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In situ photoemission and near edge X-ray absorption fine structure (NEXAFS) techniques have been used to study the interaction of CO2 with an ionic liquid thin film. A thin film of the superbasic ionic liquid (SBIL) trihexyltetradecylphosphonium benzimidazolide ([P66614][benzim]) was prepared on a rutile TiO2 (110) surface and exposed to CO2 at near-ambient pressures. NEXAFS measurements combined with density functional theory calculations indicate a realignment of [benzim]- anions from 27° from the surface normal to 54° upon exposure to CO2. Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) shows evidence of irreversible CO2 absorption in thin films of [P66614][benzim] and a greater concentration of CO2-reacted anions in the deeper layers. These results give a new perspective on CO2 uptake in ionic liquids and fundamental interactions at the liquid-gas interface. Understanding this interfacial behaviour is important for developing ILs for gas capture applications and may influence the performance of other IL-based technologies.

We describe the growth and characterization of 10 nm to 10 micron-scale islands created by depositing Ag onto Si(111) at elevated temperatures. By varying the surface coverage of Ag, we are able to produce and control the distribution of Ag(111) and/or Ag(100) single-crystal islands. These were examined using scanning tunneling microscopy (STM), X-ray diffraction (XRD), helium ion microscopy (HIM), and atomic force microscopy. The formation of 3D islands with orientations of either (111) or (100) was confirmed by STM and XRD analysis. As these islands manifest as tiny single crystals of elemental Ag, they can be ideally used as low-cost or disposable substrates to host molecular architectures; we demonstrate this by comparing absorption and thermal behavior of 1,3,5-benzenetricarboxylic acid molecules on the islands and noting identical behavior and reactivity to experiments performed on Ag single-crystal counterparts. These islands provide an economical and practical method for facilitating molecular adsorption on two distinct microsubstrates at the same time while under identical experimental conditions.

The molecular characteristics, stacking structure, and magnetic properties of Tb-phthalocyanine (TbPc2) with and without the absorption of CH2Cl2 molecules were systematically investigated. The fir...

In this study, cationic local structures in the series of MgAl2O4–NiAl2O4 solid solutions (Mg1-xNixAl2O4) were examined using Mg, Al, and Ni K-edge X-ray absorption near-edge structure (XANES). The...

Infrared (IR) absorption and Raman spectra of methane hydrate (MH) were measured at low temperatures and high pressures to reveal the dynamics and cage occupancy of CH4 molecules and the hydration ...

The optical properties of two sets of donor-acceptor-donor molecules with terminal bithiophene donor units and a central diketopyrrolopyrrole (DPP) acceptor unit are studied. The two sets differ in the alkyl chains on the DPP, which are either branched at the α-carbon (3-pentyl) (1-4) or linear (n-hexyl) (5-8). Within each set, the molecules differ by the absence or presence of n-hexyl chains on the terminal thiophene rings in the 3′, 4′, or 5′ positions. While in solution, the optical spectra differ only subtly; they differ dramatically in the solid state. In contrast to 5-8, 1-4 are nonplanar as a consequence of the sterically demanding 3-pentyl groups, which inhibit π-stacking of the DPP units. Using the crystal structures of 2 (brick layer stacking) and 6 (slipped stacking), we quantitatively explain the solid state absorption spectra. By computing the molecular transition charge density and solving the dispersion relation, the optical absorption of the molecules in the crystal is predicted and in agreement with experiments. For 2, a single resonance frequency is obtained, while for 6 two transitions are seen, with the lower-energy transition being less intense. The results demonstrate how subtle changes in substitution exert large effects in optical properties.

Mixed-metal oxides, AM2C6Te3O18 (A = Pb, Sr; M = Mn, Cd; C = Ni, Co), have been synthesized employing traditional solid-state methods. The prepared compounds were characterized by powder X-ray diffraction (PXRD) and the structures refined by Rietveld analysis. The optical absorption studies of the compounds were carried out employing UV–vis spectroscopy and the observed transitions were assigned to the octahedral transition metal ions. Magnetic studies were carried out on PbCd2Co6Te3O18, SrCd2Co6Te3O18, and SrCd2Ni6Te3O18, which indicated that the compounds order antiferromagnetically around 10 K. Computational approaches were employed to fit the observed magnetic behavior.

Photophysical and diffusion properties of excitons generated in perylene and pyrene nanoaggregates have been investigated using steady state as well as time-resolved absorption and emission spectro...

Pressure-driven permeation of water in a poorly wettable material results in a conversion of mechanical work into surface free energy representing a new form of energy storage or absorption. When w...

The release of the radioisotope 131I represents a major health concern because of its absorption by the thyroid gland. Capture materials, such as activated carbon, provide a means to efficiently mi...

We have characterized the surface of a single-atom alloy consisting of a low coverage of Pd deposited onto a Ag(111) surface. For this purpose, we used reflection absorption infrared spectroscopy (...

By compressing the organic solid luminescent material 2,7-di(naphthalen-1-yl)fluorenone (1-DNFO), a consecutive and massive modulation of its UV–vis absorption and photoluminescence spectra has bee...

The gold nanoparticle exhibits strong absorption and emission due to its unique physical geometry and surface plasmon resonance phenomena. The current investigation illustrates a unique preparation...

Singlet fission (SF) creates two triplet excitons following absorption of a photon by two electronically interacting chromophores. Quaterrylene-3,4:13,14-bis(dicarboximide) (QDI) is a strongly absorbing chromophore that readily fulfills the energetic requirements for SF, E(S1) > 2E(T1), and thus should undergo rapid and efficient SF. SF was studied in thin films of the QDI derivative N,N-bis(2,6-diisopropylphenyl)-QDI (ArQDI), which undergoes SF in

Temperature-dependent short-range structural evolution of Au44Ga56 liquid eutectic alloy has been studied by in situ extended X-ray absorption fine structure (EXAFS), in situ high-energy X-ray diffraction (HEXRD) together with first-principles molecular dynamics (FPMD) simulations. It is found that the short-range structure of Au44Ga56 liquid strongly inherits the local atomic packing of the AuGa compound. A short-range structural change in Ga-centered clusters is revealed by in situ EXAFS data at the Ga K-edge at about 970 K, while no such change in Au-centered clusters appears at the Au LIII-edge. The in situ HEXRD and FPMD simulations also confirm the existence of a liquid-to-liquid crossover (LLC) in the Au44Ga56 liquid at a temperature range of about 1000–1100 K, mainly lying in the local structural change around Ga atoms. Indeed, the alloys quenched from the liquid phases below 1000 K and above 1100 K exhibit differences in structure and magnetic properties, which opens a possibility to fabricate ne...

Inthis work, we focus on macrocyclic structures comprised of two dihydroazulene (DHA) units and one azobenzene (AZB) unit and the possibility for photoisomerizing one unit selectively by tuning the excitation energies of each individual unit. An unfortunate overlap between the absorption bands of DHA and AZB as well as trans-and cis-AZB prevents us to have a full control onthese macrocyclic structures, and their absorption bands need to be separated. By means of time-dependent density-functional theory calculations, we investigate the effects of ortho substitutions of the AZB unitby fluorine and chlorine atoms on the absorption spectra of the DHA/AZB macrocycles. The calculations on the isolated AZB show that substitutions lead to distortion of the planar molecular structure because of the repulsive interactions between halogen atoms and a systematic blueshift of the ππ* bands between 25 and 50 nm. Moreover, separations between 10 and 48 nm, depending on the substituent, are observed in the nπ* bands. The results from the calculations on the substituted AZB–DHA–DHA macrocycles reveal significant separations of the DHA/trans-AZB and trans-/cis-AZB absorption bands by values of 46–73 and 15–52 nm, respectively, for different substitutions. We realize that ortho substitutions with mixed fluorine–chlorine-atoms can provide the best separations in both ππ* and nπ* bands of AZB–DHA–DHA photoisomers. The results of this work offer a guideline for designing and synthesizing new, efficient, and highly controllable materials applicable in devices for optical data storage and molecular electronics.

The fundamental understanding of adsorption, absorption, diffusion, and permeation of hydrogen and its isotopes is of paramount importance in controlling the hydrogen-induced embrittlement and also...

Hypochlorous acid (HOCl) and hypochlorite anions (−OCl) are nonselective oxidants produced by activated neutrophils and monocytes and play an important role in the formation of immune response of a living organism. At the same time, because of the strong oxidative properties of hypochlorites, their concentrations in cells need to be under strict control. In this paper, cerium oxide nanoparticles (nanoceria) were used for spectroscopically controlled catalytic decomposition of hypochlorite anions. The processes of scavenging of hypochlorite anions by ceria nanoparticles and regeneration of nanoceria were monitored using the changes in hypochlorite absorption and 5d → 4f luminescence of Ce3+ ions during oxidation–reduction cycles. The high oxygen deficiency of ceria nanoparticles provides sufficient mobility of oxygen ions, leading to the involvement of both surface and bulk Ce3+ ions into oxidation, whereas the recovery of initial Ce3+/Ce4+ ratio is terminated by the slow diffusion of oxygen out of ceria n...

The essential states model (ESM) for donor–acceptor–donor (D–A–D) chromophores is used to explore absorption and photoluminescence (PL) in molecular dimers composed of centrosymmetric and non-centrosymmetric squaraine molecules. The spectral line shapes and shifts relative to the monomer spectrum are due to an interesting interplay between three-center charge distributions responsible for ground- and excited-state (permanent) dipole and quadrupole moments and two-center charge distributions responsible for transition dipole moments. The Davydov splitting is sensitive only to the interactions between the (extended) transition dipoles , whereas the permanent dipole-dipole and quadruple-quadrupole interactions impact the midpoint frequency of the two Davydov components, leading to a generally asymmetric splitting relative to the peak monomer transition frequency. The theory accurately reproduces the steady-state absorption and PL line shapes recently obtained for covalently bound squaraine dimers. The ESM also predicts an extreme type of non-Kasha behavior, where both Davydov components are blue-shifted above the monomer transition frequency.

A facile strategy for preparing carbon-supported Co95Pt5 nanocatalysts (NCs) with low platinum (Pt) loading and high Pt utilization via thermal reduction treatment in a carbon monoxide (CO) atmosphere is reported. By cross-referencing results of microscopy, X-ray spectroscopy, and electrochemical analysis, we demonstrate that the Pt atoms tend to form disordered atomic clusters capping on the Co nanoparticle surface. The values of unfilled d-states (hTs) extracted from X-ray absorption near-edge spectroscopy were used to calculate the d-band vacancies of Pt. Accordingly, CoPt-CO570 (reduced in CO at 570 K) possesses the lowest hTs value (0.302) (i.e., the lowest Pt d-band vacancies) among experimental samples, indicating a strong electron relocation from Co atoms. Such electron relocations are attributed to the high extent of the heteroatomic intermix between Pt and Co atoms and thus improves the oxygen reduction reaction activity of CoPt-CO570. For providing further evidence, structural and electrochemic...

We have investigated the molecular and electronic structure of a TiO2-supported oxomolybdate phase upon reduction under methanol or dihydrogen atmosphere. In situ Mo K-edge X-ray absorption spectro...

We investigated molecular absorption in the proximity of metal surfaces. Previously observed modifications in the spectra were found to be specific to treated silver nanoparticles. Moreover, we sho...

Over the last years, carbon nano-onions (CNOs) have been in focus in material science research. Their red-shifted absorption allows utilizing CNOs as promising photosensitizers. We report here a systematic study of excited state properties of six double-layered Li+ doped fullerenes of Ih symmetry: [Li@C60@C240]+, [Li@C60@C540]+, [Li@C60@C960]+, [Li@C240@C540]+, [Li@C240@C960]+ and [Li@C540@C960]+. On the basis of TDDFT calculations, we show that the long-wave absorption by the Li+ doped species leads to charge transfer (CT) between the inner and the outer shells unlike their neutral double-layered precursors. The CT energy depends strongly on the size of the concentric fullerenes and it can easily be tuned by varying both the encapsulated metal ion and the size of the shells. Two types of low-lying excited states are identified (1) capacitor-like structures, as Li+@C60-@C240+, with alternating positive and negative charges, and (2) states, where the positive charge is delocalized over the outer shell, as in Li@C240@C540+. We suggest a simple expression to estimate the energy difference of these excited states and to predict the type of the lowest CT state in nested fullerenes. The effect of nature of the encapsulated ion on the charge transfer state energies is considered. The HOMO - LUMO transition energy is found to vary significantly when going from [Li@C60@C240]+ to [Li@C540@C960]+

The protonation mechanism in Mn-doped CaZrO3 (CZM), which involves a direct hydrogen dissolution from the surrounding H2 gas, was investigated by thermogravimetry (TG) and X-ray absorption spectroscopy (XAS). The TG results implied the formation of oxygen vacancies in a H2 atmosphere. The Mn K-edge XAS spectra indicated a reduction of the Mn ions and local structure variations around the Mn ion, but the Zr K-edge spectra were independent of the surrounding atmosphere. The amount of oxygen vacancies was smaller with respect to the reduction of the Mn ions, suggesting direct dissolution of hydrogen. Unlike many typical perovskite-type proton conductors, protonation by direct dissolution of hydrogen and not hydration was the predominant reaction in Mn-doped CaZrO3. Our experimental results demonstrated that the hydration reaction was suppressed because the oxygen vacancy was stable in the distorted ZrO6 symmetry in the CaZrO3 crystal host, whereas protonation proceeded by the direct dissolution of hydrogen stabilizing near the Mn ions in the interstitial sites at the distorted MnO6 octahedron symmetry. The experimental results showed that the structural configurations around dopants play important roles in the stabilization of protons in perovskite-type CZM materials. We demonstrated a new group of proton conductors that can overcome issues with conventional proton conductors by utilizing the direct hydrogen dissolution reaction.

Symmetric multipolar (e.g., quadrupolar and octupolar) chromophores that undergo excited-state symmetry breaking in polar solvents have been drawing considerable attention for a long time as promising two-photon absorption and luminescent materials. However, this process has been generally restricted to liquid media. Herein, we report the excited-state symmetry breaking of a centrosymmetric D−π–D (donor−π–donor) quadrupolar molecule, DB2, occurring at a polymer/glass interface. In polar liquids, DB2 exhibits pronounced emission solvatochromism originating from symmetry-breaking intramolecular charge transfer in the S1 state. Single-molecule fluorescence spectroscopy shows that the fluorescence characteristics of DB2 at the interface are strikingly different from those of DB2 embedded in a polymer film, that is, the dramatic lengthening of fluorescence lifetimes and pronounced sharpening of fluorescence spectra are observed. With the aid of theoretical calculations, it is revealed that these characteristic...

The effect of Ag+ incorporation into stellerite, a natural zeolite with STI framework type, was investigated by means of single-crystal X-ray diffraction (SC-XRD), molecular dynamics (MD) simulations, and X-ray absorption fine structure spectroscopy (XAFS). At room temperature (RT), the complete exchange of the original extraframework ions with Ag+ provoked a distortion of the framework accompanied by symmetry reduction from orthorhombic Fmmm to monoclinic F2/m space group. Ag+ ions were strongly disordered, with occupancies ranging from 0.02 to 0.24, at partially occupied sites within zeolitic cages. The combination of ab initio MD simulations and XAFS spectroscopy suggested that Ag+ is coordinated by three H2O oxygens at 2.37 A and two framework oxygen atoms between 2.55 and 3.00 A. The thermal stability was monitored in situ by SC-XRD (from 25 to 400 °C) and XAFS (from 25 to 650 °C). Upon heating, the structure transformed to three different topologies: B phase, D′ phase, observed here for the first ti...

We studied the adsorption geometry and bonding of mono- and tetraphosphonic-acid-functionalized tetraphenylporphyrin molecules on rutile TiO2(110) surfaces. The investigation was carried out by means of X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure (NEXAFS) measurements. We found that the molecules bind covalently to the surface in a mixed monodentate and bidentate mode implying deprotonation of one or two phosphonate hydroxyl groups. Our NEXAFS data suggest that molecules containing one functional phosphonic acid group are on average tilted further away from the surface than molecules with four functional groups. The highest occupied electronic state of both molecules is in the band gap at 2.1 eV below the Fermi level. Our results demonstrate that the number of functional phosphonic acid groups determine the adsorption geometry of tetraphenylporphyrins. Fil: Fernández, Cynthia Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Wechsler, Daniel. Universitat Erlangen-Nuremberg; Alemania Fil: Rocha, Tulio C. R.. Brazilian Center for Research on Energy and Materials ; Brasil Fil: Steinrück, Hans-Peter. Universitat Erlangen-Nuremberg; Alemania Fil: Lytken, Ole. Universitat Erlangen-Nuremberg; Alemania Fil: Williams, Federico José. Universitat Erlangen-Nuremberg; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina

We report ultrafast transient UV–vis absorption and electrochemical spectroscopies on the photoinduced charge separation dynamics in a recently synthesized family of metal-free donor–acceptor syste...

Two-photon absorption (2PA) and three-photon absorption (3PA) processes feature many technological applications for fluorescence microscopy, photodynamic therapy, optical data storage, and so on, Herein, we reveal that the giant 2PA and 3PA properties for all-inorganic CsPbX3 (X = Cl, Br, I, and mixed Cl/Br and Br/I) perovskite quantum dots (PQDs) can be enhanced several orders of magnitude, respectively, by simply changing the halide stoichiometry at the X site. Notably, reported data show excellent 2PA and 3PA properties for CsPbI3 (σ2 ∼ 2.1 × 106 GM and σ3 ∼ 1.1 × 10–73 cm8 s3/photon3), which is 2–4 orders of magnitude higher than those of conventional red-emitting QDs and 5–7 orders of magnitude higher than well documented organic molecules. Experimental results show multiphoton absorption (MPA) cross sections can be adjusted 2–3 orders of magnitude by band gap engineering in a predictable manner, via increasing the Pauling electronegativity of the halide. Two-photon luminescence imaging data show tha...

Spectral properties and morphologies of 1,1′-disulfobutyl-3,3′-diethyl-5,5′,6,6′-tetrachlorobenzimidazolylcarbo-cyanine (TDBC) J-aggregates formed in two different types of polymer films (neutral spin-coated and charged layered) were studied using steady-state, picosecond, and femtosecond spectroscopies as well as optical and atomic force microscopies. It was found that the J-aggregates adopt different morphologies in the films: quasi one-dimensional rod-like in the spin-coated films and two-dimensional island-like in the layered films. The TDBC J-aggregates exhibit very similar absorption and fluorescence spectra in different films, but their fluorescence lifetimes and quantum yields differ strongly (∼4% for spin-coated films and ∼0.5% for layered films). By pump-probe spectroscopy, three different contributions to the population dynamics and relaxation to lower lying levels are identified with exciton–exciton annihilation dominating the observed kinetics. Low-temperature experiments reveal strong excito...

Hybrid Au/CuO NPs supported on carbon (Vulcan-XC72) with different Au/Cu molar ratios (i.e., 13/1, 4/1, 1/1, and 1/17) were synthesized by the solvated metal atom dispersion approach. High-resolution transmission electron microscopy, scanning transmission electron microscopy electron energy loss spectroscopy maps, and extended X-ray absorption fine structure measurements showed the presence of a Au/CuO core shell heterostructure having narrow size distributions (mean diameter < 4.7 nm) regardless of their composition. The role of their structure and composition was evaluated for catalytic liquid-phase selective benzyl alcohol oxidation with respect to their monometallic counterparts. As a result, a strong synergistic effect of Au/CuO heterostructures was revealed, which is strictly dependent on the CuO coverage degree of the Au-rich core and thus to the Au/Cu molar ratio. Highest catalytic activity was observed when the CuO shell only partially covers the Au-NP surface (i.e., at high Au/Cu molar ratios: 13/1, 4/1). On the other hand, at high Cu loadings (i.e., Au/Cu molar ratios: 1/1 and 1/17), the CuO shell wraps the Au core completely, inhibiting the catalytic activity.

The transmission of chirality to an achiral metal surface after adsorption of chiral or achiral molecules is an exciting approach toward new materials systems. The interaction of racemic 2,3-dimethylsuccinic acid and its achiral meso form with a Cu(110) surface has been investigated in ultrahigh vacuum by means of X-ray photoelectron spectroscopy, low-energy electron diffraction, reflection absorption infrared spectroscopy, scanning tunneling microscopy, temperature-programmed desorption, and density functional theory. Racemic as well as meso-2,3-dimethylsuccinic acid form extended enantiomorphous structures, coexisting with extended two-dimensional structures that do not break the mirror symmetry of the substrate surface. Copper adatoms decorating the molecules suggest a chiral reconstruction of the surface. The thermally induced decomposition proceeds autocatalytically in a so-called surface explosion and shows a profound difference for the diastereomers.

The synthesis of Au nanowires (NWs) in hexane solution of HAuCl4·3H2O, oleylamine and triisopropylsilane at room temperature was "in situ" monitored by means of X-ray absorption fine structure spectroscopies and small-angle X-ray scattering to determine, under identical synthesis conditions, both the changes in the oxidation state of gold atoms and the evolution of the size and shape of the objects involved in the formation of Au NWs. We propose a multistage process for the formation of the NWs: first, Au(III) atoms form a planar-square geometry complex that is continuously reduced to give Au(I) disk-like structures with diameters bigger than that of the final NWs. In a second stage, characteristic length/thickness ratio of these disk-like objects increases to form cylinders, presumably through aurophilic interactions between Au(I) centers and stacking of the disks. When most of the Au atoms have been reduced to Au(I), the reduction to Au(0) begins (third stage), and the NWs grow to form an hexagonal arrangement, separated by a bilayer of oleylamine molecules (fourth stage). Finally, a slow reduction leads the reaction to the final product, formed by bundles of long, ultrathin Au NWs. Fil: Pschunder, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Puig, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Giovanetti, Lisandro Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Huck Iriart, Cristián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de San Martín; Argentina Fil: Requejo, Felix Gregorio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Buceta, David. Universidad de Santiago de Compostela; España Fil: Hoppe, Cristina Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Ramallo Lopez, Jose Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina

In this paper, the combined effect of gold nanoparticles and high-pressure densification on the luminescence of Pr3+-doped heavy metal GeO2–PbO photonic glass was investigated. Localized states related to ion-trapped exciton defects, S1 and S2, were observed at 342 and 412 nm before densification. After densification under 7.7 GPa, the structure of the glass host changed irreversibly, as indicated by the infrared spectrum, refractive index, and density measurements. Transmission electron microscopy analyses indicated that the high-pressure densification induced the formation of clusters of gold nanoparticles. The modifications observed in the absorption and luminescence spectra of Pr3+ ions in the VIS–NIR range were associated to the changes in the local field surrounding the Pr3+ ions in the host glass induced by high pressure. For excitation at 445 nm (luminescence from 3P2) and 593 nm (luminescence from 1D2), the combined effect of densification and gold nanoparticles induced an increase in the emissio...

We report the temperature dependence of the electron spin resonance (ESR) absorption and magnetic susceptibility of plastic crystal [(CH3)4N]FeCl4. We demonstrate the extreme sensitivity of ESR to the static and dynamic structural transitions, characteristic of this material. We observed the narrowing of the ESR line in the high temperature plastic-crystal phase, which is due to fast rotation (τ ≈ 10–9 s) of the [FeCl4]− anion. This is a rare example of the effect of fast motional narrowing in crystalline solids, in which ions occupy fixed positions in the crystal lattice.

Ag-based catalysts are efficient materials for formaldehyde (HCHO) oxidation in the low-temperature range. It has been reported that K addition can increase the catalytic performance of Ag-based catalysts, whereas the specific role of K doping remains ambiguous. In this work, Ag/Al2O3 and K–Ag/Al2O3 catalysts with different K doping levels were prepared and subsequently tested for catalytic HCHO oxidation. It was observed that K doping has a dramatic promotion effect on the activity of the Ag/Al2O3 catalyst. The 2K–Ag/Al2O3 sample was the most active catalyst, over which HCHO could be completely converted into CO2 and H2O in a gas hourly space velocity of 100 000 mL/(gcat h) at 65 °C. The catalysts were next characterized by X-ray powder diffraction, Brunauer–Emmett–Teller, transmission electron microscopy, H2-temperature-programmed reduction, UV–vis, X-ray absorption fine structure, and in situ diffuse reflectance infrared Fourier transform spectroscopy methods. The characterization results show that add...

A model of photoinduced intramolecular proton-coupled electron transfer is derived. The model includes three states as follows: the ground, excited, and product states. The charge transfer is associated with both stages, photoexcitation and product formation. A larger part of the model parameters can be extracted from the stationary absorption and fluorescence spectra of a particular fluorophore. Two different reaction coordinates are associated with the two stages, which are not independent. The angle between the reaction coordinates strongly influences on the kinetics of ultrafast product formation. The stochastic multichannel approach is exploited for simulations of the kinetics. The simulations well reproduce the kinetics of ultrafast intramolecular proton-coupled electron transfer in 2-((2-(2-hydroxyphenyl)benzo[d]oxazol-6-yl)methylene)malononitrile in a few solvents. The transfer is shown to occur totally or partly, depending on the solvent, in the nonequilibrium regime. Analysis of the kinetics of ...

Because organic electronics suffer from degradation-inducing oxidation processes, oxygen-tolerant organic molecules could solve this issue and be integrated to improve the stability of devices during operation. In this work, we investigate how lutetium double-decker phthalocyanine (LuPc2) reacts toward molecular oxygen and we report microscopic details of its interaction with LuPc2 film by combining X-ray photoemission spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and density functional theory. Surprisingly, LuPc2 molecules are found to weakly physisorb below 120 K and appear rather inert to molecular oxygen at more elevated temperatures. We are able to draw a microscopic picture at low temperature, in which oxygen molecules stick on top of the pyrrolic carbon of LuPc2. Our work sheds light on a class of semiconducting molecules, namely, double-decker phthalocyanines, which present a high tolerance toward molecular oxygen, opening promising perspectives for the design of stable materials to be applied in the next generation of organic-based electronic devices operating under ambient conditions.

In this study, we investigated the detailed mechanisms of CO2 absorption and desorption on A2CO3-promoted MgO absorbents (A = Na, K, Rb, and Cs). We analyzed the materials formed at various stages of the absorbents during CO2 absorption and desorption by thermal decomposition-gas chromatography/mass spectroscopy, in situ IR spectroscopy, solid-state magic-angle spinning NMR spectroscopy on 13C, 23Na, 25Mg, and 39K nuclei, diffuse reflectance UV–vis spectroscopy, and in situ X-ray diffraction as well as the conventional thermogravimetric analysis, ex situ X-ray diffraction, and elemental distribution mapping by energy-dispersive X-ray analysis using scanning electron microscopy. The absorption of CO2 of the absorbents occurs in two steps. The first step is a fast process involving basic sites on the MgO surface formed by the interaction between A2CO3 and MgO. Because the basicity of these sites depends on the size of A ion, the kinetics and capacity of CO2 absorption and the desorption properties of this p...

Self-assembly of organic macrocycles has been exploited as a preliminary step in the synthesis of soluble and tailorable carbon-based nanostructures. Functionalized nanotubes have been prepared using, as core building blocks, nearly planar ring structures containing several alkyne units, exploiting the geometry achieved in the spontaneous preassembling step driven by π interaction. Covalent cross-linking between these units was achieved by thermal or photochemical activation with UV light. Here, we apply a moderate pressure in a sapphire anvil cell (1.0 GPa) to facilitate the preassembling and induce the cross-linking under pressure either with visible light, absorbed by two-photon absorption, or thermally. We observe a high yield of enhanced quality cross-linked nanotubes in a sample, showing, at ambient pressure, only side-chain decomposition. These results show that moderate pressures, easily achievable in large volume cells, are able to selectively favor topochemical reactions in such complex organic ...

We report the reversible transitions from two distinct chemical environments (interfacial and bulk) to a single, globally ordered dominant environment that extends to 800 nm, within two triflate-based ionic liquid (IL) films. Vibrational spectra for supported IL films exhibit multiple peaks for the same vibrational mode, indicating the presence of multiple chemical environments (interfacial and bulk) in the film. After a quiescent maturation time, the vibrational spectra show much simpler absorption profiles indicating coalescence of the IL molecules into a global preferred phase, which resembles the interfacial environment that propagates throughout the film as a function of time. Data analysis suggests significant reorientation of the triflate anion with small changes of the cation, indicating a weakly interacting cation–anion pair. The distal extent of the self-organization is much thicker than that generally reported for solid–fluid interfaces. The ordering is reversible on replenishing the film with ...

Despite the widespread application of engineered multilayered polyelectrolyte-coated gold nanoparticles (AuNPs), their interparticle interaction is not fully understood in part because of a lack of molecular scale observation of the layer-by-layer assembly of the polyelectrolyte coating. While top-down coarse-grained models of polyelectrolyte-coated AuNPs have focused on polyelectrolytes of short length, from 10 to a 100 monomers represented as one charged bead per monomer, here we use molecular dynamics and bottom-up coarse-grained approaches to access more typical polymer lengths on the order of 200 monomers. Specifically, we simulate the adsorption dynamics and structure of one or two such long polycations on negatively charged 4 nm citrate-coated AuNPs within implicit or explicit solvents. The first polycation coats approximately half of the AuNP surface regardless of solvent model and leaves a significant part of the anionic citrate layer exposed to absorption by a second polycation. We find that the...

Absorption modes and the reactivity of nonhalogenated ionic liquids (ILs) at inorganic oxide surfaces of γ-Al2O3, MgO, and SiO2 particles were characterized using multinuclear (11B, 31P, and 29Si) solid-state magic-angle-spinning NMR, FTIR, and Raman spectroscopy. ILs are composed of the trihexyl(tetradecyl)phosphonium cation, [P6,6,6,14]+, and bis(mandelato)borate, [BMB]−, or bis(salicylato)borate, [BScB]−, anions. Spectroscopic measurements were performed on room-temperature (298 K) samples and samples exposed to 15 h at 373 K. The single-pulse 11B NMR data of heated [P6,6,6,14][BMB] mixed with the inorganic oxides showed a significant change in the spectra of the anion for all three oxides. In contrast, no such spectral changes were detected for heated [P6,6,6,14][BScB] mixed with the inorganic oxides. 31P MAS NMR data for the IL/metal oxide systems revealed interactions between [P6,6,6,14]+ and the surfaces of oxides. A significant intensity of 31P CP-MAS NMR signals indicated a low mobility of cation...

A detailed understanding of the reaction of a range of molecules on surfaces will be key to developing targeted strategies for on-surface synthesis. Here, we studied the deprotonation and decarboxylation reactions of 3,5-pyridinedicarboxylic acid (PDC) on Cu(111) using synchrotron radiation photoelectron spectroscopy (SRPES), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and density functional theory (DFT). PDC partially deprotonates upon deposition on Cu(111) at room temperature and adsorbs with the plane of its aromatic ring inclined at an average of ∼45° with respect to the surface. By heating to 100 °C, the deprotonation of the molecule increases. When the PDC is partially deprotonated the plane of its aromatic ring adopts a more upright orientation with respect to the surface. Additional heating to 160 °C causes complete deprotonation, upon which the molecule returns to a more planar molecular adsorption geometry. By examining both the N 1s core level and the NEXAFS results, we ascribe these changes in adsorption to a reaction-induced change in the predominant molecule–surface interaction, which is driven by the nitrogen lone pair prior to deprotonation, and by the carboxylate groups after deprotonation of the −COOH groups. These interaction channels and adsorption geometries are supported by our DFT calculations. Heating above 200 °C induces decarboxylation of the molecule; by observing the rate of reaction over a range of fixed temperatures, we extract an activation energy of 1.93 ± 0.17 eV for the decarboxylation reaction. Around this temperature we also begin to observe the ring opening of the molecule, suggesting that if PDC is to be used as a building block for on-surface synthesis of polymers, careful control of temperature is necessary for obtaining decarboxylation and covalent coupling of the molecule without destroying the aromatic core.

Small-angle neutron scattering combined with powder neutron diffraction was employed to study the phase formation upon absorption/desorption of hydrogen gas in Li- and Na-intercalated fullerides. The comparative system analysis, addressing changes in the sample phase compositions and the morphology of powders, revealed a higher degree of complexity in the Na-based samples. Results also showed that the disappearance of crystalline lithium/sodium hydride during desorption was accompanied by an increased surface roughness in both systems, most likely because of the formation of a local surface strain. Furthermore, an increased specific internal surface of the studied materials upon subsequent deuterium absorption/desorption cycles was demonstrated. This could indicate moderate fracturing of crystallites.

The localized surface plasmon of a metal nanoparticle can influence the optical properties of a molecule in the plasmon field. In a previous study of molecular oxygen adjacent to nanodisks on a flat substrate, we showed that a plasmon field can increase the probability of the O2(a1Δg) → O2(X3Σg–) radiative transition at 1275 nm. For the present study, we set out to ascertain if metal nanoparticles suspended in a liquid solvent could likewise induce measurable plasmonic effects on optical transitions in oxygen. Metal nanoparticles were prepared with the intent of selectively perturbing the 765 nm O2(X3Σg–) → O2(b1Σg+) absorption transition. Because O2(b1Σg+) efficiently decays to O2(a1Δg), we used the spectrally distinct O2(a1Δg) → O2(X3Σg–) phosphorescent transition at 1275 nm to probe the potential plasmon effects at 765 nm. Although we indeed observed nanoparticle-mediated effects on the O2(X3Σg–) → O2(b1Σg+) transition, our present data are readily explained in terms of a nanoparticle-dependent change ...

A representative thiolate (RS)-protected gold cluster, Au25(SR)18, shows a fingerprint-like characteristic spectral profile regardless of the R-groups, reflecting the common motif of the structural backbone made of Au and S: an icosahedral Au13 core fully protected by six staple units of Au2(SR)3. On the other hand, we reported in 2006 that an Au25(SPG)18 cluster (PGSH = N-(2-mercaptopropionyl)glycine) exhibited an optical absorption spectrum significantly different from that of the conventional Au25(SR)18, suggesting the formation of a nonicosahedral Au core. Here, we investigated the structure of Au25(SPG)18 by UV–vis spectroscopy, extended X-ray absorption fine structure analysis and density functional theory calculations. Spectroscopic results indicated that Au25(SPG)18 has a face-centered cubic (FCC) Au core. We proposed a model structure formulated as Au15(SPG)4[Au2(SPG)3]2[Au3(SPG)4]2 in which an Au15(SPG)4 core with an FCC motif is protected by two types of staples with different lengths, Au2(SPG)...

Experimental conditions favoring the tryptophan tight binding to the surface of citrate-reduced gold nanoparticles (Cit-AuNPs) were explored. For this, the adsorption of three molecular compounds, free amino acid (Trp), tripeptide NH2-Gly-Trp-Gly-CONH2, and lanreotide, a synthetic cyclic somatostatin analogue, on large-size (∼70 nm) Cit-AuNPs was analyzed. UV–visible absorption, transmission electron microscopy, and surface-enhanced Raman scattering (SERS) were jointly used in the present investigation. At low pH (∼3.5), when the repulsive electrostatic interactions between gold particles are sufficiently reduced, both peptides can induce strong NP aggregation, leading particularly to substantial changes in the characteristic tryptophan Raman markers, as well as to the appearance of strong SERS markers at 1228 and 1113 cm–1. In contrast, upon increasing the pH toward a neutral value, the mentioned Trp Raman markers tend to adopt a spectral shape comparable to that observed in solution (bulk). In free amin...

Naphthalene was deposited from the vapor phase on ice surfaces at 77 or 253 K to yield strongly distinct behavior, forming either an amorphous glass layer or submicrometer-sized crystals, respectively. The results stand upon optical emission spectroscopy combined with differential scanning calorimetry and X-ray analysis. The amorphous layer of naphthalene on the ice behaves in the same manner as on an inert metallic support: it starts to relax at 105 K and crystallizes at 185 K. The formed microcrystals exhibit distinct absorption behavior on the ice surface and are thus expected to have a photokinetic profile varying from freeze-concentrated solutions. The observations bring implications toward environmental and extraterrestrial ice sciences.

In order to learn more about the origin of chirality in chiral organometallic complexes and to contribute to the understanding of the differences in chiroptical activity of metal clusters stabilized by various phosphine ligands, we examined the optical properties of undecagold (Au113+) and octagold (Au82+) clusters protected by two types of bisphosphine ligands [BINAP (2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) and DIOP (o-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane)]. The chirality of pairs of clusters [Au11(BINAP)4Cl2]+, [Au11(DIOP)4Cl2]+ and [Au8(BINAP)3(PPh3)2]2+, [Au8(DIOP)3(PPh3)2]2+ are investigated with density functional theory (DFT) and time–dependent density functional theory (TDDFT). The geometries of the octa- and undecagold cores in the model clusters are similar to the gold cores of the crystal structures. Theoretical optical absorption and CD spectra of the model clusters are in good agreement with experimental data. Three main hypotheses to explain the different chirop...