Synthesis and optical properties of poly[4-methacryloxy-(4′-carboxy)-azobenzene]

Abstract

In the present work, the homopolymer built from the free radical polymerization of methacrylic monomer incorporating an azobenzene side-group has been synthesized and structurally characterized. The optical properties such as refractive index, extinction coefficient, absorption coefficient and optical energy band gap of poly[4-methacryloxy-(4′-carboxy)-azobenzene] thin film prepared by high vacuum sublimation method were determined using spectroscopic ellipsometry combined with transmittance measurements.

We found that in the spectrum of extinction coefficient there are absorption bands, which are assigned as the n-π* and π-π* electronic transitions of the azo compound.     

Growth and some properties of Ce3+-doped LiYbF4 single crystals

LiYbF₄ single crystals, nominally pure and doped with Ce³⁺ ions, of optical quality and up to 60 mm in diameter, have been grown by vertical directed crystallization. The optical and mechanical properties of the crystals have been studied. The refractive index dispersion for LiYbF₄ in the range of 0.4–0.6 μm can be described by the dependence n ²(λ) − 1 = Aλ²/(λ² − λ ₀²), where A = 1.14 and 1.21 and λ₀ = 0.074 and 0.080 μm for n _o and n _e, respectively. The sample microhardness exceeds 2.6 GPa. LiYbF₄ crystals are transparent in the range of 0.17–9 μm and have an absorption band in the range of 0.9–1.2 μm. It is shown that LiYbF₄ crystals doped with Ce³⁺ ions can be used as optical cut-off UV filters in the operating range λ = 0.25−0.28 μm.     

Spectroscopy of Charge Transfer Complexes of Aniline Blue

Charge transfer (CT) complexes of aniline blue (AB) were prepared with standard organic acceptors such as TCNQ, TCNE, DDQ, and chloranil and studied with UV-VIS-NIR spectra showing σ→π* and π→π* transitions along with free-carrier absorption due to scattering of light particles which has been found involving phonon–photon, electron–photon, and electron–electron scattering. Infrared spectra contain half power beta density due to hopping conduction and an asymmetric band corresponding to A(k) = A₀k exp(?bk) as absorption associated with diffraction of IR light from the crystalline particles.     

Valence states and coordination of titanium ions in beryl crystals

The valence states and coordination of titanium ions in beryl crystals grown from flux and by gastransport reactions have been studied by the methods of electron paramagnetic resonance (EPR) and optical spectroscopy. The parameters of the EPR spectra for Ti³⁺ in the Al³⁺ and Si⁴⁺ sites are determined. It is found that at concentrations exceeding 0.1–0.15 wt %, the EPR-spectra have additional lines due to exchange-bonded pairs of Ti³⁺ ions. It is shown that the two-humped absorption band with the maxima at 495 (π), 545 (π), and 495 (π) nm are formed due to Ti³⁺ ions located in the octahedral position.     

Synthesis and Crystal Structures of (E)-1-Phenyl-3-[(2,4,6-Trimethylphenyl)]prop-2-En-1-One and (E)-1-Phenyl-3-[(4-Trifluoromethylphenyl)]prop-2-En-1-One

Two chalcone compounds, namely (E)-1-phenyl-3-[(2,4,6-trimethylphenyl)]prop-2-en-1-one (1) and (E)-1-phenyl-3-[(4-trifluoromethylphenyl)]prop-2-en-1-one (2), have been synthesized and structurally characterized by elemental analysis, ¹H NMR spectrum, and single-crystal X-ray diffraction analysis. The chalcone molecules in (1) and (2) have the common skeleton of 1,3-diaryl-2-propen-1-one and adopt an (E)-configuration about the C = C double bonds. In addition, X-ray analysis reveals that the π···π stacking interactions are well observed in the crystal structure of (1) and (2).     

Synthesis and characterization of copper(II) tetraaza macrocyclic complex with 2- benzimidazolepropionate ligand

A mononuclear complex [Cu(L)(bip)₂] (1) (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo [14,4,0^1.18, 0^7.12]docosane; bip = 2-benzimidazolepropionate) has been synthesized and structurally characterized by X-ray crystal structure analysis. The crystals are monoclinic P2 ₁/n with a = 10.2990(2), b = 15.9400(3), c = 11.991(14) Å, = 101.92(7)°, V = 1926(2) ų, Z = 2. The copper(II) coordination geometry exhibits an axially elongated octahedron with four nitrogen atoms from the macrocycle and two oxygen atoms from the bip ligands. The cyclic voltammogram of 1gives 2 one-electron waves corresponding to Cu^II/Cu^III and Cu^II/Cu^I processes.     

Suitable Stress Waveforms for the Deformation-Induced Electronic Excitation in Crystals

A quantum mechanical approach is made to the deformation-induced electronic excitation in crystals. The ML intensity is assumed to be related to the transition probability P(m, n) from n^th to m^th state, and it may be expressed as I_ML = βP(m, n) where P(m, n) = 4π²/hα² |σ_mn (ω_mn)|² ·( n · μ )_mn·². It is shown that the ML excitation can take place only by the time-dependent applied stress. The ML excitation probability is analysed for different waveforms of the applied stress such as constant stress, δ-function, rectangular stress, single sided and double sided exponential stress, unit step function, external sinusoidal signals cos ω₀t and sin ω₀t, external exponential function, a periodic function and the stress of sequence of equidistant impulses of unit strength separated by a particular time. It is found that when the stress is a δ-function, a rectangular waveform, sinusoidal singals cos ω₀t and sin ω₀t or a sequence of equidistant impulses of unit strength and separated by a particular time, then there is a considerable probability of electronic excitation by the resonance transfer mechanism between the Fourier transform of the stress waveform and the frequency of the emitting electronic system i.e. (E₂ – E₁)/h.     

Influence of γ-Irradiation on Some Properties of NaCl: Eu++ Crystals (I). Optical and Dielectrical Characteristics of the Dopant Ions

The present work opens a series of papers describing a variety of properties of the same material, and deals with the effect of Eu⁺⁺ ions, and y–irradiation on the optical and dielectrical characteristics of NaCl crystals. For nonirradiated crystals four types of Eu⁺⁺-related absorption spectra have been identified and correlated with I.V. dipoles and three types of precipitates stable in the well aged crystals. For the solution—treated samples the effect of irradiation was to diminish the concentration of I.V. dipoles and to change the absorption spectrum in a remarkable way. These changes are explained in terms of the formation of some dopant—related clusters different of those obtainable thermally. No spectroscopic evidences have been obtained for the radiation—induced changes of the valence state of the dopant irrespective of its dispersion degree.     

Magnetic and Electric Birefringence in the Isotropic Phase of a Nematic of Large Positive Dielectric Anisotropy

Abstract

Magnetic (Δn_H ) and electric birefringence (Δn_E ) in the isotropic phase of strongly positive (Δ 8)trans-p-n-octyloxy α-methyl-p'-cyanophenyl cinnamate (8 OMCPC) have been measured. It is established that they both exhibit a (T - T*)^?1 dependence, T _NI - T* being 1.4 K. Also, the induced birefringence is found to be proportional to the square of the applied field, magnetic or electric.     

Synthesis and Crystal Structure of the Fluorite-Related Ruthenate, Trilanthanum Ruthenium Septaoxide La3RuO7

Abstract Single crystals of the lanthanum-containing ruthenate, trilanthanum ruthenium septaoxide, La₃RuO₇, were prepared via high-temperature flux growth and structurally characterized by single-crystal X-ray diffraction. The compound crystallizes in the orthorhombic space group Cmcm with a = 11.2077(6) ?, b = 7.4531(4) ?, and c = 7.6042(4) ? and is a member of a well-known family of compounds with the general formula Ln₃MO₇. Graphical abstract Synthesis and crystal structure of the fluorite-related ruthenate, trilanthanum ruthenium septaoxide La ₃ RuO ₇ William R. Gemmill, Mark D. Smith and Hans-Conrad zur Loye* Single crystals of La₃RuO₇ were isolated from a high-temperature KCl flux and characterized by single crystal X-ray diffraction. A view of the crystal structure approximately along [001] of La₃RuO₇ and displacement ellipsoids drawn at 50% probability level. The vertex-sharing RuO₆ octahedra are shown in blue, La³⁺ are shown in yellow, and O²⁻ are shown in red.      

An Iodoargentate Hybrid Coordination Polymer Constructed by Methyl Viologen: Structure,Properties and Theoretical Study

Abstract  

An iodoargentate hybrid coordination polymer induced by MV²⁺, [MV(Ag₂I₄)] _n (1) (MV = methyl viologen, i.e., 1,1-dimethyl-4,4-bipyridinium), has been obtained and structurally determined. In 1, (Ag₂I₄) _n ²⁻ chain exhibits a new type of zigzag-like configuration constructed from edge-sharing of normal and distorted AgI₄ tetrahedra, hydrogen bonds between MV²⁺ cations and (Ag₂I₄) _n ²⁻ chains contributed to the formation of quasi-two-dimensional structure. The band gap of 2.12 eV based on optical absorption spectrum indicated its semiconductor nature. Quantum chemistry calculation with DFT method was carried out to reveal its electronic structure.     

Principal Electrical Conductivities in the Organic Conductors TEA.(TCNQ)2 and TTF.TCNQ: The Microwave Approach

Abstract

We describe a microwave technique to measure the directions and magnitude of the principal electrical conductivities and permittivities of organic conductors. The method is applied to single crystals of triethylammonium-bis 7,7,8,8-tetracyano-p-quinodimethane (TEA.(TCNQ)₂) and of tetrathiafulvalenium-7,7,8,8-tetracyano-p-quinodimethane (TTF.TCNQ). For the former, the apriori set of principal axes (a*, (a*∧c), c) is confirmed with principal conductivities of 430, 5.3 and 0.41–0.77 Ω^?1m^?1 respectively. The room temperature permittivities have been measured for the first time (ε*_α ～ 5.4–5.5, ε*_α∧c ～ 7.5). For the latter it is clearly shown that the principal electrical axes are (a, b, c*) and, in contrary to earlier d.c data, we observe σ_c· < σ<a which is more consistent with the anisotropy of interchain interactions in this compound. The observed transverse and longitudinal anisotropies (～3.3 10² and 2.8 10⁴ respectively) are larger than believed up to now.     

Optical Properties of Pyrochlore Lead Scandium Tantalate Crystals

Optically homogeneous Pb₂Sc_0.5Ta_1.5O_6.5 crystals with pyrochlore structure are prepared by the method of high-temperature solution growth (HTSG). The refractive index in the visible region of the spectrum is measured. From the transmission spectra in the visible and infrared region the optical transmission window is estimated. From the fundamental absorption edge in the visible region of the spectrum the optical bandgap is determined corresponding to the intrinsic absorption. From the behaviour of the absorption coefficient α(hν) and α^1/2(hν) and the Raman spectrum permit to suggest that the absorption edge below 2.75 eV is due to indirect transitions.     

The Absorption,Fluorescence and Phosphorescence and Phosphorescence of Single Crystals of 1,2,4,5-Tetrachlorobenzene and 1,4-Dichlorobenzene at Low Temperatures

Abstract

The emission spectra of ultra pure single crystals of 1, 2, 4, 5. tetrachlorobenzene (TCB) and 1, 4-dichlorobenzene (DCB) at temperatures from 4.2°K upwards are reported. In addition, by use of the phosphorescence excitation technique the singlet-triplet absorption spectrum at 4.2°K has been obtained.

The phosphorescence emission of TCB at 4.2°K occurs predominantly from a defect origin “X” situated 48 cm^?1 below the triplet exciton band. The triplet exciton energy level is at 26676 cm^?1 from both emission and absorption studies. This is the triplet emission origin when the crystal is above 12°K. The temperature dependence of the emission intensity from the defect has an activation energy of 40±8 cm^?1. This value is consistent with our suggestion of thermal depopulation of the traps.

Single crystals of DCB show strong excimer emission and weak triplet exciton emission. There is no evidence for trapping levels. The triplet exciton emission. There is no evidence for trapping levels. The triplet exciton origin is 27890 cm^?1 from both emission and absorption studies.

Weak fluorescence (φ < 10⁰²) is detected from both TCB and DCB.

Vibrational analyses are reported for the absorption, fluorescence and phosphorescence spectra.     

Crystal and molecular structure of 1-phenyl-3-(2-hydroxyphenylamino)-2-buten-1-one,C16H15NO2

Orange, yellow, and colorless crystals were obtained for the title compound. The orange crystals are triclinic, space groupP¯1,a=9.181(2),b=10.734(2),c=15.245(3) Å,=73.06(2),=79.21(2), =67.83(2)°,V=1325.9(5) ų,Z=4. Two different symmetry-independent molecules (moleculeA andB) were determined in the crystal unit. The conformation ofA is stabilized by an intramolecular H bond from the amino NH to the keto and phenolic O atoms [1.89(2) and 2.38(2) Å, respectively]. The conformation ofB is stabilized by only one intramolecular H bond, from the amino NH to the keto O atom [1.925(2) Å]. The colorless crystals (moleculeC) are monoclinic, space groupP2₁/n,a=11.883(3),b=11.004(3),c=10.053(3) Å,=95.93(3)°,V=1307.5(6) ų,Z=4. This conformation is stabilized by one intramolecular H bond, the same as in B, with N-HO, 1.84(3) Å. An intermolecular H bond is observed forA,B, and C, O-HO, 2.634(2), 2.640(2), and 2.697(2) Å, respectively. The yellow crystals are adducts with ethanol (¹H NMR, infrared and GC measurements).     

Conformational polymorphism in thiophenyl substituted quinones and the disappearing NMR spectrum

The stepwise addition of thiophenol to benzoquinone gives thiophenylbenzoquinone (1b), 2,5-and 2,6-di-(thiophenyl)benzoquinone (2,3),2,3,6-tri(thiophenyl)benzoquinone (4) and 2,3,5,6-tetra(thiophenyl)benzoquinone. (5). Compounds1–4 can be crystallized, and the¹³C NMR spectra are readily interpreted. Compound5 could not be crystallized easily, and the NMR showed more than twice as many lines as the number of carbon atoms. Slow evaporation in an NMR tube produced three distinct crystals. X-ray analysis of two crystals (5a and5c) showed the compounds to be conformational polymorphs. Direct synthesis of5 from tetrachlorobenzoquinone and thiophenol yielded only conformer5a, and the¹³C NMR spectrum showed only the 6 lines expected for four equivalent phenyl substituents on benzoquinone. Subjecting5a to a variety of solvents, reagents and temperatures did not regenerate the original¹³C NMR spectrum. The crystal structures, conformations, and polymorphs are discussed.     

Imidazolium based ionic liquid crystals: structure,photophysical and thermal behaviour of [Cnmim]Br·xH2O (n = 12, 14; x=0, 1)

The long chain imidazolium halides [C_nmim]Br·xH₂O (n = 10, 12; x = 0, 1) have been synthesized and their structural and thermal behaviour together with their photophysical properties characterized. X‐ray structure analyses of the monohydrates ([C₁₂mim]Br·H₂O: triclinic, P1, no. 2, Z = 2, Pearson code aP112, a = 550.0(5) pm, b = 779.4(5) pm, c = 2296.1(5) pm, α = 81.89(5)°, β = 83.76(5)°, γ = 78.102(5)°, 3523 unique reflections with I_o > 2σ(I_o), R₁ = 0.0263, wR₂ = 0.0652, GooF = 1.037, T = 263(2) K; [C₁₄mim]Br•H₂O: triclinic, P1, no. 2, Z = 12, Pearson code aP11, a = 549.86(8) pm, 782.09(13) pm, c = 2511.3(4) pm, α = 94.86(2)°, β = 94.39(2)°, γ = 101.83(2)°, 2063 unique reflections with I_o > 2σ(I_o), R₁ = 0.0429, wR₂ = 0.0690, GooF = 0.770, T = 293(2) K) show for both compounds similar bilayered structures. Sheets composed of hydrophilic structure regions constituted by positively charged imidazolium head groups, bromide anions and hydrogen bonded water alternate with hydrophobic areas formed by interdigitated long alkyl chains belonging to imidazolium cations with different orientation. Combined differential scanning calorimetry and polarizing optical microscopy shows that the monohydrates as well as the anhydrous imidazolium salts are thermotropic liquid crystals which adopt smectic mesophases. The mesophase region is larger in case of the monohydrates when compared to the anhydrous compounds indicating that water obviously stabilizes the mesophase. All compounds show an intense whitish photoluminescence with short lived (¹π←¹π*) and long lived (¹π←³π*) transitions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal structures and conformations of two new biisoquinoline derivatives

Crystal structural studies of two new biisoquinoline derivatives, a neutral compound C₂₀H₂₄N₂ (3) and a salt C₁₈H₂₁N₂ ⁺C₁₀H₁₄BrO₄S^– H₂O (4) are described and discussed. Compound 3 crystallizes in the monoclinic space group P2 ₁/c, with a = 11.039(2), b = 7.791(2), c = 19.001(4) Å, = 104.31(3)°, and Z = 4. Compound 4 crystallizes in the monoclinic space group P2 ₁, with a = 12.0021(3), b = 8.9189(2), c = 12.8685(4) Å, = 100.7600(10)°, and Z = 2. The absolute stereochemistry of 4 in the solid state has been determined. The biisoquinoline rings in both compounds adopt twist-boat conformations with significant deviations from ideal geometry. The two heterocyclic rings in each species are oriented so that they are not overlayed with each other and the phenyl rings are oppositely directed. The cations and the anions in 4 are linked together through an elaborate system of hydrogen bonding involving the water molecule.     

Thermally activated de-excitation of the EL2 metastable state in GaAs

Measurements of absorption in the near infrared have been performed on n-type and undoped semi-insulating GaAs containing EL2 the main native defect in GaAs. The whole band of absorption related to EL2 disappeared after 1 μm light illumination when the crystal was cooled to helium temperatures. Measurements of the thermally activated recovery of EL2 absorption have been made. The rate of the de-excitation is well described by the formula: r = 1.7 · 10¹² · exp (−0.36 eV/kT) + 1.6 · 10⁻⁹ · n · exp (−0.085 eV/kT) s⁻¹ where n [cm⁻³] is the concentration of free electrons.     

Growth and microhardness studies of melt-grown lead (II) chloride single crystals

In the present work, lead (II) chloride material is purified by directional solidification and single crystals of PbCl₂ are grown by vertical Bridgman technique employing double zone furnace. The growth conditions and the problems overcome are discussed. The grown crystals of pure and K₊-doped crystals are cleaved and subjected to microindentation tests. The validity of Kick's relation is checked, the value of K₁ the standard hardness number and n the work-hardening coefficient are discussed. The microhardness behaviour of pure and K⁺-doped lead(II) chloride have been compared.