Substituent Dependent Optical Properties of <Emphasis Type="Italic">p</Emphasis>-phenyl Substituted ethenyl-<Emphasis Type="Italic">E</Emphasis>-thiophenes

Various electron donor and acceptor substituted (NO₂, CN, Cl, H, OCH₃, NH₂) p-phenyl ethenyl-E- thiophenes (1–6) were synthesized and substituent dependent optical properties (dipole moment, transition dipole moment, oscillator strength, optical band gap, hyperpolarizability) were studied using Solvatochromism and Density functional theory. It is shown that thiophene acts as a weak electron donor in presence of an electron withdrawing p-phenyl substituent (NO₂, CN, Cl), whereas thiophene acts as a weak electron acceptor in presence of an electron donating p-phenyl substituent (OCH₃, NH₂). In comparison to ethenyl thiophene 4, the HOMO-LUMO energy band gap is decreased upon increasing the electron donating or electron withdrawing capacity of p-phenyl substituent. From the excited state dipole moment calculation, it is shown that the excited state is highly dipolar for nitro and amino compounds 1 and 6, whereas compounds 2–5 show a non-polar excited state. As compared to the ethenyl thiophene 4, the first hyperpolarizability (β) increases upon substitution either with a strong electron withdrawing or strong electron donating p-phenyl substituent. A large β value is found for p-nitro phenyl ethenyl-E-thiophene and p-amino phenyl ethenyl-E- thiophene. Overall, these studies provide useful information in understanding the optical properties of phenyl and heterocyclic based ethenyl systems.     

Dual Fluorescence and Solvatochromic Study on 3-Acyl Coumarins

Electronic absorption and emission spectra of 3-acetyl coumarin, 3-(bromoacetyl) coumarin and 3-(di bromoacetyl) coumarin have been recorded at room temperature in thirteen solvents with different polarities. Both ground and excited state dipole moments have been calculated for both locally excited and charge transfer transitions by using the solvatochromic method. Excited state dipole moments of all the three compounds are higher than their ground state values. DFT calculations have been profound to estimate their ground and excited state dipole moments. The estimated change in dipole moment by the application of microscopic solvent polarity parameter and bulk solvent polarity methods are in close agreement. Concentration dependent dual fluorescence has been observed in the emission spectra of all the three compounds.

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Graphical Abstract Dual fluorescence of 3-acetyl coumarin (I) in different solvents.

     

Molecular Stark effect spectroscopy of diflavonol and inhomogeneous broadening of its electronic spectra in erythrocyte membranes

Using spectroscopy of the molecular Stark effect and fluorescence spectroscopy, we study the characteristics of diflavonol 3,7-dihydroxy-2,8-di(4-dimethylaminophenyl)-4H,6H-pyrano[3,2-g]chromene-4,6-dione (DFME), which demonstrates intramolecular charge and proton phototransfer. In the ground state, this dye has only one form and, in the excited state, it has two forms, i.e., normal and phototautomeric. We found that, for the normal form of DFME, the transition dipole moment that is responsible for the absorption (m _a ), the dipole moment in the equilibrium ground state (μ _g ), and the change of the dipole moment upon transition of the molecule in the excited Franck-Condon state (Δ ^a μ) are parallel. In the ground equilibrium state, the dipole moments in 1,4-dioxane and cyclohexane are equal to μg = 12.2 × 10⁻³⁰ C m and μ _g = 11.0 × 10⁻³⁰ C m, respectively. Upon excitation, they increase by Δ ^a μ = 61 × 10⁻³⁰ C m and Δ ^a μ = 50.2 × 10⁻³⁰ C m in these solvents. We study the spectral characteristics of DFME in organic solvents and erythrocyte membranes. A spectral inhomogeneity of DFME in erythrocyte ghosts is found. The inhomogeneous broadening of fluorescence spectra is manifested as a long-wavelength shift of the band of the normal form of DFME by 1640 cm⁻¹ upon excitation at the red edge of the absorption spectrum.     

On the effect of inhomogeneous magnetoelectric (flexomagnetoelectric) interaction on the spectrum and properties of magnons in multiferroics

The features of the magnon spectrum in easy-plane multiferroics (such as BiFeO₃), which allow inhomogeneous magnetoelectric (flexomagnetoelectric) interaction P[(L?)L ? LdivL], where L and P are the antiferromagnetic moment and electric polarization, respectively, have been theoretically analyzed. It has been shown that, in contrast to the magnon spectrum of a usual easy-plane antiferromagnet, a multiferroic with this magnetic structure is characterized by, first, the interaction between magnons of both branches propagating along the weak ferromagnetic moment and the appearance of a minimum (or zero) of the frequency of one of the branches, which reflects the instability of the system with respect to the transition to an inhomogeneous state with increasing flexomagnetoelectric interaction and, second, the nonequivalence (nonreciprocity) of the propagation of spin waves along and against the antiferromagnetism vector, which coincides with the toroidal moment in this system.     

The dynamic structure of <Emphasis Type="Italic">cis</Emphasis> and <Emphasis Type="Italic">trans</Emphasis> conformers of substituted phosphinous acids

The potential energy surfaces of bis-(trifluoromethyl)-phosphinous (III), diemthylphosphinous (IV), and bis-(pentafluorophenyl)-phosphinous (V) acids, the geometric parameters of the cis and trans conformers of these acids, and their P-O and O-H stretching vibration frequencies were calculated by the density functional theory method (PBE, 4Z). The potential energy surface sections corresponding to internal rotations about the P-O bonds were constructed, and dynamic problems for such a motion of the proton in a cyclic potential were solved by the Ritz method using a basis set of 100 trigonometric functions. According to calculations, the energy differences between the cis and trans conformers of acids III–V were of 4–7 kJ/mol, and the heights of potential barriers separating these conformers were of from 11 to 16 kJ/mol. In acids III and V, the cis, and, in IV, the trans conformer was stabler. At 298 K, only the ground vibrational states were populated for both rotamers of IV and V and the cis conformer of III. The special features of the potential of III were such that, at 298 K, the first excited vibrational level of its trans conformer was also noticeably populated.     

Dipole Moments of 4′-Aminoflavonol Fluorescent Probes in Different Solvents

Electrooptical absorption measurements (EOAM) were used to measure the dipole moments of the normal form of 4-(dimethylamino)-3-hydroxyflavone (FME), and 4 N-(15-azacrown-5)-3-hydroxyflavone (FCR) in 1,4-dioxane, toluene, and cyclohexane. With these probes excited-state intramolecular proton transfer (ESIPT) takes place. For comparison, the dipole moments of 4-(dimethylamino)-3-metoxyflavone (FME3ME), for which ESIPT is lacking, were measured, too. For all three probes the ground (_g) and excited Franck-Condon state (_e^FC) electrical dipole moments are parallel to each other and also parallel to the transition dipole moment. The electrical dipole moments of FCR, FME, and FME3ME in their ground state have values within the range (12.0–17.7) × 10^–30 C m. Upon optical excitation, the dipole moments increase by (41.9–52.9) ×10^–30 C m. The value of the change of the dipole moment vector ^a with excitation to the Franck-Condon state and the value of the vector _e^FC for FCR and FME are practically independent on the solvent polarity. From this point of view and due to large values of the dipole moments FCR and FME are very promising probes for the investigation of the distribution of the local polarity in biological systems using site-selective excitation of the different sites. Our steady-state fluorescence studies on FME and FCR have demonstrated a high spectral sensitivity of the normal form to such solvent characteristics as polarity.     

Experimental Determination of Ground and Excited State Dipole Moments of N,N-Bis (2, 5-di-tert-butylphenyl)-3, 4:9, 10-perylenebis (dicarboximide) (DBPI) A Photostable Laser Dye

In the present work, the absorption, emission spectra and dipole moments(μ_g, μ_e) of N, N-bis (2, 5-di-tert-butylphenyl)-3, 4:9, 10- perylenebis (dicarboximide) (DBPI) have been studied in solvents of various polarities at room temperature. Using the methods of solvatochromism, the difference between the first excited singlet state (μ_e) and ground state (μ_g) dipole moments was estimated from Lippert – Mataga,, Bakhshiev, Kawski – Chamma – Viallet equations. The change in dipole moment (Δμ) was also calculated using the variation of the Stokes shift with microscopic solvent polarity parameter (E _T ^N ). It was observed that the value of excited singlet state dipole moment is higher (3.53 Debye) than the ground state one (1.92Debye), showing that the excited state of DBPI is more polar than the ground state.     

Ground and excited state dipole moments of coumarin 337 laser dye

This paper reports that the effects of spectral properties of coumarin 337 laser dye have been investigated in different solvents considering solvent parameters like dielectric constant (?) and refractive index (n) of different solvent polarities. The ground state (μ_g) and excited state (μ_e) dipole moments are calculated using Lippert's, Bakhshiev's, and Kawski-Chamma-Viallet's equations. In all these three equations the variation of Stokes shift was used to calculate the excited state (μ_e) dipole moment. It is observed that the Bakhshiev method is comparatively better than the other two methods for ground state and excited state dipole moment calculations. The angle between the excited state and ground state dipole moments is also calculated.     

X-ray optical activity: Applications of sum rules

Edge-selective sum rules are proposed for a variety of X-ray dichroisms related to natural or nonreciprocal optical activity. Four spherical operators are identified that mix orbitals of different parities in what is assumed to be the ground state. The orbital anapole moment Ω⁽¹⁾ is primarily responsible for the magnetochiral dichroism; the time-even rank-2 tensor N⁽²⁾=[L, Ω]⁽²⁾ for natural circular dichroism; the time-odd rank-2 tensor W⁽²⁾=[L, n]⁽²⁾ for nonreciprocal magnetic linear dichroisms. At higher orders, the time-odd rank-3 tensor Γ⁽³⁾=[L, L, Ω]⁽³⁾ can also contribute to all nonreciprocal dichroisms. The physical content of these operators is analyzed. For every magnetoelectric group, one can predict which dichroic effect can be measured with either a single crystal or a powdered sample. Experimental spectra are produced to illustrate the value of the sum rules and the practical conditions of their application. Regarding nonreciprocal activity, one should be cautious about discussing magnetic symmetry because the deep core hole can couple the true ground state with low-lying excited states.     

Phase diagram of a surface superconductor in parallel magnetic field

The universal phase diagram of a 2D surface superconductor with generic Rashba interaction in a parallel magnetic field is found. In addition to the uniform BCS state, we find two inhomogeneous superconductive states, the stripe phase with Δ (r) ∝ cos(Qr) at high magnetic fields, and a new “helical” phase with Δ(r) ∝ exp(iQr) which intervenes between the BCS state and stripe phase at an intermediate magnetic field and temperature. We prove that the ground state for helical phase carries no current.     

Quadrupole deformation of the nucleus and dynamic vibrations of its surface

Based on the new Chart (database) of deformations of atomic nuclei, a systematic comparative analysis of quadrupole deformation parameters obtained by different methods for a large number of even-even nuclei is performed. It is shown that all nuclides whose quadrupole deformation parameters are deduced from the data on quadrupole moments (Q-type data) and on the reduced probability B(E2)↑ of quadrupole electric transitions 0⁺ → 2 ₁ ⁺ (B-type data) are clearly divided into two groups. In one of them, the data of both types show good agreement (within experimental errors) and in the other the B-type deformations are systematically (sometimes greatly) larger than the Q-type deformations. It is shown that this relationship among the data from different sources may be explained by assuming that a deformation parameter depends upon vibrations of the nuclear surface in the ground state. In this case, the B-type data, unlike the Q-type data, are believed to allow for these nuclear surface vibrations. In other words, the B-type data take into account not only static deformation, i.e., the “shape” of the nucleus, but also dynamic deformation resulting from vibrations of the nuclear surface in the ground state. The assumption that the nuclear dynamic deformation affects the nuclear shape allows one to assess “rigidity” of nuclei dividing them into two groups: “rigid” and “nonrigid”, i.e., “loose”. A comparison of the static and total deformations may yield data on nuclear properties, e.g., estimates of relationships between mass parameters and rigidity parameters.     

Fluorescent Styryl Dyes Based on Novel 4-Methoxy-9-Methyi-9H-Carbazole-3-Carbaldehyde—Synthesis,Photophysical Properties and DFT Computations

Novel carbazole based styryl derivatives (6a–6c) having styryl group at third position and a methoxy substitution were synthesized by condensing 4-methoxy-9-methyl-9H-carbazole-3-carbaldehyde 3 and different active methylene derivatives (5a–5c). Evaluated photophysical properties of these synthesized novel chromophores, studied the effect of solvent polarity on absorption, emission and quantum yield of these styryl derivatives. DFT and TD-DFT computations are carried out to study structural, molecular, electronic and photophysical parameters of dyes. The ratio of ground state to excited state dipole moment was calculated using Bakhshiev and Kawski-Chamma-Viallet correlations.     

Electronic structure and fluorescent properties of malononitrile-based merocyanines with positive and negative solvatochromism

The behavior of the positions and shapes of the fluorescence bands of di-, tetra-, and hexamethine merocyanine dyes with 3H-indolyliden (dyes 1–3) and benzoimidazolyliden (dyes 4–6) as electron-donating substituents and malononitrile as an electron-accepting substituent is studied by the method of moments in solvents of different polarity. The solvatofluorochromic shifts have been found to be smaller than the solvatochromic shifts not only for negatively solvatochromic merocyanines 4–6, but also for dyes 1–3 whose solvatochromism is positive. For dyes 4–6, cases of a change of the sign of solvatofluorochromism with respect to the sign of solvatochromism are revealed. These nontrivial effects are accounted for by transitions between the polyene and polymethine electronic structures of merocyanines in the fluorescence state S ₁ that occur with increasing medium polarity. In contrast to the absorption spectra of merocyanines 1–3, an increase in the chain length results in an increase in the vinylene shifts in the fluorescence spectra of these dyes, as well as in a decrease in the deviations and in the narrowing of the bands. This is explained by the fact that the electronic structure of these merocyanines in the S ₁ state is closer to that of the ideal polymethine (the cyanine limit) than in the S ₀ state. The fluorescence bands of merocyanines 4–6 are observed to be broader compared to the absorption bands. This broadening is caused by a change in the relation between intermolecular and vibronic interactions during absorption and emission of light. The interactions of these types have a decisive effect on the behavior of the Stokes shifts and fluorescence quantum yields of merocyanines 1–6.     

Intramolecular charge transfer state and unusual fluorescence from an upper excited singlet of a nonplanar derivative of p-cyano-N,N-dimethylaniline

The TICT (twisted internal charge transfer state) fluorescence of 4-cyano-2,6,N,N-tetramethylaniline (CTMA) was found in the vapour phase. The dipole moments of excited Franck-Condon and Franck-Condon twisted ground states were estimated from the solvent shifts of absorption and fluorescence. The near-equality of excited Franck-Condon and relaxed TICT state dipole moments is discussed. The fluorescence from an upper excited singlet state is found and its mechanism is explained.     

High-frequency susceptibility and ferromagnetic resonance in multidomain thin films of the yttrium-iron garnet type

The field dependence of the high-frequency susceptibility and the ferromagnetic resonance were experimentally studied in a thin (d≈0.1 µm) (111)-oriented single-crystal film of substituted yttrium-iron garnet with the factor q?1. It was shown that the anomaly in the high-frequency susceptibility observed in a magnetic field H parallel to the normal to the film surface in the magnetization saturation region (H≈H_s) has a dual nature; more specifically, this anomaly is associated with an abrupt collapse of the stripe domain structure and a ferromagnetic resonance in the experimental configuration H ∥ [111] and h ⊥ H. In this case, the film transition from the inhomogeneous multidomain state to the homogeneous (single-domain) state at the point H≈H_s has no indications of a second-order phase transition. The experimental frequency-field dependence of ferromagnetic resonance (FMR) in the sample under study, having a characteristic minimum at the point ω₀=5 MHz and H_FMR=H_s, agrees qualitatively and quantitatively with calculations. The influence of the cubic magnetic anisotropy and the film thickness on the FMR spectrum and the orientation of the spontaneous magnetization in domains with respect to the film plane in the zero field H was theoretically studied.     

Influence of the polarity of a medium on the photonics of a merocyanine dye with a high quadratic polarizability

The influence of the polarity of a medium on the spectral and luminescent properties of 2-[(2E,4E)-6-(1,3,3-trimethyl-2,3-dihydro-1H-2-indolyliden)-2,4-hexadienyliden]malononitrile (THDM) in solutions and polymer matrices is studied at room temperature under conditions of steady-state and pulsed laser excitation. A large bathochromic shift of the absorption spectra observed upon an increase in the polarity of a solvent is caused by a strong increase in the molecular dipole moment μ due to a transition of molecules from the ground state (μ_g = 7.6 D) to an excited Franck-Condon state (μ^FC = 33.5 D). Based on the solvatochromic data, the quadratic polarizability was calculated to be β = (3.2 ± 0.6) × 10^?28 esu, which is close to the experimentally determined value β_ex = (3.9 ± 0.2) × 10^?28 esu. A strong narrowing of the fluorescence spectra in comparison with the absorption spectra is observed upon an increase in the solvent polarity. This narrowing is explained by a decrease in the bond length alternation parameter and by weakening of vibronic interactions in the singlet excited state. The dynamic solvatofluorochromism of THDM in the picosecond range is caused by reorientations of molecules of the polar environment occurring during a time period consistent with the dielectric relaxation time of these molecules.     

Magnetic properties and phase transitions in hexagonal DyMnO3 single crystals

DyMnO₃ single crystals of hexagonal modification were grown for the first time by zone melting, and their anisotropic magnetic properties were studied in detail. At T ～ 7 K, a small uncompensated magnetic moment (～1 μ_B per formula unit) is shown to occur along the hexagonal axis. At temperatures 7–45 K, a transition from the purely antiferromagnetic state to a state with uncompensated magnetic moment was revealed; the transition is induced by a magnetic field H parallel to the c axis. This transition seems to be due to a ferrimagnetic ordering of the moments of Dy cations located in nonequivalent crystallographic positions.     

Orange Fluorescent Ru(III) Complexes Based on 4′-Aryl Substituted 2,2′:6′,2″-Terpyridine for OLEDs Application

A series of ruthenium (III) complexes of the formulae [Ru(4-Mephtpy)₂]Cl₃(1) [Ru(L ₁ )], [Ru(3,4,5-tmphtpy)₂]Cl₃(2) [Ru(L ₂ )], and [Ru(4-thptpy)₂]Cl₃(3) [Ru(L ₃ )], (where L?=?terpy?=?2.2′:6′2″ terpyridine ligands) are synthesized. The complexes were characterized by elemental analyses, spectroscopic and electrochemical data. The density functional theory (DFT) outlines the geometric optimisation and electronic charge transition of these complexes. Photophysical studies describe that the luminescence of Ru(III) complexes is due to electronic transition between the energy levels of singly unoccupied molecular orbitals (SUMO) and singly occupied molecular orbitals (SOMO). It also exhibits the potential charge transfer to π–π* and n–π* states due to MLCT and ILCT processes of the complexes. The observed bands centered at 591 and 620 nm demonstrate that these emissions originated from the transition of SUMO to SOMO energy levels, that is, from the radiative decay from the doublet exciton. Due to the heavy metal effect of Ru(III) ions the photophysical behaviour depends on the MLCT process. In conclusion, that the all three Ru(L ₁ -L ₃ ) complexes are fallen orange emission.     

Spin-orbit interactions in heterocyclic analogues of fluorene

For carbazole, dibenzofuran, and dibenzothiophene—heterocyclic analogues of fluorene containing N-H, O, and S groups, respectively—the transition dipole moments P ₀₀ ⁱ for the transitions ³ B ₂→S ₀ and ³ A ₁→S ₀ from the sublevels i=z, y, x of the triplet electronic ππ* states, which are caused by intramolecular spin-orbit (SO) interactions, are calculated. The effect that the SO coupling between the S ₀ state and highest triplet states has on the calculation results is considered. The effects exerted on the value of P ₀₀ ⁱ by such specific features of the molecular structure as the position of a heteroatom on the symmetry axis, its valence, and different constants of SO coupling in heteroatoms are discussed. The reason for the weak influence of the quantity ?_HA on the rate constant of radiative deactivation of the lowest T state is ascertained.