Thermally Activated D₂ Emission upon Decomposition of Thin Deuterofullerene Films on Au(111)

We have studied the formation and thermal properties of thin, deuterofullerene-containing films on Au(111) under ultrahigh vacuum conditions. The films were prepared in situ by exposure of predeposited C₆₀ layers to a flux of atomic deuterium. With increasing deuterium dose, a D + C₆₀ → C₆₀D_<i>x</i> reaction front propagates through the fullerene film toward the gold surface. Heating the resulting deuterofullerene-containing films to >600 K leads to desorption of predominantly C₆₀ and C₆₀D_<i>x</i>. Interestingly, some D₂ is also evolved while a significant fraction of the carbon initially deposited is left on the surface as nondesorbable residue. This is in contrast to analogous deuterofullerene-containing films prepared on graphite, which sublime completely but do not measurably evolve D₂, suggesting that the gold surface can act as a catalyst for D₂ formation. To explore this further, we have systematically studied (i) the thermal properties of C₆₀/Au­(111) reference films, (ii) the reaction of C₆₀/Au­(111) films with D atoms, and (iii) the heating-induced degradation of deuterofullerene-containing films on Au(111). In particular, we have recorded temperature-resolved mass spectra of the desorbing species (sublimation maps) as well as performed ultraviolet photoionization spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and scanning tunneling microscopy measurements of the surfaces at various stages of study. We infer that heating deuterofullerene-containing films generates mobile deuterium atoms which can recombine to form molecular deuterium either at the gold surface or on fullerene oligomers in direct contact with it

Separation of Single-Walled Carbon Nanotubes by 1‑Dodecanol-Mediated Size-Exclusion Chromatography

A simple, single-column, high-throughput fractionation procedure based on size-exclusion chromatography of aqueous sodium dodecyl sulfate suspensions of single-walled carbon nanotubes (SWCNTs) is presented. This procedure is found to yield monochiral or near monochiral SWCNT fractions of semiconducting SWCNTs. Unsorted and resulting monochiral suspensions are characterized using optical absorption and photoluminescence spectroscopy

Ultrafast Dynamics of the First Excited-State of Quasi Monodispersed Single-Walled (9,7) Carbon Nanotubes

Time-resolved two color pump/probe spectroscopy was used to unravel the dynamics of ultrafast decay occurring upon population of the first optical bright excitonic level (E₁₁) in quasi-monodispersed, polymer-wrapped, single-walled (9,7)-carbon nanotubes (SWNTs) in toluene at room temperature. After resonant E₁₁ excitation, transfer of population to at least one optically dark level near E₁₁ was observed to take place within the first picosecond. In addition, phonon-assisted E₁₁-excitation led to transients similar to those observed upon resonant E₁₁-excitation indicating ultrafast vibrational relaxation convoluted with the temporal resolution of 60 fs

Separation of Single-Walled Carbon Nanotubes with a Gel Permeation Chromatography System

A gel permeation chromatography system is used to separate aqueous sodium dodecyl sulfate suspensions of single-walled carbon nanotubes (SWCNTs). This automated procedure requires no precentrifugation, is scalable, and is found to yield monochiral SWCNT fractions of semiconducting SWCNTs with a purity of 61–95%. Unsorted and resulting monochiral fractions are characterized using optical absorption and photoluminescence spectroscopy

Isomer-Selected Photoelectron Spectroscopy of Isolated DNA Oligonucleotides: Phosphate and Nucleobase Deprotonation at High Negative Charge States

Fractionation according to ion mobility and mass-to-charge ratio has been used to select individual isomers of deprotonated DNA oligonucleotide multianions for subsequent isomer-resolved photoelectron spectroscopy (PES) in the gas phase. Isomer-resolved PE spectra have been recorded for tetranucleotides, pentanucleotides, and hexanucleotides. These were studied primarily in their highest accessible negative charge states (3–, 4–, and 5–, respectively), as provided by electrospraying from room temperature solutions. In particular, the PE spectra obtained for pentanucleotide tetraanions show evidence for two coexisting classes of gas-phase isomeric structures. We suggest that these two classes comprise: (i) species with excess electrons localized exclusively at deprotonated phosphate backbone sites and (ii) species with at least one deprotonated base (in addition to several deprotonated phosphates). By permuting the sequence of bases in various [A_5–<i>x</i>T_<i>x</i>]^4– and [GT₄]^4– pentanucleotides, we have established that the second type of isomer is most likely to occur if the deprotonated base is located at the first or last position in the sequence. We have used a combination of molecular mechanics and semiempirical calculations together with a simple electrostatic model to explore the photodetachment mechanism underlying our photoelectron spectra. Comparison of predicted to measured photoelectron spectra suggests that a significant fraction of the detected electrons originates from the DNA bases (both deprotonated and neutral)

Length-Sorted, Large-Diameter, Polyfluorene-Wrapped Semiconducting Single-Walled Carbon Nanotubes for High-Density, Short-Channel Transistors

Samples of highly enriched semiconducting SWCNTs with average diameters of 1.35 nm have been prepared by combining PODOF polymer wrapping with size-exclusion chromatography. The purity of the material was determined to be >99.7% from the transfer characteristics of short-channel transistors comprising densely aligned sc-SWCNTs. The transistors have a hole mobility of up to 297 cm²V^–1 s^–1 and an On/Off ratio as high as 2 × 10⁸

Effect of Proton Substitution by Alkali Ions on the Fluorescence Emission of Rhodamine B Cations in the Gas Phase

The photophysics of chromophores is strongly influenced by their environment. Solvation, charge state, and adduct formation significantly affect ground and excited state energetics and dynamics. The present study reports on fluorescence emission of rhodamine B cations (RhBH⁺) and derivatives in the gas phase. Substitution of the acidic proton of RhBH⁺ by alkali metal cations, M⁺, ranging from lithium to cesium leads to significant and systematic blue shifts of the emission. The gas-phase structures and singlet transition energies of RhBH⁺ and RhBM⁺, M = Li, Na, K, Rb, and Cs, were investigated using Hartree–Fock theory, density functional methods, second-order Møller–Plesset perturbation theory, and the second-order approximate coupled-cluster model CC2. Comparison of experimental and theoretical results highlights the need for improved quantum chemical methods, while the hypsochromic shift observed upon substitution appears best explained by the Stark effect due to the inhomogeneous electric field generated by the alkali ions

Polymer Library Comprising Fluorene and Carbazole Homo- and Copolymers for Selective Single-Walled Carbon Nanotubes Extraction

To date, (<i>n</i>, <i>m</i>) single-walled carbon nanotubes (SWNTs) cannot be selectively synthesized. Therefore, postprocessing of SWNTs including solubilization and sorting is necessary for further applications. Toward this goal, we have synthesized a polymer library consisting of fluorene- and carbazole-based homo- and copolymers. Variations of the connection of these aromatics together with the incorporation of further conjugated monomers give access to a broad diversity of polymers. Their ability to selectively wrap specific (<i>n</i>, <i>m</i>) species is investigated toward HiPco SWNTs raw material which contains more than 40 (<i>n</i>, <i>m</i>) species. Absorption and fluorescence spectroscopies were used to analyze SWNTs/polymer suspensions. These results provide evidence for selective SWNTs/polymer interactions and allow a more detailed assessment of polymer structure–property relationships, thus paving the way toward custom synthesis of polymers for single (<i>n</i>, <i>m</i>) SWNTs extraction

Probing the Influence of Size and Composition on the Photoelectron Spectra of Cadmium Chalcogenide Cluster Dianions

We have synthesized a series of compounds comprising the halide-free cadmium chalcogenide cluster dianions [Cd₈Se­(SePh)₁₆]^2–, [Cd₁₇Se₄(SePh)₂₈]^2–, [Cd₁₇S₄(SPh)₂₈]^2–, and [Cd₁₇Se₄(SPh)₂₈]^2– to study their size- and composition-dependent electronic properties free of matrix effects. Toward this end, photoelectron spectra of the isolated dianions electrosprayed from solution were recorded at several detachment photon energies. Together with quantum chemical calculations, these data reveal a systematic correlation between electronic properties such as electron affinities or repulsive Coulomb barriers and the composition/size of these semiconducting cluster complexes. We infer that the excess negative charges are localized at the apical sites of these near-tetrahedral molecules

Mononuclear and Tetranuclear Compounds of Yttrium and Dysprosium Ligated by a Salicylic Schiff-Base Derivative: Synthesis, Photoluminescence, and Magnetism

The Schiff-base (2-aminoethyl)­hydroxybenzoic acid (H₂L) as a proligand was prepared in situ from 3-formylsalicylic acid and ethanolamine (ETA). The mononuclear {[Y­(HL)₄]­[ETAH]·H₂O} (<b>1</b>) and {[Dy­(HL)₄] [ETAH]·3MeOH·H₂O} (<b>2</b>) and tetranuclear {[Y₄(HL)₂(L)₄(μ₃-OH)₂]·4MeOH·4H₂O} (<b>3</b>), {[Dy₄(HL)₂(L)₄(μ₃-OH)₂]·5­(MeOH)₂·7H₂O (<b>4</b>), and {[Dy₄(HL)₈(L)₂]·4MeOH·2H₂O}­(<b>5</b>) rare-earth metal complexes of this ligand could be obtained as single-crystalline materials by the treatment of H₂L in the presence of the metal salts [Ln­(NO₃)₃·(H₂O)_<i>m</i>] (Ln = Y, Dy). In the solid state, the tetranuclear compounds <b>3</b> and <b>4</b> exhibit butterfly structures, whereas <b>5</b> adopts a rectangular arrangement. Electrospray ionization mass spectrometry data of the ionic compounds <b>1</b> and <b>2</b> support single-crystal X-ray analysis. The yttrium compounds <b>1</b> and <b>3</b> show fluorescence with 11.5% and 13% quantum yield, respectively, whereas the quantum yield of the dysprosium complex <b>4</b> is low. Magnetic studies on the dysprosium compounds <b>4</b> and <b>5</b> suggest the presence of weak antiferromagnetic interactions between neighboring metal centers. Compound <b>4</b> shows single-molecule-magnet behavior with two relaxation processes, one with the effective energy barrier <i>U</i>_eff = 84 K and the preexponential factor τ₀ = 5.1 × 10^–9 s