The work presents the results of investigation of the phase behavior, crystal growth from solutions, structure, and absorption-fluorescent properties of the crystals of 4,7-bis(5-(4-(trimethylsilyl)phenyl)thien-2-yl)benzothiadiazole (TMS-P-T-BTD) and its isomer 4,7-bis(4-(5-(trimethylsilyl)thien-2-yl)phenyl)benzothiadiazole (TMS-T-P- BTD). The structure of the toluene-grown single crystals of both TMS-P-T-BTD and TMS-T-P-BTD was investigated using single-crystal X-ray diffraction at temperatures of 295 and 90 K. In the crystal unit cell of TMS-P-TBTD, which is triclinic (space group P1, Z = 1), statistical disorder in the arrangement of molecules was established, resulting in the emergence of a so-called "average" molecule with dual (50 %) orientation of the central 2,1,3-benzothiadiazole fragment., The molecules of TMS-P-T-BTD in the crystal exhibit an almost planar conformation. It was found that crystals of the isomer TMS-T-P-BTD of triclinic modification (space group P-1, Z = 2) are solvated: in the unit cell there is one solvent molecule- toluene- per two molecules of the basic compound. In the asymmetric block of the unit cell of the solvated crystals of TMS-T-P-BTD, there are two molecules with different conformations. Studies of the absorption-fluorescent properties of TMS-P-T-BTD and TMS-T-P-BTD molecules in the crystals showed that swapping the thiophene and phenyl fragments significantly alters the energy and probability of electronic transitions, as well as the relative position of n pi* and pi pi* levels. Both the probability of singlet- singlet transitions and the probability of singlet- triplet conversion change. The splitting of n pi* levels, caused by the arrangement of thiophene fragments in the TMS-P-T-BTD molecule, leads to a strong dependence of the fluorescent (kr) and phosphorescent (knr) characteristics of the isomer on the immediate environment. In the TMS-P-T-BTD crystal, this results in the complete suppression of fluorescence.

The results of the study of the photoluminescent and X-ray luminescent properties of a p-terphenyl crystalline element made of a single crystal grown from a melt using the Bridgman method are presented. The transmission, photoluminescence, and X-ray luminescence spectra of the crystals were obtained and analyzed. The kinetics of photoluminescence and X-ray luminescence decay have been studied for p-terphenyl single crystal, and the absolute light yield of X-ray luminescence has been determined.

The crystallization and absorption/fluorescent properties of linear conjugated molecules derived from 2,1,3-benzothiadiazole, specifically, 4,7-bis(2,5-dimethyl-[1,1'-biphenyl]-4-yl)benzothiadiazole (Ph-Xy-BTD) and 4,7-bis(4'-hexyl-2,5-dimethyl-[1,1'-biphenyl]-4-yl)benzothiadiazole (Hex-Ph-Xy-BTD), have been studied. The synthesis of a new derivative of Hex-Ph-Xy-BTD is described. It was found that the presence of terminal n-hexyl substituents in Hex-Ph-Xy-BTD reduces the melting temperature, increases solubility, and has a positive effect on crystallization as compared to Ph-Xy-BTD. Hex-Ph-Xy-BTD single crystals were grown from a hexane solution, and their structure was elucidated using single-crystal X-ray diffraction, confirming a monoclinic system (sp. gr. P21/c, Z = 4). Absorption and fluorescence spectra were obtained and analyzed for solutions in tetrahydrofuran, as well as for the Ph-Xy-BTD and Hex-Ph-Xy-BTD crystals, along with the study of the quantum yield and fluorescence lifetime.

Inelastic neutron scattering measurements on the hexagonal Zn67Mg33S semiconductor alloy reveal a bimodal pattern of the optical modes across the Brillouin zone, confirmed by first-principles simulations. Such modes are sensitive to the local fluctuations in the composition inherent to random Zn/Mg alloying, distinguishing homo from hetero environments of a given bond (1-bond/2-mode), as is formalized for cubic alloys by the percolation model. The latter model thus emerges as a generic framework for systematizing the optical modes of semiconductor alloys in various crystal structures.

The results of the crystallization studies of anthracene, tetracene, and pentacene under conditions of vapor phase transport in growth systems with single- and two-zone thermal fields are presented. The features of the phase behavior and thermal stability of the compounds were studied by using the methods of differential scanning calorimetry and thermogravimetric analysis to establish the heating regimes of substances ensuring crystal growth without damage from chemical degradation. Conditions for growing crystals of centimeter scale (0.2–2 cm) were determined for growth systems with single- and two-zone thermal fields. Based on the grown pentacene crystals, a series of field-effect transistors with top drain/source electrodes and top gate were fabricated and their electrical characteristics were studied.

Linear conjugated molecules consisting of benzothiadiazole (BTD) and phenyl rings are highly efficient organic luminophores. Crystals based on these compounds have great potential for use as light-emitting elements, in particular, scintillation detectors. This paper compares the peculiarities of growth, structure, and fluorescent properties of crystals based on 4,7-diphenyl-2,1,3-benzothiadiazole (P-2-BTD) and its organosilicon derivative 4,7-bis(4-(trimethylsilyl)phenyl) BTD ((TMS-P)(2)-BTD). The conditions for the formation of centimeter-scale single crystals were found for the former, while it was possible to prepare also bulky faceted individual crystals for the latter. The structures of P-2-BTD and (TMS-P)(2)-BTD crystals at 85 and 293 K were investigated by single-crystal X-ray diffraction. The crystal structure of P-2-BTD has been refined (sp. gr. P1, Z = 4), and for (TMS-P)(2)-BTD crystals, the structure has been solved for the first time (sp. gr. P2(1)/c, Z = 32). Experimental and theoretical investigations of the absorption-fluorescent properties of solutions and crystals of the molecules have been carried out. The luminophores are characterized by a large Stokes shift for both solutions and crystals with a high fluorescence quantum yield of 75-98% for solutions and 50-85% for the crystals. A solvatochromic effect was observed for solutions of both luminophores: an increase in the values of the fluorescence quantum yield and the excited state lifetime were established with increasing the solvent polarity. Fluorescence properties of solutions and crystals have been analyzed using the data on crystal structure and conformation structure of the molecules as well as density functional theory calculations of their electronic structure. The results have shown that the crystal packing of P-2-BTD molecules exhibits uniformity in conformational states, while (TMS-P)(2)-BTD molecules display a variety of conformational structures in the crystals. This unique combination of features makes them a remarkable example among the other molecular systems for identifying the relationship between the structure and absorption-fluorescence properties through comparative analysis.

The results of studying the growth of para-quaterphenyl (4P) and its derivative—4,4”'-bis(trimethylsilyl)-para-quaterphenyl (TMS-4P-TMS)—crystals from solutions are presented. It has been established that TMS-4P-TMS crystals exhibit better growth characteristics as compared to 4Р. Parameters of the phase transitions of 4P and TMS-4P-TMS in closed crucibles were refined using differential scanning calorimetry. The crystal structure of TMS-4P-TMS in the triclinic space group P 1̅ (Z = 2) has been decrypted for the first time using single-crystal X-ray diffraction and was studied in a wide temperature range. A crystallographic analysis of the studied compounds in crystals was performed using the Hirshfeld surface method, and modeling of intermolecular interactions was performed.

On the basis of first-principles electronic structure calculations, crystallographic parameters have been refined for calcium hydroxozincate (Qatranaite mineral), and the vibration properties (frequencies and eigenvectors) calculated. A detailed analysis of vibration modes is done, in the context of comparison with infrared and Raman spectra previously available. Special attention is paid to a posteriori symmetry analysis of vibration modes, discussing the latters' attribution to four irreducible representations of the P2(1)/c space group, and to identifying stretchings and bendings of particular chemical bonds, pronounced in different vibrations. It turns out that high-frequency (>700 cm(-1)) vibrations of hydroxyl groups bridging the Ca or Zn cations differ quite considerably for crystallographically distinct hydroxyl positions. It is shown that the vibrations involving hydroxyl groups and crystalline water typically come about in quadruplets at very close frequencies, whereby different irreducible representations reflect different combinations of similar "molecular" vibrations of four identical entities (of each hydroxyl or water) present in the unit cell. However, some vibrations show exceptions from this rule. In addition to interpretation of earlier experimental investigations, our study indicates that the low-frequency (<700 cm(-1)) vibrations within the cation-hydroxyl connected skeleton are of more "solid-state-like" character and cannot be reasonably interpreted in terms of "molecular" vibrations within ZnO4 or CaO6 units.

Though extensively studied since the emergence of zincblende cubic A(B,C) semiconductor alloys (zb-SCA) in the sixties, the phonon mode behavior of Ga(As,P) remains a subject of debate to this day. Recently Zollner and co-authors reported on a thorough far-infrared (IR) ellipsometry study of the vibrational spectra of Ga(As,P) spanning the composition domain. They suggest that their experimental data are better described by the cluster model than by our percolation model. On the basis of Zollner experimental data, kindly made available to us, we show that the percolation model basically applies to Ga(As,P), contrary to the authors original allusion.

The authors discuss results from studying the photophysical properties of linear molecules based on 2,1,3-benzothiadiazole, specifically 4,7-di([para-biphenyl]-4-yl)benzothiadiazole (Ph-Ph-BTD) and 4,7-bis(2,5-dimethyl-[1,1'-biphenyl]-4-yl)benzothiadiazole (Ph-Xy-BTD). The synthesis of a new phenylxylene derivative of benzothiadiazole—Ph-Xy-BTD—is described. The thermal stability of the Ph-Ph-BTD and Ph-Xy-BTD compounds is studied. Their parameters of melting and solubility are determined, and the absorption spectra of solutions in n-hexane and THF are recorded. It is shown that having pendant methyl substituents in Ph-Xy-BTD lowers its melting point, increases its solubility, reduces the probability of a transition between the ground and excited state orbitals, and raises the energy of transition. The effect solvation has on the spectra, fluorescence quantum yield, and lifetime of the fluorescence of compounds in THF and n-hexane is studied. Static dipole moments in the ground (HOMO) and excited states (LUMO) of Ph-Ph-BTD and Ph-Xy-BTD molecules are determined. It is shown that the conformation of the excited state (LUMO) changes during the relaxation of the solvate and becomes more planar than that of the ground state (HOMO). A relationship is revealed between the conformation of the excited state of the studied compounds and the polarity of the solvent.

In the context of effective detection of iodine species (I2, CH3I) formed in nuclear power plants and nuclear fuel reprocessing facilities, we perform a comparative study of the potential sensing performance of four expectedly promising 2D materials (8-Pmmn borophene, BC3, C3N, and BC6N) towards the iodine-containing gases and, with the view of checking selectivity, towards common inhibiting gases in the containment atmosphere (H2O and CO), applying methods of dispersion-corrected density functional theory with periodic boundary conditions. A covalent bond is formed between the CO molecule and boron in BC3 or in 8-Pmmn borophene, compromising the anticipated applicability of these materials for iodine detection. The presence of nitrogen atoms in BC6N-2 prevents the formation of a covalent bond with CO; however, the closeness of adsorption energies for all the four gases studied does not distinguish this material as specifically sensitive to iodine species. Finally, the energies of adsorption on C3N yield a significant and promising discrimination between the adsorption energies of (I2, CH3I) vs. (CO, H2O), revealing possibilities for this material's use as an iodine sensor. The conclusions are supported by simulations at finite temperature; underlying electronic structures are also discussed.

Backward/near-forward Raman scattering and ab initio Raman/phonon calculations are combined, together with x-ray diffraction and ellipsometry measurements to further inform the debate on the compact phonon behavior of the II–VI Cd1−xZnxTe alloy. The compacity favors the coupling of polar optic modes in both the transverse and longitudinal symmetries via the related (EL,T) long-wave electric fields. The EL-coupling achieves maximum in the Zn-dilute limit, which enhances the (upper) ZnTe-like (impurity) mode at the expense of the (lower) CdTe-like (matrix-like) one, leaving the impression of a unique {Cd-Te,Zn−Te}-mixed longitudinal optic (LO) phonon across most of the composition domain. However, the purely mechanical (non-polar) transverse optic (PM-TO) phonons, that hardly couple, reveal an underlying three-mode {1 × (Cd-Te),2 × (Zn-Te)} fine structure that distinguishes between Zn–Te vibrations in Zn- and Cd-like environments up to second neighbors. Further refinement arises by exploring the phonon–polariton (i.e., polar-TO) regime at large Zn content. On reducing the scattering angle, the ET-coupling develops into a sequential softening of phonon–polaritons from ZnTe- down to CdTe-like ones, which transiently unveils a bimodal pattern behind the Cd–Te signal. Altogether, this results in a (rare) canonical four-mode {2 × (Cd-Te),2 × (Zn-Te)} percolation pattern for Cd1−xZnxTe, i.e., a close II–VI replica of the twin III−V In1−xGaxAs one—yet differing by two apparent LO modes and a sensitivity of bond vibrations limited to first-neighbors. Retrospectively, the difference in sensitivity of bond vibrations to the local environment between In1−xGaxAs (limited to first neighbors) and Cd1−xZnxTe (extending up to second neighbors) emerges as a rule throughout common (covalent) III–V and (ionic) II–VI semiconductor alloys.

Among short donor–acceptor molecules with a central benzothiadiazole fragment, 4,7-di-2-thienyl-2,1,3-benzothiadiazole (T-BTD) is one of the most well-known compounds, valued for its photophysical and semiconductor properties. We have synthesized a derivative of 4,7-di-2-thienyl-2,1,3-benzothiadiazole with trimethylsilyl end-substituents, 4,7-bis(5-(trimethylsilyl)thiophen-2-yl)benzothiadiazole (TMS-T-BTD). The phase transition parameters and thermal stability of T-BTD and TMS-T-BTD were investigated using DSC and TGA methods. The presence of the trimethylsilyl end-groups in TMS-T-BTD significantly enhances solubility, increases the melting temperature, and improves the resistance of TMS-T-BTD to evaporation in the liquid state. Single crystals of T-BTD and TMS-T-BTD were grown from solutions, with the largest sizes being 7 × 2 × 0.5 mm3 and 8 × 1 × 0.45 mm3, respectively. Using single-crystal X-ray diffraction at 293 K, the crystal structure of T-BTD was refined in the rhombic system (sp.gr. Pcab, Z = 8), while for TMS-T-BTD, it was determined for the first time in the monoclinic system (sp.gr. P21/c, Z = 4). The relationship between observed growth anisotropy and molecular packing in the crystals was analyzed. The results of investigations into the spectral-fluorescent properties of solutions in hexane and THF are presented. The solvatochromic effect was studied in a series of solvents, including hexane, THF, dichloromethane, and acetonitrile. The photostability of the compounds in hexane solutions was examined. It was found that the quantum yield of photodestruction for T-BTD is 13 times higher than that of TMS-T-BTD. The fluorescent properties of T-BTD and TMS-T-BTD crystals were investigated.

trans-Stilbene single crystals are of great interest for researchers as scintillators characterized by a high specific light yield. Bulk trans-stilbene single crystals have been grown from an anisole solution. The transmission and photoluminescence spectra have been recorded, and the single-crystal photoluminescence quenching kinetics has been investigated. The scintillation properties of an element (17 × 12 × 5 mm in size) prepared from a grown trans-stilbene crystal, irradiated by γ radiation and X rays, have also been investigated. It is shown that the specific light yield of the obtained crystal is no less than that of a scintillation detector based on a trans-stilbene crystal (31.5 × 10 mm) grown from melt.

The solubility of tetracene crystals has been investigated experimentally and theoretically within the approximation of regular-solution model. The grown crystals had a shape of thin elongated plates. The largest tetracene crystal (8 mm × 50 μm in size) was grown from a benzene solution by precipitant vapor diffusion into solution. The X-ray diffraction pattern from a developed crystal face is the result of the X-ray beam reflection from the (001) plane of a set of monolayers with a thickness d001 = 1.21 nm. An analysis of the surface morphology of the (001) face of tetracene crystal by atomic force microscopy (AFM) revealed the presence of elementary growth steps, whose height coincides (within the measurement error) with the monolayer thickness d001. The parameters of melting (Tm = 343.0°C, ΔHm = 35.6 kJ/mol) and polymorphic transition (Ttr =310.0°C, ΔHtr = 0.9 kJ/mol) of tetracene were refined using differential scanning calorimetry (DSC). A comparison of the optical absorption and luminescence spectra of solutions of a pure tetracene sample and a processed (previously molten in a hermetic crucible in an inert atmosphere) sample in toluene confirms degradation of the material subjected to overheating above the melting temperature.

Purpose: The terahertz (THz) medical imaging is a promising noninvasive technique for monitoring the skin's conditions, early detection of the human skin cancer, and recovery from burns and wounds. It can be applied for visualization of healing process directly through clinical dressings and restorative ointments, minimizing the frequency of dressing changes. The THz imaging technique is cost effective, as compared to the magnetic resonance method. Our aim was to develop an approach capable of providing better image resolution than the commercially available THz imaging cameras. Approach: The terahertz-to-infrared (THz-to-IR) converters can visualize the human skin cancer by converting the latter's specific contrast patterns recognizable in THz radiation range into IR patterns, detectable by a standard IR imaging camera. At the core of suggested THz-to-IR converters are flat matrices transparent both in the THz range to be visualized and in the operating range of the IR camera; these matrices contain embedded metal nanoparticles, which, when irradiated with THz rays, convert the energy of THz photons into heat and become nanosources of IR radiation detectable by an IR camera. Results: The ways of creating the simplest converter, as well as a more complex converter with wider capabilities, are considered. The first converter is a gelatin matrix with gold 8.5 nm diameter nanoparticles, the second is a polystyrene matrix with 2 nm diameter nanoparticles from copper-nickel MONEL (c) alloy 404. Conclusions: An approach with a THz-to-IR converter equipped with an IR camera is promising in that it could provide a better image of oncological pathology than the commercially available THz imaging cameras do.