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Horwitz, Noah E.

Publications and source records attributed to Horwitz, Noah E..

10 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Linker Redox Mediated Control of Morphology and Properties in Semiconducting Iron‐Semiquinoid Coordination Polymers**

Abstract The emergence of conductive 2D and less commonly 3D coordination polymers (CPs) and metal–organic frameworks (MOFs) promises novel applications in many fields. However, the synthetic parameters for these electronically complex materials are not thoroughly understood. Here we report a new 3D semiconducting CP Fe 5 (C 6 O 6 ) 3 , which is a fusion of 2D Fe‐semiquinoid materials and 3D cubic Fe x (C 6 O 6 ) y materials, by using a different initial redox‐state of the C 6 O 6 linker. The material displays high electrical conductivity (0.02 S cm −1 ), broad electronic transitions, promising thermoelectric behavior ( S 2 σ=7.0×10 −9 W m −1 K −2 ), and strong antiferromagnetic interactions at room temperature. This material illustrates how controlling the oxidation states of redox‐active components in conducting CPs/MOFs can be a “pre‐synthetic” strategy to carefully tune material topologies and properties in contrast to more commonly encountered post‐synthetic modifications.

Wang, Lei↗
DOE OSTI2020

Synthesis, modular composition, and electrochemical properties of lamellar iron sulfides

Transition metal chalcogenides with layered structures are promising materials for energy storage, catalysis, and electronics, among other areas. We have identified a new layered phase of iron sulfide containing interlayer solvated cations. We present an optimized synthesis for the Li + -containing material from an Fe(III) xanthate complex. Structure and composition data indicate the material consists of poorly-ordered iron sulfide layers separated by solvated cations. The lamellar spacing in these materials can be tuned by changing the identity of the cation. Furthermore, the lamellar spacing can also be reversibly tuned by the degree of solvation of the material. The material is electrically conductive and can serve as a pseudocapacitor with comparable performance to commercial materials such as MnO 2 . Finally, these materials also show promise as lithium or sodium ion battery cathodes with good capacity and reversibility.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Redox-Active 1D Coordination Polymers of Iron–Sulfur Clusters

Here we describe the combination of an archetypal redox-active metal sulfide cluster, Fe 4 S 4 , with an organic linker, 1,4-benzenedithiolate, to prepare coordination polymers containing infinite chains of Fe 4 S 4 clusters. The crystal structures of two solid materials have been solved from synchrotron X-ray powder diffraction data using simulated annealing and re-fined by a least-squares Rietveld refinement procedure. The electronic properties of these chains have also been characterized by UV-visible and Mössbauer spectroscopies. Additional experiments demonstrated that these chains can be solubilized by variation of the countercation and that the chain structure is maintained in solution. The redox-activity of the Fe 4 S 4 clusters can be accessed with chemical reagents. Introduction of charge carriers by reduction of the Fe 4 S 4 clusters is found to increase the electrical conductivity of the materials by up to four orders of magnitude. These results highlight the utility of Fe 4 S 4 clusters as redox-active building blocks in preparing new classes of coordination polymers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Unified model for singlet fission within a non-conjugated covalent pentacene dimer

When molecular dimers, crystalline films or molecular aggregates absorb a photon to produce a singlet exciton, spin-allowed singlet fission may produce two triplet excitons that can be used to generate two electron–hole pairs, leading to a predicted B50% enhancement in maximum solar cell performance. The singlet fission mechanism is still not well understood. Here we report on the use of time-resolved optical and electron paramagnetic resonance spectroscopy to probe singlet fission in a pentacene dimer linked by a non-conjugated spacer. We observe the key intermediates in the singlet fission process, including the formation and decay of a quintet state that precedes formation of the pentacene triplet excitons. In conclusion, using these combined data, we develop a single kinetic model that describes the data over seven temporal orders of magnitude both at room and cryogenic temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Marked Consequences of Systematic Oligothiophene Catenation in Thieno[3,4- c ]pyrrole-4,6-dione and Bithiopheneimide Photovoltaic Copolymers

As effective building blocks for high-mobility transistor polymers, oligothiophenes are receiving attention for polymer solar cells (PSCs) because the resulting polymers can effectively suppress charge recombination. In this work we investigate two series of in-chain donor–acceptor copolymers, PTPDnT and PBTInT, based on thieno[3,4-c]pyrrole-4,6-dione (TPD) or bithiopheneimide (BTI) as electron acceptor units, respectively, and oligothiophenes (nTs) as donor counits, for high-performance PSCs. Intramolecular S···O interaction leads to more planar TPD polymer backbones, however backbone torsion yields greater open-circuit voltages for BTI polymers. Thiophene addition progressively raises polymer HOMOs but marginally affects their band gaps. FT-Raman spectra indicate that PTPDnT and PBTInT conjugation lengths scale with nT catenation up to $n$ = 3 and then saturate for longer oligomer. Furthermore, the effects of oligothiophene alkylation position are explored, revealing that the alkylation pattern greatly affects film morphology and PSC performance. The 3T with “outward” alkylation in PTPD3T and PBTI3T affords optimal $π$-conjugation, close stacking, long-range order, and high hole mobilities (0.1 cm 2 /(V s)). These characteristics contribute to the exceptional ~80% fill factors for PTPD3T-based PSCs with PCE = 7.7%. The results demonstrate that 3T is the optimal donor unit among nTs ($n$ = 1–4) for photovoltaic polymers. Grazing incidence wide-angle X-ray scattering, transmission electron microscopy, and time-resolved microwave conductivity measurements reveal that the terthiophene-based PTPD3T blend maintains high crystallinity with appreciable local mobility and long charge carrier lifetime. These results provide fundamental materials structure-device performance correlations and suggest guidelines for designing oligothiophene-based polymers with optimal thiophene catenation and appropriate alkylation pattern to maximize PSC performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Electrochemically addressable trisradical rotaxanes organized within a metal–organic framework

Significance This research paper presents a strategy for the organization of artificial molecular switches based on mechanically interlocked molecules within a porous crystalline framework. Once arranged within the pores of the framework, the electronic state of the switches can be altered by the application of an electrochemical potential. This strategy is particularly useful when it comes to integrating dynamic, stimulus-responsive, mechanically interlocked molecules with the robustness and periodicity of porous solids. The findings of the research establish proof-of-concept for the application of postsynthetic transformations of porous crystalline frameworks in the creation of solid-state molecular switches and machines.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗