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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

An Optical Oxygen Sensor for Long-Term Continuous Monitoring of Dissolved Oxygen in Perfused Bioreactors

For long-term growth of man1ITlalian cells in perfused bioreactors, it is essential to monitor the concentration of dissolved oxygen (DO) present in the culture medium to quantitate and control level of DO. Continuous measurement of the amount of DO in the cell culture medium in-line under sterile conditions in NASA's perfused bioreactor requires that the oxygen sensor provide increased sensitivity and be sterilizable and nontoxic. Additionally, long-term cell culture experiments require that the calibration be maintained several weeks or months. Although there are a number of sensors for dissolved oxygen on the market and under development elsewhere, very few meet these stringent conditions. An optical oxygen sensor (BOXY) based on dynamic fluorescent quenching and a pulsed blue LED light source was developed in our laboratory to address these requirements. Tris( 4,7 -diphenyl-l, 1 O-phenanthroline )ruthenium(II) chloride is employed as the fluorescent dye indicator. The sensing element consists of a glass capillary (OD 4.0 mm; ID 2.0 mm) coated internally with a thin layer of the fluorescent dye in silicone matrix and overlayed with a black shielding layer. Irradiation of the sensing element with blue light (blue LED with emission maximum at 475 nm) generates a red fluorescence centered at 626 nm. The fluorescence intensity is correlated to the concentration of DO present in the culture medium, following the modified non-linear Stern-Volmer equation. By using a pulsed irradiating light source, the problem of dye-bleaching, which is often encountered in long-term continuous measurements of tIns type, 'is minimized. To date we achieved sensor resolution of 0.3 mmHg at 50 mmHg p02, and 0.6 mmHg at 100 mmHg p02, with a response time of about one minute. Calibration was accomplished in sterile phosphate-buffered saline with a blood-gas analyzer (BGA) measurement as reference. Stand-alone software was also developed to control the sensor and bioreactor as well as to acquire data. Two HOXY sensors with a single calibration were employed to continuously monitor the DO in GTSF-2 medium during a Baby Hamster Kidney (BHK-21) cell culture in a Rotating Wall Perfused Vessel (RWPV) bioreactor for 90 days. HOXY sensors were located at the inlet to and outlet from the bioreactor. One of the sensors was placed between an oxygenator and the inlet to the bioreactor. The dissolved oxygen concentrations determined by both sensors were compared with those measured regularly with the BGA reference. The cell culture was maintained for 110 days. Sensor output was found to correlate well with the BGA data throughout the experiment, where the DO of the medium ranged between 25 and 50 mmHg at the bioreactor outlet and 90-130 mmHg at the bioreactor inlet. Measuring DO with the HOXY sensors versus the BGA reference indicated bias values of -2 mmHg and -15 mmHg, and precision values of +/-3mmHg and +/-16 mmHg at the bioreactor inlet and outlet, respectively.

Gao, F. G.↗
NASA NTRS2011

Flight Testing of the Forward Osmosis Bag for Water Recovery on STS-135

The Forward Osmosis Bag (FOB) is a personal water purification device for recovery of potable liquid from almost any non-potable water source. The FOB experiment was flown as a sortie mission on STS-135/ULF7 using flight-certified materials and a design based on the X-Pack(TradeMark) from Hydration Technology Innovations (Albany, OR). The primary objective was to validate the technology for use under microgravity conditions. The FOB utilizes a difference in solute concentration across a selectively permeable membrane to draw water molecules from the non-potable water while rejecting most chemical and all microbial contaminants contained within. Six FOB devices were tested on STS-135 for their ability to produce a potable liquid permeate from a feed solution containing 500 mL potassium chloride (15 g/L) amended with 0.1% methyl blue dye (w:v) tracer against an osmotic gradient created by addition of 60 mL of concentrate containing the osmolytes fructose and glucose, and 0.01% sodium fluorescein (w:v) tracer. Three FOB devices were physically mixed by hand for 2 minutes by a crewmember after loading to augment membrane wetting for comparison with three unmixed FOB devices. Hydraulic flux rate and rejection of salt and dye in microgravity were determined from a 60-mL sample collected by the crew on orbit after 6 hours. Post-flight analysis of samples collected on orbit demonstrated that the Forward Osmosis Bag achieved expected design specifications in microgravity. The hydraulic flux rate of water across the membrane was reduced approximately 50% in microgravity relative to ground controls that generated an average of 50 mL per hour using the same water and osmolyte solutions. The membrane rejected both potassium and chloride at >92% and methyl blue dye at >99.9%. Physical mixing of the FOB during water recovery did not have any significant effect on either flux rate or rejection of solutes from the water solution. The absence of buoyancy-driven convection in microgravity suggests that mass transport was dominated by diffusion, slowing the rate of permeate production across the membrane. It is possible that a predicted reduction in concentration polarization at the membrane surface that may have acted to increase the rate of permeate production in microgravity was negligible under the described test conditions.

Roberts, Michael S.↗
NASA NTRS2012

Fluorescence-Doped Particles for Simultaneous Temperature and Velocity Imaging

Polystyrene latex microspheres (PSLs) have been used for particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) measurements for several decades. With advances in laser technologies, instrumentation, and data processing, the capability to collect more information about fluid flow beyond velocity is possible using new seed materials. To provide additional measurement capability, PSLs were synthesized with temperature-sensitive fluorescent dyes incorporated within the particle. These multifunctional PSLs would have the greatest impact if they could be used in large scale facilities with minimal modification to the facilities or the existing instrumentation. Consequently, several potential dyes were identified that were amenable to existing laser systems currently utilized in wind tunnels at NASA Langley Research Center as well as other wind and fluid (water) tunnels. PSLs incorporated with Rhodamine B, dichlorofluorescein (DCF, also known as fluorescein 548 or fluorescein 27) and other dyes were synthesized and characterized for morphology and spectral properties. The resulting particles were demonstrated to exhibit fluorescent emission, which would enable determination of both fluid velocity and temperature. They also would allow near-wall velocity measurements whereas laser scatter from surfaces currently prevents near-wall measurements using undoped seed materials. Preliminary results in a wind tunnel facility located at Virginia Polytechnic Institute and State University (Virginia Tech) have verified fluorescent signal detection and temperature sensitivity of fluorophore-doped PSLs.

Danehy, Paul M.↗
NASA NTRS2012

Late Effects of Heavy Ion Irradiation on Ex Vivo Osteoblastogenesis and Cancellous Bone Microarchitecture

Prolonged spaceflight causes degeneration of skeletal tissue with incomplete recovery even after return to Earth. We hypothesize that heavy ion irradiation, a component of Galactic Cosmic Radiation, damages osteoblast progenitors and may contribute to bone loss during long duration space travel beyond the protection of the Earth's magnetosphere. Male, 16 week old C57BL6/J mice were exposed to high LET (56 Fe, 600MeV) radiation using either low (5 or 10cGy) or high (50 or 200cGy) doses at the NASA Space Radiation Lab and were euthanized 3 - 4, 7, or 35 days later. Bone structure was quantified by microcomputed tomography (6.8 micron pixel size) and marrow cell redox assessed using membrane permeable, free radical sensitive fluorogenic dyes. To assess osteoblastogenesis, adherent marrow cells were cultured ex vivo, then mineralized nodule formation quantified by imaging and gene expression analyzed by RT PCR. Interestingly, 3 - 4 days post exposure, fluorogenic dyes that reflect cytoplasmic generation of reactive nitrogen/oxygen species (DAF FM Diacetate or CM H2DCFDA) revealed irradiation (50cGy) reduced free radical generation (20-45%) compared to sham irradiated controls. Alternatively, use of a dye showing relative specificity for mitochondrial superoxide generation (MitoSOX) revealed an 88% increase compared to controls. One week after exposure, reactive oxygen/nitrogen levels remained lower(24%) relative to sham irradiated controls. After one month, high dose irradiation (200 cGy) caused an 86% decrement in ex vivo nodule formation and a 16-31% decrement in bone volume to total volume and trabecular number (50, 200cGy) compared to controls. High dose irradiation (200cGy) up regulated expression of a late osteoblast marker (BGLAP) and select genes related to oxidative metabolism (Catalase) and DNA damage repair (Gadd45). In contrast, lower doses (5, 10cGy) did not affect bone structure or ex vivo nodule formation, but did down regulate iNOS by 0.54 - 0.58 fold. Thus, both low and high doses of heavy ion irradiation cause time dependent, adaptive changes in redox state within marrow cells but only high doses (50, 200cGy) inhibit osteoblastogenesis and cause cancellous bone loss. We conclude space radiation has the potential to cause persistent damage to bone marrow derived stem and progenitor cells for osteoblasts despite adaptive changes in cellular redox state.

Tran, Luan Hoang↗
NASA NTRS2018

Late Effects of Heavy-Ion Irradiation on Ex Vivo Osteoblastogenesis and Cancellous Bone Microarchitecture

Prolonged spaceflight causes degeneration of skeletal tissue with incomplete recovery even after return to Earth. We hypothesize that heavy-ion irradiation, a component of Galactic Cosmic Radiation, damages osteoblast progenitors and may contribute to bone loss during long duration space travel beyond the protection of the Earth's magnetosphere. Male, 16 week-old C57BL6/J mice were exposed to high-LET (56-Fe, 600MeV) radiation using either low (5 or 10cGy) or high (50 or 200cGy) doses at the NASA Space Radiation Lab and were euthanized 3-4, 7, or 35 days later. Bone structure was quantified by microcomputed tomography (6.8 μm pixel size) and marrow cell redox assessed using membrane permeable, free radical-sensitive fluorogenic dyes. To assess osteoblastogenesis, adherent marrow cells were cultured ex vivo, then mineralized nodule formation quantified by imaging and gene expression analyzed by RT-PCR. Interestingly, 3-4 days post-exposure, fluorogenic dyes that reflect cytoplasmic generation of reactive nitrogen/oxygen species (DAF-FM Diacetate or CM-H2DCFDA) revealed irradiation (50cGy) reduced free radical generation (20-45%) compared to sham-irradiated controls. Alternatively, use of a dye showing relative specificity for mitochondrial superoxide generation (MitoSOX) revealed an 88% increase compared to controls. One week after exposure, reactive oxygen/nitrogen levels remained lower (24%) relative to sham-irradiated controls. After one month, high dose irradiation (200 cGy) caused an 86% decrement in ex vivo nodule formation and a 16-31% decrement in bone volume to total volume and trabecular number (50, 200cGy) compared to controls. High dose irradiation (200cGy) up-regulated expression of a late osteoblast marker (BGLAP) and select genes related to oxidative metabolism (Catalase) and DNA damage repair (Gadd45). In contrast, lower doses (5, 10cGy) did not affect bone structure or ex vivo nodule formation, but did down-regulate iNOS by 0.54-0.58 fold. Thus, both low- and high-doses of heavy-ion irradiation cause time-dependent, adaptive changes in redox state within marrow cells but only high doses (50, 200cGy) inhibit osteoblastogenesis and cause cancellous bone loss. We conclude space radiation has the potential to cause persistent damage to bone marrow-derived stem and progenitor cells for osteoblasts despite adaptive changes in cellular redox state.

LATE EFFECTS OF HEAVY-ION IRRADIATION↗
DOE OSTI2025

Scalable thin graphene oxide membranes enabled by polydopamine gutter layer

Two-dimensional (2D) nanosheets have been widely used to fabricate thin-film composite membranes for dye desalination. However, they often need to be thick to mitigate the defects resulting from their random stacking and rough support surface. Herein, bio-adhesive polydopamine (PDA) is used as a gutter layer to prepare graphene oxide (GO)-based membranes by improving the adhesion between the GO and porous support and providing a smooth surface to form thin, highly selective layers. For example, the PDA priming reduces the GO layer thickness by 57 %, from 447 to 190 nm, while achieving similar dye desalination properties. The effect of the dopamine concentration, exposure time, and GO layer thickness on the membrane structure and desalination performance are thoroughly investigated using various techniques, such as scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), and x-ray diffraction (XRD). The PDA gutter layer is also applied for hollow fiber membranes, achieving water permeance of 79 L m -2 h −1 bar−1 and rejection of ∼99 % for Direct red 80. The membranes were challenged by simulated dye/salt mixtures to elucidate the complicated effect of the compositions on the desalination performance. Furthermore, this study unveils a new avenue to improve separation performance and large-scale manufacturability of 2D material-based membranes.

Dye desalination↗
DOE OSTI2025

Understanding and controlling the fundamental photochemistry of protonic solar energy conversion (Final Scientific/Technical Report)

The selectivity and activity of most fuel-forming reactions are tunable by the concentration of electrons, holes, protons, and/or hydroxides. That is one reason why traditional solar energy conversion processes are used to drive these reactions, where light directly increases the concentration of electrons and holes. We, instead, took a different approach, using light to increase the concentration of protons and/or hydroxides. For this, we leveraged photophysical and solid-state physics theories, techniques, and design strategies previously developed for the study of traditional solar energy conversion processes. We designed and fabricated several materials platforms based on molecular photoacid and photobase dyes coupled with ion-exchange polymer membranes and assessed their fundamental photoelectrochemistry. We demonstrated control over built-in electric potentials, photovoltages, proton-transfer kinetics, and efficiency limits to our approach. Understanding the basic science of these dye-sensitized protonic membranes and their photochemical mechanisms is of use to the DOE-relevant processes of solar photochemical fuel formation, solar photodialytic desalination, and solar cells. Moreover, functional materials that we developed from this project may be of use to several broad-reaching fields and may provide the foundation for a completely new, inexpensive, and robust solar energy conversion technology.

14 SOLAR ENERGY↗
NASA NTRS1994

Rapid in situ assessment of physiological activities in bacterial biofilms using fluorescent probes

Two rapid in situ enumeration methods using fluorescent probes were used to assess the physiological activities of Klebsiella pneumoniae biofilms on stainless steel. Fluorescent dyes, 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and rhodamine 123 (Rh 123), were chosen to perform this study. CTC is a soluble redox indicator which can be reduced by respiring bacteria to fluorescent CTC-formazan crystals. Rh 123 is incorporated into bacteria with respect to cellular proton motive force. The intracellular accumulation of these fluorescent dyes can be determined using epifluorescence microscopy. The results obtained with these two fluorescent probes in situ were compared to the plate count (PC) and in situ direct viable count (DVC) methods. Viable cell densities within biofilms determined by the three in situ methods were comparable and always showed approximately 2-fold higher values than those obtained with the PC method. As an additional advantage, the results were observed after 2 h, which was shorter than the 4 h incubation time required for the DVC method and 24 h for colony formation. The results indicate that staining with CTC and Rh 123 provides rapid information regarding cell numbers and physiological activities of bacteria within biofilms.

NASA Discipline Number 04-10↗
NASA NTRS2008

Analysis of Proposed 2007-2008 Revisions to the Lightning Launch Commit Criteria for United States Space Launches

Ascending space vehicles are vulnerable to both natural and triggered lightning. Launches under the jurisdiction of the United States are generally subject to a set of rules called the Lightning Launch Commit Criteria (LLCC) (Krider etal., 1999; Krider etal., 2006). The LLCC protect both the vehicle and the public by assuring that the launch does not take place in conditions posing a significant risk of a lightning strike to the ascending vehicle. Such a strike could destroy the vehicle and its payload, thus causing failure of the mission while releasing both toxic materials and debris. To assure safety, the LLCC are conservative and sometimes they may seriously limit the ability of the launch operator to fly as scheduled even when conditions are benign. In order to safely reduce the number of launch scrubs and delays attributable to the LLCC, the Airborne Field Mill (ABFM II) program was undertaken in 2000 - 2001. The effort was directed to collecting detailed high-quality data on the electrical, microphysical, radar and meteorological properties of thunderstorm-associated clouds. Details may be found in Dye et al., 2007. The expectation was that this additional knowledge would provide a better physical basis for the LLCC and allow them to be revised to be less restrictive while remaining at least as safe. That expectation was fulfilled, leading to significant revisions to the LLCC in 2003 and 2005. The 2005 revisions included the application of a new radar-derived quantity called the Volume Averaged Height Integrated Radar Reflectivity (VAHIRR) in the rules governing flight through anvil clouds. VAHIRR is the product of the volume averaged radar reflectivity times the radardetermined cloud thickness. The reflectivity average extends horizontally 5 km west, east, south and north of a point along the flight track and vertically from the 0 C isotherm to the top of the radar cloud. This region is defined as the "Specified Volume". See Dye et al., 2006 and Merceret et al., 2006 for a more thorough description of VAHIRR. The units are dBZ km (not dBZ per kilometer) and the threshold is 10 dBZ km. It is safe to fly through an anvil cloud for which VAHIRR is below this threshold everywhere along the flight track as long as (1) the entire cloud within 5 nmi. (9.26 km) of the flight track is colder than 0 C, (2) the points at which VAHIRR must be evaluated are at least 20 km from any active convective cores and recent lightning, and (3) the radar return is not being attenuated within the Specified Volume around those points.

Dye, James E.↗
DOE OSTI2024

Molecular Dynamical and Quantum Mechanical Exploration of the Site-Specific Dynamics of Cy3 Dimers Internally Linked to dsDNA

Performing spectroscopic measurements on biomolecules labeled with fluorescent probes is a powerful approach to locating the molecular behavior and dynamics of large systems at specific sites within their local environments. The indocarbocyanine dye Cy3 has emerged as one of the most commonly used chromophores. The incorporation of Cy3 dimers into DNA enhances experimental resolution owing to the spectral characteristics influenced by the geometric orientation of excitonically coupled monomeric units. Various theoretical models and simulations have been utilized to aid in the interpretation of the experimental spectra. In this study, we employ all-atom molecular dynamics simulations to study the structural dynamics of Cy3 dimers internally linked to the dsDNA backbone. We used quantum mechanical calculations to derive insights from both the linear absorption spectra and the circular dichroism data. Furthermore, we explore potential limitations within a commonly used force field for cyanine dyes. The molecular dynamics simulations suggest the presence of four possible Cy3 dimeric populations. The spectral simulations on the four populations show one of them to agree better with the experimental signatures, suggesting it to be the dominant population. Furthermore, the relative orientation of Cy3 in this population compares very well with previous predictions from the Holstein–Frenkel Hamiltonian model.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Adsorption and Solvation Modulate Rhodamine B Diffusion in Ethanol/Water-Filled Anodic Alumina Nanopores

Confinement of solvents and solutes within nanoporous materials frequently leads to the emergence of unique mass transport behaviors that, once fully understood, may lead to improved chemical separations. Here, the diffusion of Rhodamine B (RhB) dye within 10 and 20 nm diameter anodic aluminum oxide (AAO) nanopores filled with binary ethanol/water mixtures is investigated. Mixture compositions spanning from pure ethanol to pure water are employed. The results of confocal fluorescence correlation spectroscopy studies reveal that RhB diffusion occurs by a two-component mechanism comprising composition-dependent fast and slow motions, characterized by diffusion coefficients D f and D s . The results are consistent with those of previous studies performed under more limited conditions [J. Phys. Chem. C, 2023, 127, 411-420]. The fast component scales with mixture viscosity and is assigned to hindered bulk-like diffusion in central pore regions. Slow diffusion likely involves adsorption of RhB to the pore surface and may be described by a desorption mediated mechanism. The occurrence of RhB adsorption to the AAO surface is verified at the single-molecule level by wide-field fluorescence imaging of membrane cross-sectional surfaces. Unique composition dependent trends in the autocorrelation amplitude and in D s that mimic bulk RhB solubility are revealed. D s is found to be smallest in pure ethanol and pure water and largest in intermediate mixtures. These results suggest that RhB surface adsorption is strongest in the pure liquids and weakest in mixtures of intermediate composition, where the dye is least soluble, and most soluble, respectively. As a result, molecular dynamics simulations reveal that a water layer appears on the pore surface under most conditions, while RhB is solvated primarily by ethanol. The composition dependence of RhB diffusion is concluded to reflect its solvation dependent interactions with the pore walls.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Fabrication of Catalytic Distillation Membranes with Atomic Layer Deposition

The integration of catalysts onto the surface of membranes enables simultaneous physical separation and catalytic transformation of constituents in a feed stream, facilitating improved contaminant removal and fouling mitigation. Distillation membranes are a particularly attractive platform for catalytic membranes because they reject nonvolatile species and exhibit exceptional resistance to oxidative and radical-driven degradation. However, imparting catalytic functionality onto hydrophobic, porous distillation membranes has proven challenging since the membranes used are chemically inert and difficult to modify. Furthermore, catalysts on the membrane surface can decrease hydrophobicity and increase the membrane’s susceptibility to pore wetting and failure. In this work, we create a catalytic distillation membrane by coating a polytetrafluoroethylene membrane surface with titanium dioxide (TiO 2 ) via plasma-assisted atomic layer deposition (ALD). By precisely tuning the ALD parameters, we demonstrate localized growth of TiO 2 near (within approximately 1 μm) the surface of polytetrafluoroethylene membranes, forming a catalytically active interface while preserving the underlying hydrophobic pore structure. Localized growth of TiO 2 is confirmed by electron microscopy and spectroscopy techniques, and membranes coated with 500 cycles of ALD show pressure tolerance up to 12.8 bar and higher than 95% salt rejection in pressure-driven distillation. Photocatalytic activity is demonstrated via the degradation of methylene blue dye under UV irradiation, where increasing TiO2 loading leads to an enhancement in dye degradation. These results establish a general strategy for integrating catalytic functionality into chemically inert, hydrophobic membranes without compromising distillation performance, providing a pathway toward multifunctional membranes that couple advanced oxidation with membrane separation for water treatment.

atomic layer deposition↗
DOE OSTI2025

Fabrication of α-Fe 2 O 3 Nanoparticles/g-C 3 N 4 Direct Z-Scheme Heterojunction of Durable Photocatalytic Activity

The fabrication of a nanohybrid photocatalyst that combines α-Fe 2 O 3 nanoparticles with graphitic carbon nitride (g-C 3 N 4 ) is reported. The ensuing direct Z-scheme heterojunction greatly boosts the photocatalytic activity of the α-Fe 2 O 3 /g-C 3 N 4 nanohybrids. This results in organic dye degradation rates more than two times higher than its individual components, promoted by the efficient charge separation and transfer of the Z-scheme heterojunction mechanism of the nanohybrid photocatalyst. In addition, recyclability tests show an outstanding stability of the nanohybrids spanning five consecutive dye degradation experiments, during which the degradation rate is slightly improved. The origin of the improved photocatalytic performance of the nanohybrid lies in the intimate interaction between α-Fe 2 O 3 and g-C 3 N 4 afforded by the two-step fabrication process, which enables the direct and controlled growth of α-Fe 2 O 3 nanoparticles on g-C 3 N 4 . A first ultrasound impregnation step promotes the effective anchoring of stable Fe species via Fe–N and C–N/C–O bonding, while a second microwave phase conversion step induces the subsequent growth of α-Fe 2 O 3 nanoparticles on the g-C 3 N 4 sheets. Careful control of the FeCl 3 precursor concentration up to a threshold value of 0.25 M during impregnation enables complete control over their size and phase. This approach clearly highlights the benefits of microwave reactor systems in the fabrication of hematite-based Z-scheme photocatalytic, overcoming the limitations of conventional thermal treatment technology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

3D Printing of Polyelectrolyte Complex-Integrated Photocurable Hydrogel Resins

In this study, we developed a photocurable hydrogel resin incorporating a polyelectrolyte complex (PEC) for 3D printing. Acrylamide-based monomers were formulated with varying PEC contents (0–15 wt %) in an aqueous KBr medium to fabricate patterned porous hydrogel structures. The morphology of printed hydrogels was characterized by field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. Notably, the PEC5 and PEC10 formulations exhibited optimal thermal stability and compressive properties, attributed to the homogeneous distribution of PEC domains within the hydrogel matrix. Furthermore, dye adsorption experiments demonstrated excellent removal efficiency, highlighting the potential of PEC-containing hydrogels for environmental remediation applications, particularly in the treatment of dye-contaminated wastewater.

Yang, Jinchul [University of Tennesse Knoxville]↗
DOE OSTI2026

Interfacial Charge Transfer Pathways in Photoelectrochemical H 2 Evolution by a Single-Component Molecular Catalyst on a Conductive Metal Oxide

Dye-sensitized photoelectrosynthesis cells traditionally combine a photosensitizing dye to harvest light and a catalyst to generate chemical fuels on a semiconductor. Here, in this work, a photoactive catalyst capable of both light absorption and fuel formation, [Cp*Ir(4,4′-Y 2 -bpy)Cl][Cl] (Cp* = pentamethylcyclopentadienyl, bpy = 2,2′-bipyridine, Y = CH 2 PO 3 H 2 ), is anchored to a mesoporous tin-doped indium oxide (ITO) electrode and facilitates photoelectrochemical H 2 evolution in water without the need for additional photosensitizers or sacrificial reductants. Spectroelectrochemistry indicates a single-site H 2 evolution mechanism involving charge injection to ITO, in contrast to the bimetallic mechanism observed in solution. Cyclic voltammetry and variable-potential chronoamperometry under illumination probe competing pathways via interfacial electron transfer between the Ir hydride excited state and the conductive ITO electrode. A Marcus theory framework provides reorganization energies for competing interfacial electron transfer pathways from potential-dependent quantum yield measurements. The light-driven H 2 evolution catalysis on conducting oxide proceeds with high Faradaic efficiency and current densities comparable to photoelectrodes utilizing p-type semiconductors. By uncovering the principal electron transfer pathways that govern photocatalytic efficiency, this study establishes design principles for hybrid molecular photoelectrocatalysts.

catalysts↗
DOE OSTI2026

Phonon modulation of strongly coupled gold tetrahedral plasmonic nanoparticles and a carbocyanine J-aggregate

Coupling exciton and plasmon excitations to form polaritons are of great interest for manipulating energy transfer at the nanoscale via the formation of hybrid light–matter states. In this study, we successfully couple gold tetrahedral nanoparticles with the J-aggregate forming dye 5,5′,6,6′-tetrachloro-1,1′-diethyl-3,3′-di(4-sulfobutyl)-benzimidazolocarbocyanine (TDBC) to form a strongly coupled colloidal polariton system with a Rabi splitting energy of ∼206 meV. These gold tetrahedra exhibit coherent phonon modes upon photoexcitation, which produce transient oscillations of the LSPR energy for isolated tetrahedra. Transient absorption measurements of the polariton system were performed and show how these coherent phonon modes influence the polariton states’ extinction. We found that the oscillation period increases by 0.5 ± 0.14 ps upon surface deposition of TDBC dye, demonstrating LSPR sensitivity to the refractive index environment. Shifts in the plasmon resonance due to the coherent phonon modes transiently alters LSPR alignment with the J-aggregate exciton peak, resulting in shifts of the hybrid polariton states’ oscillator strength.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Ballistic Frenkel-exciton gate with a high on-off ratio

Here it is shown that the exciton interactions within organic dye aggregates, as modeled by the Frenkel Hamiltonian, enable the construction of an on/off switchable exciton gate. In this construction, a single exciton residing on a controlling gate molecule may pass or inhibit the ballistic propagation of an exciton in a proximal gate channel consisting of an array of dye molecules. High on-off ratios in excess of 102 can be achieved through the use of static difference dipole-dipole interactions between the gate and the gate channel which effectively creates a switchable Bragg grating. The gate channel and controlling gate molecule exhibit entanglement with the quantum mechanical superposition of the presence and absence of exciton occupation on the gate molecule.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Performance of chatbots in queries concerning fundamental concepts in photochemistry

Abstract The advent of chatbots raises the possibility of a paradigm shift across society including the most technical of fields with regard to access to information, generation of knowledge, and dissemination of education and training. Photochemistry is a scientific endeavor with roots in chemistry and physics and branches that encompass diverse disciplines ranging from astronomy to zoology. Here, five chatbots have each been challenged with 13 photochemically relevant queries. The chatbots included ChatGPT 3.5, ChatGPT 4.0, Copilot, Gemini Advanced, and Meta AI. The queries encompassed fundamental concepts (e.g., “Why is the fluorescence spectrum typically the mirror image of the absorption spectrum?”), practical matters (e.g., “What is the inner filter effect and how to avoid it?”), philosophical matters (“Please create the most important photochemistry questions.”), and specific molecular features (e.g., “Why are azo dyes non‐fluorescent?”). The chatbots were moderately effective in answering queries concerning fundamental concepts in photochemistry but were glaringly deficient in specialized queries for dyes and fluorophores. In some instances, a correct response was embedded in verbose scientific nonsense whereas in others the entire response, while grammatically correct, was utterly meaningless. The unreliable accuracy makes present chatbots poorly suited for unaided educational purposes and highlights the importance of domain experts.

Taniguchi, Masahiko↗