Surface enhanced Raman scattering in organic thin films covered with silver, indium and magnesium

In situ resonant Raman spectroscopy was applied for the investigation of the interface formation between silver, indium and magnesium with polycrystalline organic semiconductor layers of 3,4,9,10-perylene tetra-carboxylic dianhydride (PTCDA). The spectral region of internal as well as external vibrational modes was recorded in order to achieve information related to the chemistry and the structure of the interface as well as to morphology of the metal layer. The experiments benefit from a strong enhancement of the internal mode scattering intensities which is induced by the rough morphology of deposited metals leading to surface enhanced Raman scattering (SERS). The external modes, on the other hand, are attenuated at different rates indicating that the diffusion of the metal atoms into the crystalline layers is highest for indium and lowest for magnesium.     

Surface-enhanced Raman scattering study of silver deposition on thin Alq3 layers

Surface-enhanced Raman scattering (SERS) spectroscopy is applied to study in situ the interface formation of silver on thin Alq₃ films. The changes in the frequencies of Alq₃ vibrational modes are moderate and their line-shape is preserved upon Ag deposition. Moreover, a good correspondence appears between the SERS and powder spectra and frequencies predicted by density functional calculations for the meridianal isomer. The behaviour of Raman spectra indicates that no chemical interaction occurs between the Ag atoms and Alq₃ molecules.     

A Surfactants Walk to Work: Modes of Action of Citrate Controlling (10–10) and (000–1) Zinc Oxide Surface Growth from Solution

Molecular dynamics simulations unravel the association of citrate to (10–10) and (000–1) growth fronts of zinc oxide and demonstrate an unexpected mobility of the surfactant. Citrate association to perfectly planar (10–10) and (000–1) ZnO‐ethanol interfaces was found to be favored over dissociation by 1.5–2 eV hence suggesting strongly bound, immobilized surfactants. However, intramolecular stress prevents binding of all three carboxyl groups to planar surfaces and the typical arrangement is that of two carboxyl‐Zn contacts (including two salt bridges each) whilst the remaining carboxyl group is dangling into the solvent. As a consequence, the surfactant exhibits a “walking” mechanism to move along the surface by exchanging the role of its carboxyl groups. This finding has strong implications for the role of citrate during crystal growth as illustrated by a recently developed simulation scheme based on hundreds of individual Zn²⁺ and OH^– ion association steps. In particular, for the (10–10) surface – which grows via formation of ridges embedded by {10–10} faces – these simulations show how citrate ions move towards steps and bind to the growth front by additional 4 eV per surfactant molecule.     

P--P bond cleavage of tetraphenyltetraphosphane-1,4-diide facilitated by nickel(0)

One equivalent of [Na2(thf)5-(P4Ph4)] (1) reacts with one equivalent of [Ni(cod)2] (cod=1,5-cyclooctadiene) to give the unexpected ionic compound [Na(Et2O)3][Na3(Et2O)2Ni3(micro-P2Ph2)2-(P2Ph2)3] (2), whereas the reaction of [Ni(cod)2] with the less reactive [K2(pmdeta)2(P4Ph4)] (3) leads to the formation of [K(pmdeta)]2[Ni(P4Ph4)-(P2Ph2)] (4) (PMDETA=NMe(CH2CH2NMe2)2), in which K--Ni interactions are observed. The calculations for 4 confirm the structural parameters obtained by X-ray diffraction studies. A shared electron number (SEN) analysis was applied to investigate the K...Ni interactions. These studies indicate a SEN value of a typical three-center, two-electron bond for K1-Ni-K2 indicating a covalent contribution in the interaction between nickel and potassium.     

Solution structure of a DNA duplex containing a biphenyl pair

Hydrogen-bonding and stacking interactions between nucleobases are considered to be the major noncovalent interactions that stabilize the DNA and RNA double helices. In recent work we found that one or multiple biphenyl pairs, devoid of any potential for hydrogen bond formation, can be introduced into a DNA double helix without loss of duplex stability. We hypothesized that interstrand stacking interactions of the biphenyl residues maintain duplex stability. Here we present an NMR structure of the decamer duplex d(GTGACXGCAG) d(CTGCYGTCAC) that contains one such X/Y biaryl pair. X represents a 3',5'-dinitrobiphenyl- and Y a 3',4'-dimethoxybiphenyl C-nucleoside unit. The experimentally determined solution structure shows a B-DNA duplex with a slight kink at the site of modification. The biphenyl groups are intercalated side by side as a pair between the natural base pairs and are stacked head to tail in van der Waals contact with each other. The first phenyl rings of the biphenyl units each show tight intrastrand stacking to their natural base neighbors on the 3'-side, thus strongly favoring one of two possible interstrand intercalation structures. In order to accommodate the biphenyl units in the duplex the helical pitch is widened while the helical twist at the site of modification is reduced. Interestingly, the biphenyl rings are not static in the duplex but are in dynamic motion even at 294 K.     

Magnetic and optical properties of Cu(II)-bis(oxamato) complexes: combined quantum chemical density functional theory and vibrational spectroscopy studies

Vibrational spectroscopies are shown to be highly sensitive to the structural modifications of paramagnetic mono- and trinuclear Cu(II)-bis(oxamato) complexes. The vibrational bands are assigned using density functional theory (DFT) calculations. Moreover, Raman spectroscopy investigations for different temperatures of thin films show that the onset of superexchange interactions at low temperatures does not involve a modification of the structural parameters. The influence of packing effects, however, on the magnetic properties is significant, as demonstrated by means of DFT using the broken symmetry approach.