New chromophores based on 2-(4-vinylchromen-2-ylidene)malononitrile and 2-(2-vinylchromen-4-ylidene)malononitrile

New derivatives of 2-(4-vinylchromen-2-ylidene)malononitrile and 2-(2-vinylchromen-4-ylidene)malononitrile were synthesized using the Knoevenagel reaction of 2-(4-methyl-chromen-2-ylidene)malononitrile and 2-(2-methylchromen-4-ylidene)malononitrile, respectively, with the participation of [1-(2-n-butoxyethyl)-2,2,4,7-tetramethyl-1,2,3,4-tetrahydroquinolin-6-yl)]-carbaldehyde. First hyperpolarizability (β) was calculated for the obtained compounds using the M05-2X functional and 6-31+G (d) basis. Optical properties and solvatochromism in solvents of different polarity (toluene, 1,4-dioxane, chlorobenzene, dichloromethane, DMF, and ethanol) were also investigated.

     

Point defects patterning in irradiated α-zirconium: numerical study in the framework of the rate theory

We study point defects patterning in irradiated α-zirconium numerically. In our consideration, we exploit reaction-rate theory by taking into account sink density dynamics and a change in internal stress fields due to the presence of defects. Dynamics of defect populations are studied at different irradiation conditions. It is found that point defects patterning is accompanied by a formation of vacancy clusters; their morphology change is governed by irradiation temperature and damage rate. By using statistical analysis of spatially distributed vacancy clusters, it was shown that the characteristic size of these clusters is of several nanometers. Vacancy clusters' occupation densities and distributions over their sizes are studied in detail.     

LixV2O5 nanobelts for high capacity lithium-ion battery cathodes

5–10 μm long, typically 200–300 nm wide, and several nanometers thick Li_xV₂O₅ (× ～ 0.8) nanobelts with the δ-type crystal structure were synthesized by a hydrothermal treatment of Li⁺-exchanged V₂O₅ gel. When dried at 200 °C under vacuum prior to electrochemical testing, the as-prepared nanobelts underwent the well-known δ → ε → γ-phase transition giving a mixture of ε and γ phases as a nanocomposite electrode material. Such a simple preparation procedure guarantees a yield of material with drastically enhanced initial discharge specific capacity of 490 mAh/g and great cyclability. The enhanced electrochemical performance is attributed to the complex of experimental procedures including post-synthesis treatment of the single-crystalline Li_xV₂O₅ nanobelts.     

Communication: κ-dynamics--an exact method for accelerating rare event classical molecular dynamics

κ-dynamics is an accelerated molecular dynamics method for systems with slow transitions between stable states. Short trajectories are integrated from a transition state separating a reactant state from products. The first trajectory found that leads directly to a product without recrossing the transition state and starts in the reactant state is followed. The transition time is drawn from a distribution given by the transition state theory rate and the number of attempted trajectories. Repeating this procedure from each state visited gives a statistically exact state-to-state trajectory.     

Reactions of dibromotetrafluorobenzene derivatives with sodium phenoxide salts. Competing hydrodebromination and SNAr processes

1,2- and 1,3-dibromotetrafluorobenzene react with sodium phenoxide derivatives at sites para to ring bromine because these positions are activated by fluorine atoms ortho and meta to the site of nucleophilic substitution. Fluorine para to the site of nucleophilic attack is usually deactivating in nucleophilic aromatic substitution processes and this is reflected in the significantly reduced reactivity of 1,4-dibromotetrafluorobenzene which undergoes competing hydrodebromination processes to afford, primarily, 3-bromo-1,2,4,5-tetrafluorobenzene.     

Accelerating Reactive Transport Modeling: On-Demand Machine Learning Algorithm for Chemical Equilibrium Calculations

Transport in Porous Media - During reactive transport modeling, the computing cost associated with chemical equilibrium calculations can be 10 to 10,000 times higher than that of fluid flow, heat...     

π‐Extended Indenofluorenes

A series of π‐extended aromatic indenofluorene (IF) analogues with naphthalene and anthracene cores have been synthesized through acid‐catalyzed intramolecular cyclization. The regioselectivity of the reaction is controlled by a combination of steric and electronic factors and in some cases several possible regioisomers have resulted from the same precursor. The effects of ring connectivity on the optoelectronic properties were investigated by DFT calculations, absorption/emission spectroscopy, cyclic voltammetry, and spectroelectrochemical studies. All regioisomers exhibited a redshift of their absorption/emission bands relative to the parent IF analogues, but the magnitude of this shift and other optoelectronic properties (luminescence quantum yield, etc.) depends on the ring connectivity in a less obvious manner.     

Asymptotic Expansions for Stationary Distributions of Nonlinearly Perturbed Semi-Markov Processes. 1

Methodology and Computing in Applied Probability - New algorithms for construction of asymptotic expansions for stationary distributions of nonlinearly perturbed semi-Markov processes with finite...