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[EN]Computational methods, or computer-aided material design (CAMD), used for the analysis and design of materials have a relatively long history. However, the applicability of CAMD has been limited by the scales of computational resources generally available in the past. The surge in computational power seen in recent years is enabling the applicability of CAMD to unprecedented levels. Here, we focus on the CAMD for materials critical for the continued advancement of the complementary metal oxide semiconductor (CMOS) semiconductor technology. In particular, we apply CAMD to the engineering of high-permittivity dielectric materials. We developed a Reax forcefield that includes Si, O, Zr, and H. We used this forcefield in a series of simulations to compute the static dielectric constant of silica glasses for low Zr concentration using a classical molecular dynamics approach. Our results are compared against experimental values. Not only does our work reveal numerical estimations on ZrO2-doped silica dielectrics, it also provides a foundation and demonstration of how CAMD can enable the engineering of materials of critical importance for advanced CMOS technology nodes. This research was enabled in part by support provided by Compute Canada (www.computecanada.ca). Computations were performed on the Niagara supercomputer at the SciNet HPC Consortium. SciNet is funded by the Canada Foundation for Innovation, the Government of Ontario, Ontario Research Fund.Research Excellence, and the University of Toronto.

A comprehensive mechanistic study on the title reaction by using DFT(B3LYP-D3) computational method is reported. Explicit consideration of mono- (m-xylylic) and dicarboxylic acid (phthalic) in the key transition states reveals active participation of the carboxylic acid, beginning with the generation of a monomeric Rh(I) active catalyst and in the ensuing catalytic steps. In the early catalytic event, uptake of alkyne is predicted to take place only after the oxidative addition of the Rh(I) active catalyst to the carboxylic acid. The hydrometalation of the alkyne bound to the Rh(III)-H intermediate then generates a Rh(III)-vinyl intermediate, which in turn converts to a Rh(III)-allyl species. The inclusion of m-xylylic acid results in a two-step pathway to Rh(III)-allyl species via Rh-allene intermediate. A number of weak noncovalent interactions (hydrogen bonding and C-H center dot center dot center dot pi) between the catalyst and the substrates and that involving m-xylylic acid are found to have a direct impact on the regiochemical preference toward the branched product and the enantiocontrolling hydroamination step involving C-N bond formation leading to the major enantiomer (S-allylic amine). The chiral induction is enabled by cumulative effect of noncovalent interactions, which is an insight that could aid future developments of chiral ligands for asymmetric hydroamination.

The axially chiral ligand of R-BINOL scaffold was synthesized by a series of manipulations which involved different chemical reactions to obtain the desired sliver(I) and gold(I) $$\{[\hbox {L}(\hbox {L}'\hbox {-NHC})_{2}]\hbox {M}\}\hbox {Cl}$$ ( $$\hbox {L} = 3{,}3'\hbox {-dimethyl-2}{,}2'\hbox {-dimethoxy-1,1}'\hbox {-binaphthyl}, \hbox {L}' = i\hbox {-propyl-benzo}[\hbox {d}]\hbox {imidazole})$$ (M =Ag and Au) complexes. Enantiopure R-BINOL was employed as a basic unit to synthesize a benzimidazole based bis-NHC ligand 1g which was obtained through the formation of different intermediate 1(a-f) compounds. The newly synthesized bis-NHC ligand precursor (1g) and its corresponding $$\{[\hbox {L}(\hbox {L}'\hbox {-NHC})_{2}]\hbox {Ag}\}\hbox {Cl}$$ (1h) and $$\{[\hbox {L}(\hbox {L}'\hbox {-NHC})_{2}]\hbox {Au}\}\hbox {Cl}$$ (1i) complexes were characterized by different spectroscopic techniques. The geometries of the optimized structure of the complexes 1h and 1i were computed at the B3LYP/SDD, 6-31G(d) level. Low temperature fluorescence spectroscopic studies did not show any evidence for the weak metal-metal interaction in these complexes. SYNOPSIS Synthesis, characterization of $$\{[\hbox {L}(\hbox {L}'\hbox {-NHC})_{2}]\hbox {M}\}\hbox {Cl}$$ (M = Ag and Au) (1h) and (1i) type sliver(I) and gold(I) complexes are reported. Molecular structures of these benzimidazole based, axially chiral complexes of R-BINOL scaffolds were determined by the computational studies. The results of spectroscopic and analytical data as well as the computational study show that the ligand (1g) prefers to form mononuclear bis-NHC silver(I) and gold(I) complexes in the given conditions.

Mixed organohalidopalladium complexes of the type trans-(NHC)(2)Pd(R)Br were conveniently obtained from trans-(NHC)(2)PdBr2 type complexes by a ligand-substitution reaction. In particular, the trans-[1-(1S)-menthyl-4-(R-1)-1,2,4-triazol-5-ylidene](2)Pd(R-2)Br [R-1 = Et, R-2 = CH2Ph (3a(1)); R-1 = Et, R-2 = o-OMeC6H4 (3a(2)); R-1 = R-2 = CH2Ph (3b(1)); R-1 = CH2Ph, R-2 = o-OMeC6H4 (3b(2))] complexes were obtained from the corresponding palladium(II) precursor complexes, 2a,b, by reaction with the respective Grignard reagents, in good to excellent yields (74-93%). Three of the four mixed organohalidopalladium complexes, 3a(1),a(2),b(1), have been structurally characterized by single-crystal X-ray diffraction, which revealed the trans disposition of the NHC ligands around the palladium center. The use of these mixed organohalidopalladium complexes in the Suzuki-Miyaura cross-coupling reaction was established for all of the complexes, 3a(1)-b(2), which yielded the desired cross-coupled products upon treatment with various ArB(OH)(2) [Ar = 1-naphthyl, 4-(1,1-biphenyl), 9-phenanthrenyl, 4-FC6H4, and 2,6-Me2C6H3] compounds, in the presence of NaOH as a base, in CH3CN, in three hours, under reflux conditions.

Nonfullerene acceptors (NFAs) dominate organic photovoltaic (OPV) research due to their promising efficiencies and stabilities. However, there is very little investigation into the molecular processes of degradation, which is critical to guiding design of novel NFAs for long‐lived, commercially viable OPVs. Here, the important role of molecular structure and conformation in NFA photostability in air is investigated by comparing structurally similar but conformationally different promising NFAs: planar O‐IDTBR and nonplanar O‐IDFBR. A three‐phase degradation process is identified: i) initial photoinduced conformational change (i.e., torsion about the core–benzothiadiazole dihedral), induced by noncovalent interactions with environmental molecules, ii) followed by photo‐oxidation and fragmentation, leading to chromophore bleaching and degradation product formation, and iii) finally complete chromophore bleaching. Initial conformational change is a critical prerequisite for further degradation, providing fundamental understanding of the relative stability of IDTBR and IDFBR, where the already twisted IDFBR is more prone to degradation. When blended with the donor polymer poly(3‐hexylthiophene), both NFAs exhibit improved photostability while the photostability of the polymer itself is significantly reduced by the more miscible twisted NFA. The findings elucidate the important role of NFA molecular structure in photostability of OPV systems, and provide vital insights into molecular design rules for intrinsically photostable NFAs.

This work investigates the energy and spatial properties of excess electrons in polyethylene in bulk phases and, for the first time, at amorphous vacuum interfaces using a pseudopotential single-electron method (Lanczos diagonalisation) and density functional theory (DFT). DFT calculations are made employing two approaches: with pseudopotentials/plane waves and the local-density approximation; and with all-electron Gaussian basis functions at the B3LYP level of theory, supplemented with a lattice of ghost atoms. All three methods predict similar spatial localisation of the excess electron, but a reliable comparison of its energy can only be made between the Lanczos and DFT using Gaussian bases. While Lanczos predicts that an excess electron would preferentially localise in nanovoids with diameters smaller than 1 nm, DFT suggests that it would localise on surfaces in nanovoids larger than 1 nm. Overall we conclude that in DFT studies of polyethylene/vacuum interfaces at the current level of theory, orbital-based methods provide a useful representation of excess electron properties.

International audience; A series of palladium complexes of the abnormal N-heterocyclic carbene ligands of the type (a-NHC)PdI2(L) [L = NC5H5(1–3)b and PPh3(1–3)c] effectively catalyzed the Hiyama coupling of aryl bromides and iodides with PhSi(OMe)3 under the highly desired fluoride-free conditions. Interestingly enough, the pyridine based trans-(1–3)b complexes and a PPh3 derived cis-3c complex exhibited higher yields than the related PPh3 derived trans-(1–2)c complexes. The superior performances of the pyridine based trans-(1–3)b complexes and the PPh3 derived cis-3c complex have been correlated to a tighter binding of the a-NHC ligand to the palladium center in these complexes, leading to a greater (a-NHC) ligand influence on the metal center partaking in the catalysis

A metal mediated coordination-insertion pathway for the ring-opening polymerization (ROP) of L-lactide by an ionic {(NHC)(2)Ag}(+)X(-) (X = halide) type silver complex of N-heterocyclic carbene (NHC) has been investigated using the density functional theory (DFT) method. A clear insight into the lactide insertion process could be obtained by modeling two consecutive monomer addition steps with the first one mimicking chain initiation with the second representing a propagation step. In particular, in each of the cycles, the reaction initiates with the formation of a lactide coordinated species, [1+LL] and [2+LL] that transforms into a metal bound cyclic lactide intermediate, I([1+LL] -> 2) and I([2+LL] -> 3), which subsequently ring opens to give the lactide inserted products, 2 and 3. The estimated overall activation barrier for the initiation step is 42.0 kcal mol(-1) while the same for the propagation step is 31.5 kcal mol(-1). Studies on higher monomer insertions showed a decrease in the relative product energies as anticipated for an addition polymerization pathway.

We have calculated the self-consistent Green's function for a number of atoms and diatomic molecules. This Green's function is obtained from a conserving self-energy approximation, which implies that the observables calculated from the Green's functions agree with the macroscopic conservation laws for p;article number, momentum, and energy. As a further consequence, the kinetic and potential energies agree with the virial theorem, and the many possible methods for calculating the total energy all give the same result. In these calculations we use the finite temperature formalism and calculate the Green's function on the imaginary time axis. This allows for a simple extension to nonequilibrium systems. We have compared the energies from self-consistent Green's functions to those of nonselfconsistent schemes and also calculated ionization potentials from the Green's functions by using the extended Koopmans' theorem. (c) 2005 American Institute of Physics.

Stationary points for four geometrically different states of methylene: bent and linear triplet methylene, bent and linear singlet methylene were investigated using the highly reliable post-HF CCSD(T) method. Extrapolations to the CCSD(T) basis set (CBS) limit from Dunning triple to quintuple correlation consistent polarized basis sets were performed for total energies, for the equilibrium CH distances re(CH), for singlettriplet separation energies, for energy barriers to linearity and for correlation energies. Post-HF calculations with Dunning basis sets of the literature are presented for comparisons.

A promising approach to influence and control the photophysical properties of conjugated polymers is directing their molecular conformation by templating. We explore here the templating effect of single-stranded DNA oligomers (ssDNAs) on cationic polythiophenes with the goal to uncover the intermolecular interactions that direct the polymer backbone conformation. We have comprehensively characterized the optical behavior and structure of the polythiophenes in conformationally distinct complexes depending on the sequence of nucleic bases and addressed the effect on the ultrafast excited-state relaxation. This, in combination with molecular dynamics simulations, allowed us a detailed atomistic-level understanding of the structure−property correlations. We find that electrostatic and other noncovalent interactions direct the assembly with the polymer, and we identify that optimal templating is achieved with (ideally 10−20) consecutive cytosine bases through numerous π-stacking interactions with the thiophene rings and side groups of the polymer, leading to a rigid assembly with ssDNA, with highly ordered chains and unique optical signatures. Our insights are an important step forward in an effective approach to structural templating and optoelectronic control of conjugated polymers and organic materials in general.&nbsp

We report a high molar extinction coefficient metal-free sensitizer composed of a triarylamine donor in combination with the 2-(2,2'-bithiophen-5-yl)acrylonitrile conjugation unit and cyanoacrylic acid as an acceptor. In conjugation with a volatile acetonitrile-based electrolyte or a solvent-free ionic liquid electrolyte, we have fabricated efficient dye-sensitized solar cells showing a corresponding 7.5% or 6.1% efficiency measured under the air mass 1.5 global sunlight. The ionic liquid cell exhibits excellent stability during a 1000 h accelerated test under the light-soaking and thermal dual stress. Intensity-modulated photocurrent and photovolatge spectroscopies were employed along with the transient photoelectrical decay measurements to detail the electron transport in the mesoporous titania films filled with these two electrolytes.