Invited for the cover of this issue are the groups of Enrico Dalcanale at the University of Parma and Timothy M. Swager at Massachusetts Institute of Technology alongside collaborators at the University of Trieste. The image depicts the capture of aromatic hydrocarbons molecules by the ditrypticene quinoxaline cavitand that was employed as fiber coating for solid-phase microextraction monitoring in air. Read the full text of the article at 10.1002/chem.201504229.

Two novel triptycene quinoxaline cavitands (DiTriptyQxCav and MonoTriptyQxCav) have been designed, synthesized, and applied in the supramolecular detection of benzene, toluene, ethylbenzene, and xylenes (BTEX) in air. The complexation properties of the two cavitands towards aromatics in the solid state are strengthened by the presence of the triptycene moieties at the upper rim of the tetraquinoxaline walls, promoting the confinement of the aromatic hydrocarbons within the cavity. The two cavitands were used as fiber coatings for solid-phase microextraction (SPME) BTEX monitoring in air. The best performances in terms of enrichment factors, selectivity, and LOD (limit of detection) values were obtained by using the DiTriptyQxCav coating. The corresponding SPME fiber was successfully tested under real urban monitoring conditions, outperforming the commercial divinylbenzene–Carboxen–polydimethylsiloxane (DVB–CAR–PDMS) fiber in BTEX adsorption.

Human exposure to hazardous chemicals can have adverse short- and long-term health effects. In this Communication, we have developed a single-use wearable hazard badge that dosimetrically detects diethylchlorophosphate (DCP), a model organophosphorous cholinesterase inhibitor simulant. Improved chemically actuated resonant devices (CARDs) are fabricated in a single step and unambiguously relate changes in chemiresistance to a wireless readout. To provide selective and readily manufacturable sensor elements for this platform, we developed an ionic-liquid-mediated single walled carbon nanotube based chemidosimetric scheme with DCP limits of detection of 28 ppb. As a practical demonstration, an 8 h workday time weighted average equivalent exposure of 10 ppb DCP effects an irreversible change in smartphone readout.

Human exposure to hazardous chemicals can have adverse short- and long-term health effects. In this Communication, we have developed a single-use wearable hazard badge that dosimetrically detects diethylchlorophosphate (DCP), a model organophosphorous cholinesterase inhibitor simulant. Improved chemically actuated resonant devices (CARDs) are fabricated in a single step and unambiguously relate changes in chemiresistance to a wireless readout. To provide selective and readily manufacturable sensor elements for this platform, we developed an ionic-liquid-mediated single walled carbon nanotube based chemidosimetric scheme with DCP limits of detection of 28 ppb. As a practical demonstration, an 8 h workday time weighted average equivalent exposure of 10 ppb DCP effects an irreversible change in smartphone readout.

Sensoren auf Basis von chemischen Widerständen gewinnen derzeit stark an Bedeutung. Im Vergleich zu herkömmlichen Analysegeräten sind sie preisgünstig, lassen sich leicht in elektronische Bauteile integrieren und benötigen weniger Strom. Nanodrähte (NWs) spielen für die Entwicklung von Chemosensoren eine zentrale Rolle. Mit ihrer großen Oberfläche, den Übergängen zwischen den Nanodrähten und den definierten Leitungswegen gewährleisten sie eine hervorragende Sensoransprache und verfügen über neuartige Mechanismen, wie ein Bindungsereignis oder eine andere Aktion des Analyten in ein Signal weitergeleitet wird. Dieser Aufsatz erläutert den aktuellen Entwicklungsstand der NW-Chemosensoren. Wir beginnen mit dem Prinzip der Signalübertragung in NW-Sensoren. Anschließend erhält der Leser einen Überblick über die Leistungsparameter der Bauelemente. Dann gehen wir auf die verschiedenen NW-Typen und die Architektur der NW-Bauelemente ein und erläutern die unterschiedlichen Strategien zur NW-Funktionalisierung. Zum Abschluss entwerfen wir einen Fahrplan für die weitere Entwicklung, der Selektivität, Drift und Empfindlichkeit, die Analyse der Messantwort sowie neue Anwendungen berücksichtigt.

A chemosensory system is reported that operates without the need for separation techniques and is capable of identifying anions and structurally similar bioactive molecules. In this strategy, the coordination of analytes to a metal complex with an open binding cleft generates “static structures” on the NMR timescale. Unique signals are created by strategically placing fluorine atoms in close proximity to bound analytes so that small structural differences induce distinct ¹⁹F NMR shifts that can be used to identify each analyte. The utility of this method is illustrated by quantifying caffeine levels in coffee, by identifying ingredients in tea and energy drinks, and by discriminating between multiple biogenic amines with remote structural differences six carbon atoms away from the binding site. We further demonstrate the simultaneous identification of multiple neutral and anionic species in a complex mixture.

Chemiresistive sensors are becoming increasingly important as they offer an inexpensive option to conventional analytical instrumentation, they can be readily integrated into electronic devices, and they have low power requirements. Nanowires (NWs) are a major theme in chemosensor development. High surface area, interwire junctions, and restricted conduction pathways give intrinsically high sensitivity and new mechanisms to transduce the binding or action of analytes. This Review details the status of NW chemosensors with selected examples from the literature. We begin by proposing a principle for understanding electrical transport and transduction mechanisms in NW sensors. Next, we offer the reader a review of device performance parameters. Then, we consider the different NW types followed by a summary of NW assembly and different device platform architectures. Subsequently, we discuss NW functionalization strategies. Finally, we propose future developments in NW sensing to address selectivity, sensor drift, sensitivity, response analysis, and emerging applications.

A chemosensory system is reported that operates without the need for separation techniques and is capable of identifying anions and structurally similar bioactive molecules. In this strategy, the coordination of analytes to a metal complex with an open binding cleft generates “static structures” on the NMR timescale. Unique signals are created by strategically placing fluorine atoms in close proximity to bound analytes so that small structural differences induce distinct ¹⁹F NMR shifts that can be used to identify each analyte. The utility of this method is illustrated by quantifying caffeine levels in coffee, by identifying ingredients in tea and energy drinks, and by discriminating between multiple biogenic amines with remote structural differences six carbon atoms away from the binding site. We further demonstrate the simultaneous identification of multiple neutral and anionic species in a complex mixture.

Efficient methods for the preparation of functionalized metallated cavitands are described. Functional groups can be either introduced by an imidation of metal-oxo complexes or by a late-stage elaboration of the imido ligands. By using diversified iminophosphorane (PPh₃=NR) reagents, π-conjugated pyrene, redox active ferrocene, and polymerizable norbornene moieties were successfully introduced. Furthermore, the iodo and alkynyl groups on the imido ligands are capable of undergoing efficient Sonogashira cross-coupling and copper-catalyzed azide alkyne cycloaddition reactions, thereby providing facile access to complex architectures containing metallated cavitands.

Chemiresistive detectors for amine vapors were made from single-walled carbon nanotubes by noncovalent modification with cobalt meso-arylporphyrin complexes. We show that through changes in the oxidation state of the metal, the electron-withdrawing character of the porphyrinato ligand, and the counteranion, the magnitude of the chemiresistive response to ammonia could be improved. The devices exhibited sub-ppm sensitivity and high selectivity toward amines as well as good stability to air, moisture, and time. The application of these chemiresistors in the detection of various biogenic amines (i.e. putrescine, cadaverine) and in the monitoring of spoilage in raw meat and fish samples (chicken, pork, salmon, cod) over several days was also demonstrated.

Chemiresistive detectors for amine vapors were made from single-walled carbon nanotubes by noncovalent modification with cobalt meso-arylporphyrin complexes. We show that through changes in the oxidation state of the metal, the electron-withdrawing character of the porphyrinato ligand, and the counteranion, the magnitude of the chemiresistive response to ammonia could be improved. The devices exhibited sub-ppm sensitivity and high selectivity toward amines as well as good stability to air, moisture, and time. The application of these chemiresistors in the detection of various biogenic amines (i.e. putrescine, cadaverine) and in the monitoring of spoilage in raw meat and fish samples (chicken, pork, salmon, cod) over several days was also demonstrated.

A series of conjugated cationic polymers, differentiated only by their accompanying counter-anions, was prepared and characterized. The choice of counter-anion (CA) was found to drastically impact the solubility of the polymers and their optical properties in solution and in the solid state. Fluorescent polymer thin films were found to be instantaneously quenched by volatile amines in the gas phase at low ppm concentrations, and a mini-array with CAs as variable elements was found to be able to differentiate amines with good fidelity.

The development of new conjugated organic materials for dyes, sensors, imaging, and flexible light emitting diodes, field-effect transistors, and photovoltaics has largely relied upon assembling π-conjugated molecules and polymers from a limited number of building blocks. The use of the dithiolodithiole heterocycle as a conjugated building block for organic materials is described. The resulting materials exhibit complimentary properties to widely used thiophene analogues, such as stronger donor characteristics, high crystallinity, and a decreased HOMO–LUMO gap. The dithiolodithiole (C₄S₄) motif is readily synthetically accessible using catalytic processes, and both the molecular and bulk properties of materials based on this building block can be tuned by judicious choice of substituents.

A series of conjugated cationic polymers, differentiated only by their accompanying counter-anions, was prepared and characterized. The choice of counter-anion (CA) was found to drastically impact the solubility of the polymers and their optical properties in solution and in the solid state. Fluorescent polymer thin films were found to be instantaneously quenched by volatile amines in the gas phase at low ppm concentrations, and a mini-array with CAs as variable elements was found to be able to differentiate amines with good fidelity.

The development of new conjugated organic materials for dyes, sensors, imaging, and flexible light emitting diodes, field-effect transistors, and photovoltaics has largely relied upon assembling π-conjugated molecules and polymers from a limited number of building blocks. The use of the dithiolodithiole heterocycle as a conjugated building block for organic materials is described. The resulting materials exhibit complimentary properties to widely used thiophene analogues, such as stronger donor characteristics, high crystallinity, and a decreased HOMO–LUMO gap. The dithiolodithiole (C₄S₄) motif is readily synthetically accessible using catalytic processes, and both the molecular and bulk properties of materials based on this building block can be tuned by judicious choice of substituents.

Chemiresistive sensor arrays for cyclohexanone and nitromethane are fabricated using single-walled carbon nanotubes (SWCNTs) that are covalently functionalized with urea, thiourea, and squaramide containing 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.

New tetraalkylcyclobutadiene–C₆₀ adducts are developed via Diels–Alder cycloaddition of C₆₀ with in situ generated cyclobutadienes. The cofacial π-orbital interactions between the fullerene orbitals and the cyclobutene are shown to decrease the electron affinity and thereby increase the lowest unoccupied molecular orbital (LUMO) energy level of C₆₀ significantly (ca. 100 and 300 meV for mono- and bisadducts, respectively). These variations in LUMO levels of fullerene can be used to generate higher open-circuit voltages (V_OC) in bulk heterojunction polymer solar cells. The tetramethylcyclobutadiene–C₆₀ monoadduct displays an open-circuit voltage (0.61 V) and a power conversion efficiency (2.49%) comparable to the widely used P3HT/PCBM (poly(3-hexylthiophene/([6,6]-phenyl-C61-butyric acid methyl ester) composite (0.58 V and 2.57%, respectively). The role of the cofacial π-orbital interactions between C₆₀ and the attached cyclobutene group was probed chemically by epoxidation of the cyclobutene moiety and theoretically through density functional theory calculations. The electrochemical, photophysical, and thermal properties of the newly synthesized fullerene derivatives support the proposed effect of functionalization on electron affinities and photovoltaic performance.

Current research in materials has devoted much attention to graphene, with a considerable amount of the chemical manipulation going through the oxidized state of the material, known as graphene oxide (GO). In this report, the hydroxyl functionalities in GO, the vast majority that must be allylic alcohols, are subjected to Johnson−Claisen rearrangement conditions. In these conditions, a [3, 3] sigmatropic rearrangement after reaction with triethyl 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 conductivity is observed. The ester groups are easily saponified to carboxylic acids in situ with basic conditions, to give water-soluble 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 Å, suggesting utility of this material in capacitors and in gas storage. Other functionalization schemes, which include the installation of terminal alkynes and dipolar cycloadditions, allow for the synthesis of a highly positively charged, water-soluble graphene. The highly negatively and positively charged graphenes (zeta potentials of −75 mV and +56 mV, respectively), are successfully used to build layer-by-layer (LBL) constructs.

Several new triptycene-containing polyetherolefins were synthesized via acyclic diene metathesis (ADMET) polymerization. The well-established mechanism, high selectivity and specificity, mild reaction conditions, and well-defined end-groups make the ADMET polymerization a good choice for studying systematic variations in polymer structure. Two types of triptycene-based monomer with varying connectivities were used in the synthesis of homopolymers, block copolymers, and random copolymers. In this way, the influence of the triptycene architecture and concentration in the polymer backbone on the thermal behavior of the polymers was studied. Inclusion of increasing amounts of triptycene were found to increase the glass transition temperature, from −44 °C in polyoctenamer to 59 °C in one of the hydrogenated triptycene homopolymers (H-PT2). Varying the amounts and orientations of triptycene was found to increase the stiffness (H-PT1), toughness (PT1₁-b-PO₁) and ductility (PT1₁-ran-PO₃) of the polymer at room temperature. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

The ability of conjugated polymers to function as electronic materials is dependent on the efficient transport of excitons along the polymer chain. Generally, the photophysics of the chromophore monomer dictate the excited state behavior of the corresponding conjugated polymers. Different molecular structures are examined to study the role of excited state lifetimes and molecular conformations on energy transfer. The incorporation of rigid, three-dimensional scaffolds, such as iptycenes and cyclophanes, can encourage an oblique packing of the chromophore units of a conjugated polymer, thus allowing the formation of electronically-coupled aggregates that retain high quantum yields of emission. Rigid iptycene scaffolds also act as excellent structural directors that encourage complete solvation of PPEs in a liquid crystal (LC) solvent. LC-PPE mixtures display both an enhanced conformational alignment of polymer chains and extended effective conjugation lengths relative to isotropic solutions, which leads to enhanced energy transfer. Facile exciton migration in poly(p-phenylene ethynylene)s (PPEs) allows energy absorbed over large areas to be funneled into traps created by the binding of analytes, resulting in signal amplification in sensory devices. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Photoluminescent energy transfer was investigated in conjugated polymer-fluorophore blended thin films. A pentiptycene-containing 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-infrared emitting squaraines and terrylenes were identified as excellent energy acceptors. These results, where a new fluorescent signal occurs in the near-infrared 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