Crystal Molecules Research Articles

Time-Resolved and Temperature-Dependent Fractional Amplitude Contributions to the Broadband Emission of CdSe Quantum Dots

The broadband spontaneous emission of excitons in CdSe quantum dots (QDs) is of great interest for the spectral imaging of living organisms or specific substances in the visible spectral region as well as in the biological optical window near the infrared spectral region. Semiconductor QDs that are near the bulk Bohr radius exhibit wide spectral tunability and high color purity due to quantum confinement of excitons within the dot boundary. However, with reducing dot size, the role of the surface-trapped state increases. The temperature-dependent photoluminescence (PL) confirms this with a ~3:1 emission intensity decrease from the surface-trapped state compared to the band edge. Large crystal irregularity, dangling ions, and foreign molecules can introduce new electronic transitions from surface-trapped states that provide broad spontaneous emission in the spectral region from visible to near IR in addition to the band edge emission. The time-resolved PL analyzed the fractional contributions of band edge, surface-trapped states, and possible intermediate trapped states to the broad spectral emission in order to characterize the CdSe QDs.

Sublimation Enthalpies of Substituted Pyridine N-Oxides.

The enthalpies of sublimation of five substituted pyridine N-oxides were determined by the Knudsen effusion method with mass spectrometric control of the vapor composition within the framework of the second law of thermodynamics. The sublimation enthalpy of mono-substituted compounds 4-X-PyO depends on the nature of the substituent X and increases in the order CH3→NO2→OCH3. A difference is noted in the nature of dissociative ionization of disubstituted derivatives 2-CH3-4-NO2PyO and 3-CH3-4-NO2PyO. The relationship between the packing of molecules in crystals and the ΔH°subl values is considered.

Comparison of Spatial Structures and Packaging of Phosphorybosil Pyrophosphate Synthetase 2 from Thermus thermophilus HB27 in Rhombohedral and Tetragonal Crystals

We report the spatial structure of phosphoribosyl pyrophosphate synthetase 2 from the thermophilic bacterium Thermus thermophilus HB27 (TthPRPPS2) obtained at a 1.85 Å resolution using a diffraction set collected from rhombohedral crystals (space group R32-h), grown with lithium sulfate as a precipitant. This crystal structure was compared with the structure of TthPRPPS2, previously obtained at a 2.2 Å resolution using diffraction sets from the tetragonal crystals (space group P41212), grown with ammonium sulfate as a precipitant. The comparison of these structures allows the study of the differences between protein molecules in both crystalline structures, as well as the packaging of enzyme molecules in crystals of both spatial groups. Our results may contribute to the research of the structural basis of catalytic activity and substrate specificity of this enzyme.

The impact of the molecular structure on aggregation and solid state luminescence of 2,3-diarylfumaronitriles

This work focuses on the substituent effect in 2,3-diarylfumaronitriles on the optical properties and intermolecular interactions in the solid state. 2,3-Diarylfumaronitriles show various luminescence behaviour in solution and in the solid state. Aggregation patterns of 2,3-diarylfumaronitriles govern their luminescent properties in the solid state. The weak intermolecular interactions NC···NC, C–H···Cl, and C–H···NC were detected in the X-ray structures of 2,3-diarylfumaronitriles and studied by DFT calculations at the M06–2X/6–311++G(d,p) level of theory and topological analysis of the electron density distribution within the framework of QTAIM method. The estimated strength of these non-covalent bonds is 0.8–1.3 kcal/mol. The orientation of molecules in crystals depends on the substituents in 2,3-diarylfumaronitriles. Distinct molecular orientation and packing arrangements in crystalline 2,3-diarylfumaronitriles ensured perturbed electronic communication amongst the nearest and non-nearest molecules through an interplay of excimer and dipole couplings. As a result, the intermolecular interactions govern the solid state luminescence of molecules.

Disorder and dynamics of free and caged molecules in crystals

Disorder and dynamics of free and caged molecules in crystals

Vertical Orientation of Liquid Crystal on Polystyrene Substituted with n-alkylbenzoate-p-oxymethyl Pendant Group as a Liquid Crystal Precursor.

We synthesized a series of polystyrene derivatives modified with precursors of liquid crystal (LC) molecules via polymer modification reactions. Thereafter, the orientation of the LC molecules on the polymer films, which possess part of the corresponding LC molecular structure, was investigated systematically. The precursors and the corresponding derivatives used in this study include ethyl-p-hydroxybenzoate (homopolymer P2BO and copolymer P2BO#, where # indicates the molar fraction of ethylbenzoate-p-oxymethyl in the side chain (# = 20, 40, 60, and 80)), n-butyl-p-hydroxybenzoate (P4BO), n-hexyl-p-hydroxybenzoate (P6BO), and n-octyl-p-hydroxybenzoate (P8BO). A stable and uniform vertical orientation of LC molecules was observed in LC cells fabricated with P2BO#, with 40 mol% or more ethylbenzoate-p-oxymethyl side groups. In addition, the LC molecules were oriented vertically in LC cells fabricated with homopolymers of P2BO, P4BO, P6BO, and P8BO. The water contact angle on the polymer films can be associated with the vertical orientation of the LC molecules in the LC cells fabricated with the polymer films. For example, vertical LC orientation was observed when the water contact angle of the polymer films was greater than ~86°. Good orientation stability was observed at 150 °C and with 20 J/cm2 of UV irradiation for LC cells fabricated with the P2BO film.

Crystal structure and optical property of a Cadmium(II) complex based on triphenylamine derivative—Theoretical and experimental investigation

A triphenylamine derivative (E)-N,N-diphenyl-4-(2-(pyridin-2-yl)vinyl)benzenamine (L) was synthesized, and the corresponding cadmium complex CdI2L2 crystal was obtained and solved by single crystal X-ray diffraction analysis. The experimental resutls of one photon absorption (OPA) and one photon excited fluorescence (OPEF) indicate that coordination of CdI2 only has slight effect on the spectrum peak position relative to the free ligand. Besides the Stokes shift, the full width half maximum of OPEF and the variation of the “peak span between solvents” from OPA to OPEF can also indicate the electron transition direction of the excitation process. The laser experiments show that both the ligand and complex have considerable two photon excited fluorescence (TPEF) emission. The experimental Stokes shift is correlated with the computational solvent polarity rMPI, and the results illustrate that the curve of “experimental Stokes shift vs. solvent rMPI” is exactly the Boltzmann S-curve. The computational results also indicate that the static interaction between the CdI2L2 molecules in crystal has strong effect on OPA properties. Considering the weak coordination bond strength of the complex CdI2L2, the S1→S0′ fluorescence emission may occur on both ligands, although the S0→S1′ excitation only occurs on the right ligand.

Structural characterization of hydrogen bonding for antipyrine derivatives: Single-crystal X-ray diffraction and theoretical studies

Objectives. The paper is devoted to the crystal structure characterization of 5-methyl-2-phenyl4H-pyrazol-3-one (compound I) and 2-(4-chlorophenyl)-5-methyl-4H-pyrazol-3-one (compound II).Methods. Single-crystal X-ray diffraction studies and theoretical calculations: Density functional theory and quantum theory of atoms in molecules.Results. In the solid state, the crystal structure of compound I is characterized by the alternation of OH and NH tautomers connected via O–H---O and N–H---N hydrogen bonds. For compound II, the existence of chains built from the NH monomers via hydrogen bonding can be explained by the peculiarities of cooperative effects. In the framework of quantum theory of atoms in molecules, the following topological characteristics are calculated for all dimers: electron density, Laplacian of electron density, density of kinetic, potential, and total energy in the critical point of the intermolecular hydrogen bond. It is concluded that the hydrogen bond in dimers 1–4, 7 (compound I), and 8–11 (compound II) can be assigned to the intermediate (between covalent and dispersion types) interaction owing to hydrogen bond formation with the participation of electronegative oxygen- (and/or nitrogen-) atoms, whereas H-bond in dimers 5 and 6 (compound I) can be attributed to the dispersion one (no hydrogen bond formation or weak H-bond formation), and it represents the weak interaction, being in agreement with length for intermolecular hydrogen bond in dimers. The electron density and total energy density values demonstrate that the strongest intermolecular H-bonds take place in dimers 1 (OH---O), 4 (OH---O), 7 (OH---N), 8 (OH---O), 9 (NH---N), and 11 (OH---N). The results obtained for compounds I and II are compared with data for antipyrine (1,2-dihydro-1,5-dimethyl-2-phenyl-3H-pyrazol-3-one; compound III)Conclusions. An important role of intermolecular hydrogen bonding in the crystal packing, molecule association and self-organization via dimer- or more extended species formation has been demonstrated.

Vertical Orientation of Liquid Crystal on Comb-Like 4-(trans-4-alkylcyclohexyl)phenoxymethyl-substituted Polystyrene Containing Liquid Crystal Precursor.

We synthesized a series of polystyrene derivatives modified with precursors of liquid crystal (LC) molecules, including 4-(trans-4-ethylcyclohexyl)phenol (homopolymer PECH and copolymer PECH#; # = 5, 10, 15, 20, 40, 60, and 80, where # indicates the molar fraction of 4-(trans-4-ethylcyclohexyl)phenoxymethyl in the side chain), 4-(trans-4-propylcyclohexyl)phenol (PPCH), 4-(trans-4-butylcyclohexyl)phenol (PBCH), and 4-(trans-4-amylcyclohexyl)phenol (PAmCH) via polymer modification reactions in order to investigate the orientation of LC molecules on polymer films exhibiting part of the LC molecular structure. A stable and uniform vertical orientation of LC molecules was observed in LC cells fabricated with PECH#, having 15 mol% or more of 4-(trans-4-ethylcyclohexyl)phenoxymethyl side groups. In addition, the vertical orientation of LC molecules was observed in LC cells fabricated with homopolymers of PECH, PPCH, PBCH, and PAmCH. The water contact angle on the polymer films could be associated with the vertical orientation of the LC molecules in the LC cells fabricated with polymer films. For example, a vertical LC orientation was observed when the water contact angle of the polymer films was higher than ~81°. Good orientation stability was observed at 200 °C and 15 mW/cm2 of UV irradiation for LC cells fabricated with PECH films.

Synthesis and crystal structures of 7,8-bromo (dibromo)-3-tert-butylpyrazolo[5,1-c][1,2,4]triazines.

Single crystal structures in a series of 7-bromo-, 8-bromo-, and 7,8-dibromo-3-tert-butylpyrazolo[5,1-c][1,2,4]triazin-4(1H)-ones have been investigated by X-ray diffraction. Novel 7-bromo- and 7,8-dibromo-3-tert-butylpyrazolo[5,1-c][1,2,4]triazines were synthesized by reduction of triazine carbonyl with dehydrative aromatization in acidic media, and their XRD structural features were compared with that of the 4-oxo analogs. The lengths and bond angles and the packing of molecules in crystals have been considered. Non-valence interactions for some of the studied compounds were observed. Correlations between the presence of bromine atoms at different positions and structural features are determined.Graphical abstract Supplementary InformationThe online version contains supplementary material available at 10.1007/s11224-021-01768-0.

Ball-milling synthesis technique for Cu(II)-Schiff base complexes with variable anions; characterization, potentiometric study and in-vitro assay confirmed by in-silico method

The condensation reaction of 3-oxo-N-(pyridine-2-yl)butanamide and 4-chlorobenzo hydrazide yields a new Schiff base ligand which was characterized to be a mixture of tautomer forms. Two new Cu(II) complexes were prepared from chloride or acetate salt and then characterized to recognize the effect of conjugated anion nature on the chemical formulae of complexes. IR, UV–Vis, ESR, EDX, SEM, TEM and XRD were used to analyze the two complexes. Two discriminating modes were appeared, mono-basic bidentate within square-planer geometry and di-basic tridentate within octahedral geometry. Hamiltonian factors and field vector obtained from ESR spectra, assert on octahedral and square-planer geometries. The two complexes appeared nano-crystalline with different morphology and their particle-sizes were in nanometer range. In order to determine the ionization constants for the ligand and stability constants of the complex in solution, potentiometric studies were performed. Molecular modeling was executed by advanced programs to confirm some aspects. Important parameters and maps were obtained and promising biological efficiency of the ligand, is strongly expected. Properties of molecular surface contact inside crystal packing, were evaluated by Crystal Explorer program. Oxygen and hydrogen atoms play a good role in contact efficiency between crystal molecules. Antimicrobial, antioxidant and antitumor efficiency of all compounds were examined and the ligand achieved excellent superiority. In-silico assay was carried out by MOE-docking approach for confirmation and comparison with in-vitro results. Two tautomer forms of Schiff base ligand exhibited excellent inhibition towards 1cca and 2h80 co-crystal proteins. The high conformity and credibility of in-silico and in-vitro results may be concluded.

Vertical Orientation of Liquid Crystal on 4-n-Alkyloxyphenoxymethyl-Substituted Polystyrene Containing Liquid Crystal Precursor

We synthesized a series of polystyrene derivatives that were modified with precursors of liquid crystal (LC) molecules, such as 4-ethyloxyphenol (homopolymer PEOP and copolymer PEOP#; # = 20, 40, 60, and 80, where # indicates the molar fraction of 4-ethyloxyphenoxymethyl in the side chain), 4-n-butyloxyphenol (PBOP), 4-n-hexyloxyphenol (PHOP), and 4-n-octyloxyphenol (POOP), via polymer modification reaction to investigate the orientation of LC molecules on polymer films, exhibiting part of the LC molecular structure. LC molecules showed a stable and uniform vertical orientation in LC cells fabricated with polymers that have 4-ethyloxyphenoxymethyl in the range of 40–100 mol%. In addition, similar results were obtained in LC cells fabricated with homopolymers of PEOP, PBOP, PHOP, and POOP. The vertical orientation of LC molecules in LC cells fabricated with polymer films correlated to the surface energy of polymer films. For example, vertical LC orientation was observed when the total surface energies of the polymer films were lower than approximately 43.2 mJ/m2. Good alignment stabilities were observed at 150 °C and 20 J/cm2 of ultraviolet irradiation for LC cells fabricated with PEOP film.

Atomically Precise Insights into Metal–Metal Bonds Using Comparable Endo-Units of Sc 2 and Sc 2 C 2

The precise identification of metal–metal bonds is critical to fully understanding the nature of metal–metal bonding but remains a fundamental challenge. Herein, we show the essence of Sc–Sc bonds ...

Bioapplications Manipulated by AIEgens with Nonlinear Optical Effect

The modern medicine requires precise diagnostic techniques while the fluorescent imaging shows great potential in such applications due to its excellent sensitivity and high resolution. However, conducting fluorescent imaging in deep-tissue is not so easy because most luminogens show short-wavelength excitation, which may undergo severe light scattering by the bio-tissue. The marriage of fluorescent imaging with nonlinear optical(NLO) effect can alleviate such adverse effects by utilizing NIR laser to reduce light scattering. On the other hand, scientists are enthusiastic in pursuing luminescent materials, which can match well with NLO application. Aggregation-induced emission(AIE) materials exhibit huge advantages in such aspect not only because of its high luminescent efficiency in aggregate state but also due to its excellent photo-stability (a key factor to meet laser application because of its ultrahigh energy density). Inspired by this, many interesting and meaningful works have sprung up based on AIE luminogens with NLO effect in recent years, and for such reason, it motivates us to summarize them to give a systematic presentation. Here, we first give a brief introduction of the principle of NLO effect. Secondly, the strategies for improving the NLO effect of AIE materials, such as increasing molecular conjugation, introduction of donor-acceptor effect, induction of centrally asymmetric array of AIE molecules in crystals and introduction of intermolecular interactions are clarified. In the final part, we also present the multiple applications of AIEgens with NLO effect in cell imaging, deep-tissue tumor and brain blood vessel imaging and photodynamic therapy. We believe, with this review, the topic will attract more attention from the scientists in multi-science field to accelerate the development of AIE materials in biomedical applications.

Quantum Rotation and Orientational Ordering of Molecules in Crystals

Quantum Rotation and Orientational Ordering of Molecules in Crystals

Electrical conductivity of composites based on 6CB liquid crystal and (Cu6PS5I)0.5(Cu7PS6)0.5 superionic nanoparticles

In the frequency range of 6–106 Hz at a temperature of 293 K, the influence of (Cu6PS5I)0.5(Cu7PS6)0.5 superionic nanoparticles on electrical conductivity and dielectric properties of 6CB liquid crystal are investigated. Parameters of near-electrode and bulk processes are evaluated as well as their changes at introducing nanoparticles into the LC are investigated. It is shown that the effect of nanoparticles of solid solution (Cu6PS5I)0.5(Cu7PS6)0.5 is smaller than the effect of Cu6PS5I nanoparticles. It is suggested that the surface properties of solid solution nanoparticles are mainly determined by Cu7PS6 component of a solid solution. Significantly less interaction of nanoparticles of solid solution (Cu6PS5I)0.5(Cu7PS6)0.5 with molecules of 6CB LC than the interaction of Cu7PS6 nanoparticles with molecules of liquid crystal is established.

Electric field effect on 31P NMR magnetic shielding.

Magnetic shielding depends on molecular structure and noncovalent interactions. This study shows that it is also measurably dependent on the electric field generated by surrounding molecules. This effect has been observed explicitly for 31P nucleus using the adduct under field approach. The results obtained indicate that the field strength experienced by molecules in crystals consisting of molecules with large dipole moments is similar to that in polar solvents. Therefore, magnetic shielding should explicitly depend on solvent polarity. It is important to note that this effect cannot be reproduced correctly within the polarizable continuum model approach.

(8-Hy-droxy-6-meth-oxy-1-oxo-1H-isochromen-3-yl)methyl formate: a supra-molecular framework.

In the title compound, C12H10O6, an intra-molecular O-H⋯O hydrogen bond forms an S(6) ring motif. The mol-ecule is essentially planar with an r.m.s. deviation of 0.051 Å for all non-H atoms. In the crystal mol-ecules are linked by C-H⋯O hydrogen bonds and a C-H⋯π inter-action, forming a supra-molecular framework.

Structure and Conformational Analysis of 5-Methyl-2,2-diphenyl-1,3-dioxane

The structure of 5-methyl-2,2-diphenyl-1,3-dioxane has been studied by1H and 13C NMR spectroscopy and X-ray analysis. Its molecules in crystal, as well as in CDCl3 and C6D6 solutions, have achair conformation with equatorial methyl group. The conformational transformation pathways, ΔG0298 value for the 5-methyl group in CDCl3 and C6D6, and the optimal number of solvent molecules in the nearest solvation shell of 5-methyl-2,2-diphenyl-1,3-dioxane have been determined by quantum chemical calculations at the PBE/3ξ and RI-MP2/λ2 levels of theory and by comparing the theoretical and experimental vicinal spin–spin coupling constants.

Synthesis, X-ray structures and magnetic properties of Ni(II) complexes of heteroaromatic hydrazone

Two binuclear double end-on azido bridged Ni(II) complexes, [Ni2L2(μ-1,1-N3)2(N3)2]⋅2H2O (1a), and [Ni2L2(μ-1,1-N3)2(N3)2]⋅4H2O (1b) having the same inner sphere, where L=((E)-N,N,N-trimethyl-2-oxo-2-(2-(1-(thiazol-2-yl)ethylidene)hydrazinyl)ethan-1-aminium, were synthesized from the same solution and characterized by single-crystal X-ray diffraction methods. Variable‐temperature magnetic susceptibility measurements showed intra-dimer ferromagnetic coupling between Ni(II) ions. The ferromagnetic coupling is supported by the broken-symmetry DFT calculations, with the level of theory chosen based on a benchmark study on 19 additional structurally related binuclear Ni(II) complexes. The role of water molecules in crystals of 1a and 1b is explained by DFT based energy decomposition analysis.