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2013
Sensory Arrays of Covalently Functionalized Single-Walled Carbon Nanotubes for Explosive Detection.
Advanced Functional Materials,vol.23,p.5285–5291,2013Chemiresistive sensor arrays for cyclohexanone and nitromethane are fabricated using single-walled carbon nanotubes (SWCNTs) that are covalently functionalized with urea, thiourea, and squaramide contg. selector units. Based on initial sensing results and 1H NMR binding studies, the most promising selectors are chosen and further optimized. These optimized selectors are attached to SWCNTs and simultaneously tested in a sensor array. The sensors show a very high level of reproducibility between measurements with the same sensor and across different sensors of the same type. Furthermore, the sensors show promising long-term stability, which renders them suitable for practical applications. [on SciFinder(R)] -
2013
Metathesis Step-Growth Polymerizations in Ionic Liquid.
ACS Macro Letters,vol.2,p.1061–1064,2013Metathesis step-growth polymns. in ionic liqs. (ILs) was explored to take advantage of the high b.ps. of ILs, thereby permitting the use of low pressures at high temps. Optimization reactions found that high polymers form efficiently using small amts. of catalyst and short reaction times. For example, high mol. wt. main-chain triptycene polymers with high triptycene incorporation were synthesized. This new methodol. is applicable to various metathesis reactions that require removal of volatile byproducts as a driving force, including acyclic diene metathesis (ADMET). [on SciFinder(R)] -
2013
Observation of strongly forbidden solid effect dynamic nuclear polarization transitions via electron-electron double resonance detected NMR.
The Journal of chemical physics,vol.139,p.214201,2013We present electron paramagnetic resonance experiments for which solid effect dynamic nuclear polarization transitions were observed indirectly via polarization loss on the electron. This use of indirect observation allows characterization of the dynamic nuclear polarization (DNP) process close to the electron. Frequency profiles of the electron-detected solid effect obtained using trityl radical showed intense saturation of the electron at the usual solid effect condition, which involves a single electron and nucleus. However, higher order solid effect transitions involving two, three, or four nuclei were also observed with surprising intensity, although these transitions did not lead to bulk nuclear polarization–suggesting that higher order transitions are important primarily in the transfer of polarization to nuclei nearby the electron. Similar results were obtained for the SA-BDPA radical where strong electron-nuclear couplings produced splittings in the spectrum of the indirectly observed solid effect conditions. Observation of high order solid effect transitions supports recent studies of the solid effect, and suggests that a multi-spin solid effect mechanism may play a major role in polarization transfer via DNP. -
2013
Functional Graphenic Materials Via a Johnson-Claisen Rearrangement.
Advanced Functional Materials,vol.23,p.1873–1882,2013The hydroxyl functionalities in graphene oxide (GO), the vast majority that must be allylic alcs., have been subjected to Johnson-Claisen rearrangement conditions. Under these conditions, a [3, 3] sigmatropic rearrangement after reaction with tri-Et orthoacetate gives rise to an ester functional group, attached to the graphitic framework via a robust C-C bond. This variation of the Claisen rearrangement offers an unprecedented versatility of further functionalizations, while maintaining the desirable properties of unfunctionalized graphene. The resultant functional groups were found to withstand reductive treatments for the deoxygenation of graphene sheets and a resumption of electronic cond. is obsd. The ester groups are easily sapond. to carboxylic acids in situ with basic conditions, to give water-sol. graphene. The ester functionality can be further reacted as is, or the carboxylic acid can easily be converted to the more reactive acid chloride. Subsequent amide formation yields up to 1 amide in 15 graphene carbons and increases intergallery spacing up to 12.8 AA, suggesting utility of this material in capacitors and in gas storage. Other functionalization schemes, which include the installation of terminal alkynes and dipolar cycloaddns., allow for the synthesis of a highly pos. charged, water-sol. graphene. The highly neg. and pos. charged graphenes (zeta potentials of -75 mV and +56 mV, resp.), are successfully used to build layer-by-layer (LBL) constructs. [on SciFinder(R)] -
2013
Detection and differentiation of neutral organic compounds by 19F NMR with a tungsten calix[4]arene imido complex.
Journal of the American Chemical Society,vol.135,p.18770–3,2013Fluorinated tungsten calix[4]arene imido complexes were synthesized and used as receptors to detect and differentiate neutral organic compounds. It was found that the binding of specific neutral organic molecules to the tungsten centers induces an upfield shift of the fluorine atom appended on the arylimido group, the extent of which is highly dependent on electronic and steric properties. We demonstrate that the specific bonding and size-selectivity of calix[4]arene tungsten-imido complex combined with (19)F NMR spectroscopy is a powerful new method for the analysis of complex mixtures. -
2012
Norbornadiene End-Capping of Cross-Coupling Polymerizations: A Facile Route to Triblock Polymers
ACS Macro Letters,vol.1,p.334–337,2012The potential use of conjugated polymers in device applications is often limited by their less than optimal physicochem. properties. This work describes an efficient protocol to end-cap conjugated polymers synthesized via palladium-catalyzed cross-coupling polymns. with norbornene groups. Specifically, the hydroarylation of norbornadiene is shown to be a high-yielding end-capping method. These strained bicyclic alkenyl end groups can be transformed into macroinitiators via ring-opening metathesis polymn. and can polymerize other strained monomers, such as norbornene, yielding elastomeric triblock copolymers. [on SciFinder(R)] -
2012We report a versatile new synthetic route to poly(para-phenylene)s (PPPs) and related poly(para-arylene)s containing high degrees of substitution not readily available by other methods. Our method transforms highly soluble, alkyne-containing polymers into PPPs via high-yielding, transition metal-mediated {[}2+2+2] cyclizations.
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2012
A review. A perspective on selected recent advances in graphene functionalization is offered. The activation of graphite as a means to create exfoliated sheets is highlighted as an important approach to achieve dispersions of individual graphene sheets. [on SciFinder(R)]
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2012
Improving the performance of P3HT-fullerene solar cells with side-chain-functionalized poly(thiophene) additives: a new paradigm for polymer design.
ACS nano,vol.6,p.3044–56,2012The motivation of this study is to determine if small amounts of designer additives placed at the polymer-fullerene interface in bulk heterojunction (BHJ) solar cells can influence their performance. A series of AB-alternating side-chain-functionalized poly(thiophene) analogues, P1-6, are designed to selectively localize at the interface between regioregular poly(3-hexylthiophene) (rr-P3HT) and PC(n)BM (n = 61, 71). The side chains of every other repeat unit in P1-6 contain various terminal aromatic moieties. BHJ solar cells containing ternary mixtures of rr-P3HT, PC(n)BM, and varying weight ratios of additives P1-6 are fabricated and studied. At low loadings, the presence of P1-6 consistently increases the short circuit current and decreases the series resistance of the corresponding devices, leading to an increase in power conversion efficiency (PCE) compared to reference P3HT/PC(61)BM cells. Higher additive loadings (>5 wt %) lead to detrimental nanoscale phase separation within the active layer blend and produce solar cells with high series resistances and low overall PCEs. Small-perturbation transient open circuit voltage decay measurements reveal that, at 0.25 wt % incorporation, additives P1-6 increase charge carrier lifetimes in P3HT/PC(61)BM solar cells. Pentafluorophenoxy-containing polymer P6 is the most effective side-chain-functionalized additive and yields a 28% increase in PCE when incorporated into a 75 nm thick rr-P3HT/PC(61)BM BHJ at a 0.25 wt % loading. Moreover, devices with 220 nm thick BHJs containing 0.25 wt % P6 display PCE values of up to 5.3% (30% PCE increase over a control device lacking P6). We propose that additives P1-6 selectively localize at the interface between rr-P3HT and PC(n)BM phases and that aromatic moieties at side-chain termini introduce a dipole at the polymer-fullerene interface, which decreases the rate of bimolecular recombination and, therefore, improves charge collection across the active layer. -
2012
An air-stable low-bandgap n-type organic polymer semiconductor exhibiting selective solubility in perfluorinated solvents.
Angewandte Chemie, International Edition,vol.51,p.9042–6,2012A thin-film transistor: An n-type polymer semiconductor, poly(2,3-bis(perfluorohexyl)thieno[3,4-b]pyrazine), was synthesized through a Pd-catalyzed polycondensation employing a perfluorinated multiphase solvent system. This is the first example of an n-type polymer semiconductor with exclusive solubility in fluorinated solvents. The fabrication of organic field effect transistors containing this new n-type polymer semiconductor is shown. -
2012
Triptycene diols: a strategy for synthesizing planar $π$ systems through catalytic conversion of a poly(p-phenylene ethynylene) into a poly(p-phenylene vinylene).
Angewandte Chemie, International Edition,vol.51,p.1182–6,2012A highly efficient method to introduce planarity and rigidity into a conjugated polymer backbone using a catalytic main-chain alteration to convert alkynes of PPE into annulated alkenes in PPV was developed. Post-polymn. cyclization provided a rare O-substitution of vinyl units of PPV and endowed products with greater planarity and rigidity, resulting in red-shifts in absorbance and fluorescence and defined vibrational features. We hope to extend this cyclization strategy to establish higher order of planarity for other conjugated polymer classes. [on SciFinder(R)] -
2012
Mechanical drawing of gas sensors on paper.
Angewandte Chemie, International Edition,vol.51,p.10740–5,2012Mech. abrasion of compressed single-walled carbon nanotubes (SWCNTs) on the surface of paper produces sensors capable of detecting NH3 gas at sub-ppm concns. This method of fabrication is simple, inexpensive, and entirely solvent-free, and avoids difficulties arising from the inherent instability of many SWCNT dispersions. [on SciFinder(R)] -
2012
Selective Detection of Ethylene Gas Using Carbon Nanotube-Based Devices: Utility in Determination of Fruit Ripeness.
Angewandte Chemie, International Edition,vol.51,p.5507,2012Ethylene is the smallest ripening hormone in plants. In their Communication (DOI: 10.1002/anie.201201042), T. M. Swager et al. show that from a simple mixture of single-walled carbon nanotubes and a copper(I) complex, chemoresistive devices can be prepared that are highly sensitive and selective to sub-ppm concentrations of ethylene. The utility of the sensor was demonstrated by following ripening stages in different fruits. -
2012
Polycyclic aromatic triptycenes: oxygen substitution cyclization strategies.
Journal of the American Chemical Society,vol.134,p.7282–5,2012The cyclization and planarization of polycyclic aromatic hydrocarbons with concomitant oxygen substitution was achieved through acid catalyzed transetherification and oxygen-radical reactions. The triptycene scaffold enforces proximity of the alcohol and arene reacting partners and confers significant rigidity to the resulting $π$-system, expanding the tool set of iptycenes for materials applications. -
2012
Strain release in organic photonic nanoparticles for protease sensing.
Journal of the American Chemical Society,vol.134,p.6932–5,2012Proteases are overexpressed in most cancers and proteolytic activity has been shown to be a viable marker for cancer imaging in vivo. Herein, we describe the synthesis of luminescence-quenched shell cross-linked nanoparticles as photonic nanoprobes for protease sensing. Protease sensing scheme is based on a \”turn-on\” mechanism where the protease cleaves peptide cross-linkers of the fluorescence-quenched shell cross-linked NP (OFF state) leading to a highly emissive non-cross linked NP (ON state). The cross-linked particles can be strained by exposure to a good solvent and proteolysis allows for particle expansion (swelling) and a recovery of the luminescence. -
2012
Enhanced electrochemical expansion of graphite for in situ electrochemical functionalization.
Journal of the American Chemical Society,vol.134,p.17896–9,2012An all electrochemical route to functionalized graphene directly from a graphite electrode is described herein obviating the need for defect inducing oxidative or prolonged sonication treatments. Enhanced electrochemical expansion of graphite is achieved by sequential treatment, beginning with the established method of expansion by electrolysis in a Li(+) containing electrolyte, and then with the much larger tetra-n-butylammonium. The result is a hyperexpansion of the graphite basal planes. As a demonstration of the utility of this method, we successfully performed a subsequent in situ electrochemical diazonium functionalization of the hyperexpanded graphite basal planes to give functional graphene sheets. This potential controlled process is more effective than chemical processes and also provides a means of controlling the degree of functionalization. We have further demonstrated that the functionalized graphene could be converted to a pristine low defect form via laser ablation of the funtional groups. As a result, this method presents a potentially scalable approach for graphene circuit patterning. -
2012
Water-soluble narrow-line radicals for dynamic nuclear polarization.
Journal of the American Chemical Society,vol.134,p.14287–90,2012The synthesis of air-stable, highly water-soluble organic radicals containing a 1,3-bis(diphenylene)-2-phenylallyl (BDPA) core is reported. A sulfonated derivative, SA-BDPA, retains the narrow electron paramagnetic resonance linewidth (<30 MHz at 5 T) of the parent BDPA in highly concentrated glycerol/water solutions (40 mM), which enables its use as polarizing agent for solid effect dynamic nuclear polarization (SE DNP). A sensitivity enhancement of 110 was obtained in high-field magic-angle-spinning (MAS) NMR experiments. The ease of synthesis and high maximum enhancements obtained with the BDPA-based radicals constitute a major advance over the trityl-type narrow-line polarization agents. -
2012
Cavitand-functionalized SWCNTs for N-methylammonium detection.
Journal of the American Chemical Society,vol.134,p.6540–3,2012Single-walled carbon nanotubes (SWCNTs) have been functionalized with highly selective tetraphosphonate cavitand receptors. The binding of charged N-methylammonium species to the functionalized SWCNTs was analyzed by X-ray photoelectron spectroscopy and confirmed by (31)P MAS NMR spectroscopy. The cavitand-functionalized SWCNTs were shown to function as chemiresistive sensory materials for the detection of sarcosine and its ethyl ester hydrochloride in water with high selectivity at concentrations as low as 0.02 mM. Exposure to sarcosine and its derivative resulted in an increased conductance, in contrast to a decreased conductance response observed for potential interferents such as the structurally related glycine ethyl ester hydrochloride. -
2012
Chain-growth polymerization of 2-chlorothiophenes promoted by Lewis acids.
Journal of the American Chemical Society,vol.134,p.18916–9,2012Lewis acids promote the polymerization of several 2-chloroalkylenedioxythiophenes, providing high-molecular-weight conjugated polymers. The proposed mechanism is a cationic chain-growth polymerization, as confirmed by end-capping reactions and a linear correlation of molecular weight with percent conversion. The “living” character of this process was used to prepare new block copolymers. -
2012
Synthesis and optical properties of phenylene-containing oligoacenes.
Journal of the American Chemical Society,vol.134,p.15351–6,2012Synthesis of a new class of fully unsaturated ladder structures, phenylene-containing oligoacenes (POAs), using 3,4-bis(methylene)cyclobutene as a building block for sequential Diels-Alder reactions is described. The geometric effects of strain and energetic cost of antiaromaticity can be observed via the optical and electrochemical properties of the reported compounds. The resulting shape-persistant ladder structures contain neighboring chromophores that are partially electronically isolated from one another while still undergoing a reduction in the band gap of the material.
