Corrosion-stable nickel- and cobalt-based alloys for dental applications

In a comparative study the in vitro corrosion behavior of a selection of nickel- and cobalt-based alloys for application in dentistry containing no noble metals was studied with slow scan cyclic voltammetry. The obtained breakthrough potentials, the repassivation behavior and further typical features of the cyclic voltamograms are correlated with the chemical composition as measured with electron beam microanalysis. Surface inhomogenities detected with the latter method are discussed with respect to the electrochemical behavior. For all alloys stabilities in terms of breakthrough potential superior to previously reported data for nickel-base alloys are found.     

Spectroscopic characterization of N(2)O aggregates: from clusters to the particulate state

Collisional cooling is used to generate N(2)O particles with radii ranging from the subnanometer to the submicrometer region. The vibrational dynamics of the aggregates is studied by Fourier transform infrared spectroscopy. In the region of the stretching fundamentals and combination bands, the infrared spectra of the particles exhibit characteristic size-dependent features. For the very small particles, the results obtained from collisional cooling are compared for the first time with corresponding results from supersonic jet expansions. It turns out that with both methods very similar clusters are generated. A pronounced temperature dependence of a combination band maximum in the collisional cooling cell spectra is found. This correlation is exploited to estimate cluster temperatures in supersonic jet spectra.     

Solvatochromic azamethine dyes for probing the polarity of gold-cluster-functionalized silica particles

Azamethine dyes of the merocyanine type [4-(N,N-di-n-butylamino)-2-methylphenyl][2,4-di-keto-3-[N'-(n-hexyl)]-5-cyano-6-methyl-3-pyridinio]-1-azamethine (1) and [4-(N,N-diethylamino)-2-(N'-tert-butylcarboxy)-amidophenyl]-[2,4-diketo-3-[N"-(n-hexyl)]-5-cyano-6-methyl-3-pyridinio]-1-azamethine (2) have been used as surface-polarity indicators for gold-cluster-functionalized silica particles. Their UV/Vis absorption maxima range from about lambda=600 to 700 nm as a function of solvent polarity and are clearly separated from the surface plasmon UV/Vis absorption band of gold (lambda approximately 520-540 nm). Solvatochromism of both dyes has been investigated in 26 solvents of different polarity. The positive solvatochromic band shifts of 1 and 2 can be well expressed in terms of the empirical Kamlet-Taft solvent polarity parameters alpha and pi*. They are mainly sensitive to the dipolarity/polarizability (pi* term; 70-75 %) and HBD (hydrogen-bond donating) acidity (alpha term) of the solvent. Both dyes adsorb readily on functionalized silica samples from solutions in 1,2-dichloroethane or cyclohexane. The surface polarities of gold-cluster-functionalized silica particles, with and without co-adsorbed L-cysteine and poly(ethylenimine), have been investigated by using these solvatochromic dyes. The specific interaction of dye 2 with cysteine has been examined independently by quantum-chemical calculations by using the AM1 and PM3 methods.     

On the crystal structures of the fluorite-related intermediate rare-earth oxides

The binary oxides of the rare-earth elements are, except for the A- and B-type sesquioxides, members of a fluorite-related homologous series R_nO_2n?2 (n = 4, 6, 7, 9, 10, 11, 12, ∞ are well established and a related phase with $\text{n = 10}\text{1}\text{3}$ has been reported). In this paper an electron optical study of members of the series is discussed which reveals the unit cell dimensions and possible space groups of the intermediate phases as well as the transformation matrices in terms of the fluorite substructure. This information reveals the structural relationships among the members of the series as well as the highest common structural feature involved. Structures are proposed for members of this series consistent with the new results obtained and with the data already in existence.     

Supramolecular Organization of Dye Molecules in Zeolite L Channels: Synthesis,Properties, and Composite Materials

Sequential insertion of different dyes into the 1D channels of zeolite L (ZL) leads to supramolecular sandwich structures and allows the formation of sophisticated antenna composites for light harvesting, transport, and trapping. The synthesis and properties of dye molecules, host materials, composites, and composites embedded in polymer matrices, including two‐ and three‐color antenna systems, are described. Perylene diimide (PDI) dyes are an important class of chromophores and are of great interest for the synthesis of artificial antenna systems. They are especially well suited to advancing our understanding of the structure–transport relationship in ZL because their core fits tightly through the 12‐ring channel opening. The substituents at both ends of the PDIs can be varied to a large extent without influencing their electronic absorption and fluorescence spectra. The intercalation/insertion of 17 PDIs, 2 terrylenes, and 1 quaterrylene into ZL are compared and their interactions with the inner surface of the ZL nanochannels discussed. ZL crystals of about 500 nm in size have been used because they meet the criteria that must be respected for the preparation of antenna composites for light harvesting, transport, and trapping. The photostability of dyes is considerably improved by inserting them into the ZL channels because the guests are protected by being confined. Plugging the channel entrances, so that the guests cannot escape into the environment is a prerequisite for achieving long‐term stability of composites embedded in an organic matrix. Successful methods to achieve this goal are described. Finally, the embedding of dye–ZL composites in polymer matrices, while maintaining optical transparency, is reported. These results facilitate the rational design of advanced dye–zeolite composite materials and provide powerful tools for further developing and understanding artificial antenna systems, which are among the most fascinating subjects of current photochemistry and photophysics.     

Unraveling the origin of band shapes in infrared spectra of N2O-12CO2 and 12CO2-13CO2 ice particles

Band structures in the region of strong infrared absorption bands for different N2O-12CO2 and 12CO2-13CO2 composite particles are investigated by combining quantum mechanical exciton calculations with systematic experimental investigations. The ice particles are generated by collisional cooling and characterized with rapid-scan infrared spectroscopy. The size of the particles lies between approximately 10 and 100 nm. The calculated spectra show excellent agreement with the experimental data. This work leads to a detailed understanding on a molecular level of shape effects in pure and statistically mixed particles as well as of the characteristic features observed for core-shell particles.     

Singlet Fission for Photovoltaics with 130 % Injection Efficiency

A novel pentacene dimer ( P2 ) and a structurally analogous monomer ( P1 ) were synthesized for use in n‐type dye‐sensitized solar cells. In P2 , the triplet excited states formed by the rapid, spin‐allowed process singlet fission were expected to enable carrier multiplication in comparison to the slow, spin‐forbidden intersystem crossing seen in P1 . A meta‐positioning of the two pentacenes and the carboxylate anchor were chosen in P2 to balance the intramolecular dynamics of singlet fission and electron injection. Electron injection from energetically low‐lying triplet excited states of pentacene units necessitated the intrinsic and extrinsic lowering of the Fermi level of the semiconductor. Indium‐zinc oxide in the presence of Li⁺ was found to be the optimum choice for the photoelectrodes. Efficient electron injection from the triplet excited states of P1 and P2 was found, with a carrier multiplication of nearly 130 %.     

The Yellow Color of Silver-Containing Zeolite A

Not the Ag clusters, but rather the O atoms are responsible for the yellow color of silver-containing zeolite A. The reason for this has remained unclear since 1962. It is now shown that a charge-transfer transition from the lattice oxygen atoms to the empty 5s orbital of the silver ions (shown schematically on the right) is responsible for the yellow coloring.