The terahertz and infrared frequency vibration modes of room-temperature ionic liquids with imidazolium cations and halogen anions were extensively investigated. There is an intermolecular vibrational mode between the imidazolium ring of an imidazolium cation, a halogen atomic anion with a large absorption coefficient and a broad bandwidth in the low THz frequency region (13–130 cm−1), the intramolecular vibrational modes of the alkyl-chain part of an imidazolium cation with a relatively small absorption coefficient in the mid THz frequency region (130–500 cm−1), the intramolecular skeletal vibrational modes of an imidazolium ring affected by the interaction between the imidazolium ring, and a halogen anion with a relatively large absorption coefficient in a high THz frequency region (500–670 cm−1). Interesting spectroscopic features on the interaction between imidazolium cations and halogen anions was also obtained from spectroscopic studies at IR frequencies (550–3300 cm−1). As far as the frequency of the intermolecular vibrational mode is concerned, we found the significance of the reduced mass in determining the intermolecular vibration frequency.

Infrared spectroscopy was performed on ionic liquids (ILs) that had imidazolium cations with different alkyl chain lengths and various halogen or molecular anions with and without a small amount of water. The molar concentration normalized absorbance due to C-H vibrational modes in the range of 3000 to 3200 cm was nearly identical for ILs that had imidazolium cations with different alkyl chain lengths and the same anions. A close correlation was found between the red-shifted C-H vibrational modes, the chemical shift ofC(2)-H proton, and the energy stabilization of the hydrogen-bonding interaction. The vibrational modes of the water molecules interacting with anions in the range between 3300 and 3800 cm was examined. The correlation between the vibrational frequencies of water, the frequencies of C-H vibrational modes, and the center frequency of intermolecular vibrational modes due to ion pairs was discussed.

The terahertz- and infrared-frequency vibrational modes of various room-temperature imidazolium-based ionic liquids with molecular anions were examined extensively. We found that the molar-concentration-normalized absorption coefficient spectra in the low-wavenumber range for imidazolium cations with different alkyl-chain lengths were nearly identical for the same anion. Regarding the overall view of a wide range of imidazolium-based ionic liquids, we found that the reduced mass of the combination of an imidazolium-ring cation and the anion and the force constant play significant roles in determining the central frequency of the broad absorption band. In addition to these findings, we also discuss the correlation between the (+)C-H stretching vibrational modes in the 3000-3300 cm(-1) range of the infrared spectra and the intermolecular vibrational band in the low-wavenumber range. Finally, we describe some interesting characteristics of the intermolecular vibrational band observed in a wide range of imidazolium-based ionic liquids.

Within density functional theory with the general gradient approximation for the exchange and correlation, the bimetallic clusters AuPt and Au(6)Pt have been studied for their structure and reactivity. The bond strength of AuPt lies between those of Au(2) and Pt(2), and it is closer to that of Au(2). The Pt atom is the reactive center in both AuPt and AuPt(+) according to electronic structure analysis. AuPt(+) is more stable than AuPt. Au(6)Pt prefers electronic states with low multiplicity. The most stable conformation of Au(6)Pt is a singlet and has quasi-planar hexagonal frame with Pt lying at the hexagonal center. The doping of Pt in Au cluster enhances the chemical regioselectivity of the Au cluster. The Pt atom essentially serves as electron donor and the Au atoms bonded to the Pt atom acts as electron acceptor in Au(6)Pt. The lowest triplet of edge-capped rhombus Au(6)Pt clusters is readily accessible with very small singlet-triplet energy gap (0.32 eV). O(2) prefers to adsorb on Au and CO prefers to adsorb on Pt. O(2) and CO have stronger adsorption on AuPt than they do on Au(6)Pt. CO has a much stronger adsorption on AuPt bimetallic cluster than O(2) does. The adsorption of CO on Pt modifies the geometry of AuPt bimetallic clusters.

We present a study on the structural and electronic properties of the Pt7 cluster by using density functional theory within the generalized gradient approximation for the exchange and correlation. The structures, relative stabilities, and vibrational frequencies of various isomers are calculated and compared with the well-studied Au7 cluster. The ground state of the Pt7 cluster favors a three-dimensional geometrytwo-dimensional local minima are not locatedwhereas for its neighbor, gold heptamer, a two-dimensional geometry is favored. The most stable isomer of Au7 is found to be an edge-capped rhombus structure and an edge-capped tetrahedron structure is found to be the most stable three-dimensional local minimum. The ground state of the Pt7 cluster is found to be a coupled tetragonal pyramid structure with the quintet state in contrast to a pentagonal bipyramid structure obtained by semiempirical molecular dynamics calculation. The natural orbital analysis shows that the overall charge transfer is from 6s to 5d orbitals in the Pt7 cluster, whereas in Au7 cluster it is from 5d to 6s. The molecular orbital picture shows that the bonding orbitals are due to the hybridization between 5d and 6s molecular orbitals in Pt7 cluster, and the nonbonding and antibonding orbitals lie close to the highest occupied molecular orbital. This may be compared with the Au7 electronic structure, where the nonbonding and antibonding orbitals mainly consists of 5d6s hybridized molecular orbitals.

No abstract

We determined the electric-field distribution in organic light emitting diode LED structures fabricated with 4,4′-bis [N-(1-naphthyl)-N-phenylamino]-biphenyl (α-NPD) as hole-transport material and tris-(8-hydroxyquinoline) aluminum (Alq) as electron-transport and emissive material. The electric-field distribution was obtained from an investigation of the linear and the nonlinear Stark effect of the materials when employed in organic LEDs using electroabsorption spectroscopy. We measured the electric-field distribution as a function of the applied voltage in the forward and in the reverse direction. Whilst the average electric fields in the α-NPD and the Alq layers are equal in the reverse direction, the field in the Alq layer is considerably larger than that in the α-NPD layer in the forward direction, and the factor by which these fields differ changes with increasing voltage, in particular in the vicinity of the turn-on voltage. We discuss the electric-field distribution in terms of the charge injection and charge transport in devices as well as the possibility of charge accumulation at the α-NPD/Alq interface.

No abstract