Vestwilcox3442

The combination of two two-photon-induced processes in a Förster resonance energy transfer (FRET)-operated photochromic fluorene-dithienylethene dyad lays the foundation for the observation of a quartic dependence of the fluorescence signal on the excitation light intensity. While this photophysical behavior is predicted for a four-photon absorbing dye, the herein proposed approach opens the way to use two-photon absorbing dyes, reaching the same performance. Hence, the spatial resolution limit, being a critical parameter for applications in fluorescence imaging or data storage with common two-photon absorbing dyes, is dramatically improved.Discovering acid-stable, cost-effective, and active catalysts for oxygen evolution reaction (OER) is critical since this reaction is a bottleneck in many electrochemical energy conversion systems. The current systems use extremely expensive iridium oxide catalysts. Identifying Ir-free or less-Ir containing catalysts has been suggested as the goal, but no systematic strategy to discover such catalysts has been reported. In this work, we perform first-principles-based high-throughput catalyst screening to discover OER-active and acid-stable catalysts focusing on equimolar bimetallic oxides with space groups derived from those of IrO x . We develop an approach to evaluate acid-stability under the reaction condition by utilizing the Materials Project database and density functional theory (DFT) calculations. For acid-stable materials, we further investigate their OER catalytic activities and identify promising OER catalysts that satisfy all the desired properties Co-Ir, Fe-Ir, and Mo-Ir bimetallic oxides. Based on the calculated results, we provide insights to efficiently perform future high-throughput screening to discover catalysts with desirable properties and discuss the remaining challenges.The functional properties of a surface, such as its anti-fogging or anti-fouling performance, are influenced by its wettability. To quantify surface wettability, the most common approach is to measure the contact angles of a liquid droplet on the surface. While well established and relatively easy to perform, contact angle measurements were developed to describe macroscopic wetting properties and are difficult to perform for submillimetric droplets. Selleck Anisomycin Moreover, they cannot spatially resolve surface heterogeneities that can contribute to surface fouling. To address these shortcomings, we report on using an atomic force microscopy technique to quantitatively measure the interaction forces between a microdroplet and a surface with piconewton force resolution. We show how our technique can be used to spatially map topographical and chemical heterogeneities with micron resolution.Surface-enhanced Raman scattering (SERS) is a multidisciplinary trace analysis technique based on plasmonic effects. The development of SERS microfluidic chips has been exploited extensively in recent times impacting on applications in diverse fields. However, despite much progress, the excitation of label-free molecules is extremely challenging when analyte concentrations are lower than 1 nM because of the blinking SERS effect. In this paper, a novel analytical strategy which can achieve detection limits at an attomolar level is proposed. This performance improvement is due to the use of a glass microfluidic chip that features an analyte air-solution interface which forms on the SERS substrate in the microfluidic channel, whereby the analyte molecules aggregate locally at the interface during the measurement, hence the term liquid interface-assisted SERS (LI-SERS). The microfluidic chips are fabricated using hybrid femtosecond (fs) laser processing consisting of fs laser-assisted chemical etching, selective metallization, and metal surface nanostructuring. The novel LI-SERS technique can achieve an analytical enhancement factor of 1.5 × 1014, providing a detection limit below 10-17 M ( less then 10 aM). The mechanism for the extraordinary enhancement afforded by LI-SERS is attributed to Marangoni convection induced by the photothermal effect.Axial coordination to metalloporphyrins is important in many biological and catalytic processes. Experiments found the axial coordination of nitrogenous bases to nickel(II) porphyrins to be strongly favored by electron-withdrawing substituents such as perfluorophenyls at the meso carbon positions. Careful analysis of the electronic structure reveals that the natural explanation in terms of density change of the nickel(II) porphyrin system (in particular the metal), does not apply. Electron density changes, by the assumed inductive or polarizing effects on the metal or on the porphyrin ring system, are slight. The effect is caused by a remarkable through-space electric field effect on the metalloporphyrin system, originating from the charge distribution inside the perfluorphenyl groups (mostly the C-F dipoles).CeIV6-based metal-organic frameworks (MOFs) have gained increasing attention recently because of their diverse potential applications and similarity to prominent Zr-MOFs, e.g., the UiO-66 series. link2 However, the reported CeIV6-based MOFs were all structurally determined by means of the powder X-ray diffraction technique, indicative of less practice and convenience. Herein, four single-crystalline CeIV6-based MOFs were successfully isolated and characterized by single-crystal X-ray diffraction, disclosing two series of topologically distinct isoreticular nets accompanied by nine-coordinated central CeIV ions, i.e., 8-connected hex and 12-connected fcu, respectively, in contrast to the previously reported sole fcu topology based on the combination of linear dicarboxylate ligands and a CeIV6 cluster associated with eight-coordinated central CeIV ions according to the UiO-66 structural model. link3 Moreover, all four single-crystalline compounds exhibit permanent microporous porosities and a certain amount of gas uptake toward CO2, CH4, and H2.Obtaining highly valuable Xe from air or other sources is highly important but still seriously restricted by its inherent inert nature and the great difficulty in separation from other inert gases, especially for Xe and Kr that show comparable size. In this work, we show both experimental and theoretical research of how to boost the selective adsorption of Xe over Kr by double-accessible open-metal site in metal-organic framework (MOF). The MOF, namely, UTSA-74, shows a high Xe uptake up to 2.7 mmol/g and a lower Kr uptake of 0.58 mmol/g at 298 K and 1 bar, leading to a high selectivity of 8.4. The effective Xe/Kr separation was further confirmed by both transient breakthrough simulation and experimental breakthrough. The separation mechanism, as unveiled by the grand canonical Monte Carlo simulation and dispersion-corrected density functional theory calculation, is due to the unique double-accessible open-metal site in UTSA-74 that affords stronger interaction toward Xe than Kr.Lithium stannate (Li2SnO3) is currently being considered as a material for electrode and electrode coating applications in Li-ion batteries. The intrinsic defect formation and Li-ion transport properties of Li2SnO3 doped with divalent and trivalent transition-metal dopants (Mn, Fe, Co, and Ni) are explored in this work using atomistic simulations. Defect formation simulations reveal that all divalent dopants occupy the Li site with charge compensation through Li vacancies. For trivalent doping, occupation of the Sn site is energetically preferred with charge compensation from Li interstitials. Molecular dynamics simulations reveal that divalent and trivalent dopants increase Li-ion diffusion and reduce its activation energy compared with the undoped system. We show that Li2SnO3 with Li excess or deficiency as a result of doping has improved Li-transport properties. This study highlights the substantial improvement in Li-ion diffusion of Li2SnO3 for both current commercial and next-generation Li-ion battery technologies that can be achieved through transition-metal doping.Iron porphyrin methoxy complexes, of the general formula [Fe(porphyrin)(OCH3)], are able to catalyze the reaction of diazo compounds with alkenes to give cyclopropane products with very high efficiency and selectivity. The overall mechanism of these reactions was thoroughly investigated with the aid of a computational approach based on density functional theory calculations. The energy profile for the processes catalyzed by the oxidized [FeIII(Por)(OCH3)] (Por = porphine) as well as the reduced [FeII(Por)(OCH3)]- forms of the iron porphyrin was determined. The main reaction step is the same in both of the cases, that is, the one leading to the terminal-carbene intermediate [Fe(Por)(OCH3)(CHCO2Et)] with simultaneous dinitrogen loss; however, the reduced species performs much better than the oxidized one. Contrarily to the iron(III) profile in which the carbene intermediate is directly obtained from the starting reactant complex, the favored iron(II) process is more intricate. The initially formed reactant adduthe geometrical features around the reactive core of the system remain unchanged, the energy barriers become much lower, thus revealing the profound effects that can be exerted by the three-dimensional organic scaffold surrounding the reaction site.Herein, we present the synthesis, single-crystal X-ray structures, and spectroscopic properties for the 11 donor-acceptor complexes of 1,2,4,5-tetracyanobenzene (TCNB) with annelated 3a,6a-diaza-1,4-diphosphapentalenes (DDPs) based on cyclohexanone azine (2) and tetralone azine (4). These are the first complexes of an organic π-acceptor with donor phosphorus heterocycles. According to the X-ray study, the DDPs and TCNB molecules are alternately stacked with interplanar distances of 3.335 and 3.404 Å for 2 and 4, respectively, which are suitable for intermolecular π···π interactions. The bond lengths and angles in the component molecules agree with values for neutral species, and the infrared spectra indicate a very slight degree of ionicity. The estimated HOMO-LUMO gap from the onset of optical absorption (1.40 eV) is in agreement with the band gap estimated from the density functional theory calculations for 2 (1.47 eV). By contrast, in a reaction with the related electron acceptor, tetrachloroterephthalonitrile, the DDPs proved to be donors of lone electron pairs in a nucleophilic aromatic substitution reaction of chlorine atoms demonstrating the duality of their electronic nature.We synthesized a new organosiloxane bridge on the basis of an isocyanurate derivative through a simple melt-fusion approach by the reaction of 3-isocyanatopropyltriethoxysilane (IPTES) with 1,3,5-tris(2-hydroxyethyl)-1,3,5-triazinane-2,4,6(1H,3H,5H)-trione (THEIC). The obtained carbamate-isocyanurate-based organosiloxane bridge precursor was used for the preparation of chemo- and thermostable periodic mesoporous organosilica (PMO-THEIC) on condensation with tetrathoxysilane silicon precursor through a soft-template approach. Furthermore, the synthesized PMO-THEIC with unique surface functionality was investigated for CO2 capture. The results show that the PMO-THEIC has higher activity than pure SBA-15 for CO2 capture due to the high affinity of carbamate functionalities embedded within the pore walls toward CO2 molecules. The affinity of organosiloxane bridge for CO2 molecules is mainly facilitated via the van der Waals force with carbamate functional groups rather than the isocyanurate ring, according to the density functional calculations.