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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Microscopic theory, analysis, and interpretation of conductance histograms in molecular junctions

Molecular electronics break-junction experiments are widely used to investigate fundamental physics and chemistry at the nanoscale. Reproducibility in these experiments relies on measuring conductance on thousands of freshly formed molecular junctions, yielding a broad histogram of conductance events. Experiments typically focus on the most probable conductance, while the information content of the conductance histogram has remained unclear. Here we develop a microscopic theory for the conductance histogram by merging the theory of force-spectroscopy with molecular conductance. The procedure yields analytical equations that accurately fit the conductance histogram of a wide range of molecular junctions and augments the information content that can be extracted from them. Our formulation captures contributions to the conductance dispersion due to conductance changes during the mechanical elongation inherent to the experiments. In turn, the histogram shape is determined by the non-equilibrium stochastic features of junction rupture and formation. The microscopic parameters in the theory capture the junction’s electromechanical properties and can be isolated from separate conductance and rupture force (or junction-lifetime) measurements. The predicted behavior can be used to test the range of validity of the theory, understand the conductance histograms, design molecular junction experiments with enhanced resolution and molecular devices with more reproducible conductance properties.

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

Enabling rapid COVID-19 small molecule drug design through scalable deep learning of generative models

We improved the quality and reduced the time to produce machine learned models for use in small molecule antiviral design. Our globally asynchronous multi-level parallel training approach strong scales to all of Sierra with up to 97.7% efficiency. We trained a novel, character-based Wasserstein autoencoder that produces a higher quality model trained on 1.613 billion compounds in 23 minutes while the previous state of the art takes a day on 1 million compounds. Reducing training time from a day to minutes shifts the model creation bottleneck from computer job turnaround time to human innovation time. Our implementation achieves 318 PFLOPs for 17.1% of half-precision peak. We will incorporate this model into our molecular design loop enabling the generation of more diverse compounds; searching for novel, candidate antiviral drugs improves and reduces the time to synthesize compounds to be tested in the lab.

Jacobs, Sam Ade↗
DOE OSTI2024

From Coherence to Function: Exploring the Connection in Chemical Systems

The role of quantum mechanical coherences or coherent superposition states in excited state processes has received considerable attention in the last two decades largely due to advancements in ultrafast laser spectroscopy. These coherence effects hold promise for enhancing the efficiency and robustness of functionally relevant processes, even when confronted with energy disorder and environmental fluctuations. Understanding coherence deeply drives us to unravel mechanisms and dynamics controlled by order and synchronization at a quantum mechanical level, envisioning optical control of coherence to enhance functions or create new ones in molecular and material systems. In this frontier, the interplay between electronic and vibrational dynamics, specifically the influence of vibrations in directing electronic dynamics, has emerged as the leading principle. Here, two energetically disparate quantum degrees of freedom work in-sync to dictate the trajectory of an excited state reaction. Moreover, with the vibrational degree being directly related to the structural composition of molecular or material systems, new molecular designs could be inspired by tailoring certain structural elements. In the realm of chemical kinetics, our understanding of the dynamics of chemical transformations is underpinned by fundamental theories, such as transition state theory, activated rate theory, and Marcus theory. These theories elucidate reaction rates by considering the energy barriers that must be overcome for reactants to transform into products. Those barriers are surmounted by the stochastic nature of energy gap fluctuations within reacting systems, emphasizing that the reaction coordinate, the pathway from reactants to products, is not rigidly defined by a specific vibrational motion but encompasses a diverse array of molecular motions. While less is known about the involvement of specific intramolecular vibrational modes, their significance in certain cases cannot be overlooked. In this Account, we summarize key experimental findings that offer deeper insights into the complex electronic–vibrational trajectories encompassing excited states afforded from state-of-the-art ultrafast laser spectroscopy in three exemplary processes: photoinduced electron transfer, singlet–triplet intersystem crossing, and intramolecular vibrational energy flow in molecular systems. We delve into the rapid decoherence, or loss of phase and amplitude correlations, of vibrational coherences along promoter vibrations during subpicosecond intersystem crossing dynamics in a series of binuclear platinum complexes. This rapid decoherence illustrates the vibration-driven reactive pathways from the Franck–Condon state to the curve crossing region. We also explore the generation of new vibrational coherences induced by impulsive reaction dynamics rather than by the laser pulse in these systems, which sheds light on specific energy dissipation pathways and thereby on the progression of the reaction trajectory in the vicinity of the curve crossing on the product side. Another property of vibrational coherences, amplitude, reveals how energy can flow from one vibration to another in the electronic excited state of a terpyridine–molybdenum complex hosting a nonreactive dinitrogen substrate. In conclusion, a slight change in vibrational energy triggers a quasi-resonant interaction, leading to constructive wavepacket interference and ultimately intramolecular vibrational redistribution from a Franck–Condon active terpyridine vibration to a dinitrogen stretching vibration, energizing the dinitrogen bond.

Electrical energy↗
NASA NTRS1997

Microgravity Processing and Photonic Applications of Organic and Polymeric Materials

In recent years, a great deal of interest has been directed toward the use of organic materials in the development of high-efficiency optoelectronic and photonic devices. There is a myriad of possibilities among organics which allow flexibility in the design of unique structures with a variety of functional groups. The use of nonlinear optical (NLO) organic materials such as thin-film waveguides allows full exploitation of their desirable qualities by permitting long interaction lengths and large susceptibilities allowing modest power input. There are several methods in use to prepare thin films, such as Langmuir-Blodgett (LB) and self-assembly techniques, vapor deposition, growth from sheared solution or melt, and melt growth between glass plates. Organics have many features that make them desirable for use in optical devices such as high second- and third-order nonlinearities, flexibility of molecular design, and damage resistance to optical radiation. However, their use in devices has been hindered by processing difficulties for crystals and thin films. In this chapter, we discuss photonic and optoelectronic applications of a few organic materials and the potential role of microgravity on processing these materials. It is of interest to note how materials with second- and third-order nonlinear optical behavior may be improved in a diffusion-limited environment and ways in which convection may be detrimental to these materials.

Frazier, Donald O.↗
NASA NTRS1998

Microgravity Processing and Photonic Applications of Organic and Polymeric Materials

In recent years, a great deal of interest has been directed toward the use of organic materials in the development of high-efficiency optoelectronic and photonic devices. There is a myriad of possibilities among organic which allow flexibility in the design of unique structures with a variety of functional groups. The use of nonlinear optical (NLO) organic materials such as thin-film waveguides allows full exploitation of their desirable qualities by permitting long interaction lengths and large susceptibilities allowing modest power input. There are several methods in use to prepare thin films, such as Langmuir-Blodgett (LB) and self-assembly techniques, vapor deposition, growth from sheared solution or melt, and melt growth between glass plates. Organics have many features that make Abstract: them desirable for use in optical devices such as high second- and third-order nonlinearities, flexibility of molecular design, and damage resistance to optical radiation. However, their use in devices has been hindered by processing difficulties for crystals and thin films. In this chapter, we discuss photonic and optoelectronic applications of a few organic materials and the potential role of microgravity on processing these materials. It is of interest to note how materials with second- and third-order nonlinear optical behavior may be improved in a diffusion-limited environment and ways in which convection may be detrimental to these materials. We focus our discussion on third-order materials for all-optical switching, and second-order materials for all-optical switching, and second-order materials for frequency conversion and electrooptics.

Frazier, Donald 0↗
DOE OSTI2026

Molecular Tuning of Ether Cosolvent Chemistry for High-Voltage Sodium-Ion Batteries

Ethers as electrolyte cosolvents in sodium-ion batteries (SIBs) provide favorable Na + solvation and interfacial properties, but their low oxidative stability limits their use in high-voltage SIBs. Herein, we address this limitation via molecular tuning of ether cosolvents for high-voltage (4.2 V) hard carbon || NaNi 0.33 Fe 0.33 Mn 0.33 O 2 full cells. Tetrahydropyran (THP) is functionalized with a nitrile group to form tetrahydropyran-4-carbonitrile (THPCN). To delineate the effect of nitrile functionalization and benchmark ether against a conventional carbonate, THP, THPCN, and diethyl carbonate (DEC) are evaluated as cosolvents with ethylene carbonate. Nitrile functionalization lowers the HOMO energy of the ether, extends the electrolyte stability window, and alters Na⁺ solvation. Spectroscopic techniques and molecular dynamics simulations reveal that THPCN exhibits predominantly aggregate-dominated solvation (95.1 %) with weakened Na + -solvent interactions, producing the most anion-rich environment relative to DEC and THP cosolvents. THPCN-modified solvation promotes the formation of highly conductive, fluorine-enriched interphases that suppress parasitic reactions. Pouch full cells with THPCN sustained ~ 600 cycles at 4.2 V, outperforming THP and DEC. Operando gas analysis reveals that THPCN reduces CO 2 generation by 45% and H 2 generation by 30% relative to THP. Furthermore, the findings demonstrate nitrile functionalization as a molecular design strategy to stabilize ethers and enable high-voltage SIBs.

25 ENERGY STORAGE↗
NASA NTRS1998

The Effects of Ground and Space Processing on the Properties of Organic, Polymeric, and Colloidal Materials

In recent years, a great deal of interest has been directed toward the use of organic materials in the development of high-efficiency optoelectronic and phototonic devices. There is a myriad of possibilities among organic materials which allow flexibility in the design of unique structures with a variety of functional groups. The use of nonlinear optical (NLO) organic materials as thin film wave-guides allows full exploitation of their desirable qualifies by permitting long interaction lengths and large susceptibilities allowing modest power input. There are several methods in use to prepare thin films such as Langmuir-Blodgett (LB) and self-assembly techniques, vapor deposition, growth from sheared solution or melt, and melt growth between glass plates. Organic-based materials have many features that make them desirable for use in optical devices, such as high second-and third-order nonlinearity, flexibility of molecular design, and damage resistance to optical radiation. However, their use in devices has been hindered by processing difficulties for crystals and thin films. We discuss the potential role of microgravity processing of a few organic and polymeric materials. It is of interest to note how materials with second-and third-order NLO behavior may be improved in a diffusion-limited environment and ways in which convection may be detrimental to these materials. We focus our discussion on third-order materials for all-optical switching, and second-order materials for frequency conversion and electrooptics. The goal of minimizing optical loss obviously depends on processing methods. For solution-based processes, such as solution crystal growth and solution photopolymerization, it is well known that thermal and solutal density gradients can initiate buoyancy-driven convection. Resultant fluid flows can affect transport of material to and from growth interfaces and become manifest in the morphology and homogeneity of the growing film or crystal. Likewise, buoyancy-driven convection can hinder production of defect-free, high-quality crystals or films during crystal and film growth by vapor deposition.

Frazier, Donald O.↗
DOE OSTI2023

Autonomous hydrogel locomotion regulated by light and electric fields

Autonomous robotic functions in materials beyond simple stimulus-response actuation require the development of functional soft matter that can complete well-organized tasks without step-by-step control. We report the design of photo- and electroactivated hydrogels that can capture and deliver cargo, avoid obstacles, and return without external, stepwise control. By incorporating two spiropyran monomers with different chemical substituents in the hydrogel, we created chemically random networks that enabled photoregulated charge reversal and autonomous behaviors under a constant electric field. In addition, using perturbations in the electric field induced by a dielectric inhomogeneity, the hydrogel could be attracted to high dielectric constant materials and autonomously bypasses the low dielectric constant materials under the guidance of the electric field vector. The photo- and electroactive hydrogels investigated here can autonomously perform tasks using constant external stimuli, an encouraging observation for the potential development of molecularly designed intelligent robotic materials.

42 ENGINEERING↗
DOE OSTI2022

Scalable training of graph convolutional neural networks for fast and accurate predictions of HOMO-LUMO gap in molecules

Abstract Graph Convolutional Neural Network (GCNN) is a popular class of deep learning (DL) models in material science to predict material properties from the graph representation of molecular structures. Training an accurate and comprehensive GCNN surrogate for molecular design requires large-scale graph datasets and is usually a time-consuming process. Recent advances in GPUs and distributed computing open a path to reduce the computational cost for GCNN training effectively. However, efficient utilization of high performance computing (HPC) resources for training requires simultaneously optimizing large-scale data management and scalable stochastic batched optimization techniques. In this work, we focus on building GCNN models on HPC systems to predict material properties of millions of molecules. We use HydraGNN, our in-house library for large-scale GCNN training, leveraging distributed data parallelism in PyTorch. We use ADIOS, a high-performance data management framework for efficient storage and reading of large molecular graph data. We perform parallel training on two open-source large-scale graph datasets to build a GCNN predictor for an important quantum property known as the HOMO-LUMO gap. We measure the scalability, accuracy, and convergence of our approach on two DOE supercomputers: the Summit supercomputer at the Oak Ridge Leadership Computing Facility (OLCF) and the Perlmutter system at the National Energy Research Scientific Computing Center (NERSC). We present our experimental results with HydraGNN showing (i) reduction of data loading time up to 4.2 times compared with a conventional method and (ii) linear scaling performance for training up to 1024 GPUs on both Summit and Perlmutter.

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

Molecularly engineered ZnO–carbon nanosheets from fumaric acid precursors for efficient photocatalytic water purification

The photocatalytic breakdown of organic contaminants is crucial for the development of water purification technology. Zinc oxide (ZnO) is an extensively researched photocatalyst; however, its efficacy is hindered by rapid charge recombination and limited utilization of UV irradiation. Resolving these issues necessitates integrating ZnO with conductive carbon phases via scalable, low-temperature synthesis. We provide a molecularly designed sol–gel method that converts zinc–fumarate coordination networks into two-dimensional ZnO–carbon nanosheets utilizing solely aqueous precursors and mild annealing temperatures (400–600 °C). This method utilizes fumaric acid as a dicarboxylate linker and polyvinylpyrrolidone (PVP) as a structural carbon source to produce ultrathin wurtzite ZnO nanosheets embedded inside an amorphous carbon matrix. The resultant ZnO-C hybrid achieves nearly complete methylene blue degradation within 10 min under UV-A illumination, demonstrating first-order kinetics and outstanding recyclability. Compared with commercial ZnO, the ZnO–C nanosheets exhibit comparable rapid photocatalytic degradation, enhanced adsorption behavior, a porous nanosheet morphology, and an integrated ZnO–carbon interfacial structure. These findings provide a viable molecular-templating approach to fabricating various metal oxide–carbon photocatalysts and underscore substantial enhancements in semiconductor efficacy in eco-friendly water treatment systems.

Ozcan, Muca [ORNL] (ORCID:0000000320020474)↗
DOE OSTI2020

Molecular Recognition at Mineral Interfaces: Implications for the Beneficiation of Rare Earth Ores

Ce-bastnäsite is the single largest mineral source for light rare-earth elements. In view of the growing industrial importance of rare-earth minerals, it is critical to develop more efficient methods for separating the valuable rare-earth-containing minerals from the surrounding gangue. In this work, we employ a combination of periodic density functional theory (DFT) and molecular mechanics (MM) calculations together with the de novo molecular design program HostDesigner to identify bis-phosphinate ligands that preferentially bind to the (100) Ce-bastnäsite surface rather than the (104) calcite surface. DFT calculations for a simple phosphinate ligand were employed to qualitatively understand key behaviors involved in ligand–metal, ligand–solvent, and solvent–metal interactions. These insights were then used to guide the search for flexible, rigid, and semirigid hydrocarbon linkers to identify candidate bis-phosphinate ligands with the potential to bind preferentially to Ce-bastnäsite. Among the five most promising bis-phosphinate ligands suggested by theoretical studies, three ligands were synthesized and their adsorption characteristics to bastnäsite (100) interfaces were characterized using vibrational sum-frequency (vSFG) spectroscopy, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and isothermal titration calorimetry (ITC). The efficacy of the selective interfacial molecular binding was demonstrated by identifying a bis-phosphinate ligand capable of providing an overall higher surface coverage of alkyl groups relative to a monophosphinate ligand. The results highlight the interplay between adsorption binding strength and maximum surface coverage in determining ligand efficiency to render the mineral surface hydrophobic. DFT calculations further indicate that all tested ligands have higher affinity for Ce-bastnäsite than for calcite. Finally, this is consistent with the ITC data showing stronger adsorption enthalpy to bastnäsite than to calcite, making these ligands promising candidates for selective flotation of Ce-bastnäsite.

58 GEOSCIENCES↗
DOE OSTI2025

Dielectric constant engineering of nonfullerene acceptors enables a record fill factor of 83.58% and a high efficiency of 20.80% in organic solar cells

Organic solar cells (OSCs) have achieved power conversion efficiencies (PCEs) surpassing 20%, but their development remains hindered by the inherently low dielectric constant (εr) of organic semiconductors, which limits charge transport and contributes to serious recombination losses. Herein, we present a comprehensive strategy to overcome the challenge by engineering the dielectric properties of nonfullerene acceptors (NFAs). Two Y-series NFAs of BTP-N3F and BTP-C3F have been synthesized featuring trifluoromethyl (CF 3 ) end-capped alkyl side chains. This molecular design significantly enhances the dipole moment and ε r (up to ∼5.9) when compared to the reference acceptor Y6 (∼3), reducing the exciton binding energy (E b ) and improving charge transport. Furthermore, the incorporation of a high-εr polymer additive, poly(pentafluorostyrene) (PPFS), synergistically improves the active layer morphology and dielectric properties, enabling efficient charge extraction and reduced recombination losses. Devices based on the optimized D18-Cl/BTP-C3F system have achieved a record-high fill factor (FF) of 83.58% and an impressive PCE of 20.80%, setting a new benchmark for OSCs. Finally, our results underscore the pivotal role of ε r in enhancing device performance and establish a versatile pathway for advancing OSC efficiency and stability through molecular and morphological optimization.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Incorporation of an Asymmetric Mo−Fe−S Cluster as an Artificial Cofactor into Nitrogenase

Abstract Nitrogenase employs a sophisticated electron transfer system and a Mo−Fe−S−C cofactor, designated the M‐cluster [(cit)MoFe 7 S 9 C]), to reduce atmospheric N 2 to bioaccessible NH 3 . Previously, we have shown that the cofactor‐free form of nitrogenase can be repurposed as a protein scaffold for the incorporation of a synthetic Fe−S cluster [Fe 6 S 9 (SEt) 2 ] 4− . Here, we demonstrate the utility of an asymmetric Mo−Fe−S cluster [Cp*MoFe 5 S 9 (SH)] 3− as an alternative artificial cofactor upon incorporation into the cofactor‐free nitrogenase scaffold. The resultant semi‐artificial enzyme catalytically reduces C 2 H 2 to C 2 H 4 , and CN − into short‐chain hydrocarbons, yet it is clearly distinct in activity from its [Fe 6 S 9 (SEt) 2 ] 4− ‐reconstituted counterpart, pointing to the possibility to employ molecular design and cluster synthesis strategies to further develop semi‐artificial or artificial systems with desired catalytic activities.

Tanifuji, Kazuki↗
NASA NTRS2022

Overcoming Universal Restrictions on Metal Selectivity by Protein Design

Selective metal coordination is central to the functions of metalloproteins:1,2 each metalloprotein must pair with its cognate metallocofactor to fulfl its biological role3 . However, achieving metal selectivity solely through a three-dimensional protein structure is a great challenge, because there is a limited set of metal-coordinating amino acid functionalities and proteins are inherently fexible, which impedes steric selection of metals3,4 . Metal-binding afnities of natural proteins are primarily dictated by the electronic properties of metal ions and follow the Irving–Williams series5 (Mn2+ < Fe2+ < Co2+ < Ni2+ Zn2+) with few exceptions6,7 . Accordingly, metalloproteins overwhelmingly bind Cu2+ and Zn2+ in isolation, regardless of the nature of their active sites and their cognate metal ions1,3,8 . This led organisms to evolve complex homeostatic machinery and non-equilibrium strategies to achieve correct metal speciation1,3,8–10. Here we report an artifcial dimeric protein, (AB)2, that thermodynamically overcomes the Irving–Williams restrictions in vitro and in cells, favouring the binding of lower-Irving–Williams transition metals over Cu2+, the most dominant ion in the Irving–Williams series. Counter to the convention in molecular design of achieving specifcity through structural preorganization, (AB)2 was deliberately designed to be fexible. This fexibility enabled (AB)2 to adopt mutually exclusive, metal-dependent conformational states, which led to the discovery of structurally coupled coordination sites that disfavour Cu2+ ions by enforcing an unfavourable coordination geometry. Aside from highlighting fexibility as a valuable element in protein design, our results illustrate design principles for constructing selective metal sequestration agents.

Tae Su Choi↗
DOE OSTI2023

Suppressing phase disproportionation in quasi-2D perovskite light-emitting diodes

Electroluminescence efficiencies and stabilities of quasi-two-dimensional halide perovskites are restricted by the formation of multiple-quantum-well structures with broad and uncontrollable phase distributions. Here, we report a ligand design strategy to substantially suppress diffusion-limited phase disproportionation, thereby enabling better phase control. We demonstrate that extending the π-conjugation length and increasing the cross-sectional area of the ligand enables perovskite thin films with dramatically suppressed ion transport, narrowed phase distributions, reduced defect densities, and enhanced radiative recombination efficiencies. Consequently, we achieved efficient and stable deep-red light-emitting diodes with a peak external quantum efficiency of 26.3% (average 22.9% among 70 devices and cross-checked) and a half-life of ~220 and 2.8 h under a constant current density of 0.1 and 12 mA/cm 2 , respectively. Our devices also exhibit wide wavelength tunability and improved spectral and phase stability compared with existing perovskite light-emitting diodes. These discoveries provide critical insights into the molecular design and crystallization kinetics of low-dimensional perovskite semiconductors for light-emitting devices.

14 SOLAR ENERGY↗
DOE OSTI2021

Boosting photovoltaic performance of ternary organic solar cells by integrating a multi-functional guest acceptor

Constructing ternary structure is one of the most effective design strategies to break the efficiency ceiling of traditional binary organic solar cells (OSCs). Here, a new Y-series non-fullerene acceptor (Y-T) featuring 1,3-diethyl-2-thiobarbituric acid (DTBA) end groups is developed as a third component for the classical PM6:Y6 binary system. The champion power conversion efficiency of ternary OSCs is increased from 15.64% to 17.37% via incorporating 10 wt% Y-T, with the simultaneously enhanced open-circuit voltage (Voc) of 0.865 V, a short-circuit current density (Jsc) of 26.90 mA/cm 2 , and a fill factor (FF) of 74.97%. The positive contribution of Y-T in the ternary blend can be ascribed to the improved spectroscopic complementarity and enhanced exciton utilization ratio due to the additional energy transfer process. Moreover, Y-T guest acceptor plays a critical role in adjusting the active layer morphology and facilitating three-dimension phase separation, resulting in a balanced charge transport and enhanced FF of ternary OSCs. Overall, this work provides insight into the molecular design of non-fullerene acceptor and suggest guidelines to rationally select guest component for ternary OSCs.

14 SOLAR ENERGY↗
DOE OSTI2025

Asymmetric ether solvents for high-rate lithium metal batteries

Recent electrolyte solvent design based on weakening lithium-ion solvation have shown promise in enhancing cycling performance of Li-metal batteries. However, they often face slow redox kinetics and poor cycling reversibility at high rate. Here we report using asymmetric solvent molecules substantially accelerates Li redox kinetics. Asymmetric ethers (1-ethoxy-2-methoxyethane, 1-methoxy-2-propoxyethane) showed higher exchange current densities and enhanced high-rate Li 0 plating/stripping reversibility compared to symmetric ethers. Adjusting fluorination levels further improved oxidative stability and Li 0 reversibility. The asymmetric 1-(2,2,2-trifluoro)-ethoxy-2-methoxyethane, with 2 M lithium bis(fluorosulfonyl)imide, exhibited high exchange current density, oxidative stability, compact solid–electrolyte interphase (~10 nm). This electrolyte exhibited superior performance among state-of-the-art electrolytes, enabling over 220 cycles in high-rate Li (50 μm)||LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811, 4.9 mAh cm −2 ) cells and for the first time over 600 cycles in anode-free Cu | |Ni95 pouch cells (200 mAh) under electric vertical take-off and landing cycling protocols. Our findings on asymmetric molecular design strategy points to a new pathway towards achieving fast redox kinetics for high-power Li-metal batteries.

batteries↗
DOE OSTI2020

Tuning the Mechanical Properties of a Polymer Semiconductor by Modulating Hydrogen Bonding Interactions

Conjugation breakers (CBs) with different H-bonding chemistry and linker flexibility are designed and incorporated into a Diketopyrrolopyrrole (DPP)-based conjugated polymer backbone. The effects of H-bonding interactions on polymer semiconductor morphology, mechanical properties and electrical performance are systematically investigated. We observe that CBs with H-bonding self-association constant >0.7 or denser packing tendency are able to induce higher polymer chain aggregation and crystallinity in as-casted thin film, resulting in higher modulus and crack on-set strain. Additionally, the rDoC (relative degree of crystallinity) of the stretched thin film with the highest crack on-set strain only suffers a small decrease, suggesting the main energy dissipation mechanism is the breakage of H-bonding interactions. By contrast, other less stretchable polymer films dissipate strain energy through the breakage of crystalline domains, indicated by drastic decrease in rDoC. Furthermore, we evaluate their electrical performance under mechanical strain in fully stretchable field-effect transistors. The polymer with the highest crack on-set strain has the least degradation in mobility as a function of strain. Overall, these observations suggest that we can aptly tune the mechanical properties in polymer semiconductors by modulating intermolecular interactions, such as H-bonding chemistry and linker flexibility. Such understanding provides molecular design guidelines for future stretchable semiconductors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗