Articles you may be interested in 2-methyl furan: An experimental study of the excited electronic levels by electron energy loss spectroscopy, vacuum ultraviolet photoabsorption, and photoelectron spectroscopy

Electronic structures of evaporated films of five organic light-emitting and carrier-injecting materials for organic electroluminescent devices were studied by ultraviolet photoemission spectroscopy. The compounds examined were (i) light-emitting materials tris(8-hydroxyquinolino) aluminum (Alq3) and 1,2,3,4,5-pentaphenylcyclopentadiene, (ii) a hole-injecting material N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine, and (iii) electron-injecting materials N,N′-diphenyl-1,4,5,8-naphthyletracarboxyldiimide and 1,3,5-tris(5-phenyl-1,3,4-oxadiazol-2-yl)benzene. The spectral features corresponding to the top parts of the valence states, which dominate the electric properties of the materials, were assigned by the comparison with the simulated density of states obtained from PM3 molecular orbital calculations. Using these calculations, the evolution of the electronic structure of each molecule from those of constituent parts was discussed. The characters of the unoccupied states obtained by these calculations were also presented. Using these data, the correlation between the ionization threshold energies determined by ultraviolet photoemission spectroscopy and the carrier-injecting and light-emitting properties were discussed.

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Articles you may be interested inImpedance spectroscopy characterization of inverted type organic solar cells based on poly(3-hexylthiophene-2,5-diyl) AIP Conf.Electronic structure of poly(1,10-phenanthroline-3,8-diyl) and its K-doped state studied by photoelectron spectroscopy Ultraviolet photoelectron spectra were measured using synchrotron radiation for two kinds of -conjugated polymers, poly͑pyridine-2,5-diyl͒ ͑PPy͒ and poly͑2,2Ј-bipyridine-5,5Ј-diyl͒ ͑PBPy͒ which exhibit n-type electrically conducting properties. The two compounds show similar spectra and they were analyzed with MO calculations and the comparison with the data of related molecules. The ionization threshold energies of PPy and PBPy were found to be 6.3 and 6.35 eV, respectively. These values are higher than those of -conjugated conducting polymers capable of p doping. Upon potassium doping of PBPy, two new states appeared in the originally empty energy gap and the intensity of the state at 0.65 eV from E F grows as the doping proceeds. This finding and the change of optical absorption spectra upon doping indicate that bipolaron bands are formed in K-doped PBPy. While K-doped PPy also shows similar gap states, it requires higher dopant concentration to create bipolaron bands than in the case of K-doped PBPy. The difference of the dependence on dopant concentration between K-doped PPy and K-doped PBPy is discussed based on the conformational difference between these polymers.

Ultraviolet photoelectron spectra (UPS) of LaC82 questioning whether the La atom is inside the C cage or not are measured for the first time. The UPS of LaC82 is analogous to those of €32, but there is a critical difference in the region just below the Fermi level. It is an appearance of two new peak components at 0.9 and 1.6 eV with the intensity ratio of 1:2 in the UPS of LaC82. Their origin is the transfer of three electrons from La to C82 to form the electronic structure of La'^^C82~^. Present results combined with theoretical calculations on the position of the La atom in the molecule assert an encapsulation of the LA atom inside the C cage.PACS numbers: 79.60. indicated that there is an air stable and solvent extractable metailofullerene, LaCgi, in the laser vaporized soot of a composite rod of La203 and graphite. They suggested that the metal atom of the metailofullerene was entrapped inside the C cage (endohedral form, to be described as La^Cgi). Since then, many attempts have been made to obtain metallofullerenes [2][3][4][5][6][7][8]. An ESR measurement [2] indicates the 4-3 oxidation state for the La atom of LaC82. An x-ray photoelectron spectroscopy (XPS) [9] result on the mixture of metailofullerene LaC" also indicates that the La atom is in a formal charge state close to +3 and is effectively protected from water and oxygen. These experiments strongly suggest that the La atom is inside the cage. However, there still remains an ambiguity whether the metal atom is actually inside the C cage. The basis of an encapsulation of the metal atom inside the cage is the +3 oxidation state which is obtained by the measurements of the mixture of empty fullerenes, metallofullerenes, and a carbon soot. There is a possibility that the +3 oxidation state of the metal atom is the result of the formation of La carbides. Further, an extended x-ray absorption fine structure study [10] on the mixture of fullerenes and YC" (containing a small amount of YCgi) is inconsistent with the endohedral form of the metailofullerene; it claims that the Y atom is outside the cage. A settlement of the controversy on the position of the metal atom requires a precise electronic structure of pure LaC82 itself.Recently a sufficient amount of LaC82 was separated and purified [11] and its optical absorption property ranging from ir to the visible/uv region strongly suggests that the metal atom is inside the cage. Here we report the first measurement of ultraviolet photoelectron spectra (UPS) of LaC82. Comparison between the UPS of LaC82 and pristine C82 [12] together with ab initio calculations of La@C82 and empty C82 [13] reveal whether the molecular geometry of LaC82 is the same as that of C82 and how the La atom affects the electronic structure of C82-LaC82 was separated and purified from the extract of the solution of the carbon soot produced by an arc heating of the La203 and graphite composite rods by means of a preparative high performance liquid chromatography (HPLC) [11]. Details of the preparation are described elsewhere [1][2][3...