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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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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Long-Range Resonant Charge Transport through Open-Shell Donor–Acceptor Macromolecules

A grand challenge in molecular electronics is the development of molecular materials that can facilitate efficient longrange charge transport. Research spanning more than two decades has been fueled by the prospects of creating a new generation of miniaturized electronic technologies based on molecules whose synthetic tunability offers tailored electronic properties and functions unattainable with conventional electronic materials. However, current design paradigms produce molecules that exhibit off-resonant transport under low bias, which limits the conductance of molecular materials to unsatisfactorily low levels several orders of magnitude below the conductance quantum 1 G 0 and often results in an exponential decay in conductance with length. Here, we demonstrate a chemically robust, air-stable, and highly tunable molecular wire platform comprised of open-shell donor−acceptor macromolecules that exhibit remarkably high conductance close to 1 G 0 over a length surpassing 20 nm under low bias, with no discernible decay with length. Single-molecule transport measurements and ab initio calculations show that the ultralong-range resonant transport arises from extended π-conjugation, a narrow bandgap, and diradical character, which synergistically enables excellent alignment of frontier molecular orbitals with the electrode Fermi energy. The implementation of this long-sought-after transport regime within molecular materials offers new opportunities for the integration of manifold properties within emerging nanoelectronic technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Ultrathin electron and proton-conducting membranes for nanoscale integrated artificial photosystems

Reducing the thickness of separation membranes without compromising their selectivity and robustness is the most effective way of maximizing the areal conductivity. This is especially important for the integration of visible light-driven water oxidation and carbon dioxide (or proton) reduction into a complete artificial photosystem on the shortest possible length scale – the nanoscale – because of the efficiency advantages over macroscale photosystems. In addition to their excellent separation property, ultrathin membranes of 10 nm thickness or less need to exhibit sufficient electrical and proton conductivity in order for the photocatalytic rates to keep up with the photon flux at maximum solar intensity. Furher, two materials, graphene and amorphous silica with embedded molecular wires, have emerged as promising ultrathin membranes for the development of nanoscale integrated solar-fuel systems. Moreover, electrically conducting metal–organic or covalent–organic frameworks can be used to fabricate high surface area-supports that enable the use of molecular catalysts and/or light absorbers at an adequate areal density for nanoscale integration with graphene membranes. Following an overview of the electron and proton conductivity of these ultrathin materials and recent examples of photoelectrocatalytic applications that take advantage of some but not all the properties that constitute a complete functional membrane, the status and future opportunities for complete nanoscale integrated photosystems featuring an ultrathin membrane are discussed.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Single-Molecule Charge Transport through Positively Charged Electrostatic Anchors

The charge transport in single-molecule junctions depends critically on the chemical identity of the anchor groups that are used to connect the molecular wires to the electrodes. In this research, we report a new anchoring strategy — called the electrostatic anchor here — formed through the efficient Coulombic interaction between the gold electrodes and the positively charged pyridinium terminal groups. Our results show that these pyridinium groups serve as efficient electrostatic anchors forming robust gold–molecule–gold junctions. Here, we have also observed binary switching in dicationic viologen molecular junctions, demonstrating an electron injection-induced redox switching in single-molecule junctions. We attribute the difference in low- and high conductance states to a dicationic ground state and a radical cationic metastable state, respectively. Overall, this anchoring strategy and redox switching mechanism could constitute the basis for a new class of redox-activated single-molecule switches.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Role of Intact Hydrogen-Bond Networks in Multiproton-Coupled Electron Transfer

The essential role of a well-defined hydrogen-bond network in achieving chemically reversible multiproton translocations triggered by one-electron electrochemical oxidation/reduction is investigated by using pyridylbenzimidazole–phenol models. The two molecular architectures designed for these studies differ with respect to the position of the N atom on the pyridyl ring. In one of the structures, a hydrogen-bond network extends uninterrupted across the molecule from the phenol to the pyridyl group. Experimental and theoretical evidence indicates that an overall chemically reversible two-protoncoupled electron-transfer process (E2PT) takes place upon electrochemical oxidation of the phenol. This E2PT process yields the pyridinium cation and is observed regardless of the cyclic voltammogram scan rate. In contrast, when the hydrogen-bond network is disrupted, as seen in the isomer, at high scan rates (~1000 mV s –1 ) a chemically reversible process is observed with an E 1/2 characteristic of a one-proton-coupled electron-transfer process (E1PT). At slow cyclic voltammetric scan rates (<1000 mV s –1 ) oxidation of the phenol results in an overall chemically irreversible two-proton-coupled electron-transfer process in which the second proton-transfer step yields the pyridinium cation detected by infrared spectroelectrochemistry. In this case, we postulate an initial intramolecular proton-coupled electron-transfer step yielding the E1PT product followed by a slow, likely intermolecular chemical step involving a second proton transfer to give the E2PT product. Insights into the electrochemical behavior of these systems are provided by theoretical calculations of the electrostatic potentials and electric fields at the site of the transferring protons for the forward and reverse processes. Furthermore, this work addresses a fundamental design principle for constructing molecular wires where protons are translocated over varied distances by a Grotthuss-type mechanism.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1999

Single Particle Transport Through Carbon Nanotube Wires: Effect of Defects and Polyhedral Cap

The ability to manipulate carbon nanotubes with increasing precision has enabled a large number of successful electron transport experiments. These studies have primarily focussed on characterizing transport through both metallic and semiconducting wires. Tans et al. demonstrated ballistic transport in single-wall nanotubes for the first time, although the experimental configuration incurred large contact resistance. Subsequently, methods of producing low contact resistances have been developed and two terminal conductances smaller than 50 k-ohms have been repeatably demonstrated in single-wall and multi-wall nanotubes. In multi-wall nanotubes, Frank et al. demonstrated a resistance of approximately h/2e(exp 2) in a configuration where the outermost layer made contact to a liquid metal. This was followed by the work of de Pablo et al. where a resistance of h(bar)/27e(exp 2) (approximately 478 ohms) was measured in a configuration where electrical contact was made to many layers of a multi-wall nanotube. Frank et al. and Pablo et al. note that each conducting layer contributes a conductance of only 2e(exp 2)/h, instead of the 4e(exp 2)/h that a single particle mode counting picture yields. These small resistances have been obtained in microns long nanotubes, making them the best conducting molecular wires to date. The large conductance of nanotube wires stems from the fact that the crossing bands of nanotubes are robust to defect scattering.

Anantram, M. P.↗
DOE OSTI2020

A Unified Mechanism on the Formation of Acenes, Helicenes, and Phenacenes in the Gas Phase

Abstract A unified low‐temperature reaction mechanism on the formation of acenes, phenacenes, and helicenes—polycyclic aromatic hydrocarbons (PAHs) that are distinct via the linear, zigzag, and ortho ‐condensed arrangements of fused benzene rings—is revealed. This mechanism is mediated through a barrierless, vinylacetylene mediated gas‐phase chemistry utilizing tetracene, [4]phenacene, and [4]helicene as benchmarks contesting established ideas that molecular mass growth processes to PAHs transpire at elevated temperatures. This mechanism opens up an isomer‐selective route to aromatic structures involving submerged reaction barriers, resonantly stabilized free‐radical intermediates, and systematic ring annulation potentially yielding molecular wires along with racemic mixtures of helicenes in deep space. Connecting helicene templates to the Origins of Life ultimately changes our hypothesis on interstellar carbon chemistry.

Zhao, Long↗
DOE OSTI2019

A Unified Mechanism on the Formation of Acenes, Helicenes, and Phenacenes in the Gas Phase

A unified low-temperature reaction mechanism on the formation of acenes, phenacenes, and helicenes—polycyclic aromatic hydrocarbons (PAHs) that are distinct via the linear, zigzag, and ortho-condensed arrangements of fused benzene rings—is illustrated. This mechanism is mediated through a barrierless, vinylacetylene mediated gas-phase chemistry utilizing tetracene, [4]phenacene, and [4]helicene as benchmarks contesting established ideas that molecular mass growth processes to PAHs transpire at elevated temperatures. This mechanism opens up an isomer-selective route to aromatic structures involving submerged reaction barriers, resonantly stabilized free-radical intermediates, and systematic ring annulation potentially yielding molecular wires along with racemic mixtures of helicenes in deep space. Thus, connecting helicene templates to the Origins of Life ultimately changes our hypothesis on interstellar carbon chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Formation and Evolution of Metallocene Single-Molecule Circuits with Direct Gold-π Links

Single molecule circuits with group 8 metallocenes are formed without additional linker groups in Scanning Tunnelling Microscope-based break junction (STMBJ) measurements at cryogenic and room temperature conditions with gold (Au) electrodes. We investigate the nature of this direct gold-π binding motif and its affect on molecular conductance and persistence characteristics during junction evolution. The measurement technique under cryogenic conditions tracks molecular plateaus through the full cycle of extension and compression. Analysis reveals that junction persistence when the metal electrodes are pushed together correlates with whether electrodes are locally sharp or blunt, suggesting distinct scenarios for metallocene junction formation and evolution. The top and bottom surfaces of the "barrel" shaped metallocenes present the electron-rich π system of cyclopentadienyl rings which interacts with the gold electrodes in two distinct ways. An undercoordinated gold atom on a sharp tip forms a donor-acceptor bond to a specific carbon atom in the ring. However, a small, flat patch on a dull tip can bind more strongly to the ring as a whole through Van der Waals interactions. Density functional theory (DFT) based calculations of model electrode structures provide an atomic-scale picture of these scenarios, demonstrating the role of these bonding motifs during junction evolution and showing that the conductance is relatively independent of tip atomic-scale structure. Furthermore, the non-specific interaction of the cyclopentadienyl rings with the electrodes enables extended conductance plateaus, a mechanism distinct from that identified for the more commonly studied, rod-shaped organic molecular wires.

25 ENERGY STORAGE↗
DOE OSTI2024

Cyclically conjugated porphyrin trimers linked through benzo[4,5]imidazo[2,1- a ]isoindole bridges

Cyclically conjugated porphyrin trimers were prepared via a concise synthetic method. Zn-Trimer-1 displayed strong exciton coupling, suggesting the presence of effective electronic interactions. UV-Vis absorption and fluorescence spectra obtained through titration studies on the donor–acceptor adduct (Zn-Trimer-1–C60Im) indicate the occurrence of excited state photo-events. Inspired by nature's photosynthetic process of plants and bacteria, electronically interacting multiporphyrinic systems have long been investigated as synthetic models of natural photosynthetic systems. Remarkable successes have been achieved with cyclic porphyrin arrays, where porphyrins are arranged in a wheel-like structure or nanoring as photosynthetic antennae. Considerable efforts have also been devoted to constructing other porphyrin arrays such as molecular wires for potential applications in sensors, solar energy conversion, non-linear optical (NLO) materials, and more. Due to synthetic difficulties, cyclically conjugated porphyrin arrays in which porphyrins are arranged in planar geometry are very rare. Very recently, Anderson and coworkers have reported unprecedented β,β-directly linked porphyrin trimers and tetramers with different geometries, propeller and saddle, respectively, which result in distinct photophysical and electrochemical properties (Fig. 1a). In this paper, we present novel cyclically conjugated porphyrin trimers, which feature planar geometry with porphyrins assembled around the aromatic triphenylene at the center (Fig. 1b).

Han, Ting↗
DOE OSTI2024

A red-emitting carborhodamine for monitoring and measuring membrane potential

Biological membrane potentials, or voltages, are a central facet of cellular life. Optical methods to visualize cellular membrane voltages with fluorescent indicators are an attractive complement to traditional electrode-based approaches, since imaging methods can be high throughput, less invasive, and provide more spatial resolution than electrodes. Recently developed fluorescent indicators for voltage largely report changes in membrane voltage by monitoring voltage-dependent fluctuations in fluorescence intensity. However, it would be useful to be able to not only monitor changes but also measure values of membrane potentials. This study discloses a fluorescent indicator which can address both. We describe the synthesis of a sulfonated tetramethyl carborhodamine fluorophore. When this carborhodamine is conjugated with an electron-rich, methoxy (-OMe) containing phenylenevinylene molecular wire, the resulting molecule, CRhOMe, is a voltage-sensitive fluorophore with red/far-red fluorescence. Using CRhOMe, changes in cellular membrane potential can be read out using fluorescence intensity or lifetime. In fluorescence intensity mode, CRhOMe tracks fast-spiking neuronal action potentials (APs) with greater signal-to-noise than state-of-the-art BeRST 1 (another voltage-sensitive fluorophore). CRhOMe can also measure values of membrane potential. The fluorescence lifetime of CRhOMe follows a single exponential decay, substantially improving the quantification of membrane potential values using fluorescence lifetime imaging microscopy (FLIM). The combination of red-shifted excitation and emission, mono-exponential decay, and high voltage sensitivity enable fast FLIM recording of APs in cardiomyocytes. The ability to both monitor and measure membrane potentials with red light using CRhOMe makes it an important approach for studying biological voltages.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2000

Computational Nanotechnology of Materials, Devices, and Machines: Carbon Nanotubes

The mechanics and chemistry of carbon nanotubes have relevance for their numerous electronic applications. Mechanical deformations such as bending and twisting affect the nanotube's conductive properties, and at the same time they possess high strength and elasticity. Two principal techniques were utilized including the analysis of large scale classical molecular dynamics on a shared memory architecture machine and a quantum molecular dynamics methodology. In carbon based electronics, nanotubes are used as molecular wires with topological defects which are mediated through various means. Nanotubes can be connected to form junctions.

Srivastava, Deepak↗
NASA NTRS2009

Nanoscale content-addressable memory

A combined content addressable memory device and memory interface is provided. The combined device and interface includes one or more one molecular wire crossbar memories having spaced-apart key nanowires, spaced-apart value nanowires adjacent to the key nanowires, and configurable switches between the key nanowires and the value nanowires. The combination further includes a key microwire-nanowire grid (key MNG) electrically connected to the spaced-apart key nanowires, and a value microwire-nanowire grid (value MNG) electrically connected to the spaced-apart value nanowires. A key or value MNGs selects multiple nanowires for a given key or value.

Davis, Bryan↗
DOE OSTI2023

Molecular weaving of chicken-wire covalent organic frameworks

Molecular weaving is the interlacing of covalently linked threads to make extended structures. Although weaving based on 3D networks has been reported, the 2D forms remain largely unexplored. Reticular chemistry uses mutually embracing tetrahedral metal complexes as crossing points, which, when linked, typically lead to 3D woven structures. Realizing 2D weaving patterns requires crossing points with an overall planar geometry. We show that polynuclear helicates composed of multiple metal-complex units, and therefore multiple turns, are well suited in this regard. By reticulating helicate units, we successfully obtained 2D weaving structures based on the familiar chicken-wire pattern.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1997

Demonstration of mechanical connections between integrins, cytoskeletal filaments, and nucleoplasm that stabilize nuclear structure

We report here that living cells and nuclei are hard-wired such that a mechanical tug on cell surface receptors can immediately change the organization of molecular assemblies in the cytoplasm and nucleus. When integrins were pulled by micromanipulating bound microbeads or micropipettes, cytoskeletal filaments reoriented, nuclei distorted, and nucleoli redistributed along the axis of the applied tension field. These effects were specific for integrins, independent of cortical membrane distortion, and were mediated by direct linkages between the cytoskeleton and nucleus. Actin microfilaments mediated force transfer to the nucleus at low strain; however, tearing of the actin gel resulted with greater distortion. In contrast, intermediate filaments effectively mediated force transfer to the nucleus under both conditions. These filament systems also acted as molecular guy wires to mechanically stiffen the nucleus and anchor it in place, whereas microtubules acted to hold open the intermediate filament lattice and to stabilize the nucleus against lateral compression. Molecular connections between integrins, cytoskeletal filaments, and nuclear scaffolds may therefore provide a discrete path for mechanical signal transfer through cells as well as a mechanism for producing integrated changes in cell and nuclear structure in response to changes in extracellular matrix adhesivity or mechanics.

NASA Discipline Cell Biology↗
NASA NTRS1980

Interactive display of molecular models using a microcomputer system

A simple, microcomputer-based, interactive graphics display system has been developed for the presentation of perspective views of wire frame molecular models. The display system is based on a TERAK 8510a graphics computer system with a display unit consisting of microprocessor, television display and keyboard subsystems. The operating system includes a screen editor, file manager, PASCAL and BASIC compilers and command options for linking and executing programs. The graphics program, written in USCD PASCAL, involves the centering of the coordinate system, the transformation of centered model coordinates into homogeneous coordinates, the construction of a viewing transformation matrix to operate on the coordinates, clipping invisible points, perspective transformation and scaling to screen coordinates; commands available include ZOOM, ROTATE, RESET, and CHANGEVIEW. Data file structure was chosen to minimize the amount of disk storage space. Despite the inherent slowness of the system, its low cost and flexibility suggests general applicability.

Egan, J. T.↗
DOE OSTI2020

Cumulene Wires Display Increasing Conductance with Increasing Length

One-dimensional sp-hybridized carbon wires, including cumulenes and polyynes, can be regarded as finite versions of carbynes. They are likely to be good candidates for molecular-scale conducting wires as they are predicted to have a high-conductance. In this study, we first characterize the single-molecule conductance of a series of cumulenes and polyynes with a backbone ranging in length from 4 to 8 carbon atoms, including [7]cumulene, the longest cumulenic carbon wire studied to date for molecular electronics. We observe different length dependence of conductance when comparing these two forms of carbon wires. Polyynes exhibit conductance decays with increasing molecular length, while cumulenes show a conductance increase with increasing molecular length. Their distinct conducting behaviors are attributed to their different bond length alternation, which is supported by theoretical calculations. Furthermore, this study confirms the long-standing theoretical predictions on sp-hybridized carbon wires and demonstrates that cumulenes can form highly conducting molecular wires.

36 MATERIALS SCIENCE↗