1,721,232 research outputs found
Conjugated Amplifying Polymers for Optical Sensing Applications
No full textThanks to their unique optical and electrochemical properties, conjugated polymers have attracted considerable attention over the last two decades and resulted in numerous technological innovations. In particular, their implementation in sensing schemes and devices was widely investigated and produced a multitude of sensory systems and transduction mechanisms. Conjugated polymers possess numerous attractive features that make them particularly suitable for a broad variety of sensing tasks. They display sensory signal amplification (compared to their small-molecule counterparts) and their structures can easily be tailored to adjust solubility, absorption/emission wavelengths, energy offsets for excited state electron transfer, and/or for use in solution or in the solid state. This versatility has made conjugated polymers a fluorescence sensory platform of choice in the recent years. In this review, we highlight a variety of conjugated polymer-based sensory mechanisms together with selected examples from the recent literature.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologie
Water-Soluble Cationic Conjugated Polymers: Response to Electron-Rich Bioanalytes
No full textWe report the concise synthesis of a symmetrical monomer that provides a head-to-head pyridine building block for the preparation of cationic conjugated polymers. The obtained poly(pyridinium-phenylene) polymers display appealing properties such as high electron affinity, charge-transport upon n-doping, and optical response to electron-donating analytes. A simple assay for the optical detection of low micromolar amounts of a variety of analytes in aqueous solution was developed. In particular, caffeine could be measured at a 25 μM detection limit. The reported polymers are also suitable for layer-by-layer film formation.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologie
Detection of Ethylene Gas by Fluorescence Turn-On of a Conjugated Polymer
Full text linkRipe fruits: The fluorescence of a conjugated polymer is quenched by the presence of copper(I) moieties. Upon exposure to ethylene gas the copper complexes bind to ethylene and no longer quench the polymer fluorescence (see picture). This sensory concept can be used in solution and in thin films.German Academy of Sciences Leopoldina (Fellowship LPDS 2009-8)National Science Foundation (U.S.
Synthesis and Optical Properties of Phenylene-Containing Oligoacenes
No full textSynthesis 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.National Science Foundation (U.S.) (DMR-1005810)National Science Foundation (U.S.) (CHE-0946721)United States. Dept. of Energy. Center for Excitonics (Award DE-SC0001088
Chain-Growth Polymerization of 2-Chlorothiophenes Promoted by Lewis Acids
No full textLewis 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.United States. Air Force Office of Scientific Research (FA9550-10-1-0395
STM Study of Gold(I) Pyrazolates: Distinct Morphologies, Layer Evolution, and Cooperative Dynamics
No full textWe describe the first study of trinuclear gold(I) pyrazolates on the molecular level by time-dependent scanning tunneling microscopy (STM). On the graphite/1-octanoic acid interface dodecyl-functionalized gold pyrazolates formed concentration-controlled morphologies. We found two types of monomeric packing and one dimeric type with two trinuclear gold pyrazolates next to each other on the surface. For an octadecyl-functionalized derivative all studied concentrations resulted in a dimeric morphology. However, different concentrations led to different transient states during the layer evolution. At low concentrations, a transient monomeric state was present with the alkyl chains in a gauche-conformation that subsequently converted to a more optimized anti-conformation. At higher concentrations a less stable “line” polymorph was observed. The confinement of the molecules to the surface led to cooperative dynamics, in which two molecules in a dimer moved as if they were one particle. Furthermore, in a higher level of cooperativity, the rotation of one dimer appears to induce rotations in coupled neighboring dimers.National Science Foundation (U.S.) (DMR-1055810)United States. Air Force Office of Scientific Research (FA9550-10-1-0395)Massachusetts Institute of Technology. Energy Frontier Research Center for Excitonics (DF-SC0001088
Redox Switchable Thianthrene Cavitands
Full text linkA redox activated vase-to-kite conformational change is reported for a new resorcinarene-based cavitand appended with four quinoxaline-fused thianthrene units. In its neutral state, the thianthrene-containing cavitand was shown by 1H NMR to adopt a closed vase conformation. Upon oxidation the electrostatic repulsion among the thianthrene radical cations promotes a kite conformation in the thianthrene-containing cavitand. The addition of acid produced a shoulder feature below 300 nm in the cavitand’s UV-Vis spectrum that we have assigned to the vase-to-kite conformation change. UV-Vis spectroelectrochemical studies of the cavitand revealed a development of a similar shoulder peak consistent with the oxidation-induced vase-to-kite conformation change. To support that the shoulder peak is diagnostic for a vase-to-kite conformation change, a model molecule constituting a single quinoxaline wall of the cavitand was synthesized and studied. As expected UV-Vis spectroelectrochemical studies of the cavitand arm did not display a shoulder peak below 300 nm. The oxidation-induced vase-to-kite conformation is further confirmed by the distinctive upfield shift in 1H chemical shift of the methine signal. Key words: redox active, thianthrene, resorcinarene cavitands, electrochemical switching, conformation changeNational Science Foundation (U.S.). Center for Energy Efficient Electronics Science (Award ECCS0939514)Singapore. Agency for Science, Technology and Research (Graduate Scholarship
Bispyridinium-phenylene-based copolymers: low band gap n-type alternating copolymers
No full textBispyridinium-phenylene-based conjugated donor–acceptor copolymers were synthesized by a Stille cross-coupling and cyclization sequence. These polyelectrolytes are freely soluble in organic solvents and display broad optical absorption bands that extend into the near-infrared region. They show ambipolar redox properties with high electron affinities (LUMO levels) of 3.9–4.0 eV as well as high degrees of electroactivity. When reduced (n-doped) these materials display in situ conductivities as high as 180 S/cm. The high conductivity is attributed to the planar structure that is enforced by the cyclic structures of the polymer. The electron affinities are compared to PCBM, a C[subscript 60] based n-type material and hence may find utility in photovoltaic devices.National Science Foundation (U.S.) (DMR-0706408
Poly(3-hexylthiophene)-block-poly(pyridinium phenylene)s: Block Polymers of p- and n-Type Semiconductors
No full textConjugated crystalline−crystalline donor−acceptor−donor block copolymer semiconductors, with regioregular poly(3-hexylthiophene) as a donor (p-type) block and poly(pyridinium pheneylene) as an acceptor (n-type) block within the backbone, were produced by sequential Grignard metathesis synthesis of poly(3-hexylthiophene), a Yamamoto-type cross-coupling polymerization−cyclization sequence. These conjugated block copolymers are soluble in organic solvents and display broad optical absorption bands extending close to the near-infrared region. They show reversible ambipolar redox properties with high electron affinities of 3.8−4.0 eV as well as useful ionization potentials of 5.1 eV that are characteristic of the respective blocks. Block copolymers from p- and n-type organic semiconductors are of interest for the formation of nanostructured bulk heterojunctions in photovoltaic devices.National Science Foundation (DMR-1005810)Toray Industries Inc
Selective Detection of Ethylene Gas Using Carbon Nanotube-based Devices: Utility in Determination of Fruit Ripeness
No full textComparing apples and oranges: A chemoresistive sensor for ethylene can be obtained simply by mixing copper complex 1 with single-walled carbon nanotubes. The resulting devices show sub-ppm sensitivity and high selectivity towards ethylene. The utility of the sensor was demonstrated by following ripening stages in different fruits.United States. Air Force Office of Scientific Research (Contract W911NF-07-D-0004)German Academy of Sciences Leopoldina (Fellowship LPDS 2009-8
- …
