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

Charge Transfer and Recombination Pathways through Fullerene Guests in Porphyrin-Based MOFs

Porphyrin-based metal–organic frameworks (MOFs) offer a unique platform for building porous donor–acceptor networks that exhibit long-lived charge separation and transport upon incorporation of electron acceptor guest species. Here, in this work, porphyrin-based MOFs, PCN-222(H 2 ) and PCN-222(Zn), synthesized as nanoparticle suspensions, are successfully infiltrated with fullerene acceptor molecules, C 60 or PC 61 BM, in both polar and nonpolar solvent environments. The location and relative binding strength of these guest species are evaluated through a combination of N 2 physisorption measurements, photoluminescence quenching, and UV–vis absorption titration experiments. Semiempirical tight binding calculations are used to screen potential locations of the fullerene guest within the MOF pores, and hybrid density functional theory (DFT)-computed interaction energies confirm the energetically favorable positions. The fundamental photophysics of these donor–acceptor host–guest combinations are probed using ultrafast transient absorption spectroscopy. Sub-picosecond electron transfer involving initial exciplex population is observed, with slow charge recombination lifetimes on the order of τ ~1 ns for all systems in both dimethylformamide and 1,4-dioxane. Charge recombination occurs through population of fullerene and/or framework porphyrin triplet states depending on the porphyrin metalation status. The photophysics of the fullerene-loaded MOFs are discussed in the context of relevant porphyrin–fullerene donor–acceptor molecules to highlight the unique role of the framework environment in dictating photoinduced electron transfer and decay pathways.

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

Verifying the structure-property-performance relationship of Y6-based small molecule acceptors by alkoxy-side chain isomerization and conjugated skeleton asymmetry

Non-fullerene small molecule acceptors (NF-SMAs) such as Y6 derivatives were the current working horse for the top performing polymer solar cells (PSCs). For this reason, numerous chemical modifications have been explored for establishing structure–property-performance relationship for Y6-based NF-SMAs. In this work, we explored the isomerization on asymmetrical Y6 derivatives by varying the position of alkoxy side chain on the thiophene linkage between the core and one of the end groups of Y6. The isomers with differences in conformational restriction raised by noncovalent interactions as well as steric hindrance revealed distinctive behavior in crystallization and polymorphism, which led to a significant contrast in PSC performances. Here the X-TO1 molecule with alkoxy side chain facing the end group (outward) displayed preferred molecular configuration and polymorph, delivering power conversion efficiency (PCE) of 15.63%, while its isomer X-TO2 showed coexisted polymorphs significantly increased the charge recombination in the PSC devices led to a low PCE around 3%. This structure–property-performance relationship not only highlighted the elegancy of isomerization in tuning the photovoltaic performances but also identified polymorphism as one of the causes for impairing photovoltaic performances of PSCs.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Electronic coarse-graining of long conjugated molecules: Case study of non-fullerene acceptors

By considering only one electronic state per molecule, charge transport models of molecular solids neglect intramolecular charge transfer. This approximation excludes materials with quasi-degenerate spatially separated frontier orbitals, such as non-fullerene acceptors (NFAs) and symmetric thermally activated delayed fluorescence emitters. By analyzing the electronic structure of room-temperature molecular conformers of a prototypical NFA, ITIC-4F, we conclude that the electron is localized on one of the two acceptor blocks with the mean intramolecular transfer integral of 120 meV, which is comparable with intermolecular couplings. Therefore, the minimal basis for acceptor–donor–acceptor (A–D–A) molecules consists of two molecular orbitals localized on the acceptor blocks. This basis is robust even with respect to geometry distortions in an amorphous solid, in contrast to the basis of two lowest unoccupied canonical molecular orbitals withstanding only thermal fluctuations in a crystal. The charge carrier mobility can be underestimated by a factor of two when using single site approximation for A–D–A molecules in their typical crystalline packings.

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

Synergistic Alignment of Low Aspect‐Ratio π‐Conjugated Molecules Enables Exceptional UV–vis–NIR Polarization Detection

Abstract Polarization detection enhances signal contrast and is widely utilized in diverse advanced applications. An ongoing challenge is the development of high‐performance polarization‐sensitive photodetectors based on optically anisotropic organic semiconductors, particularly in the near‐infrared (NIR) region. While uniaxially aligned π‐conjugated polymers with high aspect ratios exhibit strong linear dichroism and have shown promise, their limited NIR performance and heavy reliance on polymer material now represent critical limitations. Here, a breakthrough is reported in achieving giant linear dichroism and exceptional polarization detection with low aspect‐ratios (AR) non‐fullerene small‐molecule (NFSM) acceptors, extending polarization sensitivity from the UV–vis to the NIR range. An impressive dichroic ratio of 27.1 at 605 nm and 12.0 at 780 nm is demonstrated. The maximum polarization photocurrent ratio is 11.2 at 780 nm under parallel versus perpendicular polarized light. This unprecedented performance originates from synergistic molecular alignment, wherein NFSMs significantly enhance the uniaxial orientation of both the polymer matrix and the NFSMs themselves during self‐assembly and thermal annealing. Besides, such a linear‐polarization‐sensitive photodetectors (LPS‐PDs) are showcased in generating degree‐of‐linear‐polarization imaging. The work establishes NFSMs as a viable material system for next‐generation of organic LPS‐PDs and provides fundamental insights into structural origins of polarization sensitivity in low AR organic semiconductors.

Xue, Yingying↗
NASA NTRS2018

Interstellar PAHs: From Ground to Space, Expanding Spectroscopic Frontiers

Recent progress in astrochemistry and in our understanding of the Molecular Universe has been driven by new detector technologies and advances in ground-, airborne- and space astronomy coupled to new, innovative approaches in molecular spectroscopy. The search for the complex carbon-based molecules (PAHs, Fullerenes, nanoparticles) thought to be responsible for the ubiquitous infrared emission bands (UIBs) and optical absorption bands (DIBs) that are observed in various regions of the interstellar medium of local- and extragalactic environments illustrates the progress in spectroscopy techniques that has been driven by astronomy. Recent progresses reached in this domain will be discussed together with the laboratory techniques that have been developed to measure the spectra of laboratory analogs of cosmic molecules in the UV Visible-NIR range under experimental conditions that attempt to reproduce the interstellar conditions.

Laboratory astrophysics and astrochemistry↗
DOE OSTI2020

Efficient, Thermally Stable, and Mechanically Robust All-Polymer Solar Cells Consisting of the Same Benzodithiophene Unit-Based Polymer Acceptor and Donor with High Molecular Compatibility

All-polymer solar cells (all-PSCs) are a highly attractive class of photovoltaics for wearable and portable electronics due to their excellent morphological and mechanical stabilities. Recently, new types of polymer acceptors (P A s) consisting of non-fullerene small molecule acceptors (NFSMAs) with strong light absorption have been proposed to enhance the power conversion efficiency (PCE) of all-PSCs. However, polymerization of NFSMAs often reduces entropy of mixing in PSC blends and prevents the formation of intermixed blend domains required for efficient charge generation and morphological stability. One approach to increase compatibility in these systems is to design P A s that contain the same building blocks as their polymer donor (P D ) counterparts. Here, a series of NFSMA-based P A s [P(BDT2BOY5-X), (X = H, F, Cl)] are reported, by copolymerizing NFSMA (Y5-2BO) with benzodithiophene (BDT), a common donating unit in high-performance P D s such as PBDB-T. All-PSC blends composed of PBDB-T PD and P(BDT2BOY5-X) P A show enhanced molecular compatibility, resulting in excellent morphological and electronic properties. Specifically, PBDB-T:P(BDT2BOY5-Cl) all-PSC has a PCE of 11.12%, which is significantly higher than previous PBDB-T:Y5-2BO (7.02%) and PBDB-T:P(NDI2OD-T2) (6.00%) PSCs. Additionally, the increased compatibility of these all-PSCs greatly improves their thermal stability and mechanical robustness. For example, the crack onset strain (COS) and toughness of the PBDB-T:P(BDT2BOY5-Cl) blend are 15.9% and 3.24 MJ m -3 , respectively, in comparison to the PBDB-T:Y5-2BO blends at 2.21% and 0.32 MJ m -3 .

14 SOLAR ENERGY↗
DOE OSTI2022

Improving the performance of PM6 donor polymer by random ternary copolymerization of BDD and DTBT segments

Developing high-performance wide bandgap polymer donors to match the rapidly growing non-fullerene small molecule acceptors (NF-SMAs) is of great importance to further improve the photovoltaic performances of organic solar cells (OSCs). PM6 and D18 are two leading wide bandgap donor polymers, but their performances are highly sensitive to the molecular weights, which have distinct impact on the morphology and thereby the charge generation and recombination processes. Here, in this work, we reported the random ternary copolymerization of PM6 and D18 segments to develop random terpolymers with finely tuned photoelectronic properties and optimized blend morphology for high-performance OSCs. The resulting random terpolymers (PMD-5, PMD-10, PMD-15 and PMD-20) exhibited finely tuned absorptions, energy levels and blend morphology. The optimal morphology of PMD-15:L8-BO contributed to the fast exciton diffusion and dissociation, efficient charge extraction with suppressed recombination. Thus, the power conversion efficiency was improved from 17.22% of the control PM6 devices and 17.47% of the control D18 devices to 18.12% of PMD-15 based devices, which is the top performance of random terpolymers. Moreover, the PMD-15 exhibited much higher batch-to-batch reproducibility at a broad molecular weight range than that of PM6 and D18, showing promising for practical applications.

36 MATERIALS SCIENCE↗
DOE OSTI2021

GFCCLib: Scalable and efficient coupled-cluster Green's function library for accurately tackling many-body electronic structure problems

Coupled-cluster Green’s function (GFCC) calculation has drawn much attention in the recent years for targeting the molecular and material electronic structure problems from a many-body perspective in a systematically improvable way. However, GFCC calculations on scientific computing clusters usually suffer from expensive higher di- mensional tensor contractions in the complex space, expensive inter-process communi- cation, and severe load imbalance, which limits it’s routine use for tackling electronic structure problems. Here we present a numerical library prototype that is specifically designed for large-scale GFCC calculations. The design of the library is focused on a systematically optimal computing strategy to improve its scalability and efficiency. The performance of the library is demonstrated by the relevant profiling analysis of running GFCC calculations on remote giant computing clusters. The capability of the library is highlighted by computing a wide near valence band of a fullerene C60 molecule for the first time at the GFCCSD level that shows excellent agreement with the experimental spectrum.

Peng, Bo↗
DOE OSTI2021

Influence of Disorder and State Filling on Charge-Transfer-State Absorption and Emission Spectra

We conduct comprehensive temperature-dependent measurements of the charge-transfer-(CT) state photocurrent and emission spectra for two organic small molecule donor:fullerene (C 60 ) acceptor bulk heterojunction solar cells. We reveal that the CT spectral width and position are affected by static energetic disorder in the blend, especially evident at low temperatures. The relative contributions of the static and dynamic disorder broadening in the CT spectra are effectively extracted through consideration of a Gaussian CT energetic distribution. However, electroluminescence (EL) spectra can only be interpreted when injected carriers reach thermal equilibrium sites within the disordered density of states and emission occurs from the lowest possible CT energy. For the blend with the smaller energetic disorder, this is the case near room temperature; for the other blend with larger static disorder, carriers fail to reach thermal equilibrium sites even at room temperature and EL spectra need to be interpreted with care. For example, in the latter case, the effect of energetic disorder might not be apparent from EL spectra because the lowest energy sites are not participating. Nonetheless, these states contribute to the photocurrent generation-recombination and energy-loss processes and thus demand accurate characterization, which we show is feasible through temperature-dependent external quantum-efficiency measurements.

14 SOLAR ENERGY↗
NASA NTRS2001

Protective Fullerene (C60) Packaging System for Microelectromechanical Systems Applications

The invention involves a method for locating the probe of a scanning tunneling micrograph a predetermined distance from its conducting surface, and specifically the deposition of a monolayer of fullerene C 60 onto the conducting plate. The Fullerene C 60 molecule is approximately spherical and a monolayer of fullerene has a thickness of one nanometer. By providing a monolayer of fullerene on the conducting surface and locating the probe on the surface of the monolayer, a distance of one nanometer can be established between the probe tip and the conducting surface.

John D Olivas↗
NASA NTRS2004

Protective Fullerene (C60) Packaging System for Microelectromechanical Systems Applications

The invention involves tunneling tips to their conducting surface, and specifically the deposition of a monolayer of fullerene C 60 onto the conducting plate surface to protect the tunneling tip from contact. The Fullerene C 60 molecule is approximately spherical, and a monolayer of fullerene has a thickness of one nanometer, such that a monolayer thereby establishing the theoretical distance desired between the MEMS tunneling tip and the conducting plate. Exploiting the electrical conductivity of C 60 the tip can be accurately positioned by simply monitoring conductivity between the fullerene and the tunneling tip. By monitoring the Conductivity between the tip and the fullerene layer as the tip is brought in proximity, the surfaces can be brought together without risk of contacting the underlying conducting surface. Once the tunneling tip is positioned at the one nanometer spacing, with only the monolayer of fullerene between the tunneling tip and the conducting plate, the monolayer of C 60 , can be broken down thermally and removed chemically leaving only the tunneling tip and the conducting plate at the ideal tunneling spacing. Alternatively, the properties of fullerene allow the tunneling process to occur directly across the fullerene monolayer.

John D Olivas↗
DOE OSTI2022

A charged diatomic triple-bonded U≡N species trapped in C 82 fullerene cages

Actinide diatomic molecules are ideal models to study elusive actinide multiple bonds, but most of these diatomic molecules have so far only been studied in solid inert gas matrices. Herein, we report a charged U≡N diatomic species captured in fullerene cages and stabilized by the U-fullerene coordination interaction. Two diatomic clusterfullerenes, viz. UN@C s (6)-C 82 and UN@C 2 (5)-C 82 , were successfully synthesized and characterized. Crystallographic analysis reveals U-N bond lengths of 1.760(7) and 1.760(20) Å in UN@C s (6)-C 82 and UN@C 2 (5)-C 82 . Moreover, U≡N was found to be immobilized and coordinated to the fullerene cages at 100 K but it rotates inside the cage at 273 K. Quantum-chemical calculations show a (UN) 2+ @(C 82 ) 2- electronic structure with formal +5 oxidation state (f 1 ) of U and unambiguously demonstrate the presence of a U≡N bond in the clusterfullerenes. This study constitutes an approach to stabilize fundamentally important actinide multiply bonded species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1992

Composite materials for the extravehicular mobility unit

The extravehicular mobility unit (EMU), commonly known as the astronaut space suit assembly (SSA) and primary life support system (PLSS), has evolved through the years to incorporate new and innovative materials in order to meet the demands of the space environment. The space shuttle program which is seeing an increasing level of extravehicular activity (EVA), also called space walks, along with interest in an EMU for Lunar-Mars missions means even more demanding conditions are being placed on the suit and PLSS. The project for this NASA-ASEE Summer Program was to investigate new materials for these applications. The focus was to emphasize the use of composite materials for every component of the EMU to enhance the properties while reducing the total weight of the EMU. To accomplish this, development of new materials called fullerene reinforced materials (FRM's) was initiated. Fullerenes are carbon molecules which when added to a material significantly reduce the weight of that material. The Faculty Fellow worked directly on the development of the fullerene reinforced materials. A chamber for fullerene production was designed and assembled and first generation samples were processed. He also supervised with the JSC Colleague, a study of composite materials for the EMU conducted by the student participant in the NASA-ASEE Program, Hector Tello a Rice University graduate student, and by a NASA Aerospace Technologist (Materials Engineer) Evelyne Orndoff, in the Systems Engineering Analysis Office (EC7), also a Rice University graduate student. Hector Tello conducted a study on beryllium and Be alloys and initiated a study of carbon and glass reinforced composites for space applications. Evelyne Orndoff compiled an inventory of the materials on the SSA. Ms. Orndoff also reviewed SSA material requirements and cited aspects of the SSA design where composite materials might be further considered. Hector Tello spent part of his time investigating the solar radiation sensitivity of anodic coatings. This project was directed toward the effects of ultra-violet radiation on high emissivity anodic coatings. The work of both Evelyne Orndoff and Hector Tello is of interest to the Engineering Directorate at NASA/JSC and is also directed toward their research as Rice University graduate students.

Barrera, Enrique V.↗
DOE OSTI2020

Fused ring non-fullerene acceptors with benzothiophene dioxide end groups and their side chain effect investigations

The development of small molecule-based non-fullerene acceptors (NF-SMAs) greatly advanced the performances of polymer solar cells (PSCs) in recent years. As the foreseeability of commercializing this technology in the future, interest in reducing the materials cost is rising. To this end, efforts have been made in this work on exploring the usage of commercially available chemical segment of benzothiophene dioxide (BC) in constructing efficient NF-SMAs. Thus, we designed and synthesized two BC-based NF-SMAs, which showed high power conversion efficiency (PCE) of 7.59% also by device engineering and side chain engineering. Our work revealed the full potential of using BC end groups in constructing high-performance NF-SMAs and demonstrated the application of side chain engineering in tuning material properties and performances.

36 MATERIALS SCIENCE↗
NASA NTRS2019

Titan's Ionospheric Chemistry, Fullerenes, Oxygen, Galactic Cosmic Rays and the Formation of Exobiological Molecules on and within its Surfaces and Lakes

We discuss the formation of aerosols within Titan's thermosphere-ionosphere and the different chemical pathways. Negative ion measurements by the Cassini Plasma Spectrometer (CAPS) Electron Spectrometer (ELS) give evidence for formation of unsaturated anion carbon chains, while positive ion measurements of the Cassini Ion Neutral Mass Spectrometer (INMS) indicate formation of more aromatic cation hydrocarbons. There is presently no direct observational evidence for large neutral molecule growth in Titan's thermosphere-ionosphere. The hydrocarbon cations are expected to form Polycyclic Aromatic Hydrocarbons (PAH), those with the addition of nitrogen being called PAHNs. We theorize anion carbon chains can eventually become long enough to fold into fullerene C(60,70) carbon shells, of various charge states. Based on laboratory data the fullerenes can trap incoming O(sup +) magnetospheric ions that have relatively high energy collisions with the fullerenes and, once trapped, protect the oxygen atom from Titan's reducing thermosphere-ionosphere. The fullerenes can form into larger onion fullerenes and condense into larger embryo aerosols (i.e., m/q > 10,000 amu/q anions as observed by CAPS/ELS) eventually falling onto Titan's surface and precipitating to the bottom of its hydrocarbon lakes. Molecule production composed of H, C, N is known to occur in Titan's atmosphere with energy input from the magnetosphere, solar UV, and deeppenetrating irradiation from galactic cosmic rays (GCR). Space radiation effects by GCR irradiation of Titan's surface and lakes can lead to the manufacture of exobiological molecules with oxygen as the new ingredient. We have developed a model of galactic cosmic ray irradiation of Titan's atmosphere, surface, subsurface and bottoms of Titan lakes. GCR would provide further energy for processing of the aerosols into more complex organic forms such as tholins and precursor molecules for amino acids. A second process called hydrolysis then converts the precursor molecules into amino acids. Hydrolysis is provided via meteor impacts with size > 10 km and cryovolcanism both which can produce liquid water on Titan's surface for episodic periods > several 100 to 1000 years. Our model shows that GCR secondary particles can penetrate ~ 100 m below the ice surface (including the bottom of Titan's less dense hydrocarbon lakes ~ 150 m depths) and produce chemically significant dosages over very long timescales ~ 450 Myrs. The GCR model is combined with laboratory data from experiments in which dry methyl ices were irradiated to doses producing prebiotic amino acids such as glycine. The model calculations show glycine can form to ~ 2.5 ppb levels near the surface after ~450 Myrs of GCR proton irradiation and potentially to 5 ppb if heavy-ion GCRs up through Fe are included. If such molecules were detected, this would not only confirm this model but indicate that life forms different from ours may not be required.

Edward C. Sittler Jr↗
NASA NTRS2020

Titan's Ionospheric Chemistry, Fullerenes, Oxygen, Galactic Cosmic Rays and the Formation of Exobiological Molecules on and Within Its Surfaces and Lakes

We discuss the formation of aerosols within Titan's thermosphere-ionosphere and the different chemical pathways. Negative ion measurements by the Cassini Plasma Spectrometer (CAPS) Electron Spectrometer (ELS) give evidence for formation of unsaturated anion carbon chains, while positive ion measurements of the Cassini Ion Neutral Mass Spectrometer (INMS) indicate formation of more aromatic cation hydrocarbons. There is presently no direct observational evidence for large neutral molecule growth in Titan's thermosphere-ionosphere. The hydrocarbon cations are expected to form Polycyclic Aromatic Hydrocarbons (PAHs), those with the addition of nitrogen being called PAHNs. We theorize anion carbon chains can eventually become long enough to fold into fullerene C60,70 carbon shells, of various charge states. Based on laboratory data the fullerenes can trap incoming O+ magnetospheric ions that have relatively high energy collisions with the fullerenes and, once trapped, protect the oxygen atom from Titan's reducing thermosphere-ionosphere. The fullerenes can form into larger onion fullerenes and condense into larger embryo aerosols (i.e., m/q (mass-to-charge ratio) greater than 10,000 amu/q (atomic mass unit-to-charge ratio) anions as observed by CAPS/ELS) eventually falling onto Titan's surface and precipitating to the bottom of its hydrocarbon lakes. Molecule production composed of H, C, N is known to occur in Titan's atmosphere with energy input from the magnetosphere, solar UV (ultraviolet), and deep-penetrating irradiation from galactic cosmic rays (GCR). Space radiation effects by GCR irradiation of Titan's surface and lakes can lead to the manufacture of exobiological molecules with oxygen as the new ingredient. We have developed a model of galactic cosmic ray irradiation of Titan's atmosphere, surface, subsurface and bottoms of Titan lakes. GCR would provide further energy for processing of the aerosols into more complex organic forms such as tholins and precursor molecules for amino acids. A second process called hydrolysis then converts the precursor molecules into amino acids. Hydrolysis is provided via meteor impacts with size greater than 10 kilometers and cryovolcanism both which can produce liquid water on Titan's surface for episodic periods more than several 100 to 1000 years. Our model shows that GCR secondary particles can penetrate ~100 meters below the ice surface (including the bottom of Titan's less dense hydrocarbon lakes ~150-meter depths) and produce chemically significant dosages over very long timescales ~450 million years. The GCR model is combined with laboratory data from experiments in which dry methyl ices were irradiated to doses producing prebiotic amino acids such as glycine. The model calculations show glycine can form to ~2.5 parts-per-billion levels near the surface after ~450 million years of GCR proton irradiation and potentially to 5 parts-per-billion if heavy-ion GCRs up through Fe are included. If such molecules were detected, this would not only confirm this model but indicate that life forms different from ours may not be required.

Edward C. Sittler Jr↗