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2010
Detection of ethylene gas by fluorescence turn-on of a conjugated polymer.
Angewandte Chemie, International Edition,vol.49,p.8872–5,2010The sensing scheme the authors have designed for the detection of ethylene is based on a fluorescence turn-on mechanism and mimics nature by using a copper(I) complex to bind to ethylene. The fluorescence of the conjugated polymer is partially quenched by the presence of copper(I) moieties that can coordinate to the polymer. Upon exposure to ethylene gas, the copper complexes bind to the ethylene mols. and no longer quench the polymer fluorescence. The advantage of this fluorescence turn-on over a turn-off mechanism is that it requires a specific binding event to the copper to create a new signal, whereas fluorescence quenching can occur in multiple ways. Furthermore, if a completely dark background (completely quenched) state can be achieved, even a weak turn-on signal can be readily measured and thereby can allow trace detection. [on SciFinder(R)] -
2010
Radiation detection: resistivity responses in functional poly(olefin sulfone)/carbon nanotube composites.
Angewandte Chemie, International Edition,vol.49,p.95–8,2010A novel sensing scheme that is not based on scintillation or charge generation in semiconductors can be deployed for the detection of uncharged ionization radiation using small devices. Functional POSs were accessed by click chem. methods, and several strategies were successfully deployed to increase sensor sensitivity. Systematic improvements in sensitivity can be accomplished by rational design, and incorporation of the appropriate chem. components to achieve sensitivities in the 103 rad range. [on SciFinder(R)] -
2010
Biocompatible post-polymerization functionalization of a water soluble poly(p-phenylene ethynylene).
Chemical Communications,vol.46,p.5761–3,2010A biocompatible post-polymerization functionalization reaction takes advantage of a polymer’s structural motif for the controllable attachment of biotin as a model biosensor that responds to streptavidin. -
2010
Multichromophoric phthalocyanine-(perylenediimide)(8) molecules: a photophysical study.
Chemistry (Weinheim an der Bergstrasse, Germany),vol.16,p.10021–9,2010We describe the synthesis of a series of phthalocyanine (Pc)-perylenediimide (PDI)(8) öctad” molecules, in which eight PDI moieties are attached to a Pc core through alkyl-chain linkers. There is clear spectroscopic evidence that these octads can exist as non-aggregated “monomers” or form aggregates along the Pc cores, depending on the type of Pc and the solvent medium. In the low dielectric constant solvents, into which the octads are soluble, photoexcitation of the PDI units leads to rapid energy transfer to the Pc centre, rather than a charge separation between moieties. In octad monomers, the Pc singlet excited-state decays within tens of ps, whereas the excitons are stabilised in the aggregated form of the molecules, typically with lifetimes in the order of 1-10 ns. By contrast, in an octad design in which pi-pi interactions are suppressed by the steric hindrance of a corona of incompatible glycol tails around the molecule, a more straightforward photophysical interaction of Förster energy transfer between the PDI moieties and Pc core may be inferred. We consider these molecules as prototypical multichromophoric aggregates, giving delocalised states with considerable flexibility of design. -
2010
Stabilization of the nematic mesophase by a homogeneously dissolved conjugated polymer
Journal of Materials Chemistry,vol.20,p.8107,2010A semi-conjugated iptycene polymer contg. a special “crankshaft” backbone leading to superior soly. in a nematic LC medium was synthesized. The incorporation of this polymer in the LC leads to thermodn. stabilization of the nematic mesophase. This effect is attributed to organizational coupling of the LC mols. to the polymer chains. [on SciFinder(R)] -
2010
Photoluminescent energy transfer from poly(phenyleneethynylene)s to near-infrared emitting fluorophores
Journal of Polymer Science Part A: Polymer Chemistry,vol.48,p.3382–3391,2010Photoluminescent energy transfer was investigated in conjugated polymer-fluorophore blended thin films. A pentiptycene-contg. poly(phenyleneethynylene) was used as the energy donor, and 13 fluorophores were used as energy acceptors. The efficiency of energy transfer was measured by monitoring both the quenching of the polymer emission and the enhancement of the fluorophore emission. Near-IR emitting squaraines and terrylenes were identified as excellent energy acceptors. These results, where a new fluorescent signal occurs in the near-IR region on a completely dark background, offer substantial possibilities for designing highly sensitive turn-on sensors. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3382-3391, 2010. [on SciFinder(R)] -
2010
Addressable terminally linked DNA-CNT nanowires.
Journal of the American Chemical Society,vol.132,p.14009–11,2010Despite many advances in carbon nanotube (CNT) research, several issues continue to plague the field with regard to the construction of well-defined hybrid CNT materials. Regiospecific covalent functionalization, nonspecific surface absorption, and carbon nanotube aggregation/bundling present major difficulties when working with these materials. In this communication, we circumvent these problems and report a new addressable hybrid material composed of single-walled carbon nanotubes terminally linked by oligonucleotides into a nanowire motif. We show that the oligonucleotide junctions are addressable and can be targeted by gold nanoparticles. -
2010
Conjugated polymers that respond to oxidation with increased emission.
Journal of the American Chemical Society,vol.132,p.7758–68,2010Thioether-containing poly(para-phenylene-ethynylene) (PPE) copolymers show a strong fluorescence turn-on response when exposed to oxidants in solution as a result of the selective conversion of thioether substituents into sulfoxides and sulfones. We propose that the increase in fluorescence quantum yield (Phi(F)) upon oxidation is the result of both an increase in the rate of fluorescence (k(F)), as a result of greater spatial overlap of the frontier molecular orbitals in the oxidized materials, and an increase in the fluorescence lifetime (tau(F)), due to a decrease in the rate of nonradiative decay. Contrary to established literature, the reported sulfoxides do not always act as fluorescence quenchers. The oxidation is accompanied by spectral changes in the absorption and emission of the polymers, which are dramatic when oxidation causes the copolymer to acquire a donor-acceptor interaction. The oxidized polymers have high fluorescence quantum yields in the solid state, with some having increased photostability. A turn-on fluorescence response to hydrogen peroxide in organic solvents in the presence of an oxidation catalyst indicates the potential of thioether-containing materials for oxidant sensing. The reported polymers show promise as new materials in applications where photostability is important, where tunability of emission across the visible spectrum is desired, and where efficient emission is an advantage. -
2010
Probing substituent effects in aryl-aryl interactions using stereoselective Diels-Alder cycloadditions.
Journal of the American Chemical Society,vol.132,p.3304–11,2010Stereoselective Diels-Alder cycloadditions that probe substituent effects in aryl-aryl sandwich complexes were studied experimentally and theoretically. Computations on model systems demonstrate that the stereoselectivity in these reactions is mediated by differential pi-stacking interactions in competing transition states. This allows relative stacking free energies of substituted and unsubstituted sandwich complexes to be derived from measured product distributions. In contrast to gas-phase computations, dispersion effects do not appear to play a significant role in the substituent effects, in accord with previous experiments. The experimental pi-stacking free energies are shown to correlate well with Hammett sigma(m) constants (r = 0.96). These substituent constants primarily provide a measure of the inductive electron-donating and -withdrawing character of the substituents, not donation into or out of the benzene pi-system. The present experimental results are most readily explained using a recently proposed model of substituent effects in the benzene sandwich dimer in which the pi-system of the substituted benzene is relatively unimportant and substituent effects arise from direct through-space interactions. Specifically, these results are the first experiments to clearly show that OMe enhances these pi-stacking interactions, despite being a pi-electron donor. This is in conflict with popular models in which substituent effects in aryl-aryl interactions are modulated by polarization of the aryl pi-system. -
2010
Disassembly of Elastomers: Poly(olefin sulfone)−Silicones with Switchable Mechanical Properties
Macromolecules,vol.43,p.10422–10426,2010An elastomeric polymer composite that can be disassembled at will into its individual components when exposed to mild bases is presented. The composite is formed of a poly(olefin sulfone) and a silicone bound together using “click” chem. The mech. properties of the composites can be varied depending on their formulation. Its base-triggered decompn. is advantageous from the point of view of composite recycling and controlled release of chems. [on SciFinder(R)] -
2010We report the synthesis of annulated azepines, conjugated seven-membered ring systems with nitrogen, designed to undergo an electrochem. controlled bent-to-planar transformation driven by aromatization. A Pd-catalyzed double amination strategy enabled us to synthesize annulated azepines, which are thermally and electrochem. stable even in highly oxidized states. Several methods of chem. and electrochem. polymn. yielded azepine-based materials that were demonstrated to retain their redox properties in the solid state under ambient conditions. Because of their redox stability and cond., these polymers could find utility in actuating materials research. [on SciFinder(R)]
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2010
Synthesis of Stair-Stepped Polymers Containing Dibenz[ a , h ]anthracene Subunits
Macromolecules,vol.43,p.2789–2793,2010Polycyclic arom. monomers based on substituted dibenz[a,h]anthracene frameworks have been prepd. in high yields. From these, several fluorescent stair-stepped conjugated polymers contg. fused arom. subunits have been synthesized via Sonogashira polycondensations and Glaser-type oxidative couplings. The new polymers were characterized by NMR spectroscopy, gel-permeation chromatog. (GPC), UV-vis, and fluorescence spectroscopy. [on SciFinder(R)] -
2010
Regiospecific synthesis of Au-nanorod/SWCNT/Au-nanorod heterojunctions.
Nano letters,vol.10,p.2466–9,2010The synthesis of precisely defined nanoscale hybrid materials remains a challenge at the frontier of chemistry and material science. In particular, the assembly of diverse high-aspect ratio one-dimensional materials such as gold nanorods and carbon nanotubes into functional systems is of ever increasing interest due to their electronic and sensing applications. To meet these challenges, methods for interfacing gold nanorods with carbon materials such as single-walled carbon nanotubes (SWCNTs) in a regio-controlled manner are needed. Herein, we report a method for the regiospecific synthesis of terminally linked gold nanorod-SWCNTs based on a nanotube surface protection strategy. The key to our approach is a SWCNT surface protection procedure allowing for selective functionalization of the SWCNT termini. -
2010
Carbanionic route to electroactive carbon-centered anion and radical oligomers.
Organic letters,vol.12,p.4324–7,2010The synthesis of poly-1,3-bisdiphenylene-2-phenyl allyl (BDPA) radicals via a new anionic oligomerization strategy is reported. The material displays a reversible reduction from the orange-red radical to the blue carbanion in solution. -
2010
Rigid hydrophilic structures for improved properties of conjugated polymers and nitrotyrosine sensing in water.
Organic letters,vol.12,p.1292–5,2010The efficient synthesis of a hydrophilic monomer bearing a three-dimensional noncompliant array of hydroxyl groups is described that prevents water-driven excimer features of hydrophobic poly(p-phenylene ethynylene) backbones. Sensitivity of the polymer to 3-nitrotyrosine is also discussed. -
2010
Synthesis, reactivity, and electronic properties of 6,6-dicyanofulvenes.
Organic letters,vol.12,p.5302–5,2010A series of 6,6-dicyanofulvene derivatives are synthesized starting from masked, dimeric, or monomeric cyclopentadienones. The reactivities of 6,6-dicyanofulvenes relative to their parent cyclopentadienones are discussed. 6,6-Dicyanofulvenes are capable of undergoing two consecutive, reversible, one-electron reductions and are presented as potential n-type small molecules. -
2010The syntheses of two azaperylene 9,10-dicarboximides are presented. 1-Aza- and 1,6-diazaperylene 9,10-dicarboximides contg. a 2,6-diisopropylphenyl substituent at the N-imide position were synthesized in two steps starting from naphthalene and isoquinoline derivs. [on SciFinder(R)]
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2010
Synthesis of a water-soluble 1,3-bis(diphenylene)-2-phenylallyl radical.
The Journal of organic chemistry,vol.75,p.3533–6,2010The design and synthesis of a water-soluble 1,3-bis(diphenylene)-2-phenylallyl (BDPA) radical via the conjugate addition of a derivatized fluorene nucelophile is described. The compound is designed for use in dynamic nuclear polarization NMR. Its 9 GHz EPR spectrum in glycerol/water is reported. -
2010We report the design and synthesis of annulated thiepins designed to undergo bent-to-planar transformation driven by aromatization under electrochemical control. Thiepins are conjugated seven-membered ring systems with a thioether in the macrocycle. We synthesized thermally stable thiepins that are electropolymerizable to give rise to thiepin-containing electroactive polymers. Extended thiepin systems undergo sulfur extrusion with oxidation, and this feature has utility in peroxide sensing.
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2009
Cobalt Porphyrin Functionalized Carbon Nanotubes for Oxygen Reduction
Chemistry of Materials,vol.21,p.3234–3241,2009Carbon nanotube (CNT) compns. were prepd. by covalently grafting a Co(II) porphyrin to functionalized multiwalled carbon nanotubes (MWCNTs) via zwitterionic functionalization of the CNT sidewalls followed by a SN2 substitution reaction. The MWCNT-Co-porphyrin compns., mixed with Nafion, displayed excellent catalytic performance for oxygen redn. in acidic media (pH = 0.0-5.0) at room temp. With low catalyst loading, the oxygen redn. rates achieved are more than one order of magnitude higher than previously reported values for similar Co-porphyrin catalysts. These results demonstrate the advantages of systems of MWCNTs covalently linked to electrocatalytic mols. The electrodes are easily fabricated by a drop-casting vacuum drying procedure. Rotating disk electrode and rotating ring disk electrode measurements revealed the mechanism to be a direct four-proton and four-electron redn. of oxygen to water. These results demonstrate that new MWCNT electrocatalytic systems are potential substitutes for platinum or other metal-based cathode materials in proton conducting membrane fuel cells. [on SciFinder(R)]
