EPR study of radical anions of C60 and C70

Utilizing highly polar solvents for the stabilization of Fullerene anions, electrochemical and chemical reduction resulted in narrow single line EPR spectra for the monoanions of C₆₀ and C₇₀ being characterized byg=2.0001(1), ΔB=0.075 mT,g=2.0019(1), ΔB=0.016 mT, respectively. Apparently, the orbital degeneracy of the C₆₀ monoanion is lifted under these conditions to such an extent, that the abnormal large spin lattice relaxation rate believed to be responsible for the approximately 5 mT line width of the monoanion is sufficiently reduced.¹³C enrichment resulted in noticeable line broadening, allowing an estimate of the average¹³C hyperfine coupling constanta _ave=0.1 mT.     

Optimizing the least nucleophilic anion. A new, strong methyl(+) reagent

The icosahedral carborane anions H-CB11X6H5- (X = Cl, Br, I) are among the most inert, least coordinating, and least basic anions known. These properties are enhanced by 2,3,4,5,6-pentamethylation with methyl triflate. The resulting anions, H-CB11X6Me5-, are more inert than their unmethylated precursors, have improved NMR handles, and their salts have higher solubility in low dielectric media. They sustain superacidity in H(H-CB11X6Me5). Protonated benzene has been isolated and characterized by X-ray crystallography, moving Wheland intermediates from the status of spectroscopically observable transients to weighable reagents. The new anions sustain extreme Lewis acidity in silylium ion-like R3Si(H-CB11X6Me5) species. Treatment of Et3Si(H-CB11Br6Me5) with methyl triflate leads to a new methyl+ reagent CH3(H-CB11Br6Me5) that is more potent than methyl triflate. It methylates benzene without heating or acid catalysis to give the toluenium ion. The H-CB11X6Me5- anions come as close as any to the concept of a univeral weakly coordinating anion and, with cheaper starting materials now available, promise to become specialty chemicals of wide usage.     

Control of a coupled map lattice model for vortex shedding in the wake of a cylinder

The flow behind a vibrating flexible cable at low Reynolds numbers can exhibit complex wake structures such as lace-like patterns, vortex dislocations and frequency cells. These structures have been observed in experiments and numerical simulations, and are predicted by a previously developed low-order coupled map lattice (CML). The discrete (in time and space) CML models consist of a series of diffusively coupled circle map oscillators along the cable span. Motivated by a desire to modify the complex wake patterns behind flexible vibrating cables we have studied the addition of control terms into the highly efficient CML models and explored the resulting dynamics. Proportional, adaptive proportional and discontinuous non-linear (DNL) control methods were used to derive the control laws. The first method employed occasional proportional feedback. The adaptive method used spatio-temporal feedback control. The DNL method used a discontinuous feedback linearization procedure, and the controller was designed for the resulting linearized system using eigenvalue assignment. These techniques were applied to a modeled vortex dislocation structure in the wake of a vibrating cable in uniform freestream flow. Parallel shedding patterns were achieved for a range of forcing frequency-forcing amplitude combinations studied to validate the control theory. The adaptive proportional and DNL methods were found to be more effective than the proportional control method due to the incorporation of a spatially varying feedback gain across the cylinder span. The DNL method was found to be the most efficient controller of the low-order CML model. The required control level across the cable span was correlated to the 1/1 lock-on behavior of the temporal circle map.     

The development of information storage materials — How microscopy can help?

The response of giant magnetoresistance (GMR) devices depends critically on the film microstructure, with parameters such as layer thickness and interfacial abruptness being crucial. This paper presents results obtained using high resolution electron microscopy (HREM), chemical mapping and atom probe microanalysis. Local variations in the magnetic properties are induced by the microstructure and also when the films are patterned to form small elements. These lead to changes in the magnetization reversal mechanism. Some results of the studies of the magnetization reversal carried out using in situ in Lorentz transmission electron microscopy (LTEM) magnetizing experiments are also included.     

UV-induced reduction of Ag<Superscript>+</Superscript> by diazene sulphonates: new method of metallisation of surfaces

The metallisation of surfaces would be technologically very simple if it were possible to use the properties of the substances that decompose upon UV irradiation and produce species with a strong redox potential. In this work, diazene sulphonates are presented as possible reducing agents for Ag⁺ in aqueous solutions and in thin solid layers. The photo-formation of Ag^m+_n clusters in the presence of diazene sulphonates in solutions was investigated via UV-VIS spectroscopy. Significant differences were observed in the electrical properties of surfaces after photo reduction; these occurred without any additional reducing agent.     

Diazene sulphonate as a cross-linking agent for polymers with pendant triarylamine hole-conducting units

Diazene sulphonates are readily available compounds which are soluble in water and polar solvents. They strongly absorb the UV-VIS light and they decompose under UV irradiation via radical or ionic intermediates. These properties render them valuable, e.g. for analytical purposes and for photo-printing. In this presentation, it will be demonstrated that polymers with a pendant diazene sulphonate function as cross-linking agents and with pendant aromatic amines as hole-transporters can be considered as useful materials for organic light-emitting device (OLED) technology.