2,498 research outputs found

    Applications of the Conceptual Density Functional Theory Indices to Organic Chemistry Reactivity

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    Indexación: Web of ScienceTheoretical reactivity indices based on the conceptual Density Functional Theory (DFT) have become a powerful tool for the semiquantitative study of organic reactivity. A large number of reactivity indices have been proposed in the literature. Herein, global quantities like the electronic chemical potential μ, the electrophilicity ω and the nucleophilicity N indices, and local condensed indices like the electrophilic and nucleophilic Parr functions, as the most relevant indices for the study of organic reactivity, are discussed.http://www.mdpi.com/1420-3049/21/6/74

    Electron correlation effects in electron-hole recombination in organic light-emitting diodes

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    We develop a general theory of electron--hole recombination in organic light emitting diodes that leads to formation of emissive singlet excitons and nonemissive triplet excitons. We briefly review other existing theories and show how our approach is substantively different from these theories. Using an exact time-dependent approach to the interchain/intermolecular charge-transfer within a long-range interacting model we find that, (i) the relative yield of the singlet exciton in polymers is considerably larger than the 25% predicted from statistical considerations, (ii) the singlet exciton yield increases with chain length in oligomers, and, (iii) in small molecules containing nitrogen heteroatoms, the relative yield of the singlet exciton is considerably smaller and may be even close to 25%. The above results are independent of whether or not the bond-charge repulsion, X_perp, is included in the interchain part of the Hamiltonian for the two-chain system. The larger (smaller) yield of the singlet (triplet) exciton in carbon-based long-chain polymers is a consequence of both its ionic (covalent) nature and smaller (larger) binding energy. In nitrogen containing monomers, wavefunctions are closer to the noninteracting limit, and this decreases (increases) the relative yield of the singlet (triplet) exciton. Our results are in qualitative agreement with electroluminescence experiments involving both molecular and polymeric light emitters. The time-dependent approach developed here for describing intermolecular charge-transfer processes is completely general and may be applied to many other such processes.Comment: 19 pages, 11 figure

    Photoelectron spectroscopy of ethylene, isobutylene, trimethylethylene, and tetramethylethylene at variable angles

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    Using a HeI line 58.4 nm source lamp, photoelectron angular distributions were measured for the series of four olefins: ethylene, isobutylene (2‐methyl‐propene), trimethylethylene (2‐methyl‐2‐butene), and tetramethylethylene (2,3‐dimethyl‐2‐butene). From these, the asymmetry parameter β as a function of photoelectron energy was obtained for each of these molecules. The following important effects in the behavior of β are observed: (a) In the π orbital ionization regions of the spectrum of each molecule, β increases with increasing electron energy across the vibrational envelopes. (b) With increasing methyl substitution (and at a fixed photoelectron enegy) β for this band decreases. (c) In the region of the spectra of each of the methyl‐substituted ethylenes involving several 2pσ bands, this energy dependence of β behaves as if they constituted a single band, in spite of the widely differing orbital symmetries. (d) Over most of the 2pσ region of each molecule, β decreases with increasing photoelectron energy, except for the high ionization potential end of this region, where β increases instead. We attribute effects (b) and (d) to σ–π orbital mixing

    A comparative study of electrochemical, spectroscopic and structural properties of phenyl, thienyl and furyl substituted ethylenes

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    a detailed electrochemical and photophysical comparative study of three parallel series of phenyl, thienyl and furyl substituted ethylenes has been carried out, implemented by the computational calculation of selected terms. Relationships have been highlighted between molecular structure (number and type of aromatic rings) and important functional properties (in particular, electronic features and oligomerization ability). Interestingly, some of the studied heteroaryl-ethylenes show emission in the solid state displaying an aggregation-induced emission behavior

    Variable angle photoelectron spectroscopy of the fluoroethylenes

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    He I photoelectron spectra of fluoroethylene, 1,1‐difluoroethylene, cis‐1,2‐difluoroethylene, trans‐1,2‐difluoroethylene, trifluoroethylene, and perfluoroethylene were obtained over the scattering angle range of 45° to 120° and compared with those of ethylene. Vibrational frequencies of the ionic states were measured and their symmetry modes assigned. The asymmetry parameter β as a function of the ionization potential was measured for each molecule. The value of β for the first ionization potential band of these molecules was found to decrease monotonically with increasing fluorine substitution. This variation was interpreted as being due to resonance mixing of the lone pair F π orbitals with C–C π orbitals. The data obtained were used to assign some of the spectral bands observed
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