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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Thermally Activated Delayed Fluorescence (TADF) Path toward Efficient Electroluminescence in Purely Organic Materials: Molecular Level Insight
Since the seminal work of Tang and Vanslyke in 1987 on small-molecule emitters and that of Friend and co-workers in 1990 on conjugated-polymer emitters, organic light-emitting diodes (OLEDs) have attracted much attention from academia as well as industry, as the OLED market is estimated to reach the $30B mark by the end of 2018. In these first-generation organic emitters, on the basis of simple spin statistics, electrical excitation resulted in the formation of ~25% singlet excitons and ~75% triplet excitons. Radiative decay of the singlet excitons to the singlet ground state leads to a prompt fluorescence emission, while the triplet excitons only lead to weak phosphorescence due to the very small spin-orbit couplings present in purely organic molecules. The consequence is a ca. 75% energy loss, which triggered wide-ranging efforts to try and harvest as many of the triplet excitons as possible. In 1998, Thompson, Forrest, and their co-workers reported second-generation OLED emitters based on coordination complexes with heavy transition metals (e.g., iridium or platinum). Here, the triplet excitons stimulate efficient and fast phosphorescence due to the strong spin-orbit couplings enabled by the heavy-metal atoms. Internal quantum efficiencies (IQE) up to 100% have been reported, which means that for every electron injected into the device, a photon is emitted. Here, while these second-generation emitters are those mainly exploited in current OLED applications, there is strong impetus from both cost and environmental standpoints to find new ways of exploiting purely organic emitters, which in addition can offer greater flexibility to fine tune the electronic and optical properties by exploiting the synthetic organic chemistry toolbox.
An Aromatic Cluster in the Active Site of epi-Isozizaene Synthase Is an Electrostatic Toggle for Divergent Terpene Cyclization Pathways
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Transient-State Analysis of Human Isocitrate Dehydrogenase I: Accounting for the Interconversion of Active and Non-Active Conformational States
Abstract not provided
Template-Assisted, Seed-Mediated Synthesis of Hierarchically Mesoporous Core–Shell UiO-66: Enhancing Adsorption Capacity and Catalytic Activity through Iterative Growth
A hierarchically mesoporous (HM) UiO-66-F 4 shell with ~8 nm mesopores can be iteratively grown on top of UiO-66 nanoparticle (NP) seeds over several cycles templated by Pluronic F-127 micelles. Presumably, the Pluronic micelles that were formed in water can surround UiO-66 NPs to facilitate the overgrowth of an HM-UiO-66-F 4 shell in the presence of Zr IV precursors and BDC-F 4 linkers. The UiO-66 NP seeds play an important role in directing the continuous growth of the HM-UiO-66-F 4 shell, as only a nonporous phase was obtained in their absence. Furthermore, this template-assisted, seed-mediated method can be extended to produce other UiO-66-X (X = (OH) 2 , (COOH) 2 , etc.) shells, demonstrating its generality for the UiO-66 family of metal–organic frameworks. Notably, the incorporation of mesopores into the thrice-overgrown UiO-66@HM|3rd-UiO-66-F 4 materials leads to impressive enhancements in the per-mass uptake capacity of Direct Blue 86, a large anionic dye: 320% better than the parent UiO-66 seeds and 150% better than that for a [UiO-66 + UiO-66-F 4 ] physical mixture at the same mass proportion. Similar enhancements were also observed in the catalyzed oxidation of thioanisole.
Interstitial Lithium Doping in BiVO4 Thin Film Photoanode for Enhanced Solar Water Splitting Activity
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Lattice Anharmonicity of Stereochemically Active Lone Pairs Controls Thermochromic Band Gap Reduction of PbVO3Cl
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Effect of the Number and Substitution Pattern of Carbazole Donors on the Singlet and Triplet State Energies in a Series of Carbazole-Oxadiazole Derivatives Exhibiting Thermally Activated Delayed Fluorescence
Substitution of a varying number of 9H-carbazole donors onto 2-(pentafluorophenyl)-5-phenyl-1,3,4-oxadiazole yields a series of donor–acceptor compounds with similar electrochemical band gaps, but dissimilar optical properties. Each substitution of a carbazole onto the 2- and 4-positions results in a 150–200 meV stabilization of the first singlet excited state, evident in the fluorescent emission. Here, the first triplet excited state is less sensitive to these substitutions, leading to a reduced energy separation between the singlet and triplet states, ΔE ST , with increasing carbazole content. OLED devices made using the donor–acceptor compounds exhibiting the lowest ΔE ST were fabricated and exhibit sky blue emission with an external quantum efficiency of up to 24.4% at a luminance of 10 cd m –2 , and 9.2% at 1000 cd m –2 .
Molybdenum Carbides, Active and In Situ Regenerable Catalysts in Hydroprocessing of Fast Pyrolysis Bio-Oil
We assessed molybdenum carbides as a potential catalyst for fast pyrolysis bio-oil hydroprocessing. Currently, high catalyst cost, short catalyst lifetime, and lack of effective regeneration methods are hampering the development of this otherwise attractive renewable hydrocarbon technology. A series of metal-doped bulk Mo carbides were synthesized, characterized and evaluated in sequential low-temperature stabilization and high-temperature deoxygenation of a pine-derived bio-oil. During a typical 60-h run, Mo carbides were capable of upgrading raw bio-oil to a level suitable for direct insertion into the current hydrocarbon infrastructure with residual oxygen content and total acid number of upgraded oils below 2 wt% and 0.01 mg KOH g-1, respectively. The performance was shown to be sensitive to the type of metal dopant, Ni-doped Mo carbides outperforming Co-, Cu-, or Ca-doped counterparts; a higher Ni loading led to a superior catalytic performance. No bulk oxidation or other significant structural changes were observed. Besides the structural robustness, another attractive property of Mo carbides was in situ regenerability. The effectiveness of regeneration was demonstrated by successfully carrying out four consecutive 60-h runs with a reductive decoking between two adjacent runs. These results strongly suggest that Mo carbides are promising catalytic materials which could lead to a significant cost reduction in hydroprocessing bio-oils. This paper highlights areas for future research which will be needed to further understand carbide structure-function relationships and help design practical bio-oil upgrading catalysts based on Mo carbides.
Discovery of Orally Active Inhibitors of Brahma Homolog (BRM)/SMARCA2 ATPase Activity for the Treatment of Brahma Related Gene 1 (BRG1)/SMARCA4-Mutant Cancers
Abstract not provided
Light-Driven Redox Activation of CO 2 - and H 2 -Activating Complexes in a Self-Assembled Triad
We report a self-assembled triad for artificial photosynthesis composed of a chromophore, carbon-dioxide reduction catalyst, and hydrogen oxidation complex, which is designed to operate without conventional sacrificial redox equivalents. Excitation of the zinc-porphyrin chromophore of the triad results in ultrafast charge transfer between a tungsten-alkylidyne donor and a rhenium diimine tricarbonyl acceptor, producing a charge-separated state that persists on the time scale of tens of nanoseconds and is thermodynamically capable of the primary dihydrogen and carbon dioxide binding steps for initiating the reverse water-gas shift reaction. The charge-transfer behavior of this system was probed using transient absorption spectroscopy in the visible, near-infrared, and mid-infrared spectral regions. Here, the behavior of the triad was compared with that of the zinc-porphyrin-rhenium-diimide dyad; the triad was found to have a significantly longer charge-separated lifetime than other previously reported porphyrin-rhenium diimine compounds.
Predicted Efficient Visible-Light Driven Water Splitting and Carbon Dioxide Reduction Using Photoredox-Active UiO-NDI Metal Organic Framework
The structural and electronic properties of metal–organic frameworks (MOFs) constructed from stable Zr(IV) oxide-based nodes and naphthalenediimide-based linkers (UiO(Zr)-NDI) can be tuned to make them useful for specific photoredox processes. The NDI linker presents outside, inside, and core positions where functionalization can influence its optical properties, and such substitution in combination with suitable optical band gaps and band edge positions in UiO(Zr)-NDI offers a platform for the design of efficient MOF-based photocatalysts for water splitting and CO 2 reduction. Here, the band gaps and edge positions remain similar for UiO nodes when Zr is substituted with Ti, Th, or Ce. However, in contrast to the case for Zr-, Ti-, and Th-based UiO-NDIs, where photoexcitation remains localized on the NDI linkers owing to the very high energies of unoccupied node-based bands, for UiO(Ce)-NDI, the availability of low-lying empty f orbitals in the metal node offers the potential for energy transfer and exciton migration, which could further boost photocatalytic performance by extending exciton lifetimes.
Temperature-activated PEG surface segregation controls the protein repellency of polymers
Abstract not provided