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| 2. |
- Cornil, J, et al.
(författare)
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Influence of interchain interactions on the absorption and luminescence of conjugated oligomers and polymers: A quantum-chemical characterization
- 1998
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society. - 0002-7863 .- 1520-5126. ; 120:6, s. 1289-1299
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Tidskriftsartikel (refereegranskat)abstract
- Correlated quantum-chemical calculations are used to investigate the influence of interchain interactions on the absorption and emission of pi-conjugated chains. The results are discussed in relation to the utilization of conjugated materials as active elements in electro-optic devices; they provide guidelines on how to prevent a substantial decrease in luminescence yield in solid films. In high-symmetry cofacial configurations, interchain interactions lead to a blue shift of the lowest optical transition compared to that calculated for an isolated chain; the appearance of an additional red-shifted component is expected when positional disorder is considered. The absence of any significant oscillator strength in the transition between the ground state and the lowest excited state in highly symmetric complexes implies that the luminescence emission will be strongly quenched. This picture is. however, modified when one takes account of the relaxation processes which occur in the lowest excited state. The nature of the most stable photogenerated species and the role played by chemical impurities are also addressed.
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| 3. |
- Crispin, X, et al.
(författare)
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A density functional model for tuning the charge transfer between a transition metal electrode and a chemisorbed molecule via the electrode potential
- 2001
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Ingår i: Journal of Chemical Physics. - 0021-9606 .- 1089-7690. ; 115:22, s. 10493-10499
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Tidskriftsartikel (refereegranskat)abstract
- A simple approach is proposed to predict the magnitude of charge transfer between a polarized transition metal electrode and a chemisorbed molecule in an electrolytic solution. The approach is based on the equalization of the chemical potentials, as defined in density-functional theory (DFT). The system is modeled by a metal cluster, a molecule, and a set of point charges (counter ions) and the properties evaluated using methods derived from DFT, specifically, we study here the chemisorption of acrylonitrile on nickel. This approach allows us to point out the various factors determining the charge transfer. The results show a linear increase in the amount of charge transferred to the chemisorbed molecule with the polarization of the metal electrode. (C) 2001 American Institute of Physics.
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| 4. |
- Crispin, X, 1968-, et al.
(författare)
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Controlling the electrografting of polymers onto transition metal surfaces through solvent vs monomer adsorption
- 1999
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society. - 0002-7863 .- 1520-5126. ; 121:1, s. 176-187
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Tidskriftsartikel (refereegranskat)abstract
- Electropolymerization of methacrylic monomers opens the possibility of chemically grafting a wide range of polymers onto transition metal surfaces. In this work, the electropolymerization of polyacrylonitrile and polyethyl acrylate is studied in different solvents; we experimentally confirm that the choice of solvent is a critical parameter for obtaining electrografted polymers. A density-functional theory-based study modeling the interaction of solvent (acetonitrile, dimethylformamide, and pyridine) or monomer (acrylonitrile and ethyl acrylate) molecules with the Ni(100) metal surface provides the means to classify the organic molecules with respect to their ability to interact with the surface. The surface binding-energy difference between monomer and solvent is introduced in a Frumkin-type isotherm. This allows us to rationalize the experimental observations in terms of a competitive adsorption at the metal surface between the monomer and the solvent. The first step in the electrografting mechanism thus appears to be the chemisorption of the monomer at the electrode surface before cathodic polarization is applied; the chemisorbed monomer is therefore the first species reduced, giving rise to an adsorbed reactive intermediate, which is thus able to start the polymerization of a grafted chain.
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| 5. |
- da Silva, DA, et al.
(författare)
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Vibronic coupling in the ground and excited states of the naphthalene cation
- 2004
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; :15, s. 1702-1703
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Tidskriftsartikel (refereegranskat)abstract
- The hole - vibrational coupling in naphthalene is studied using high-resolution gas-phase photoelectron spectroscopy and density functional theory calculations (DFT), and a remarkable increase of the coupling with low-frequency vibrations is observed in the excited states.
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| 6. |
- Fahlman, Mats, et al.
(författare)
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Iron-polyaniline interfaces : Implications for corrosion protection
- 2003
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Ingår i: American Chemical Society Symposium Series (ACS). - 0097-6156 .- 1947-5918. ; 843, s. 76-89
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Tidskriftsartikel (refereegranskat)abstract
- The early stages of interface formation between iron and a three-ring model molecule (trimer) of emeraldine base form of polyaniline (EB) were investigated using theoretical (DFT) and experimental (XPS) methods: Iron atoms were sputter-deposited in ultra high vacuum onto thin oligomer films, with X-ray photoelectron spectroscopy (XPS) core level spectra taken after each deposition. Similar studies were carried out for Fe sputter-deposited on EB polymer films as well. Based on the chemical shifts of the core level peaks and the theoretical results, iron was determined to donate charge (e(-)) into the trimer and EB films. The reverse case where thin films of trimer and EB were deposited on iron also was studied. The C(1s) core level shake up spectra show that the pi-electronic structure is modified for trimer and EB coatings on iron as compared to coatings on gold. (C) 2003 American Chemical Society.
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| 7. |
- Keil, M, et al.
(författare)
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Influence of the morphology on the electronic structure of hexa-peri-hexabenzocoronene thin films
- 2000
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Ingår i: JOURNAL OF PHYSICAL CHEMISTRY B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 104:16, s. 3967-3975
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Tidskriftsartikel (refereegranskat)abstract
- Ultrathin films of hexa-peri-hexabenzocoronene (HBC), prepared in ultrahigh vacuum by sublimation and studied using a combination of atomic force microscopy, X-ray absorption spectroscopy, and photoelectron spectroscopy were interpreted with the help of results of quantum chemical calculations. The important role of the nature of the surface of the substrate as well as the effect of postdeposition annealing on the morphology and the subsequent electronic structure were studied. In particular, on the (0001) surfaces of highly oriented pyrolitic graphite (HOPG) or molybdenum disulfide (MoS2), there is a high degree of molecular order induced by the crystal structure of the substrate surface. When deposited at room temperature on HOPG, the molecules are epitaxially ordered, while crystals from the epitaxially ordered films nucleate and grow during heating. On oxidized silicon(001) or polycrystalline gold surfaces, only totally disordered molecular solid films are formed. The epitaxial films assume a layered structure and exhibit a graphite-like electronic structure. In particular, the relationship between electronic structure and topology is discussed. The results of these studies indicate methods for the preparation of the crystalline seeds to molecular wires.
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| 8. |
- Salaneck, William R, et al.
(författare)
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Electronic structure of conjugated polymers : consequences of electron-lattice coupling
- 1999
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Ingår i: Physics reports. - 0370-1573 .- 1873-6270. ; 319:6, s. 232-251
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Forskningsöversikt (refereegranskat)abstract
- Conjugated organic polymers can be doped, via oxidation or reduction chemistry or via acid-base chemistry, to induce very high electrical conductivity. Conjugated polymers are beginning to find uses, in both the neutral and the doped states, in prototype molecular-based electronics applications and in electronic and opto-electronic devices. The physical basis for the many of the unusual properties of these new materials is discussed, at a sufficient level of approximation to enable an understanding of the important issues by the general condensed matter physicist. In particular, emphasis is placed on the interconnections of the electronic. geometric and chemical structures, Lu the ground stale and especially in the excited states. The important role of electron-electron and electron-lattice interactions are pointed out, and justified through a combined experimental-theoretical approach. (C) 1999 Elsevier Science B.V. All rights reserved.
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| 9. |
- Sancho-Garcia, JC, et al.
(författare)
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Joint theoretical and experimental characterization of the structural and electronic properties of poly(dioctylfluorene-alt-N-butylphenyl diphenylamine)
- 2004
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 108:18, s. 5594-5599
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Tidskriftsartikel (refereegranskat)abstract
- Fluorene-based copolymers are currently attracting considerable interest for use in a wide range of optoelectronic devices. Here, we present the results of a joint quantum-chemical and experimental characterization of the structural, electronic, and optical properties of an alternating fluorene-triphenylamine copolymer. We compare the results from this study with those from similar studies of polyfluorene. Although calculations are performed for the gas phase and experiments are performed on the solid state, the results from the two methodologies are in good agreement: the relevant electronic levels, HOMO and LUMO, of polyfluorene are found to be destabilized by incorporation of triphenylamine units in the conjugated backbone, whereas the optical properties of polyfluorene chains are largely unperturbed by the presence of triphenylamine.
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