic molecules with zero total charge and the set of 613 conformations of electroneutral 2'-deoxycytidine-5'-monophosphate molecule, it has been found that the error in approximating the total dipole moment of the molecule by the sum of localized contributions, determined in the framework of the proposed model, is close to 10%, and is noticeably below the similar error when only the NPA charges are used to compute the approximate dipole moment. The typical angle between the true dipole moment vector and the dipole moment vector approximated with the proposed model is 5.5 deg.

COMFORMATIONAL ANALYSIS AND ELECTRONIC PROPERTIES OF FLUOROMETHYLFURAN OLIGOMERS: SEMIEMPIRICAL AND DFT STUDY

Structural and electronic properties of oligomers of fluoromethylfurans (FMFs), OC4H4-CHnF3-n with n = 1, 2, 3 and 4 have been studied using ZINDO/AM1 and B3LYP/6-31G(d) basis set. Preliminary study using AM1 and ab initio (HF) 6-31G(d) with medium basis set was carried out on di-, tri- and tetramer FMFs in order to investigate the stability of configuration of the polymer chains and conformation analysis of the dimers. There is noticeable effect of substituents on the geometries of FMFs as compared to polyfuran, polymethylfuran and chloromethylfuran (CMF) analogues [11]as well as improved characteristics as conducting polymers compared polymethylfurans and CMFs. The most stable conformation is the anti-planar conformation except in fluoromethylfuran in which antigauche conformation is most stable. The energy band gaps, electronic spectroscopy and electronic dipole moment vectors of the compounds are presented. Generally FMFs present lower energy band gaps, longer wavelength and higher electric dipole moments and are therefore more suitable as monomer for conducting polymer especially trifluoromethylfuran.

Tunable Anisotropic Photon Emission from Self-Organized CsPbBr3 Perovskite Nanocrystals.

We report controllable anisotropic light emission of photons originating from vertically aligned transition dipole moments in spun-cast films of CsPbBr3 nanocubes. By depositing films of nanocrystals on precoated substrates we can control the packing density and resultant radiation pattern of the emitted photons. We develop a technical framework to calculate the average orientation of light emitters, i.e., the angle between the transition dipole moment vector (TDM) and the substrate. This model is applicable to any emissive material with a known refractive index. Theoretical modeling indicates that oriented emission originates from an anisotropic alignment of the valence band and conduction band edge states on the ionic crystal lattice and demonstrates a general path to model the experimentally less accessible internal electric field of a nanosystem from the photoluminescent anisotropy. The uniquely accessible surface of the perovskite nanoparticles allows for perturbation of the normally isotropic emissive transition. The reported sensitive and tunable TDM orientation and control of emitted light will allow for applications of perovskite nanocrystals in a wide range of photonic technologies inaccessible to traditional light emitters.

Guest–host systems containing anthraquinone dyes with multiple visible transitions giving positive and negative dichroic order parameters: an assessment of principal molecular axes and computational methods

ABSTRACTThree 1,4-disubstituted anthraquinone dyes with bis(4-n-butylphenyl) substituents connected via amine or amide linking groups have been studied as guest molecules dissolved in the nematic host E7. UV-visible absorption spectroscopy has shown each of the dyes to exhibit multiple absorption bands in the visible region, and dichroic order parameters obtained from polarised spectra of aligned guest–host samples were shown to differ significantly between the bands for each dye, and between the dyes. Time-dependent density functional theory calculations indicated that each dye exhibits several transitions, giving transition dipole moment vectors with a range of orientations, and fully atomistic molecular dynamics simulations of the guest–host mixtures showed differences in the calculated molecular alignments of the dyes. Combining the results from these two sets of calculations enabled a comparison of molecular alignment models based on the moments of inertia and the surface tensors of the dyes. The match between calculated and experimental values was improved significantly when using the surface tensor rather than the moment of inertia model, indicating that the shapes of the molecular surfaces of these dyes are crucial to their alignment. A novel method of calculating polarised UV-visible absorption spectra of dyes in liquid crystal hosts is also presented.

Tuning of Second-Order Nonlinear Optical Response Properties of Aryl-Substituted Boron-Dipyrromethene Dyes: Unidirectional Charge Transfer Coupled with Structural Tailoring

Controlling the nonlinear optical (NLO) response properties at the molecular level is a key to develop strong NLO active materials for technological applications. In this paper, we report quantum chemical investigation of NLO response properties of select aryl-substituted Boron-Dipyrromethene (BODIPY) dyes, a class of intramolecular charge transfer (ICT) probes. Density functional theory (DFT) with long-range corrected CAM-B3LYP functional and cc-pVTZ, 6-31G(d,p) and 6-31+G(d,p) basis sets are employed to compute the electronic structures and NLO response of the aforesaid molecules. Calculations at the second order M{\o}ller-Plesset perturbation (MP2) level of theory are performed for comparison. The results suggest that the charge transfer process in these molecules is mostly unidirectional and the total first hyperpolarizability (\b{eta}total) values of these molecules are dominantly dictated by the response in the direction of charge transfer. Alteration of conjugation strength through donor/acceptor substitution as well as twisting of the phenyl ring obtained through incorporation of methyl groups affect the NLO response of thesemolecules. The vector components of first hyperpolarizability (\b{eta}vec) of the probe molecules are also studied to analyze the angle between the vector components of \b{eta}vec and the dipole moment vector. The results presented here are expected to shed light on the origin of NLO response of several aryl-substituted BODIPY dyes and provide means to optimizing it for future technological applications.

Molecular dynamic simulations of N2-broadened methane line shapes and comparison with experiments

Absorption spectra of methane transitions broadened by nitrogen have been calculated for the first time using classical molecular dynamic simulations. For that, the time evolution of the auto-correlation function of the dipole moment vector, assumed along a C–H axis, was computed using an accurate site-site intermolecular potential for CH4–N2. Quaternion coordinates were used to treat the rotation of the molecules. A requantization procedure was applied to the classical rotation and spectra were then derived as the Fourier-Laplace transform of the auto-correlation function. These computed spectra were compared with experimental ones recorded with a tunable diode laser and a difference-frequency laser spectrometer. Specifically, nine isolated methane lines broadened by nitrogen, belonging to various vibrational bands and having rotational quantum numbers J from 0 to 9, were measured at room temperature and at several pressures from 20 to 945 mbar. Comparisons between measured and calculated spectra were made through their fits using the Voigt profile. The results show that ab initio calculated spectra reproduce with very high fidelity non-Voigt effects on the measurements and that classical molecular dynamic simulations can be used to predict spectral shapes of isolated lines of methane perturbed by nitrogen.

Synthesis, spectroscopic, theoretical study, and biological activities of vanadium(IV) and vanadium(V) complexes with isonipecotic acid

Vanadium(IV) and vanadium(V) complexes 1–7 have been synthesized by the reaction of isonipecotic acid with VOSO4 · 3 H2O, VCl3(THF)3, and NH4VO3 at different metal/ligand ratios under stirring/ reflux conditions. The synthesized complexes have been characterized by elemental analyses and UV/Vis and FT-IR spectra. The FT-IR spectroscopic data suggest bidentate nature of the ligand, which is also confirmed by semiempirical study. Electrostatic surface potential (ESP) map shows that the coordinating oxygen atoms in complex 1 have more negative charges than the V=O oxygen atom. The dipole moment vectors of the optimized structures of complexes 1 and 5 are not aligned along the V=O bond due to the lack of symmetry. DNA binding study of complexes 1–7 showed that increase of the DNA concentration is accompanied by considerable decrease of the absorbance and by a 1–4-nm blue shift of the absorption maximum, indicating intercalative binding mode of the complexes to the DNA base pairs. In vitro DNA damage protection assay showed that complexes 1 and 3 exhibited plasmid DNA protection by scavenging oxidation products.

Self-Assembly of Open Protein Systems: A Comprehensive View Based onthe Interactions between 3d Hydrophobic and Electric Dipole MomentVectors

One of the most important phenomena in biology and medicine is protein self-assembly. In previous studies we mostly considered closed assemblies with a finite number of components. This article further explores self-assemblies involving an indeterminate number of components or open systems. In spite of the great variety of sizes, shapes and functions that self-assembled complexes of proteins are present in nature, they all seem to obey a relative simple law regarding their hydrophobic interactions. This law can be stated in very simple terms with the help of the definition of the hydrophobic moment vector applied to the double layer of phospholipids in biological membranes as a model. Simply stated, proteins assemble by tending to align their hydrophobic moments vectors, H. The reason that only a few examples of assemblies show a perfect alignment of their H vectors is due to the modifying action of their electrostatic interactions by means of their electric dipole moments, D. This principle works in all scales of protein sizes and allows higher-order assemblies, that is, assemblies of assemblies.

Comparative analysis of interactions between the hydropyridine dicarboxylate derivatives and different proteins by molecular docking and charge density analysis

Molecular docking and charge density analysis were carried out to understand the geometry, charge density distribution and electrostatic properties of one of newly synthesized 4-substituted-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylates (PDE), which is regarded as the best [Formula: see text]-Glucosidase inhibitor among the hydropyridine dicarboxylate derivatives. The different bonding models of the PDE molecule in the active sites of proteins Human serum albumin (HSA) and Saccharomyces cerevisiae [Formula: see text]-glucosidase (SAG) are firstly compared, which is important to understand the different intermolecular interactions between drug-transport protein and drug-target protein. The deformation density maps suggest that the electron densities of the PDE molecule are redistributed when it presents in the active sites. When the molecule presents in the active site of the SAG, it is evident to find that the negative region does not appear at the vicinity of the oxygen atoms on one of the carboxylic acid dimethyl ester group. Frontier molecular orbital density distributions for the PDE molecule are similar in all forms. The highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) energy gaps in the active sites are higher than that of the molecule in pure solution phase. It is generally noticed that all of the orientations of the dipole moment vectors are reoriented in both active sites. These fine details at electronic level allow to better understand the exact drug-transport protein and drug-target protein interactions.

Effect of solvent composition on the structural and dynamical properties of sodium chloride solutions in water-methanol mixtures

Molecular dynamics (MD) simulations have been performed on sodium chloride solutions in water-methanol mixtures under ambient conditions with methanol mole fractions (xm) ranging from 0.09 to 0.87. MD simulations are performed with the flexible SPC water model and the flexible six-site model for methanol. The ions are modeled as charged Lennard–Jones spheres. The structural properties of the solutions are discussed on the basis of radial distribution functions. A chain cluster of methanol is predominant in the mixture where xm exceeds 0.7. The number of methanol molecules are higher than water molecules in the first coordination shell of sodium and chloride ions beyond xm=0.5 and 0.48 respectively. With increasing xm, the diffusion coefficients for water (DH2O) and for methanol (DCH3OH) initially decrease. From xm=0.29 DCH3OH increases while DH2O rises only from about 0.7. The two diffusion coefficients are equal at xm=0.8. The deduced first and second reorientational correlation times for the OH and the dipole moment vectors for water speed up with increasing xm. Through the τ1/τ2 ratio, the reorientational motion of water molecules can be entirely ascribed to a jump. OH methanol vector reorientational occurs by a mechanism similar to that of water.

Solvatochromism and intramolecular hydrogen-bonding assisted dipole moment of phenyl 1-hydroxy-2-naphthoate in the ground and excited states

Absorption and steady state fluorescence spectra of phenyl 1-hydroxy-2-naphthoate (abbreviated as PHN) have been recorded in a series of non-polar, polar protic and polar aprotic solvents at room temperature. The pH effect on the excited state intramolecular proton transfer (ESIPT) has been discussed. FT-IR spectra in solid phase, CHCl3 and CDCl3 are analyzed. The ground state (μg) dipole moment is estimated by using Bilot-Kawski method and the excited state (μe) dipole moment is calculated by using Bilot-Kawski, Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet and Reichardt solvatochromic shift methods as a function of dielectric constant (ε) and refractive index (n) of solvents. μe is observed as higher than μg for all of the used methods which indicates the more polar PHN in the excited state. The studied compound is observed to have intramolecular hydrogen bonding assisted dipole moments in the ground and excited state. The rate of μe/μg is found as 34.857. The ground and excited state dipole moment vectors are observed to make an angle with 3.842°. Solvatochromic behavior of PHN is investigated by means of linear solvation energy relationship (LSER) by using Kamlet-Taft and Catalan parameters. Kamlet-Taft solvatochromic model indicates that non-specific solute solvent interactions are controlled by solvent dispersion-induction forces and specific interactions are directed by hydrogen-bond acceptor capacity of solvent. Catalan solvatochromic model designates that solute-solvent interactions are governed by solvent dipolarity/polarizability and solvent acidity. Theoretical μg and μe have been determined by quantum chemical calculations using DFT-B3LYP/6-31G(d) and TDDFT-B3LYP/6-31G(d) level of theory, respectively. HOMO, LUMO, molecular electrostatic potential (MEP) of PHN are calculated by the same methods in the ground and excited states.

Molecular Design Parameters of Anthraquinone Dyes for Guest–Host Liquid-Crystal Applications: Experimental and Computational Studies of Spectroscopy, Structure, and Stability

A set of five anthraquinone dyes with bis(4-propylphenyl) substituent groups, connected via sulfide or amine linkages at the 1,5-positions or directly at the 2,6-positions, have been studied in solution by UV–vis spectroscopy and electrochemistry, allied with density functional theory calculations of structures, electronic transitions, and redox potentials. The visible transitions and redox potentials are shown to vary with the HOMO and LUMO energies, with the variation in both color and redox stability between the dyes being attributable principally to variations in the HOMOs located mainly on the substituents and outer anthraquinone rings. The calculated molecular structures and visible transition dipole moments are shown to vary subtly with substituent, giving variations in the molecular aspect ratios, minimum moment of inertia axes, and transition dipole moment vector orientations that can rationalize the alignment trends reported in the literature for such anthraquinone dyes in liquid crystal hosts, ...

Do Hydrogen Bonds Influence Excitonic Splittings?

The excitonic splitting and vibronic quenching of the inversion-symmetric homodimers of benzonitrile, (BN)2, and meta-cyanophenol, (mCP)2, are investigated by two-color resonant two-photon ionization spectroscopy. These systems have very different hydrogen bond strengths: the OH···N≡C bonds in (mCP)2 are ∼10 times stronger than the CH···N≡C hydrogen bonds in (BN)2. In (BN)2 the S0((1)Ag) → S1((1)Ag) transition is electric-dipole forbidden, while the S0((1)Ag) → S2((1)Bu) transition is allowed. The opposite holds for (mCP)2 due to the different transition dipole moment vector alignment. The S0 → S1S2 spectra of the dimers are compared and their excitonic splittings and vibronic quenchings are investigated by measuring the (13)C-substituted heterodimer isotopomers, for which the centrosymmetry is broken and both transitions are allowed. The excitonic splittings are determined as Δexc = 2.1 cm(-1) for (BN)2 and Δexc = 7.3 cm(-1) for (mCP)2. The latter exhibits a much stronger vibronic quenching, as the purely electronic splitting resulting from ab initio calculations is determined to be Δcalc = 179 cm-1, while in (BN)2 the calculated splitting is Δcalc = 10 cm(-1). The monomer site-shifts upon dimerization and comparing certain vibrations that deform the hydrogen bonds confirm that the OH···N≡C hydrogen bond is much stronger than the CH···N≡C bond. We show that the H-bonds have large effects on the spectral shifts, but little or no influence on the excitonic splitting.

Attaching an alkali metal atom to an alkaline earth metal oxide (BeO, MgO, or CaO) yields a triatomic metal oxide with reduced ionization potential and redirected polarity.

The existence of a series of neutral triatomic metal oxides MON and their corresponding cations MON (+) (M=Be, Mg, Ca; N=Li, Na, K) was postulated and verified theoretically using ab initio methods at the CCSD(T)/6-311+G(3df)//MP2/6-311+G(3df) level of theory. The calculations revealed that the vertical ionization potentials (IPs) of the MON radicals (calculated using the outer-valence Green's function technique (OVGF) with the 6-311+G(3df) basis set) were ca. 2-3eV smaller than the IPs of the corresponding MO and NO systems or that of the isolated M atom. Population analysis of the neutral triatomic MON molecules and their corresponding MO counterparts indicated that the attachment of an alkali metal atom to any oxide MO (BeO, MgO, CaO) reverses its polarity, which manifests itself as the redirection of the dipole moment vector.

Photochemistry of carbon dioxide from first principles: Application to photoabsorption of hot CO2

This paper analyzes the temperature dependence of the absorption spectrum of carbon dioxide in the wavelength range λ≤250nm by means of a first principles model. The model combines the high level ab initio potential energy surfaces of four excited electronic states and their coordinate dependent transition dipole moment vectors with quantum mechanical calculations of the photodissociation dynamics and the absorption spectra corresponding to excitations from many initial rovibrational states of the parent CO2. The calculations demonstrate that photodynamics from first principles can be realized for CO2 with high accuracy: The absorption cross section can be reliably calculated for λ≤250nm and T≤2500K and used for modeling the one-step photolytic reduction of CO2 to CO. An ab initio-based estimate of the contribution of low lying triplet states to the optical absorption of hot CO2 is also given.

Vector description of electric and hydrophobic interactions in protein homodimers.

This article describes the formation of homodimers from their constituting monomers, based on the rules set by a simple model of electric and hydrophobic interactions. These interactions are described in terms of the electric dipole moment (D) and hydrophobic moment vectors (H) of proteins. The distribution of angles formed by the two dipole moments of monomers constituting dimers were analysed, as well as the distribution of angles formed by the two hydrophobic moments. When these distributions were fitted to Gaussian curves, it was found that for biological dimers, the D vectors tend mostly to adopt a perpendicular arrangement with respect to each other, in which the constituting dipoles have the least interaction. A minor population tends towards an antiparallel arrangement implying maximum electric attraction. Also in biological dimers, the H vectors of most monomers tend to interact in such a way that the total hydrophobic moment of the dimer increases with respect to those of the monomers. This shows that hydrophobic moments have a tendency to align. In dimers originating in the crystallisation process, the distribution of angles formed by both hydrophobic and electric dipole moments appeared rather featureless, probably because of unspecific interactions in the crystallisation processes. The model does not describe direct interactions between H and D vectors although the distribution of angles formed by both vectors in dimers was analysed. It was found that in most cases these angles tended to be either small (both moments aligned parallel to each other) or large (antiparallel disposition).

Shear stress-induced enhancement of the piezoelectric properties of PVDF-TrFE thin films

Material properties of PVDF-TrFE related to dipole alignment and crystallinity, such as surface potential, polarization direction, piezoelectric coefficient, and remnant polarization, have been systematically examined to explain the improvement in the piezoelectric properties of PVDF-TrFE formed at a high spin-coating speed. The correlations between the distribution of the dipole moment vector and the degree of crystallinity were studied as a function of strain rate using a computational molecular dynamic simulation.

Understanding and predicting the orientation of heteroleptic phosphors in organic light-emitting materials.

Controlling the alignment of the emitting molecules used as dopants in organic light-emitting diodes is an effective strategy to improve the outcoupling efficiency of these devices. To explore the mechanism behind the orientation of dopants in films of organic host materials, we synthesized a coumarin-based ligand that was cyclometalated onto an iridium core to form three phosphorescent heteroleptic molecules, (bppo)2Ir(acac), (bppo)2Ir(ppy) and (ppy)2Ir(bppo) (bppo represents benzopyranopyridinone, ppy represents 2-phenylpyridinate, and acac represents acetylacetonate). Each emitter was doped into a 4,4'-bis(N-carbazolyl)-1,1'-biphenyl host layer, and the resultant orientation of their transition dipole moment vectors was measured by angle-dependent p-polarized photoluminescent emission spectroscopy. In solid films, (bppo)2Ir(acac) is found to have a largely horizontal transition dipole vector orientation relative to the substrate, whereas (ppy)2Ir(bppo) and (bppo)2Ir(ppy) are isotropic. We propose that the inherent asymmetry at the surface of the growing film promotes dopant alignment in these otherwise amorphous films. Modelling the net orientation of the transition dipole moments of these materials yields general design rules for further improving horizontal orientation.

ChemInform Abstract: Styryl‐Based NLO Chromophores: Synthesis, Spectroscopic Properties, and Theoretical Calculations.

AbstractA series of styryl‐based push‐pull chromophores are synthesized.