1,721,198 research outputs found
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
Poly(para-arylene)s via [2+2+2]
No full textWe 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.National Science Foundation (U.S.) (Grant DMR-1005810
50th Anniversary Perspective: Conducting/Semiconducting Conjugated Polymers. A Personal Perspective on the Past and the Future
No full textIt has been about 40 years since the field of organic conducting polymers was ignited by the demonstration of metallic conductivity in polyacetylene. A retrospective view of this research area suggests some areas remain ripe for discovery/innovation. The breadth of activities is too large to be comprehensive; hence, selected seminal, as well as some personal, contributions will be used to illustrate concepts and anecdotal ways to think about conducting polymer systems. This Perspective can serve as a tutorial for newcomers to the field and will also remind experts about results from the past. It begins with some history and simple views of electronic structure, with selected examples. Segmented polymers containing isolated redox units will be discussed as well as how these materials can be made to have high conductivity. Key examples illustrating the matching of redox potentials are transition metal hybrid structures. Interchain interactions are emphasized along with their role in determining the nature of the charges. Recent results that demonstrate dramatic magneto-optical properties wherein the transmission of polarized light through conjugated polymers displays dramatic sensitivity to applied magnetic fields (Faraday effect) will also be discussed
Impedance for Endocrine Disruption Compounds
No full textAn unintended consequence of our chemical innovations is the introduction of trace chemicals into our environment that are not necessarily directly toxic, but can impact nature. Mutations in animals/people can happen naturally, but perhaps in many cases human chemical ingenuity is to blame. Our motivations as chemists are honorable, and we have generated pesticides that help us to grow more food, agents to extract hydrocarbons from the earth, and durable materials that can be washed and reused in drinking and baby bottles. Functionally detecting these chemicals in our environment at trace levels, in real time, and in a cost-effective manner has been a challenge. Professor Matthew Francis and co-workers Ariel Furst and Alexander Hoepker have devised a powerful new method to detect suspect compounds known as endocrine disrupting chemicals. In this issue they report a novel assay that can functionally detect suspect compounds that bind to the estrogen receptor α. This approach involves direct electrical detection, which has the benefit of being readily interfaced with a number of existing platforms. Specifically, this team developed electrochemical impedance methods for the detection of endocrine disrupting compounds by using a novel sandwich scheme. Engineered Escherichia coli is produced that expresses the estrogen receptor α on its surface, and this structure behaves as a very large blocking scaffold that can restrict diffusion of ions to an electrode
Thiophene-Fused Tropones as Chemical Warfare Agent-Responsive Building Blocks
No full textWe report the synthesis of dithienobenzotropone-based conjugated alternating copolymers by direct arylation polycondensation. Postpolymerization modification by hydride reduction yields cross-conjugated, reactive hydroxyl-containing copolymers that undergo phosphorylation and ionization upon exposure to the chemical warfare agent mimic diethylchlorophosphate (DCP). The resulting conjugated, cationic copolymer is highly colored and facilitates the spectroscopic and colorimetric detection of DCP in both solution and thin-film measurements.United States. Defense Threat Reduction Agency. Chemical and Biological Technologies Department (Grant BA12PHM123
Homoconjugated and Spiro Push–Pull Systems: Cycloadditions of Naphtho- and Anthradiquinones with Electron-Rich Alkynes
No full textWe report the synthesis and characterization of three new classes of push–pull chromophores using [2+2]-cycloaddition reactions of electron-rich alkynes and electron-poor alkenes. Previous investigations have focused on the reactions of cyano-substituted electron acceptors. This study demonstrates that cyano-free electron acceptors, naphtho- and anthradiquinones, can also be used to access extended push–pull systems. The effects of the structural changes on the spectroscopic and electronic properties were investigated by UV/vis spectroscopy. Structures were confirmed by X-ray and NMR analysis in solution. Keywords: homoconjugation - cycloaddition - push–pull - quinones - spirocyclesSwiss National Science Foundation (Early Postdoc Mobility Fellowship)United States. Air Force. Office of Scientific Research (FA9550-14-1-0226
An Organocobalt–Carbon Nanotube Chemiresistive Carbon Monoxide Detector
Full text linkA chemiresistive detector for carbon monoxide was created from single-walled carbon nanotubes (SWCNTs) by noncovalent modification with diiodo(η⁵:η¹-1-[2-(N,N-dimethylamino)ethyl]-2,3,4,5-tetramethylcyclopentadienyl)-cobalt(III) ([Cp[superscript ∧]CoI₂]), an organocobalt complex with an intramolecular amino ligand coordinated to the metal center that is displaced upon CO binding. The unbound amino group can subsequently be transduced chemiresistively by the SWCNT network. The resulting device was shown to have a ppm-level limit of detection and unprecedented selectivity for CO gas among CNT-based chemiresistors. This work, the first molecular-level mechanistic elucidation for a CNT-based chemiresistive detector for CO, demonstrates the efficacy of using an analyte’s reactivity to produce another chemical moiety that is readily transduced as a strategy for the rational design of chemiresistive CNT-based detectors.National Science Foundation (U.S.) (DMR-1410718)National Science Foundation (U.S.) (1122374
19F NMR Fingerprints: Identification of Neutral Organic Compounds in a Molecular Container
Full text linkImproved methods for quickly identifying neutral organic compounds and differentiation of analytes with similar chemical structures are widely needed. We report a new approach to effectively “fingerprint” neutral organic molecules by using 19F NMR and molecular containers. The encapsulation of analytes induces characteristic up- or downfield shifts of 19F resonances that can be used as multidimensional parameters to fingerprint each analyte. The strategy can be achieved either with an array of fluorinated receptors or by incorporating multiple nonequivalent fluorine atoms in a single receptor. Spatial proximity of the analyte to the 19F is important to induce the most pronounced NMR shifts and is crucial in the differentiation of analytes with similar structures. This new scheme allows for the precise and simultaneous identification of multiple analytes in a complex mixture.National Institute of General Medical Sciences (U.S.) (Grant GM095843)German Academic Exchange Service (Postdoctoral Fellowship)Shanghai Institute of Organic Chemistry (Postdoctoral Fellowship)Zhejiang Medicine Co., Ltd. (Postdoctoral Fellowship)Pharmaron (Postdoctoral Fellowship
Columnar Liquid Crystallinity and Mechanochromism in Cationic Platinum(II) Complexes
No full textCationic 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.National Science Foundation (U.S.) (Award DMR-1005810)American Society for Engineering Education (Award 2291100
Synthesis of Miktoarm Branched Conjugated Copolymers by ROMPing In and Out
No full textArchitecture represents an underutilized yet promising 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 polymerization. In this
work, we graft to and from telechelic poly(3-hexylthiophene), which is end-capped by oxime click chemistry, using various norbornene monomers. The self-assembly of the resulting miktoarm Hshaped conjugated polymers is studied in solution and in the solid state. A dual stimuli-responsive miktoarm polymer is prepared which displays pH-switchable lower critical solution temperature and fluorescence.United States. Army Research Office. Institute for Soldier Nanotechnologies (Contract W911NF-13-D-0001)United States. Air Force Office of Scientific Research (Grant (FA9550-14-1-0226)National Institutes of Health (U.S.). Ruth L. Kirschstein National Research Service Award (Fellowships Award GM106550
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