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Transport measurements have revealed several exotic electronic properties of graphene. The possibility to influence the electronic structure and hence control the conductivity by adsorption or doping with adatoms is crucial in view of electronics applications. Here, we show that in contrast to expectation, the conductivity of graphene increases with increasing concentration of vacancy defects, by more than one order of magnitude. We obtain a pronounced enhancement of the conductivity after insertion of defects by both quantum mechanical transport calculations as well as experimental studies of carbon nano-sheets. Our finding is attributed to the defect induced mid-gap states, which create a region exhibiting metallic behaviour around the vacancy defects. The modification of the conductivity of graphene by the implementation of stable defects is crucial for the creation of electronic junctions in graphene-based electronics devices. [ABSTRACT FROM AUTHOR]

In-plane defects have been introduced into graphene nanosheets by treatment with hydrochloric acid. Acid treatment induces bond cleavage in the C-C network via electrophilic attack. These resultant vacancy sites will then undergo further reactions with the surrounding ambient to produce C-O and C-H bonds. A s* resonance at 287 eV in the carbon K-edge x-ray absorption spectra is observed with acid treatment and is assigned to C-O states. Theoretical modelling of a di-vacancy in a graphene bilayer reproduces all essential features of this resonance and in addition predicts a metallic conductivity of states around this vacancy. The possibility of engineering the properties of graphene via the routes explored here is an important step towards establishing strategies for building devices based on this material. [ABSTRACT FROM AUTHOR]

The graphene oxide (GO) microstructure, in terms of flake distribution, folding, and crumpling, in thin films affects properties such as electrical conductivity and optical transparency after GO reduction. A thin film can be tailored to the user's application if the microstructure resulting from different deposition methods can be controlled. In this work, we compare the microstructures of GO coatings created through electrospray deposition (ESD) with random deposition processes. The comparisons include both MATLAB simulations and a dip coating process. The microstructure of ESD GO thin films can be altered by changing the distance between the nozzle and the substrate. We developed a semi-automatic image analysis script that analyzes scanning electron microscopy images to find effects of GO stacking or agglomeration, without the risk of human bias. A low nozzle to substrate distance creates structures of flat GO flakes, but solvent flooding the samples causes drying patterns. A high nozzle to substrate distance causes folding and crumpling of the GO flakes due to solvent evaporation, resulting in agglomerated GO on the substrate. For our ESD setup, a nozzle to substrate distance of 2-4 mm produced GO coatings with the lowest combined influence of drying effects and GO flake folding or crumpling., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

Isolation and purification of functionalized fullerenes from often complex reaction mixtures is challenging due to the hydrophobic nature and low solubility in regular organic solvents. We have developed an HPLC method that efficiently, employing regular reversed phase stationary phases, separates not only C 60 from C 70 in a model mixture, but also C 60 monoadducts from polyadducts and unreacted C 60 from fulleropyrrolidine and hydroarylation example reaction mixtures. Six HPLC columns with regular reversed phase stationary phases were evaluated using varying proportions of acetonitrile in toluene as eluent; with C18 and C12 stationary phases with high surface area (450-400 m 2 g -1 ) being the most efficient regarding separation efficiency and analysis time for all mixtures. The analytical method is effectively transferrable to a preparative scale to isolate the monoaddition products from complex fullerene reaction mixtures., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The first hydrogenation step of benzene, which is endergonic in the electronic ground state (S 0 ), becomes exergonic in the first triplet state (T 1 ). This is in line with Baird's rule, which tells that benzene is antiaromatic and destabilized in its T 1 state and also in its first singlet excited state (S 1 ), opposite to S 0 , where it is aromatic and remarkably unreactive. Here we utilized this feature to show that benzene and several polycyclic aromatic hydrocarbons (PAHs) to various extents undergo metal-free photochemical (hydro)silylations and transfer-hydrogenations at mild conditions, with the highest yield for naphthalene (photosilylation: 21%). Quantum chemical computations reveal that T 1 -state benzene is excellent at H-atom abstraction, while cyclooctatetraene, aromatic in the T 1 and S 1 states according to Baird's rule, is unreactive. Remarkably, also CVD-graphene on SiO 2 is efficiently transfer-photohydrogenated using formic acid/water mixtures together with white light or solar irradiation under metal-free conditions.

Ditopic binding of various dinitrogen compounds to three bisporphyrin molecular tweezers with spacers of varying conformational rigidity, incorporating the planar enediyne (1), the helical stiff stilbene (2), or the semi-rigid glycoluril motif fused to the porphyrins (3), are compared. Binding constants Ka = 10⁴-10⁶ M(-1) reveal subtle differences between these tweezers, that are discussed in terms of porphyrin dislocation modes. Exciton coupled circular dichroism (ECCD) of complexes with chiral dinitrogen guests provides experimental evidence for the conformational properties of the tweezers. The results are further supported and rationalized by conformational analysis.

High-pressure photoelectron spectroscopy is a rapidly developing technique with applications in a wide range of fields ranging from fundamental surface science and catalysis to energy materials, environmental science, and biology. At present the majority of the high-pressure photoelectron spectrometers are situated at synchrotron end stations, but recently a small number of laboratory-based setups have also emerged. In this paper we discuss the design and performance of a new laboratory based high pressure photoelectron spectrometer equipped with an Al Kα X-ray anode and a hemispherical electron energy analyzer combined with a differentially pumped electrostatic lens. The instrument is demonstrated to be capable of measuring core level spectra at pressures up to 30 mbar. Moreover, valence band spectra of a silver sample as well as a carbon-coated surface (graphene) recorded under a 2 mbar nitrogen atmosphere are presented, demonstrating the versatility of this laboratory-based spectrometer.

Annealing of C 60 in hydrogen at temperatures above the stability limit of C-H bonds in C 60 H x (500-550 °C) is found to result in direct collapse of the cage structure, evaporation of light hydrocarbons, and formation of solid mixture composed of larger hydrocarbons and few-layered graphene sheets. Only a minor part of this mixture is soluble; this was analyzed using matrix-assisted laser desorption/ionization MS, Fourier transform infrared (FTIR), and nuclear magnetic resonance spectroscopy and found to be a rather complex mixture of hydrocarbon molecules composed of at least tens of different compounds. The sequence of most abundant peaks observed in MS, which corresponds to C 2 H 2 mass difference, suggests a stepwise breakup of the fullerene cage into progressively smaller molecular fragments edge-terminated by hydrogen. A simple model of hydrogen-driven C 60 unzipping is proposed to explain the observed sequence of fragmentation products. The insoluble part of the product mixture consists of large planar polycyclic aromatic hydrocarbons, as evidenced by FTIR and Raman spectroscopy, and some larger sheets composed of few-layered graphene, as observed by transmission electron microscopy. Hydrogen annealing of C 60 thin films showed a thickness-dependent results with reaction products significantly different for the thinnest films compared to bulk powders. Hydrogen annealing of C 60 films with the thickness below 10 nm was found to result in formation of nanosized islands with Raman spectra very similar to the spectra of coronene oligomers and conductivity typical for graphene.

The relative stereochemistry of acyclic diamines with several stereogenic centers has been analyzed by NMR spectroscopy in combination with conformational deconvolution. Binding to a bisporphyrin molecular clip improves the stereochemical assignment significantly. The diamines were synthesized from inexpensive sugar alcohols, and their stable hydrochlorides were quantitatively converted into free bases by treatment with ion-exchange resin., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Suspensions of graphene, prepared from graphite foil by sonochemical exfoliation, have been treated with new nonpolar pyrenebutyric amides. The assemblies, in suspension and after deposition on solid supports, were characterized by NMR, absorption, and fluorescence spectroscopy and by transmission electron microscopy, where the well-defined shape and size of an appended [60]fulleropyrrolidine unit facilitates TEM detection of the nonstationary molecules. The accumulated evidence, also including direct comparisons of carbon nanotubes treated with pyrene amides under the same conditions, proves the successful noncovalent functionalization of graphene suspended in non-polar solvent with non-polar pyrene derivatives.

A new [60]fullerene dumbbell consisting of two fulleropyrrolidines connected to a central ferrocene unit by amide linkages has been prepared and fully characterized by elemental analysis, (1)H NMR, UV/Vis, fluorescence and mass spectrometry. The electrochemical properties as determined by cyclic voltammetry show ground state electronic communication between the ferrocene and the fullerene units. In addition, the preparaton of a ferrocene building block for an alternative linking approach is presented.

Two pyrazoline- and one pyrrolidine-bridged Ru(II)bipyridine-[60]fullerene dyads have been prepared and studied by ultrafast time-resolved spectroscopy. A silver-assisted synthesis route, in which Ag(I) removes the chlorides from the precursor complex Ru(bpy) 2Cl 2 facilitates successful coordination of the [60]fullerene-substituted third ligand. Upon light excitation of the ruthenium moiety, the emission was strongly quenched by the fullerene. The main quenching mechanism is an exceptionally fast direct energy transfer ( k obs > 1 x 10 (12) s (-1) in the pyrazoline-bridged dyads), resulting in population of the lowest excited triplet state of fullerene. No evidence for electron transfer was found, despite the extraordinarily short donor-acceptor distance that could kinetically favor that process. The observations have implications on the ongoing development of devices built from Ru-polypyridyl complexes and nanostructured carbon, such as C 60 or nanotubes.

Silver ion complexation to bisarene ligands is enhanced by providing a conformationally rigid molecular cleft in the (Z)-acenaphthylene dimer 1. NMR titrations were used to determine complexation constants K for a series of ligands in tetrahydrofuran solution, with K = 4.9 M(-1) for the Z dimer 1 and 0.4 M(-1) for the E dimer 2. Higher values of K were observed in CDCl(3)/CD(3)OD 9:1 with K = 38 M(-1) for 1 and K = 4.1 M(-1) for 2. In the solid state, isolated clusters of [1 x (AgCF(3)SO(3))(2)](2) form a novel, pleated-sheet motif based on non-ionic interactions between clusters.

A rapid, mild and readily scaleable method for purification and isolation of single-walled nanotubes (SWNTs) using aqueous nitric acid that, in only 1-2 hours at reflux temperature, not only decrease the content of residual metal particles but also the relative ratio of small diameter and metallic NTs. The acid-treated SWNTs have been characterised by TEM, FT-IR, and Raman spectroscopy (514 and 783 cm(-1)). The results are discussed in relation to observations from other acid-mediated treatments and the reactive chemical species involved at different conditions.

Basicity constants for a series of 3,7-diazabicyclo[3.3.1]nonane derivatives in acetonitrile with a variation over 13 orders of magnitude have been determined using a spectrophotometric titration technique. An excellent correlation between basicity and calculated proton affinities obtained at PCM-B3LYP/6-31+G(d)//B3LYP/6-31G(d) level was found. The results are discussed in terms of substituent effects and compared to (15)N NMR chemical shifts.

Thermal cycloaddition of 1,3-dipolar azomethine ylides to the sidewalls of multiwalled carbon nanotubes (MWNTs) has been used to prepare MWNTs that contain 2-methylenethiol-4-(4-octadecyloxyphenyl) (4), N-octyl-2-(4-octadecyloxyphenyl) (5) or 2-(4-octadecyloxyphenyl)pyrrolidine (6) units. All these contain the 4-octadecyloxyphenyl substituent that acts as a solubilizing group. Microwave (MiW)-assisted heating was found to be highly efficient for soluble MWNTs, for which the amount of added groups after only 2 h of MiW heating at 200 degrees C, determined by using thermogravimetric analysis, was found to be in the same range as that obtained after 100-120 h of conventional heating of soluble and insoluble MWNTs. Solubility is a key feature for a successful MiW-heated reaction; MWNTs insoluble in the reaction medium yielded considerably less addends in the MiW-heated reactions than in the conventionally heated reaction. The location and even distribution of the pyrrolidine units over the outermost layer of the MWNTs was verified by transmission electron microscopy analysis of 4 that had been treated with gold nanoparticles and thoroughly washed to remove gold particles adsorbed on nonfunctionalized parts of the MWNTs.

Three pyridine-substituted fullerene adducts, bis(2,2'-bipyridine)(2'-phenyl-5'-(2-pyridinyl)-2'H-[5,6]fullereno(C(60)-I(h))[1,9]pyrazole)ruthenium-bis(hexafluorophosphate) (1), bis(2,2'-bipyridine)(2'-phenyl-5'-(4-(4'-methyl-2,2'-bipyridinyl))-2'H-[5,6]fullereno(C(60)-I(h))[1,9]pyrazole)ruthenium-bis(hexafluorophosphate) (2), and bis(2,2'-bipyridine)(1',5'-dihydro-3'-methyl-2'-(4-(4'-methyl-2,2'-bipyridinyl))-2'H-[5,6]fullereno(C(60)-I(h))[1,9]pyrrole)ruthenium-bis(hexafluorophosphate) (3), have been prepared. The common features for these complexes are the short bridges between the fullerene and the pyridine moieties. [structure: see text]

Semiempirical and density functional electronic structure theory methods were used to study SWNT-X--R bond strengths, where the single-walled carbon nanotube (SWNT) had an armchair or zigzag structure, the link heteroatom X was O, N(H), or S and the hydrocarbon chain R was CH(2)CH(3), CH(OH)CH(3), CHCH(2), or CH(CF(3))CH(3). In all systems the hydrocarbon was bonded to the end of the nanotube. The SWNT-X--R bond (that is, the bond joining the link atom to the hydrocarbon) is more than 0.4 eV stronger for armchair than for zigzag nanotubes with the same diameters, irrespective of whether O, N, or S are used as link atoms or whether OH, C==C, or CF(3) groups are present in the hydrocarbon chain. This raises the possibility for selective manipulation of armchair/zigzag nanotubes using a variety of link atoms and hydrocarbon structures. The SWNT-O--CH(CF(3))CH(3) bond is weaker than the SWNT-O--CH(2)CH(3) bond (for both armchair and zigzag nanotubes), while inclusion of a double bond in the ethyl chain increases the bond strengths. Also, SWNT-S--CH(2)CH(3) and SWNT-N(H)--CH(2)CH(3) bonds are stronger than SWNT-O--CH(2)CH(3) bonds.

The chiral chelating ligand N,N'-bis(phenylethyl)bispidine (1) forms a rigid cavity which accommodates (pi-allyl)palladium species with high selectivity. In the resulting complex, the absolute configuration of the pi-allyl ligand can be determined by the detection in NMR spectra of a few unambiguous interligand NOEs. Dynamic processes involving the pi-allyl ligand can be investigated. Depending on the analytical target, ligand (S,S)-1 or (R,R)-1 may be used.