Hexathiophenalenylium Cations: Syntheses, Structures, and Redox Chemistry

Preparations of two hexathiophenalenylium compounds as stable salts from the reaction of 3,4,6,7-tetrathio-9-hydroxyphenalenone with Lawesson’s reagent have been reported. The presence of three disulfide linkages on the periphery of the core phenalenyl unit is confirmed by X-ray crystallographic characterizations. Electrochemical cell potentials are lower than those of related dithio- and tetrathio-bridged phenalenyl radicals, and the hexathiophenalenyl radical shows a strong electron paramagnetic resonance (EPR) signal in the solid state

Hexathiophenalenylium Cations: Syntheses, Structures, and Redox Chemistry

Preparations of two hexathiophenalenylium compounds as stable salts from the reaction of 3,4,6,7-tetrathio-9-hydroxyphenalenone with Lawesson’s reagent have been reported. The presence of three disulfide linkages on the periphery of the core phenalenyl unit is confirmed by X-ray crystallographic characterizations. Electrochemical cell potentials are lower than those of related dithio- and tetrathio-bridged phenalenyl radicals, and the hexathiophenalenyl radical shows a strong electron paramagnetic resonance (EPR) signal in the solid state

Single-Walled Carbon Nanotube–Poly(porphyrin) Hybrid for Volatile Organic Compounds Detection

Porphyrins due to their unique and interesting physicochemical properties have been widely investigated as functional materials for chemical sensor fabrication. However, their poor conductivity is a major limitation toward the realization of porphyrin-based field-effect transistor/chemiresistor sensor. The issue of conductivity can be overcome by exploiting the excellent electrical property of single-walled carbon nanotubes (SWNTs) to make a SWNTs-based hybrid device in which SWNTs would act as a transducer and porphyrin as a sensory layer. The present attempt was to fabricate a SWNTs–poly­(tetraphenylporphyrin) hybrid through electrochemical route and to evaluate its potential as a low-power chemiresistor sensor for sensing acetone vapor as a model for volatile organic compounds. Functionalization of SWNTs with porphyrin polymer by the electrochemical method resulted in a fuller coverage of SWNTs surface compared to a partial coverage by adsorption and thereby higher sensitivity. SWNTs were coated with poly­(tetraphenylporphyrin) of different thickness by applying different charge density to optimize sensing performance. Differences in sensing performance were noticed for hybrids fabricated at varying charge densities, and the optimum sensing response was found at 19.65 mC/cm². The hybrid exhibited a wide dynamic range for acetone vapor sensing from 50 to ∼230 000 ppm with a limit of detection of 9 ppm. The field-effect transistor studies showed a negative threshold voltage shift and almost constant transconductance when exposed to air/analyte, indicating electrostatic gating dominated sensing mechanism. Further, the results confirmed a good stability of the device over a period of 180 days. The long-term device stability along with the sensing capability at low analyte concentration with a wide dynamic range and easily scalable fabrication technique signify the potential of SWNT–poly­(porphyrin) hybrid for volatile organic compound sensing applications

Chemically Engineered Graphene-Based 2D Organic Molecular Magnet

Carbon-based magnetic materials and structures of mesoscopic dimensions may offer unique opportunities for future nanomagnetoelectronic/spintronic devices. To achieve their potential, carbon nanosystems must have controllable magnetic properties. We demonstrate that nitrophenyl functionalized graphene can act as a room-temperature 2D magnet. We report a comprehensive study of low-temperature magnetotransport, vibrating sample magnetometry (VSM), and superconducting quantum interference (SQUID) measurements before and after radical functionalization. Following nitrophenyl (NP) functionalization, epitaxially grown graphene systems can become organic molecular magnets with ferromagnetic and antiferromagnetic ordering that persists at temperatures above 400 K. The field-dependent, surface magnetoelectric properties were studied using scanning probe microscopy (SPM) techniques. The results indicate that the NP-functionalization orientation and degree of coverage directly affect the magnetic properties of the graphene surface. In addition, graphene-based organic magnetic nanostructures were found to demonstrate a pronounced magneto-optical Kerr effect (MOKE). The results were consistent across different characterization techniques and indicate room-temperature magnetic ordering along preferred graphene orientations in the NP-functionalized samples. Chemically isolated graphene nanoribbons (CINs) were observed along the preferred functionality directions. These results pave the way for future magnetoelectronic/spintronic applications based on promising concepts such as current-induced magnetization switching, magnetoelectricity, half-metallicity, and quantum tunneling of magnetization

Chemically Functionalized Water-Soluble Single-Walled Carbon Nanotubes Modulate Morpho-Functional Characteristics of Astrocytes

We report the use of chemically functionalized water-soluble single-walled carbon nanotubes (ws-SWCNTs) for the modulation of morpho-functional characteristics of astrocytes. When added to the culturing medium, ws-SWCNTs were able to make astrocytes larger and stellate/mature, changes associated with the increase in glial fibrillary acidic protein immunoreactivity. Thus, ws-SWCNTs could have more beneficial effects at the injury site than previously thought; by affecting astrocytes, they could provide for a more comprehensive re-establishment of the brain computational power

Networks of Semiconducting SWNTs: Contribution of Midgap Electronic States to the Electrical Transport

ConspectusSingle-walled carbon nanotube (SWNT) thin films provide a unique platform for the development of electronic and photonic devices because they combine the advantages of the outstanding physical properties of individual SWNTs with the capabilities of large area thin film manufacturing and patterning technologies. Flexible SWNT thin film based field-effect transistors, sensors, detectors, photovoltaic cells, and light emitting diodes have been already demonstrated, and SWNT thin film transparent, conductive coatings for large area displays and smart windows are under development. While chirally pure SWNTs are not yet commercially available, the marketing of semiconducting (SC) and metallic (MT) SWNTs has facilitated progress toward applications by making available materials of consistent electronic structure. Nevertheless the electrical transport properties of networks of separated SWNTs are inferior to those of individual SWNTs. In particular, for semiconducting SWNTs, which are the subject of this Account, the electrical transport drastically differs from the behavior of traditional semiconductors: for example, the bandgap of germanium (<i>E</i> = 0.66 eV) roughly matches that of individual SC-SWNTs of diameter 1.5 nm, but in the range 300–100 K, the intrinsic carrier concentration in Ge decreases by more than 10 orders of magnitude while the conductivity of a typical SC-SWNT network decreases by less than a factor of 4. Clearly this weak modulation of the conductivity hinders the application of SC-SWNT films as field effect transistors and photodetectors, and it is the purpose of this Account to analyze the mechanism of the electrical transport leading to the unusually weak temperature dependence of the electrical conductivity of such networks. Extrinsic factors such as the contribution of residual amounts of MT-SWNTs arising from incomplete separation and doping of SWNTs are evaluated. However, the observed temperature dependence of the conductivity indicates the presence of midgap electronic states in the semiconducting SWNTs, which provide a source of low-energy excitations, which can contribute to hopping conductance along the nanotubes following fluctuation induced tunneling across the internanotube junctions, which together dominate the low temperature transport and limit the resistivity of the films. At high temperatures, the intrinsic carriers thermally activated across the bandgap as in a traditional semiconductor became available for band transport. The midgap states pin the Fermi level to the middle of the bandgap, and their origin is ascribed to defects in the SWNT walls. The presence of such midgap states has been reported in connection with scanning tunneling spectroscopy experiments, Coulomb blockade observations in low temperature electrical measurements, selective electrochemical deposition imaging, tip-enhanced Raman spectroscopy, high resolution photocurrent spectroscopy, and the modeling of the electronic density of states associated with various defects.Midgap states are present in conventional semiconductors, but what is unusual in the present context is the extent of their contribution to the electrical transport in networks of semiconducting SWNTs. In this Account, we sharpen the focus on the midgap states in SC-SWNTs, their effect on the electronic properties of SC-SWNT networks, and the importance of these effects on efforts to develop electronic and photonic applications of SC-SWNTs

Changes in the Morphology and Proliferation of Astrocytes Induced by Two Modalities of Chemically Functionalized Single-Walled Carbon Nanotubes are Differentially Mediated by Glial Fibrillary Acidic Protein

Alterations in glial fibrillary acidic protein (GFAP) levels accompany the changes in the morphology and proliferation of astrocytes induced by colloidal solutes and films of carbon nanotubes (CNTs). To determine if GFAP is required for the effects of CNTs on astrocytes, we used astrocytes isolated from GFAP null mice. We find that selected astrocytic changes induced by CNTs are mediated by GFAP, i.e., perimeter, shape, and cell death for solutes, and proliferation for films

Enhanced Electrical Conductivity in a Substitutionally Doped Spiro-bis(phenalenyl)boron Radical Molecular Solid

We report the crystallization of a subsitutionally doped organic conductor based on a host lattice composed of spiro-bis­(phenalenyl)­boron radicals. Co-crystallization of solutions of spiro-bis­(9-oxido­phenalenone)­boron radical [PLY­(O,O)]₂B mixed with selected amounts of spiro-bis­(9-oxido­phenalenone)­beryllium [PLY­(O,O)]₂Be leads to the formation of a series of solid-state solutions of composition [PLY­(O,O)]₂­B_{(1–<i>x</i>)}Be_<i>x</i>. The dopant molecules [PLY­(O,O)]₂Be serve to introduce holes into the lattice of spins provided by the [PLY­(O,O)]₂B radicals and lead to a systematic increase in the conductivity while decreasing the activation energy of the conduction process and leaving the solid-state structure relatively unperturbed. While the energies of the hole sites are expected to be high, the results are consistent with the interpretation of the electronic structure of [PLY­(O,O)]₂B in terms of the resonating valence bond model

Band Structure Engineering by Substitutional Doping in Solid-State Solutions of [5-Me-PLY(O,O)]₂B_{(1–<i>x</i>)}Be_<i>x</i> Radical Crystals

We report the substitutional doping of solid-state spiro-bis­(5-methyl-1,9-oxido-phenalenyl)­boron radical ([<b>2</b>]₂B) by co-crystallization of this radical with the corresponding spiro-bis­(5-methyl-1,9-oxido-phenalenyl)­beryllium compound ([<b>2</b>]₂Be). The pure compounds crystallize in different space groups ([<b>2</b>]₂B, <i>P</i>1̅, <i>Z</i> = 2; [<b>2</b>]₂Be, <i>P</i>2₁/<i>c</i>, <i>Z</i> = 4) with distinct packing arrangements, yet we are able to isolate crystals of composition [<b>2</b>]₂B_{(1–<i>x</i>)}Be_<i>x</i>, where <i>x</i> = 0–0.59. The phase transition from the <i>P</i>1̅ to the <i>P</i>2₁/<i>c</i> space group occurs at <i>x</i> = 0.1, but the conductivities of the solid solutions are enhanced and the activation energies reduced for values of <i>x</i> = 0–0.25. The molecular packing is driven by the relative concentration of the spin-bearing ([<b>2</b>]₂B) and spin-free ([<b>2</b>]₂Be) molecules in the crystals, and the extended Hückel theory band structures show that the progressive incorporation of spin-free [<b>2</b>]₂Be in the lattice of the [<b>2</b>]₂B radical (overall bandwidth, <i>W</i> = 1.4 eV, in the pure compound) leads to very strong narrowing of the bandwidth, which reaches a minimum at [<b>2</b>]₂Be (<i>W</i> = 0.3 eV). The results provide a graphic picture of the structural transformations undergone by the lattice, and at certain compositions we are able to identify distinct structures for the [<b>2</b>]₂B and [<b>2</b>]₂Be molecules in a single crystalline phase

Chemically Functionalized Single-Walled Carbon Nanotube Films Modulate the Morpho-Functional and Proliferative Characteristics of Astrocytes

We used single-walled carbon nanotube (CNT) films to modulate the morpho-functional and proliferative characteristics of astrocytes. When plated on the CNT films of various thicknesses, astrocytes grow bigger and rounder in shape with a decrease in the immunoreactivity of glial fibrillary acidic protein along with an increase in their proliferation, changes associated with the dedifferentiation of astrocytes in culture. Thus, CNT films, as a coating material for electrodes used in brain machine interface, could reduce astrogliosis around the site of implantation