Access to a large stokes shift in functionalized fused coumarin derivatives by increasing the geometry relaxation upon photoexcitation: An experimental and theoretical study

A series of new fluorophores with a fused coumarin framework were prepared. The dyes show red-shifted and enhanced absorption compared to the model compound, 7-hydroxycoumarin. The new coumarin bearing a 4-dimethylaminophenylacetylide group, shows absorption at 389 nm (ɛ = 14,300 M⁻¹ cm⁻¹), compared to the model compound which shows blue shifted absorption bands (ɛ = 11,500 M⁻¹ cm⁻¹ at 320 nm). The emission of the new coumarin bearing a 4-dimethylaminophenylacetylide group is remarkably red-shifted (λ_em = 555 nm) compared to the model compound (λ_em = 356 nm). The fluorescence quantum yields of the new coumarins are increased up to ca. 9-fold compared to the model compound. The Stokes shifts (84 nm–166 nm) are also much larger than that of the model compound. TDDFT calculations show that the fused coumarins undergo significant geometry relaxation upon photoexcitation, which is responsible for the large Stokes shift. Population of the triplet excited state was observed for the bromo-functionalized coumarin.     

First-principles study of the stability,electronic and mechanical properties of Cr2N and CrN with the variation of Ni doping concentration

First-principles approach was applied to investigate the stability, electronic and mechanical properties of Cr_2-xNi_xN (x = 0, 0.083, 0.167,0.250, 0.333) and Cr_1-xNi_xN (x = 0,0.125,0.25,0.375, 0.5). The calculated formation enthalpy and mechanical stability results show that Cr_2-xNi_xN and Cr_1-xNi_xN are all stable. The bulk, shear and Young's modulus results indicate that different variation trend is observed in Cr_2-xNi_xN and Cr_1-xNi_xN with the increase of x. Base on Pugh and Pettifor criteria, Cr₂N belongs to the brittle area and the ductility of Cr_2-xNi_xN increases with the increment of x, obtain the maximum results when x = 0.333. However, CrN, which belongs to the ductile area, alloying with Ni decreases its ductility and increases its brittleness, reach the maximum brittleness when x = 0.5. The charge density difference study reveals that the doped Ni atom affects the interaction between Cr and N in Cr_2-xNi_xN and Cr_1-xNi_xN differently. Furthermore, the stress-strain curve of Cr₂N, Cr_1.833Ni_0.167N, and Cr_1.667Ni_0.333N under shear and tensile deformation shows that the ultimate stress of Cr₂N is decreased and its ductility increased. Nevertheless, the stress-strain curve of CrN, Cr_0.75Ni_0.25N, and Cr_0.5Ni_0.5N under shear and tensile deformation indicates that the strength of CrN can be enhanced and its deformation process is significantly changed when x = 0.25.     

Foaming of polypropylene with supercritical carbon dioxide: An experimental and theoretical study on a new process

A new process was used to foam polypropylene (PP) with batch foaming technique with supercritical carbon dioxide (scCO₂) as the blowing agent. Comparing with the conventional process, the new one takes less time to foam and the foaming temperature range is much broader, which is about 2.5 h and 55°C, respectively. An activation model was established on the basis of mass equilibrium, this model was combined with classical nucleation theory and S‐L EOS model to explain foaming behaviors of PP and simulate the cell nucleation and cell diameter. A satisfactory agreement between calculated and experimental values was obtained. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2877–2885, 2013     

Photophysical properties of arylcarbonitrile derivatives: Synthesis, absorption and emission spectra, and quantum chemical studies

A new series of aromatic cyanovinyl compounds were synthesized via one-pot reactions of tri- or tetracyanoethylenes with nucleophilic reagents. The ground-state geometries and UV-vis absorption spectra of the compounds were computationally analyzed by means of density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations, respectively. None of the compounds were fluorescent in solution, but some showed intense emission in the solid state. The first excited singlet states (S₁) potential energy surfaces (PESs) were explored using complete active space SCF (CASSCF) calculations for the compounds in order to elucidate nonradiative decay mechanism that takes into account the involvement of conical intersections (CI).     

Structural and dielectric properties,and nonlinear electrical response of the CaCu3-xZnxTi4O12 ceramics: Experimental and computational studies

CaCu_3-xZn_xTi₄O₁₂ ceramics (x = 0, 0.05, 0.10) were successfully prepared by a conventional solid-state reaction method. Their structural and dielectric properties, and nonlinear electrical response were systematically inspected. The X-ray diffraction results indicated that single-phase CaCu₃Ti₄O₁₂ (JCPDS no. 75–2188) was obtained in all sintered ceramics. Changes in the lattice parameter are well-matched with the computational result, indicating an occupation of Zn²⁺ doping ions at Cu²⁺ sites. The overall tendency shows that the average grain size decreases when x increases. Due to a decrease in overall grain size, the dielectric permittivity of CaCu_3-xZn_xTi₄O₁₂ decreases expressively. Despite a decrease in the dielectric permittivity, it remains at a high level in the doped ceramics (~3,406–11,441). Besides retention in high dielectric permittivity, the dielectric loss tangent of x = 0.05 and 0.10 (~0.074–0.076) is lower than that of x = 0 (~0.227). A reduction in the dielectric loss tangent in the CaCu_3-xZn_xTi₄O₁₂ ceramics is closely associated with the enhanced grain boundary response. Increases in grain boundary resistance, breakdown electric field, and conduction activation energy of grain boundary as a result of Zn²⁺ substitution are shown to play a crucial role in improved grain boundary response. Furthermore, the XPS analysis shows the existence of Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺, indicating charge compensation due to the loss of oxygen lattice. Based on all results of this work, enhanced dielectric properties of the Zn-doped CCTO can be explained using the internal barrier layer capacitor model.     

The photophysical anisotropy and electronic structure of new narrow band gap perovskites Ln2AlMnO6 (Ln = La,Pr, Nd): An experimental and DFT perspective

Perovskite oxides have exhibited multi-dimensional applications in light driven photophysical processes like optoelectronics and photocatalysis. A detailed first-principles density functional theory (DFT) approach is undertaken to explore the electronic structure and photophysical properties of new double perovskites La₂AlMnO₆ (LAM), Pr₂AlMnO₆ (PAM) and Nd₂AlMnO₆ (NAM) crystallizing in monoclinic P2₁/n symmetry. The optical band gap of the synthesized perovskites range between 1.28 and 1.77 eV which is promising for optimal photophysical performance. The investigated electronic structures reveal a direct band gap for LAM and PAM, in contrast to an indirect band structure for NAM. The direct nature of LAM and PAM facilitates a faster separation and recombination mechanism of electron-hole pairs as compared to the indirect nature of NAM. The linear optical properties of these compounds have been extracted to understand their applications as promising photophysical materials. The optical response functions exhibit an anisotropy which exists due to the preferential spatial polarization of the monoclinic structure of the perovskites. The calculations show that LAM and PAM show relatively higher birefringence (Δn ~ 0.2) than NAM (Δn ~0.05). The calculated optical properties result from predicted inter-band transitions between the O 2p and Mn 3d states constituting the band edges. The optical properties are compared to related experimental results of other well-known perovskites to demonstrate the applicability of LAM, PAM and NAM in photophysical applications.     

Electronic structures and molecular properties of FLBDOB and its derivatives: A combined experimental and theoretical study

Theoretical studies on a new unsymmetrical electrolyte salt, lithium [3-fluoro-1,2-benzenediolato(2-)-o,o′ oxalato]borate (FLBDOB), and its derivatives, lithium bis[3-fluoro-1,2-benzenediolato(2-)-o,o]borate (FLBBB), and lithium bis(oxalate)borate (LBOB) are carried out using density functional theory (DFT) method and B3LYP theory level. Bidentate structures involving two oxygen atoms are preferred. Based on these conformations, a linear correlation is observed between the highest occupied molecular orbital (HOMO) energies and the limiting oxidation potentials measured by linear sweep voltammetry, which supports experimental results that strongly electron-withdrawing substituent anions are more resistant against oxidation. The correlations are also observed between ionic conductivity and binding energy, solubility and theoretical set of parameters of anion, thermal stability and the hardness (η). Wave function analyses are performed by natural bond orbital (NBO) method to further investigate the cation-anion interactions.     

Lanthanide (=Ce,Pr, Nd and Tb) ions substitution at calcium sites of hydroxyl apatite nanoparticles as fluorescent bio probes: Experimental and density functional theory study

An interesting property of hydroxyl apatite is the ability to undergo cationic and anionic substitution. In this study, nano hydroxyl apatite(nHAp) substituted with four different lanthanide ions(LnO)(Cerium,Praseodymium,Neodymium and Terbium) is prepared by co-precipitation method and characterized by X-Ray Diffraction, Fourier Transform Infrared, Fluorescence and UV‐Visible Spectroscopy and Transmission Electron Microscopy, and Magic Angle Nuclear Magnetic Resonance techniques. Rietveld refinement and computational study using Density Functional Theory has provided information about the effect of LnO substitution on nHAp phase. These studies reveal changes in lattice parameters and preferential calcium sites for LnO substitution in apatite structure. Experimental results have shown that LnO substituted particles have shown an intense fluorescent emission under UV‐Visible excitation. The ability of prepared LnO substituted nHAp particles to inhibit oxidative stress in terms of reduction of hydrogen peroxide is also demonstrated. In- vitro biocompatibility has been assessed via adsorption of human plasma/serum proteins on the surface of nHAp. Adsorption of the protein on nHAp also leads to passivation against corrosion. Particles have shown excellent cell viability and better proliferation of MG-63 cell lines. These results may open new avenues for the development of bioactive materials for bone regeneration and smart fluorescent probes for bio imaging applications.     

Structural properties,electronic structures and optical properties of WB2 with different structures: A theoretical investigation

The structural, electronic and optical properties of six WB₂ diborides with hP3, hP6, hP12, oP6, hR9 and hR18 structures were systematically investigated using the first-principles calculation based on density functional theory. The optimized atomic coordinates and lattice parameters agree well with the corresponding experimental and theoretical results. All WB₂ are energetically stable, and hP6-WB₂ has the best phase stability and hP3-WB₂ shows the worst phase stability. The results of density of states and the charge density differences indicate that WB₂ have the strong W–B and B–B covalent bonds. The hardness was obtained from the Mulliken population. The predicted values of absorption coefficient α(ω) and reflectivity R(ω) reveal that the laser with a longer wavelength is recommended during the synthesis of WB₂ coatings on the substrate surface using the Nd-YAG laser. Finally, the anisotropy in optical properties for WB₂ was discussed via the polycrystalline and directional static dielectric constants ε₁(0) and static refractive indexes n(0).     

Two-dimensional M2CO2/MoS2 (M = Ti,Zr and Hf) van der Waals heterostructures for overall water splitting: A density functional theory study

Because of the wide applications for photocatalysis, electronics and optoelectronics, two-dimensional (2D) van der Waals (vdW) heterojunctions have attracted substantial attentions. In this work, we carried out a systematic investigation on the geometry structures, electronic properties, optical properties and carrier mobilities of the M₂CO₂-II (M = Ti, Zr and Hf) and MoS₂ heterostructures with a hybridized density functional theory (DFT). The BʹCʹ stacked M₂CO₂-II/MoS₂ heterostructure with a short interlayer distance is energetically favorable. All M₂CO₂-II/MoS₂ bilayer and sandwich-like structures are indirect semiconductors. The maximum of valence band (VBM) and conduction band minimum (CBM) of M₂CO₂-II/MoS₂ heterostructures are dominated by different layers, implying the spatial separation of photogenerated electron-hole pairs. Three M₂CO₂-II/MoS₂ heterostructures, including Zr₂CO₂-II/MoS₂ –S-BʹCʹ, Hf₂CO₂-II/MoS₂–B-BʹCʹ, and Hf₂CO₂-II/MoS₂–S-BʹCʹ, are considered as the promising candidates for overall water splitting due to their appropriate band structures, suppressed recombination of photogenerated electron-hole pairs, enhanced optical absorption and carrier mobilities. In addition, the gaint hole mobility makes Ti₂CO₂-II/MoS₂ heterostructure a potential candidate for the application for 2D electronic devices.     

Foaming of polymers with supercritical CO2: An experimental and theoretical study

Microcellular polystyrene (PS) foams and porous structures of the biodegradable poly(d,l-lactic acid) (P_d,lLA) were prepared with the batch foaming technique (pressure quench) using supercritical CO₂ as blowing agent. The effect of pressure, temperature and depressurization rate on the final porous structure was investigated. The results revealed that the size of the pores decreases and their population density increases with pressure increase, or decrease of temperature, and/or increase of the depressurization rate. The results were correlated by combining nucleation theory with NRHB model in order to account for and emphasize the physical mechanism related to nucleation of bubbles inside the supersaturated polymer matrix. A satisfactory agreement between correlations and experimental data was obtained indicating that the nucleation theory yields quantitative correlations when variables such as sorption, degree of plasticization, and surface tension of the system polymer-supercritical fluid are accurately described.     

Effect of lithium extraction on the stabilities,electrochemical properties,and bonding characteristics of LiFePO4 cathode materials: A first-principles investigation

The impact of lithium extraction on the structural stabilities, electronic structures, bonding characteristics, and electrochemical performances of LiFePO₄ compound was investigated by first-principles technique. The results demonstrated that the partition scheme of electrons not only affects the calculated atomic charges but also the magnetic properties. In FePO₄ and LiFePO₄ compounds, all Fe ions take high spin arrangements and have large magnetic moments (MMs), while the MMs of other ions are very small. The magnetisms of Li_xFePO₄ compounds are mainly originated form Fe ions. It was found that the changes in d band electrons of the transition metals do play an important role in determining the voltage of a battery (versus Li/Li⁺). Furthermore, the variations in d band electrons also provide us a method to control the density of states (DOS) and carrier concentration at the Fermi energy. Our calculations confirmed that the substitution of Fe by Co and Ni ions leads to a voltage increase by about 0.70 V and 1.23 V respectively. According to the bond populations, it can be identified that strong covalent bonds are formed between O and P ions. The P–O bonds are much stronger than Fe–O ones. The partial DOSs further revealed that the covalent bonds in Li_xFePO₄ are derived from the orbital overlaps between O_2s,2p and P_3s,3p states, and the overlap between Fe_3d and O_2p states. Such covalent bonds are of particularly importance for the excellent thermodynamic stabilities of the two-ends structures of Li_xFePO₄.     

Guaiacol derivatives and inhibiting species adsorption over MoS2 and CoMoS catalysts under HDO conditions: A DFT study

We have investigated using DFT calculations the η¹ adsorption of guaiacol, phenol, anisole and phenol over CoMoS and MoS₂ phases under HDO conditions. This adsorption mode should lead to a direct deoxygenation (DDO) reaction, which is low hydrogen-consuming. The most stable mode is an adsorption through the OH group of the molecule. The calculation of adsorption Gibbs free energies of inhibiting compounds (H₂O, H₂S, and CO) which can be present under reaction conditions shows that these molecules adsorb more strongly than oxygenated compounds, which suggests that CO will be a major inhibitor of the HDO process of real feeds.     

Copolymerization of norbornene with ethylene: A high-resolution liquid NMR, DSC and solid state NMR study

In this paper, we report the monomer reactivity on the copolymerization of norbornene and ethylene. The reactivity ratios for ethylene (M₁) and norbornene (M₂) are 18.5 and 0.035, respectively. Different copolymerization conditions can produce COC with different microstructures. A ¹³C NMR shift assignment in pentad sequences in copolymers has been obtained. More isolated polynorbornene or a micro-block length can be obtained using a low Zr/Al catalyst/co-catalyst ratio and at a lower NB/ethylene feed ratio. The T_1p ^C decay curve shows two component decays in all resonance peaks. These two component decays come from different norbornene microstructures, while the block and alternative have similar T_1p ^C values.     

Tunable optical,electronic and magnetic properties of semiconductor nanoparticles induced by magnetic and nonmagnetic dopants: A comparative experimental and theoretical study

While combining semiconductor and magnetic properties at the nanoscale provides dilute magnetic semiconductor (DMS) nanomaterials with a wide range of applications in next-generation electronic devices, tuning DMS properties still presents a challenge. Here, the synthesis of pure ZnO and transition metal (TM)-doped ZnO nanoparticles (NPs) with different magnetic (Fe and Co) and nonmagnetic (Mn) dopant concentrations (ranging from 2% to 10%) is reported using a co-precipitation method. Introducing the TM-dopants into ZnO NPs with 35?nm wurtzite structure causes crystallite and mean NP sizes to decrease, as characterized by X-ray diffraction and field-emission scanning electron microscopic analyses. Room-temperature magnetic measurements indicate coexistence of paramagnetic and ferromagnetic phases with tunability in the resulting TM-doped NPs. The maximum ferromagnetic coercivity and saturation magnetization are found to be 89?Oe and 0.074?emu/g for 10% Fe-doped ZnO NPs. UV–visible spectra showed a blue shift with increasing the dopant concentration, being in agreement with increasing trend in band gap energy calculated from band structure and density of state of TM-doped ZnO nanocrystal systems.     

From single crystals to supported nanoparticles in experimental and theoretical studies of H2 oxidation over platinum metals (Pt, Pd): Intermediates, surface waves and spillover

The present paper reviews our investigations concerning the mechanism of H₂ + O₂ reaction on the metal surfaces (Pt, Pd) at different structures: single crystals (Pt(1 1 1), Pt(1 0 0), Pd(1 1 0)); microcrystals (Pt tips); and nanoparticles (Pd–Ti³⁺/TiO₂). Field electron microscopy (FEM), field ion microscopy (FIM), high-resolution electron energy loss spectroscopy (HREELS), XPS, UPS, work function (WF), TDS and temperature-programmed reaction (TPR) methods have been applied to study the kinetics of H₂ oxidation on a nanolevel. The adsorption of both O₂ and H₂ and several dissociative products (H_ads, O_ads, OH_ads) was studied by HREELS. Using the DFT technique the equilibrium states and stretching vibrations of H, O, OH, H₂O, adsorbed on the Pt(1 1 1) surface, have been calculated depending on the surrounding of the metal atoms. Sharp tips of Pt, several hundreds angstroms in radius, were used to perform in situ investigations of the dynamic surface processes. The FEM and FIM studies on the Pt-tip surface demonstrate that the self-oscillations and waves propagations are connected with periodic changes in the surface structure of nanoplane (1 0 0)-(hex) ↔ (1 × 1), varying the catalytic property of metal. The role of defects (Ti³⁺-□_O) in the adsorption centers formation, their stabilization by the palladium nanoparticles, and then the defects participation in H₂ + O₂ steady-state reaction over Pd–Ti³⁺/TiO₂ surface have been studied by XPS, UPS and photodesorption techniques (PhDS). This reaction seems to involve the “protonate” hydrogen atoms (H⁺/TiO_x) as a result of spillover effect: diffusion of H_ads atoms from Pd particles on a TiO_x surface. The comprehensive study of H₂, O₂ adsorption and H₂ + O₂ reaction in a row: single crystals → tips → nanoparticles has shown the same nature of active centers over these metal surfaces.     

Studies on the mechanical,thermal, and morphological properties of poly(ether ether ketone)/poly(ether sulfone)/barium titanate nanocomposites: Correlation of experimental results with theoretical predictive models

In this study, mechanical, thermal, and morphological properties of the nanocomposites fabricated with the optimized blend of poly(ether ether ketone) (PEEK) and poly(ether sulfone) (PES) incorporated with nanobarium titanate (BT) were investigated. The optimized blend was based on the mechanical and thermal properties of the PEEK and PES in the ratio of 75 : 25 wt %. Nanoparticles were incorporated into the optimized blend with the help of twin‐screw extruder. The concentration of nano‐BT was varied from 2 to 6 wt % (0.41–1.28 vol %). With the increase in the nanosized BT concentrations, the tensile strength, tensile modulus, and elongation at break increased, whereas the crystallinity of the nanocomposites calculated by using differential scanning calorimetry method was found to decrease marginally. Morphological studies were carried out using scanning electron microscopy. The nanocomposites were evaluated by using theoretical predictive models according to “Pukanszky model” applicable to tensile strength and “Takayanagi's model” and “Guth and Smallwood model” applicable to tensile modulus. Upper and lower boundary of Hashin–Shtrikman model as well as Paul's model, applicable to tensile modulus, were also used to compare the experimental data. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

An experimental and computational study of intramolecular charge transfer: Diarylamino derivatives of 7H-benzimidazo(2,1-a)benz(d,e)isoquinolin-7-ones

A novel intramolecular donor–acceptor system of four isomers consisting of 7H-benzimidazo(2,1-a)benz(d,e)isoquinolin-7-ones and diarylamine units was synthesized and characterized; the absorption and fluorescence spectra of the system in a variety of solvents were investigated. Intramolecular charge transfer was confirmed within the system by virtue of shifts in emission maximum with increasing solvent polarity; a high dipole moment for the intramolecular excited state was calculated using the Lippert equation. Shorter lifetimes were observed in polar solvents compared with those in non-polar solvents, indicating strong dipole–dipole interactions occurred. The ground-state geometry, lowest energy transition and the UV–vis spectrum of the system were studied using density functional theory and time-dependent density functional theory at B3LYP/6-31G^* level, which showed that the calculated outcomes were in good agreement with experimental data.