Polarization modification of PZT thin films by means of electric fields and stress in scanning force microscopy

Polarization switching in scanning force microscopy (SFM) is influenced by both electric fields and stress, whereby the latter can arise inherently from Maxwell stress. We discuss the influence of electric charges and of the polarization asymmetry on the switching behaviour. For single crystallites of PZT(53/47) thin films, the sectors for ferroelectric, ferroelastoelectric and ferroelastic switching are represented in a field-stress map. The influence of stress on the second harmonic of the SFM is also discussed.     

Nonlinear and bistable properties of doped PMMA lightguides

Polymer lightguides of PMMA doped with the azo dyes methyl-red and N, N-dihexyl-4-amino-4'-nitro-azobenzene (DHANA) are investigated with respect to their opto-optical properties. The trans-cis photoisomerisation of the dyes leads to reversible polarization-dependent optically induced refractive index changes. The index changes are anisotropic. Birefringence is measured using index matched lightguides. The changes with respect to each polarization are determined by leaky mode spectroscopy and by using a half-integrated interferometer. These changes are intensity dependent and, with a suitable geometry, bistability at low intensities (3 mW/mm³) can be obtained.     

An integrated organic photoconductive detector for optoelectronics

In the system (poly-(N-vinyl carbazole) (PVK): trinitrofluorenone (TNF) a photoconductive complex is formed. Thin metal films are sputtered on BK7 glass substrates, forming two electrodes with 1 mm separation. The photoconductive complex is deposited from a solution in chlorobenzene/tetrahydrofurane on the glass substrate between the electrodes, forming a photoconductive detector. Photoconductivity of these planar detectors is studied using He-Ne laser light (=633 nm) as a function of electric field and for different TNF concentrations. An increase of photosensitivity is found for high TNF concentrations.Time resolution of the photoconductive PVK:TNF detector is investigated using a ruby pulse laser (=694 nm). The possible use of such detectors in combination with other polymer lightguides is demonstrated. Compared to most polymer waveguide materials PVK exhibits a rather high refractive index ofn=1.7. Thus the coupling of light into the photoconductive film is achieved directly. The planar structure allows further integration of polymeric components for optoelectronics.     

The electronic structure of benzvalene : Photoelectronspectroscopic studies

The photoelectron(PE)spectrum of tricyclo[3.1.0.0^2,6] hex-2-ene(benzvalene 1) has been recorded. The first four bands in the PE spectrum of 1 can be assigned to transitions to ²B₂, ²A₁, ²A₂ and ²B₁ states of 1¹. This assignment is discussed in terms of the results of semiempirical and ab initio calculations on 1. Furthermore the highest occupied MO's of 1 are derived qualitatively from an interaction diagram between a distorted bicyclobutane and an ethylene moiety.     

Cis di-oxomolybdenum(VI) complexes with a tridentate ONO donor ligand; synthesis,X-ray crystal structure,spectroscopic properties and oxotransfer chemistry

The molybdenum complexes of Schiff base ligands viz. [MoO₂LH₂O] where L¹ = tris(hydroxymethyl)(salicylide-neamino)methane, L² = tris(hydroxymethyl)(2,3-dihydroxybenzylideneamino)methane and L³ = tris(hydroxymethyl)(2,3,4-trihydroxybenzylideneamino)methane have been synthesized and characterized by spectroscopic and electrochemical techniques. The X-ray crystal structure of the complex [MoO₂L¹H₂O] reveals a distorted octahedral geometry with one ligand and a water molecule coordinated to the MoO₂ center. No previous complex of this type contains a coordinated water molecule. The complex undergoes an oxotransfer in the presence of Bu₃P to form a -oxobridged molybdenum(V,V) dimer. This rules out Mo—S coordination as a prerequisite for oxotransfer in such molybdenum(VI) complexes.     

Synthesis of Cannabinoid Model Compounds. Part 3. (6aR, 10aR)-N-ethyl-Δ8-tetrahydrocannabinol-18-amide, (6aR, 10aR, 17 RS)-N-ethyl-17-methyl-Δ8- tetrahydrocannabinol-18-amide and (6aR, 10aR)-17,18-didehydro-Δ8-tetrahydrocannabinol

The novel cannabinoids (6aR, 10aR)-N-ethyl-Δ⁸-tetrahydrocannabinol-18-amide (15) and (6aR, 10aR, 17 RS)-N-ethyl-17-methyl-Δ⁸- tetrahydrocannabinol-18-amide (16) , designed as cannabinoid affinity ligands, were synthesized from the corresponding acids 11 and 12 via the N-hydroxysuccinimide esters. Amide 16 was tested in the rat and was generalized to Δ⁹-tetrahydrocannabinol, being 5 times less potent than the training drug. An improved synthesis of (6aR, 10aR)-17,18-didehydro-Δ⁸-tetrahydrocannabinol (23) is reported. As model reaction for the preparation of a tritiated Δ⁸-tetrahydrocannabinol, compound 23 was selectively deuterated at C(17) and C(18) in benzene/Et₃N using [(C₆H₅)₃P]₃RuCl₂ as catalyst.     

Synthetische Juvenilhormone 3. Mitteilung. p-Substituierte 4-Phenyl-buten(1)-carbonsäurederivate

The syntheses of p-substituted 2-methyl-4-phenylbuten(1)-carboxylic acid derivatives are described, using Blanc's chloromethylation reaction, the Friedel-Crafts alkylation of unsaturated ketones or the Meerwein arylation; the formed intermediates react in subsequent steps to the title compounds.