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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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72 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Promoting the Furan Ring‐Opening Reaction to Access New Donor–Acceptor Stenhouse Adducts with Hexafluoroisopropanol

Abstract Donor–acceptor Stenhouse adducts (DASAs) are visible‐light‐responsive photoswitches with a variety of emerging applications in photoresponsive materials. Their two‐step modular synthesis, centered on the nucleophilic ring opening of an activated furan, makes DASAs readily accessible. However, the use of less reactive donors or acceptors renders the process slow and low yielding, which has limited their development. We demonstrate here that 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) promotes the ring‐opening reaction and stabilizes the open isomer, allowing greatly reduced reaction times and increased yields for known derivatives. In addition, it provides access to previously unattainable DASA‐based photoswitches and DASA–polymer conjugates. The role of HFIP and the photochromic properties of a set of new DASAs is probed using a combination of 1 H NMR and UV/Vis spectroscopy. The use of sterically hindered, electron‐poor amines enabled the dark equilibrium to be decoupled from closed‐isomer half‐lives for the first time.

Clerc, Michèle↗
DOE OSTI2021

Promoting the Furan Ring‐Opening Reaction to Access New Donor–Acceptor Stenhouse Adducts with Hexafluoroisopropanol

Abstract Donor–acceptor Stenhouse adducts (DASAs) are visible‐light‐responsive photoswitches with a variety of emerging applications in photoresponsive materials. Their two‐step modular synthesis, centered on the nucleophilic ring opening of an activated furan, makes DASAs readily accessible. However, the use of less reactive donors or acceptors renders the process slow and low yielding, which has limited their development. We demonstrate here that 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) promotes the ring‐opening reaction and stabilizes the open isomer, allowing greatly reduced reaction times and increased yields for known derivatives. In addition, it provides access to previously unattainable DASA‐based photoswitches and DASA–polymer conjugates. The role of HFIP and the photochromic properties of a set of new DASAs is probed using a combination of 1 H NMR and UV/Vis spectroscopy. The use of sterically hindered, electron‐poor amines enabled the dark equilibrium to be decoupled from closed‐isomer half‐lives for the first time.

Clerc, Michèle↗
DOE OSTI2026

Polarons are probes of the dynamic nanoscale environments found in electrochemically doped π-conjugated polymers

Charge carriers (i.e., polarons) in electrochemically doped organic (semi)conductors are proposed to be regulated by several physicochemical features, including the chemical compositions and structures of the π-conjugated frameworks of the semiconductor building blocks, the chemistry of the electrolyte (considering both the salt and solvent), multiscale and time-dependent morphology variations across the material as a function of electrochemical processes, and assorted permutations of these and other factors. To address these hypotheses, we investigate the energetic, optoelectronic, chemical, and local structural properties of negative polarons (radical anions) as a function of electrochemical doping in the donor–acceptor, π-conjugated redox copolymer P(NDI2OD-T2), also referred to as N2200. A critical finding is that there is not just “one type” of polaron in electrochemically doped P(NDI2OD-T2). Rather, an ensemble of polarons exists, with the polarons having optoelectronic signatures that are defined by their nanoscale environments. Importantly, the polaron optical signatures serve as local probes for how the operando electrochemical environments are dynamically working in concert to facilitate charge transport. Collectively, the distinctive and extensive integration of theory and measurement science presented here establishes a baseline for the roles that semiconductor and electrolyte chemistries and dynamic structural features have on polarons in electrochemically doped organic semiconductors and how these factors influence the energetics and rates of polaron transport.

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

Polaron Delocalization in Donor–Acceptor Polymers and its Impact on Organic Electrochemical Transistor Performance

Abstract Donor–acceptor (D‐A) polymers are promising materials for organic electrochemical transistors (OECTs), as they minimize detrimental faradaic side‐reactions during OECT operation, yet their steady‐state OECT performance still lags far behind their all‐donor counterparts. We report three D‐A polymers based on the diketopyrrolopyrrole unit that afford OECT performances similar to those of all‐donor polymers, hence representing a significant improvement to the previously developed D‐A copolymers. In addition to improved OECT performance, DFT simulations of the polymers and their respective hole polarons also reveal a positive correlation between hole polaron delocalization and steady‐state OECT performance, providing new insights into the design of OECT materials. Importantly, we demonstrate how polaron delocalization can be tuned directly at the molecular level by selection of the building blocks comprising the polymers’ conjugated backbone, thus paving the way for the development of even higher performing OECT polymers.

Moser, Maximilian↗
DOE OSTI2020

Foldable semi-ladder polymers: novel aggregation behavior and high-performance solution-processed organic light-emitting transistors

A critical issue in developing high-performance organic light-emitting transistors (OLETs) is to balance the trade-off between charge transport and light emission in a semiconducting material. Although traditional materials for organic light-emitting diodes (OLEDs) or organic field-effect transistors (OFETs) have shown modest performance in OLET devices, design strategies towards high-performance OLET materials and the crucial structure–performance relationship remain unclear. Our research effort in developing cross-conjugated weak acceptor-weak donor copolymers for luminescent properties lead us to an unintentional discovery that these copolymers form coiled foldamers with intramolecular H-aggregation, leading to their exceptional OLET properties. An impressive external quantum efficiency (EQE) of 6.9% in solution-processed multi-layer OLET devices was achieved.

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

Resonant Tender X-ray Scattering for Disclosing the Backbone Conformation of Conjugated Polymers

The backbone conformation of conjugated polymers (CPs) is essential to their performance in electronic applications. Contrast-variation small-angle neutron scattering (CV-SANS) techniques were used to assess the CP’s backbone conformation, which relies on synthesis of deuterated polymers. Such a technique has been proven mature and effective. One drawback is that deuteration labeling might subtly alter polymer’s physical properties due to structural modifications. To address these challenges, we introduce a novel approach utilizing tender Xray scattering near the sulfur K-edge to distinctly evaluate the backbone versus whole chain conformation for a low-bandgap donor−acceptor CP, poly[(5,6-difluoro- 2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-dialkyl-2,2′;5′,2″;5″,2‴-quaterthiophen-5,5‴- diyl)] (PffBT4T). For PffBT4T dissolved in trimethylbenzene (TMB), the sulfur K-edge is identified at approximately 2477 eV using near-edge X-ray absorption fine structure spectroscopy (NEXAFS). Tender X-ray scattering conducted at presulfur K-edge and on-sulfur K-edge at elevated temperatures facilitated the distinction between the backbone and whole chain conformations. The results demonstrate that for highly flexible polymer, the backbone’s persistence length could be lower than that of the whole chains, suggesting a more flexible backbone. This rapid, label-free method enhances our ability to characterize CP’s backbone conformation efficiently, offering significant implications for the design and optimization of CPs for advanced electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Hydroporphyrin-Doped Near-Infrared-Emitting Polymer Dots for Cellular Fluorescence Imaging

We report Near-infrared (NIR) fluorescent semiconductor polymer dots (Pdots) have shown great potential for fluorescence imaging due to their exceptional chemical and photophysical properties. This paper describes the synthesis of NIR emitting Pdots with great control and tunability of emission peak wavelength. The Pdots were prepared by doping poly [(9,9-dioctylfluorenyl-2,7-diyl)-altco-(1,4-benzo-(2,1’,3)-thiadiazole)] (PFBT), a semiconducting polymer commonly used as a host polymer in luminescent Pdots, with a series of chlorins and bacteriochlorins with varying functional groups. Chlorins and bacteriochlorins are ideal dopants due to their high hydrophobicity, which precludes their use as molecular probes in aqueous biological media but on the other hand prevents their leakage when doped into Pdots. Additionally, chlorins and bacteriochlorins have narrow deep-red to NIR emission bands and the wide array of synthetic modifications available for modifying their molecular structure enables tuning their emission predictably and systematically. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements show the chlorin and bacteriochlorin-doped Pdots to be nearly spherical with an average diameter of 46±12 nm. Efficient energy transfer between PFBT and the doped chlorins or bacteriochlorins decreases the PFBT donor emission to near baseline level and increases the emission of the doped dyes that serve as acceptors. The chlorin and bacteriochlorindoped Pdots show narrow emission bands ranging from 640 nm to 820 nm depending on the doped dye. The paper demonstrates the utility of the systematic chlorin and bacteriochlorin synthesis approach by preparing Pdots of varying emission peak wavelength, utilizing them to visualize multiple targets using wide field fluorescence microscopy, binding them to secondary antibodies, and determining the binding of secondary antibody-conjugated Pdots to primary antibody-labeled receptors in plant cells. Additionally, the chlorin and bacteriochlorin doped Pdots show a blinking behavior that could enable their use in super resolution imaging methods like STORM.

13C-NMR↗
DOE OSTI2024

Solution-Processable Polymer Donor-Small Molecule Acceptor Bulk Heterojunction Organocatalysts for Enhancing CO 2 -to-CO Photoconversion

Metal-free organic semiconductors have emerged as a kind of promising star material in photocatalysis. However, their photocatalytic efficacy is impeded by the great recombination rate of the photogenerated charge carriers. Herein, we demonstrate the devising of solution-processable organic semiconductor bulk heterojunction (BHJ) systems with varying ratios by using BP3DT and PC 61 BM as the donor (D) and acceptor (A) candidates, respectively, for enhanced selective CO production from CO 2 photoreduction. The prepared BP3DT/PC 61 BM BHJs are solution-processed on both glass substrates (GS) and molecular sieves (MS) via a drop-casting technique to form an active thin film and porous photocatalysts to catalyze CO production. All BP3DT/PC 61 BM BHJs efficiently produce CO as the primary product in the existence of trace-level TEA/H 2 O (0.5 mL). Our results show that the photocatalytic efficiency depended on the D/A w% ratios and its nanoscale phase separation morphology within the BHJ, contributing to the promotion of exciton dissociation. Additionally, the BHJ undergoes an ostensible morphological transition from large-scale phase-separation to a fine mixed homogeneous nanoscale by varying the BP3DT/PC 61 BM blend ratio from 30/70 w% to 70/30 w%, which increases the interfacial area and shortens the distance of the exciton to the D/A surface, and promotes charge carrier separation, corroborated by photo-optical and photoelectrochemical experimental results. Accordingly, the resulting BP3DT/PC 61 BM BHJ@MS with a D/A ratio of 70/30 w% achieves a CO yield of 819 μmol·g cat -1 h -1 , surpassing those of pure PC 61 BM (126 μmol·g cat -1 h -1 ) and BP3DT (72 μmol·g cat -1 h -1 ) by 6.5- to 11.3-fold and also exceeding that of metal-free linear conjugated polymer-based organocatalysts reported to date. Specifically, this is the first work to develop an organic-semiconductor-based BHJ photocatalyst, which may offer a nascent way to design more efficient organocatalysts for CO 2 reduction.

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

High performance polymerized small molecule acceptor by synergistic optimization on $\pi$-bridge linker and side chain

The polymerized small-molecule acceptors have attracted great attention for application as polymer acceptor in all-polymer solar cells recently. The modification of small molecule acceptor building block and the π-bridge linker is an effective strategy to improve the photovoltaic performance of the polymer acceptors. In this work, we synthesized a new polymer acceptor PG-IT2F which is a modification of the representative polymer acceptor PY-IT by replacing its upper linear alkyl side chains on the small molecule building block with branched alkyl chains and attaching difluorene substituents on its thiophene π-bridge linker. Through this synergistic optimization, PG-IT2F possesses more suitable phase separation, increased charge transportation, better exciton dissociation, lower bimolecular recombination, and longer charge transfer state lifetime than PY-IT in their polymer solar cells with PM6 as polymer donor. Therefore, the devices based on PM6:PG-IT2F demonstrated a high power conversion efficiency of 17.24%, which is one of the highest efficiency reported for the binary all polymer solar cells to date. This work indicates that the synergistic regulation of small molecule acceptor building block and π-bridge linker plays a key role in designing and developing highly efficient polymer acceptors.

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

Implementing the donor–acceptor approach in electronically conducting copolymers via electropolymerization

Electropolymerization has become a convenient method for synthesizing and characterizing complex organic copolymers having intrinsic electronic conductivity, including the donor (D)–acceptor (A) class of electronically conducting polymers (ECPs). This review begins with an introduction to the electrosynthesis of common second-generation ECPs. The information obtainable from electroanalytical studies, charge carriers such as polarons (positive and negative) and bipolarons (positive and negative) and doping will be discussed. The evolutionary chain of ECPs is then presented. ECPs comprising electron-rich D and electron-deficient A moieties have been shown to possess intrinsic electronic conductivity and unique optical and electronic properties. They are third generation ECPs and electropolymerization of mixtures of D and A leads to stoichiometrically controlled block copolymers. These D–A type ECPs are discussed on the basis of selected representative materials. Since the discovery of electropolymerization as a powerful tool to synthesize copolymers of conjugated monomers with a pre-determined ratio of D and A repeat units present in the polymer, the field of D–A type ECPs has grown considerably and the literature available since 2004 to 2021 is summarized and tabulated. Electronic and optical properties of the materials determined by computational chemistry are presented. The data obtained from electrochemical and optical methods are compared with those obtained from computational methods and reasons for discrepancies are given. The literature on the concept of electropolymerization extended to synthesizing triblock and many-block copolymers is reviewed. Finally, applications of D–A polymers in optoelectronic devices (organic solar cells and field-effect transistors) and in bio-imaging are explained quoting appropriate examples.

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

Soft and Stretchable Thienopyrroledione–Based Polymers via Direct Arylation

π-conjugated polymers (CPs) that are concurrently soft and stretchable are needed for deformable electronics. Molecular-level modification of indacenodithiophene (IDT) copolymers, a class of CPs that exhibit high hole mobilities (μ hole ), is an approach that can help realize intrinsically soft and stretchable CPs. Numerous examples of design strategies to adjust the stretchability of CPs exist, but imparting softness is comparatively less studied. In this study, a systematic molecular weight (MW) series is constructed on a promising candidate for soft CPs, poly(indacenodithiophene-co-thienopyrroledione) (p(IDT C16- TPD C8 )), by optimizing direct arylation polymerization conditions in hopes of improving stretchability and μhole without significantly impacting softness. We found p(IDT C16- TPD C8 ) at a degree of polymerization of 32 shows high stretchability (crack onset strain, CoS > 100%) without significantly impacting softness (elastic modulus, E = 32 MPa), which to the best of our knowledge outperforms previously reported stretchable and soft CPs. To further study how molecular-level modifications impact polymer properties, a MW series of a new extended donor unit polymer, poly(indacenodithienothiophene-co-thienopyrroledione) (p(IDTT C16- TPD C8 )), was synthesized. The IDTT C16 copolymers did not result in a greater average μ hole when comparing between p(IDTT C16- TPD C8 ) and p(IDT C16- TPD C8 ) despite their higher crystallinity observed by GIWAXS. While these findings warrant further investigation, this study points toward unique charge transport properties of IDT-based polymers.

direct arylation polymerization↗
DOE OSTI2020

Toward the Prediction and Control of Glass Transition Temperature for Donor–Acceptor Polymers

Semiconducting donor–acceptor (D–A) polymers have attracted considerable attention toward the application of organic electronic and optoelectronic devices. However, a rational design rule for making semiconducting polymers with desired thermal and mechanical properties is currently lacking, which greatly limits the development of new polymers for advanced applications. Here, polydiketopyrrolopyrrole (PDPP)-based D–A polymers with varied alkyl side-chain lengths and backbone moieties are systematically designed, followed by investigating their thermal and thin film mechanical responses. The experimental results show a reduction in both elastic modulus and glass transition temperature (Tg) with increasing side-chain length, which is further verified through coarse-grained molecular dynamics simulations. Informed from experimental results, a mass-per-flexible bond model is developed to capture such observation through a linear correlation between Tg and polymer chain flexibility. Using this model, a wide range of backbone Tg over 80 °C and elastic modulus over 400 MPa can be predicted for PDPP-based polymers. This study highlights the important role of side-chain structure in influencing the thermomechanical performance of conjugated polymers, and provides an effective strategy to design and predict Tg and elastic modulus of future new D–A polymers.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Highly stretchable organic electrochemical transistors with strain-resistant performance

Realizing fully stretchable electronic materials is central to advancing new types of mechanically agile and skin-integrable optoelectronic device technologies. Here we demonstrate a materials design concept combining an organic semiconductor film with a honeycomb porous structure with biaxially prestretched platform that enables high-performance organic electrochemical transistors with a charge transport stability over 30-140% tensional strain, limited only by metal contact fatigue. In this work, the prestretched honeycomb semiconductor channel of donor-acceptor polymer poly(2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2-yl)-2,5-diketo-pyrrolopyrrole-alt-2,5-bis(3-triethyleneglycoloxy-thiophen-2-yl) exhibits high ion uptake and completely stable electrochemical and mechanical properties over 1,500 redox cycles with 10(4) stretching cycles under 30% strain. Invariant electrocardiogram recording cycles and synapse responses under varying strains, along with mechanical finite element analysis, underscore that the present stretchable organic electrochemical transistor design strategy is suitable for diverse applications requiring stable signal output under deformation with low power dissipation and mechanical robustness. Highly stretchable organic electrochemical transistors with stable charge transport under severe tensional strains are demonstrated using a honeycomb semiconducting polymer morphology, thereby enabling controllable signal output for diverse stretchable bioelectronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Photo-Induced Charge Transfer of Fullerene and Non-Fullerene Conjugated Polymer Blends via Ab Initio Excited-State Dynamics

Organic conjugated polymers (CPs) are promising candidates for organic photovoltaic (OPV) devices due to their unique tunable mechanical and optoelectronic performance. Over the last decade, optoelectronic properties of narrow band gap CPs as a blend with acceptor units are largely optimized, which leads to noticeable progress in OPV technology. However, their power conversion efficiency is still lower than their organic counterparts (i.e., silicon), limiting their practical usage. In this study, we employ ab initio molecular dynamics to explore photo-induced charge transfer (CT) of the diketopyrrolopyrrole-based polymer as a blend with non-fullerene (i.e., ITIC) and fullerene (i.e., PCBM) acceptor units. The results of charge carrier dynamics induced by selected photoexcitation show that hole density redistribution in space is much faster than electron relaxation. We track the relaxation rates of charge carriers over time, where the derivative of the difference between the rate of electron and hole implies the current density at zero voltage. Furthermore, this can be utilized to characterize the CT performance of CPs blended with different acceptor units. Relaxation rate results indicate that CP blend with ITIC promises a better PV performance, illustrating that the current computational approach opens the door to determine bulk heterojunctions’ electronic performance for OPV devices and narrowing down the list of potential donor–acceptor candidates.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Highly fluorescent purine-containing conjugated copolymers with tailored optoelectronic properties

Conjugated copolymers containing electron donor and acceptor units in their main chain have emerged as promising materials for organic electronic devices due to their tunable optoelectronic properties. In this work, we describe the use of direct arylation polymerization to create a series of fully π-conjugated copolymers containing the highly tailorable purine scaffold as a key design element. To create efficient coupling sites, dihalopurines are flanked by alkylthiophenes to create a monomer that is readily copolymerized with a variety of conjugated comonomers, ranging from electron-donating 3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine to electron-accepting 4,7-bis(5-bromo-3-hexylthiophen-2-yl)benzo[c][1,2,5]thiadiazole. The comonomer choice and electronic nature of the purine scaffold allow the photophysical properties of the purine-containing copolymers to be widely varied, with optical bandgaps ranging from 1.96–2.46 eV, and photoluminescent quantum yields as high as Φ = 0.61. Frontier orbital energy levels determined for the various copolymers using density functional theory tight binding calculations track with experimental results, and the geometric structures of the alkylthiophene-flanked purine monomer and its copolymer are found to be nearly planar. The utility of direct arylation polymerization and intrinsic tailorability of the purine scaffold highlight the potential of these fully conjugated polymers to establish structure–property relationships based on connectivity pattern and comonomer type, which may broadly inform efforts to advance purine-containing conjugated copolymers for various applications.

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

Molecular Origin of Strain-Induced Chain Alignment in PDPP-Based Semiconducting Polymeric Thin Films

Donor–acceptor (D–A) type semiconducting polymers have shown great potential for the application of deformable and stretchable electronics in recent decades. However, due to their heterogeneous structure with rigid backbones and long solubilizing side chains, the fundamental understanding of their molecular picture upon mechanical deformation still lacks investigation. Here, the molecular orientation of diketopyrrolopyrrole (DPP)-based D–A polymer thin films is probed under tensile deformation via both experimental measurements and molecular modeling. The detailed morphological analysis demonstrates highly aligned polymer crystallites upon deformation, while the degree of backbone alignment is limited within the crystalline domain. Besides, the aromatic ring on polymer backbones rotates parallel to the strain direction despite the relatively low overall chain anisotropy. Additionally, the effect of side-chain length on the DPP chain alignment is observed to be less noticeable. These observations are distinct from traditional linear-chain semicrystalline polymers like polyethylene due to distinct characteristics of backbone/side-chain combination and the crystallographic characteristics in DPP polymers. Furthermore, a stable and isotropic charge carrier mobility is obtained from fabricated organic field-effect transistors. This study deconvolutes the alignment of different components within the thin-film microstructure and highlights that crystallite rotation and chain slippage are the primary deformation mechanisms for semiconducting polymers.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Energy Transfer in Aqueous Light Harvesting Antennae Based on Brush-like Inter-Conjugated Polyelectrolyte Complexes

Conjugated polyelectrolytes (CPEs) have the potential to serve as building blocks of artificial light-harvesting systems. This is primarily due to their delocalized electronic states and potential for hierarchical self-assembly. We showed previously that inter-CPE complexes composed of oppositely charged exciton-donor and exciton-acceptor CPEs displayed efficient electronic energy transfer. However, near ionic charge equivalence, complexed CPE chains become net-neutral and thus experience a precipitous drop in aqueous solubility. To increase the stability and to rationally manipulate the phase behavior of inter-CPE complexes, we synthesized a series of highly water-soluble exciton-donor CPEs composed of alternating ionic and polar nonionic fluorene monomers. The nonionic monomer contained oligo(ethyleneglycol) sidechains of variable length. We then formed exciton donor-acceptor complexes and investigated their relative energy transfer efficiencies in the presence of a fixed exciton-acceptor CPE. We find that, even when the polar nonionic sidechains become quite long (nine ethyleneglycol units), the energy transfer efficiency is hardly affected so long as the inter-CPE network retains a net polyelectrolyte charge. However, near the onset of spontaneous phase separation, we observe a clear influence of the length of the oligo(ethyleneglycol) sidechains on the photophysics of the complex. Our results have implications for the use of polyelectrolyte phase separation to produce aqueous light-harvesting soft materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗