Search

The interactions between different low work function metals aluminium, calcium and sodium, and α,ω-diphenyltetradecaheptaene, a model molecule for certain conjugated polymers, have been investigated using both x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. The spectra are interpreted with the help of the results of quantum chemical calculations performed within the local spin density (LSD) approximation methodology. The metals are found to interact with the conjugated system in very different ways. Aluminium forms a covalent bond, which strongly modifies the π-electronic structure of the conjugated molecule, while both the sodium and the calcium atoms act as doping agents, inducing new states in the otherwise forbidden bandgap. These new gap states can be viewed as a soliton–antisoliton pair for the Na/DP7 and a bipolaronic-like defect for Ca/DP7. [ABSTRACT FROM AUTHOR]

The undoped and ferric chloride p-doped ‘‘head-to-head’’ ‘‘tail-to-tail’’ analog of poly(3-decylthiophene) obtained from substituted bithiophenes, i.e., poly(4,4’didecyl-2,2’bithiophene)-PDDBT has been investigated. The samples were studied by means of ultraviolet photoelectron spectroscopy, optical absorption measurements, and polymer bands structure calculations. Experiments were carried out at different temperatures between 100 °C and -180 °C. The results indicate that PDDBT is nonplanar in the undoped state. No temperature effects have been observed in the π-electron properties. In the doped state, however, lowering of the temperature results in an increase of the system planarity that modifies the electronic band structure. This effect has been shown to be fully reversible with temperature. [ABSTRACT FROM AUTHOR]

The shake-up features of the N1s and C1s core-level x-ray photoelectron spectra of model molecules of polyaniline are studied theoretically using the intermediate neglect of differential overlap method in combination with configuration interaction. The calculations are performed on N,N’-diphenyl-1,4-phenylenediamine and N,N’-diphenyl-1,4-benzo-quinondiimine, which are model molecules for fully reduced and fully oxidized polyaniline, respectively. The core-level spectra of these two molecules are also studied experimentally by means of x-ray photoelectron spectroscopy. Experimental and theoretical results are found to be in excellent agreement, which allows for a detailed interpretation of the observed shake-up spectra. Core ionization of imine nitrogens is shown to be accompanied by large shake-up intensity. Our studies of model molecules are compared with recently published core-level spectra of polyaniline at various oxidation levels. The increase in imine nitrogen content upon oxidation of the polymer give rise to an increase in the N1s shake-up intensity, a result which is in agreement with what we find for the model molecules. [ABSTRACT FROM AUTHOR]

The electronic structure of poly-3-hexylthiophene (P3HT) is studied in the solid state with photoelectron spectroscopy, as the polymer is gradually doped from NOPF6. Solubility and processability of P3HT allow for the preparation of very clean and very thin films, which are then doped without air-exposure. The evolution of the core level binding energies is related to the modification of the electron density on the conjugated backbone, due to the creation of polaron and bipolaron defects. Upon doping, valence spectra show a shift in the Fermi level of the system, and at saturation doping a finite density of states at the Fermi level is observed unambiguously for the first time in electrically conducting polymers with photoelectron spectroscopy. The experimental data on core and valence levels can be interpreted in terms of the formation of a polaron lattice at high doping. [ABSTRACT FROM AUTHOR]