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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Encoding Multilayer Complexity in Anti‐Counterfeiting Heterometallic MOF‐Based Optical Tags

Abstract Optical tags provide a way to quickly and unambiguously identify valuable assets. Current tag fluorophore options lack the tunability to allow combined methods of encoding in a single material. Herein we report a design strategy to encode multilayer complexity in a family of heterometallic rare‐earth metal–organic frameworks based on highly connected nonanuclear clusters. To impart both intricacy and security, a synergistic approach was implemented resulting in both overt (visible) and covert (near‐infrared, NIR) properties, with concomitant multi‐emissive spectra and tunable luminescence lifetimes. Tag authentication is validated with a variety of orthogonal detection methodologies. Importantly, the effect induced by subtle compositional changes on intermetallic energy transfer, and thus on the resulting photophysical properties, is demonstrated. This strategy can be widely implemented to create a large library of highly complex, difficult‐to‐counterfeit optical tags.

Deneff, Jacob I.↗
DOE OSTI2021

Doubling the Stakes: The Promise of Halide Double Perovskites

Abstract When the stakes are doubled in a wager, a player must correctly place two consecutive bets to win, but the payout is larger. Similarly, two B sites in combination dictate the properties of A 2 BB′X 6 (A=monocation, X=halide) double perovskites. Correctly picking two B sites is more challenging than picking just one, as in the A I B II X 3 single perovskites, but the options are greater and, we believe, the rewards are higher when the stakes are doubled. In this Minireview, we emphasize fundamental aspects of halide double perovskites to provide a foundation for interested readers to explore this extraordinary class of materials. In particular, we highlight the differences and similarities between double and single perovskites and describe how the double perovskite structure potentially offers greater control over photophysical properties.

Wolf, Nathan R.↗
DOE OSTI2021

Heterometallic Actinide‐Containing Photoresponsive Metal‐Organic Frameworks: Dynamic and Static Tuning of Electronic Properties

Abstract Acquiring fundamental knowledge of properties of actinide‐based materials is a necessary step to create new possibilities for addressing the current challenges in the nuclear energy and nuclear waste sectors. In this report, we established a photophysics–electronics correlation for actinide‐containing metal‐organic frameworks (An‐MOFs) as a function of excitation wavelength, for the first time. A stepwise approach for dynamically modulating electronic properties was applied for the first time towards actinide‐based heterometallic MOFs through integration of photochromic linkers. Optical cycling, modeling of density of states near the Fermi edge, conductivity measurements, and photoisomerization kinetics were employed to shed light on the process of tailoring optoelectronic properties of An‐MOFs. Furthermore, the first photochromic MOF‐based field‐effect transistor, in which the field‐effect response could be changed through light exposure, was constructed. As a demonstration, the change in current upon light exposure was sufficient to operate a two‐LED fail‐safe indicator circuit.

Martin, Corey R.↗
DOE OSTI2020

Cryogenic Correlative Single-Particle Photoluminescence Spectroscopy and Electron Tomography for Investigation of Nanomaterials

Cryogenic single-particle photoluminescence (PL) spectroscopy has been used with great success to directly observe the heterogeneous photophysical states present in a population of luminescent particles. Cryogenic electron tomography provides complementary nanometer scale structural information to PL spectroscopy, but the two techniques have not been correlated due to technical challenges. Here, we present a method for correlating single-particle information from these two powerful microscopy modalities. We simultaneously observe PL brightness, emission spectrum, and in-plane excitation dipole orientation of CdSSe/ZnS quantum dots suspended in vitreous ice. Stable and fluctuating emitters were observed, as well as a surprising splitting of the PL spectrum into two bands with an average energy separation of 80 meV. In some cases, the onset of the splitting corresponded to changes in the in-plane excitation dipole orientation. These dynamics were assigned to structures of individual quantum dots and the excitation dipoles were visualized in the context of structural features.

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

Encoding Multilayer Complexity in Anti-Counterfeiting Heterometallic MOF-based Optical Tags

Optical tags provide a way to quickly and unambiguously identify valuable assets. Current tag fluorophore options lack the tunability to allow combined methods of encoding in a single material. Here we report a design strategy to encode multilayer complexity in a family of heterometallic rare-earth metal-organic frameworks based on highly connected nonanuclear clusters. To impart both intricacy and security, a synergistic approach was implemented resulting in both overt (visible) and covert (near infrared, NIR) properties, with concomitant multi-emissive spectra and tunable luminescence lifetimes. Tag authentication is validated with a variety of orthogonal detection methodologies. Importantly, the effect induced by subtle compositional changes on intermetallic energy transfer, and thus on the resulting photophysical properties, is demonstrated. This strategy can be widely implemented to create a large library of highly complex, difficult to counterfeit optical tags.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Doubling the Stakes: The Promise of Halide Double Perovskites

When the stakes are doubled in a wager, a player must correctly place two consecutive bets to win, but the payout is larger. Similarly, two B sites in combination dictate the properties of A 2 BB'X 6 (A=monocation, X=halide) double perovskites. Correctly picking two B sites is more challenging than picking just one, as in the A I B II X 3 single perovskites, but the options are greater and, we believe, the rewards are higher when the stakes are doubled. In this Minireview, we emphasize fundamental aspects of halide double perovskites to provide a foundation for interested readers to explore this extraordinary class of materials. In particular, we highlight the differences and similarities between double and single perovskites and describe how the double perovskite structure potentially offers greater control over photophysical properties.

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

Assembling Phenothiazine into a Porous Coordination Cage to Improve Its Photocatalytic Efficiency for Organic Transformations

Abstract Photo‐catalysis by small‐molecules is often limited by catalyst degradation and low electron‐transfer efficiency. Herein we report a stable N‐phenyl‐phenothiazine (PTH)‐derived porous coordination cage (PCC) as a highly efficient photocatalyst. By the incorporation of the photocatalytic PTH moiety into a PCC, aggregation‐induced quenching (AIQ) was shown to be reduced. An improvement in catalyst stability was discovered, ascribed to the synergistic effects of the PTH moieties. The catalyst, operating through a photolytic single‐electron transfer, was utilized for photo‐catalyzed dehalogenation and borylation. Evaluation of the catalytic mechanism in the borylation reaction showed that the improved performance results from the more efficient formation of the electron donor‐acceptor (EDA) complex with the cage. This discovery provides a potential strategy to improve the photophysical properties and stabilities of small‐molecule organic photocatalysts via supramolecular chemistry.

Chemistry↗
DOE OSTI2023

Triplet Generation Through Singlet Fission in Metal-Organic Framework: An Alternative Route to Inefficient Singlet-Triplet Intersystem Crossing

High quantum yield triplets, populated by initially prepared excited singlets, are desired for various energy conversion schemes in solid working compositions like porous MOFs. However, a large disparity in the distribution of the excitonic center of mass, singlet-triplet intersystem crossing (ISC) in such assemblies is inhibited, so much so that a carboxy-coordinated zirconium heavy metal ion cannot effectively facilitate the ISC through spin-orbit coupling. Circumventing this sluggish ISC, singlet fission (SF) is explored as a viable route to generating triplets in solution-stable MOFs. Efficient SF is achieved through a high degree of interchromophoric coupling that facilitates electron super-exchange to generate triplet pairs. Here we show that a predesigned chromophoric linker with extremely poor ISC efficiency (k ISC ) but E S 1 ≥ 2E T 1 form triplets in MOF in contrast to the frameworks that are built from linkers with sizable k ISC but E S 1 ≤ 2E T 1 . Finally, this work opens a new photophysical and photochemical avenue in MOF chemistry and utility in energy conversion schemes.

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

The Acetylene Bridge in Intramolecular Singlet Fission: A Boon or A Nuisance?

Various analogues of the alkylsilylacetylene group are frequently used as auxiliary groups to enhance the solubility and stability of the acene dimer core, widely used as platforms to investigate intramolecular singlet fission (iSF) mechanisms. However, while in the 2,2’-linked dimers they are primarily auxiliary groups, these are essential fragments of the bridging units in 6,6’/5,5’-linked dimers, the two preferred choices for dimerization. The starkly different iSF dynamics observed in the two variants raise the question of what role the acetylene bridges play. Here, we systematically designed a set of (oligo-)para-phenylene bridged 2,2’-linked pentacene dimers with an additional acetylene fragment in the bridging unit to mimic the structure of 6,6’-linked dimers. Contrasting the results with previously reported analogous 2,2’-linked and 6,6’-linked pentacene dimers reveals that the acetylene bridges contribute to significant conformational freedom. This effect provides a mechanism to promote spin evolution within the triplet pair to achieve free triplets but also offers new parasitic pathways for triplet-pair recombination, revealing that this structural motif can be both a boon and a nuisance. Additionally, our analysis reveals that these bridges directly modify the electronic states, highlighting significant pitfalls of the standard chromophore-bridge-chromophore framework used to design and interpret photophysics of iSF materials.

14 SOLAR ENERGY↗
DOE OSTI2020

π‐Extended Donor–Acceptor Porphyrins and Metalloporphyrins for Antimicrobial Photodynamic Inactivation

Abstract Free base, zinc and palladium π‐extended porphyrins containing fused naphthalenediamide units were employed as photosensitizers in antimicrobial photodynamic therapy (aPDT). Their efficacy, assessed by photophysical and in vitro photobiological studies on Gram‐positive bacteria, was found to depend on metal coordination, showing a dramatic enhancement of photosensitizing activity for the palladium complex.

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

The Coordination Behaviour of Cu I Photosensitizers Bearing Multidentate Ligands Investigated by X-ray Absorption Spectroscopy

A systematic series of four novel homo- and heteroleptic CuI photosensitizers based on tetradentate 1,10-phenanthroline ligands of the type X^N^N^X containing two additional donor moieties in the 2,9-position (X=SMe or OMe) were designed. Their solid-state structures were assessed by X-ray diffraction. Cyclic voltammetry, UV-vis absorption, emission and X-ray absorption spectroscopy were then used to determine their electrochemical, photophysical and structural features in solution. Following, time-resolved X-ray absorption spectroscopy in the picosecond time scale, coupled with time-dependent density functional theory calculations, provided in-depth information on the excited state electron configurations. For the first time, a significant shortening of the Cu–X distance and a change in the coordination mode to a pentacoordinated geometry is shown in the excited states of the two homoleptic complexes. These findings are important with respect to a precise understanding of the excited state structures and a further stabilization of this type of photosensitizers.

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

Room‐Temperature Phosphorescent Platinum(II) Alkynyls with Microsecond Lifetimes Bearing a Strong‐Field Pincer Ligand

Abstract The use of organometallic triplet emitters in organic light emitting diodes (OLEDs) is motivated by the premise of efficient intersystem crossing leading to unit internal quantum efficiencies. However, since most devices are based on solid‐state components, an inherent limitation to square‐planar platinum(II) phosphors is their tendency toward aggregation‐based quenching. Here, a new class of emissive, four‐coordinate Pt II species based on the bisimidazolyl carbazolide (BIMCA) ligand is introduced, which displays highly efficient, long‐lived solid‐state phosphorescence at room temperature. A set of four BIMCAPt phenyl acetylides were synthesized that emit in the green ( λ max =507–540 nm) with >60 % quantum yield and millisecond lifetimes. The structures of the resulting species reveal a non‐planar structure imposed by steric clashes between BIMCA and the iodo or alkynyl co‐ligand. Ground‐state and photophysical characterization are presented. Density functional theory calculations indicate that the BIMCA ligand dominates the frontier orbitals along with the first Franck–Condon singlet and triplet excited states.

Liska, Tadeas↗
DOE OSTI2022

Construction of Photo‐Responsive Pd 2 L 4 ‐Type Nanocages based on Feringa's Second‐Generation Motor and Its Guest Binding Ability for C 60

Abstract We present the construction of a M 2 L 4 ‐type metal‐organic nanocage featuring four endohedral Feringa's motor motifs and its adaptive encapsulation towards a C 60 guest molecule. The structure of the cage, though complicated on the 1 H NMR spectrum due to the adoption of mixed ligands, was unambiguously characterized with a combination of ESI‐MS, 2D DOSY, 13 C NMR and particularly the SAXS technique. The molecular motor within the cage demonstrated similar photophysical properties to the uncoordinated one, indicating the motor's function was not compromised when it was anchored in such a confined nanospace. Furthermore, the nanocage showed good guest encapsulation ability towards C 60 , and a guest induced‐fit behavior of the cage was revealed based on the extensive SAXS analysis and molecular dynamics simulation. The adaptive motorized nanocage reported here represents one of the very few examples of integrating individual motors into a discrete nanoconfined system and offers prospects to achieve its non‐equilibrium functions.

Chemistry↗
DOE OSTI2023

Anthradithiophene (ADT)-Based Polymerized Non-Fullerene Acceptors for All-Polymer Solar Cells

Realizing efficient all-polymer solar cell (APSC) acceptors typically involves increased building block synthetic complexity, hence potentially unscalable syntheses and/or prohibitive costs. Here we report the synthesis, characterization, and implementation in APSCs of three new polymer acceptors P1–P3 using a scalable donor fragment, bis(2-octyldodecyl)anthra[1,2-b : 5,6-b’]dithiophene-4,10-dicarboxylate (ADT) co-polymerized with the high-efficiency acceptor units, NDI, Y6, and IDIC. Further, all three copolymers have comparable photophysics to known polymers; however, APSCs fabricated by blending P1, P2 and P3 with donor polymers PM5 and PM6 exhibit modest power conversion efficiencies (PCEs), with the champion P2-based APSC achieving PCE=5.64 %. Detailed morphological and microstructural analysis by AFM and GIWAXS reveal a non-optimal APSC active layer morphology, which suppresses charge transport. Despite the modest efficiencies, these APSCs demonstrate the feasibility of using ADT as a scalable and inexpensive electron rich/donor building block for APSCs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Naphthodithiophene‐Fused Porphyrins: Synthesis, Characterization, and Impact of Extended Conjugation on Aromaticity

The fusion of tetrapyrroles with aromatic heterocycles constitutes a useful tool for manipulating their opto-electronic properties. In this work, the synthesis of naphthodithiophene-fused porphyrins was achieved through a Heck reaction-based cascade of steps followed by the Scholl reaction. The naphthodithiophene-fused porphyrins display a unique set of optical and electronic properties. Fusion of the naphtho[2,1-b:3,4-b’]dithiophene to porphyrin (F2VTP) leads to a ~20% increase in the fluorescence lifetime, which is accompanied, unexpectedly, by a more than two-fold drop in the emission quantum yield (ϕ=0.018). In contrast, fusion of the isomeric naphtho[1,2-b:4,3-b’]dithiophene to porphyrin (F3VPT) results in a ~1.5-fold increase in the fluorescence quantum yield (ϕ=0.13) with a concomitant ~30 % increase in the fluorescence lifetime. This behavior suggests that fusion of the porphyrin with the naphthodithiopheno-system mainly affects the radiative rate constant in the Q-state deactivation pathway, where the effects of the isomeric naphtho[2,1-b:3,4-b’]dithiophene- versus naphtho[1,2-b:4,3-b’]dithiophene-fusion are essentially the opposite. Interestingly, nucleus-independent chemical shifts analysis revealed a considerable difference between the aromaticities of these two isomeric systems. Furthermore, our results demonstrate that subtle structural differences in the fused components of the porphyrin can be reflected in rather significant differences between the photophysical properties of the resulting systems.

Chemistry↗
DOE OSTI2020

Recent Progress in Engineering Metal Halide Perovskites for Efficient Visible‐Light‐Driven Photocatalysis

Abstract Artificial photosynthesis has attracted increasing attention due to recent environmental and energy concerns. Metal halide perovskites (MHPs) demonstrating excellent optoelectronic properties have currently emerged as novel and efficient photocatalytic materials. Herein, the structural features of MHPs that are responsible for the photoinduced charge separation and charge migration properties are briefly introduced, and then important and necessary photophysical and photochemical aspects of MHPs related to photoredox catalysis are summarized. Subsequently, the applications of MHPs for solar energy harvesting and photocatalytic conversion, including H 2 evolution, CO 2 reduction, degradation of organic pollutants, and photoredox organic synthesis, are extensively demonstrated, with a focus on strategies for improving the performance (e.g., selectivity, activity, stability, recyclability, and environmental compatibility) of these MHP‐based photocatalytic systems. To conclude, existing challenges and prospects on the future development of MHP‐based materials towards photoredox catalysis applications are detailed.

Han, Chuang↗