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51.
Brillante A Della Valle RG Farina L Venuti E Cavazzoni C Emerson AP Syassen K 《Journal of the American Chemical Society》2005,127(9):3038-3043
We have investigated the high-pressure properties of the molecular crystal para-diiodobenzene, by combining optical absorption, reflectance, and Raman experiments with Car-Parrinello simulations. The optical absorption edge exhibits a large red shift from 4 eV at ambient conditions to about 2 eV near 30 GPa. Reflectance measurements up to 80 GPa indicate a redistribution of oscillator strength toward the near-infrared. The calculations, which describe correctly the two known molecular crystal phases at ambient pressure, predict a nonmolecular metallic phase, stable at high pressure. This high-density phase is characterized by an extended three-dimensional network, in which chemically bound iodine atoms form layers connected by hydrocarbon bridges. Experimentally, Raman spectra of samples recovered after compression show vibrational modes of elemental solid iodine. This result points to a pressure-induced molecular dissociation process which leads to the formation of domains of iodine and disordered carbon. 相似文献
52.
Luigi Angiolini Daniele Caretti Carlo Carlini 《Journal of polymer science. Part A, Polymer chemistry》1994,32(6):1159-1168
The synthesis of photochromic optically active copolymers from trans-4-(phenylazo)-1-naphthyl acrylate (PANA), or trans-4-(1-naphthylazo)-phenyl acrylate (NAPA), and (?)-menthyl acrylate (MtA) is described. The copolymers prepared, having different contents of trans-phenylazonaphthalene moieties, have been characterized by IR, 1H-NMR, UV, and GPC techniques. The chiroptical properties have been investigated by circular dichroism (CD) and the induced optical activity on the side-chain trans-phenylazonaphthalene chromophores discussed in terms of different conformational situations of the macromolecules in both the copolymer series. © 1994 John Wiley & Sons, Inc. 相似文献
53.
Carlo Bruno Eleonora Ussano Gianni Barucca Davide Vanossi Giovanni Valenti Edward A. Jackson Andrea Goldoni Lucio Litti Simona Fermani Luca Pasquali Moreno Meneghetti Claudio Fontanesi Lawrence T. Scott Francesco Paolucci Massimo Marcaccio 《Chemical science》2021,12(23):8048
The presence of non-hexagonal rings in the honeycomb carbon arrangement of graphene produces rippled graphene layers with valuable chemical and physical properties. In principle, a bottom-up approach to introducing distortion from planarity of a graphene sheet can be achieved by careful insertion of curved polyaromatic hydrocarbons during the growth of the lattice. Corannulene, the archetype of such non-planar polyaromatic hydrocarbons, can act as an ideal wrinkling motif in 2D carbon nanostructures. Herein we report an electrochemical bottom-up method to obtain egg-box shaped nanographene structures through a polycondensation of corannulene that produces a new conducting layered material. Characterization of this new polymeric material by electrochemistry, spectroscopy, electron microscopy (SEM and TEM), scanning probe microscopy, and laser desorption-ionization time of flight mass spectrometry provides strong evidence that the anodic polymerization of corannulene, combined with electrochemically induced oxidative cyclodehydrogenations (Scholl reactions), leads to polycorannulene with a wavy graphene-like structure.A bottom-up synthesis of wavy graphene structures obtained through an anodic polymerization process, combined with an electrochemically triggered oxidative cyclodehydrogenation, of the bowl-shaped polyaromatic hydrocarbon corannulene. 相似文献
54.
Substituted polythiophene and triethylenglycolpyrrolidino-C(60) blends are examined by time-resolved electron paramagnetic resonance (TR-EPR) at different temperatures. TR-EPR spectra recorded on the microsecond time scale after a short laser pulse are assigned to polythiophene and fullerene radical ion pairs, generated by electron transfer from the excited state of polythiophene to fullerene. At low temperatures, TR-EPR spectra show polarized lines with an antiphase emission/absorption pattern. The origin of the polarization pattern is described in the frame of spin correlated radical pair theory, in which two unpaired electron spins (on radical cation and anion, respectively) interact through isotropic spin exchange and anisotropic dipolar interactions. The polarization pattern is accounted for assuming a singlet excited state as the precursor of the charge-separated state. Spectral simulations yield dipolar and spin exchange coupling constants between unpaired electrons of the radical ion pair. Their values correspond to a mean distance between opposite charges of 22 A. When the temperature is increased, the spectra gradually loose their antiphase character and eventually consist of a signal totally in emission. This behavior is explained by a polarization mechanism involving a spin-selective charge recombination (ST(-1) mixing). The polarization pattern at different temperatures is examined in detail, and its generating mechanism is discussed. 相似文献
55.
We describe a new branch-and-bound algorithm for the exact solution of the maximum cardinality stable set problem. The bounding phase is based on a variation of the standard greedy algorithm for finding a colouring of a graph. Two different node-fixing heuristics are also described. Computational tests on random and structured graphs and very large graphs corresponding to real-life problems show that the algorithm is competitive with the fastest algorithms known so far.This work has been supported by Agenzia Spaziale Italiana. 相似文献
56.
We propose a bi-Hamiltonian formulation of the Euler equation for the free n-dimensional rigid body moving about a fixed point. This formulation lives on the physical phase space so(n), and is different from the bi-Hamiltonian formulation on the extended phase space sl(n), considered previously in the literature. Using the bi-Hamiltonian structure on so(n), we construct new recursion schemes for the Mishchenko and Manakov integrals of motion. 相似文献
57.
58.
Anna Daghetti Carlo Gatti Sergio Trasatti 《Journal of Electroanalytical Chemistry》1985,196(1):179-197
Three isotherms are considered: Frumkin's Bennes' and Mohilner's. The relationship between the interaction parameters in the first two and the adsorbate activity coefficient in the last is discussed. The significance of various standard states for the definition of ΔG° ads is analysed. The operational derivation of ΔG°ads in the three cases and the relationship between the resulting three quantities are illustrated. The isotherms have been used to describe the adsorption of 1,4-dioxane on a polarized Hg electrode. The analysis has been carried out both at constant potential and constant charge. The picture emerging in each of the three cases is discussed in the light of the results obtained in the other two. It is concluded that the three approaches give the same qualitative information about the interfacial behaviour of dioxane, especially as far as the effect of the electric field and the particle-particle lateral interaction are concerned. The usefulness of the Frumkin isotherm for analysing promptly experimental adsorption data is thus maintained. Limitations of the present approach are discussed. 相似文献
59.
Lim H Carraro C Maboudian R Pruessner MW Ghodssi R 《Langmuir : the ACS journal of surfaces and colloids》2004,20(3):743-747
InP(100) surfaces treated with Na2Sx9H20 and CnH(2n+1)SH are examined by contact angle measurement, X-ray photoelectron spectroscopy, and atomic force microscopy to determine the chemical and thermal behavior of these passivated surfaces. The surfaces coated by octadecanethiol (n = 18) self-assembled monolayers (SAMs) are found to be more stable toward oxidation than the S-passivated surface. The chemical stability of octadecanethiol SAMs in various environments is examined. The thiol monolayer is found to be stable in 0.1 M HCl but degrades in 0.1 M NaOH, boiling chloroform, and water. The behavior of these surfaces at elevated temperatures under a vacuum is also investigated. The octadecanethiol-coated InP(100) is stable up to 473 K, above which the films begin to degrade. Unlike other substrates on which the entire molecule including the sulfur headgroup desorbs together, on InP, the sulfur headgroup remains on the surface even after annealing to 673 K. These observations suggest that the desorption occurs by S-C bond cleavage as well as In-S bond cleavage. The sulfur of S-passivated InP is found to be more thermally stable than that of the octadecanethiol monolayer, perhaps due to their different bonding geometries and hence energies. 相似文献
60.
Second-order rate constants (k(n)) for the aminolysis of some phenyl acetates with poly(ethylenimine) (PEI) were obtained in a pH range 4.36-11.20 at 25 degrees C in 1 M KCl. Linear Bronsted-type plots (log k(n) vs pK(N) of PEI) were found for less reactive esters 2-nitrophenyl acetate, 4-acetoxy-3-chlorobenzoic acid, and 4-acetoxybenzenesulfonate with slopes of 0.92, 0.99, and 0.82, respectively. Curved plots were obtained for 3-acetoxy-2,6-dinitrobenzoic acid and 4-acetoxy-3-nitrobenzenesulfonate, which are consistent with a stepwise reaction. The most likely mechanism involves the existence of a tetrahedral intermediate (T(+/-)) and a change in the rate-determining step from its breakdown to its formation when the basicity of the polyamine increases. A semiempirical equation was used to calculate the values of limiting slopes of the plots (0.9 and 0.1 for both esters) and pK(N) at the center of the curvature of the plots (pK(N degrees ) = 7.94 and 9.02, respectively). The values of pK(N degrees ) are lower than those estimated for the aminolysis of the same esters with simple monomeric amines (pK(n degrees ) > 11) because of a better leaving ability of the aryl oxide ion from the tetrahedral intermediate when amino groups of PEI instead of simple amines are involved. Estimation of the pK's of the reactive intermediates and of the microscopic rate constants for the proton transfer from T(+/-) to PEI or from PEIH(+) to T(+/-) indicates that either base or acid catalysis is unimportant in the aminolysis of these esters by PEI. 相似文献