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2015
Single-Walled Carbon Nanotube–Metalloporphyrin Chemiresistive Gas Sensor Arrays for Volatile Organic Compounds
Chemistry of Materials,vol.27,p.3560-3563,2015 -
2015
Functionalized Metalated Cavitands via Imidation and Late-Stage Elaboration
European Journal of Organic Chemistry,vol.2015,p.4593–4597,2015Efficient methods for the preparation of functionalized metallated cavitands are described. Functional groups can be either introduced by an imidation of metal-oxo complexes or by a late-stage elaboration of the imido ligands. By using diversified iminophosphorane (PPh3=NR) reagents, π-conjugated pyrene, redox active ferrocene, and polymerizable norbornene moieties were successfully introduced. Furthermore, the iodo and alkynyl groups on the imido ligands are capable of undergoing efficient Sonogashira cross-coupling and copper-catalyzed azide alkyne cycloaddition reactions, thereby providing facile access to complex architectures containing metallated cavitands.
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2015
Tunneling Nanoelectromechanical Switches Based on Compressible Molecular Thin Films
ACS Nano,vol.9,p.7886-7894,2015Abrupt switching behavior and near-zero leakage current of nanoelectromechanical (NEM) switches are advantageous properties through which NEMs can outperform conventional semiconductor electrical switches. To date, however, typical NEMs structures require high actuation voltages and can prematurely fail through permanent adhesion (defined as stiction) of device components. To overcome these challenges, in the present work we propose a NEM switch, termed a “squitch,” which is designed to electromechanically modulate the tunneling current through a nanometer-scale gap defined by an organic molecular film sandwiched between two electrodes. When voltage is applied across the electrodes, the generated electrostatic force compresses the sandwiched molecular layer, thereby reducing the tunneling gap and causing an exponential increase in the current through the device. The presence of the molecular layer avoids direct contact of the electrodes during the switching process. Furthermore, as the layer is compressed, the increasing surface adhesion forces are balanced by the elastic restoring force of the deformed molecules which can promote zero net stiction and recoverable switching. Through numerical analysis, we demonstrate the potential of optimizing squitch design to enable large on–off ratios beyond 6 orders of magnitude with operation in the sub-1 V regime and with nanoseconds switching times. Our preliminary experimental results based on metal–molecule–graphene devices suggest the feasibility of the proposed tunneling switching mechanism. With optimization of device design and material engineering, squitches can give rise to a broad range of low-power electronic applications.
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2015
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2015
Thermally Activated Delayed Fluorescence Materials Based on Homoconjugation Effect of Donor–Acceptor Triptycenes
Journal of the American Chemical Society,vol.137,p.11908-11911,2015Donor–acceptor triptycences, TPA-QNX(CN)2 and TPA-PRZ(CN)2, were synthesized and their emissive properties were studied. They exhibited a blue-green fluorescence with emission lifetimes on the order of a microsecond in cyclohexane at room temperature. The long lifetime emission is quenched by O2 and is attributed to thermally activated delayed florescence (TADF). Unimolecular TADF is made possible by the separation and weak coupling due to homoconjugation of the HOMO and LUMO on different arms of the three-dimensional donor–acceptor triptycene. Organic light emitting devices (OLEDs) were fabricated using TPA-QNX(CN)2 and TPA-PRZ(CN)2 as emitters which displayed electroluminescence with efficiencies as high as 9.4% EQE.
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2015
Synthesis of Miktoarm Branched Conjugated Copolymers by ROMPing In and Out.
ACS Macro Letters,vol.4,p.1229–1233,2015Architecture represents a promising yet underutilized control element in polymer design due to the challenging synthesis of compositionally varied branched copolymers. We report the one-pot synthesis of miktoarm branched polymers by ring-opening metathesis polymn. In this work, we graft to and from telechelic poly(3-hexylthiophene), which is end-capped by oxime click chem., using various norbornene monomers. The self-assembly of the resulting miktoarm H-shaped conjugated polymers is studied in soln. and in the solid state. A dual stimuli-responsive miktoarm polymer is prepd. that displays pH-switchable lower crit. soln. temp. and fluorescence.
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2015
Colorimetric Stimuli-Responsive Hydrogel Polymers for the Detection of Nerve Agent Surrogates
Macromolecules (Washington, DC, United States),vol.48,p.7990–7994,2015The threat of chem. warfare agents (CWAs) necessitates the development of functional materials that not only quickly detect the presence of CWAs but also actively protect against their toxicity. The authors have synthesized responsive units that exhibit colorimetric responses upon exposure to CWAs and incorporated them into a versatile detection platform based on copolymers prepd. by ring-opening metathesis polymn. (ROMP). The theor. detection limits for CWA simulants in soln. for these polymers are as low as 1 ppm. By incorporating hydrogel-promoting units as pendant chains, the authors are able to obtain polymers that instantly respond to CWA vapors and are easy to regenerate to the deactivated state by simple treatment with ammonium hydroxide vapor. The authors further demonstrate a collapse of the polymer gels in response to trifluoroacetic acid (TFA), a strong acid that produces a more fully ionized state as a result of its more caustic nature.
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2015
Simultaneous Identification of Neutral and Anionic Species in Complex Mixtures without Separation
Angewandte Chemie, International Edition,p.Ahead of Print,2015A chemosensory system is reported that operates without the need for sepn. techniques and is capable of identifying anions and structurally similar bioactive mols. In this strategy, the coordination of analytes to a metal complex with an open binding cleft generates "static structures" on the NMR timescale. Unique signals are created by strategically placing fluorine atoms in close proximity to bound analytes so that small structural differences induce distinct 19F NMR shifts that can be used to identify each analyte. The utility of this method is illustrated by quantifying caffeine levels in coffee, by identifying ingredients in tea and energy drinks, and by discriminating between multiple biogenic amines with remote structural differences six carbon atoms away from the binding site. We further demonstrate the simultaneous identification of multiple neutral and anionic species in a complex mixture
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2015
Chemiresistive Sensor Arrays from Conductive 2D Metal-Organic Frameworks
Journal of the American Chemical Society,vol.137,p.13780–13783,2015Applications of porous metal-org. frameworks (MOFs) in electronic devices are rare, owing in large part to a lack of MOFs that display elec. cond. Here, we describe the use of conductive two-dimensional (2D) MOFs as a new class of materials for chemiresistive sensing of volatile org. compds. (VOCs). We demonstrate that a family of structurally analogous 2D MOFs can be used to construct a cross-reactive sensor array that allows for clear discrimination between different categories of VOCs. Exptl. data show that multiple sensing mechanisms are operative with high degrees of orthogonality, establishing that the 2D MOFs used here are mechanistically unique and offer advantages relative to other known chemiresistor materials.
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2015
Functionalized nanostructures and devices including photovoltaic devices.
vol.PCT/US2015/026379,2015Embodiments described herein provide functionalized carbon nanostructures for use in various devices, including photovoltaic devices (e.g., solar cells). In some cases, the carbon nanostructures are fullerenes substituted with one or more isobenzofulvene species and/or indane species. Devices including such materials may exhibit increased efficiency, increased open circuit potential, high electron/hole mobility, and/or low elec. resistance. [on SciFinder(R)]
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2014
Templating fullerenes by domain boundaries of a nanoporous network.
Langmuir : the ACS journal of surfaces and colloids,vol.30,p.762–7,2014We present a new templating approach that combines the templating properties of nanoporous networks with the dynamic properties and the lattice mismatch of domain boundaries. This templating approach allows for the inclusion of guests with different sizes without the need for a strict molecular design to tailor the nanoporous network. With this approach, nonperiodic patterns of functional molecules can be formed and studied. We show that domain boundaries in a trimesic acid network are preferred over pores within the network as adsorption sites for fullerenes by a factor of 100-200. Pristine fullerenes of different sizes and functionalized fullerenes were templated in this way. -
2014
Phosphate functionalized graphene with tunable mechanical properties.
Advanced materials (Deerfield Beach, Fla.),vol.26,p.718–23,2014The synthesis of a covalently modified graphene oxide derivative with exceptional and tunable compressive strength is reported. Treatment of graphene oxide with triethyl phosphite in the presence of LiBr produces monolithic structures comprised of lithium phosphate oligomers tethered to graphene through covalent phosphonate linkages. Variation of the both phosphate content and associated cation produces materials of various compressive strengths and elasticity. -
2014
High field dynamic nuclear polarization NMR with surfactant sheltered biradicals.
The journal of physical chemistry. B,vol.118,p.1825–30,2014We illustrate the ability to place a water-insoluble biradical, bTbk, into a glycerol/water matrix with the assistance of a surfactant, sodium octyl sulfate (SOS). This surfactant approach enables a previously water insoluble biradical, bTbk, with favorable electron-electron dipolar coupling to be used for dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) experiments in frozen, glassy, aqueous media. Nuclear Overhauser enhancement (NOE) and paramagnetic relaxation enhancement (PRE) experiments are conducted to determine the distribution of urea and several biradicals within the SOS macromolecular assembly. We also demonstrate that SOS assemblies are an effective approach by which mixed biradicals are created through an assembly process. -
2014
Columnar Liquid Crystallinity and Mechanochromism in Cationic Platinum(II) Complexes.
Journal of the American Chemical Society,vol.136,p.2952–2955,2014Cationic square planar Pt(II) complexes are reported with high degrees of intermolecular association. These complexes display thermotropic columnar liquid crystalline behavior in spite of having only a single side chain. Crystals undergo mechanochromic transformations that can be reversed with solvent. -
2014
Topical Developments in High-Field Dynamic Nuclear Polarization.
Israel Journal of Chemistry,p.Ahead of Print,2014We report our recent efforts directed at improving high-field dynamic nuclear polarization (DNP) expts. We investigated a series of thiourea nitroxide radicals and the assocd. DNP enhancements ranging from $ε$=25 to 82, which demonstrate the impact of mol. structure on performance. We directly polarized low-gamma nuclei, including 13C, 2H, and 17O, by the cross effect mechanism using trityl radicals as a polarization agent. We discuss a variety of sample prepn. techniques for DNP with emphasis on the benefits of methods that do not use a glass-forming cryoprotecting matrix. Lastly, we describe a corrugated waveguide for use in a 700 MHz/460 GHz DNP system that improves microwave delivery and increases enhancements up to 50 %. [on SciFinder(R)] -
2014
Spray-Layer-by-Layer Carbon Nanotube/Electrospun Fiber Electrodes for Flexible Chemiresistive Sensor Applications.
Advanced Functional Materials,vol.24,p.492–502,2014Development of a versatile method for incorporating conductive materials into textiles could enable advances in wearable electronics and smart textiles. One area of crit. importance is the detection of chems. in the environment for security and industrial process monitoring. Here, the fabrication of a flexible, sensor material based on functionalized multi-walled carbon nanotube (MWNT) films on a porous electrospun fiber mat for real-time detection of a nerve agent simulant is reported. The material is constructed by layer-by-layer (LbL) assembly of MWNTs with opposite charges, creating multilayer films of MWNTs without binder. The vacuum-assisted spray-LbL process enables conformal coatings of nanostructured MWNT films on individual electrospun fibers throughout the bulk of the mat with controlled loading and elec. cond. A thiourea-based receptor is covalently attached to the primary amine groups on the MWNT films to enhance the sensing response to di-Me methylphosphonate (DMMP), a simulant for sarin nerve agent. Chemiresistive sensors based on the engineered textiles display reversible responses and detection limits for DMMP as low as 10 ppb in the aq. phase and 5 ppm in the vapor phase. This fabrication technique provides a versatile and easily scalable strategy for incorporating conformal MWNT films into three-dimensional substrates for numerous applications. [on SciFinder(R)] -
2014
Templating fullerenes by domain boundaries of a nanoporous network
Langmuir : the ACS journal of surfaces and colloids,vol.30,p.762–767,2014We present a new templating approach that combines the templating properties of nanoporous networks with the dynamic properties and the lattice mismatch of domain boundaries. This templating approach allows for the inclusion of guests with different sizes without the need for a strict molecular design to tailor the nanoporous network. With this approach, nonperiodic patterns of functional molecules can be formed and studied. We show that domain boundaries in a trimesic acid network are preferred over pores within the network as adsorption sites for fullerenes by a factor of 100-200. Pristine fullerenes of different sizes and functionalized fullerenes were templated in this way.[on SciFinder (R)] -
2014
Organic conductive materials including iptycene-based structure and devices.
PCT Int. Appl.,p.44pp.,2014Embodiments described herein relate to compns. including iptycene-based structures and extended iptycene structures. The iptycene-based compd. comprises an iptycene core and at least one optionally substituted heterocyclyl or optionally substituted heteroaryl moiety rigidly bonded to the iptycene core, wherein the optionally substituted heterocyclyl or optionally substituted heteroaryl moiety defines at least a portion of the iptycene core. In some embodiments, the compns. may be useful in org. light-emitting diodes (OLEDs), org. photovoltaics, and other devices. [on SciFinder(R)] -
2014
Overhauser effects in insulating solids.
Journal of Chemical Physics,vol.141,p.064202/1–064202/8,2014We report magic angle spinning, dynamic nuclear polarization (DNP) expts. at magnetic fields of 9.4 T, 14.1 T, and 18.8 T using the narrow line polarizing agents 1,3-bisdiphenylene-2-phenylallyl (BDPA) dispersed in polystyrene, and sulfonated-BDPA (SA-BDPA) and trityl OX063 in glassy glycerol/water matrixes. The 1H DNP enhancement field profiles of the BDPA radicals exhibit a significant DNP Overhauser effect (OE) as well as a solid effect (SE) despite the fact that these samples are insulating solids. In contrast, trityl exhibits only a SE enhancement. Data suggest that the appearance of the OE is due to rather strong electron-nuclear hyperfine couplings present in BDPA and SA-BDPA, which are absent in trityl and perdeuterated BDPA (d21-BDPA). In addn., and in contrast to other DNP mechanisms such as the solid effect or cross effect, the exptl. data suggest that the OE in non-conducting solids scales favorably with magnetic field, increasing in magnitude in going from 5 T, to 9.4 T, to 14.1 T, and to 18.8 T. Simulations using a model two spin system consisting of an electron hyperfine coupled to a 1H reproduce the essential features of the field profiles and indicate that the OE in these samples originates from the zero and double quantum cross relaxation induced by fluctuating hyperfine interactions between the intramol. delocalized unpaired electrons and their neighboring nuclei, and that the size of these hyperfine couplings is crucial to the magnitude of the enhancements. Microwave power dependent studies show that the OE sats. at considerably lower power levels than the solid effect in the same samples. Our results provide new insights into the mechanism of the Overhauser effect, and also provide a new approach to perform DNP expts. in chem., biophys., and phys. systems at high magnetic fields. (c) 2014 American Institute of Physics. [on SciFinder(R)] -
2014
Stereospecific Ring-Opening Metathesis Polymerization of Norbornadienes Employing Tungsten Oxo Alkylidene Initiators.
Journal of the American Chemical Society,vol.136,p.10910–10913,2014We report here the polymn. of several 7-isopropylidene-2,3-disubstituted norbornadienes, 7-oxa-2,3-dicarboalkoxynorbornadienes, and 11-oxa-benzonorbornadienes with a single tungsten oxo alkylidene catalyst, W(O)(CH-t-Bu)(OHMT)(Me2Pyr) (OHMT = 2,6-dimesitylphenoxide; Me2Pyr = 2,5-dimethylpyrrolide) to give cis, stereoregular polymers. The tacticities of the menthyl ester derivs. of two polymers were detd. for two types. For poly(7-isopropylidene-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis, isotactic, while for poly(7-oxa-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis, syndiotactic. A bis-trifluoromethyl-7-isopropylidene norbornadiene was not polymd. stereoregularly with W(O)(CHCMe2Ph)(Me2Pyr)(OHMT) alone, but a cis, stereoregular polymer was formed in the presence of 1 equiv of B(C6F5)3. [on SciFinder(R)]
