Fluorescence Detection of a Broad Class of Explosives with One Zinc(II)-Coordination Nanofiber

In this work, we report the development of one fluorescent carbazole-based oligomer <b>1</b>-zinc­(II) coordination nanofiber which enabled the detection of five classes of explosives, i.e., nitroaromatics (dinitrotoluene, DNT, and trinitrotoluene, TNT), aliphatic nitro-organics (2,3-dimethyl-2,3-dinitrobutane, DMNB), nitramines (cyclotrimethylenetrinitramine, RDX), nitro-esters (pentaerythritol tetranitrate, PETN), and black powder (sulfur). We demonstrate that the coordination of zinc ion with a carbazole-based oligomer <b>1</b> allows the formation of the Lewis acid–base complex between explosives and the nanofiber that enhances the electron-accepting ability of the nitro-based explosives and the binding interactions between the sensing nanofibers and explosives. Furthermore, the resulting nanofiber-based sensor exhibited highly sensitive fluorescence quenching when exposed to trace sulfur, thereby enabling the sensitive detection of black powder. Herein, we present a new fluorescent sensor for five classes of explosives, which represents an important advance toward a richer identification of threats

Corannulene-Based Coordination Cage with Helical Bias

We report here the first corannulene-based molecular cage, constructed via metal-induced self-assembly of corannulene-based ligands. In sharp contrast to those assembled via the planar π-conjugated analogues of corannulene, at ambient and elevated temperatures, the molecular cage exists as an ensemble of four stereoisomers (two pairs of enantiomers), all of which possess a <i>D</i>₅-symmetric (regardless of the counteranions) and inherently helical structure. Decreasing the temperature shifts the equilibrium between different pairs of enantiomers. At low temperature, only one pair of enantiomers is present. Helical bias for the cage could be efficiently achieved by inducing asymmetry with enantiopure anions. When nonenantiopure anions are used, the asymmetry induction abides by the “majority rule”, i.e., the major enantiomer of the chiral anions controls the bias of helical sense of the cages

Discrimination of Five Classes of Explosives by a Fluorescence Array Sensor Composed of Two Tricarbazole-Nanostructures

In this work, we report a two-member fluorescence array sensor for the effective discrimination of five classes of explosives. This smallest array sensor is composed of tricarbazole-based nanofibers (sensor member <b>1</b>) and nanoribbons (sensor member <b>2</b>) deposited as two film bands in a quartz tube. On the basis of a simple comparison of the resulting fluorescence quenching ratios between two sensor members and the response reversibility upon exposure to vaporized explosives, five classes of explosives can be sensitively detected and easily discriminated. This array sensor that has only two sensor members and no complex data analysis represents a new design way for discrimination of a broad class of explosives

Preorganized Aryltriazole Foldamers as Effective Transmembrane Transporters for Chloride Anion

Preorganized aryltriazole foldamers <b>1</b> and <b>2</b> were designed and synthesized. NMR studies and X-ray analysis demonstrate that <b>1</b> adopts a crescent conformation driven by a series of continuous hydrogen bonds at the periphery of the foldamer, whereas <b>2</b> displays a coil conformation. NMR titrations reveal that the affinities of fully preorganized foldamer <b>1</b> for halogen anions are much stronger that those of partially preorganized foldamer <b>2</b>. Furthermore, it is found that such full preorganization makes <b>1</b> an effective transmembrane transporter for the chloride anion across a lipid bilayer

Interpenetrated Binary Supramolecular Nanofibers for Sensitive Fluorescence Detection of Six Classes of Explosives

In this work, we develop a sequential self-assembly approach to fabricate interpenetrated binary supramolecular nanofibers consisting of carbazole oligomer <b>1</b>–cobalt­(II) (<b>1</b>-Co²⁺) coordination nanofibers and oligomer <b>2</b> nanofibers for the sensitive detection of six classes of explosives. When exposed to peroxide explosives (e.g., H₂O₂), Co²⁺ in <b>1</b>-Co²⁺ coordination nanofibers can be reduced to Co⁺ that can transfer an electron to the excited <b>2</b> nanofibers and thereby quench their fluorescence. On the other hand, when exposed to the other five classes of explosives, the excited <b>2</b> nanofibers can transfer an electron to explosives to quench their fluorescence. On the basis of the distinct fluorescence quenching mechanisms, six classes of explosives can be sensitively detected. Herein, we provide a new strategy to design broad-band fluorescence sensors for a rich identification of threats

Temperature-Controlled, Reversible, Nanofiber Assembly from an Amphiphilic Macrocycle

One-dimensional nanostructures are self-assembled from an amphiphilic arylene-ethynylene macrocycle (AEM) in solution phase. The morphology and size of the nanostructures are controlled by simply changing the temperature, reversibly switching between monomolecular cross-sectioned nanofibers and large bundles. At elevated temperature in aqueous solutions, the tri­(ethylene glycol) (Tg) side chains of the AEM become effectively more hydrophobic, thus facilitating intermolecular association through side chain interactions. The enhanced intermolecular association causes the ultrathin nanofibers to be bundled, forming an opaque dispersion in solution. The reported observation provides a simple molecular design rule that may be applicable to other macrocycle molecules for use in temperature-controlled assembly regarding both size and morphology

Visible-Light-Responsive TiO₂‑Coated ZnO:I Nanorod Array Films with Enhanced Photoelectrochemical and Photocatalytic Performance

Control of structural and compositional characteristics during fabrication of a versatile visible-light active ZnO-based photocatalyst is a crucial step toward improving photocatalytic pollutant degradation processes. In this work, we report a multifunctional photocatalytic electrode, i.e., TiO₂ coated ZnO:I nanorods (ZnO:I/TiO₂ NRs) array films, fabricated via a hydrothermal method and a subsequent wet-chemical process. This type of hybrid photocatalytic film not only enhances light absorption with the incorporation of iodine but also possesses increased electron transport capability and excellent chemical stability arising from the unique TiO₂-coated 1D structure. Owing to these synergic advantages, the degradation efficiency of the ZnO:I samples reached ∼97% after irradiation for 6 h, an efficiency 62% higher than that of pure ZnO. For RhB photocatalytic degradation experiments in both acidic (pH = 3) and alkaline (pH = 11) solutions, as well as in repeat photodegradation experiments, the ZnO:I/TiO₂ NRs films demonstrated high stability and durability under visible-light irradiation. Thus, ZnO:I/TiO₂ NRs are considered a promising photocatalytic material to degrade organic pollutants in aqueous eco-environments

Internanofiber Spacing Adjustment in the Bundled Nanofibers for Sensitive Fluorescence Detection of Volatile Organic Compounds

In this work, we report the fabrication of hierarchical nanofiber bundles from a perylene monoimide molecule that enable the sensitive detection of various inert volatile organic compounds (VOCs). We demonstrate that the internanofiber spacing of the bundles with appropriate packing interactions can be effectively adjusted by various VOCs, which is in turn translated into the dynamic fluorescence responses. Upon further decreasing the size of the nanofiber bundles, of which the internanofiber spacing is more favorably adjusted, enhanced fluorescence responses to various VOC vapors can be achieved. Our work presents a new protocol, i.e., translating the stimuli-responsive internanofiber spacing into fluorescence responses, to construct novel fluorescence sensors for various hazardous chemical vapors

2,6-Pyridodicarboxamide-Bridged Triptycene Molecular Transmission Devices: Converting Rotation to Rocking Vibration

A series of <i>N</i>²,<i>N</i>⁶-bis­(triptycene-9-yl)­pyridine-2,6-dicarboxamides <b>1</b>–<b>4</b> were designed and synthesized. Due to rotational constraint of the 2,6-diamidopyridine bridge, the triptycene components in the systems are held together. X-ray structures of <b>1</b>–<b>4</b> show that the molecules adopt a gear-like geometry in the solid states. DFT (B3LYP/6-31G­(d)) calculations predict the gear-like <i>C</i>₂ conformation as global minimum structures for <b>1</b> and <b>2</b> and suggest that, through a slippage transition process, rotation of one triptycene component would give rise to a rocking vibration of the counter component due to the barrier for rotation of the triptycene components. VT NMR studies on <b>1</b>–<b>4</b> show that the pair of triptycene components undergo ceaseless slippage at room temperature but nearly freeze at temperatures as low as 183 K. Decreasing the temperature freezes the slippage between triptycene components as well, thus producing the appearance of phase isomers of <b>3</b> and <b>4</b>. The dynamic features of the studied molecules indicate that this kind of molecule is able to function as a kind of molecular transmission device for transforming the mode of motion from rotation to rocking vibration

Aromatic Triazole Foldamers Induced by C–H···X (X = F, Cl) Intramolecular Hydrogen Bonding

Aryl-triazole oligomers based on isobutyl 4-fluorobenzoate and isobutyl 4-chlorobenzoate were designed and synthesized. Crystal structure and ¹H–¹H NOESY experiments demonstrate that the oligomers adopt stable helical conformation, which are induced by C⁵–H···X–C (X = F, Cl) intramolecular hydrogen bonding between triazole protons and halogen atoms. The stabilities of the folded conformations are confirmed by DFT calculations, which show that each C⁵–H···F–C planar interaction lowers the energy by ∼3 kcal mol^–1 on average, and by ∼1 kcal mol^–1 when C⁵–H···Cl–C bridges are formed. The hydrogen-bonding networks are disrupted in competitive hydrogen-bonding media such as DMSO, generating the unfolded oligomers