Electrochromic devices have widespread application potential, but the currently available switching speeds limit broad real-world implementation of this technology. Here, we report surface-engineered two-dimensional polymers with ionophilic pores that offer unprecedented switching speeds in solid-state, two-terminal, electrochromic devices. In particular, we demonstrate that a crystalline donor-acceptor 2DP functionalized with ethylene glycol oligomers exhibits multistate infrared absorption that is 4× faster (tc = 320 ms) with 3× coloration efficiency (491 cm2 C-1) compared to an alkyl functionalized 2DP constructed from the same chromophores. The functionalized nanoporous surfaces enable rapid switching in these materials under either oxidative or reductive conditions, allowing us to access a range of robust, stable optical responses in a single electrochromic layer. These attributes led us to leverage surface-functionalized 2DPs as multistate infrared logic gates. Collectively, this work demonstrates that surface engineering of nanoporous crystalline lattices is a promising approach to co-optimize the electronic and ionic conductivities required to achieve rapidly switchable electrochromic layers. Beyond speed and efficiency, the demonstration of multistate infrared characteristics shows that electrochromic frameworks are useful in integrated optoelectronic circuits. This positions surface-engineered 2DPs as improved electrochromic coatings and a new material platform for photonic information processing and adaptive devices.

Nuclear spin hyperpolarization utilizing parahydrogen has the potential for broad applications in chemistry, catalysis, biochemistry, and medicine. This review examines recent chemical and biochemical insights gained using parahydrogen-induced polarization (PHIP). We begin with photoinduced PHIP, which allows the investigation of short-lived and photoactivated catalysis. Next, we review the partially negative line effect, in which distinctive line shape helps to reveal information about rapid exchange with parahydrogen and the role of short-lived catalytic species. The NMR signal enhancement of a single proton in oneH-PHIP is discussed, challenging the underpinning concept of the necessity of pairwise hydrogenation. Furthermore, we examine metal-free PHIP facilitated by frustrated Lewis pair molecular tweezers and radicaloids, demonstrating alternative routes to hydrogenation. Although symmetric molecules incorporating parahydrogen are NMR silent, we showcase methods that reveal hyperpolarized states through post-hydrogenation reactions. We discuss chemical exchange processes that mediate polarization transfer between parahydrogen and a molecular target, expanding the reach of PHIP without synthesizing specialized precursors. We conclude this review by highlighting the role of PHIP in uncovering the H2 activation mechanisms of hydrogenases. By providing a detailed review of these diverse phenomena, we aim to familiarize the reader with the versatility of PHIP and its potential applications for mechanistic studies and chemical analysis.

Polyacetylene, a versatile material with an electrical conductivity that can span 7 orders of magnitude, is the prototypical conductive polymer. In this letter, we report the observation of a significant Overhauser effect at the high magnetic field of 14.1 T that operates at 100 K and room temperature in both linear and cyclic polyacetylene. Significant NMR signal enhancements ranging from 24 to 45 are obtained. The increased sensitivity enabled the characterization of the polymer chain defects at natural abundance. The absence of end methyl group carbon-13 signals provides proof of the closed-loop molecular structure of cyclic polyacetylene. The remarkable efficiency of the soliton based Overhauser effect DNP mechanism at high temperature and high field holds promise for applications and extension to other conductive polymer systems.

Nuclear spin hyperpolarization utilizing parahydrogen (pH2) has broad applications in chemistry, biochemistry, and medicine. This review focuses on examining the less traveled roads associated with parahydrogen-induced polarization (PHIP) leading to MR signal enhancement. We begin with photo-induced PHIP, which allows the investigation of short-lived processes and photo-activated catalysis on timescales as short as microseconds. Next, we review the partially negative line (PNL) effect, in which distinctive lineshape helps to reveal information about rapid exchange with pH2 and the role of short lived catalytic species. The signal enhancement of a single proton in oneH-PHIP is discussed which challenges the underpinning concept of pairwise hydrogenation. Furthermore, we examine metal-free PHIP facilitated by novel molecular tweezers and radicaloids, thereby demonstrating alternative routes to conventional hydrogenation using metal-based catalysts. Although symmetric molecules incorporating pH2 are NMR silent, we showcase methods that reveal hyperpolarized states through post-hydrogenation reactions. Additionally, we discuss chemical exchange processes that mediate polarization transfer between pH2 and a molecular target, expanding the reach of PHIP without synthesizing specialized precursors. We conclude this review by highlighting the role PHIP has played in uncovering the H2 activation mechanisms of hydrogenases. By providing a detailed review of these diverse phenomena, we aim to broaden the understanding and hidden potential of PHIP, which keeps evolving rapidly close to 40 years after its first discovery.

Carbon–carbon bond cleavage reactions, adapted to deconstruct aliphatic hydrocarbon polymers and recover the intrinsic energy and carbon value in plastic waste, have typically been catalysed by metal nanoparticles or air-sensitive organometallics. Metal oxides that serve as supports for these catalysts are typically considered to be inert. Here we show that Earth-abundant, non-reducible zirconia catalyses the hydrogenolysis of polyolefins with activity rivalling that of precious metal nanoparticles. To harness this unusual reactivity, our catalytic architecture localizes ultrasmall amorphous zirconia nanoparticles between two fused platelets of mesoporous silica. Macromolecules translocate from bulk through radial mesopores to the highly active zirconia particles, where the chains undergo selective hydrogenolytic cleavage into a narrow, C 18 -centred distribution. Calculations indicated that C–H bond heterolysis across a Zr–O bond of a Zr(O) 2 adatom model for unsaturated surface sites gives a zirconium hydrocarbyl, which cleaves a C–C bond via β-alkyl elimination.

A novel closed loop, continuous flow (CF) reactor system for parahydrogen enhanced nuclear magnetic resonance (NMR) of liquids via heterogeneous catalysis is introduced which enables recycling of unreacted liquid substrate reactant. This system consists of an HPLC pump, a liquid substrate reservoir incorporating a gas diffuser, an all-metal packed bed catalytic reactor, and an AF-2400 tube-in-tube gas permeable membrane for removal of normal H2. Two types of supported metal nanoparticle catalysts were tested: mesoporous silica encapsulated Pt3Sn intermetallic nanoparticles and a Rh on anatase TiO2 support. In the CF hydrogenation of propargyl acetate to allyl acetate, the hyperpolarized signals exhibited stability over 20 min of recirculation, with signal enhancements of up to 626 using 99% p-H2 and negligible leaching of the catalyst into the flowing solutions. These results demonstrate the practicality of performing systematic optimization of conditions for continuous flow catalysis and polarization transfer to heteronuclei with important implications for biomedical magnetic resonance imaging.

Supported noble metals offer key advantages over homogeneous catalysts for in vivo applications of parahydrogen-based hyperpolarization. However, their performance is compromised by randomization of parahydrogen spin order resulting from rapid hydrogen adatom diffusion. The diffusion on Pt surfaces can be suppressed by introduction of Sn to form Pt-Sn intermetallic phases. Herein, an unprecedented pairwise selectivity of 19.7 ± 1.1% in the heterogeneous hydrogenation of propyne using silica encapsulated Pt-Sn intermetallic nanoparticles is reported. This high level of selectivity exceeds that of all supported metal catalysts by at least a factor of 3. Moreover, the pairwise selectivity for alkyne hydrogenation is about 2 times higher than for alkene hydrogenation, an observation attributed to the higher coverage of the former and its effect on diffusion. Lastly, PtSn@mSiO2 nanoparticles exhibited improved coking resistance, and any loss of activity is shown to be fully reversible through high-temperature oxidation-reduction cycling.

Level anticrossings (LACs) are ubiquitous in quantum systems and have been exploited for spin-order transfer in hyperpolarized nuclear magnetic resonance spectroscopy. This paper examines the manifestations of adiabatic passage through a specific type of LAC found in homonuclear systems of chemically inequivalent coupled protons incorporating parahydrogen (pH2). Adiabatic passage through such a LAC is shown to elicit translation of the pH2 spin order. As an example, with prospective applications in biomedicine, proton spin polarizations of at least 19.8 ± 2.6% on the methylene protons and 68.7 ± 0.5% on the vinylic protons of selectively deuterated allyl pyruvate ester are demonstrated experimentally. After ultrasonic spray injection of a precursor solution containing propargyl pyruvate and a dissolved Rh catalyst into a chamber pressurized with 99% para-enriched H2, the products are collected and transported to a high magnetic field for NMR detection. The LAC-mediated hyperpolarization of the methylene protons is significant because of the stronger spin coupling to the pyruvate carbonyl 13C, setting up an ideal initial condition for subsequent coherence transfer by selective INEPT. Furthermore, the selective deuteration of the propargyl side arm increases the efficiency and polarization level. LAC-mediated translation of parahydrogen spin order completes the first step toward a new and highly efficient route for the 13C NMR signal enhancement of pyruvate via side-arm hydrogenation with parahydrogen.

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTInstrumentation for Hydrogenative Parahydrogen-Based Hyperpolarization TechniquesAndreas B. Schmidt*Andreas B. SchmidtDepartment of Radiology−Medical Physics, Medical Center, Faculty of Medicine, University of Freiburg, Killianstraße 5a, Freiburg 79106, GermanyGerman Cancer Consortium (DKTK), partner site Freiburg and German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg 69120, Germany*Email: [email protected]More by Andreas B. SchmidtView Biographyhttps://orcid.org/0000-0001-8944-7463, C. Russell BowersC. Russell BowersDepartment of Chemistry, University of Florida, 2001 Museum Road, Gainesville, Florida 32611, United StatesNational High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United StatesMore by C. Russell BowersView Biography, Kai BuckenmaierKai BuckenmaierHigh-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Max-Planck-Ring 11, 72076 Tübingen, GermanyMore by Kai BuckenmaierView Biography, Eduard Y. ChekmenevEduard Y. ChekmenevIntergrative Biosciences (Ibio), Department of Chemistry, Karmanos Cancer Institute (KCI), Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United StatesRussian Academy of Sciences (RAS), Leninskiy Prospect, 14, 119991 Moscow, RussiaMore by Eduard Y. ChekmenevView Biographyhttps://orcid.org/0000-0002-8745-8801, Henri de MaissinHenri de MaissinDepartment of Radiology−Medical Physics, Medical Center, Faculty of Medicine, University of Freiburg, Killianstraße 5a, Freiburg 79106, GermanyGerman Cancer Consortium (DKTK), partner site Freiburg and German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg 69120, GermanyMore by Henri de MaissinView Biography, James EillsJames EillsInstitute for Physics, Johannes Gutenberg University, D-55090 Mainz, GermanyGSI Helmholtzzentrum für Schwerionenforschung GmbH, Helmholtz-Institut Mainz, 55128 Mainz, GermanyMore by James EillsView Biographyhttps://orcid.org/0000-0001-8468-6860, Frowin EllermannFrowin EllermannSection Biomedical Imaging, Molecular Imaging North Competence Center (MOIN CC), Department of Radiology and Neuroradiology, University Medical Center Kiel, Kiel University, Am Botanischen Garten 14, 24118 Kiel, GermanyMore by Frowin EllermannView Biographyhttps://orcid.org/0000-0001-6446-6641, Stefan GlögglerStefan GlögglerNMR Signal Enhancement Group Max Planck Institutefor Biophysical Chemistry Am Fassberg 11, 37077 Göttingen, GermanyCenter for Biostructural Imaging of Neurodegeneration of UMG, Von-Siebold-Straße 3A, 37075 Göttingen, GermanyMore by Stefan GlögglerView Biography, Jeremy W. GordonJeremy W. GordonDepartment of Radiology & Biomedical Imaging, University of California San Francisco, 185 Berry Street, San Francisco, California 94158, United StatesMore by Jeremy W. GordonView Biography, Stephan KnechtStephan KnechtNVision Imaging Technologies GmbH, 89081 Ulm, GermanyMore by Stephan KnechtView Biography, Igor V. KoptyugIgor V. KoptyugInternational Tomography Center, Siberian Branch of the Russian Academy of Sciences (SB RAS), 3A Institutskaya St., Novosibirsk 630090, RussiaMore by Igor V. KoptyugView Biographyhttps://orcid.org/0000-0003-3480-7649, Jule KuhnJule KuhnSection Biomedical Imaging, Molecular Imaging North Competence Center (MOIN CC), Department of Radiology and Neuroradiology, University Medical Center Kiel, Kiel University, Am Botanischen Garten 14, 24118 Kiel, GermanyMore by Jule KuhnView Biography, Andrey N. PravdivtsevAndrey N. PravdivtsevSection Biomedical Imaging, Molecular Imaging North Competence Center (MOIN CC), Department of Radiology and Neuroradiology, University Medical Center Kiel, Kiel University, Am Botanischen Garten 14, 24118 Kiel, GermanyMore by Andrey N. PravdivtsevView Biography, Francesca ReineriFrancesca ReineriDepartment of Molecular Biotechnology and Health Sciences, University of Torino, Via Nizza 52, 10124 Torino, ItalyMore by Francesca ReineriView Biography, Thomas TheisThomas TheisDepartments of Chemistry, Physics, and Biomedical Engineering, North Carolina State University, Raleigh, North Carolina 27695, United StatesMore by Thomas TheisView Biographyhttps://orcid.org/0000-0001-6779-9978, Kolja ThemKolja ThemSection Biomedical Imaging, Molecular Imaging North Competence Center (MOIN CC), Department of Radiology and Neuroradiology, University Medical Center Kiel, Kiel University, Am Botanischen Garten 14, 24118 Kiel, GermanyMore by Kolja ThemView Biographyhttps://orcid.org/0000-0002-5512-0910, and Jan-Bernd Hövener*Jan-Bernd HövenerSection Biomedical Imaging, Molecular Imaging North Competence Center (MOIN CC), Department of Radiology and Neuroradiology, University Medical Center Kiel, Kiel University, Am Botanischen Garten 14, 24118 Kiel, Germany*Email: [email protected]More by Jan-Bernd HövenerView Biographyhttps://orcid.org/0000-0001-7255-7252Cite this: Anal. Chem. 2022, 94, 1, 479–502Publication Date (Web):January 1, 2022Publication History Published online1 January 2022Published inissue 11 January 2022https://pubs.acs.org/doi/10.1021/acs.analchem.1c04863https://doi.org/10.1021/acs.analchem.1c04863review-articleACS PublicationsCopyright © 2022 American Chemical SocietyRequest reuse permissionsACS Editors' Choice® is a collection designed to feature scientific articles of broad public interest. Read the latest articlesArticle Views7813Altmetric-Citations33LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Hydrogenation,Magnetic properties,Order,Polarization,Quantum mechanics Get e-Alerts

Here we demonstrate the synthesis of cyclic polyacetylene (c-PA), or [∞]annulene, via homogeneous tungsten-catalysed polymerization of acetylene. Unique to the cyclic structure and evidence for its topology, the c-PA contains >99% trans double bonds, even when synthesized at −94 °C. High activity with low catalyst loadings allows for the synthesis of temporarily soluble c-PA, thus opening the opportunity to derivatize the polymer in solution. Absolute evidence for the cyclic topology comes from atomic force microscopy images of bottlebrush derivatives generated from soluble c-PA. Now available in its cyclic form, initial characterization studies are presented to elucidate the topological differences compared with traditionally synthesized linear polyacetylene. One advantage to the synthesis of c-PA is the direct synthesis of the trans–transoid isomer. Low defect concentrations, low soliton concentration, and relatively high conjugation lengths are characteristics of c-PA. Efficient catalysis permits the rapid synthesis of lustrous flexible thin films of c - PA, and when doped with I 2 , they are highly conductive (398 (±76) Ω −1 cm −1 ).

Intermetallic nanoparticles (iNPs) have been the subject of many recent reports for their demonstrated applications as highly active and selective heterogeneous catalysts. As a subclass of alloys, intermetallic compounds possess ordered crystal structures and, therefore, well-defined atomic environments, unlike the solid solution of alloys whose atomic arrangements are random and locally unpredictable. Catalytically active iNPs typically contain a group 8-10 transition metals as the "active" metals. They usually also include an "inactive" metal that does not directly participate in the catalytic reaction but can significantly modify the active metal's behavior. The choice of the inactive metal component can range across the periodic table. A few general challenges remain to design iNPs as heterogeneous catalysts with outstanding performance. Synthetically, the high surface energy of small nanopartides is prone to their aggregation, while maximizing the surface-to-volume ratios is highly desired for efficient noble metal utilization. Additionally, even though the formation of bulk intermetallic compounds has been extensively studied, the formation of intermetallic phases at the nanoscale can behave differently. For example, the formation temperatures of iNPs are often drastically different from those predicted from the bulk phase diagrams. This behavior often leads to further challenges in the synthesis of iNPs. In addition to synthetic challenges, it is also critical to demonstrate the performance of iNPs in catalysis and establish the structure- property relationships. Instrumental and computational techniques often assist the understanding of catalytic properties. Due to the long-range order of intermetallic structure, various electron and X-ray techniques are often used to precisely determine the structure of iNPs. Structural modeling in density functional theory (DFT) calculation can also benefit from such ordered structures. These techniques have siginificantly improved the understanding of enhanced catalytic properties of iNPs in thermo-, electro-, and photocatalysis. Hydrogenation of furfural to furfuryl alcohol, for example, is a model reaction where PtSn iNPs show enhanced activity and chemoselectivity in hydrogenating C=O rather than C=C bonds. This superior catalytic performance can be correlated to the change in the geometric and electronic surface structure of the PtSn iNPs based on careful instrumental and computational characterizations. Additionally, intermetallic surfaces can be further modified by ligands or defects. While adding complexity to iNP systems, these modifiers provide additional control over their catalytic properties. In this Account, taking encapsulated iNPs in mesoporous silica as an example, we review the current strategies to develop iNPs as high-performance heterogeneous catalysts, with insights on the distinct formation behavior of iNPs compared to bulk intermetallic materials. We then highlight thermo- and electro-catalysis reactions to which these iNP catalysts are applied. We also discuss the unique pairwise hydrogenation reaction with parahydrogen catalyzed by iNPs. In this reaction, iNPs show unparalleled potential. We anticipate that this Account could foster additional interests in studying intermetallic catalysts and lay the foundation for their applications.

Side-arm hydrogenation (SAH) by homogeneous catalysis has extended the reach of the parahydrogen enhanced NMR technique to key metabolites such as pyruvate. However, homogeneous hydrogenation requires rapid separation of the dissolved catalyst and purification of the hyperpolarised species with a purity sufficient for safe in-vivo use. An alternate approach is to employ heterogeneous hydrogenation in a continuous-flow reactor, where separation from the solid catalysts is straightforward. Using a TiO2-nanorod supported Rh catalyst, we demonstrate continuous-flow parahydrogen enhanced NMR by heterogeneous hydrogenation of a model SAH precursor, propargyl acetate, at a flow rate of 1.5 mL/min. Parahydrogen gas was introduced into the flowing solution phase using a novel tube-in-tube membrane dissolution device. Without much optimization, proton NMR signal enhancements of up to 297 (relative to the thermal equilibrium signals) at 9.4 Tesla were shown to be feasible on allyl-acetate at a continuous total yield of 33 %. The results are compared to those obtained with the standard batch-mode technique of parahydrogen bubbling through a suspension of the same catalyst.

Hyperpolarized propane produced by heterogeneous hydrogenation of cyclopropane with parahydrogen has been proposed as a safe inhalant for sensitivity-enhanced in vivo magnetic resonance imaging. The present studies were initially motivated by the possibility to improve the pairwise selectivity of hydrogenation using Pt-Sn intermetallic nanoparticle catalysts which achieved a record high pairwise selectivity in the hydrogenation of propene. The performance of the Pt 3 Sn catalysts is found to be comparable to that of the Rh/TiO2 catalyst employed in a recent publication. However, significant amounts of propene are also produced by isomerization over the Pt-Sn catalysts. The isomerization is promoted by weakening of the propene-surface binding energy and depletion of the H adatom density. While this is a remarkable finding from the perspective of catalysis science, the isomerization to propene over the Pt-Sn catalysts negates the advantages of using cyclopropane rather than propene as the safer reactant for in vivo use.

Nuclear spin hyperpolarization derived from parahydrogen can enable nuclear magnetic resonance spectroscopy and imaging with sensitivity enhancements exceeding four orders of magnitude. The NMR signal enhancement is proportional to 4(xp)-1, where xp is the parahydrogen mole fraction. For convenience, many labs elect to carry out the ortho-para conversion at 77 K where 50% enrichment is obtained. In theory, enrichment to 100% yields an automatic three-fold increase in the NMR signal enhancement. Herein, construction and testing of a simple and inexpensive continuous-flow converter for high paraenrichment is described. During operation, the converter is immersed in liquid helium contained in a transport dewar of the type commonly found in NMR labs for filling superconducting magnets. A maximum enrichment of 97.3 +/- 1.9% at 30 K was observed at 4.5 bar and 300 mL/min flow rate. The theoretically predicted 2.9-fold increase in the signal enhancement factor was confirmed in the heterogeneous hydrogenation of propene to propane over a PdIn/SBA-15 catalyst. The relatively low-cost to construct and operate this system could make high parahydrogen enrichment, and the associated increase in the parahydrogen-derived NMR signals, more widely accessible. (C)2020 Published by Elsevier Inc.

The molecular basis for the high cis-alkene selectivity over intermetallic PtSn for alkyne semi-hydrogenation is demonstrated. Unlike the universal assumption that the bimetallic surface is saturated with atomic hydrogen, molecular hydrogen has a higher barrier for dissociative adsorption on intermetallic PtSn due to the deficiency of Pt three-fold sites. The resulting molecular behavior of adsorbed hydrogen on intermetallic PtSn nanoparticles leads to pairwise-hydrogenation of three alkynes to the corresponding cis-alkenes, satisfying both high stereoselectivity and high chemoselectivity.

We study light-induced nuclear spin-polarization in a thin film of Ga1-xMnxAs (x 0.04), a dilute ferromagnetic semiconductor, grown on a GaAs substrate. High-field inductively-detected Ga-71 NMR was performed with samples immersed in superfluid He to investigate the effects of continuous-wave near band-edge optical illumination on lattice nuclear spins in the ferromagnetic phase. The photon energy dependence of the light-induced NMR signals for GaAs and the GaMnAs film samples were recorded using circularly polarized light. Interpretation of the data was guided by electronic band structure calculations using the k.p method in the presence of an external magnetic field using the modified 8-band Pidgeon-Brown model. The photon energy dependence of the NMR transition intensity exhibited a shift of the absorption band edge; invariance with respect to the sense of helicity of the exciting light; and an absence of oscillations in the photon energy dependence, all of which are consistent with theoretical predictions. The dynamics of the optically activated NMR experiments was investigated by variable optical intensity studies and light/dark modulated optical pumping experiments. This is because doping with Mn (a p-type dopant) can push the Fermi level deep into the valence bands and block the optical transitions (Burstein-Moss effect) needed to create spin polarized electrons. Additionally, the calculated enhancement of the conduction electron g-factor by over two orders of magnitude is expected to quench the electron-nuclear spin angular moment transfer, which impedes the hyperpolarization of lattice nuclei. Experiments with variable light intensity and optical gating reveal a mechanism consistent with light-induced quadrupolar relaxation, a process that will certainly interfere with the optical transfer and storage of quantum information in the lattice nuclear spin states in this material.