Synthesis of size-tunable zinc blende ZnS nanocrystals

Quasi-polyhedral ZnS nanocrystals with monodisperse tunable sizes of 40, 52, 62, 73, 82, 94, 103, and 110 nm have been synthesized in aqueous solution by regulating the amounts of thioacetamide, zinc acetate, and acetic acid added. The mixture was heated to 120°C in an oven for 10–20 min to produce the nanocrystals. Structural characterization reveals the formation of cubic zinc blende ZnS with some polycrystallinity, which possibly influences their optical properties, that is, the measured band gaps do not give a continuous narrowing trend with increasing particle size. However, when particle sizes are expressed in terms of volumes, the absorption band positions show steady red shifts with increasing crystal dimensions and very small wavelength changes for nanocrystals beyond 90 nm. Thus, these ZnS nanocrystals still possess some size-dependent optical properties despite their polycrystalline nature.     

Synthesis of high quality zinc blende CdSe nanocrystals

Highly homogeneous and luminescent CdSe colloidal nanocrystals in the less common zinc blende crystal structure have been obtained at high temperature in a noncoordinating organic solvent. The key parameter appears to be the addition of a phosphonic acid to the trioctylphosphine-selenium complex before its injection into the hot cadmium mixture, while the role of temperature is less relevant. Compared to standard (wurtzite) colloidal CdSe preparations, we find that the growth rate is considerably reduced, and the energy gap between the first two absorption bands becomes larger.     

[2]Benzothiophene bent-shaped liquid crystals

New liquid crystalline (LC) compounds containing the [2 Weissflog, W., Nádasi, H., Dunemann, U., Pelzl, G., Diele, S., Eremin, A. and Kresse, H. 2001. J. Mater. Chem., 11: 2748–2758. [Crossref], [Web of Science ®] , [Google Scholar]]benzothiophene chromophore unit have been synthesised and their mesomorphic properties studied. Mesomorphic and fluorescent properties have been modified by various chemical moieties. Among others, terminal fluoroalkyl and/or chiral chains were introduced to stabilise mesophases and support the formation of polar phases. In spite of the bent shape due to the central 1,3-diphenylbenzo[c]thiophene unit, all compounds exhibit phases typical for the rod-like LC: nematic, smectic A and smectic C or their chiral analogues using the chiral (S)-C₂H₅CH(CH₃)(CH₂)₆CO or (S)-C₁₀H₂₁OCH(CH₃)CO chain. The orientational order in the nematic phase was studied by polarised infrared measurements. The fluorescent properties of the studied compounds have been measured and their parameters established.     

Stereoselective transformation of indole diazabicyclo[3.2.2]nonedione to azepinoindole

[reaction: see text] The synthesis of an indole diazabicyclo[3.2.2]nonedione derivative was achieved in a few steps starting from L-tryptophan. Reduction with borane-THF complex leads to fragmentation of the bicycle and the stereoselective formation of an azepinoindole derivative was observed.     

Porous molecular crystals of calix[4]arenes

X-ray diffraction, thermogravimetric, and adsorption measurements were applied to study the thermal decomposition of the complexes of 25,26,27,28-tetrahydroxycalix[4]arene and 4-tert-butylcalix[4]arene with the solvents resulting in the formation of porous phases. Diffusion of the "guest" (solvent, gas) through the molecular crystal of calixarene-host proceeds via the consecutive formation of a series of thermodynamically unstable porous phases of the "host." Owing to the structural reorganization of calixarene, the transport of the "guest" occurs through the "host" matrix followed by complexation and formation of the thermodynamically stable structure.     

The transformation of saccharin into derivatives of lmidazo[1,2-b] [1,2]-benzisothiazole and benzo[g] [1,2,5]thiadiazocine

Reaction of 3-(2-hydroxyethylamino) benzo[d]isothiazole 1,1-dioxide ( 5a ) with thionyl chloride gives a mixture of the expected chloroethyl derivative ( 5h ) and the rearranged saccharin 2-(2-aminoethyl)-3-oxo-2,3-dihydrobenzo[d]isothiazole 1,1-dioxide hydrochloride ( 6a ). Separate treatment of the chloroethyl compound ( 5h ) with dilute alkali gives the expected cyclization product 2,3-dihydroimidazo[1,2-b] [1,2] benzisothiazole 5, 5-dioxide ( 7a ). Acidification of the liquors of the above reaction yields the ring expanded derivative 6-oxo-3,4,5,6-tetrahydro-[2H]benzo[g][1,2,5]thiadiazocine 1,1-dioxide ( 12f ), a representative of a new ring-system. Treatment of the imidazo derivative ( 7a ) with concentrated hydrochloric acid again yields the N-substituted saccharin ( 6a ) which upon treatment with alkali also produces the thiadiazocine ( 12f ). In contrast, treatment of the imidazo compound ( 7a ) with alkali leads to attack on the sulphonamide function to give 2-(2-imidazolin-2-yl)benzenesulphonic acid ( 8 ). It is suggested that the multitude of chemical interconversions which can be induced within this series of compounds (Scheme II) can only be accounted for if two separate cyclol intermediates are invoked. Related reactions observed with variously substituted derivatives of the starting saccharin derivative ( 5a ) are discussed as are the spectral properties and chemical reactivity of the new compounds prepared.     

Synthesis of Mn-doped zinc blende CdSe nanocrystals for quantum dot-sensitized solar cells

Mn-doped CdSe quantum dots (QDs) with a zinc blende structure were synthesized via a phosphine-free method in octadecene (ODE) and oleic acid. The structure, size, morphology, and optical property of the QDs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–visible absorption spectra (UV–Vis), respectively. The QDs were assembled onto a microporous TiO₂ photoanode by an ex situ ligand exchange route. Quantum dot-sensitized solar cells (QDSCs) based on the above-synthesized QDs and polysulfide electrolytes were fabricated. The photovoltaic performance and impedance of the CdSe and Mn-doped CdSe QDSCs were further investigated. An improvement in efficiency to 1.84 % was achieved as compared with 0.94 % for the QDSCs based on the pure CdSe QDs. The improvement was ascribed to the existence of long-lived high-energy doping levels on the large-sized Mn-doped CdSe QDs, which provides a significant driving force for faster charge separation and electron transfer.     

Applying click chemistry to synthesis of chiral [1,2,3]-triazole liquid crystals

1,3-Dipolar cycloaddition of organic azides to triple bonds, or 'click chemistry' has been used in order to obtain chiral 1,4-disubstituted [1,2,3]-triazoles. Liquid crystalline compounds bearing such heterocycles were prepared and SmA and N* (cholesteric) phases identified. Contact experiments indicated a right-handed helix (RH-helix) for the cholesteric phase, and attempts to corroborate experimental and theoretical results are presented.     

Spiro[4-azafluorenepyrazolenines] and their thermal rearrangement to pyrazoloazaphenanthrenes

Reaction of 9-diazo-4-azafluorene with phenylacetylene gives spiro[4-azafluorene-9,3-pyrazolenines], isomeric according to the position of the substituent in the pyrazolenine ring. Their thermal rearrangement to pyrazolo-4-azaphenanthrenes that are isomeric according to ring linkage and position of the substituent in the pyrazole ring has been studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1522–1525. November, 1988.     

A novel acid-catalyzed transformation of octadienynedial derivatives to cyclopenta[b]-thiapyrans and cyclopenta[b]pyran.

Substituted 2,6-octadien-4-ynedial derivatives were synthesized, which give cyclopenta[b]thiapyran or cyclopenta[b]pyran derivatives by intramolecular cyclization.     

Self-organization of phthalocyanine--[60]fullerene dyads in liquid crystals

The use of blends in which a mesogen induces mesomorphism into a non-mesogenic compound has made possible the self-organization of phthalocyanine--[60]fullerene (Pc-C60) dyads into liquid crystals. Pc-C60 dyads 1, 2, or 3, in which two photoactive units are brought together by a phenylenevinylene spacer, have been synthesized through a Heck reaction that links 4-vinylbenzaldehyde to a monoiodophthalocyanine precursor, followed by standard cycloaddition of azomethine ylides--generated from the formylPc derivative and N-methylglycine--to one of the double bonds of C60. The mesomorphic and thermal properties of different mixtures formed by the liquid-crystalline phthalocyanine 4 and dyads 1, 2, or 3 were examined using polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). DSC diagrams of the blends show clear transitions from the crystalline state to a mesophase, and the measured structural parameters obtained from the powder diffraction experiments are consistent with a discotic hexagonal columnar (Col h) structure. Considering that segregation in domains of separated molecules of Pc-C60 dyad and phthalocyanine 4 would preclude mesomorphism due to the mismatch in the column diameter and to the lack of mesogenic character of the pure dyads, a predominance of alternating stacking is proposed. Additionally, the observed decrease in the calculated density of the blend mesophases relative to the mesophase of pure compound 4 is important evidence in this direction.     

Pyrazolo[1, 2-a]pyrazoliumolates as novel structure elements in liquid crystals [1]

A series of pyrazolo[1, 2-a]pyrazoliumolates of type 3, 4, and 5 was prepared. Compound 4(R³ = CH₃) shows liquid crystalline properties (C 158.5 N 162 I).     

Deuterium NMR studies of inositol liquid crystals [1]

Deuterium NMR investigations are presented on members of two new mesogenic series derived from the naturally occurring stereoisomers myo- and scW/o-inositol. Tetraethers of these two series exhibit thermotropic columnar phases in which the columns are apparently formed by stacked hydrogen bonded dimers of these molecules which chemically are vicinal diols. Deuterium NMR measurements were performed on the tetraoctyl homologues 2e (a cis diol) and 3e (a trans diol) of these series. We have investigated mixtures of these diols with small amounts of benzene-d₆ as probe molecules as well as samples of the neat diol compounds deuteriated at their hydroxyl groups. The results obtained show that the mesophases of both compounds are uniaxial and align partially in a magnetic field upon slow cooling from their isotropic liquids. The alignment is with the director parallel to the field direction indicating that the anisotropic magnetic susceptibility of this mesophase is positive. The deuterium quadrupole splitting of the benzene-d₆ probe in both systems is temperature dependent and in the trans diol 3e it even changes sign. This is interpreted in terms of a model in which the benzene-d₆ probe equilibrates rapidly between two (or more) solvation sites with quadrupole splittings of opposite signs The deuterium spectra of the neat deuterium labelled cis diol 2e exhibit two different signals due to the two deuterons which are located at the axial and equatorial hydroxyl groups. This indicates that there is no fast intra- or intermolecular exchange of the hydroxyl hydrogens. The overall quadrupole splittings of the hydroxyl deuterons in this compound are highly reduced compared to their static values and this is interpreted in terms of motional modes involving both reorientation of the hydroxyl deuterons about their C-O axis and overall reorientation of the molecules (or pairs of molecules) around the columnar axes. The corresponding spectra of the neat deuteriated trans diol 3e exhibit a single spectrum indicating that both hydroxyl deuterons in this compound are equivalent, or very nearly so. Within the mesophase region the spectrum undergoes gradual changes due to the increase in the molecular mobility, but the overall motional narrowing is less than in the cis isomer 2e. Apparently due to stronger hydrogen bonding in the trans isomer 3e the precession of the hydroxyl groups is hindered and a fast molecular reorientation is only possible at high temperatures.     

Organic phase conversion of bulk (wurtzite) ZnO to nanophase (wurtzite and zinc blende) ZnO

We describe the all-organic phase conversion of bulk commercial ZnO in the wurtzite modification to sub-30 nm ZnO that we find to be partially in the zinc blende [, a=4.568(3) Å] modification. The conversion involves refluxing ZnO in 2,4-pentanedione (acetylacetone) at 413 K to form the zinc 2,4-pentanedionate, which is decomposed by heating at 573 K in an appropriate high-temperature solvent such as dibenzylether to form nanophase ZnO. This nanophase, partially zinc blende ZnO can also be obtained in a single step by heating commercial zinc 2,4-pentanedionate in refluxing dibenzylether. Thermodiffractometry suggests that the conversion of zinc blende ZnO to wurtzite ZnO commences near 650 K.     

Laser Raman study of the low-temperature phase transformation in [N(CH3)4]2CuCl4 single crystals

The results of a detailed temperature-dependent Raman study of single crystals of [N(CH₃)₄]₂CuCl₄ are reported in different spectral regions. The observed splittings of the symmetric stretching modes of the N(CH₃)⁺₄ ion below 250 K and the CuCl²⁻₄ ion below 50 K into doublets have been explained as being due to the presence of ions on two energetically inequivalent positions within the lattice. From a temperature dependence of the half-widths, frequency separation, relative intensities of the two components of the CN stretch and other thermosensitive spectral changes, we have discovered a new first order type phase transition in this system at ∼50 K due to ordering of ions from one configuration to another. The reordering in phase IV up to 50 K takes place via continuous movement of cations from the disordered to ordered configuration, but below 50 K the ions freeze in the two inequivalent configurations. The dynamics of ordering of the ions at different temperatures is discussed in this communication.     

Anion-dependent binding of zinc calix[4]pyrrole-bisporphyrinate triethylenediamine

The complexation properties of zinc 10,20-bis[5-(2,3,7,8,12,13,17,18-octaethylporphyrinate)ethynylphenyl]-5,5′,10′,15,15′,20′-hexamethylcalix[4]pyrrole toward halide ions, triethylenediamine, and 4,4′-bipyridyl were studied by spectrophotometric titration and ¹H NMR spectroscopy. The influence of binding of anions (F⁻ and Cl⁻) by the calix[4]pyrrole fragment of zinc calixpyrrole-bisporphyrinate on the complexation properties of its interporphyrin cavity toward the bidentate organic ligand triethylenediamine.     

Novel liquid crystals based on [1]benzothieno[3,2- b][1]benzothiophene

Four series of new [1]benzothieno[3,2- b][1]benzothiophene derivatives have been synthesized. In the non-chiral series a SmA phase occurs, while the chiral series exhibits a rather wide antiferroelectric SmC^A* phase just below the SmA phase. The SmA-SmC^A* phase transition has been studied using DSC and dielectric spectroscopy. In the SmC^A* phase the spontaneous quantities have been measured. The tilt angle shows a typical temperature dependence and the values of spontaneous polarization are rather moderate. The length of the helical pitch increases on increasing the length of the non-chiral alkyl chain.     

Novel liquid crystals based on [1]benzothieno[3,2- b ][1]benzothiophene

Four series of new [1]benzothieno[3,2- b ][1]benzothiophene derivatives have been synthesized. In the non-chiral series a SmA phase occurs, while the chiral series exhibits a rather wide antiferroelectric SmC * A phase just below the SmA phase. The SmA-SmC * A phase transition has been studied using DSC and dielectric spectroscopy. In the SmC * A phase the spontaneous quantities have been measured. The tilt angle shows a typical temperature dependence and the values of spontaneous polarization are rather moderate. The length of the helical pitch increases on increasing the length of the non-chiral alkyl chain.     

Thermal conductivity of wurtzite and zinc blende cubic phases of BeO from ab initio calculations

The structural, mechanical, thermal and thermodynamic properties of Beryllium oxide (BeO) in the zinc blende (ZB) and wurtzite (WZ) form have been calculated using the density functional theory (DFT) in the general gradient approximation (GGA). The ground state structural and elastic properties of wurtzite BeO (w-BeO) is calculated using the new GGA ultrasoft pseudopotentials for solids (pbesol); the simulated results have shown excellent agreement with the experiments. The thermodynamic properties are studied using quasi-harmonic approximation (QHA), and the predicted properties agree well for the WZ phase for which the experimental data are available, while for ZB phase it remains to be validated with future experiments. Both Boltzmann transport equation (BTE) and Slack model were used to calculate the lattice thermal conductivity of wurtzite BeO (w-BeO). Furthermore, the thermal conductivity along the crystallographic ‘a’ and ‘c’ axis of wurtzite BeO is investigated using BTE. Our calculation of w-BeO agrees well with the available experimental measurements. Apart from these studies on w-BeO, we have also compared the mechanical, structural and phonon dispersions of z-BeO with previously reported theoretical studies. Additionally we report the volume thermal expansion and the heat capacity at constant pressure of z-BeO for the first time and the bulk thermal conductivity of zinc blende BeO (z-BeO) using BTE.