Cyclic voltammetry and bulk electronic properties of soluble carbon nanotubes

The bulk electronic properties of pyrrolidine-functionalized nanotubes are obtained from cyclic voltammetry measurements and discussed in the light of quantum chemical calculations. The functionalization is found to preserve the metallic character and to hardly affect the average density of electronic states.     

A light-harvesting fluorinated fullerene donor-acceptor ensemble; long-lived charge separation

In a first example of a trannulene-based donor-acceptor dyad visible light photoexcitation generates a long-lived (870 ns) charge-separated state.     

Modulation of the reduction potentials of fullerene derivatives

The cyclic voltammetric (CV) study of a series of novel bisfulleropyrrolidines (3) and bisfulleropyrrolidinium ions (4) is reported. The eight possible stereoisomers of each series were systematically investigated under strictly aprotic conditions that allowed the observation of up to four and five subsequent reversible reductions in 3 and 4, respectively. Because of the stabilizing effect of positive charges, a significant enhancement of the electronegative properties was observed in 4. In fact, 4-trans-2 and 4-trans-1 result among the strongest reversible electron-accepting C(60) oligoadducts. Furthermore, the study evidenced that, in both 3 and 4, the CV pattern, and in particular the potential separation between the second and third reductions, changes significantly with the addition pattern. A sequential pi-electron model that simulates the effect of subsequent reductions of C(60) bis-adducts gives a good correlation (r > 0.96) with the cyclic voltammetry data when the molecules are divided in two sets dependent on the location of the addends in the same or in opposite hemispheres.     

Auger lineshape analysis as a tool to study surface reactions: kinetics of the dissociation of NO on Rh(110)

We present a new method for following the kinetics of the dissociation of chemisorbed molecules, by Auger electron spectroscopy (AES) in the pulse counting mode. By following the time evolution of the Auger lineshape, it is possible to quantify the relative weight of the dissociated and undissociated chemisorbed species as a function of time. As an example, we have applied the method to the case of NO chemisorbed on rhodium (110). The high signal to noise ratio which can be obtained by AES in the pulse counting mode makes it possible to measure the kinetics with good accuracy, without affecting the reaction.     

Reconstruction of cosmic and beam-halo muons with the CMS detector

The powerful muon and tracker systems of the CMS detector together with dedicated reconstruction software allow precise and efficient measurement of muon tracks originating from proton-proton collisions. The standard muon reconstruction algorithms, however, are inadequate to deal with muons that do not originate from collisions. This note discusses the design, implementation, and performance results of a dedicated cosmic muon track reconstruction algorithm, which features pattern recognition optimized for muons that are not coming from the interaction point, i.e., cosmic muons and beam-halo muons. To evaluate the performance of the new algorithm, data taken during Cosmic Challenge phases I and II were studied and compared with simulated cosmic data. In addition, a variety of more general topologies of cosmic muons and beam-halo muons were studied using simulated data to demonstrate some key features of the new algorithm.     

Preparation and crystal structure of bis(protonated 2,6-diacetylpyridine bis(phenylhydrazone)) uranyl tetrachloride,CH3CN

The reaction of 2,6-diacetylpyridine-bis(phenylhydrazone),L, with commercial uranyl chloride under a variety of different conditions gave only complexes of the type [2LH]²⁺[UO₂Cl₄]^2?,xCH₃CN (x = 1 or 2). The structure of the title compound was determined by X-ray analysis. The crystals are triclinic, space groupP¯1,a=12.77(1),b= 23.12(2),c= 8.11(1) Å, α = 94.33(3) °, β = 89.43(3) °, γ = 98.22(3) ° andZ= 2. The structure was solved by Fourier methods, and refined by least-squares toR= 0.074 for 5210 reflections which were measured on an automatic diffractometer. The [UO₂Cl₄]^2? anions have approximately^4mm _m (D _4h ) symmetry, with the uranyl group perpendicular to a plane in which the four chlorine atoms occupy the corners of a square. The organic cations are approximately planar. Shortening in the C-N (chain) bond distances suggests the presence of a mesomeric effect extended over the entire organic system.     

Polypyridyl ruthenium(II) complexes with tetrazolate-based chelating ligands. Synthesis, reactivity, and electrochemical and photophysical properties

In this contribution, we report the synthesis, the chemical and photophysical characterization, and the study of the reactivity toward electrophiles of two mononuclear complexes of the type [Ru(bpy)2L]+ (bpy is 2,2'-bipyridyl), in which L is represented by the deprotonated form of 2-(1,H-tetrazol-5-yl)pyridine (L1) or 2-(1,H-tetrazol-5-yl)pyrazine (L2). The 1H and 13C NMR experiments that were performed on complexes RuL1 and RuL2 allowed us to establish that the tetrazolate moiety is bonded to the metal center via the N-1 nitrogen, while the coplanar arrangement adopted by the coordinated ligand upon coordination and the consequent interannular conjugation effect accounts for the unexpectedly low field resonance of the tetrazole carbon. The 13C NMR spectroscopy is also of fundamental importance to determine the chemo- and regioselectivity of the addition of a methyl group to RuL1 and RuL2, which takes place at the N-3 nitrogen of the five-membered ring. All these features were confirmed by the X-ray diffraction structures of RuL1 and of the methylated compounds RuL1Me and RuL2Me. Relative to these latter complexes, the presence of a methyl moiety does not cause any distortion from coplanarity of the coordinated tetrazolates. The redox properties of the complexes were investigated by cyclic voltammetry and indicated a quite different behavior between the pyrazinyl-tetrazolate and the pyridyl-tetrazolate complexes as the consequence of the higher electron-withdrawing character of the pyrazine ring. The study of the photophysical properties of the complexes also shows a significant diversity between the luminescent RuL1 and the rather poorly emissive RuL2. Interestingly, the methylated compounds RuL1Me and RuL2Me display radiative excited-state decays with longer lifetimes than their precursors; this feature indicates that methylation is a useful reaction for the tuning of the light emission performances of similar tetrazolate complexes. The synthesis and the characterization of a novel dinuclear complex of type [(bpy)2Ru-L3-Ru(bpy)2]2+, Ru(L3)Ru, where L3 is the bis-anion derived from bis-2,3-(1,H-tetrazol-5-yl)pyrazine, is also reported.     

Cuntz�CKrieger Algebras and Wavelets on Fractals

We consider representations of Cuntz–Krieger algebras on the Hilbert space of square integrable functions on the limit set, identified with a Cantor set in the unit interval. We use these representations and the associated Perron–Frobenius and Ruelle operators to construct families of wavelets on these Cantor sets.