Time filter

Source Type

Song Y.,HIGH-TECH | Yao H.,HIGH-TECH | Tan H.,HIGH-TECH | Zhu S.,HIGH-TECH | And 3 more authors.
Journal of Polymer Science, Part A: Polymer Chemistry | Year: 2017

A series of hyperbranched polyimides (HBPIs) were synthesized by reacting a triamine monomer N,N′,N″-tris(4-methoxyphenyl)-N,N′,N″-tris(4-phenylamino)-1,3,5-benzenetriamine with various dianhydrides such as oxydiphthalic dianhydride (ODPA), 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), and pyromellitic dianhydride (PMDA). The hyperbranched polyimide (6FHBPI) using 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) as dianhydride monomer was also added into the discussion. All the hyperbranched polyimides exhibited excellent organo-solubility and high thermal stability. Memory devices with a sandwiched structure of indium tin oxide (ITO)/HBPI/Al were constructed by using these HBPIs as the active layers. All these HBPIs based memory devices exhibited favorable memory performances, with switching voltages between -1.3 V and -2.5 V, ON/OFF current ratios up to 107 and retention times long to 104 s. Tunable memory characteristics from electrical insulator to volatile memory, and then to nonvolatile memory were obtained by adjusting the electron acceptors of these HBPIs. Molecular simulation results suggested that the electron affinity and the dipole moment of these HBPIs were responsible for the conversion of the memory characteristics. With the electron affinity and dipole moment of these HBPIs increasing, the memory characteristics turned from volatile to nonvolatile. The present study suggested that tunable memory performance could be achieved through adjusting the acceptor moieties of the hyperbranched polyimides. © 2017 Wiley Periodicals, Inc.


Liu J.-Y.,Institute of Theoretical Chemistry
International Journal of Quantum Chemistry | Year: 2016

The structures and nonlinear optical properties of a novel class of alkali metals doped electrides B12N12-M (M=Li, Na, K) were investigated by ab initio quantum chemistry method. The doping of alkali atoms was found to narrow the energy gap values of B12N12 in the range 3.96-6.70 eV. Furthermore, these alkali metals doped compounds with diffuse excess electron exhibited significantly large first hyperpolarizabilities (β0) as follows: 5571-9157 au for B12N12-Li, 1537-18,889 au for B12N12-Na, and 2803-11,396 au for B12N12-K. Clearly, doping of the alkali atoms could dramatically increase the β0 value of B12N12 (β0=0). Furthermore, their transition energies (ΔE) were also calculated. The results showed that these compounds had low ΔE values in the range 1.407-2.363 eV, which was attributed to large β0 values of alkali metals doped B12N12 nanocage. © 2016 Wiley Periodicals, Inc.


Zhang J.-P.,Jilin Institute of Chemical Technology | Jin L.,Jilin Institute of Chemical Technology | Zhang H.-X.,Institute of Theoretical Chemistry
Wuli Huaxue Xuebao/ Acta Physico - Chimica Sinica | Year: 2011

The geometries of ground and excited states of a series of ruthenium complexes [Ru(iph)(L)2]2+ (L=cpy (1), mpy (2), npy (3); iph=2,9-di(1-methyl-2-imidazole)-1,10-phenanthroline, cpy=4-cyano pyridine, mpy=4-methyl pyridine, npy=4-N-methyl pyridine) were optimized by the Becke's three-parameter functional and the Lee-Yang-Parr (B3LYP) functional and unrestricted B3LYP methods, respectively. Timedependent density functional theory (TD-DFT) method at the B3LYP level together with the polarized continuum model (PCM) were used to obtain their absorption and phosphorescent emission spectra in acetone media based on their optimized ground and excited-state geometries. The results revealed that the optimized structural parameters agreed well with the corresponding experimental results. The highest occupied molecular orbitals were localized mainly on the d orbital of the metal and the π orbital of the iph ligand for 1 and 2, and the npy ligand for 3, while the lowest unoccupied molecular orbitals were mainly composed of π* orbital of the iph ligand. Therefore, the lowest-lying absorptions and emissions were assigned to the metal to ligand charge transfer (MLCT)/intra-ligand charge transfer (ILCT) transition for 1 and 2, and the ligand to ligand charge transfer (LLCT) transition for 3. The lowest-lying absorptions are at 509 nm (1), 527 nm (2), and 563 nm (3) and the phosphorescence emissions at 683 nm (1), 852 nm (2), and 757 nm (3). The calculation results show that the absorption and emission transition characteristics and the phosphorescence color can be changed by altering the π electron-donating ability of the L ligand. © Editorial office of Acta Physico-Chimica Sinica.


Richter M.,Institute of Theoretical Chemistry | Mai S.,Institute of Theoretical Chemistry | Marquetand P.,Institute of Theoretical Chemistry | Gonzalez L.,Institute of Theoretical Chemistry
Physical Chemistry Chemical Physics | Year: 2014

Ab initio molecular dynamics simulations have been performed in order to investigate the relaxation dynamics of uracil after UV excitation in gas phase. Intersystem crossing (ISC) has been included for the first time into time-dependent simulations of uracil, allowing the system to relax in the singlet as well as in the triplet states. The results show a qualitatively different picture than similar simulations that include singlet states only. The inclusion of ISC effectively quenches the relaxation to the singlet ground state and instead privileges transitions from the low-lying nπ∗ state (S1) to a ππ∗ triplet state (T2) followed by rapid internal conversion to the lowest triplet state. © 2014 the Partner Organisations.


Larbi T.,Tunis el Manar University | Doll K.,University of Ulm | Doll K.,Institute of Theoretical Chemistry | Manoubi T.,Tunis el Manar University
Journal of Alloys and Compounds | Year: 2016

We present a combined theoretical and experimental investigation concerning the magnetic semiconductor Mn3O4. We measured the absorbance spectra with ultraviolet-visible spectrophotometry in the near infrared region (UV-Vis-NIR) using a spectrophotometry technique, and deduced this way the band gap. Electron paramagnetic resonance (EPR) spectroscopy is performed to study the paramagnetic properties of the Mn2+ center. Fourier transform infrared spectroscopy (FTIR) of the film displays the characteristic absorption bands of Mn3O4 located at around 553 cm−1 and 673 cm−1. Morphological properties are studied using the scanning electron microscopy (SEM) technique which revealed a smooth and rough surface. In order to interpret our experimental data obtained, we explored the ferromagnetic and ferrimagnetic order of Mn3O4 in a spinel structure by employing density functional theory (DFT) on the level of the PBE0 hybrid functional as implemented in the CRYSTAL14 code. Our results include the optimized geometries, the density of states, the infrared and Raman spectra and infrared dielectric properties. The theoretical results show an excellent agreement with the experimental ones. Correlations between infrared (IR) phonon modes and dielectric properties are also established. © 2016 Elsevier B.V.


Cao H.,CAS Beijing National Laboratory for Molecular | Huang Y.,Institute of Theoretical Chemistry | Liu Z.,CAS Beijing National Laboratory for Molecular
Proteins: Structure, Function and Bioinformatics | Year: 2016

To clarify the interplay between the binding affinity and kinetics of protein-protein interactions, and the possible role of intrinsically disordered proteins in such interactions, molecular simulations were carried out on 20 protein complexes. With bias potential and reweighting techniques, the free energy profiles were obtained under physiological affinities, which showed that the bound-state valley is deep with a barrier height of 12-33 RT. From the dependence of the affinity on interface interactions, the entropic contribution to the binding affinity is approximated to be proportional to the interface area. The extracted dissociation rates based on the Arrhenius law correlate reasonably well with the experimental values (Pearson correlation coefficient R=0.79). For each protein complex, a linear free energy relationship between binding affinity and the dissociation rate was confirmed, but the distribution of the slopes for intrinsically disordered proteins showed no essential difference with that observed for ordered proteins. A comparison with protein folding was also performed. © 2016 Wiley Periodicals, Inc.


Potzel O.,Institute of Theoretical Chemistry | Taubmann G.,Institute of Theoretical Chemistry
Journal of Solid State Chemistry | Year: 2011

In this work, we considered the pressure induced B1B2 phase transition of AB compounds. The DFT calculations were carried out for 11 alkaline halides, 11 alkaline earth chalcogenides and the lanthanide pnictide CeP. For both the B1 and the B2 structures of each compound, the energy was calculated as a function of the cell volume. The transition pressure, the bulk moduli and their pressure derivatives were obtained from the corresponding equations of state. The transition path of the Buerger mechanism was described using roots of the transition matrix. We correlated the computed enthalpies of activation to some structure defining properties of the compounds. A fair correlation to Pearsons hardness of the ions was observed. © 2011 Elsevier Inc. All rights reserved.


Zheng Y.,Northeast Normal University | Xiong T.,Northeast Normal University | Lv Y.,Northeast Normal University | Zhang J.,Northeast Normal University | And 2 more authors.
Organic and Biomolecular Chemistry | Year: 2013

A combination of computational and experimental methods was carried out to elucidate the mechanism of palladium-catalyzed water-assisted benzylic C-H amination with N-fluorobenzenesulfonimide (NFSI), which involved the oxidative addition of PdII to PdIV-species as a rate-limiting step, followed by water-assisted concerted metalation-deprotonation (CMD) of the PdIV complex and water-assisted reductive elimination (RE) processes, and then a nucleophilic addition process to generate the final product and complete the catalytic cycle. The stability of the PdIV complex could be ascribed to the suitable ligands with strong σ-donors and resistance to decomposition, as well as being sufficiently bulky because the water-clusters assembled the ligands through hydrogen bonds to act as one multidentate ligand. Calculation results suggested that water also plays a crucial role as a proton transferring bridge in water-assisted CMD and RE processes. The corresponding experimental findings substantiate the expectation. Additionally, NFSI was found to act as both the oxidant and the nitrogen source to facilitate the reaction, while the steric effect of the bulky -N(SO2Ph)2 group contributed to circumventing the o-C-H amination. In this reaction, we investigated a novel spiro-cyclopalladation intermediate, formed by the reaction of the PdIV centre with pristine-carbon instead of ortho-carbon, which might be valuable for our understanding and further development of transition metal catalyzed C-H functionalization. © 2013 The Royal Society of Chemistry.


Liu P.,Institute of Theoretical Chemistry | Song K.,Institute of Theoretical Chemistry | Zhang D.,Institute of Theoretical Chemistry | Liu C.,Institute of Theoretical Chemistry
Journal of Molecular Modeling | Year: 2012

The detailed mechanisms of catalytic CO oxidation over Au 2 - and AuAg - dimers, which represent the simplest models for monometal Au and bimetallic Au-Ag nanoparticles, have been studied by performing density functional theory calculations. It is found that both Au 2 - and AuAgdimers catalyze the reaction according to the similar monocenter Eley-Rideal mechanism. The catalytic reaction is of the multi-channel and multi-step characteristic, which can proceed along four possible pathways via two or three elementary steps. In AuAg -, the Au site is more active than the Ag site, and the calculated energy barrier values for the ratedetermining step of the Au-site catalytic reaction are remarkably smaller than those for both the Ag-site catalytic reaction and the Au 2 - catalytic reaction. The better catalytic activity of bimetallic AuAg - dimer is attributed to the synergistic effect between Au and Ag atom. The present results provide valuable information for understanding the higher catalytic activity of Au-Ag nanoparticles and nanoalloys for lowtemperature CO oxidation than either pure metallic catalyst. © Springer-Verlag 2011.


PubMed | The Interdisciplinary Center and Institute of Theoretical Chemistry
Type: Journal Article | Journal: Chemistry (Weinheim an der Bergstrasse, Germany) | Year: 2016

Herein, the Zimmerman Mbius/Hckel concept is extended to pericyclic reactions involving transition metals. While sigmatropic hydrogen shifts in parent hydrocarbons are either uniquely antarafacial or suprafacial, we have shown by theoretical orbital topology considerations and quantum chemical computations at DFT level that both modes of stereoselectivity must become allowed in the same system as a consequence of Craig-Mbius-type orbital arrays, in which a transition metal d orbital induces a phase dislocation in metallacycles. This may have fundamental implications for the understanding of reactivity and bonding in organometallic chemistry.

Loading Institute of Theoretical Chemistry collaborators
Loading Institute of Theoretical Chemistry collaborators