Retail Clerks International Protective Association, Local 872 (1936)

Improved 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

Water-Soluble Cationic Conjugated Polymers: Response to Electron-Rich Bioanalytes

We 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

Covalent Functionalization of Carbon Nanomaterials with Iodonium Salts

Covalent functionalization significantly enhances the utility of carbon nanomaterials for many applications. Herein, we report an efficient method for the covalent functionalization of carbon nanotubes (CNTs) and graphite. This reaction involves the reduction of carbon nanomaterials with sodium naphthalide, followed by the addition of diaryliodonium salts. CNTs, including single-walled, double-walled, and multi-walled variants (SWCNTs, DWCNTs, and MWCNTs, respectively), as well as graphite, can be efficiently functionalized with substituted arene and heteroarene iodonium salts. The preferential transfer of phenyl groups containing electron-withdrawing groups was demonstrated by reactions with unsymmetrical iodonium salts. The lower reactivity of iodonium salts, relative to the more commonly used diazonium ions, presents opportunities for greater diversity in the selective functionalization of carbon nanomaterials

Simultaneous Chirality Sensing of Multiple Amines by ¹⁹F NMR

The rapid detection and differentiation of chiral compounds is important to synthetic, medicinal, and biological chemistry. Palladium complexes with chiral pincer ligands are demonstrated to have utility in determining the chirality of various amines. The binding of enantiomeric amines induces distinct ¹⁹F NMR shifts of the fluorine atoms appended on the ligand that defines a chiral environment around palladium. It is further demonstrated that this method has the ability to evaluate the enantiomeric composition and discriminate between enantiomers with chiral centers several carbons away from the binding site. The wide detection window provided by optimized chiral chemosensors allows the simultaneous identification of as many as 12 chiral amines. The extraordinary discriminating ability of this method is demonstrated by the resolution of chiral aliphatic amines that are difficult to separate using chiral chromatography

Highly Emissive Excimers by 2D Compression of Conjugated Polymers

Interactions between π-conjugated polymers are known to create ground-state aggregates, excimers, and exciplexes. With few exceptions, these species exhibit decreased fluorescence quantum yields relative to the isolated polymers in liquid or solid solutions. Herein, we report a method to assemble emissive conjugated polymer excimers and demonstrate their applicability in the detection of selected solvent vapors. Specifically, poly­(phenylene ethynylene)­s (PPEs) with amphiphilic side chains are organized in a Langmuir monolayer at the air–water interface. Compression of the monolayer results in the reversible conversion from a face-on organization of the π-system relative to the water to what appears to be an incline-stack conformation. The incline-stack organization creates a bright yellow emissive excimeric state with increases of 28% in relative fluorescence quantum yields to the face-on monolayer conformation. Multilayers can be transferred onto the glass substrate via a Langmuir–Blodgett method with preservation of the excimer emission. These films are metastable and the fluorescence reverts to a cyan color similar to the spectra obtained in solution and spin-cast films after exposure to selected solvent vapors. This behavior has practical utility as a fluorescence-based indicator for selected volatile organic compounds

Polymer Valence Isomerism: Poly(Dewar‑<i>o</i>‑xylylene)s

Poly­(<i>o</i>-xylylene) (POX) has long been a challenging synthetic target despite its simple structure and potentially useful physical properties. In this report, we demonstrate a valence isomer strategy that leads to the formation of high molecular weight POX via an intermediate polymer of a unique structure, namely poly­(Dewar-<i>o</i>-xylylene) (PDOX). We show that the free radical polymerization of highly strained Dewar-<i>o</i>-xylylene (DOX) monomer afforded PDOX, a material with a high density of Dewar benzene units in the backbone through ring-retaining propagation. The thermal- and photoinduced isomerizations of PDOX to produce POX were investigated. This chemistry yields POXs that are difficult to obtain using traditional methods. Moreover, it also provides a potential entry into new reconfigurable materials featuring highly efficient postpolymerization main chain structural transformations

Chain-Growth Polymerization of 2‑Chlorothiophenes Promoted by Lewis Acids

Lewis 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

Carbon Nanotube Formic Acid Sensors Using a Nickel Bis(<i>ortho</i>-diiminosemiquinonate) Selector

Formic acid is corrosive, and a sensitive and selective sensor could be useful in industrial, medical, and environmental settings. We present a chemiresistor for detection of formic acid composed of single-walled carbon nanotubes (CNTs) and nickel bis­(<i>ortho</i>-diiminosemiquinonate) (<b>1</b>), a planar metal complex that can act as a ditopic hydrogen-bonding selector. Formic acid is detected in concentrations as low as 83 ppb. The resistance of the material decreases on exposure to formic acid, but slightly increases on exposure to acetic acid. We propose that <b>1</b> assists in partial protonation of the CNT by formic acid, but the response toward acetic acid is dominated by inter-CNT swelling. This technology establishes CNT-based chemiresistive discrimination between formic and acetic acid vapors

Detection and Differentiation of Neutral Organic Compounds by ¹⁹F NMR with a Tungsten Calix[4]arene Imido Complex

Fluorinated 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 ¹⁹F NMR spectroscopy is a powerful new method for the analysis of complex mixtures

Detection and Differentiation of Neutral Organic Compounds by ¹⁹F NMR with a Tungsten Calix[4]arene Imido Complex

Fluorinated 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 ¹⁹F NMR spectroscopy is a powerful new method for the analysis of complex mixtures