pinecone/core-2020-05-10-deduplication huggingface dataset:
Chemical Bonding of Transition-metal Co$_{13}$ Clusters with Graphene

We carried out density functional calculation to study Co$_{13}$ clusters on
graphene. We deposit several free isomers in different disposition respect to
hexagonal lattice nodes, studying even the $hcp$ $2d$ isomer recently obtained
as the most stable one. Surprisingly, Co$_{13}$ clusters bonded to graphene
prefer $icosahedron-like$ structures where the low lying isomer is much
distorted, because it is linked with more bonds than in previous works. For any
isomer the most stable position binds to graphene by the Co atoms that can lose
electrons. We find that the charge transfers between graphene and clusters are
small enough to conclude that the Co-graphene binding is not ionic-like but
chemical. Besides, the same order of stability among the different isomers on
doped graphene is well kept. These findings could also be of interest for
magnetic clusters on graphenic nanostructures such as ribbons and nanotubes.Comment: 12 pages, 6 figure
Strategies for controlled electronic doping of colloidal quantum dots

Over the last several years tremendous progressed progress has been made in incorporating\ud
Colloidal Quantum Dots (CQDs) as photoactive components in optoelectronic devices. A\ud
significant part of that progress is associated with significant advancements made in\ud
achievingon controlled electronic doping of the CQDs and thus improving the electronic\ud
properties of CQDs solids. Today, a variety of strategies exists towards that purpose and this\ud
minireview aims at surveying major published works in this subject. Additional attention is\ud
given to the many challenges associated with the task of doping CQDs as well as to the\ud
optoelectronic functionalities and applications being realized when successfully achieving light\ud
and heavy electronic doping of CQDs.Peer ReviewedPostprint (author's final draft
Successive translocation of the rings in a [3]rotaxane

This research was financially supported by the Netherlands Organization for the Advancement of Research (NOW).A [2]rotaxane, a [3]rotaxane and the corresponding thread containing two succinamide (succ) binding stations and a central redox-active pyromellitimide (pmi) station were studied. Infrared spectroelectrochemical experiments revealed the translocation of the macrocycle between the succinamide station and the electrochemically reduced pmi station (radical anion and dianion). Remarkably, in the [3]rotaxane, the rings can be selectively translocated. One-electron reduction leads to the translocation of one of the two macrocycles from the succinamide to the pyromellitimide station, whereas activation of the shuttle through two-electron reduction results in the translocation of both macrocycles: the dianion, due to its higher electron density and hence greater hydrogen-bond accepting affinity, is hydrogen bonded to both macrocycles. Systems with such an on-command contraction are known as molecular muscles. The relative strengths of the binding between the macrocycle and the imide anions could be estimated from the hydrogen-bond-induced shifts in the C=O stretching frequencies of hydrogen-bond accepting amide groups of the macrocycle.PostprintPeer reviewe
Improvement of molecular gel formation efficiency by adjusting preorganization of amino acid-derived flexible molecules. A NMR and thermodynamic study

The efficiency of the formation of molecular gels of simple de-rivatives of l-valineand l-isoleucine is greatl yimproved in dif-ferent organic solvents when ahexyl fragment is replaced byabulkier cyclohexyl one. Astudy using NMR and IR spectrosco-py provides information on the preferred conformation softhemolecules, indicat ing that the cyclohexyl moiety preclud es in-tramolecular Hbondingand preorganises the system for inter-molecular interactions, which are responsible for fiber forma-tion. NMR data of the gels provides thermod ynamic data on fi-brillization, revealing that the origin of this effect is mainly en-tropic. Electron microscopy (SEM and TEM) images show fibril-lar and tape-like objects, which are observed commonly inmolecular gels. Rheological measurements revealsignificantdifferences between cyclohexyl and hexyl appendedgelators.These findings could contribute to the rational design of small,flexible, buildingblocks forself-assemblyMinistry of Science and Innovat ionofSpain (grantCTQ2012-37735) and UniversitatJaume I(grant P1.1B2012-25) are thankedfor financial support
Fabrication of a high-quality, porous, surface-confined covalent organic framework on a reactive metal surface

Funding: EPSRC DTA (EP/M506631/1)A major goal of heterogeneous catalysis is to optimize catalytic selectivity. Selectivity is often limited by the fact that most heterogeneous catalysts possess sites with a range of reactivities, resulting in the formation of unwanted by-products. The construction of surface-confined covalent organic frameworks (sCOFs) on catalytically active surfaces is a desirable strategy, as pores can be tailored to operate as catalytic nanoreactors. Direct modification of reactive surfaces is impractical, because the strong molecule–surface interaction precludes monomer diffusion and formation of extended architectures. Herein, we describe a protocol for the formation of a high-quality sCOF on a Pd-rich surface by first fabricating a porous sCOF through Ullmann coupling on a Au-rich bimetallic surface on Pd(111). Once the sCOF has formed, thermal processing induces a Pd-rich surface while preserving the integrity of the sCOF architecture, as evidenced by scanning tunneling microscopy and titration of Pd sites through CO adsorption.Publisher PDFPeer reviewe
Production of ultracold 87Rb133Cs in the absolute ground state : complete characterisation of the STIRAP transfer.

We present the production of ultracold 87 RbCs molecules in the electronic, rovibrational and hyperfine ground state, using stimulated Raman adiabatic passage to transfer the molecules from a weakly bound Feshbach state. We measure one-way transfer efficiencies of 92(1)% and fully characterise the strengths and linewidths of the transitions used. We model the transfer, including a Monte Carlo simulation of the laser noise, and find this matches well with both the transfer efficiency and our previous measurements of the laser linewidth and frequency drifts
Thermometry of Guided Molecular Beams from a Cryogenic Buffer-Gas Cell

We present a comprehensive characterization of cold molecular beams from a
cryogenic buffer-gas cell, providing an insight into the physics of buffer-gas
cooling. Cold molecular beams are extracted from a cryogenic cell by
electrostatic guiding, which is also used to measure their velocity
distribution. Molecules' rotational-state distribution is probed via
radio-frequency resonant depletion spectroscopy. With the help of complete
trajectory simulations, yielding the guiding efficiency for all of the
thermally populated states, we are able to determine both the rotational and
the translational temperature of the molecules at the output of the buffer-gas
cell. This thermometry method is demonstrated for various regimes of buffer-gas
cooling and beam formation as well as for molecular species of different sizes,
$\rm{CH_3F}$ and $\rm{CF_3CCH}$. Comparison between the rotational and
translational temperatures provides evidence of faster rotational
thermalization for the $\rm{CH_3F-He}$ system in the limit of low He density.
In addition, the relaxation rates for different rotational states appear to be
different
Exploring the loading capacity of generation six to eight dendronized polymers in aqueous solution

Aspects of size, structural (im)perfection, inner density, and guest loading capacity of dendronized polymers (DPs) of high generation g (6≤g≤8) in aqueous solution were studied using electron paramagnetic resonance (EPR) spectroscopy on amphiphilic, spin- labeled guest molecules. The presented results show that the interior of the charged DPs is strongly polar, especially in comparison to their lower generation analogues 1-4. This is a direct sign of large amounts of water penetrating the DP surface, which in return mirrors structural imperfections and much lower than theoretically achievable segmental densities of these high generation DPs. Images obtained with atomic force microscopy (AFM) reveal that the high g DPs show no aggregation and give further insights into structural (im)perfections. EPR- spectroscopic data further show that despite their structural imperfections, these DPs can bind and release large numbers of amphiphilic molecules. It can be concluded that attention should be paid to synthesis which needs to develop a protocol that avoids the relatively large amount of defects generated in the direct conversion of PG4 to PG6 which had to be employed here
Herringbone Pattern and CH–π Bonding in the Crystal Architecture of Linear Polycyclic Aromatic Hydrocarbons

The herringbone pattern is a pervasive structural motive found in most molecular crystals involving aromatic compounds. A plot of the experimental sublimation enthalpies of members of increasing size of the acene, phenacene and p-phenyl families versus the number of carbons uncovers a linear relationship between the two magnitudes, suggesting a major role of CH–π bonding. In this work we undertake the task of evaluating the relevance of the edge-to-face interaction (or CH–π bond) in the overall reticular energy of the crystal, to quantitatively assess the importance of this structural element. Following a heuristic approach, we considered the series of acenes, phenacenes and p-phenyls and analyzed the edge-to-face interaction between the molecules as they occur in the experimental crystal network. Isolation of the relevant molecular dimers allows to incorporate some of the most sophisticated tools of quantum chemistry and get a reliable picture of the isolated bond. When compared to the experimental sublimation energy, our results are conclusive: this sole interaction is the largest contribution to the lattice energy, and definitively dictates the crystal architecture in all the studied cases. Elusive enough, the edge-to-face interaction is mainly dominated by correlation interactions, specifically in the form of dispersion and, to a less extent, of charge-transfer terms. A suggestive picture of the bond has been obtained by displaying the differences in local electron densities calculated by either correlated or non-correlated methods.Financial support by the spanish “Ministerio de Ciencia e Innovación MICINN” (grants CTQ2011-24165, FIS2012-33521 and FIS2012-35880) and the Universidad de Alicante is gratefully acknowledged. We also acknowledge support from the DGUI of the Comunidad de Madrid under the R&D Program of activities MODELICO-CM/S2009ESP-1691
A Dynamic Ion-Atom Hybrid Trap for High-Resolution Cold-Collision Studies

We present a dynamic ion-atom hybrid trap for studies of cold ion-neutral collisions and reactions with a significantly improved energy resolution compared with previous experiments. Our approach is based on pushing a cloud of laser-cooled Rb atoms through a stationary Coulomb crystal of cold ions by using precisely controlled, tunable radiation pressure forces. We demonstrate the tuning of the atom kinetic energies over an interval ranging from 30 mK up to 350 mK with energy spreads as low as 24 mK, inferred from the comparison of experimental time-of-flight measurements with Monte Carlo trajectory simulations. We also demonstrate the first applications of our method to the investigation of chemical reactions. Our development opens up perspectives for accurate studies of the energy dependence of the reaction rates, the dynamics, and the reaction-product ratios of the ion-neutral processes in the cold regime. It also paves the way for the realization of fully energy- and state-controlled cold-collision experiments
Vibronic spectroscopy of sympathetically cooled CaH$^+$

We report the measurement of the 1$^{1}\Sigma\longrightarrow$ 2$^{1}\Sigma$
transition of CaH$^+$ by resonance-enhanced photodissociation of CaH$^+$ that
is co-trapped with laser-cooled Ca$^+$ . We observe four resonances that we
assign to transitions from the vibrational $v$=0 ground state to the $v'$=1-4
excited states based on theoretical predictions. A simple theoretical model
that assumes instantaneous dissociation after resonant excitation yield results
in good agreement with the observed spectral features except for the unobserved
$v'$=0 peak. The resolution of our experiment is limited by the mode-locked
excitation laser, but this survey spectroscopy enables future rotationally
resolved studies with applications in astrochemistry and precision measurement.Comment: pre-peer-reviewed version of R. Rugango et al. ChemPhysChem, (Early
  online see DOI) (2016). Peer-reviewed version will be arxived after the
  embargo perio
The iImportance of vibronic coupling for efficient reverse intersystem crossing in thermally activated delayed fluorescence molecules.

Factors influencing the rate of reverse intersystem crossing (krISC) in thermally activated delayed fluorescence (TADF) emitters are critical for improving the efficiency and performance of third-generation heavy-metal-free organic light-emitting diodes (OLEDs). However, present understanding of the TADF mechanism does not extend far beyond a thermal equilibrium between the lowest singlet and triplet states and consequently research has focused almost exclusively on the energy gap between these two states. Herein, we use a model spin-vibronic Hamiltonian to reveal the crucial role of non-Born-Oppenheimer effects in determining krISC. We demonstrate that vibronic (nonadiabatic) coupling between the lowest local excitation triplet (3LE) and lowest charge transfer triplet (3CT) opens the possibility for significant second-order coupling effects and increases krISC by about four orders of magnitude. Crucially, these simulations reveal the dynamical mechanism for highly efficient TADF and opens design routes that go beyond the Born-Oppenheimer approximation for the future development of high-performing systems
Quantum Transport Characteristics of Lateral pn-Junction of Single Layer
  TiS3

Using density functional theory and nonequilibrium Greens functions-based
methods we investigated the electronic and transport properties of monolayer
TiS3 pn-junction. We constructed a lateral pn-junction in monolayer TiS3 by
using Li and F adatoms. An applied bias voltage caused significant variability
in the electronic and transport properties of the TiS3 pn-junction. In
addition, spin dependent current-voltage characteristics of the constructed
TiS3 pn-junction were analyzed. Important device characteristics were found
such as negative differential resistance and rectifying diode behaviors for
spin-polarized currents in the TiS3 pn-junction. These prominent conduction
properties of TiS3 pn-junction offer remarkable opportunities for the design of
nanoelectronic devices based on a recently synthesized single-layered material
New method to study ion-molecule reactions at low temperatures and
  application to the H$_2^+$ + H$_2$ $\rightarrow$ H$_3^+$ + H reaction

Studies of ion-molecule reactions at low temperatures are difficult because
stray electric fields in the reaction volume affect the kinetic energy of
charged reaction partners. We describe a new experimental approach to study
ion-molecule reactions at low temperatures and present, as example, a
measurement of the ${\rm H}_2^+ + {\rm H}_2\rightarrow {\rm H}_3^+ + {\rm H}$
reaction with the ${\rm H}_2^+$ ion prepared in a single rovibrational state at
collision energies in the range $E_{\rm col}/k_{\rm B} = 5$-60 K. To reach such
low collision energies, we use a merged-beam approach and observe the reaction
within the orbit of a Rydberg electron, which shields the ions from stray
fields. The first beam is a supersonic beam of pure ground-state H$_2$
molecules and the second is a supersonic beam of H$_2$ molecules excited to
Rydberg-Stark states of principal quantum number $n$ selected in the range
20-40. Initially, the two beams propagate along axes separated by an angle of
10$^\circ$. To merge the two beams, the Rydberg molecules in the latter beam
are deflected using a surface-electrode Rydberg-Stark deflector. The collision
energies of the merged beams are determined by measuring the velocity
distributions of the two beams and they are adjusted by changing the
temperature of the pulsed valve used to generate the ground-state ${\rm H}_2$
beam and by adapting the electric-potential functions to the electrodes of the
deflector. The collision energy is varied down to below $E_{\rm col}/k_{\rm B}=
10$ K, i.e., below $E_{\rm col}\approx 1$ meV, with an energy resolution of 100
$\mu$eV. We demonstrate that the Rydberg electron acts as a spectator and does
not affect the cross sections, which are found to closely follow a
classical-Langevin-capture model in the collision-energy range investigated.
Because all neutral atoms and molecules can be excited to Rydberg states, this
method of studyingComment: 39 pages, 10 figure
Rationalising heteronuclear decoupling in refocussing applications of solid-state NMR.

Factors affecting the performance of 1H heteronuclear decoupling sequences for magic-angle spinning (MAS) NMR spectroscopy of organic solids are explored, as observed by time constants for the decay of nuclear magnetisation under a spin-echo (math formula ). By using a common protocol over a wide range of experimental conditions, including very high magnetic fields and very high radio-frequency (RF) nutation rates, decoupling performance is observed to degrade consistently with increasing magnetic field. Inhomogeneity of the RF field is found to have a significant impact on math formula values, with differences of about 20 % observed between probes with different coil geometries. Increasing RF nutation rates dramatically improve robustness with respect to RF offset, but the performance of phase-modulated sequences degrades at the very high nutation rates achievable in microcoils as a result of RF transients. The insights gained provide better understanding of the factors limiting decoupling performance under different conditions, and the high values of math formula observed (which generally exceed previous literature values) provide reference points for experiments involving spin magnetisation refocussing, such as 2D correlation spectra and measuring small spin couplings
Color fine-tuning of optical materials through rational design

This is the pre-peer reviewed version of the following article: HOLZER, B. ...et al., 2017. Color fine-tuning of pptical materials through rational design. ChemPhysChem, 18(5), pp. 549-563, which has been published in final form at https://doi.org/10.1002/cphc.201601204. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim We report on the feasibility for color fine-tuning of optical materials using rational design principles based on chemical reasoning. For this purpose, a modular framework for the construction of symmetrical cap-linker-cap compounds, using triarylamine caps and oligothiophene linkers, is applied. The chosen structural scaffolds are heavily used in recent industrial applications and provide five possibilities for altering their electronic and steric properties: electron donor/acceptor groups, planarization/deplanarization, and modulation of the π-conjugation length. Permutation of the used building blocks leads to a set of 54 different molecules, out of which 32 are synthesized and characterized in solution as well as in example fabricated OLED devices. This setup allows for color fine-tuning in the range of 412 nm to 540 nm with typical steps of 4 nm. In addition, to further benefit from the large experimental data set the spectroscopic results are used to benchmark quantum chemical computations, which show excellent agreement thus highlighting the potential of these calculations to guide future syntheses
Magneto-Structural Characterization of Oxalamide Dihalo-Bridged Copper Dimers: Intra- and Interdimer Interactions Studied by Single Crystal ESR Spectroscopy

The detailed single crystal electron spin resonance (ESR) analysis of oxalamide complexes with halogen-bridged copper dimers, supported by X-ray, magnetic susceptibility and powder ESR studies, is reported. Four complexes with two different ligands were synthesized: [CuLA(μ-X)]2 and [CuLV(μ-X)]2, where LA = N-(L-alanine methyl ester)-N’-((2-pyridine-2-yl)methyl)oxalamide and LV=N-(L-valine methyl ester)-N’-((2-pyridine- 2-yl)methyl)oxalamide, while X=Cl or Br. X-ray analysis shows that geometry at each copper(II) ion is square pyramidal while two pyramids share one base-to-apex edge with parallel basal planes. The complexes are linked by hydrogen bonds into infinite chains and further into a 3D network. Susceptibility measurements show that coppers in dimers are weakly antiferromagnetically coupled (|J| = 1 − 2 cm−1). From powder ESR, g-values and dx2−y2 orbital as the ground state of unpaired electron are determined. The complexes show unusual anisotropic splitting and merging of ESR lines when their single crystals rotate in magnetic field. The observation of this partially resolved intradimer dipolar splitting enabled estimation of weak interdimer exchange interaction parameter |J0| = 0.001 cm−1
A Hydrogel/Carbon-Nanotube Needle-Free Device for Electrostimulated Skin Drug Delivery

The permeability of skin allows passive diffusion across the epidermis to reach blood vessels but this is possible only for small molecules such as nicotine. In order to achieve transdermal delivery of large molecules such as insulin or plasmid DNA, permeability of the skin and mainly the permeability of stratum corneum has to be increased. Moreover, alternative routes that avoid the use of needles will improve the quality of life of patients. A method named “electropermeabilization” has been shown to increase skin permeability. Here, we report the fabrication of an innovative hydrogel, made of nanocomposite material. This nanocomposite device aims at permeabilizing the skin and delivering drug molecules at the same time. It includes a biocompatible polymer matrix (hydrogel) and double walled-carbon-nanotubes (DWCNTs) in order to bring electrical conductivity and improve mechanical properties. Carbon nanotubes and especially DWCNTs are ideal candidates, combining high electrical conductivity with a very high specific surface area together with a good biocompatibility when included into a material. The preparation and characterization of the nanocomposite hydrogel as well as first results of electro stimulated transdermal delivery using an ex vivo mouse skin model are presented
Monitoring complex formation by relaxation-induced pulse electron paramagnetic resonance distance measurements

Funding: EPSRC DTC and Wellcome (099149/Z/12/Z).Biomolecular complexes are often multimers fueling the demand for methods that allow unraveling their composition and geometric arrangement. Pulse electron paramagnetic resonance (EPR) spectroscopy is increasingly applied for retrieving geometric information on the nanometer scale. The emerging RIDME (relaxation-induced dipolar modulation enhancement) technique offers improved sensitivity in distance experiments involving metal centers (e.g. on metalloproteins or proteins labelled with metal ions). Here, a mixture of a spin labelled ligand with increasing amounts of paramagnetic CuII ions allowed accurate quantification of ligand-metal binding in the model complex formed. The distance measurement was highly accurate and critical aspects for identifying multimerization could be identified. The potential to quantify binding in addition to the high-precision distance measurement will further increase the scope of EPR applications.Publisher PDFPeer reviewe