Luminescent Self-Assembled Monolayer on Gold Nanoparticles: Tuning of Emission According to the Surface Curvature

Until now, the ability to form a self-assembled monolayer (SAM) on a surface has been investigated according to deposition techniques, which in turn depend on surface-coater interactions. In this paper, we pursued two goals: to form a SAM on a gold nanosurface and to correlate its formation to the nanosurface curvature. To achieve these objectives, gold nanoparticles of different shapes (spheres, rods, and triangles) were functionalized with a luminescent thiolated bipyridine (Bpy-SH), and the SAM formation was studied by investigating the photo-physics of Bpy-SH. We have shown that emission wavelength and excited-state lifetime of Bpy-SH are strongly correlated to the formation of specific aggregates within SAMs, the nature of these aggregates being in close correlation to the shape of the nanoparticles. Micro-Raman spectroscopy investigation was used to test the SERS effect of gold nanoparticles on thiolated bipyridine forming SAMs.

Structure of a Fe4O6-Heteraadamantane-Type Hexacation Stabilized by Chelating Organophosphine Oxide Ligands

Metal-containing heteraadamantanes are compounds of interest due to their spectroscopic and magnetic properties, which make them promising materials for non-linear optics and semiconductors. Herein we report the comprehensive structural characterization of a new coordination compound of the formula [(µ-OH′)₂(µ-OH″)₄(O = P(Ph₂)CH₂CH₂(Ph₂)P = O)₄{Fe(t-BuOH)}₄](PF₆)₄(Cl)₂ with the chelating ligand Ph₂P(O)-CH₂CH₂-P(O)Ph₂. The compound crystallizes as a polynuclear metal complex with the adamantane-like core [Fe₄O₆] in the space group I-43d of a cubic system. The single-crystal XRD analysis showed that the crystal contains one symmetrically independent octahedrally coordinated Fe atom in the oxidation state +3. The adamantine-like scaffold of the Fe complex is formed by hydroxy bridging oxygen atoms only. Hirshfeld surface analysis of the bridging oxygen atoms revealed two types of µ-OH groups, which differ in the degree of exposure and participation in long-range interactions. Additionally, the Hirshfeld surface analysis supported by the enrichment ratio calculations demonstrated the high propensity of the title complex to form C-H^…Cl, C-H^…F and C-H^…O interactions.

Determining Factor on the Polarization Behavior of Magnesium Deposition for Magnesium Battery Anode

To clarify the origin of the polarization of magnesium deposition/dissolution reactions, we combined electrochemical measurement, operando soft X-ray absorption spectroscopy (operando SXAS), Raman, and density functional theory (DFT) techniques to three different electrolytes: magnesium bis(trifluoromethanesulfonyl)amide (Mg(TFSA)₂)/triglyme, magnesium borohydride (Mg(BH₄)₂)/tetrahydrofuran (THF), and Mg(TFSA)₂/2-methyltetrahydrofuran (2-MeTHF). Cyclic voltammetry revealed that magnesium deposition/dissolution reactions occur in Mg(TFSA)₂/triglyme and Mg(BH₄)₂/THF, while the reactions do not occur in Mg(TFSA)₂/2-MeTHF. Raman spectroscopy shows that the [TFSA]^- in the Mg(TFSA)₂/triglyme electrolyte largely does not coordinate to the magnesium ions, while all of the [TFSA]^- in Mg(TFSA)₂/2-MeTHF and [BH₄]^- in Mg(BH₄)₂/THF coordinate to the magnesium ions. In operando SXAS measurements, the intermediate, such as the Mg⁺ ion, was not observed at potentials above the magnesium deposition potential, and the local structure distortion around the magnesium ions increases in all of the electrolytes at the magnesium electrode|electrolyte interface during the cathodic polarization. Our DFT calculation and X-ray photoelectron spectroscopy results indicate that the [TFSA]^-, strongly bound to the magnesium ion in the Mg(TFSA)₂/2-MeTHF electrolyte, undergoes reduction decomposition easily, instead of deposition of magnesium metal, which makes the electrolyte inactive electrochemically. In the Mg(BH₄)₂/THF electrolyte, because the [BH₄]^- coordinated to the magnesium ions is stable even under the potential of the magnesium deposition, the magnesium deposition is not inhibited by the decomposition of [BH₄]^-. Conversely, because [TFSA]^- is weakly bound to the magnesium ion in Mg(TFSA)₂/triglyme, the reduction decomposition occurs relatively slowly, which allows the magnesium deposition in the electrolyte.

Liquid Structures and Transport Properties of Lithium Bis(fluorosulfonyl)amide/Glyme Solvate Ionic Liquids for Lithium Batteries

The liquid structures and transport properties of electrolytes composed of lithium bis(fluorosulfonyl)amide (Li[FSA]) and glyme (triglyme (G3) or tetraglyme (G4)) were investigated. Raman spectroscopy indicated that the 1:1 mixtures of Li[FSA] and glyme (G3 or G4) are solvate ionic liquids (SILs) comprising a cationic [Li(glyme)]+ complex and the [FSA]− anion. In Li[FSA]-excess liquids with Li[FSA]/glyme molar ratios greater than 1, anionic Lix[FSA]y(y–x)– complexes were formed in addition to the cationic [Li(glyme)]+ complex. Pulsed field gradient NMR measurements revealed that the self-diffusion coefficients of Li+ (DLi) and glyme (Dglyme) are identical in the Li[FSA]/glyme=1 liquid, suggesting that Li+ and glyme diffuse together and that a long-lived cationic [Li(glyme)]+ complex is formed in the SIL. The ratio of the self-diffusion coefficients of [FSA]− and Li+, DFSA/DLi, was essentially constant at ~1.1–1.3 in the Li[FSA]/glyme<1 liquid. However, DFSA/DLi increased rapidly as the amount of Li[FSA] increased in the Li[FSA]/glyme>1 liquid, indicating that the ion transport mechanism in the electrolyte changed at the composition of Li[FSA]/glyme=1. The oxidative stability of the electrolytes was enhanced as the Li[FSA] concentration increased. Furthermore, Al corrosion was suppressed in the electrolytes for which Li[FSA]/glyme>1. A battery consisting of a Li metal anode, a LiNi1/3Mn1/3Co1/3O2 cathode, and Li[FSA]/G3=2 electrolyte exhibited a discharge capacity of 105mAhg−1 at a current density of 1.3mAcm−2, regardless of its low ionic conductivity of 0.2mScm−1.

Li+ solvation in glyme–Li salt solvate ionic liquids

Raman spectra and electrode potentials corroborated that glyme–Li salt solvate ionic liquids consist of crown-ether like complex cations and counter anions with a few uncoordinated glyme molecules in the liquid state.

Structure and energetics of poly(ethylene glycol) cationized by Li(+), Na(+), K(+) and Cs(+): a first-principles study

Density functional theoretical methods, including several basis sets and two functional, were used to collect information on the structure and energetic parameters of poly(ethylene glycol) (PEG), also referred to as poly(ethylene oxide) (PEO), coordinated by alkali metal ions. The oligomer chain is found to form a spiral around the alkali cation, which grows to roughly two helical turns when the oligomer size increases to about the decamer for each alkali ion. Above this size, the additional monomer units do not build the spiral further for Li(+) and Na(+); instead, they form less organized segments outside or next to the initial spiral. The distance of the first layer of co-ordinating O atoms from the alkali cation is 1.9-2.15 Å for Li(+), 2.3-2.5 Å for Na(+), 2.75-3.2 Å for K(+) and 3.5-3.8 Å for Cs(+) complexes. The number of O atoms in the innermost shell is five, six, seven and eleven for Li(+), Na(+), K(+) and Cs(+). The collision cross sections with He increase linearly with the oligomer to a very good approximation. No sign of leaning towards the 2/3 power dependence characterizing spherical particles is observed. The binding energy of the cation to the oligomer increases up to polymerization degree of about 10, where it levels off for each alkali-metal ion, indicating that this is approximately the limit of the oligomer size that can be influenced by the alkali cation. The binding energy-degree of polymerization curves are remarkably parallel for the four cations. The limiting binding energy at large polymerization degrees is about 544 kJ mol(-1), 460 kJ mol(-1), 356 kJ mol(-1) and 314 kJ mol(-1) for Li, Na, K and Cs, respectively. The geometrical features are compared with the X-ray and neutron diffraction data on crystalline and amorphous phases of conducting polymers formed by alkali-metal salts and PEG. The implications of the observations concerning collision cross sections and binding energies to ion mobility spectroscopy and mass spectrometry are discussed.

Conformation of poly(ethylene oxide) chains in clay galleries

The conformation and arrangement of poly(ethylene oxide) (PEO) chains in clay galleries is still controversial. In our work, various spectroscopic methods have been used to explore the conformation of PEO in clay galleries. The melt intercalation process is investigated using variable-temperature Raman spectroscopy. It is found that the sharp peak at 860 cm(-1) appears with an increase of the intercalation time, suggesting the formation of a crown-ether-like association between the cations and the PEO oxygen atoms. Two-dimensional infrared correlation analysis also suggests the presence of the crown-ether-like association between them. Therefore, a distorted helical conformation may be a more accurate way to describe the conformation of the PEO chains in the clay galleries, and a single-layer arrangement is suggested.

Molecular dynamics simulation of the polymer electrolyte poly(ethylene oxide)/LiClO4. II. Dynamical properties

The dynamical properties of the polymer electrolyte poly(ethylene oxide) (PEO)LiClO(4) have been investigated by molecular dynamics simulations. The effect of changing salt concentration and temperature was evaluated on several time correlation functions. Ionic displacements projected on different directions reveal anisotropy in short-time (rattling) and long-time (diffusive) dynamics of Li(+) cations. It is shown that ionic mobility is coupled to the segmental motion of the polymeric chain. Structural relaxation is probed by the intermediate scattering function F(k,t) at several wave vectors. Good agreement was found between calculated and experimental F(k,t) for pure PEO. A remarkable slowing down of polymer relaxation is observed upon addition of the salt. The ionic conductivity estimated by the Nernst-Einstein equation is approximately ten times higher than the actual conductivity calculated by the time correlation function of charge current.