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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Polyoxometalate-Assisted Crystallization: A General Strategy Enabling Structural Characterization of Molecular Radium Complexes

A fundamental understanding of radium (Ra) coordination chemistry has been hindered by the scarcity and radiological hazards of 226 Ra, leaving the structural characterization of molecular Ra complexes almost entirely unexplored. Here, we introduce a polyoxometalate (POM)-assisted crystallization strategy that enables single-crystal X-ray diffraction analysis of Ra–chelator complexes from microgram-scale samples. Employing the plenary Keggin anion [SiW 12 O 40 ] 4– , we isolated and structurally characterized Ra 2+ complexes of 18-crown-6 and the bis-picolinate macrocycle macropa, together with their Sr 2+ and Ba 2+ analogues. The resulting structures reveal systematic, size-dependent trends in coordination number and metal-donor distances across the alkaline earth series and provide the first direct experimental measurements of Ra–N and Ra–OCOO bond distances. Together, these results establish POM-assisted crystallization as a robust approach for obtaining solid-state structural information on Ra 2+ complexes of organic chelators, opening new opportunities to advance the coordination chemistry needed to fully realize radium’s potential in isotope production and targeted radiotherapy. More broadly, this approach expands the experimental toolkit available for studying scarce, highly radioactive elements accessible only in microgram quantities.

Anions↗
DOE OSTI2023

Going around the Kok cycle of the water oxidation reaction with femtosecond X-ray crystallography

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO 2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn 4 Ca complex (Mn 4 CaO 5 ) which is progressively oxidized upon the absorption of light by the chlorophyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to dioxygen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of O X from a new water molecule, which disappears on completion of the reaction, implicating it in the O—O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn 4 Ca cluster.

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

Cyclopentadienyl coordination induces unexpected ionic Am-N bonding in an americium bipyridyl complex

Variations in bonding between trivalent lanthanides and actinides is critical for reprocessing spent nuclear fuel. The ability to tune bonding and the coordination environment in these trivalent systems is a key factor in identifying a solution for separating lanthanides and actinides. Coordination of 4,4'-bipyridine (4,4'-bpy) and trimethylsilylcyclopentadienide (Cp') to americium introduces unexpectedly ionic Am-N bonding character and unique spectroscopic properties. Here we report the structural characterization of (Cp' 3 Am) 2 (μ -4,4'-bpy) and its lanthanide analogue, (Cp' 3 Nd) 2 (μ - 4,4'-bpy), by single-crystal X-ray diffraction. Spectroscopic techniques in both solid and solution phase are performed in conjunction with theoretical calculations to probe the effects the unique coordination environment has on the electronic structure.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Multi-state Catalysts Modulated by Mechanical Force (Final Report)

The development of more efficient catalytic processes and new approaches to control catalytic activity and selectivity are central to the realization of more selective, atom economic, and energy efficient routes to value added chemicals and polymers. The reactivity and selectivity of a transition metal catalyst is intimately related to the ligand-sphere geometry and, in many cases, the ideal ligand geometry for one step of a catalytic cycle is poorly matched to the ideal ligand geometry for another, resulting in sub-optimal efficiency. Macroscopic mechanical forces are both large, potentially much larger than interatomic forces, and are directional and localized to an extent that differentiates them from other forms of energy input such as heat or light. As such, mechanical force represents a heretofore untapped approach to modulate catalyst geometry, with the potential to reversibly modulate catalyst geometry on the timescale of catalytic turnover or monomer enchainment. This project has addressed the fundamental challenges in material-to-molecule strain coupling associated with the development of a new class of mechanically responsive catalysts (mechanocatalysts) in which active organotransition metal catalysts are strategically embedded in a flexible polymer network such that application of external mechanical force (stretching or deformation) leads to modulation of catalyst geometry, and hence reactivity and selectivity. Our efforts during the tenure of this grant were directed toward the elucidation of force-reactivity relationships of elementary transformations that occur within the first coordination sphere of a transition metal complex employing stiff stilbene photoswitches tethered to a flexible bidentate phosphine ligand derived from MeOBiphep as molecular force probes which provide a range of compressive and extension forces to the coupled transition metal complex depending on the geometry of the stiff stilbene and length of the tethering chains. During the tenure of this grant, we have quantified the rate of C(sp 2 )-C(sp 2 ) reductive elimination from platinum(II) diaryl complexes containing bis(phosphine) force probe ligands as a function of mechanical force; compressive forces decreased the rate of reductive elimination whereas extension forces increased the rate relative to the strain-free MeOBiphep complex with a 3.4-fold change in rate over a ~290 pN range of restoring forces. In a similar manner, we have quantified the rate of oxidative addition of bromobenzene to low-ligated palladium(0) complexes containing force probe ligands as a function of mechanical force; compressive forces increase the rate of oxidative addition, whereas tensile forces decrease the rate with a ~6 fold change in rate across ~340 pN of force applied to the complexes. In both cases, experimental and computational analyses argue strongly against any significant force-induced perturbation of ground state geometry within the first coordination sphere of the reactant complexes. Rather, the force/rate behavior observed for these transformations across these ranges of forces is attributed to the coupling of force to the nuclear motion comprising the reaction coordinates for reductive elimination and oxidative addition. These results together inform the development of catalysts whose activity can be tuned by an external force that is adjusted within a catalytic cycle and suggest opportunities to experimentally map geometry changes associated with reactions in transition metal complexes and potential strategies for force-modulated catalysis.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2024

Linear Free Energy Relationships Associated with Hydride Transfer From [(6,6'-R 2 -bpy)Re(CO) 3 H]: A Cautionary Tale in Identifying Hydrogen Bonding Effects in the Secondary Coordination Sphere

Here, six rhenium hydride complexes, [(6,6'-R 2 -bpy)Re(CO) 3 H] (bpy = 2,2'-bipyridine, R = OEt, OMe, NHMe, Me, F, Br), were synthesized. These complexes insert CO 2 to form rhenium formate complexes of the type [(6,6'-R 2 -bpy)Re(CO) 3 {OC(O)H}]. All the rhenium formate species were characterized using X-ray crystallography, which revealed that the bpy ligand is not coplanar with the metal coordination plane containing the two nitrogen donors of the bpy ligand but tilted. A solid-state structure of [(6,6'-Me 2 -bpy)Re(CO) 3 H] determined using MicroED also featured a tilted bpy ligand. The kinetics of CO 2 insertion into complexes of the type [(6,6'-R 2 -bpy)Re(CO) 3 H] were measured experimentally and the thermodynamic hydricities of [(6,6'-R 2 -bpy)Re(CO) 3 H] species were determined using theoretical calculations. A Brønsted plot constructed using the experimentally determined rate constants for CO 2 insertion and the calculated thermodynamic hydricities for [(6,6'-R 2 -bpy)Re(CO) 3 H] revealed a linear free energy relationship (LFER) between thermodynamic and kinetic hydricity. This LFER is different to the previously determined relationship for CO 2 insertion into complexes of the type [(4,4'-R 2 -bpy)Re(CO) 3 H]. At a given thermodynamic hydricity, CO 2 insertion is faster for complexes containing a 6,6'-substituted bpy ligand. This is likely in part due to the tilting observed for systems with 6,6'-substituted bpy ligands. Notably, the 6,6'-(NHMe) 2 -bpy ligand could in principle stabilize the transition state for CO 2 insertion via hydrogen bonding. This work shows that if only the rate of CO 2 insertion into [(6,6'-(NHMe) 2 -bpy)Re(CO) 3 H] is compared to [(4,4'-R 2 -bpy)Re(CO) 3 H] systems, the increase in rate could be easily attributed to hydrogen bonding, but in fact all 6,6'-substituted systems lead to faster than expected rates.

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

Structural chemistry of penta- and hexanitrato thorium($\tiny{IV}$) complexes isolated using N–H donors

In this study, a series of fifteen tetravalent thorium phases were prepared. The compounds were isolated from acidic aqueous nitrate solutions using protonated nitrogen heterocycles of varying hydrogen-bond donation strength. Structural analysis via single crystal X-ray diffraction showed that the structures are built from pentanitrato, [Th(NO 3 ) 5 (H 2 O) 2 ] 1- , and hexanitrato, [Th(NO 3 ) 6 ] 2- , molecular units, with the latter being far more prevalent in the solid state. The vibrational properties of the compounds were examined using Raman and IR spectroscopy; the spectra are dominated by stretches characteristic of nitrate and the organic ions. The relative energetics of nitrate complexation was examined using electronic structure theory. These results confirmed that there are clear thermodynamic sinks for the penta- and hexanitrato structural units that were observed experimentally. Additionally, electrostatic surface potentials (ESPs) were calculated in an effort to better understand the counterion stabilization of the complexes. The ESP surfaces showed that the position of the water and nitrate molecules and the coordination geometry of the metal complex had a clear effect on the polarizability of the two structural motifs. Despite limited speciation of the Th–nitrate structural units, the compounds exhibit rich supramolecular chemistry resulting from hydrogen bonding of the Th complexes with the organic N–H donors and π–π stacking interactions from the protonated N-heterocycles.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Catalytic Carbodiimide Guanylation by a Nucleophilic, High Spin Iron(II) Imido Complex

Reduction of the three-coordinate iron(III) imido [Ph 2 B( t BuIm) 2 Fe=NDipp] (1) affords [Ph 2 B( t BuIm) 2 Fe=NDipp][K(18-C-6)THF 2 ] (2), a rare example of a high-spin (S = 2) iron(II) imido complex. Unusually for a late metal imido complex, the imido ligand in 2 has nucleophilic character, as demonstrated by the reaction with DippNH 2 , which establishes an equilibrium with the bis(anilido) complex [Ph 2 B( t BuIm) 2 Fe(NHDipp) 2 ][K(18-C-6)THF 2 ] (3). In an unusual transformation, formal insertion of i PrN=C=N i Pr into the Fe=N(imido) bond yields the guanidinate [Ph 2 B( t BuIm) 2 Fe( i PrN) 2 CNDipp][K(18-C-6)THF 2 ] (4). Here, reaction of 4 with excess DippNH 2 provides 3, along with the guanidine ( i PrNH) 2 C=NDipp. As suggested by these stoichiometric reactions, 2 is an efficient catalyst for the guanylation of carbodiimides, converting a wide range of aniline substrates under mild conditions.

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

Effects on Human Non-Small Lung Cancer Cell growth of Cu(II), Au(III) and Re(I) Complexes Containing N-donor Pyridyl Ligands: A Senior Undergraduate Research Project

Hands-on synthetic laboratory experiences are critically important for undergraduate chemistry majors. A senior undergraduate research experience at the College of Wooster is presented in the current work. The inorganic complexes [Cu(phenan) 2 (NO 3 ) 2 ] (1; phenan = phenanthridine) and [Au(phenan)Cl 3 ](2) were prepared by metallation of the phenan ligand in a 1:1 CH 3 OH/CH 2 Cl 2 mixture at room temperature. Complex 1 is a new inorganic coordination compound. The structures were confirmed by X-ray crystallography. Complex 1 reveals a distorted octahedral geometry around the central Cu (II) metal ion. In complex 2, the Au(III) atom exhibits a square planar geometry. In addition, we investigated [Cu(dmeobpy)(H 2 O) 2 ][NO 3 ] 2 (3; dmeobpy = 4,4’-dimethoxy-2,2’-bipyridine), [Cu(bap)(NO 3 ) 2 ](4; bap = 2,6-bis(azaindole)pyridine) and [Re(CO) 3 (dmeobpy)Cl] (5). The cytoxocities of 1-5, phenan, dmeobpy, bap and cisplatin were evaluated against several human non-small cell lung cancer cell lines (NCI-H1975, HCC827, NCI-H460, and NCI-A549). Compound 1 exhibited modest antitumor activity against the HCC827 cell line, with an IC 50 value of 19 µM. Compound 3 exhibits lower cytotoxic activity than 1. Finally, the cytotoxic activity of complex 5 (IC 50 < 11 µM) is significantly greater than 1 and 3 against the H1975 cancer cell line.

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

Vernier template synthesis of molecular knots

Molecular knots are often prepared using metal helicates to cross the strands. Here we found that coordinatively mismatching oligodentate ligands and metal ions provides a more effective way to synthesize larger knots using Vernier templating. Strands composed of different numbers of tridentate 2,6-pyridinedicarboxamide groups fold around nine-coordinate lanthanide (III) ions to generate strand-entangled complexes with the lowest common multiple of coordination sites for the ligand strands and metal ions. Ring-closing olefin metathesis then completes the knots. A 3:2 (ditopic strand:metal) Vernier assembly produces +3 1 #+3 1 and –3 1 #–3 1 granny knots. Vernier complexes of 3:4 (tetratopic strand:metal) stoichiometry selectively form a 378-atom-long trefoil-of-trefoils triskelion knot with 12 alternating strand crossings or, by using opposing stereochemistry at the terminus of the strand, an inverted-core triskelion knot with six alternating and six nonalternating strand crossings.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Photophysics of graphene quantum dot assemblies with axially coordinated cobaloxime catalysts

We report a study of chromophore-catalyst assemblies composed of light harvesting hexabenzocoronene (HBC) chromophores axially coordinated to two cobaloxime complexes. The chromophore-catalyst assemblies were prepared using bottom-up synthetic methodology and characterized using solid-state NMR, IR, and x-ray absorption spectroscopy. Detailed steady-state and time-resolved laser spectroscopy was utilized to identify the photophysical properties of the assemblies, coupled with time-dependent DFT calculations to characterize the relevant excited states. The HBC chromophores tend to assemble into aggregates that exhibit high exciton diffusion length (D = 18.5 molecule 2 /ps), indicating that over 50 chromophores can be sampled within their excited state lifetime. We find that the axial coordination of cobaloximes leads to a significant reduction in the excited state lifetime of the HBC moiety, and this finding was discussed in terms of possible electron and energy transfer pathways. By comparing the experimental quenching rate constant (1.0 × 10 9 s -1 ) with the rate constant estimates for Marcus electron transfer (5.7 × 10 8 s -1 ) and Förster/Dexter energy transfers (8.1 × 10 6 s -1 and 1.0 × 10 10 s -1 ), we conclude that both Dexter energy and Marcus electron transfer process are possible deactivation pathways in CoQD-A. No charge transfer or energy transfer intermediate was detected in transient absorption spectroscopy, indicating fast, subpicosecond return to the ground state. Finally, these results provide important insights into the factors that control the photophysical properties of photocatalytic chromophore-catalyst assemblies.

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

Homoleptic An(IV) Dimethyl Sulfoxide Complexes of Th–Pu Enable Insight into Solution Speciation and Redox

A family of 8- and 9- coordinate homoleptic dimethyl sulfoxide An(IV) complexes is used to evaluate the solvation properties of tetravalent actinide ions in dimethyl sulfoxide (DMSO) vs aqueous media. These compounds are prepared from aqueous mixtures of DMSO and yield crystalline solids, whose solid-state electronic absorption spectra are compared to solution phase spectra, providing insight into the solution speciation. The thermodynamics of the equilibria between the 8- and 9-coordinate compounds were determined experimentally and computationally, showing a trend that correlates with ionic radius. Cyclic voltammetry data for the +IV/+III couples of Np and Pu in the DMSO electrolyte indicate that the +IV ions are significantly stabilized compared to aqueous media due to the more donating nature of DMSO compared to water. As a result, computational studies of these systems indicate that further reactivity may take place upon reduction to the +III oxidation state.

Actinides↗
DOE OSTI2022

Steric and Lewis Basicity Influence of the Second Coordination Sphere on Electrocatalytic CO 2 Reduction by Manganese Bipyridyl Complexes

This study aims to provide a greater insight into the balance between steric (bpy vs (Ph) 2 bpy vs mes 2 bpy ligands) and Lewis basic ((Ph) 2 bpy vs (MeOPh) 2 bpy vs (MeSPh) 2 bpy ligands) influence on the efficiencies of the protonation-first vs reduction-first CO 2 reduction mechanisms with [Mn I (R 2 bpy)(CO) 3 (CH 3 CN)] + precatalysts, and on their respective transition-state geometries/energies for rate-determining C–OH bond cleavage toward CO evolution. The presence of only modest steric bulk at the 6,6'-diphenyl-2,2'-bipyridyl ((Ph) 2 bpy) ligand has here allowed unique insight into the mechanism of catalyst activation and CO 2 binding by navigating a perfect medium between the nonsterically encumbered bpy-based and the highly sterically encumbered mes2bpy-based precatalysts. Cyclic voltammetry conducted in CO 2 -saturated electrolyte for the (Ph) 2 bpy-based precatalyst [2-CH 3 CN] + confirms that CO 2 binding occurs at the two-electron-reduced activated catalyst [2] – in the absence of an excess proton source, in contrast to prior assumptions that all manganese catalysts require a strong acid for CO 2 binding. This observation is supported by computed free energies of the parent–child reaction for [Mn–Mn] o dimer formation, where increased steric hindrance relative to the bpy-based precatalyst correlates with favorable CO 2 binding. A critical balance must be adhered to, however, as the absence of steric bulk in the bpy-based precatalyst [1-CH 3 CN] + maintains a lower overpotential than [2-CH 3 CN] + at the protonation-first pathway with comparable kinetic performance, whereas an ~2-fold greater TOF max is observed at its reduction-first pathway with an almost identical overpotential as [2-CH 3 CN] + . Notably, excessive steric bulk in the mes2bpy-based precatalyst [3-CH 3 CN] + results in increased activation free energies of the C–OH bond cleavage transition states for both the protonation-first and the reduction-first pathways relative to both [1-CH 3 CN] + and [2-CH 3 CN] + . In fact, [3-CH 3 CN] + requires a 1 V window beyond its onset potential to reach its peak catalytic current, which is in contrast to the narrower (<0.30 V) potential response window of the remaining catalysts here studied. Furthermore, voltammetry recorded under 1 atm of CO 2 with 2.8 M (5%) H 2 O establishes [2-CH 3 CN] + to have the lowest overpotential (η = 0.75 V) in the series here studied, attributed to its ability to lie “on the fence” when providing sufficient steric bulk to hinder (but not prevent) [Mn–Mn] o dimerization, while simultaneously having a limited steric impact on the free energy of activation for the rate-determining C–OH bond cleavage transition state. While the methoxyphenyl bpy-based precatalyst [4-CH 3 CN] + possesses an increased steric presence relative to [2-CH 3 CN] + , this is offset by its capacity to stabilize the C–OH bond cleavage transition states of both the protonation-first and the reduction-first pathways by facilitating second coordination sphere H-bonding stabilization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Surface-Initiated Atom Transfer Radical Polymerization Using Hydrogel Reactors

Atom transfer radical polymerization (ATRP) is a controlled radical polymerization method that enables the synthesis of tailored polymeric materials with low dispersity, highlighting its immense potential for green fabrication of advanced materials. However, its broader implementation is limited by challenges in product isolation, maintaining catalyst activity, and mitigating atmospheric sensitivity arising from oxygen-sensitive metal catalysts. Here, gelatin hydrogels (GHs) are introduced as a soft “reactor” matrix for interfacial ATRP, operating with minimal metal-catalyst loading while exhibiting possibly an organoreductive behavior. This strategy leverages activator regeneration via electron transfer through a ligand–metal charge-transfer (LMCT) mechanism to reduce oxidized metal catalysts within the GH network. Polymerization is evaluated by growing polymer brushes at an active interface formed between GHs swollen in monomer solution and an initiating surface, and sequential growth experiments confirmed that GH-mediated ATRP preserves living character. Under UV illumination, LMCT is activated, producing polymers both at the desired interface and within the GH bulk. UV–Vis spectroscopy revealed active reduction of Cu(II) to Cu(I) along with concentration-dependent complex formation, indicating dynamic coordination chemistry within the hydrogel. The redox-active arginine- and glutamic acid-rich gelatin backbone coordinates and reduces the metal center, enabling ATRP at ppm-level catalyst concentrations. While polymerization proceeds in GH-Cu(II) reactors, adding external mobile ligands to the GH results in longer polymer brushes. Here, the results reported here are exploratory. More experiments are needed to characterize polymer brush growth in GHs and compare it to conventional surface-initiated polymerization in solution.

Absorption↗
DOE OSTI2021

Liquid-induced topological transformations of cellular microstructures

The fundamental topology of cellular structures—the location, number and connectivity of nodes and compartments—can profoundly affect their acoustic, electrical5, chemical, mechanical and optical properties, as well as heat, fluid and particle transport. Approaches that harness swelling, electromagnetic actuation and mechanical instabilities in cellular materials have enabled a variety of interesting wall deformations and compartment shape alterations, but the resulting structures generally preserve the defining connectivity features of the initial topology. Achieving topological transformation presents a distinct challenge for existing strategies: it requires complex reorganization, repacking, and coordinated bending, stretching and folding, particularly around each node, where elastic resistance is highest owing to connectivity. Here we introduce a two-tiered dynamic strategy that achieves systematic reversible transformations of the fundamental topology of cellular microstructures, which can be applied to a wide range of materials and geometries. Our approach requires only exposing the structure to a selected liquid that is able to first infiltrate and plasticize the material at the molecular scale, and then, upon evaporation, form a network of localized capillary forces at the architectural scale that ‘zip’ the edges of the softened lattice into a new topological structure, which subsequently restiffens and remains kinetically trapped. Reversibility is induced by applying a mixture of liquids that act separately at the molecular and architectural scales (thus offering modular temporal control over the softening–evaporation–stiffening sequence) to restore the original topology or provide access to intermediate modes. Guided by a generalized theoretical model that connects cellular geometries, material stiffness and capillary forces, we demonstrate programmed reversible topological transformations of various lattice geometries and responsive materials that undergo fast global or localized deformations. In conclusion, we then harness dynamic topologies to develop active surfaces with information encryption, selective particle trapping and bubble release, as well as tunable mechanical, chemical and acoustic properties.

42 ENGINEERING↗
DOE OSTI2025

Ligand substituents modulate excited-state lifetime and energy-transfer reactivity in Cu( I ) photosensitizers supported by salicylaldimine and isocyanide ligands

The design of earth-abundant molecular photosensitizers with desirable photophysical properties and good excited-state reactivity is critical for sustainable photochemical applications. Herein, we report a new family of three-coordinate heteroleptic Cu(I) complexes supported by monoanionic salicylaldimine (N^O) chelating ligands and aryl isocyanides. By systematically tuning the steric bulk on each ligand, we establish clear structure–property relationships that govern the excited-state lifetimes and photocatalytic performance metrics of these complexes. Increasing steric congestion on the salicylaldimine ligand, which contributes to the HOMO, results in faster nonradiative decay and shortens excited-state lifetimes. In contrast, introducing steric bulk on the isocyanide ligand, where the LUMO is primarily localized, suppresses nonradiative decay, most likely by inhibiting excited-state geometric relaxation, thereby extending the lifetime up to 375 ns. These photophysical trends correlate directly with performance in triplet–triplet energy transfer (TTET) photocatalysis, where longer-lived complexes enable faster E/Z isomerization of trans-stilbene. This work demonstrates that remote steric modulation of ligand frameworks offers a simple yet powerful strategy for tuning the excited-state dynamics and catalytic properties of this new class of Cu(I) photosensitizers.

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

Color center in β -Ga 2 O 3 emitting at the telecom range

Transition metal (TM) ions incorporated into a host from a wide bandgap semiconductor are recognized as a promising system for quantum technologies with enormous potential. In this work, we report on a TM color center in β-Ga 2 O 3 with physical properties attractive for quantum information applications. The center is found to emit at 1.316 μm and exhibits weak coupling to phonons, with optically addressable higher-lying excited states, beneficial for single-photon emission within the telecom range (O-band). Using magneto-photoluminescence (PL) complemented by time-resolved PL measurements, we identify the monitored emission to be internal 1 E→ 3 A 2 spin-forbidden transitions of a 3d 8 TM ion with a spin-triplet ground state—a possible candidate for a spin qubit. We tentatively attribute this color center to a complex involving a sixfold coordinated Cu 3+ ion.

36 MATERIALS SCIENCE↗