The Fluorosolvatochromism of Brooker's Merocyanine in Pure and in Mixed Solvents

The fluorescence-based solvatochromism (fluorosolvatochromism) of 4-[(1-methyl-4(1H)-pyridinylidene)-ethylidene]-2,5-cyclohexadien-1-one (Brooker's merocyanine) was studied. The results revealed that the fluorescence emission band of the dye was dependent on the medium ( nm in water and nm in DMF). The fluorescence quantum yields (φ _f) were calculated for the dye in the solvents investigated. Low φ _f values ( < 10%) were obtained for the dye and in order to better comprehend the radiative and nonradiative decay processes of this dye, its fluorescence lifetime in methanol was measured and was found to be very short (230 ps). The results suggest that the dye in the excited state decays rapidly through nonradiative processes. The behavior of the probe in binary mixtures including a hydrogen-bond accepting solvent (acetonitrile, N,N-dimethylformamide, and dimethylsulfoxide) and a hydroxylic solvent (water, methanol, ethanol, propan-2-ol, and butan-1-ol) was also investigated. All data were successfully fitted to a model based on solvent exchange equilibria, which allowed the separation of the different contributions of the solvent species in the solvation shell of the dye. The data obtained for the mixed solvents were explained based on solute–solvent and solvent–solvent interactions.     

Solvatochromic and Preferential Solvation Studies on Schiff Base 1,4-Bis(((2-Methylthio)Phenylimino)Methyl) Benzene in Binary Liquid Mixtures

The solvatochromic behavior of the 1,4-bis(((2-methylthio) phenylimino)methyl) benzene [BMTPMB] in single solvents and binary mixtures were investigated. Fluorescence spectra show the dual emission due to twisted intramolecular charge transfer (TICT) state. The preferential solvation parameters: local mole fraction, X₂^L, solvation index δ_s2, exchange constant K₁₂ were calculated for the binary mixtures, ACN+MEOH, DMSO+CCl₄ and CCl₄+1,2 DCE. The dipole moment ratios between ground and excited states were deduced using the solvatochromic shifts of absorption and fluorescence spectra as a function of dielectric constant (ε), refractive index (n) and it was found to be 1.25.     

A Spectroscopic Model for the Study of Preferential in the Ground and Excited Electronic States.

The preferential solvation of a solute molecule in mixed solvents is analysed in terms of the spectral solvent shifts. A spectroscopic model is developed in order to know the preferential solvation degree in the ground electronic state as well as in the first excited electronic state by measuring the absorption and fluorescence spectra respec tively.

Triphenylene was found to be a good model probe molecule in n-butanol/carbon tetrachloride mixtures for both electronic states. Furthermore Tryphenylene in its ground electronic state was studied in chloroform/methanol mixtures.     

Absorption and Fluorescence Emission Attributes of a Fluorescent dye: 2,3,5,6-Tetracyano-p-Hydroquinone

Four cyano groups have been substituted on the aromatic ring of p-hydroquinone (2,3,5,6-tetracyanohydroquinone) in order to study the enhanced photoacidity of this molecule. The acid-base equilibria have been studied using absorption (for ground state pK_a) and fluorescence (excited state pK_a) spectra. Three distinct species (neutral, anionic and dianionic forms) were observed in the ground state and only two species (anionic and dianionic forms) were found in the excited state when studied at different pH/H_o in water. Absorption and emission characteristics were studied in various organic solvents, including protic and aprotic solvents. Deprotonation was also investigated using binary mixtures. It has been revealed that absorption and emission spectra are considerably changed with change in media. Proton transfer to the solvent has been observed in various solvents.     

On the Photophysicochemical Properties of Selected Fluoroquinolones: Solvatochromic and Fluorescence Spectroscopy Study

The photophysicochemical properties of selected fluoroquinolones in different solvents of various physical properties, including polarity and hydrogen bonding ability, were investigated using steady state fluorescence spectroscopy. The solvent-dependant fluorescence emission spectra of selected fluoroquinolones, namely ciprofloxacin (CIPR) and enrofloxacin (ENRO), were employed to gain insights concerning its photophysicochemical properties of interests. Interestingly, fluorescence spectra of the selected drugs exhibited structured emission spectra in nonpolar solvents such as hexane, whereas unstructured spectra were observed in more polar solvents such as alcohols and water. Also, a notable bathochromic shift in $ \lambda_{{\max }}^{{em}} $ was observed in fluorescence spectra of both drugs with increasing solvent polarity that resulted in biphasic behavior upon applying the Lippert-Mataga correlation that correspond to general and specific solvent effects. Applying the Lippert-Mataga correlation to the fluorescence spectra of CIPR and ENRO in various solvents was employed to estimate the dipole moment difference between the ground and excited states of them, $ \Delta \mu \left( {{\mu_e} - {\mu_g}} \right) $ , where obtained results revealed the values of 9.4 and 16.2 Debye for the LE and ICT states of ENRO, respectively, and 8.0 and 16.2 Debye for the LE and ICT states of CIPR, respectively. Multiple linear regression analysis (MLRA) based on Kamlet-Taft equating was applied against absorption frequency (ν_abs), emission frequency (ν_em), Stokes shift (?ν), and fluorescence quantum yield (Φ_f), where obtained results revealed excellent correlation (R: 0.916–0.966) that are consistent with other results considering the effect of solvent polarizability, hydrogen bonding ability, and viscosity on the photophysicochemical properties of the studied fluoroquinolones.     

Polynomial-Time Algorithm for Simulation of Weakly Interacting Quantum Spin Systems

We describe an algorithm that computes the ground state energy and correlation functions for 2-local Hamiltonians in which interactions between qubits are weak compared to single-qubit terms. The running time of the algorithm is polynomial in n and δ⁻¹, where n is the number of qubits, and δ is the required precision. Specifically, we consider Hamiltonians of the form , where H ₀ describes non-interacting qubits, V is a perturbation that involves arbitrary two-qubit interactions on a graph of bounded degree, and is a small parameter. The algorithm works if is below a certain threshold value that depends only upon the spectral gap of H ₀, the maximal degree of the graph, and the maximal norm of the two-qubit interactions. The main technical ingredient of the algorithm is a generalized Kirkwood-Thomas ansatz for the ground state. The parameters of the ansatz are computed using perturbative expansions in powers of . Our algorithm is closely related to the coupled cluster method used in quantum chemistry.     

NMR Studies on the Internal Structure of High-T c Superconductors and Other Anorganic Compounds

Spatially-resolved NMR is used to probe internal structures in highly correlated superconductors of optimally-doped (T _c = 85 K) and a heavy fermion superconductor CeCoIn₅ (T _c = 2.3 K). The characteristic change of the properties of ²⁰⁵Tl-NMR in the vortex state provides a clear evidence of the antiferromagnetic order in the vortex cores below 20 K in . We also obtain anomalous ¹¹⁵In-NMR spectra of CeCoIn₅, which provides a microscopic evidence for the occurrence of a spatially-modulated superconducting order parameter expected in a Fulde–Ferrel–Larkin–Ovchinnkov (FFLO) state.     

Spectroscopic Studies of Fluorenone Derivatives

The absorption and steady-state fluorescence spectra of fluorenone, 1-hydroxyfluorenone, and 3-dimethylaminofluorenone have been obtained for various concentrations in a series of non-polar and polar solvents. The substituents (-OH and -N(CH₃)₂) as the electron-donating functional groups cause a large shift of the longwave absorption band and Stokes' shift of the monomer- and excimer-fluorescence bands in comparison with fluorenone. The total emission spectrum of 3-dimethylaminoflourenone in polar aprotic solvents exhibits a new band at 500 nm originating form the emission of the twisted intramolecular charge transfer (TICT) isomer. The excited state dipole moments of the emiting species of the molecule studied are determined using the solvatation shift method and calculated values of the ground state dipole moments.     

Solvatochromism,Preferential Solvation of 2,3-Bis(Chloromethyl)-1,4-Anthraquinone in Binary Mixtures and the Molecular Recognition Towards <Emphasis Type="Italic">p</Emphasis>-Tert-Butyl-Calix[4]arene

Optical absorption and fluorescence emission spectra of 2,3-bis(chloromethyl)-1,4-anthraquinone (DCMAQ) in single solvents namely, carbon tetrachloride, acetonitrile, chloroform, propan-2-ol and its binary mixtures [carbon tetrachloride/chloroform, chloroform/acetonitrile, chloroform/propan-2-ol] have been investigated. The preferential solvation of DCMAQ in above mixtures has been studied by monitoring the absorption and fluorescence spectra of DCMAQ. The spectral features indicate that DCMAQ is preferentially solvated by CHCl₃ in the above mixtures. This can be elucidated from the local mole fraction, non-linearity in transition energy plot, preferential solvation index (δ _s2) and (f ₂/f ₁) values. Molecular recognition properties of p-tert-butylcalix[4]arene (tBC) to DCMAQ via hydrogen bonding and π–π interaction were sensed successfully on the basis of absorption and fluorescence emission spectroscopies, by which the stoichiometry ratio and the binding constant of the tBC–DCMAQ complex were determined.     

2-Aminopurine optical spectra: Solvent,pentose ring,and DNA helix melting dependence

2-Aminopurine (2AP) absorption and fluorescence excitation and emission spectra in a series of solvents have been measured to assess effects of solvent polarity. Emission spectra of the free base shift to the red in solvents of a higher dielectric constant, including water but excepting dioxane. Excitation spectra also red-shift, except in water. A change in dipole moment of 2.8 D upon excitation is obtained from a Bilot-Kawski plot which includes data from potentially anomolous solvents such as alcohols but which excludes dioxane and aqueous solvents. Attachment of ribose or 2-deoxyribose causes 1 to 2-nm shifts in the position of fluorescence excitation and emission spectra of 2AP in water and little change in fluorescence yield. Melting of the DNA duplex d[CTGA(2AP)TTCAG]₂ yields a blue shift of the excitation and no shift of the emission spectrum-results consistent with increased exposure to water and formation of 2AP-water H bonds in the ground state. The spectral shift occurs 5°C or more below the helix melting temperature, implying a premelting structural change in the decamer.     

Energy dependence of the charge exchange reaction from muonic hydrogen to oxygen

The charge exchange reaction of negative muons from the atom to oxygen has been measured in gaseous mixtures of H₂ + O₂. The measurements were performed at three different relative oxygen concentrations ranging from 0.2% to 0.8% and total pressures 3.5–15 bar. A mean transfer rate of , describing the transfer from the ground state of thermalized atoms to oxygen, was determined. In order to investigate the energy dependence of the transfer rate, Monte Carlo simulations of the thermalization and the muon transfer were carried out. The comparison of measured and simulated time spectra yielded an epithermal transfer rate =3.9 10¹¹ s^-1 in the energy interval 0.12–0.22 eV. The analysis with the model of Two components shows that all measured time spectra can be reproduced with the same set of parameters.     

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.

     

(Co)cyclic (Co)homology of Bialgebroids: An Approach via (Co)monads

For a (co)monad T _l on a category , an object X in , and a functor , there is a (co)simplex in . The aim of this paper is to find criteria for para-(co)cyclicity of Z ^*. Our construction is built on a distributive law of T _l with a second (co)monad T _r on , a natural transformation , and a morphism in . The (symmetrical) relations i and w need to satisfy are categorical versions of Kaygun’s axioms of a transposition map. Motivation comes from the observation that a (co)ring T over an algebra R determines a distributive law of two (co)monads and on the category of R-bimodules. The functor Π can be chosen such that is the cyclic R-module tensor product. A natural transformation is given by the flip map and a morphism is constructed whenever T is a (co)module algebra or coring of an R-bialgebroid. The notion of a stable anti-Yetter-Drinfel’d module over certain bialgebroids, the so-called  ×  _R -Hopf algebras, is introduced. In the particular example when T is a module coring of a  ×  _R -Hopf algebra and X is a stable anti-Yetter-Drinfel’d -module, the para-cyclic object Z _* is shown to project to a cyclic structure on . For a -Galois extension , a stable anti-Yetter-Drinfel’d -module T _S is constructed, such that the cyclic objects and are isomorphic. This extends a theorem by Jara and Ştefan for Hopf Galois extensions. As an application, we compute Hochschild and cyclic homologies of a groupoid with coefficients in a stable anti-Yetter-Drinfel’d module, by tracing it back to the group case. In particular, we obtain explicit expressions for (coinciding relative and ordinary) Hochschild and cyclic homologies of a groupoid. The latter extends results of Burghelea on cyclic homology of groups.     

Preparation and characterization of nanocrystalline ZnO particles from a hydrothermal process

Rod-like ZnO nanoparticles were prepared by the hydrolysis of zinc acetate under heating in diethylene glycol (DEG). Structural characterization of the synthesized powders was investigated by XRD, FT-IR, electron paramagnetic resonance (EPR) and transmission electron microscopy (TEM). The size of the particles increased as the amount of H₂O added increased in the nano size range. The average crystallite size calculated from the XRD patterns varied from 6 to 64 nm corresponding to the amount of H₂O added. The ZnO nanopartilces possess the wurtzite type crystallographic structure. It was found that these ZnO nanoparticles had singly ionized oxygen vacancy defect () and superoxide ions from the EPR investigations. A strong near UV emission of the ZnO nanoparticles at about 380 nm was observed and its intensity decreased as the amount of H₂O increased. This emission of ZnO nanoparticles is found to be particles size dependent due to the confinement effect. A green emission at about 540 nm due to the recombination of electrons trapped at singly ionized oxygen vacancies defect () appeared when the amount of H₂O increased. The intensity of the green emission increases as the concentration of increases.     

Er-Yb Codoped Ferroelectrics for Controlling Visible Upconversion Emissions

Under a 980 nm laser pumping, quenching of green upconversion (UC) emission accompanied with enhancement of red UC emission observed was dominated by the energy back-transfer (EBT) process in Er³⁺ and Yb³⁺ co-doped PbTiO₃, BaTiO₃, and SrTiO₃ polycrystalline powders. The efficiency of the EBT process depends not only on Yb³⁺ concentration but also on level match of the doped Er³⁺ and Yb³⁺ ions caused by the crystal fields with different symmetries. Our UC emission spectra and X-ray diffraction confirm that the centrosymmetric crystal field arising from reducing tetragonality causes level match of transition of Er³⁺ and of Yb³⁺. This level match is responsible for enhancing red UC emission.     

A-site deficient lanthanum-calcium chromite-titanates doped with 3d transition metals: synthesis,oxygen nonstoichiometry,electrical conductivity,and catalytic activity

Six (M = Cr, Mn, Fe, Co, Ni, Cu) and two (M = Ni, Cu) single-phase compositions were prepared by conventional solid-state reactions. Oxygen nonstoichiometry, electrical conductivity, phase transformations under reduction-reoxidation at high temperatures and catalytic activity for hydrocarbons oxidation of these compositions were investigated in a wide temperature and oxygen partial pressure range. The Cu-, Ni-, Co-, and Fe-containing compositions are decomposed in reducing Ar/H₂O/H₂ atmosphere with pH₂O / pH₂ = 0.3 at 1,000 °C, while the Cr- and Mn-containing ceramics remain stable at the same conditions. The metallic particles of the added 3d elements formed after decomposition were registered by X-ray diffraction method in case of Cu- and Ni-containing compositions. These formed composites can be completely reoxidized with formation of initial compositions by treatment in air at 1,000 °C. The electrical conductivity of the ceramics investigated in air and Ar/H₂O/H₂ gas flow increases with rising M content. The highest catalytic activity for oxidation of CH₄ and C₃H₆, which was comparable with the activity of the composite, shows the Cu-containing powders. Dedicated to Prof. Dr. Werner Weppner     

Synthesis and spectroscopic studies of 4-Formyl-4′-N,N-dimethylamino-1,1′-biphenyl: The unusual red edge effect and efficient laser generation

The synthesis and photophysics of 4-formyl-4-N,N-dimethylamino-1,1-biphenyl are reported. The emission spectrum in various solvent polarities demonstrates solvatochromism, indicating that the fluorescence originates from an electronically excited species with a strong charge transfer character. The change in [ _max(absorption) – _max(emission)] varies from 1500 cm^–1 inn-heptane to as much as 7500 cm^–1 in acetonitrile. In protic solvents, the unusual excitation energy-dependent steady-state emission (red edge effect), resulting from solvent dielectric relaxation, was observed in media with a low viscosity. The large Stokes-shifted and high-yield fluorescence led to the observation of the efficient lasing action. The frequency tunability of the laser output is strongly solvent dependent, generating a new charge transfer laser dye in the blue-green region.     

Localization in the ground state of the ising model with a random transverse field

We study the zero-temperature behavior of the Ising model in the presence of a random transverse field. The Hamiltonian is given by $$H = - J\sum\limits_{\left\langle {x,y} \right\rangle } {\sigma _3 (x)\sigma _3 (y) - \sum\limits_x {h(x)\sigma _1 (x)} } $$ whereJ>0,x,y∈Z ^d, σ₁, σ₃ are the usual Pauli spin 1/2 matrices, andh={h(x),x∈Z ^d} are independent identically distributed random variables. We consider the ground state correlation function 〈σ₃(x)σ₃(y)〉 and prove:

1. Letd be arbitrary. For anym>0 andJ sufficiently small we have, for almost every choice of the random transverse fieldh and everyx∈Z ^d, that $$\left\langle {\sigma _3 (x)\sigma _3 (y)} \right\rangle \leqq C_{x,h} e^{ - m\left| {x - y} \right|} $$ for ally∈Z ^d withC _{x h} <∞.
2. Letd≧2. IfJ is sufficiently large, then, for almost every choice of the random transverse fieldh, the model exhibits long range order, i.e., $$\mathop {\overline {\lim } }\limits_{\left| y \right| \to \infty } \left\langle {\sigma _3 (x)\sigma _3 (y)} \right\rangle > 0$$ for anyx∈Z ^d.

     

Modules-at-Infinity for Quantum Vertex Algebras

This is a sequel to [Li4] and [Li5] in a series to study vertex algebra-like structures arising from various algebras such as quantum affine algebras and Yangians. In this paper, we study two versions of the double Yangian , denoted by DY _q (sl ₂) and with q a nonzero complex number. For each nonzero complex number q, we construct a quantum vertex algebra V _q and prove that every DY _q (sl ₂)-module is naturally a V _q -module. We also show that -modules are what we call V _q -modules-at-infinity. To achieve this goal, we study what we call -local subsets and quasi-local subsets of for any vector space W, and we prove that any -local subset generates a (weak) quantum vertex algebra and that any quasi-local subset generates a vertex algebra with W as a (left) quasi module-at-infinity. Using this result we associate the Lie algebra of pseudo-differential operators on the circle with vertex algebras in terms of quasi modules-at-infinity.     

Shift and broadening of emission lines in Nd<Superscript>3+</Superscript>:YAG laser crystal influenced by input energy

Spectroscopic properties of the flashlamp-pumped Nd ³⁺:YAG laser as a function of input energy were studied over the range of 18–75 J. The spectral widths and shifts of quasi-three-level and four-level inter-Stark emissions within the respective intermanifold transitions of \(^{\mathrm {4}}\mathrm {F}_{\mathrm {3/2}}\to ^{\mathrm {4}}{\kern -2.7pt}\mathrm {I}_{\mathrm {9/2}}\) and \(^{\mathrm {4}}\mathrm {F}_{\mathrm {3/2}}\to ^{\mathrm {4}}{\kern -2.7pt}\mathrm {I}_{\mathrm {11/2}}\) were investigated. The emission lines of \(^{\mathrm {4}}\mathrm {F}_{\mathrm {3/2}}\to ^{\mathrm {4}}{\kern -2.7pt}\mathrm {I}_{\mathrm {9/2}}\) shifted towards longer wavelength (red shift) and broadened, while the positions and linewidths of the \(^{\mathrm {4}}\mathrm {F}_{\mathrm {3/2}}\to ^{\mathrm {4}}{\kern -3.5pt}\mathrm {I}_{\mathrm {11/2}}\) transition lines remained constant by increasing the pumping energy. This is attributed to the thermal population as well as one-phonon and multiphonon emission processes in the ground state. This phenomenon degrades the output performance of the lasers.