The standard approach involving the sensibilization of naphthalene phosphorescence is employed to study the mono-substituted ortho-bromobenzophenone (2-BrBP). A new feature of the approach is the use of octane as the passive neutral matrix. This matrix is chosen due to the absence of the triplet-excitation mobility in pure 2-BrBP crystal. The problem of common phosphorescence kinetics of 2-BrBP and naphthalene is solved in analytic form. Unlike in the classical problem involving unsubstituted benzophenone, the relevant phosphorescence measurements have been performed at low temperatures (as low as 1.6 K). A new approach is suggested to account for the large difference between the typical experimental pulse-delay time and the slow naphthalene phosphorescence. Relevant computations allow us to explain the nature of the two sets of phosphorescence lines of 2-BrBP.

Thermal conductivities of two benzophenone single crystals have been measured at temperatures from 4.7 to 270 K. The experimental data for both are consistent for temperatures above 15 K. The thermal conductivity of benzophenone can be represented as a sum of two contributions: κ1 + κTA where κ1 is due to the standard phonon mechanisms accepted for ordered crystals and κTA takes into account the heat flow due to intermolecular hopping of thermally activated intramolecular vibrational modes. The thermal activation contribution in unsubstituted benzophenone is substantially smaller when compared to that in any of the two para-bromobenzophenone polymorphs studied previously. Unlike in the 4-bromobenzophenone crystals, the microscopic agent responsible for intramolecular excitation(s) was not determined. The characteristic intramolecular excitation energy was evaluated to be 220 K, about three times less compared to 4-bromobenzophenone.

The thermal conductivity of a polycrystalline sample of monoclinic polymorph of para-bromobenzophenone in the T = 3–320 K temperature range was measured using steady-state linear heat flow. The temperature dependences of thermal conductivity are presented as the sum of two independent contributions: a contribution that corresponds to the thermal conductivity of an orientationally ordered crystal structure, and a new additional thermally activated contribution that manifests itself above 130 K. A comparison is made with the data on the thermal conductivity of a single crystal triclinic polymorph of para-bromobenzophenone. It is established that the contribution corresponding to the thermal conductivity of the orientationally ordered crystal structure depends on the molecular crystal packing, and the characteristic activation energy of the thermal activation contribution, which is caused by the intramolecular vibrations of the C-Br bond, does not depend on the grain size or on the structure of the sample.

Integrated phosphorescence spectra of meta-bromobenzophenone crystals were measured in the temperature range from 1.6 to 297 K. The spectra were found to contain two series of monomeric bands associated with the stretching mode of the C=O carbonyl at all temperatures. Above 70 K in the red spectral region, a broad structureless band of unknown nature was observed, the center of gravity of which was shifted to red with increasing temperature. The above phenomena and others anomalies can be due to the structural properties of both the molecule and the crystal.

We present the first experimental investigation of the influence of the temperature on the low-frequency Raman spectra of the triclinic and monoclinic polymorphs of 4-bromobenzophenone in the temperature range 60-296 K.We have found an anomalous temperature dependence of the intensity of two bands at similar to 155 cm(-1) and similar to 30 cm(-1) in the triclinic phase as compared with its behavior in the monoclinic phase. Anomalous behavior manifests itself in the growth of the intensity of the band at 155 cm(-1), and decrease of the intensity of the band at 30 cm(-1) with decreasing temperature. The assumption that the band at 155 cm(-1) corresponds to the fundamental vibration, and the band at 35 cm(-1) to the combination vibration (the difference in the frequencies of two vibrations 155.8 and 120 cm(-1)) allows us to associate their anomalous temperature behavior with anharmonic interactions. (C) 2016 Elsevier B.V. All rights reserved.

The lattice parameters of monoclinic ortho-bromobenzophenone (2-BrBP) were determined using powder X-ray diffraction, in the temperature range of 90–300 K. It is found that ortho-bromobenzophenone has small linear expansion coefficients (about 10−5 K−1) and is characterized by weak anisotropy. There were no phase transitions in the studied temperature range.

Luminescence and other properties of solid 2-bromobenzophenone demonstrate features, which require special attention. We present results, which include DFT calculations, integrated and time-resolved phosphorescence spectra, and excitation spectra. The energies of the title molecule were calculated for the S0, S1, and T1 states. Nanosecond time-resolved phosphorescence spectra were measured at three temperature points at which the spectra undergo substantial changes. Joint analysis of energy surfaces and experimental evidence allowed reconstruction of the emission scenario that determines temperature-related variations of spectra. Upon excitation to state S1 the molecule converges very fast to T1, emission from which can occur from the minima at 60° or at 180°. At low temperatures the molecule emits from the former, whereas at higher temperatures the molecule can overcome the barrier to emit from the lower minimum. The probability of excimer formation increases with increasing temperature.

Phosphorescence spectra of two 4-bromobenzophenone polymorphs have been measured at 1.6K. Based on the actual structure data for the triclinic and monoclinic polymorphs, the relevant exciton dispersion laws have been calculated within a 1D model to show that the exciton band in the triclinic form should be appreciably wider than in the triclinic one. Comparative analysis of the shapes of the observed 0–0 phosphorescence bands at liquid-helium temperature provide evidence that the triplet exciton diffusion is more efficient in the triclinic form, which corroborates the conclusions of our simple theory.

Integrated and time resolved phosphorescence spectra of the monoclinic (M-form) and triclinic (T-form) polymorphs of 4-bromobenzophenone are measured at temperatures of 293, 77, and 1.6 K. The parameters of the damping kinetics of the most important bands are determined. At room temperature the integrated spectra of both polymorphs have a distinct monomeric structure with extremely close energies of the band maxima. At 77 K the integrated spectra of both polymorphs still have a monomer structure and close decay times for the 0-0 band, but bands of another monomeric series which is significantly shifted relative to the more intense main series are also observed. The decay times for the 0-0 bands of the polymorphs are close at 77 K, as opposed to room temperature, where this band decays three times more slowly in the T polymorph. The overall shape of the integrated spectra for both polymorphs at 1.6 K is also monomeric, but the shapes of the 0-0 bands have large, significant differences. Based on data on the structure of the polymorphs, a one-dimensional model is proposed and the corresponding triplet exciton spectra are calculated assuming close coupling. These calculations imply that the exciton band width Δ is four times wider in the T-form than in the M-form. Thus, the coefficient of tunnel diffusion (which is proportional to Δ2) should be an order of magnitude higher in the T-form than in the M-form. A comparative analysis of the integrated phosphorescence spectra at 1.6 K indicates that diffusion is considerably more efficient in the T-form, in agreement with the qualitative conclusions of our theory.

This work describes the gas-sensitive properties of a one-dimensional organic conductor before and after exposure to carbon monoxide and human breath. A sensitive material, an anion-radical salt of tetracyanoquinodimethane, has been investigated by infrared spectroscopy and electrical resistivity measurements. Drastic spectral and electrical changes are found after gas exposure showing that the compound interacts strongly with human breath, carbon monoxide, and ammonia. Under breath action the resistance changes by more than three orders of magnitude while the adsorption of CO, one of the components of breath, results in a decrease in both IR absorption and electrical conductivity. The intensity of the IR absorption spectrum of the material in the CO medium decreases down to 30% in the 2180-2500 cm(-1) range. This absorption varies by about 10% between 750 and 2500 cm(-1) after breath action. Direct electrical measurements show that actions of donor or acceptor gas result in opposite changes of electric resistance. The electrical resistance of the sample can drop down to 0.4 MΩ due to the pulse action of ammonia at 4 ppm concentration, while it increases upon exposure to carbon monoxide media at concentrations of 6-25 ppm. The response signal of the investigated samples changes proportionally to the concentration of the acting gas. The results substantiate prominent gas sensitivity of the investigated material, which might find applications for breath analysis, in particular, for the development of noninvasive diagnosis of gastric diseases.

Microsecond-level time-resolved photoluminescence spectra of 2-bromobenzophenone are measured on crystalline (at 1.6, 52, and 300K) and glassy (at 1.6 and 95K) samples. For each of these physical situations the characteristic decay times are determined for the 0–0 band of monomer emission from metastable (blue 0–0 band) and global (red 0–0 band) excited states of the 2-benzophenone molecule in the crystal and also for the bimolecular excimer emission. The time dependence of the intensity of the red 0–0 band at 52K in the crystal is found to be nonmonotonic, a fact that provides yet another beautiful demonstration of the presence of two excited states and is indicative of thermally activated nonradiative transitions from the metastable excited state to the global. The corresponding kinetics is well described by a system of equations for joint radiative decay. To gain a better understanding of the nature of the anomalies of the phosphorescence, the crystal and molecular structures of 2-benzophenone at 100 and 200K are determined by the single-crystal x-ray diffraction method. Within the temperature interval 100–300K the crystal structure of 2-benzophenone remains monoclinic, with symmetry space group P21∕a (Z=4). The coefficient of linear thermal expansion is anisotropic and of a magnitude (10−5−10−4K−1) typical for organic molecular crystals. The conformation parameters of the molecule vary relatively strongly with temperature; the behavior of the C–Br and C=O bonds is most interesting: they become shorter with increasing temperature, possibly indicating a weakening of the weak hydrogen bonds of the peripheral oxidizer atoms with the acceptors of the neighboring molecules.

The time-resolved low-temperature phosphorescence spectra of the ortho-bromobenzophenone (2-BrBP) crystal are investigated at a temperature of 52K. The spectra show that the emission of one series of vibrational bands of the phosphorescence decays in time, while the emission of another series of vibrational bands, which is identical but shifted to longer wavelengths, first rises and then decays. This behavior of the spectrum at the given temperature is explained by the overcoming of an energy barrier between two conformational states of the excited ortho-bromobenzophenone molecule. Besides the phosphorescence of the two series of vibrational bands, the time-resolved spectrum of the ortho-bromobenzophenone crystal at the given temperature exhibits excimer emission, which decays over a time ≈175μs.

Spectroscopic studies of vitreous 2-bromobenzophenone have been carried out over the respective domain of its stability. Glassy 2-bromobenzophenone samples were obtained by abrupt cooling of the melt by cold helium vapor. Quantum yield measurements allowed us to establish that the upper boundary of stable glass is slightly above 100K, while at about 220K the glass melts. Phosphorescence measurements at 4.2K showed that even at this low temperature the emission contains a strong excimer component. The energy position and shape (two bands) of the excimer emission are close to those observed in the crystal of 2-bromobenzophenone at higher temperatures. Contrary to findings in the crystal, the monomeric emission of the glass contains only one C=O stretch series, every band of which is substantially broader than in the crystal. As the temperature is raised, the monomeric emission intensity falls, disappearing completely above 70K.

The effects of a minor chemical modification such as a change in the position of a Br atom within the same phenyl ring on the optical and macroscopic properties of benzophenone derivatives are investigated by spectroscopic and calorimetry methods. More specifically, we have studied IR and Raman spectra of the two isomers of monosubstituted benzophenones: 2-bromobenzophenone (2BrBP) and 4-bromobenzophenone (4BrBP) in the wide spectral and temperature regions. It has been found that the substitution of a Br in an ortho position leads to some changes of the anharmonicity of the ν(CO) vibrations. Full geometry optimization and vibrational spectra modeling for 2BrBP and 4BrBP isolated molecules have been calculated by the density functional method (B3LYP/6-31+G(d)) using GAUSSIAN’03 software. Quantum-mechanical calculations for the isolated molecules have shown that the shape of 2BrBP molecule is strongly asymmetric in comparison with the shape of 4BrBP molecule. A change in the molecular shape translates into rather different macroscopic properties such as the crystal melting points. Namely, the melting point of 2BrBP (318K) was found to be lower than that of 4BrBP isomorphs (358K). Moreover, 2BrBP exhibits a large reluctance to crystallize, while 4BrBP crystallizes immediately below the melting point as a liquid is cooled.

Integrated and time-resolved phosphorescence spectra of vitreous ortho-bromobenzophenone are investigated at a temperature of 4.2K. An excimer emission is observed that is completely absent in the crystal. The rapid damping of the excimer emission in comparison with monomer emission is observed. It is conjectured that the excimer emission of the glass is the result of the formation of pre-dimer pairs in the preparation of the vitreous sample.

A combination of single-crystal and powder X-ray diffractometry was used to study the structure of two polymorphs of 4-bromobenzophenone over the temperature range from 100 to 300 K. One of the polymorphs of the title compound was known previously and its structure has been determined at room temperature [Ebbinghaus et al. (1997). Z. Kristallogr. 212, 339-340]. Two crystal growth methods were employed, one of which (a modification of the Bridgman-Stockbarger technique) resulted in single crystals of a previously unknown structure. The basic physical properties of the stable polymorph are: growth method, from 2-propanol solutions or gradient sublimation; space group, monoclinic P2(1)/c; melting point, T(m) = 355.2 K; X-ray density (at 100 K), D(x) = 1.646 g cm(-3). The same properties of the metastable polymorph (triclinic P\overline 1 ) are: growth method, modified Bridgman-Stockbarger method; X-ray density (at 100 K), D(x) = 1.645 g cm(-3); T(m) = 354 K. Thermograms suggest that the melting of the metastable form is accompanied by at least a partial crystallization presumably into the monoclinic form; the transformation is therefore monotropic. Analysis of short distances in both polymorphs shows that numerous weak hydrogen bonds of the C-H...pi type ensure additional stabilization within the respective planes normal to the longest dimension of the molecules. The strong temperature dependence of the lattice constants and of the weak bond distances in the monoclinic form suggest that the weak bond interactions might be responsible for both the large thermal expansion within plane bc and the considerable thermal expansion anisotropy.

The work is devoted to luminescent properties of trivalent lanthanide complexes dispersed in thermoplastic host matrices. Polyethylene films and polypropylene-rods, both doped with these complexes, were manufactured using an extrusion technique. Two kinds of dopants were used: Eu(III)-thenoyltrifluoroacetone-1,10-phenanthroline complex (1) and Eu(III)-La(III)-1,10-phenanthroline complex (2). Absorption, excitation, emission spectra and lifetime of luminescence were studied. The impact of the polymer matrix on the emission spectra was investigated. Emission spectra of the films were studied at room and helium temperatures. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) surface mapping showed that in the Eu(III)-La(III) complex europium forms islands (clusters) with a dimension of 1 mu m, whereas lanthanum was dispersed more uniformly in the polymer matrix. Dependence of emission intensity on the excitation was determined. Copyright (C) 2006 John Wiley & Sons, Ltd.

The exciton dynamics and optical characteristics of blue-emitting N,N-'-diphenyl-1,4-phenylene-diamine oligoaniline films have been determined. Transient photoluminescence experiments are consistent with internal quantum yields of similar to 5.3% and 10.1% measured for oriented and nonoriented films, respectively. The data indicate a drastic dependence on nanoscale ordering which promotes photoluminescence quenching, a large annihilation rate, and fast exciton diffusion. Therefore, the emission properties can be controlled by the textural morphologies of the layers.

The synthesis of a mixed-ligand complex 1,3-dithiole-2-thione-4,5-dithiolato-bis(1,10-phenanthroline)zinc(II), [Zn(Dmit)(Phen) 2 ], is described. The crystals are monoclinic, space group P 2 1 / n, a = 11.868(2) Å, b = 13.122(3) Å, c = 17.010(3) Å, β = 102.01(3)°, Z = 4. The coordination polyhedron of the Zn(II) atom is an octahedron formed by two sulfur atoms of the Dmit ligand and four nitrogen atoms of the two Phen ligands. The complex is studied by IR and UV spectroscopy.