The influence of solvent and ligands on characters of ZnS clusters

According to zinc blende and wurtzite structures of ZnS nanocrystals, four clusters (Zn₃S₃, Zn₄S₄, (Zn₃S₃)₂, and (Zn₃S₃)₃), were investigated at B3LYP/Lanl2dz theoretical level. In simultaneous consideration of the influence of solvent and ligands, we calculated their Raman and absorption peaks, which are agreement with experimentally reported results. The calculated Raman spectra of Zn₃S₃, Zn₄S₄, (Zn₃S₃)₂, and (Zn₃S₃)₃ are in the range of 260–310 cm⁻¹. During the calculation of absorption spectra, time-dependent density-functional theory (TDDFT) is employed. We have found an obvious blue-shift in the calculated wavelengths of the absorption peaks after consideration of the solvent. In solvent environment, the wavelength of absorption peak shifts to red with the increase of the atomic numbers from Zn₃S₃, to (Zn₃S₃)₂ and (Zn₃S₃)₃ clusters, which is induced by the quantum size effect. Since the sizes of the current calculated clusters are much smaller than the experimentally reported nano-sized ZnS nanocrystals, the calculated wavelengths of absorption peak of the four clusters are shorter than the nano-sized ZnS nanocrystals. Through the analysis of S–Zn–ligand structures, we speculate that the main influence of ligands comes from thiol of ligand because all S–Zn–ligand structures have similar Wiberg Bond Index (WBI) values, absorption spectra, and bond length in theory.     

Theoretical simulation of CdTe nanocrystals in aqueous synthesis

At the B3LYP/LANL2DZ theoretical level, Cd₃Te₃, (Cd₃Te₃)₂, (Cd₃Te₃)₃, Cd₄Te₄, and Te–Cd–ligand clusters were optimized. Firstly, hexagon Cd₃Te₃ and tetrahedron Cd₄Te₄ structures (with T_D symmetry) may be the minimum units of CdTe nanocrystals. They have similar conformations with the experimental wurtzite and zinc blende structures, respectively. Secondly, the frequencies of calculated Raman peaks of four clusters appear in about 140 cm⁻¹, which is close to the experimental data. Following, analysis of Te–Cd–ligand molecules elucidates that all our ligands have similar effect to CdTe structure, because the main influence of ligands comes from thiol, which is also the result of experiment. Finally, considering the influence of solvent and ligand, we believe that our wavelengths of absorption peaks which are calculated using the time-dependent density functional theory are perfectly identical with those of CdTe nanocrystals, according to quantum size effect. Moreover, we have testified that all these absorption peaks are the transition from d to p orbitals.     

Investigation of Zn<Subscript>m</Subscript>Cd<Subscript>n</Subscript>X<Subscript>y</Subscript> (y = m + n; X = Te,Se and S) Clusters with TDDFT Method

Based on zinc blende and wurtzite structures of experimental ZnTe and CdTe nanocrystals, Zn_mCd_nX_y (X = Te, Se and S) clusters were investigated using DFT/B3LYP/LANL2DZ. From analyses of their characters of conformations, HOMO–LUMO gaps, Raman and absorption spectra, Mulliken charges and WBI (Wiberg Bond Index) values, we have discovered that Zn_mCd_nTe_y, Zn_mCd_nSe_y and Zn_mCd_nS_y molecules had similar characters. In this paper, characters of Zn_mCd_nTe_y were investigated in detail. First, we have found that HOMO–LUMO gaps, Raman spectra, absorption spectra, bond lengths and Mulliken charges of doping Zn₂CdTe₃, ZnCd₂Te₃, Zn₃CdTe₄, Zn₂Cd₂Te₄ and ZnCd₃Te₄ structures were in the scope of corresponding naked ZnTe and CdTe clusters. These characters of doping Zn_mCd_nTe_y molecules show that their stabilities are good. Second, comparing with ZnTe structures, the wavelengths of the absorption peaks of doping Zn_mCd_nTe_y clusters shift to red in water environment. Moreover, with increasing of the number of Cd atom, their wavelengths of the absorption peaks gradually shift to red. This conclusion is consistent with the experimental fact. Third, Raman spectra of pure ZnTe clusters have higher frequencies than corresponding naked CdTe structures. As for doping molecules, the frequencies of their Raman spectra gradually shift to low frequencies with increasing of Cd atoms’ number.     

Modeling and Simulation of Bonding and Optical Characters of Ternary Nanocrystals

In this paper, conformations of the ternary structures ZnSe(Te), ZnS(Te), ZnS(Se), CdSe(Te), CdS(Te) and CdS(Se) were optimized, and their orbital, spectra have been investigated at the B3LYP/LANL2DZ level. First, we have found some rules which agreed with experimental results. HOMO–LUMO gaps, WBI values and the wavelengths of the absorption peaks of ternary structures changed gradually with the ratio of Te, Se and S atoms in ternary structures. Second, analysis of Raman spectra revealed that doped structures had the spectra of two relevant binary clusters. Namely, Raman spectra of ternary ZnSe(Te) clusters had the Raman peaks of ZnSe and ZnTe. In this way, with the help of the Raman spectra, the formations of the ternary structures can be determined in experiment. This was important to estimate during synthesis progress. Finally, calculated results have proved that ZnS and CdS structures had the shorter wavelengths of the absorption peaks, the higher excited energies of singlets, and good stability.     

Control of particle size distribution of CdS quantum dots in gel matrix

A novel sol-gel process has been developed to prepare nano-sized CdS quantum dots to improve the nonlinear optical properties. A bifunctional ligand, 3-aminopropyl triethoxysilane H₂N(CH₂)₃Si(OC₂H₅)₃, was used to disperse the Cd²⁺ ions in the gel solution. The CdO and CdS particles were observed by transmission electron microscope (TEM). The size of CdS microcrystallites with concentrations up to 13 wt.% in SiO₂ gel matrix was found to be in the range of 2–4 nm with a very sharp size distribution. A well-defined absorption edge was observed in the absorption spectrum.     

Theoretical studies on a possible synthesis reaction pathway on N8 (CS) clusters

The potential energy surfaces of N₈ clusters were investigated by density functional theory (DFT) and a possible synthesis reaction pathway for N₈ (C_S) was suggested. The species involved were fully optimized up to the B3LYP/6‐311+G* level of theory. Relative energies were further calculated at the QCISD/6‐311+G*//B3LYP/6‐311+G* level. The reaction rate constants of these steps from the 1 (N₅⁺?N₃^?, complex, C_S) to 2 (N₈, C_S), 2 (N₈, C_S) to 3 (N₈, C_S), 3 (N₈, C_S) to 4 (N₈, D_2d), and 4 (N₈, D_2d) to 5 (N₈, C_S) reactions were predicted by the VTST theory. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1334–1339, 2001     

Influence of d-p π-conjugate interaction upon electronic spectra in some cluster compounds

The UV-vis electronic absorption spectra of the clusters Mo₂S₄(dtp)₂ and Mo₃S₄(dtp)₄·Py have been observed, and the electronic excitation energies have been calculated using the INDO/S-CI method. Comparing the calculated values with the observed results, the absorption bands have been assigned. The influence of d-p π-conjugate interaction strength upon the electronic absorption spectrum is discussed in the clusters Mo₂S₄(dtp)₂ (1), Mo₃S₄(dtp)₄·Py (2), Mo₃O₄(H₂O)₉⁴⁺ (3) and Mo₃S₄(H₂O)₉⁴⁺ (4) [dtp = S₂P(OC₂H₅), Py = pyridine]. It has been found that the absorption bands of clusters 2 and 4, with larger d-p π-conjugate interaction over rings, causes a red-shift compared with those of clusters 1 and 3, with a smaller d-p π-conjugate interaction.     

Visible‐Light‐Driven,Tunable, Photoelectrochemical Performance of a Series of Metal‐Chelate,Dye‐Organized,Crystalline, CdS Nanoclusters

CdS nanoclusters of four different sizes were integrated with ruthenium‐complex dyes. The cluster–dye crystalline composites, [Cd₄(SPh)₁₀][Ru(bpy)₃], [Cd₈S(SPh)₁₆][Ru(bpy)₃], [Cd₈S(SPh)₁₃?Cl?(CH₃OCS₂)₂][Ru(phen)₃], [Cd₁₇S₄(SPh)₂₈][Ru(bpy)₃], and [Cd₃₂S₁₄(SPh)₄₀][Ru(phen)₃]₂ (phen=1,10‐phenanthroline and bpy=bipyridine), show intense absorption in the visible‐light region. They also exhibit size‐dependent photocurrent responses under the illumination of visible light. The photocurrent increases with increased cluster size. The dyes also have significant influence on the photocurrent generation of the composite.     

Patterning porous matrices and planar substrates with quantum dots

Silica hydrogels and planar substrates were patterned with CdS nanoparticles using a photolithographic method based on the photo dissociation of thiols and cadmium-thiolate complexes. Silica hydrogels were prepared via a standard base-catalyzed route. The solvent was exchanged with an aqueous solution of CdSO₄ and 2-mercaptoethanol, and the samples were then exposed to a focused ultraviolet beam. Planar substrates were patterned by illuminating a precursor solution spin coated on the substrates. CdS nanoparticles formed in the illuminated spots, and had a diameter below about 2 nm. The diameter of the spots illuminated by the UV beam could be varied from a few hundred to a few μm, on both hydrogels and planar substrates. Samples were characterized with transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and optical absorption, photoluminescence and Raman spectroscopies. All these techniques confirmed the chemical identity of the CdS nanoparticles. To investigate the mechanism of nanoparticle formation, we took absorption spectra of the precursor solution as a function of irradiation time. In unirradiated solutions, we noticed a maximum at 250 nm, characteristic of Cd-thiolate complexes. The absorption at 250 nm decreased with increasing irradiation time. A new band appeared at 265 nm for exposures around 5 min, and that band shifted to 290 nm in samples exposed for 10 min. A yellow precipitate formed after about 30 min. XRD showed that the precipitate was cubic CdS, with a mean particle size of 1.4 nm. We attribute formation of CdS to the photodissociation of the thiols and of the Cd-thiolates. UV irradiation of these precursors yields a series of species that can react with Cd²⁺, such as RS^·, S²⁻ and H₂S. Small CdS nanoparticles form in the initial stages of illumination, and present absorption bands in the 265–290 nm region. These CdS aggregates grow, coalesce and precipitate for longer irradiation times.     

CIRCULAR DICHROISM AND ELECTRONIC ABSORPTION OF RHODIUM(III) EDTA-TYPE COMPLEXES: Ethylenediamine-N,N′-diacetato-N,N′-di-3-propionatorhodate(III) and (S,S)-Ethylenediamine-N,N′-disuccinatorhodate(III) Ions

Abstract

Electronic absorption and CD spectra are reported for the sexidentate complexes, trans(O₅)-Rh(EDDDA)^?, trans(O₅ O₆)-Rh(EDDDA)^?, and trans(O₅)-Rh(S,S-EDDS)^? (EDDDA)=ethylenediamine-N,N′-di-3-propionate; S,S-EDDS=(S,S)-ethylenediamine-N,N′-disuccinate). Because of the sterospecific coordination of the S,S-EDDS ligand the absolute configuration of (+)_D-trans(O₅)-Rh(S,S-EDDS)^? is known to be Λ. By comparison of their CD spectra to that of the (+)_D isomer of trans(O₅)-Rh(S,S-EDDS)^?, the absolute configurations of the (?)_DEDDDA complexes are assigned tentatively.     

水浴法制备CdS薄膜产生的本征缺陷对光电学性质的影响

采用化学水浴沉积法(CBD)在钠钙玻璃衬底上制备硫化镉(CdS)薄膜,研究不同硫酸镉(CdSO_4)浓度下产生的本征缺陷对CdS薄膜光电学性质的影响。采用光致发光光谱、紫外-可见分光光度计及霍尔效应测试系统对薄膜的本征缺陷、光学及电学性质进行分析,发现CdS薄膜主要存在镉间隙(Cdi)及硫空位(VS)等本征缺陷,且VS随CdSO_4浓度的降低而逐渐减少。同时,VS缺陷的减少有利于薄膜透过率的提高,但在一定程度上降低了薄膜的电导率。根据透过率及其相关公式可知,半导体材料中透过率与电导率成e指数反比关系,适当减小薄膜的电导率可以使其透过率得到大幅度的提高,理论解释与实验结果相一致。     

New heavy metal ion-selective macrocyclic ligands with mixed-donor atoms and their extractant properties

Synthetic procedures for new macrocyclic diamides with N₂S₄O₃- and N₂S₅O₃-donors were given. The corresponding macrocyclic ligands were prepared by reaction of NaBH₄ with the macrocyclic diamides in the presence of boron triflouride ethyl etherate in dry tetrahydrofuran. The solvent extraction method was used to evaluate metal-ion binding properties of the new ligands. The values of the extraction constants (log K _ex) and the complex compositions were determined for the extracted complexes. The solvent extraction experiments suggested that the reduced N₂S₅O₃-donor macrocycle has Ag⁺ selectivity compared to Pb²⁺, Co²⁺, Ni²⁺, Mn²⁺, and Cd²⁺ for chloroform as organic solvent.     

4-硝基咪唑A-带激发态结构动力学

通过共振拉曼光谱实验和量子化学计算的方法研究了4-硝基咪唑(4NI)A-带激发态衰变动力学. 对4NI的振动光谱、紫外电子吸收光谱、荧光光谱和共振拉曼光谱进行了指认. 在全活化空间自洽场法(CASSCF)/6-31G(d)计算水平下获得了单重激发态S₁(n_Oπ^*)和S₂(ππ^*)和势能面交叉点S₁(n_Oπ^*)/S₂(ππ^*)的优化几何结构和能量, 分析了A-带共振拉曼光谱的强度模式特征, 获得了短时结构动力学, 并结合全活化空间自洽场法(CASSCF)理论计算结果确定了4NI 在S₂(ππ^*)态衰变通道主要是S_{2, FC}→S_{2, min}(ππ^*)→S₀辐射弛豫.     

Controllable synthesis of functionalized CdS nanocrystals and CdS/PMMA nanocomposite hybrids

We reported controllable synthesis of CdS nanocrystal-polymer transparent hybrids by using polymethylmethacrylate (PMMA) as a polymer matrix. In a typical run, the appropriate amounts of cadmium chloride (CdCl₂) and sodium sulfide (Na₂S) in the presence of 2-mercaptoethanol (ME) as the organic ligand are well dispersed in H₂O/DMF solution without any aggregation. From a combination of transmission electron microscopy (TEM) and a computing method of Brus’s model according UV-vis absorption spectra, the particle size of as-prepared hydroxyl-coated CdS nanocrystal was determined to be about 5 nm. Then, with the surface treatment with methacryloxypropyltrimethoxysilane (MPS), CdS-PMMA hybrids were obtained via free radical polymerization in situ. FT-IR characterization indicates the formation of robust bonding between CdS nanocrystals and the organic ligand and the formation of double-bond functional CdS nanocrystals. The TGA measurement displays CdS-PMMA hybrids possess better thermal stability compared with pure PMMA polymer. The fluorescence measurement shows that CdS nanocrystals and CdS-PMMA hybrids exhibit good optical properties. Also, the luminescent photographs taken under ultraviolet light prove the luminescence properties.     

Fluorescence properties of nanosized sulfides

The absorption spectra of nanosized sulfides and selenides (ZnS, CdS, CuS, Cu₂S, AgS, In₂S₃, SnS, PbS, Sb₂S₃, FeS, CoS, NiS, CdSe, and Ag₂Se) showed one absorption band with a maximum at wave-lengths shorter than 300 nm. The UV fluorescence spectra of all of these nanosized sulfides in a polyvinyl alcohol film contained maxima at 380–440 nm. Nanosized sulfides are thus characterized by a very large (up to 15000 cm⁻¹) Stokes shift of fluorescence. In a polyvinyl alcohol film, a decrease in the concentration of cadmium sulfide from 0.05 to 0.002 M led to a threefold increase in the fluorescence intensity. The dependence of the degree of fluorescence buildup on the sulfide concentration is nearly linear. An increase in sulfide concentration to more than 5 × 10⁻³ M in solution led to a complete coagulation of particles.     

Influence of Hydrogen Bonding and Polarity on the Spectral Properties of 4-Aminophthalimide Clusters Formed with Triethylamine and Dimethyl Sulfoxide in Solution

The time-dependent density functional theory (TDDFT) method has been carried out to study the influences of hydrogen bonding and solvent polarity on the spectral properties of 4-aminophthalimide (4AP) clusters formed with hydrogen-accepting solvents triethylamine (TEA) and dimethyl sulfoxide (DMSO). The ground- and S₁-state geometry structure optimizations, hydrogen bond energies, absorption and emission spectra for both the 4AP monomer and its two triply hydrogen-bonded clusters 4AP + (TEA)₃ and 4AP + (DMSO)₃ have been calculated using DFT and TDDFT methods respectively with the hybrid exchange correlation functional PBE1PBE and split-valence basis set 6-311++G(d,p). It has been demonstrated that the two hydrogen bonds I and II formed with the amine group of 4AP are significantly strengthened while the hydrogen bond III formed with the imide group is slightly weakened due to the intramolecular charge transfer from the amine group to the two carbonyl groups of the 4AP molecule upon photoexcitation. In addition, the hydrogen bonds formed by 4AP with DMSO are stronger than those formed with TEA, which together with its strong polarity, should be the main reasons for the more redshifts of both the absorption and the fluorescence spectra of 4AP in solvent DMSO than those in TEA.     

Ag2S或CuS掺杂的Zn0.5Cd0.5S纳米晶体：溶剂热法合成及光致发光性能

以异丙醇为溶剂,醇热法制备Zn_0.5Cd_0.5S和Ag₂S或CuS掺杂的Zn_0.5Cd_0.5S纳米晶体,考察了这些纳米晶体在可见光区域的光致发光性能。结果表明,反应温度和反应时间、掺杂剂的浓度和种类对Zn_0.5Cd_0.5S的发光性能有很大的影响,相比未掺杂Zn_0.5Cd_0.5S纳米晶体而言,Ag₂S或CuS掺杂后其光致发光强度明显增强、半高宽更宽。     

Optically active tetraazamacrocycles analogous to cyclam

The syntheses of enantiopure tetraazamacrocycles analogous to cyclam, (S,S)-3, (R,R)-3 and (S,S,S,S)-4, have been carried out. NMR and semiempirical studies of 3 have revealed that this compound presents a rigid conformation with C₂ symmetry, which is stabilized by intramolecular bifurcated hydrogen bonds. Structural studies for macrocycle 4 have shown that the presence of two cyclohexane rings of (S,S) configuration leads to the loss of the D₂ symmetry in solution, which is in agreement with the AM1 calculated structure.     

Energy Transfer Between Eu3+ Ions and CdS Quantum Dots in Sol-Gel Derived CdS/SiO2 : Eu3+ Gel

We have investigated the energetic correlation between rare-earth ions and semiconductor nanocrystals, using europium ion (Eu³⁺) doped silica (SiO₂) gel with adsorbed cadmium sulfide (CdS) particles. Samples were prepared by a sol-gel technique, in which several methods for the precipitation of CdS colloids were attempted. The fluorescence intensities were compared for different gels, with and without CdS particles. The intrinsic emission lines due to ⁵D₀ ⁷F_J(J = 0–4) transitions of Eu³⁺ were observed, which were enhanced for 24 h-immersed gel (dried at 50°C). From the results on the decay dynamics of fluorescence, we proposed the model that surface-trapped electrons on CdS particles nonradiatively excited 4f electrons in Eu³⁺ ions due to an energy transfer process.     

Raman scattering in mixed defect chalcopyrite crystals

We have investigated with Raman spectroscopy pseudoternary Zn_xCd_1?xGa₂S₄ and CdGa₂(S_xSe_1?x)₄ phases over the whole composition range. In Zn_xCd_1?xCd_1?xGa₂S₄ a smooth variation of the spectra and a generalized one-mode behaviour has been observed, except for the lowest frequency modes. In CdGa₂(S_xSe_1?x)₄ the anion substitution has a larger influence on the spectra. Peculiar two-mode behaviour is displayed by the strong A-symmetry breathing modes.