Defect mode emission of a dye doped cholesteric polymer network

We have observed enhanced fluorescence and laser emission due to a photonic defect mode in a dye doped cholesteric polymer network. The defect is caused by a phase jump of the cholesteric helix at the interface of two stacked layers of a cholesteric polymer film. Fluorescence spectra show an additional resonant mode inside the photonic stop band. Pulsed excitation gives rise to laser emission of the defect mode, with an exceptionally low lasing threshold. The defect mode emission has a circular polarization whose sense of rotation is opposite to that of the cholesteric helix.     

Low temperature luminescence spectra of the d10s2 complexes Cs2MX6 (M = Se,Te and X = Cl,Br). The Jahn—Teller effect in the Γ−4(3T1u) excited state

The emission spectra of the title compounds in microcrystalline form have been measured at 10 K. The extensive vibrational progression in the e_g mode is indicative of a tetragonal Jahn—Teller distortion in the Γ^?₄(³T_1u) excited state. The vibronic coupling of a threefold electronic state with a doubly degenerate e_g mode (T—e coupling), linear in the nuclear coordinates, has been reinvestigated considering spin—orbit coupling up to second order perturbation on energy levels which result from an a¹_1gt¹_1u electron configuration. For an estimation of Jahn—Teller coupling constants, the intensity distributions in the progressions were compared with the theoretical line shape functions which were obtained from a model which also permits the determination of potential energy minima and vibrational fundamentals of the excited state. The unusually large increase in the e_g vibrational frequency compared to the ground state is due to Jahn-Teller forces which distort the potential surface, yielding steeper excited state energy curves.     

[NaSn12O8Se6]3— — ein Chalkogenostannatanion mit schalenförmigem Aufbau

[NaSn₁₂O₈Se₆]^3— — a Chalcogenostannate Anion with Shell Structure In the anion of (Et₄N)₃[NaSn₁₂O₈Se₆] · DMF ( 1 · DMF) the central sodium atom is surrounded by a cube of O atoms, a Sn₁₂ cuboctahedron and an Se₆ octahedron with increasing size. 1 · DMF crystallizes in space group P2₁/c with a = 1904.6(1), b = 2266.9(1), c = 1390.35(8) pm, β = 104.538(5)°, Z = 4.     

Low symmetry distortions of hexahalo anions of Re(IV) and Os(IV) investigated by polarized absorption spectra and ligand field calculations

Polarized absorption spectra of intraconfigurational transitions of Re⁴⁺ and Os⁴⁺ in trigonal environments (D _3d site symmetry of host lattices) were measured at low temperature (110 K to 1·9 K). The vibronic side bands and electronic origins arising from electric and magnetic dipole transitions are assigned to appropriate term symbols. The vibrational fine structure is explained by normal vibrations with quanta closely related to those of the ground state. Some of the complex octahedra of doped species do not adopt the type of distortion (stretched or squeezed) to which they are predisposed by the host crystals. In the case where the space provided is not adequate for the doped compound, additional local distortions are present which are different for Re and Os. The degree of splitting due to the trigonal symmetry on octahedral Re⁴⁺ energy levels has been found always larger for the ground state, even though it has only spin degeneracy, than for the excited states. Ligand field theory is able to explain this finding by choosing parameter sets out of a relatively limited range which can be readily scanned.     

HPTLC-Bestimmung von Paracetamol im Serum

Ohne Zusammenfassung

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Determination of paracetamol in serum by HPTLC

     

Messung der Änderung des elektrischen Widerstandes von Gold bei Bestrahlung mit monoenergetischen Protonen variabler Energie

Gold foils of 0.25 mg/cm² were irradiated with the protons of a Van de Graaff accelerator at 77 °K. The increase of electrical resistivity is measured as a function of proton energy between 80keV and 1.4 MeV. Comparison with theory shows, that the calculated resistivity change is too large by a factor of 2.9 but gives the correct energy dependence.     

Nanostructured biosensors built by layer-by-layer electrostatic assembly of enzyme-coated single-walled carbon nanotubes and redox polymers

In this study, we describe the construction of glucose biosensors based on an electrostatic layer-by-layer (LBL) technique. Gold electrodes were initially functionalized with negatively charged 11-mercaptoundecanoic acid followed by alternate immersion in solutions of a positively charged redox polymer, poly[(vinylpyridine)Os(bipyridyl)2Cl(2+/3+)], and a negatively charged enzyme, glucose oxidase (GOX), or a GOX solution containing single-walled carbon nanotubes (SWNTs). The LBL assembly of the multilayer films were characterized by UV-vis spectroscopy, ellipsometry, and cyclic voltammetry, while characterization of the single-walled nanotubes was performed with transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. When the GOX solution contained single-walled carbon nanotubes (GOX-SWNTs), the oxidation peak currents during cyclic voltammetry increased 1.4-4.0 times, as compared to films without SWNTs. Similarly the glucose electro-oxidation current also increased (6-17 times) when SWNTs were present. By varying the number of multilayers, the sensitivity of the sensors could be controlled.     

Experimental verification of quadrupole-dipole interference in spin-resolved photoionization

We have measured the spin polarization of Xe (4p)(-1) photoelectrons after ionization with circularly polarized light at photon energies close to the ionization threshold where a resonant enhancement of quadrupole transitions has recently been predicted. At a reaction angle of 90 degrees a nonvanishing longitudinal spin polarization component of about 4% clearly indicates a quadrupole contribution to the photoexcitation. This is the first experimental evidence for the influence of nondipole transitions on the photoionization process at excitation energies much below 1 keV in an observable other than the intensity angular distribution.     

Existenz und physikalisches verhalten von komplexen in lösungen und schmelzen

In the introduction the methods used by the study of complexes in melts and solutions are mentioned, e.g. optical spectroscopy, ESR and nuclear resonance, Cotton and Faraday effect and electron microscopy. Then the classification of electronic transitions in complexes is given on the basis of crystal field and M.O. theory with regard to the transitive elements and rare earths. The problems connected with the charge transfer transitions are mentioned, too. Finally, the spectroscopy of melts and the production of complexes are discussed.